21119 gpo chapter 5

Mechanical Engineering

5

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F A C I L I T I E S S T A N D A R D S F O R T H E P U B L I C B U I L D I N G S S E R V I C E

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5.0 TABLE OF CONTENTS

5.1 General Requirements

5.2 Codes126 Mechanical Codes

5.3 Standards126 Mechanical Design Standards

5.4 Program Goals127 Design Integration127 Life Cycle Costing

5.5 HVAC Baseline Systems128 Baseline Selection 129 General

5.6 Design Criteria129 General Parameters 129 Outdoor Design Criteria129 Indoor Design Criteria132 Internal Heat Gain133 Zoning Criteria

5.7 Arrangement of Mechanical Spaces

5.8 Mechanical Requirements for Special Spaces

5.9 HVAC Systems and Components139 HVAC Systems141 HVAC System Components

5.10 Humidification and Water Treatment

5.11 Heating Systems149 Steam Heating150 Hot Water Heating Systems

5.12 Cooling Systems151 Chilled Water Systems152 Special Cooling Systems

5.13 Heat Recovery Systems

5.14 Pressurization and Ventilation154 Pressurization154 Special Ventilation Requirements

5.15 Air Distribution Systems155 Variable Air Volume (VAV) Systems157 Supply, Return and Exhaust Ductwork

5.16 Pumping Systems

5.17 Piping Systems

5.18 Thermal Insulation164 General165 Thermal Pipe Insulation for Plumbing Systems

5.19 Vibration Isolation, Acoustical Isolation, and Seismic Design for Mechanical Systems

5.20 Meters, Gauges, and Flow Measuring Devices

5.21 Control Systems169 Automatic Temperature and Humidity Controls169 Temperature Reset Controls

5.22 Building Automation Systems (BAS)

5.23 Startup, Testing, and Balancing Equipment and Systems

5.24 Plumbing Systems172 Domestic Water Supply Systems173 Sanitary Waste and Vent System174 Rainwater Drainage System175 Plumbing Fixtures175 Natural Gas Systems175 Fuel Oil Systems175 Fire Protection

5.25 Alterations in Existing Buildings and Historic Structures

Temecula Border Patrol Station, Murietta, CaliforniaArchitect: Garrison ArchitectsGSA Project Manager: Steve Baker

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M E C H A N I C A L E N G I N E E R I N G

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building components shall all combine together toproduce a building that meets the project’s programmedsustainability rating (LEED rating) and assigned energytarget, as referenced in Chapter 1.

Maintainability and reliability are major concerns in theoperation of Federal buildings. As such, the design andinstallation of all mechanical equipment and componentsshall allow for removal and replacement, including majorequipment such as boilers, chillers, cooling towers, pumpsand air-handling equipment.

Standby capacity shall be designed into mechanicalsystems, enabling continuous services during repair orreplacement of a failed piece of equipment or component.Redundant equipment shall typically not be designed intosystems as “stand-by” units but rather shall be used as partof the operating system with equal time cycling throughautomatic control sequencing.

Proposed systems and equipment will be evaluated byGSA for their offerings of advanced technology; however,GSA does not allow use of experimental, unproven, orproprietary equipment or systems. Documented proofof historical capability and adaptability of all equipmentand systems proposed for a project shall be made availableto GSA.

As indicated herein, the description of the mechanicalbaseline systems establishes the minimum level of quality,function, and performance that may be considered.

Submission requirements are addressed in Appendix A.3.

5.1 General Requirements

This chapter identifies criteria to program and designheating, ventilating and air conditioning (HVAC) andplumbing systems.

Mechanical systems must be coordinated and integratedwith the designs of other involved/impacted buildingsystems and features. As addressed in the Appendix,mechanical systems shall be adapted to support allperformance objectives, typically involving sustainability,workplace performance (productivity and efficiency), firesafety, security, historic preservation, and improvedoperations and maintenance.

Mechanical systems shall be specifically designed tofunction at full load and part load associated with allprojected occupancies and modes of operation. To themaximum extent possible, system solutions shall alsoaccommodate planned future occupancies and modes ofoperation. (Special emphasis shall be placed on the designconsiderations for U.S. Court Facilities to allow forrenovation, relocation, and creation of new Courtroomsand adjunct facilities or retrofitting Courtroom facilitiesfor other Agencies’ use. See Chapter 9, “Design Standardsfor U. S. Court Facilities,” for design criteria. )

The design of the mechanical systems shall generally bemore demanding in performance expectations thanrepresented within ASHRAE 90.1 and 10 CFR 434standards. All mechanical systems shall be designed toautomatically respond to the local climatic conditions andheat recovery opportunities to provide cost effectiveenergy conservation measures while assuring set pointcontrol. The design of mechanical systems and other


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5.3 StandardsMechanical Design StandardsThe latest editions of publications and standards listedhere are intended as guidelines for design. They aremandatory only where referenced as such in the text ofthis chapter or in applicable codes. The list is not meantto restrict the use of additional guides or standards.When publications and standards are referenced asmandatory, any recommended practices or features shallbe considered “required.” When discrepancies betweenrequirements are encountered, GSA shall determine therequirement.

• ASHRAE: Handbook of Fundamentals.• ASHRAE: Handbook of HVAC Applications.• ASHRAE: Handbook of HVAC Systems and Equipment.• ASHRAE: Standard 15: Safety Code for Mechanical

Refrigeration.• ASHRAE: Standard 52: Gravimetric and Dust-Spot

Procedures for Testing Air-Cleaning Devices Used inGeneral Ventilation for Removing Particulate Matter.

• ASHRAE: Standard 55: Thermal EnvironmentalConditions for Human Occupancy.

• ASHRAE: Standard 62: Ventilation for Acceptable IndoorAir Quality.

• ASHRAE: Standard 90.1: Energy Standard for BuildingsExcept Low-Rise Residential Buildings.

• ASHRAE: Standard 100: Energy Conservation in Existing Buildings.

• ASHRAE: Standard 105: Standard Method of Measuringand Expressing Building Energy Performance.

• ASHRAE: Standard 111: Practices for Measurement,Testing, Adjusting and Balancing of Building HVACSystems.

5.2 Codes

Mechanical CodesAs stated in Chapter 1, General Requirements, Codes and Standards, Building Codes, facilities shall comply with the ICC’s International Mechanical Code and theInternational Plumbing Code.


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5.4 Program Goals

Design IntegrationAs represented in Appendix A-2, mechanical systems mustbe selected to routinely address multiple program goals,including: workplace performance, sustainability, energyefficiency, security, fire safety, historic preservation andoperations/maintenance concerns, as well as other projectexpectations. Design solutions shall not sacrifice the basicneeds of one program area to optimize another. Instead,mechanical designs must optimize program areas to theextent possible, assuring attainment of all criticalperformance goals. Prior to making any mechanicalsystems solutions, their designer shall visit the WholeBuilding Design Guide website, www.wbdg.org, toidentify program goal principles and to consider availabletechnologies.

Life Cycle CostingLife cycle cost analysis shall comply with requirementsaddressed in Chapter 1. This includes consideration ofanalysis period, escalation discount rates, and otherparameters. The indicated software program, “BuildingsLife Cycle Cost”, is recommended when used withprovisions that support “Federal Analysis— ProjectsSubpart to OMB A-94 Guidelines.”

The baseline HVAC systems described in the followingsection set minimum system requirements and act as areference from which advantages and disadvantages ofother systems or sub-systems can be compared.

Any deviation from the GSA defined baseline standards or from the directives described herein shall not bepermitted unless previously identified in projectprogramming requirements, and submitted directly toand subsequently authorized by the Office of the ChiefArchitect.

• ASHRAE: Standard 114: Energy Management ControlSystems Instrumentation.

• ASHRAE: Standard 135: BACnet: A DataCommunication Protocol for Building Automation andControl Networks.

• ASHRAE: Guideline #4: Preparation of Operating andMaintenance Documentation for Building Systems.

• American National Standards Association:ANSI Z 223.1.

• National Fuel Gas Code Standard 54.• American Society of Mechanical Engineers: ASME

Manuals.• American Society of Plumbing Engineers: ASPE Data

Books.• Sheet Metal and Air Conditioning Contractors’

National Association, Inc. (SMACNA):• ASHRAE HVAC System Duct Design.• SMACNA HVAC Duct Construction Standards: Metal

and Flexible.• SMACNA HVAC Air Duct Leakage Test Manual.• SMACNA Fire, Smoke and Radiation Damper

Installation Guide for HVAC Systems.• Seismic Restraint Manual Guidelines for Mechanical

Systems.• NFPA Standard 96• All applicable regulations and requirements of local

utility companies having jurisdiction.• EIA/TIA Standard 569: Commercial Building Standard

For Telecommunications Pathways And Spaces (andrelated bulletins).


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Interior Systems. Interior zone(s) shall have 100 percentoutside air ventilation system(s) to meet the ventilationrequirements of the interior zone. The ventilationsystem(s) shall operate independently of any other airdistribution system but shall connect to the return side ofthe VAV air-handling unit(s) serving the interior zone(s).The interior zone(s) shall also have a baseline interiorheating and cooling system selected from the following:

• A ducted overhead variable air volume (VAV) systemwith VAV boxes.

• A ducted overhead variable air volume (VAV) systemwith fan-powered VAV boxes.

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• An underfloor variable air volume (VAV) air distributionsystem.

1Electric heating coils will be permitted for nominal heatingrequirements. Requests for use of electric heating coils must besubmitted directly to and subsequently authorized by the office ofthe Chief Architect. No reheat is permitted.

2Hot water heating coils in the fan-powered VAV boxes may be used on the top floor of a building for heating.

5.5 HVAC Baseline Systems

Baseline SelectionUnless otherwise directed in design programmingdocuments, a combination of the following perimeter and interior HVAC systems shall be used to set a basereference for comparison.

Perimeter Systems. Perimeter zones shall have 100-percentoutside air dedicated ventilation systems sized to meet theventilation requirements of the specified zone. Thesesystems shall provide tempered dehumidified air and shallbe completely independent of any other air distributionsystem. In addition to the dedicated 100-percent outsideair ventilation system(s), the perimeter zones shall alsohave a baseline perimeter heating and cooling systemselected from the following:

• For new construction spaces with significant latentloads and/or for alterations to existing space withceiling distribution, use a ducted overhead variable air volume (VAV) air distribution system with VAVshutoff boxes for cooling and hot water fin-tubesystems for heating.

• A ducted overhead variable air volume (VAV) airdistribution system with fan-powered VAV boxes withhot water heating coils for cooling and heating.

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• For new construction office type loads and otherspaces with low latent loads, use an underfloor,variable air volume (VAV) air distribution system, forcooling, supplemented with two-pipe, above floorperimeter hot water fin-tube systems for heating.

• For alteration projects with high skin loads use astandard four-pipe fan coil unit system for heating andcooling.


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5.6 Design Criteria

General ParametersHVAC system parameters are provided here for reference,but specific energy performance directives are also listedin 10 CFR 434. Compliance with the latest versions ofASHRAE Standard 90.1 and ASHRAE Standard 62 isrequired for the elements of the project (architectural,mechanical, and electrical).

Outdoor Design Criteria Outdoor air design criteria shall be based on weather datatabulated in the latest edition of the ASHRAE Handbookof Fundamentals. Winter design conditions shall be basedon the 99.6 percent column dry bulb temperature in theASHRAE Fundamentals Volume. Summer designconditions for sensible heat load calculations shall bebased on the 0.4 percent dry bulb temperature with itsmean coincident wet bulb temperature. Design conditionsfor the summer ventilation load and all dehumidificationload calculations shall be based on the 0.4% dew pointwith its mean coincident dry bulb temperature.

Indoor Design Criteria Indoor Design Temperatures and Relative Humidity.Indoor design temperatures and relative humidityrequirements are stated in Table 5-1. The following spaces shall be kept under negative pressure relative tosurrounding building areas: smoking lounge, detentioncells, toilets, showers, locker rooms, custodial spaces,

General• Enthalpy heat recovery shall be used for interior zones

and other special areas where the outside air exceeds30 percent of the total supply air quantity.

• Special areas such as auditoriums, atriums, andcafeterias shall have a dedicated air-handling unit withindividual controls to condition these spaces asrequired.

• A dedicated air-handling unit shall be provided formaintaining positive pressure in the main entry lobby.

• Air-handling units with a capacity over 1,416 LPS (3,000 CFM) shall have an enthalpy economizer cycle.Systems dedicated to serving only unoccupied spaceswith intermittent operation, such as elevator machinerooms, telephone equipment rooms and similar spaceswould be exempt from the requirements of having aneconomizer cycle.

• Waterside economizer system shall be employed whereairside enthalpy economizer is not practical or feasible.Systems dedicated to serving only unoccupied spaceswith intermittent operation, such as elevator machinerooms, telephone equipment rooms and similar spaceswould be exempt from the requirements of having aneconomizer cycle.


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Energy Analysis. An energy analysis of buildingcharacteristics, the mechanical and electrical components,and all other related energy consumption elements mustbe performed for each design submission level project asdescribed in Appendix A.3.

Analyses of energy-conserving designs shall include allrelevant facets of the building envelope; lighting energyinput, domestic water heating, efficient use of localambient weather conditions, building zoning, efficientpart load performance of all major HVAC equipment and the ability of building automation equipment toautomatically adjust for building partial occupancies,optimized start-stop times and systems resets. Energyanalysis shall utilize public domain DOE-2 programs.Inputs and outputs shall follow ASHRAE 90.1 Standardsand 10 CFR 434.

battery charging rooms, kitchens and dining areas. Air can be returned from the dining area space. The air fromthese spaces must be exhausted directly to the outdoors.

Building Pressurization. To keep dry air flowing throughbuilding cavities, systems shall be designed with sequenceof operations that assure continuous positive pressurewith respect to the outdoor environment until theoutdoor temperature falls below 4.5°C (40°F), when thebuilding pressure shall be brought to neutral. Thesebuilding HVAC systems shall have an active means ofmeasuring and maintaining this positive pressurerelationship. The BAS shall alarm when the buildingpressurization drops below a predetermined low limit. Inareas where exhaust systems are used or an indoor airquality contaminant source is located, a negative pressureshall be maintained relative to surrounding spaces.Calculations shall be provided that show the minimumoutside airflow rate required for pressurization. Minimumoutside airflow rates shall be adjusted as necessary toassure building pressurization.

Artwork. In general, it is important to keep within an RHrange of 30 to 70%. In a hot and dry geographic region itmakes sense to maintain a range that errs on the low side(20 to 40%), while in semitropical climates a range of 55to 75% may be practical.

Please consult Chapter 4.1, Installation Standards, of theFine Arts Program Desk Guide for additional information.



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Table 5-1Indoor Design Conditions3

Summer WinterType of Area DB

1RH

2DB

1RH

2

General Office 24 (75) 22 (72)ADP Rooms

922 (72) 45

422 (72)

Corridors 24 (75) 22 (72)Building Lobbies

10 24 (75) 22 (72)

Toilets 24 (75) 22 (72)Locker Rooms 26 (78) 21 (70)Electrical Closets 26 (78) 13 (55)Mech. Spaces 35 (95)

513 (55)

8

Elec. Switchgear 35 (95)5

13 (55)Elevator Mach. Room

1026 (78)

513 (55)

Emerg. Gen. Room 40 (104)6

18 (65)Transformer Vaults 40 (104)

5

Stairwells (none) 18 (65)Comm./Tel. Frame Room

724 (75) 45 22 (72) 30

12

Storage Room 30 (85) 18 (65)Conference Room

1124 (75) 22 (72)

Auditorium10

24 (75) 22 (72)Kitchen

1024 (75) 22 (72)

Dining10

24 (75) 22 (72)Cafeteria

1024 (75) 22 (72)

Courtrooms 24 (75) 22 (72) 454**Requires humidification in the winter.

Notes:1 Temperatures are degrees Celsius (Fahrenheit), to be maintained at +/-1 °C (+/-2 °F).2 Relative humidity is minimum permissible, stated in percent. Maximum permissible relative humidity is 60 percent in conditioned areas.3 Dry bulb and relative humidity are to be maintained 150 mm (6 inches) to 1800 mm (6 feet) above the floor.4 Relative humidity should be maintained at +/-5 percent in ADP spaces.5 Maximum temperature. Space to be mechanically cooled if necessary.6 Room must not exceed temperature with generator running.7 Must comply with EIA/TIA Standard 569.8 Minimum temperature in the building must be 13 °C (55 °F) even when unoccupied.9 Confirm equipment manufacturer ’s requirements as more stringent. Provide in-room display and monitor device (such as wall mounted temperature and humidity chart

recorder),10 System shall be designed for process cooling. Cooling system shall be a dedicated independent system.11 Provide independent temperature control.12 Minimum relative humidity requirements may be omitted in moderate southern climate zones upon approval of local GSA representatives.



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Indoor Air Quality. When a building is new, volatilecompounds (VOC) may be released in large quantitiesfrom materials, such as adhesives, vinyl and carpets. Anoutside air purge cycle shall be provided to air-handlingequipment enabling evening removal of VOC build-upsduring the first weeks of occupancy.

GSA recognizes the importance of adequate ventilation to maintain indoor air quality. The outside air andventilation rates of ASHRAE Standard 62 are the minimumacceptable in GSA buildings. Instrumentation andcontrols shall be provided to assure outdoor air intakerates are maintained within 90 percent of required levelsduring occupied hours.

Where occupancy requirements are likely to generate high levels of airborne particles, special air filtration shall be provided on the return air system or dedicatedand localized exhaust systems shall be utilized to containairborne particulates.

Dilution with outside air is the primary method of main-taining acceptable indoor air quality. The site shall besurveyed to determine if there are airborne sources ofcontaminants that may be unacceptable for use indoorswith respect to odor and sensory irritation.

Internal Heat GainOccupancy Levels. For office spaces, the average densityof the occupiable floor area of a GSA building is oneperson per 9.3 usable square meters (100 usable squarefeet). Within areas occupied by workstations, theoccupancy load can be as dense as one person per 7usable square meters (75 usable square feet) in local areas.Block loads and room loads should be calculatedaccordingly. Sensible and latent loads per person shouldbe based on the latest edition the ASHRAE Handbook ofFundamentals.

Table 5-2Air Intake Minimum SeparationDistances

MinimumDistance

Object m ftProperty line 1 3Garage entry, loading dock 7 25Driveway, street or public way 3 10Limited access highway 7 25Grade 14 50Roof* 0.5 1Cooling tower or evaporative condensers 5 15Exhaust fans and plumbing vents 3 10Kitchen supply and exhaust air 7 25

* Roof intakes must be at least 0.2 m (8 inches) above the average maximumsnow depth and the potential for drifts at the intake location must beconsidered. Outdoor intakes should be covered by 13 mm (0.5 inch) meshscreen. The screen should be of corrosion-resistant material and locatedoutside of or no more that 0.2 m (8 inches) inside of the outside face of theintake grille, louver, or rain hood entry. On buildings of more than four storiesthe outside air supply louvers shall be located on the fourth level of thebuilding or higher. On buildings of three stories or less, locate the intakes onthe roof or as high as possible. Locating intakes high on the exterior wall ispreferred to a roof location. Outside air intake is not permitted within sevenmeters (twenty-five feet) of loading dock or any other fume producing areas.

Air Intake and Exhaust. The placement and location of outside air intakes is critical to the safety of theoccupants inside a building and must be in compliancewith the security requirements of the building, asdescribed in Chapter 8, “Security Design.” Table 5-2provides a guide for minimum separation distancesbetween ventilation air intakes and other buildingfeatures.



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Lighting Levels. For preliminary design loads, heat gainfrom lighting levels described in Chapter 6: “ElectricalEngineering, Lighting, Interior Lighting, IlluminationLevels,” shall be used.

Zoning CriteriaSeparate systems shall be provided for interior andperimeter zones where simultaneous heating and coolingoperations may occur.

Single air handling units shall not serve multiple floors or scattered building loads. Multiple air handling units or floor-by-floor systems shall be considered as baseline.Systems designed for federal courthouses shall be limitedto having no more than two courtrooms served by anysingle air handling unit, and that air handling unit shallbe dedicated to serving only those two courtrooms.

For dining areas, auditoriums and other high occupancyspaces, occupancy loads should represent the number ofseats available. Areas such as storage rooms or mechanicalrooms do not have occupancy loads.

Equipment Densities. Internal heat gain from allappliances—electrical, gas, or steam—should be takeninto account. When available, manufacturer-providedheat gain and usage schedules should be utilized todetermine the block and peak cooling loads. Typical rateof heat gain from selected office equipment should bebased on the latest edition of the ASHRAE Handbook of Fundamentals. The cooling load estimated for theconnected electrical load should be based on the electricalload analysis, and the estimated receptacle demand loadoutlined in Chapter 6, “Electrical Engineering, ElectricalLoad Analysis,” and anticipated needs of GSA’s Office ofChief Information Officer. For printers and personalcomputers, 80 percent diversity shall be considered.



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Interior control zones must not exceed 180 m2 (1,500 sf)per zone for open office areas or a maximum of threeoffices per zone for closed office areas. Corner offices shallbe a dedicated zone. Perimeter zones shall be no morethan 4.7 meters (15 feet) from an outside wall along acommon exposure. Independent zones should beprovided for spaces such as conference rooms, entrancelobbies, atriums, kitchen areas, dining areas, childcarecenters and physical fitness areas. Perimeter zones shallnot exceed 30m2 (300 sf).

If a building program shows that an office building willhave an open plan layout or if the program does not state

a preference, it may be assumed that up to 40 percent ofthe floor plan will be occupied by closed offices at somepoint in the future.

The supply of zone cooling and heating shall besequenced to prevent (or at the very least, minimize) thesimultaneous operation of heating and cooling systemsfor the same zone. Supply air temperature reset controlshall be utilized to extend economizer operations and toreduce the magnitude of reheating, recooling or mixingof supply air streams.

Office of the Chief Architect, Public Building Service, Washington, DC


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Vertical Clearances. Main mechanical equipment roomsgenerally shall have clear ceiling heights of not less than 3.6m (12 feet). Catwalks shall be provided for all equipmentthat cannot be maintained from floor level. Where mainte-nance requires the lifting of heavy parts [45 kg (100pounds) or more], hoists and hatchways shall be installed.

Horizontal Clearances. Mechanical rooms shall beconfigured with clear circulation aisles and adequateaccess to all equipment. The arrangement shall considerthe future removal and replacement of all equipment.The mechanical rooms shall have adequate doorways orareaways and staging areas to permit the replacement andremoval of equipment without the need to demolish wallsor relocate other equipment. Sufficient space areas (notedby outlining manufacturer’s recommendations) formaintenance and removal of coils, filters, motors, andsimilar devices shall be provided. Chillers shall be placedto permit pulling of tubes from all units. The clearanceshall equal the length of the tubes plus 600 mm (2 feet).Air-handling units require a minimum clearance of 750mm (2 feet 6 inches) on all sides, except the side wherefilters and coils are accessed. The clearance on that sideshould equal the length of the coils plus 600 mm (2 feet).

Roof-Mounted Equipment. No mechanical equipmentexcept for cooling towers, air-cooled chillers, evaporativecondensers, and exhaust fans shall be permitted on theroof of the building. Access to roof-mounted equipmentshall be by stairs, not by ship’s ladders.

Housekeeping Pads. Housekeeping pads shall be at least150 mm (6 inches) wider on all sides than the equipmentthey support and shall be 150 mm (6 inches) thick.

Mechanical equipment rooms must be designed inaccordance with the requirements of ASHRAE Standard15: Safety Code for Mechanical Refrigeration.

5.7 Arrangement of Mechanical Spaces

Minimum Space Requirements. A minimum of 4 percentof the typical floor’s gross floor area shall be provided oneach floor for air-handling equipment. A minimum of1 percent of the building’s gross area shall be provided for the central heating and cooling plant (location to beagreed upon during preparation of concept submission.Space requirements of mechanical and electricalequipment rooms shall be based upon the layout ofrequired equipment drawn to scale within each room.

Service Access. Space shall be provided around all HVACsystem equipment as recommended by the manufacturerand in compliance with local code requirements forroutine maintenance. Access doors or panels should beprovided in ventilation equipment, ductwork andplenums as required for in-site inspection and cleaning.Equipment access doors or panels should be readilyoperable and sized to allow full access. Large centralequipment shall be situated to facilitate its replacement.The HVAC design engineer should be cognizant of thenecessity to provide for the replacement of majorequipment over the life of the building and should insurethat provisions are made to remove and replace, withoutdamage to the structure, the largest and heaviestcomponent that cannot be further broken down.

In addition, adequate methods of access shall be includedfor items such as: chillers, boilers, heat exchangers, coolingtowers, reheat coils, VAV boxes, pumps, hot water heatersand all devices that have maintenance servicerequirements.


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Auditoriums. Auditoriums shall have dedicated air-handling units equipped with enthalpy economizer cycle.Units shall be designed with 80 percent diversity factor tomaintain necessary temperature and humidity conditionsunder partial loads and partial occupancy. Providedewpoint control. Dewpoint of supply air shall not exceed10°C (50°F) dry bulb.

U.S. Marshals Service Areas. The U.S. Marshals Servicearea HVAC system shall be designed for continuousoperation and shall be independently controlled andzoned. All ductwork and air circulation openingspenetrating the secure area envelope, including prisonercirculation areas, shall be provided with security bars.Detainee holding areas shall be negatively pressurizedwith regard to adjacent spaces and exhausted directly to the outdoors. Refer also to requirements of USMSPublication 64.

Firing Range. Special HVAC considerations will berequired for firing ranges. A firing range shall be providedwith a dedicated air-handling system. Heating and coolingsupply air shall be delivered to the area along and behindthe firing line for occupant comfort conditions and tomaintain a positive pressure in this area relative to downrange and target area. Powered exhaust air shall beextracted from down range and the target areas insufficient quantity to remove smoke and maintain a clearline of vision to the target. Sixty percent of the totalexhaust shall be extracted at a point approximately one-third the distance from the firing line to the target area,and forty percent shall be extracted from above the targetarea. All exhaust air shall be filtered to preclude theemission of lead particulates and gunpowder residue intothe atmosphere. Discharge of firing range exhaust air tooutdoors shall be carefully located to prevent recirculationinto the outside air intake of any HVAC system. Firingrange systems shall be capable of continuous operation,isolated from other building systems.

United States Courthouse, White Plains, NY

5.8 Mechanical Requirementsfor Special Spaces

Courtrooms. Generally, each Courtroom and itsrespective ancillary areas coupled to the operation of theCourtroom shall constitute a primary zone. No more thantwo Courtrooms and their respective ancillary areas shallbe supplied from the same air-handling unit and system.Refer to the U.S. Courts Design Guide published by theAdministrative Office of the United States Courts (AOC)for specific requirements.


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Mechanical Rooms. All mechanical rooms must bemechanically ventilated to maintain room spaceconditions as indicated in ASHRAE 62, ASHRAE 15, andTable 5-1 of this chapter. Water lines shall not be locatedabove motor control centers or disconnect switches andshall comply with requirements of NEC Chapter 1.Mechanical rooms shall have floor drains in proximity tothe equipment they serve to reduce water streaks or drainlines extending into aisles.

Chiller Equipment Rooms. All rooms for refrigerantunits shall be constructed and equipped to comply withASHRAE Standard 15: Safety Code for MechanicalRefrigeration. Chiller staging controls shall be capable ofDDC communication to the central building EnergyManagement System.

Electrical Equipment Rooms. No water lines arepermitted in electrical rooms, except for fire sprinklerpiping. Sprinkler piping lines must not be located directlyabove any electrical equipment.

Communications Closets. Communications closets must be cooled in accordance with the requirements ofEIA/TIA Standard 569. Closets which house criticalcommunications components shall be provided withdedicated air-conditioning systems that shall be connectedto the emergency power distribution system.

Elevator Machine Rooms. A dedicated heating and/orcooling system must be provided to maintain roommechanical conditions required by equipmentspecifications, and in accordance with Table 5-1 of thischapter.

In the event the building is equipped throughout withautomatic sprinklers, hoistway venting is not required.

Kitchens and Dishwashing Areas. Kitchens with cooking ranges, steam kettles, ovens and dishwashers shall be provided with dedicated make-up air and exhausthoods/exhaust systems in accordance with latest edition ofNFPA Standard 96 and ASHRAE Applications Handbook.All components of the ventilation system shall bedesigned to operate in balance with each other, evenunder variable loads, to properly capture, contain, andremove the cooking effluent and heat, and maintainproper temperature and pressurization control in thespaces efficiently and economically. The operation of thekitchen exhaust systems should not affect the pressurerelation between the kitchen and surrounding spaces.Both supply air and makeup air shall be exhaustedthrough the kitchen hood heat recovery system while amaximum of 30 percent of the exhaust air is made upfrom the space.

Floor drains must be provided at each item of kitchenequipment that requires indirect wastes, where accidentalspillage can be anticipated, and to facilitate floor-cleaningprocedures. Drains to receive indirect wastes forequipment should be of the floor sink type of stainlessconstruction with a sediment bucket and removable grate.

Areas of Refuge. The area of refuge provided for theJudiciary in the event of emergency conditions shall beprovided with adequate ventilation energized from theemergency power distribution system and sufficientheating capacity to maintain space temperature of 21°C(70°F) with design winter outdoor temperature. Provideseparate air-handling unit to maintain positive pressure,relative to surrounding spaces, with heating-cooling coilsand differential pressure sensing system.


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Emergency Generator Rooms. The environmentalsystems shall meet the requirements of NFPA Standard110: Emergency and Standby Power Systems and meet thecombustion air requirements of the equipment. Roomsmust be ventilated sufficiently to remove heat gain fromequipment operation. The air supply and exhaust shall belocated so air does not short circuit. Generator exhaustshould be carried up to roof level (GSA preference) in aflue or exhausted by way of compliance with the generatormanufacturer’s installation guidelines. Horizontal exhaustthrough the building wall should be avoided.

UPS Battery Rooms. Battery rooms must be equippedwith eye wash, emergency showers and floor drains.The battery room must be ventilated/exhausted directly to the outdoors at a rate calculated to be in compliancewith code requirements and manufacturer’srecommendations, and the exhaust system must beconnected to the emergency power distribution system.Fans shall be spark-resistant, explosion proof, with motoroutside the air stream, ductwork to be negative pressuresystem of corrosion-resistant material, with exhaustdirectly to outdoors in a dedicated system. Acousticalenclosures shall be provided to maintain a maximum NC level of 35. Coordinate with electrical designspecifications to include HVAC support equipment inUPS extended servicing agreements.

Loading Docks. The entrances and exits at loading docksand service entrances shall be provided with a positivemeans to reduce infiltration and outside debris. Loadingdocks must be maintained at negative pressure relative tothe rest of the building.

24-Hour Spaces. All areas designated as requiring 24-houroperations shall be provided with a dedicated andindependent HVAC system. All spaces handling BAScomputer processing of Fire Alarm Monitor and ControlSystems, Security Monitor and Control Systems and/orenergy monitoring and control systems shall be providedwith dedicated HVAC systems to maintain temperature,humidity and ventilation requirements at all times.Twenty-four hour systems shall have dedicated chiller(s),cooling tower(s) boiler(s), and associated pumpingsystems. However, central system(s) can be used toprovide chilled water and hot water during the normaloperating hours, or as a backup for the 24-hour system(s).Twenty-four hour systems with a capacity of up to 50 tonsshould be configured with an air-cooled chiller. In theevent the building’s 24-hour operation load, including thededicated perimeter ventilation system, exceed 50 tons,the cooling systems may be combined with a centralsystem of which a dedicated central chilled water supplyloop shall be provided along with 24-hour chiller.

Artwork. In general, it is important to keep within an RHrange of 30 to 70%. In a hot and dry geographic region itmakes sense to maintain a range that errs on the low side(20 to 40%), while in semitropical climates a range of 55to 75% may be practical.

Please consult Chapter 4.1, Installation Standards, of theFine Arts Program Desk Guide for additional information.

Fire Protection and Smoke Control. Refer to Chapter 7:Fire Protection Engineering, for fire protection and smokecontrol requirements.


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shall have self-contained microprocessor controls capableof connecting to and interoperating with a BACnet orLONWORKS direct digital control (DDC) BuildingAutomation System. It shall also be equipped withdampers to set the design airflow through the unit, andalso an analog or digital display which measures anddisplays the amount of air flowing through the unitcontinuously.

Interior Outside Air Ventilation Systems. Interiorventilation units shall be self-contained DX packagedunits or air-handling units with chilled water-cooling coil,hot water heating coil, and supply air filtration. Interiorventilation units shall incorporate enthalpy heat recoverywheel or desiccant wheel, heating coil, and a cooling coil.Heat recovery shall include use of building relief andexhaust air. Utilize condenser waste heat for desiccantregeneration. The supply air from the ventilation unitsshall be ducted to the return plenum section of the air-handling unit(s) serving the interior zones. Supply air dewpoint leaving the unit shall be maintained at 10°C (50°F)and the supply air dry bulb temperature shall be aminimum of 21.1°C (70° F) and not greater than 25.6°C(78° F). During occupied hours, this unit shall operate toprovide conditioned ventilation air. The unit shall beinoperative during unoccupied hours. The unit shall haveair-monitoring devices to indicate that the supply air isalways 10 percent greater than the exhaust/relief air. Thededicated ventilation unit shall have self-containedmicroprocessor controls capable of connecting to andinteroperating with a BACnet or LONWORKS DirectDigital Control (DDC) Building Automation System. Itshall also be equipped with dampers to set the designairflow through the unit, and also an analog or digitaldisplay which measures and displays the amount of airflowing through the unit continuously.

5.9 HVAC Systems and Components

HVAC SystemsPerimeter Outside Air Ventilation Systems. Perimeterventilation units shall be self-contained DX package unitsor air-handling units with fan section having variablespeed drive, chilled water cooling coil, hot water heatingcoil, enthalpy heat recovery wheel, or desiccant wheel andsupply air filtration. The perimeter ventilation units shallprovide 100-percent outside air. Reheat shall be hot gasbypass, a heat pipe or a run around coil. Chilled watershall be generated by an air-cooled chiller or a 24-hourchiller. If a desiccant wheel is used for controlling thespecific humidity discharge at the wheel, condenser reheatshall be used for regeneration of the desiccant, along withminimum electric backup. Supply air dew point leavingthe unit shall be maintained at 10°C (50°F) and the supplyair dry bulb temperature leaving the air-handling unitshall be a minimum of 21.1°C (70° F) and not greaterthan 25.6°C (78° F) during occupied hours. Duringoccupied hours, this unit shall operate to deliverconditioned ventilation air and maintain positive pressurein the perimeter zone with respect to outside air pressure.During unoccupied hours, the unit shall run at 40 percentof its capacity to provide conditioned air at 10°C (50° F)dew point and at least 21.1°C (70°F) to help maintainpositive pressure in the perimeter zone with respect tooutside air. In both the occupied and unoccupied modesthe system shall operate to adjust the airflow as requiredto maintain a differential positive pressure in theperimeter zone relative to the prevailing pressure outsidethe building. When the outside air dew point drops below2.8°C (37°F), the unit shall have the capacity to maintainneutral pressure with respect to the outside by exhaustingrelief air from the return duct system. The ventilation unit


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Fan Coil System. For perimeter spaces, provide four-pipefan coil units with cooling coil, heating coil, 35 percentefficiency filters, internal condensate drain, and overflowdrain. Unit shall have self-contained microprocessorcontrols and shall be capable of connecting to andinteroperating with a BACnet or LONWORKS DirectDigital Control (DDC) Building Automation System. Fancoil units shall be capable of operating with unit mountedor remote mounted temperature sensor.

Fin Tube Heating Systems. When fin-tube radiation isused, reheat should not be featured with perimeter airdistribution systems. Fin-tube radiation shall haveindividual zone thermostatic control capable ofconnecting to a self-contained microprocessor that caninterface with a BACnet or LONWORKS Direct DigitalControl (DCC) Building Automation System.

Variable Volume System with Shutoff Boxes. Variable Air Volume (VAV) systems with full shutoff VAV boxesshall be used for perimeter zone applications only. VAVshutoff boxes shall be used only with the perimeter airdistribution systems in order to eliminate the need forreheat. The air-handling unit and associated VAV boxesshall have self-contained microprocessor controls capableof connecting to and interoperating with a Direct DigitalControl (DDC) Building Automation System.

Variable Volume System with Fan-Powered Boxes.Variable air volume (VAV) systems with fan-powered VAVboxes may be used for both perimeter and interior zoneapplications. The air-handling unit and associated VAVboxes shall have self-contained microprocessor controlscapable of connecting to and interoperating with aBACnet or LONWORKS Direct Digital Control (DDC)Building Automated System. Fan powered boxes shall be

equipped with a ducted return, featuring a filter/filter rackassembly and covered on all external exposed sides withtwo-inches of insulation. The return plenum box shall bea minimum of 61 mm (24 inches) in length and shall bedouble wall with insulation in-between or contain at leastone elbow where space allows. Fan-powered boxes mayhave hot water heating coils used for maintainingtemperature conditions in the space under partial loadconditions. Fan powered boxes located on the perimeterzones and on the top floor of the building shall containhot water coils for heating.

Underfloor Air Distribution System. Underfloor airdistribution systems shall incorporate variable air volume(VAV) units designed to distribute the supply air fromunder the floor using variable volume boxes or variablevolume dampers running out from underfloor, ducted,main trunk lines. Air shall be distributed into the spacethrough floor-mounted supply registers that shall befactory fabricated with manual volume control dampers.Supply air temperature for underfloor systems shall bebetween 10°C (50°F) dew point and 18°C (64°F) dry bulb. For perimeter underfloor systems, provide fan coilunits or fin tube radiators located beneath the floor withsupply air grilles or registers mounted in the floor.The air-handling unit, VAV boxes, and variable volumedampers shall have self-contained microprocessor controlscapable of connecting to and interoperating with a BACnetor LONWORKS direct digital control (DDC) BuildingAutomation System. The maximum zone size of anunderfloor air distribution system shall not exceed 2,360 l/s (5,000 CFM).

Underfloor Air Displacement System. Underfloor airdisplacement systems shall incorporate variable airvolume (VAV) units designed to distribute the supply air from under the floor using variable volume boxes or



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variable volume dampers running out from underfloor,ducted, main trunk lines. The VAV boxes or controldampers shall be hard ducted or connected directly to the main trunk lines. Air shall be distributed into theoccupied space through floor-mounted, low-turbulence,displacement flow, swirl diffusers and shall contain a dustcollection basket situated below the floor. Supply airtemperature for underfloor systems shall be 10°C (50°F)dew point and 18°C (64°F) Dry Bulb. For perimeterunderfloor systems, provide fan coil units or fin tuberadiators located beneath the floor with supply air grillesor registers mounted in the floor. The air-handling unit,VAV boxes, and variable volume dampers shall have self-contained microprocessor controls capable of connectingto and interoperating with a BACnet or LONWORKSDirect Digital Control (DDC) Building AutomationSystem. The maximum capacity of an underfloor airdistribution system shall not exceed 2,360 l/s (5,000 cfm).

Heat Pump Systems. Console perimeter heat pumpsystem(s) may be considered for the perimeter zone. Forthe interior zone either a packaged heat pump variablevolume system or a central station air handling unit withcooling-heating coil with VAV boxes shall be considered.Condenser water loop temperatures shall be maintainedbetween 15°C (60°F) and 27°C (80°F) year round, eitherby injecting heat from a gas fired, modular boiler if thetemperature drops below 15°C (60°F) or by rejecting theheat through a cooling tower if the temperature of theloop rises above 35°C (95°F) dry bulb. Outside air shall beducted to the return plenum section of the heat pumpunit. Heat pumps shall be provided with filter/filter rackassemblies upstream of the return plenum section of theair-handling unit.

HVAC System ComponentsAir-Handling Units (AHU’s). Air-handling units shall besized to not exceed 11,800 l/s (25,000 cfm). Smaller unitsare encouraged to facilitate flexible zone control, particu-larly for spaces that involve off-hour or high-loadoperating conditions. To the extent possible, “plug-n-play”AHU configurations should be considered, facilitatingeasy future adaptations to space-load changes.Psychrometric analyses (complete with chart diagrams)shall be prepared for each air-handling unit application,characterizing full and part load operating conditions.Air-handling unit/coil designs shall assure thatconditioned space temperatures and humidity levels arewithin an acceptable range, per programmedrequirements, and ASHRAE Standards 55 and 62.

Depending on sensible heat ratio characteristics, effectivemoisture control may require cooling coil air dischargedew point temperatures as low as 10°C (50°F). Asrequired, provide face-by-pass or heat recovery features tore-heat cooling coil discharge temperatures for acceptablespace entry. Provide a direct form of re-heat and/orhumidification only if space conditions require tightenvironmental control, or if recurring day-long periods ofunacceptable humidity levels would otherwise result.

Supply, Return and Relief Air Fans: Centrifugal double-width double-inlet forward curved and airfoil fans arepreferable for VAV systems. All fans shall bear the AMCAseal and performance shall be based on tests made inaccordance with AMCA Standard 210. Fans should beselected on the basis of required horsepower as well assound power level ratings at full load and at part loadconditions. Fan motors shall be sized so they do not runat overload anywhere on their operating curve. Fanoperating characteristics must be checked for the entire



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range of flow conditions, particularly for forward curvedfans. Fan drives shall be selected for a 1.5 service factorand fan shafts should be selected to operate below the firstcritical speed. Thrust arresters should be designed forhorizontal discharge fans operating at high static pressure.

Coils: Individual finned tube coils should generally bebetween six and eight rows with at least 2.1 mm betweenfins (12 fins per inch) to ensure that the coils can beeffectively and efficiently cleaned. Dehumidifying coilsshall be selected for no more than negligible water dropletcarryover beyond the drain pan at design conditions. Allhot water heating and chilled water cooling coils shall becopper tube and copper finned materials. Equipment andother obstructions in the air stream shall be locatedsufficiently downstream of the coil so that it will not comein contact with the water droplet carryover. Cooling coilsshall be selected at or below 2.5 m/s face velocity (500fpm) to minimize moisture carryover. Heating coils shallbe selected at or below 3.8 m/s face velocity (750 fpm).

Drains and Drain Pans: Drain pans shall be made ofstainless steel, insulated and adequately sloped andtrapped to assure drainage. Drains in draw-throughconfigurations shall have traps with a depth and heightdifferential between inlet and outlet equal to the designstatic pressure plus 2.54 mm (1 inch) minimum.

Filter Sections: Air filtration shall be provided in every air-handling system. Air-handling units shall have a disposablepre-filter and a final filter. The filter media shall be ratedin accordance with ASHRAE Standard 52. Pre-filters shallbe 30 percent to 35 percent efficient. Final filters shall befilters with 85 percent efficiency capable of filtering downto 3.0 microns per ASHRAE 52. Filter racks shall bedesigned to minimize the bypass of air around the filtermedia with a maximum bypass leakage of 0.5 percent.

The Federal Triangle Building, Washington, D.C.



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Mixing Boxes: Air-handling units shall be provided withmixing boxes where relief air is discharged from the air-handling unit. Mixing boxes may also be used on thereturn side of the unit in lieu of a plenum box. Air flowcontrol dampers shall be mounted within the mixing boxor on the ductwork connecting to the mixing box.

Terminals. VAV terminals shall be certified under the ARIStandard 880 Certification Program and shall carry theARI Seal. If fan-powered, the terminals shall be designed,built, and tested as a single unit including motor and fanassembly, primary air damper assembly and anyaccessories.

VAV terminals shall be pressure-independent type units.

Units shall have BACnet or LONWORKS self-containedcontrols.

Fan-powered terminals: Fan-powered terminals shallutilize speed control to allow for continuous fan speedadjustment from maximum to minimum, as a means ofsetting the fan airflow. The speed control shall incorporatea minimum voltage stop to ensure the motor cannotoperate in the stall mode.

All terminals shall be provided with factory-mounteddirect digital controls compatible and suitable foroperation with the BAS.

Air Delivery Devices. Terminal ceiling diffusers orbooted-plenum slots should be specifically designed forVAV air distribution. Booted plenum slots should notexceed 1.2 meters (4 feet) in length unless more than onesource of supply is provided. “Dumping” action atreduced air volume and sound power levels at maximum

Filters shall be sized at 2.5 m/s (500 FPM) maximum facevelocity. Filter media shall be fabricated so that fibrousshedding does not exceed levels prescribed by ASHRAE52. The filter housing and all air-handling componentsdownstream shall not be internally lined with fibrousinsulation. Double-wall construction or an externallyinsulated sheet metal housing is acceptable. The filterchange-out pressure drop, not the initial clean filterrating, must be used in determining fan pressurerequirements. Differential pressure gauges and sensorsshall be placed across each filter bank to allow quick andaccurate assessment of filter dust loading as reflected byair-pressure loss through the filter and sensors shall beconnected to building automation system.

UVC Emitters/Lamps: Ultraviolet light (C band) emitters/lamps shall be incorporated downstream of all coolingcoils and above all drain pans to control airborne andsurface microbial growth and transfer. Applied fixtures/lamps must be specifically manufactured for this purpose.Safety interlocks/features shall be provided to limit hazardto operating staff.

Access Doors: Access Doors shall be provided at airhandling units downstream of each coil, upstream ofeach filter section and adjacent to each drain pan and fansection. Access doors shall be of sufficient size to allowpersonnel to enter the unit to inspect and service allportions of the equipment components.

Plenum Boxes: Air-handling units shall be provided withplenum boxes where relief air is discharged from the air-handling unit. Plenum boxes may also be used on thereturn side of the unit in lieu of a mixing box. Air-flowcontrol dampers shall be mounted on the ductworkconnecting to the plenum box.



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peak capacity (each) shall be provided. The units shall bepackaged, with all components and controls factory pre-assembled. Controls and relief valves to limit pressure andtemperature must be specified separately. Burner controlshall be return water temperature actuated and controlsequences, such as modulating burner control and outsideair reset, shall be utilized to maximum efficiency andperformance. Multiple closet type condensing boilers shallbe utilized, if possible. Boilers shall have self-containedmicroprocessor controls capable of connecting to andinteroperating with a BACnet or LONWORKS DirectDigital Control (DDC) Building Automated System.Boilers shall have a minimum efficiency of 80 percent asper ASHRAE 90.1.

Individual boilers with ratings higher than 29 MW (100million Btu/hour) or boiler plants with ratings higherthan 75 MW (250 million Btu/hour) are subject to reviewby the Environmental Protection Agency.

Boilers shall be piped to a common heating water headerwith provisions to sequence boilers on-line to match theload requirements. All units shall have adequate valving toprovide isolation of off-line units without interruption ofservice. All required auxiliaries for the boiler systems shallbe provided with expansion tanks, heat exchangers, watertreatment and air separators, as required.

Gas Trains: Boiler gas trains shall be in accordance withInternational Risk Insurance (IRI) standards.

Automatic Valve Actuators: Gas valve actuators shall notcontain NaK (sodium-potassium) elements since thesepose a danger to maintenance personnel.

m3/s (cfm) delivery should be minimized. For VAVsystems, the diffuser spacing selection should not be basedon the maximum or design air volumes but rather on theair volume range where the system is expected to operatemost of the time. The designer should consider theexpected variation in range in the outlet air volume toensure the air diffusion performance index (ADPI) valuesremain above a specified minimum. This is achieved bylow temperature variation, good air mixing, and noobjectionable drafts in the occupied space, typically 150mm (6 inch) to 1830 mm (6 feet) above the floor.Adequate ventilation requires that the selected diffuserseffectively mix the total air in the room with the suppliedconditioned air, which is assumed to contain adequateventilation air.

Motors. All motors shall have premium efficiency as perASHRAE 90.1. 1/2 HP and larger shall be polyphase.Motors smaller than 1/2 HP shall be single phase. Formotors operated with variable speed drives, provideinsulation cooling characteristics as per NEC and NFPA.

Boilers. Boilers for hydronic hot water heatingapplications shall be low pressure, with a workingpressure and maximum temperature limitation aspreviously stated, and shall be installed in a dedicatedmechanical room with all provisions made for breeching,flue stack and combustion air. For northern climates, aminimum of three equally sized units shall be provided.Each of the three units shall have equal capacities suchthat the combined capacity of the three boilers shallsatisfy 120 percent of the total peak load of heating andhumidification requirements. For southern climates, aminimum of two equally sized units at 67 percent of the



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Venting: Products of combustion from fuel-firedappliances and equipment shall be delivered outside ofthe building through the use of breeching, vent, stack and chimney systems. Breeching connecting fuel-firedequipment to vents, stacks and chimneys shall generallybe horizontal and shall comply with NFPA 54. Vents,stacks and chimneys shall generally be vertical and shallcomply with NFPA 54 and 211. Breeching, vent, stack, andchimney systems may operate under negative, neutral, orpositive pressure and shall be designed relative to the flue-gas temperature and dew point, length and configurationof the system, and the value of the insulation techniquesapplied to the vent. Venting materials may be factoryfabricated and assembled in the field and may be doubleor single wall systems depending on the distance fromadjacent combustible or noncombustible materials.Material types, ratings and distances to adjacent buildingmaterials shall comply with NFPA 54 and 211.

Heat Exchangers. Steam-to-water heat exchangers shall beused in situations where district steam is supplied and ahot water space heating and domestic hot water heatingsystem have been selected. Double-wall heat exchangersshall be used in domestic hot water heating applications.Plate heat exchangers shall be used for watersideeconomizer applications.

Chillers. Chillers shall be specified in accordance with thelatest Air-conditioning and Refrigeration Institute (ARI)ratings procedures and latest edition of the ASHRAEStandard 90.1. As a part of the life cycle cost analysis, theuse of high-efficiency chillers with COP and IPLV ratingsthat exceed 6.4 (0.55 kW/ton) should be analyzed.Likewise, the feasibility of gas-engine driven chillers, icestorage chillers, and absorption chillers should beconsidered for demand shedding and thermal balancingof the total system.

BACnet or LONWORKS Microprocessor-based controlsshall be used. The control panel shall have self-diagnosticcapability, integral safety control and set point display,such as run time, operating parameters, electrical lowvoltage and loss of phase protection, current and demandlimiting, and output/input-COP [input/output (kW/ton)]information.

Chilled water machines: When the peak cooling load is1760 kw (500 tons) or more, a minimum of three chilledwater machines shall be provided. The three units shallhave a combined capacity of 120 percent of the total peakcooling load with load split percentages 40-40-40 or 50-50-20. If the peak cooling load is less than 1760 kW (500tons), a minimum of two equally sized machines at 67percent of the peak capacity (each) shall be provided. Allunits shall have adequate valving to provide isolation ofthe off-line unit without interruption of service. Coolingsystems with a capacity less than 50 tons shall use air-cooled chillers.

Chillers shall be piped to a common chilled water headerwith provisions to sequence chillers on-line to match theload requirements. All required auxiliaries for the chillersystems shall be provided with expansion tanks, heatexchangers, water treatment and air separators, asrequired. If multiple chillers are used, automatic shutoffvalves shall be provided for each chiller.

Chiller condenser bundles shall be equipped withautomatic reversing brush-type tube cleaning systems.

Chiller condenser piping shall be equipped with recircu-lation/bypass control valves to maintain incomingcondenser water temperature within chiller manufacturer’sminimum.



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Part load efficiency must be specified in accordance withARI Standard 550/590.

The design of refrigeration machines must comply withClean Air Act amendment Title VI: Stratospheric OzoneProtection and Code of Federal Regulations (CFR) 40, Part82: Protection of Stratospheric Ozone.

Chlorofluorocarbon (CFC) refrigerants are not permittedin new chillers. Acceptable non-CFC refrigerants are listedin EPA regulations implementing Section 612 (SignificantNew Alternatives Policy (SNAP) of the Clean Air Act, TitleVI: Stratospheric Ozone Protection. (Note: GSA acceptsthese criteria in documenting certification of LEEDratings. )

Refrigeration machines must be equipped with isolationvalves, fittings and service apertures as appropriate forrefrigerant recovery during servicing and repair, asrequired by Section 608 of the Clean Air Act, Title VI.Chillers must also be easily accessible for internalinspections and cleaning.

Ice Storage Equipment. Ice-on-coil systems shall beconsidered in locations where the demand costs ofelectricity are greater than $15.00 per kW (demand costsfor peak generation, transmission, and delivery costs),including prefabricated tanks with glycol coils and waterinside the tank. The tank shall be insulated and itscapacity and performance shall be guaranteed by thevendor. Self-contained, fabricated ice storage system shall

have self-contained BACnet LONWORKS microprocessorcontrols for charging and discharging the ice storagesystem and capable of being connected to a centralbuilding automation system. Other types of ice storagesystems are not permitted.

Cooling Towers. Multiple cell towers and isolated basinsare required to facilitate operations, maintenance andredundancy. The number of cells shall match the numberof chillers. Supply piping shall be connected to amanifold to allow for any combination of equipment use.Multiple towers shall have equalization piping betweencell basins. Equalization piping shall include isolationvalves and automatic shutoff valves between each cell.Cooling towers shall have ladders and platforms for easeof inspections and replacement of components. Variablespeed pumps for multiple cooling towers shall notoperate below 30 percent of rated capacity.

Induced draft cooling towers with multiple-speed orvariable-speed condenser fan controls shall be con-sidered. Induced draft towers shall have a clear distanceequal to the height of the tower on the air intake side(s)to keep the air velocity low. Consideration shall be givento piping arrangement and strainer or filter placementsuch that accumulated solids are readily removed fromthe system. Clean-outs for sediment removal and flushingfrom basin and piping shall be provided.

Forced draft towers shall have inlet screens. Forced drafttowers shall have directional discharge plenums whererequired for space or directional considerations.Consideration shall be given to piping arrangement and



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strainer or filter placement such that accumulated solidsare readily removed from the system. Clean-outs forsediment removal and flushing from basin and pipingshall be provided. The cooling tower’s foundation,structural elements and connections shall be designed fora 44 m/s (100 MPH) wind design load. Cooling towerbasins and housing shall be constructed of stainless steel.If the cooling tower is located on the building structure,vibration and sound isolation must be provided. Coolingtowers shall be elevated to maintain required net positivesuction head on condenser water pumps and to provide a4-foot minimum clear space beneath the bottom of thelowest structural member, piping or sump, to allow re-roofing beneath the tower.

Special consideration should be given to de-icing coolingtower fills if they are to operate in sub-freezing weather,such as chilled water systems designed with a water-sideeconomizer. A manual shutdown for the fan shall beprovided. If cooling towers operate intermittently duringsub-freezing weather, provisions shall be made fordraining all piping during periods of shutdown. For thispurpose indoor drain down basins are preferred to heatedwet basins at the cooling tower. Cooling towers withwaterside economizers and designed for year-roundoperation shall be equipped with basin heaters.Condenser water piping located above-grade and down to3 feet below grade shall have heat tracing. Cooling towersshall be provided with BACnet LONWORKSmicroprocessor controls, capable of connecting to centralbuilding automation systems.

Chilled Water, Hot Water, and Condenser Water Pumps.Pumps shall be of a centrifugal type and shall generally beselected to operate at 1750 RPM. Both partial load andfull load must fall on the pump curve. The number ofprimary chilled water and condenser water pumps shallcorrespond to the number of chillers, and a separatepump shall be designed for each condenser water circuit.Variable volume pumping systems should be consideredfor all secondary piping systems with pump horsepowergreater than 10 kW (15 HP). The specified pump motorsshall not overload throughout the entire range of thepump curve. Each pump system shall have a standbycapability for chilled, hot water, and condenser waterpumps.

Each boiler cooling tower and chiller group pumps shallbe arranged with piping, valves, and controls to allow eachchiller-tower group to operate independently of the otherchiller and cooling tower groups.

See Chapter 7, “Fire Protection Engineering,” for fireprotection provisions for cooling towers.


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sterilization, a separate clean steam generator shall beprovided and sized for the seasonal load. Humidifiers shallbe centered on the air stream to prevent stratification ofthe moist air. All associated equipment and piping shall bestainless steel. Humidification system shall havemicroprocessor controls and the capability to connect tobuilding automation systems.

Water Treatment. The water treatment for all hydronicsystems, including humidification systems, shall bedesigned by a qualified specialist. The design system shalladdress the three aspects of water treatment: biologicalgrowth, dissolved solids and scaling, and corrosionprotection. The performance of the water treatmentsystems shall produce, as a minimum, the followingcharacteristics; hardness: 0.00; iron content: 0.00;dissolved solids: 1,500 to 1,750 ppm; silica: 610 ppm orless; and a PH of 10.5 or above. The system shall operatewith an injection pump transferring chemicals fromsolution tank(s) as required to maintain the conditionsdescribed. The chemical feed system shall have self-contained microprocessor controls capable of connectingto and interoperating with a Direct Digital Control(DDC) Building Automation System. The methods usedto treat the systems’ make-up water shall have priorsuccess in existing facilities on the same municipal watersupply and follow the guidelines outlined in ASHRAEApplications Handbook.

5.10 Humidification and Water Treatment

Humidifiers and Direct Evaporative Coolers. Make-upwater for direct evaporation humidifiers and directevaporative coolers, or other water spray systems shalloriginate directly from a potable source that has equal orbetter water quality with respect to both chemical andmicrobial contaminants. Humidifiers shall be designed sothat microbiocidal chemicals and water treatmentadditives are not emitted in ventilation air. Allcomponents of humidification equipment shall bestainless steel. Air washer systems are not permitted forcooling.

Humidification shall be limited to building areasrequiring special conditions. Courtrooms with wallcoverings of wood shall be provided with humidification.General office space shall not be humidified unless severewinter conditions are likely to cause indoor relativehumidity to fall below 30 percent. Where humidificationis necessary, atomized hot water, clean steam orultrasound may be used and shall be generated byelectronic or steam-to-steam generators. To avoid thepotential for oversaturation and condensation at low load,the total humidification load shall be divided betweenmultiple, independently-modulated units. Single-unithumidifiers are not acceptable. When steam is requiredduring summer seasons for humidification or


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Also, the use of steam for HVAC applications shall belimited to the conversion of steam heat to hot water heatand for use in providing humidification. Steam shall notbe used as a heating medium for distribution throughouta building to terminal units, air handling units, perimeterheating units, coils, or any other form of heat transferwhere steam is converted to a source of heat for use inspace comfort control or environmental temperaturecontrol.

Steam delivered from any source other than a clean steam generation system shall be prohibited from use inproviding humidification. Steam delivered from a central

College Park, MD

5.11 Heating Systems

Steam HeatingDistrict steam heating, if available, shall be used ifdetermined to be economical and reliable through a lifecycle cost analysis. If steam is furnished to the building,such as under a district heating plan, it should beconverted to hot water with a heat exchanger in themechanical room near the entrance into the building.If steam heating is used, the designer shall investigate the use of district steam condensate for pre-heating ofdomestic hot water. Steam heating is not permitted insidethe building other than conversion of steam-to-hot waterin the mechanical room.


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plant, a district steam system, steam boilers, or anyequipment where chemicals are delivered into themedium resulting in the final product of steam shall notbe used for the purpose of providing humidification tothe HVAC system or occupied spaces.

Hot Water Heating SystemsGSA prefers low-temperature hot-water heating systems;205 kPa (30 psi) working pressure and maximumtemperature limitation of 93.3°C (200°F). The use ofelectric resistance and/or electric boilers as the primaryheating source for the building is prohibited. Design andlayout of hydronic heating systems shall follow theprinciples outlined in the latest edition of the ASHRAESystems and Equipment Handbook.

Water Treatment. See section “Humidification and WaterTreatment” of this chapter for water treatment.

Temperature and Pressure Drop. Supply temperaturesand the corresponding temperature drops for spaceheating hot water systems must be set to best suit theequipment being served. Total system temperature dropshould not exceed 22°C (72°F). The temperature drop forterminal unit heating coils shall be 11°C (52°F). Designwater velocity in piping should not exceed 2.5 meters persecond (8 feet per second) or design pressure friction lossin piping systems should not exceed 0.4 kPa per meter (4 feet per 100 feet), whichever is larger, and not less than1.3 meters per second (4 feet per second).

Freeze Protection. Propylene glycol manufacturedspecifically for HVAC systems shall be used to protect hotwater systems from freezing, where extensive runs ofpiping are exposed to weather, where heating operationsare intermittent or where coils are exposed to large

volumes of outside air. Freeze protection circulationpump shall be provided along with polypropylene glycol.Heat tracing systems are not acceptable for systems insidethe building. Glycol solutions shall not be used directly inboilers, because of corrosion caused by the chemicalbreakdown of the glycol. The water make-up line forglycol systems shall be provided with an in-line watermeter to monitor and maintain the proper percentage ofglycol in the system. Provisions shall be made for draindown, storage and re-injection of the glycol into thesystem.

Radiant Heat. Radiant heating systems (hot water or gasfired) may be overhead or underfloor type. They shouldbe considered in lieu of convective or all-air heatingsystems in areas that experience infiltration loads in excessof two air changes per hour at design heating conditions.Radiant heating systems may also be considered for highbay spaces and loading docks.

Instantaneous Hot Water. The use of instantaneous hotwater generators is prohibited except for incidental use atterminal fixtures.

Natural Gas Piping. Refer to Plumbing Systems, NaturalGas Systems section of this chapter.

Fuel Oil Piping. Refer to Plumbing Systems, Fuel OilSystems section of this chapter.

Underground Fuel Oil. Refer to Plumbing Systems, FuelOil Systems section of this chapter.


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differential in the secondary systems, at the terminalpoints of use, such as coils with a design supply watertemperature between 4°C and 7°C (40°F and 45°F).

District chilled water, if available, shall be used for coolingonly if determined to be economical and reliable througha life cycle cost analysis.

Mechanical equipment rooms must be designed inaccordance with the requirements of ASHRAE Standard15: Safety Code for Mechanical Refrigeration. Chiller leakdetection and remote alarming shall be connected to the BAS.

Freeze Protection. Propylene glycol manufacturedspecifically for HVAC Systems is used for freezeprotection, primarily in low temperature chilled water systems (less than 4°C) (less than 40°F). Theconcentration of antifreeze should be kept to a practicalminimum because of its adverse effect on heat exchangeefficiency and pump life. The water make-up line forglycol systems shall be provided with an in-line watermeter to monitor and maintain the proper percentage ofglycol in the system. All coils exposed to outside airflow(at some time) shall be provided with freeze protectionthermostats and control cycles. Provisions shall be madefor drain down, storage and re-injection of the glycol intothe system.

Condenser Water. All water-cooled condensers must beconnected to a recirculating heat-rejecting loop. The heatrejection loop system shall be designed for a 6°C (43°F)temperature differential and a minimum of 4°C (40°F) wet bulb approach between the outside air temperatureand the temperature of the water leaving the heatrejection equipment. Heat tracing shall be provided forpiping exposed to weather and for piping down to 3 feetbelow grade.

5.12 Cooling Systems

Chilled Water SystemsChilled water systems include chillers, chilled water and condenser water pumps, cooling towers, piping andpiping specialties.

The chilled water systems shall have a 10°C (50°F)temperature differential in the central system, at thecentral plant, with a design supply water temperaturebetween 4°C and 7°C (40°F and 45°F). In climates withlow relative humidity, an 8°C (46°F) may be used. Thechilled water system shall have a 6°C (43°F) temperature

U.S. Census Bureau


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Water Treatment. See section: Humidification and WaterTreatment of this chapter for water treatment.

Special Cooling SystemsWaterside Economizer Cycle. In certain climate conditionscooling towers are capable of producing condenser watercold enough to cool the chilled water system without chilleroperation. This option shall be considered in life cycle costcomparisons of water cooled chillers. Waterside economizercycles are particularly cost effective in the low humidityclimates of the western United States. In the eastern UnitedStates, enthalpy airside economizer cycles tend to producelower operating costs. However, where used, any airsideeconomizer shall be set so that no air with a dew pointabove 10°C (50°F) is allowed into the building. Watersideeconomizer systems shall be used only in areas where theoutside air temperature will be below 4.4°C (40°F) wet bulb.Waterside economizers shall utilize a plate heat exchangerpiped in parallel arrangement with its respective chiller. See“Air Distribution Systems, Air-Handling Units, and AirsideEconomizer Cycle” of this chapter.

Computer Room Air-Conditioning Units. Mainframecomputer rooms shall be cooled by self-contained unitsfor loads up to 280 kW (80 tons). These units shall bespecifically designed for this purpose and containcompressors, filters, humidifiers and controls. They shallbe sized to allow for a minimum of 50 percent redundancy,either two units at 75 percent load or three units at 50percent. If the nature of the computer room is critical (asdetermined by consulting the GSA’s Office of the ChiefInformation Officer), three units sized at 50 percent of thedesign load shall be used. Heat rejection from these self-contained units shall be by air-cooled condensers orrecirculating water-cooled condensers connected to acooling tower or evaporative-cooled condenser. Water-sidefree cooling shall be utilized when possible.

For cooling loads greater than 280 kW (80 tons), chilledwater air-handling systems shall be considered in a lifecycle cost analysis. A dedicated chiller(s) is preferred,unless other parts of the building also require 24-hourcooling. The 24-hour cooling needs of a computer roomshould be identified in the HVAC, HVAC SystemComponents, Sizing and Selection Standards for Equipmentand Systems section of this chapter. The dedicated chillerplant shall provide some means of redundant backup,either by multiple machines or connection to the facility’slarger chilled water plant.

In large computer installations (areas of 500 m2(5,000 ft2))it is recommended to segregate cooling of the sensibleload (computer load) and control of the outside airventilation and space relative humidity by using twoseparate air-handling systems. In this design, one unitrecirculates and cools room air without dehumidificationcapability. This unit is regulated by a room thermostat.The second unit handles the outside air load, provides the required number of air changes and humidifies/dehumidifies in response to a humidistat. This schemeavoids the common problem of simultaneouslyhumidifying and dehumidifying the air.

For ventilation, air-handling, and humidificationrequirements of computer rooms, see sections AirDistribution Systems, Air-Handling Units, Computer RoomAir-Handling of this chapter. The room temperatureconditions shown in Table 5-1 provide a higher availabletemperature for reduced fan power consumption andeasier winter humidification. Verify with users todetermine if the air- conditioning system must beconnected to emergency power system. These systemsshould be provided with an alternative power source,connected to emergency generators, if the computer room


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houses critical components. Consult GSA’s Office of theChief Information Officer to determine which computerrooms meet this requirement.

Desiccant Cooling. For high occupancy applicationswhere moisture removal is required, solid desiccant withsilica gel may be used in combination with mechanicalcooling. Heat recovery wheels may be used prior to themechanical cooling process. Desiccant cooling units shallbe equipped with airflow-setting devices for both processand reactivation air flows, and shall be equipped withgauges or digital displays to report those air flowscontinuously. The desiccant cooling system shall have self-contained microprocessor controls capable of connectingto and interoperating with a direct digital control (DDC)Building Automation system. Natural gas or condenserwaste heat shall be used as fuel for reactivation of thedesiccant. Lithium chloride liquid desiccants are notpermitted.

5.13 Heat Recovery Systems

Heat recovery systems shall be utilized in all ventilationunits (100 percent outside air units) and where thetemperature differentials between supply air and exhaustair is significant. Heat recovery systems shall operate at aminimum of 70 percent efficiency. The heat recoverysystems must be capable of connecting to a micropro-cessor controller that in turn can be connected to a directdigital control (DDC) Building Automation System.Prefilters shall be provided in all heat recovery systemsbefore the heat recovery equipment.

Heat Pipe. For sensible heat recovery a run around typeheat pipe shall use refrigerant to absorb heat from the airstream at the air intake and reject the heat back into theair stream at the discharge of the air-handling unit.System shall have solenoid valve control to operate underpartial load conditions.

Run-around Coil. A glycol run-around coil could be usedwith control valves and a pump for part load conditions.The run-around coils shall be used at the exhaustdischarge from the building and at the fresh air intakeinto the building. The run-around coil system shall becapable of connecting to a microprocessor controller thatin turn can be connected to a direct digital control (DDC)Building Automation system.

Enthalpy Wheel. A desiccant-impregnated enthalpy wheelwith variable speed rotary wheel may be used in thesupply and exhaust systems.

Sensible Heat Recovery. For sensible heat recovery, across-flow, air-to-air (z-duct) heat exchanger shall recoverthe heat in the exhaust and supply air streams. Z-ductsshall be constructed entirely of sheet metal. Heat-wheelsmay also be used for sensible heat recovery. Unit shallhave variable speed drive for controlling the temperatureleaving the unit.


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shut down during unoccupied hours. Maintain 10°C(50°F) dewpoint when outside air dewpoint is above thatof the outside air. Use humidification equipment, ifnecessary, to maintain 3°C (37°F) dewpoint wheneveroutside dewpoint is below 3°C (37°F). Also maintainneutral pressure by setting the exhaust air quantity toequal the supply air rate. Air monitoring devices shall beconnected to the building automation system to indicatepositive and neutral pressure.

Special Ventilation RequirementsVentilation requirements for all building spaces shallcomply with ASHRAE 62.

Entrance Vestibules and Lobbies. Sufficient heating andcooling should be provided to offset the base load plus theinfiltration load of the space. The entrance vestibuleshould be positively pressurized relative to atmosphericpressure to minimize infiltration. A separate variable airvolume (VAV) system shall serve entrance vestibules andlobby spaces. The VAV system shall operate to vary theflow of air for the space through a differential pressurecontrol system designed to maintain positive pressurerelative to the outdoors and neutral or negative pressurerelative to adjacent spaces. Also provide air monitoringdevices in the unit. The air-handling unit and the variablevolume dampers at the VAV boxes shall have self-contained microprocessor controls capable of connectingto and interoperating with a BACnet or LONWORKSdirect digital control (DDC) Building Automation System.

Atriums. A dedicated air-handling system shall beprovided to control heat gain/loss in the occupiable areasof the atrium. The atrium area should maintain negativepressure relative to adjacent interior and perimeter spacesor zones and positive or neutral pressure relative toadjacent vestibules and lobbies, and positive pressure

5.14 Pressurization and Ventilation

PressurizationPerimeter Zone. A dedicated 100 percent outside air unitshall be used to maintain positive pressure. Theventilation air for the perimeter air-handling unit shall besized based on maximum occupancy with diversity andshall operate continuously during occupied hours andoperate at 40 percent capacity during unoccupied hours.Industrial grade pressure sensors shall be located atseveral perimeter areas to communicate outside airpressure to maintain differential positive pressure(adjustable). The internal pressure need only be slightlyhigher than ambient on average to achieve the goal ofexcluding humid outdoor air from building cavities. Inany case, internal pressure shall not be greater than 10pascals. Maintain supply air discharge at the unit no morethan 10°C (50°F) dewpoint when outside air dewpoint isabove this temperature. Maintain neutral pressure (∆P=0)when the outdoor ambient temperature falls below3°C(37°F) dewpoint and neutral pressure. Differentialpressure sensors and dewpoint sensors shall be connectedto the building automation system. An alarm shall signalif positive or neutral pressures are not maintained, onaverage, based on multiple samples taken within a five-minute period. Only industrial grade sensors arepermitted.

Interior Zone. A dedicated outside air-handling unit shall be used to maintain positive pressure. The unit shallbe sized based on the fresh air requirements for maxi-mum occupancy with diversity. The unit shall have air-monitoring devices and control the exhaust rate duringoccupied hours to be less than 10 percent of the supply“air to ensure positive pressure in the space. The unit shall


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relative to the outdoors. The design of the HVAC systemmust be fully coordinated with the smoke control system.

Toilets. Toilet areas must have segregated exhausts andshould be negative in pressure relative to surroundingspaces.

Janitor/Housekeeping Closets. Janitor/housekeepingclosets must have segregated exhausts and should benegative in pressure to surrounding spaces.

Food Service Areas. Kitchen areas shall be negative inpressure relative to adjacent dining rooms, serving areasand corridors. Tempered make-up air shall be introducedat the kitchen hood and/or the area adjacent to thekitchen hood for at least 80 percent of exhaust air. Ductair velocity in the grease hood exhaust shall be no lessthan 7.5 to 9 m/s (1,500 to 1,800 FPM) to hold particulatein suspension. Dishwashing areas must be under negativepressure relative to the kitchen, and dishwashers shall beprovided with their own exhaust hoods and duct systems,constructed of corrosion-resistant material.

High Occupancy Areas. High occupancy areas, which also have largely variable occupancies, such as conferencerooms, lecture theatres, etc., and are served by dedicatedventilation and air-handling systems, shall incorporate aCO2 demand controlled ventilation (DCV) system tominimize energy consumption, while maintaining appro-priate levels of ventilation and pressure relationshipsbetween spaces and the outdoors. The DCV systemdevices shall be located for ease of maintenance and shallprovide appropriate operation of the ventilation system itis controlling. Enthalpy heat recovery system shall beutilized if economically feasible.

5.15 Air Distribution Systems

Variable Air Volume (VAV) SystemsThe VAV supply fan shall be designed for the largest block load, not the sum of the individual peaks. The airdistribution system up to the VAV boxes shall be mediumpressure and shall be designed by using the static regainmethod. Downstream of the VAV boxes the system shallbe low and medium pressure construction and shall bedesigned using the equal friction method. Sound lining is not permitted. Double wall ductwork with insulationin-between is permitted in lieu of sound lining. All VAVboxes shall be accessible for maintenance. Ducted returnshall be utilized at all locations. VAV fan-powered boxsupply and return ducts shall have double wall ductworkwith insulation in-between for a minimum distance of 5 feet.

Air Flow Diagram, Atrium, Phoenix Courthouse


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1. 30 percent of the peak supply volume;2. 0.002 m3/s per m2 (0.4 cfm/sf) of conditioned zone area;

or3. Minimum m3/s (cfm)to satisfy ASHRAE Standard 62

ventilation requirements. VAV terminal units must neverbe shut down to zero when the system is operating.Outside air requirements shall be maintained in accor-dance with the Multiple Spaces Method, Equation 6-1of ASHRAE Standard 62 at all supply air flow conditions.

Airside Economizer Cycle. An air-side enthalpyeconomizer cycle reduces cooling costs when outdoor airenthalpy is below a preset high temperature limit, usually15 to 21°C (60°F to 70°F), depending on the humidity ofthe outside air. Airside economizers shall only be usedwhen they can deliver air conditions leaving the air-handling unit of a maximum of 10°C (50°F) dewpointand a maximum of 70 percent relative humidity. Enthalpyeconomizers shall operate only when return air enthalpyis greater than the outside air enthalpy.

All air distributions systems with a capacity greater than1,416 LPS (3,000 CFM) shall have an air-side economizerin accordance with ASHRAE 90.1, unless the design ofthe air handling systems preclude the use of an airsideeconomizer.

Ductwork. Ductwork shall be designed in accordancewith ASHRAE: Handbook of Fundamentals, Duct DesignChapter, and constructed in accordance with theASHRAE: HVAC Systems and Equipment Handbook, DuctConstruction Chapter, and the SMACNA Design Manuals.All ductwork joints and all connections to air handlingand air distribution devices shall be sealed with mastic—including all supply and return ducts, any ceiling plenumsused as ducts and all exhaust ducts. Energy consumption,security and sound attenuation shall be major consider-ations in the routing, sizing and material selection for theair distribution ductwork.

Underfloor Air Distribution Systems. Provide plenumzones both for perimeter and interior in order to controlthe underfloor variable volume dampers or boxes withseparate plenum barriers between perimeter and interiorzones. The underfloor plenum shall be air tight andcompartmentalized with baffles. Provisions shall beprovided for cleaning the plenum space. When underfloorsupply air distribution is used, the ceiling plenum shall beused for the distribution of the ducted return air. Theperimeter and interior underfloor zones shall be clearlyseparated in order to maintain proper pressurization,temperature and humidity control. Zoning of theunderfloor air distribution systems shall be in accordancewith descriptions presented elsewhere in this chapter.Perimeter wall below the raised flooring system shall beprovided with R-30 insulation and vapor barrier belowthe raised floor. All VAV boxes that are part of anunderfloor air distribution system for both perimeter andinterior systems shall be located below the raised floor.The floor area used for an underfloor system shall havethe slab provided with a minimum of R-10 insulation andvapor barrier from below. This shall incorporate the entireslab area used for the underfloor system.

Volume Control. Particular attention shall be given to the volume control. VAV systems depend on air volumemodulation to maintain the required ventilation rates and temperature set points. Terminal air volume controldevices are critical to the successful operation of thesystem and shall be provided. Zone loads must be calcu-lated accurately to avoid excessive throttling of air flowdue to oversized fans and terminal units. Diffusers shall be high entrainment type (3:1 minimum) to maximize air velocity at low flow rates. If ventilation air is deliveredthrough the VAV box, the minimum volume setting ofthe VAV box should equal the larger of the following:

Table 5-3Ductwork ClassificationStatic Pressure Air Velocity Duct Class

250 Pa (1.0 in W.G.) < 10 m/s DN < (2000 FPM DN) Low Pressure

500 Pa (2.0 in W.G) < 10 m/s DN < (2000 FPM DN) Low Pressure

750 Pa (3.0 in W.G.) < 12.5 m/s DN < (2500 FPM DN) Medium Pressure

1000 Pa (+4.0 in W.G.) < 10 m/s DN > (2000 FPM UP) Medium Pressure

1500 Pa (+6.0 in W.G.) < 10 m/s DN > (2000 FPM UP) Medium Pressure

2500 Pa (+10.0 in W.G.) < 10 m/s DN > (2000 FPM UP) High Pressure



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Supply, return and exhaust air ducts shall be designed andconstructed to allow no more than 3 percent leakage oftotal airflow in systems up to 750 Pa (3 inches WG). Insystems from 751 Pa (3.1 inches WG) through 2500 Pa(10.0 inches WG) ducts shall be designed and constructedto limit leakage to 0.5 percent of the total air flow.

Pressure loss in ductwork shall be designed to complywith the criteria stated above. This can be accomplishedby using smooth transitions and elbows with a radius ofat least 1.5 times the radius of the duct. Where miteredelbows have to be used, double foil sound attenuatingturning vanes shall be provided. Mitered elbows are notpermitted where duct velocity exceeds 10m/s (2000 FPM).

Sizing of Ductwork. Supply and return ductwork shall besized using the equal friction method except for ductworkupstream of VAV boxes. Duct systems designed using the

Supply, Return and Exhaust DuctworkDuctwork Pressure. Table 5-3 provides pressureclassification and maximum air velocities for allductwork. Ductwork construction shall be tested forleakage prior to installation. Each section tested must havea minimum of a 20 ft. length straight-run, a minimum oftwo elbows and a connection to the terminal. The statedstatic pressures represent the pressure exerted on the ductsystem and not the total static pressure developed by thesupply fan. The actual design air velocity should considerthe recommended duct velocities in Table 5-4 when noisegeneration is a controlling factor. Primary air ductwork(fan connections, risers, main distribution ducts) shall bemedium pressure classification as a minimum. Secondaryair ductwork (runouts/branches from main to terminalboxes and distribution devices) shall be low pressureclassification as a minimum.

Table 5-4Recommended Duct Velocities

Controlling Factor Noise Generation (Main Duct Velocities)

Application m/s (fpm)

Private Offices 6 (1,200)Conference RoomsLibraries

Theaters 4 (800)Auditoriums

General Offices 7.5 (1,500)

Cafeterias 9 (1,800)


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equal friction method place enough static pressurecapacity in the supply and return fans to compensate forimproper field installation and changes made to thesystem layout in the future. In buildings with large areasof open plan space, the main duct size shall be increasedfor revisions in the future. Air flow diversity shall also be asizing criterion. 80 percent diversity can be taken at theair-handling unit and decreased the farther the ductworkis from the source until air flow diversity is reduced tozero for the final portion of the system.

Ductwork Construction. Ductwork shall be fabricatedfrom galvanized steel, aluminum or stainless steel sheetmetal depending on applications. Flex duct may be usedfor low pressure ductwork downstream of the terminalbox in office spaces. The length of the flex duct shall notexceed the distance between the low pressure supply air

duct and the diffuser plus 20 percent to permit relocationof diffusers in the future while minimizing replacement ormodification of the hard ductwork distribution system.Generally, flex duct runs should not exceed 3 m (10 feet)nor contain more than two bends.

Joint sealing tape for all connections shall be of reinforcedfiberglass backed material with field applied mastic. Useof pressure sensitive tape is not permitted.

Kitchen Ventilation Systems. Products of combustionfrom kitchen cooking equipment and appliances shall bedelivered outside of building through the use of kitchenventilation systems involving exhaust hoods, grease ductsand make-up air systems where required. Commercialkitchen equipment applications shall be served by a TypeI hood constructed in compliance with UL 710 anddesigned in accordance with code having jurisdiction.Grease ducts shall be constructed of black steel not lessthan 0.055 inch (1.4 mm) (No. 16 gauge) in thickness orstainless steel not less than 0.044 inch (1.1 mm) (No. 18gauge in thickness).

Make-up air systems serving kitchen exhaust hoods shallincorporate air-side heat exchange to recover energy fromthe exhaust stream to be used for heating the supply airstream.

Ceiling Plenum Supply. Ceiling plenum supply does notpermit adequate control of supply air and shall not be used.

Raised Floor Plenum Supply. In computer rooms,underfloor plenum supplies are appropriate. As a generalapplication in other areas (e.g. open offices), underfloorair distribution/displacement systems are appropriate.Where raised floor plenums are used for supply airdistribution, the plenums shall be properly sealed tominimize leakage. R-30 insulation with vapor barrier shallbe provided for perimeter of raised floor walls.

untreated outdoor air. All central multi-floor-type returnair risers must be ducted.

Other less flexible building spaces, such as permanentcirculation, public spaces, and support spaces, shall haveducted returns. Where fully ducted return systems areused, consider placing returns low in walls or on columnsto complement ceiling supply air.

Return air duct in the ceiling plenum of the floor belowthe roof shall be insulated. Double wall ductwork withinsulation in-between shall be used in lieu of sound liningfor a minimum of the last 5 feet before connecting to theair handling unit or a return air duct riser.

SLAB TO SLABPARTITION

CEILING HEIGHTPARTITION

CORE

Figure 5-2 Ceiling Return Plenum with Minimal Return Ductwork



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Plenum and Ducted Returns. With a return plenum caremust be taken to ensure that the air drawn through themost remote register actually reaches the air-handlingunit. The horizontal distance from the farthest point inthe plenum to a return duct shall not exceed 15 m (50feet). No more than 0.8 m3/s (2,000 cfm) should becollected at any one return grille. Figure 5-2 illustrates anexample of an open ceiling plenum with return airductwork. Return air plenums should be avoided. Whendeemed necessary for economic reasons, plenums shall besealed air-tight with respect to the exterior wall and roofslab or ceiling deck to avoid creating negative air pressurein exterior wall cavities that would allow intrusion of

College Park, Maryland chilled water supply and return


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5.16 Pumping Systems

Pump and Piping Systems. The system shall utilizeparallel piping systems with a two-pipe main distributionsystem arranged in a reverse return configuration. Seriesloop piping for terminal or branch circuits shall beequipped with automatic flow control valves at terminalunits (all types of heat transfer units). Reverse return isconsidered because it provides the best overall control andmaintenance of a balanced system as the system ismodified. Each terminal unit or coil shall be providedwith isolation valves on both the supply and return, and aflow-indicating balance valve on the return line. Isolationvalves shall be provided on all major pipe branches, suchas at each floor level, building wing or mechanical room.

Each pumping system shall be provided with two pumps,one operating while the other is in standby mode. Thesepumps shall be configured for automatic lead/ lagoperation.

Each boiler shall be provided with a control and pipingarrangement, which protects the boiler from thermalshock. A primary-secondary piping arrangement with amodulating mixing control valve and higher primary flowrate will assure that the boiler return water temperaturedoes not drop too low, as commonly occurs with nightsetback. Hydronic hot water space heating pumps shouldgenerally be selected to operate at 1750 RPM. Variablevolume pumping systems shall be provided for allsecondary piping systems with pump horsepower greaterthan 10 kW (15 HP).

Refer also to provisions in Piping Systems in this chapter.

Pressurized diaphragm expansion tanks shall be usedwhen available in appropriately sized manufacturedproducts. Air separators and vents must be provided on


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Flow may be varied by variable speed pumps or stagedmultiple pumps. Pumps should operate at no less than 75 percent efficiency on their performance curve. Variableflow pumping must be designed carefully. Package systemsshould be used, complete with pumps and controlsfactory-tested prior to shipment.

Chillers and most boilers may experience flow-relatedheat exchange problems if flow is not maintained above a minimum rate. For this reason, separate, constant flowprimary water pumps are recommended for variablevolume pumping systems.

Primary/Secondary Pumping. In this application,primary and secondary circuits are separate, with neitherhaving an effect on the pumping head of the other. Theprimary circuit serves source equipment (chiller orboiler), while the secondary circuit serves the load.Primary/secondary pumping arrangements allowincreased system temperature design drops, decreasedpumping horsepower and increased system control. Theprimary loop and pumps are dedicated and sized to servethe flow and temperature differential requirements of theprimary source equipment. This permits the secondarypump and loop to be sized and controlled to provide thedesign flow rate and temperature differential required tosatisfy the heating or cooling loads. Primary/secondarysystems are recommended for larger buildings (circulationof more than 76 L/s (1,000 gpm)) and campus facilities.

hot water systems to remove accumulated air within thesystem. Automatic bleed valves shall only be used inaccessible spaces in mechanical rooms where they can beobserved by maintenance personnel and must be pipeddirectly to open drains. Manual bleed valves shall be usedat terminal units and other less accessible high points inthe system. Air vents shall be provided at all localized highpoints of the piping systems and at each heating coil.Likewise, system drains shall be provided at all localizedlow points of the heating system and at each heating coil.

Hydronic, Closed Loop Systems. Closed piping systemsare unaffected by static pressure; therefore, pumping isrequired only to overcome the dynamic friction losses.Pumps used in closed loop hydronic piping shall bedesigned to operate to the left of the peak efficiency pointon their curves (higher head, less flow). This compensatesfor variances in pressure drop between calculated andactual values without causing pump overloading. Pumpswith steep curves shall not be used, as they tend to limitsystem flow rates.

Variable Flow Pumping. Variable flows occur when two-way control valves are used to modulate heat transfer.The components of a variable volume pumping systeminclude pumps, distribution piping, control valves andterminal units, and will also include boilers and chillersunless a primary-secondary arrangement is used. Allcomponents of the system are subject to variable flowrates. It is important to provide a sufficient pressuredifferential across every circuit to allow design flowcapacity at all times.


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(See Appendix A.) Cathodic protection or another meansof preventing pipe corrosion must be provided if requiredby the Geotechnical Report.

Piping Material. Table 5-5 cites which commercialstandard should be used for piping material.

Isolation of Piping at Equipment. Isolation valves,shutoff valves, by-pass circuits, flanges and unions shall beprovided as necessary for piping at equipment to facilitateequipment repair and replacement. Equipment requiringisolation includes boilers, chillers, pumps, coils, terminalunits and heat exchangers. Valves shall also be providedfor zones off vertical risers.

Provisions for Piping in Earthquake Zones. In SeismicZones 2, 3 and 4, sleeves for pipes shall be at least 25 mm(1 inch) larger than the pipe, to allow for movement.Flexible couplings shall be provided at the bottom of piperisers. Spreaders shall be used to separate adjacent pipes,unless the distance is large enough to prevent contact inan earthquake. See Chapter 4: Structural Engineering,SMACNA Seismic Restraint Manual and ASHRAEApplication Handbook for more detailed information.

Piping Supports. Provide channel supports for multiplepipes and heavy duty steel trapezes to support multiplepipes. Hanger and support schedule shall have manu-facturer’s number, type and location. Comply with MSSSP69 for pipe hanger selections. Spring hangers andsupports shall be provided in all the mechanical rooms.

Flexible Pipe Connectors. Flexible pipe connectors shallbe fabricated from annular close pitched corrugated andbraided stainless steel. All pumps, chillers, and coolingtowers shall have flexible connectors.

5.17 Piping Systems

All piping systems shall be designed and sized inaccordance with ASHRAE Fundamentals Handbook andthe ASHRAE HVAC Systems and Equipment Handbook.Materials acceptable for piping systems are black steel andcopper. No PVC or other types of plastic pipe are permitted.

Chilled Water and Condenser Water Piping. In general,HVAC systems shall utilize parallel piping systems with atwo-pipe main distribution system arranged in a reversereturn configuration. If applied, series loop piping forterminal or branch circuits shall be equipped withautomatic flow control valves at terminal units (all typesof heat transfer units).

Each terminal unit or coil shall be provided with isolationvalves on both the supply and return and a flow indicatingbalance valve on the return line. Isolation valves shall beprovided on all major branches, such as at each floor level,building wing or mechanical room.

For new chilled water HVAC distribution, a pumping and piping arrangement is generally appropriate, withconstant volume primary pumping and variable volumesecondary pumping. The primary and secondary circuitsshall be separate, with neither having an effect on thepumping head of the other. The primary circuit serves thesource equipment (chillers), while the secondary circuitserves the load. Refer also to Pumping Systems in thischapter for additional requirements.

Cathodic Protection. The need for metal protection for underground piping must be evaluated by a soilsresistivity test. This is part of the Geotechnical Report.

Table 5-5Commercial Standards for Piping Material

Standard Piping Material Use Comments

ASTM Schedule 40 Chilled water up to 300 mm (12-in) dia., 1035 kPa (150 psi) fittings. Condenser water up to 300 mm (12-in) dia. Standard weight pipe over 300 mm (12-in) diameter.

Hot water Test to 2100 kPa (300 psig)

Natural gas, fuel oil Weld and test to 2100 kPa (300 psig)

Steam (100 kPa (15 psig) to 1035 kPa (150 psi))

ASTM Schedule 30 Chilled water over 300 mm (12 in) dia 1035 kPa (150 psi) fittings.Condenser water over 300 mm (12 in) dia. Standard weight pipe over 300 mm (12-in) diameter

ASTM Schedule 80 Steam condensate

Copper Tubing Chilled water up to 102 mm (4 in) dia, Builder’s option. Use type K below groundCondenser water up to 102 mm (4 in) dia. and type L above.

Domestic water Lead-free solder connections.Refrigeration Type ACR.Cast Iron Sanitary, waste and ventStorm


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Piping System and Equipment Identification. All pipes,valves and equipment in mechanical rooms, shafts,ceilings and other spaces accessible to maintenancepersonnel must be identified with color-coded bands andpermanent tags indicating the system type and direction

of flow for piping systems or type and number forequipment. The identification system shall also tag allvalves and other operable fittings. Gas piping andsprinkler lines must be identified as prescribed by NFPA.


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5.18 Thermal Insulation

GeneralAll insulation materials shall comply with the fire andsmoke hazard ratings indicated by ASTM-E84, NFPA 255and UL 723. Accessories such as adhesives, mastics,cements and tapes shall have the same or better fire andsmoke hazard ratings.

Insulation shall be provided on all cold surfacemechanical systems, such as ductwork and piping, wherecondensation has the potential of forming and inaccordance with ASHRAE Standard 90.1. Insulation that issubject to damage or reduction in thermal resistivity ifwetted shall be enclosed with a vapor seal (such as a vaporbarrier jacket). Insulation shall have zero permeability.

Duct Insulation. Materials used as internal insulationexposed to the air stream in ducts shall be in accordancewith UL 181 or ASTM C 1071 erosion tests, and shall notpromote or support the growth of fungi or bacteria, inaccordance with UL 181 and ASTM G21 and G22.Ductwork with double wall construction havinginsulation in-between shall only be used for courtroomreturn air transfer grilles, and only if required for acousticpurposes. All exposed ductwork shall have sealed canvasjacketing. All concealed ductwork shall have foil facejacketing.

The insulation shall comply with fire and smoke hazardratings indicated by ASTM-E84, NFPA 255 and UL 723.Accessories such as adhesives, mastics, cements, tapes, etc.shall have the same or better component ratings. Allsupply air ducts must be insulated, in accordance with

ASHRAE Standard 90.1. Supply air duct insulation shallhave a vapor barrier jacket. The insulation shall cover theduct system with a continuous, unbroken vapor seal.Insulation shall have zero permeability.

Return air and exhaust air distribution systems shall beinsulated in accordance with ASHRAE Standard 90.1.The insulation of return air and exhaust air distributionsystems needs to be evaluated for each project and foreach system to guard against condensation formation andheat gain/loss on a recirculating or heat recovery system.Generally, return air and exhaust air distribution systemsdo not require insulation if located in a ceiling plenum ormechanical room used as a return air plenum. Allequipment, heat exchangers, converters and pumps shallbe insulated as per ASHRAE Standard 90.1.

Piping Insulation. All insulation material shall complywith the fire and smoke hazard ratings indicated byASTM-E84, NFPA 255 and UL 723. Accessories such asadhesives, mastics, cements, tapes, etc. shall have the sameor better component ratings. All piping systems must beinsulated in accordance with ASHRAE Standard 90.1.Piping systems conveying fluids, those having designtemperatures less than 18°C (65°F) or greater than 40°C(105°F) shall be insulated. All piping systems with surfacetemperatures below the average dew point temperature ofthe indoor ambient air and where condensate drip willcause damage or create a hazard shall be insulated with avapor barrier to prevent condensation formationregardless to whether piping is concealed or exposed.Chilled water piping systems shall be insulated with non-permeable insulation (of perm rating 0.00) such ascellular glass. All exposed and concealed piping shall havePVC jacketing.


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Equipment Insulation. All insulation material shallcomply with the fire and smoke hazard ratings indicatedby ASTM-E84, NFPA 255 and UL 723. Accessories such asadhesives, mastics, cements, tapes, etc. shall have the sameor better component ratings. All equipment including air-handling units, chilled and hot water pumps, and heatexchangers must be insulated in accordance withASHRAE Standard 90.1. All pumps shall have jacketing.

Thermal Pipe Insulation for Plumbing SystemsAll sanitary sewer vents terminating through the roofshall be insulated for a minimum of 1.83 meters (6 feet)below the roof line to prevent condensation from formingand include a vapor barrier jacket on this insulation. AllInsulation materials and accessories shall comply with thefire and smoke hazard ratings indicated by ASTM-84,NFPA 255 and UL 723.

Domestic water piping shall be insulated in accordancewith ASHRAE 90.1.

All piping exposed in plenums or above ceiling shall beinsulated to prevent condensation. All insulation materialsand accessories shall comply with the fire and smokehazard ratings indicated by ASTM-E84, NFPA 255 and UL 723.

5.19 Vibration Isolation,Acoustical Isolation, andSeismic Design for Mechanical Systems

Noise and Vibration Isolation. Refer to and incorporatethe basic design techniques as described in ASHRAEApplications Handbook, Sound and Vibration Control.Isolate all moving equipment in the building.

Mechanical Room Isolation. Floating isolation floorsshould be considered for major mechanical rooms locatedin penthouses or at intermediate levels in mid-rise andhigh-rise construction. See Chapter 3: Architectural andInterior Design, Special Design Considerations, Acoustics,Design Criteria for Building Spaces, Class X Spaces.

Mechanical Shafts and Chases. Mechanical shafts andchases should be closed at top and bottom, as well as theentrance to the mechanical room. Any piping andductwork should be isolated as it enters the shaft toprevent propagation of vibration to the buildingstructure. All openings for ducts and piping must besealed. Shafts dedicated to gas piping must be ventilated.

Acoustical criteria for all building spaces are described in Chapter 3: Architectural and Interior Design, SpecialDesign Considerations, Acoustics. For HVAC noise levelsrefer to Table 3-4, “Design Guidelines for HVAC-RelatedBackground Sound in Rooms.”

Also, for design criteria, refer to “Selection Guide forVibration Isolation,” ASHRAE 99 Application Handbook,Chapter 46.


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Floor supports for piping may be designed with springmounts or rubber pad mounts. For pipes subject to largeamounts of thermal movement, plates of Teflon orgraphite should be installed above the isolator to permithorizontal sliding.

Anchors and guides for vertical pipe risers usually mustbe attached rigidly to the structure to control pipemovement. Flexible pipe connectors should be designedinto the piping before it reaches the riser.

Noise Control in VAV Systems. System sound levels atmaximum flow must be carefully evaluated to ensureacoustic levels required in Chapter 3. Inlet guide vanesshould be evaluated for noise in their most restrictedposition. Duct noise control should be achieved bycontrolling air velocity, by the use of sound attenuators,by the use of double wall ductwork with insulation in-between (only on courtroom return air transfer grilles)and by not oversizing terminal units. Terminal unitsshould be selected so that design air volume isapproximately three-quarters of the terminal box’smaximum capacity. Volume dampers in terminal unitsshould be located at least 1.8 m (6 feet) from the closestdiffuser and the use of grille mounted balance dampersshould be restricted except for those applications withaccessibility problems.

Noise Transmission Attenuation (Courthouses).Attenuate noise trans-mission to and from courtrooms,judges’ chambers, jury rooms, prisoner consulting roomsand from prisoner detention areas.

Isolators. Isolators should be specified by type and bydeflection, not by isolation efficiency. See ASHRAE Guide forSelection of Vibration Isolators and Application Handbookfor types and minimum deflections. Specifications shouldbe worded so that isolation performance becomes theresponsibility of the equipment supplier.

Concrete Inertia Bases. Inertia bases should be providedfor reciprocating and centrifugal chillers, air compressors,all pumps, axial fans above 300 RPM, and centrifugal fansabove 37 kW (50 HP).

Ductwork. Reduce fan-generated noise immediatelyoutside any mechanical room wall by acoustically coating or wrapping the duct. The ductwork design shallappropriately consider and address airborne equipmentnoise, equipment vibration, ductborne fan noise, ductbreakout noise, airflow generated noise and ductbornecrosstalk noise. All ductwork connections to equipmenthaving motors or rotating components shall be made with 6-inch length of flexible connecters. All ductwork withinthe mechanical room or serving courtrooms shall besupported with isolation hangers.

Piping Hangers and Isolation. Isolation hangers shouldbe used for all piping in mechanical rooms and adjacentspaces, up to a 15 m (50-foot) distance from vibratingequipment. The pipe hangers closest to the equipmentshould have the same deflection characteristics as theequipment isolators. Other hangers should be springhangers with 20 mm (.75 inch) deflection. Positioninghangers should be specified for all piping 200 mm (8inches) and larger throughout the building. Spring andrubber isolators are recommended for piping 50 mm (2 inches) and larger hung below noise sensitive spaces.


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5.20 Meters, Gauges, and Flow Measuring Devices

Thermometers and Gauges. Each piece of mechanicalequipment shall be provided with the instrumentation ortest ports to verify critical parameters, such as capacity,pressures, temperatures, and flow rates. Following are thegeneral instrumentation requirements:

• Thermometers and pressure gauges are required onthe suction and discharge of all pumps, chillers, boilers,heat exchangers, cooling coils, heating coils, andcooling towers. To avoid pressure gauge toleranceerrors, a single pressure gauge may be installed, valvedto sense both supply and return conditions. For coilswith less than 10 gpm flow, provisions for use ofportable instruments to check temperatures andpressures shall be made.

• Duct static pressure gauges shall be provided for thecentral air-handling unit air supply fan discharge,branch take-offs of vertical supply risers and at all ductlocations at which static pressure readings are beingmonitored to control the operation of a VAV system.

• Differential static pressure gauges shall be placedacross filters in air-handling units and to measurebuilding pressure relative to the outdoors. A temper-ature gauge is required at the outside air intake to each air-handling unit.

Flow Measuring Devices. Airflow measuring grids arerequired for all central air-handling units. Measuring grids shall be provided at the supply air duct, return airduct, and the outside air duct. Airflow measuring gridsmust be sized to give accurate readings at minimum flow.It may be necessary to reduce the duct size at the stationto permit accurate measurement.

Water flow or energy measuring devices are required for each chilled water refrigeration machine, hot waterboiler, pump, and connections to district energy plants.Individual water flow or energy measuring devices shallbe provided for chilled water lines serving computerrooms and chilled water and hot water lines to outleasedspaces. Flow measuring devices shall be capable ofcommunicating with the central BAS. Water flow and air flow measuring devices shall confirm or validateASHRAE 90.1 requirements.

Testing Stations. Permanent or temporary testing stations shall be provided for start up and testing ofbuilding systems. Connections shall be designed sotemporary testing equipment can be installed andremoved without shutting down the system.

Water Use Meters. See Section 5.24, Plumbing Systems,Domestic Water Supply Systems, in this chapter.

Indoor Air Quality Measurement. Vehicle garage exhaust fans shall generally be activated based uponcarbon monoxide sensors within the garage. Carbonmonoxide sensors shall also be located in all floor areaswhere vertical shafts penetrate the garage areas.


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Central Air Handling UnitsStart/StopHeating ControlCooling ControlHumidification ControlSupply Air ResetStatic Pressure ResetBuilding and ZonePressurization ControlDamper Position (economizer)Supply Air Discharge TempReturn Air TempMixed Air TempSupply Air Flow RateFilter Differential PressureAir Flow Measuring Station

Refrigeration EquipmentStart/StopLeave Water Temp ResetDemand LimitingIsolation Valve PositionLeaving Water TempEntering Water TempkW DrawFlowReturn Air Flow Rate

Hot Water BoilersStart/StopLeaving Water Temp ResetResetIsolation Valve PositionLeaving Water TempEntering Water TempFlowBTU Draw

Cooling TowersStart/StopLeaving Water Temp ResetFlowIsolation Valve PositionEntering Water TempLeaving Water Temp

Terminal BoxesStart/StopDischarge Temp ResetSupply Volume ResetHeating ControlZone Temp ResetMinimum Volume ResetZone TempSupply Air ResetZone Pressurization Control

PumpsStart/StopDischarge Pressure ResetDifferential PressureFlow

Utilities Natural Gas ConsumptionElectricity Consumption &DemandWater ConsumptionFuel Oil Quantity

Table 5-6Minimum Control and Monitoring Points for Typical HVAC Equipment


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Night set-back and set-up controls must be provided forall comfort conditioned spaces, even if initial buildingoccupancy plans are for 24-hour operation. Morningwarm-up or cool-down must be part of the controlsystem. Controls for the various operating conditionsmust include maintaining pressurization requirements.

Humidity Controls. Indoor and outdoor humiditysensors shall be calibrated in-place during system startupand at least annually thereafter. Dew point control ispreferred because it tends to provide more stablehumidity levels. However, rh sensors are acceptable,provided they have been calibrated in-place, and providedthat they have co-located with dry bulb sensors so that theBAS can convert these two signals to a dew point value forcontrol purposes.

Temperature Reset ControlsAir Systems. Systems supplying heated or cooled air tomultiple zones must include controls that automaticallyreset supply air temperature required by building loads orby outside air temperature.

Hydronic Systems. Systems supplying heated and/orchilled water to comfort conditioning systems must also include controls that automatically reset supply water temperatures required by temperature changesresponding to changes in building loads (including returnwater temperature) or by outside air temperature.

5.21 Control SystemsAutomatic Temperature and Humidity ControlsA direct digital control (DDC) system with host computercontrolled monitoring and control shall be provided.

Control Systems shall be BACnet or LONWORKS,conforming to ASHRAE BACnet Standard 135.

Controls. Pre-programmed stand-alone single or multipleloop microprocessor PID controllers shall be used tocontrol all HVAC and plumbing subsystems.

PID loops shall be utilized. All chillers, boilers, terminalunits and air handling units shall have self-containedBACnet or LONWORKS controllers, capable ofcommunicating with the Building Automation System.

Temperature Controls. Heating and cooling energy ineach zone shall be controlled by a thermostat ortemperature sensor located in that zone. Independentperimeter systems must have at least one thermostat ortemperature sensor for each perimeter zone.

A 1.5°C (35°F) dead band shall be used betweenindependent heating and cooling operations within thesame zone.


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However, caution is advised when planning BAS systemswith a high level of integration. The more integration, themore complex the system becomes and the more trainingis required for the operating staff. Also, reliabilityrequirements for the different systems may vary.

Lighting control systems shall not be connected to BASexcept for monitoring of lighting system.

Fire alarm systems, security systems and elevator systemsshall not be controlled by a BAS. These systems shouldhave independent control panels and networks. The BASsystem shall monitor the status of these systems only, inorder to prompt emergency operating modes of HVACand lighting systems. See Chapter 7: Fire ProtectionEngineering, Electrical Requirements, Fire Alarm Systems,and Chapter 8: Security Design.

BAS shall utilize ‘open’ communication protocols, such asBACnet per ASHRAE Standard 135, to minimize the costsof providing integration and to allow interoperabilitybetween building systems and control vendors. Otheropen protocol language systems, such as LonTalk, mayalso be used, provided there is compatibility with overallregional and/or central monitoring and central strategies.A/E to specify and include functional design manual,hardware manual, software manual, operation manual,and maintenance manual. BAS shall have energymanagement and monitoring software.

In retrofits with an existing old-proprietary system inplace, it is recommended that life cycle cost analysisdetermine between the complete replacement of theexisting system or integrating the existing system withcustomized gateways. In the long term, with hardware and software costs falling as capabilities increase, energysavings are producing the paybacks required to justify the complete control retrofit.

5.22 Building AutomationSystems (BAS)

BAS shall be direct digital control (DDC) for providing lower operating costs and ease of operation.Microprocessor PID controllers monitor and adjustbuilding systems to optimize their performance and theperformance with other systems in order to minimizeoverall power and fuel consumption of the facility, BASmonitor systems such as HVAC and lighting.

The system shall consist of series of direct digitalcontrollers interconnected by a local area network. BASsystem shall be accessible through a web browser. Systemshall have a graphical user interface and must offertrending, scheduling, downloading memory to fielddevices, real-time “live” graphic programs, parameterchanges of properties, set point adjustments, alarm/eventinformation, confirmation of operators, and execution ofglobal commands.

A BAS is not required for every project and should beevaluated based on the size of the building. Buildings of100,000 gsf. and more shall have a BAS. The size of thebuilding, number of pieces of equipment, expected energysavings and availability of trained staff should all beconsidered before a decision is made. BAS is required andconsidered part of the system on large facilities (above9,300 gross square meters (100,000 gross square feet)),both new facilities and major modernizations.

Level of Integration. Since the advent of micro-computerBAS systems, there has been an attempt to integrate asmany systems as possible to reduce hardwarerequirements.


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Energy Conservation. The best targets for energyconservation in building systems are the HVAC systemand the lighting system. HVAC control algorithms shallinclude optimized start/stop for chillers, boilers, air-handling units and all associated equipment and feed-forward controls based on predicted weather patterns.Lighting control shall be accomplished by use of separatecontrol equipment, which allows BAS monitoring andreporting and control settings. Optimal start/stopcalculates the earliest time systems can be shut down priorto the end of occupancy hours and the latest time systemscan start up in the morning with the aim of minimizingequipment run time without letting space conditions driftoutside comfort set points. Weather prediction programsstore historic weather data in the processor memory anduse this information to anticipate peaks or part loadconditions. Programs also run economizer cycles and heatrecovery equipment.

Maintenance Scheduling. The BAS shall includeprograms for control that switch pumps and compressorsfrom operating equipment to stand-by on a scheduledbasis. Also, programs that provide maintenance schedulesfor equipment in every building system shall be included,complete with information on what parts and tools areneeded to perform each task.

System Design Considerations. BAS’s requiremeasurements at key points in the building system tomonitor part-load operation and adjust system set pointsto match system capacity to load demands. Table 5-6 ofthe previous section outlines the minimum control andmonitor points for typical HVAC equipment. Controlscannot correct inadequate source equipment, poorlyselected components, or mismatched systems. Energy

efficiency requires a design that is optimized by realisticprediction of loads, careful system selection, and fullcontrol provisions. System ability must include logs ofdata created by user selectable features. In new buildingsand major renovations, the BAS shall have approximately20 percent spare capacity for future expansion. Thesystem must provide for stand-alone operation ofsubordinate components. The primary operatorworkstation shall have a graphical user interface. Stand-alone control panels and terminal unit controllers canhave text-based user interface panels which are hand-heldor fixed.

Energy Measurement Instrumentation. BAS shall havethe capability to allow building staff to measure energyconsumption and monitor performance which is criticalto the overall success of the system. Electrical values, suchas V, A, kW, KVAR, KVA, PF, kWh, KVARH, Frequencyand Percent THD, shall be measured. See also Chapter 6:Electrical Engineering, Site Distribution, for separatemetering of power consumption.

Energy management measurements shall be totalized andtrended in both instantaneous and time-based numbersfor chillers, boilers, air-handling units and pumps. Energymonitoring data shall be automatically converted tostandard database and spreadsheet format and trans-mitted to a designated PC. Energy points are those pointsthat are monitored to ensure compliance with ASHRAEStandard 90.1.


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5.23 Startup, Testing, and Balancing Equipment and SystemsStartup. The A/E shall specify that factory representativesbe present for startup of all major equipment, such asboilers, chillers and automatic control systems.

Testing and Balancing. It shall be the responsibility of theA/E to adequately specify testing, adjusting and balancingresulting in not only proper operation of individual piecesof equipment, but also the proper operation of the overallHVAC and Plumbing systems, in accordance with thedesign intent. The Testing and Balancing contractor shallhave up to date certification by Associated Air BalanceCouncil (AABC), the National Environmental BalanceBureau (NEBB), or the Testing, Adjusting, and BalancingBureau (TABB).

Performance Testing. A/E to specify performance testingof all equipment and systems including chillers, boilers,and other systems for part load and full load duringsummer, winter, spring and fall season as per theschedules specified by the designer. A/E to specify theservices of an organization certified by NEBB or AABC.

Pressure and Leak Testing. Tests shall be conducted atstatic pressures equal to maximum design pressure ofsystem and maximum leakage allowable shall not exceed50 percent of that allowed in SMACNA’s HVAC Air DuctLeakage Manual.

A/E to specify IAQ testing for CO, CO2, volatile organiccompounds, NO2, O3, and tobacco smoke. A/E to specifyoperating tests on each air and hydronic system to measureand meet energy efficiency requirements of ASHRAE 90.1and 62. A/E to specify and validate peak summer andwinter energy consumption and performance.

5.24 Plumbing Systems

Water conservation shall be a requirement of all plumbingsystems. Use water-saving plumbing fixtures.

Domestic Water Supply SystemsCold Water Service. Cold water service shall consist of apressurized piping distribution system incorporating aseparate supply line from the tap in the existing outsidewater main to the equipment area inside the building.

Water service shall be metered inside the building bymeters furnished by the local department of public works.Incoming service shall have double check valves. Remotereading of meters will be accomplished by specialequipment over telephone lines. Irrigation systems mustbe sub-metered for deduct billing of the sewer system.

Internal distribution shall consist of a piping system thatwill supply domestic cold water to all necessary plumbingfixtures, water heaters and all mechanical make-up waterneeds.

Distribution system shall include equipment that willmaintain adequate pressure and flow in all parts of thesystem in accordance with GSA Facilities Standards.

Triplex booster pumping system shall be utilized if thewater pressure is not adequate to provide sufficientpressure at highest, most remote fixture. The waterpressure at the fixture shall be in accordance with theInternational Plumbing Code.

Hot Water Service. Hot water shall be generated byheaters utilizing natural gas, electricity or steam as anenergy source. Selection shall be supported by an


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economic evaluation incorporating first cost, operatingcosts and life cycle costs in conjunction with the HVACenergy provisions.

Instantaneous hot water heaters are not permitted as aprimary source. Domestic hot water supply temperatureshall be generated at 60°C (140°F), and shall be temperedto 49°C (120°F) using a three-way mixing valve, beforesupplying to all plumbing fixtures. Hot water supply todishwashers shall be at 82°C (180°F), and the temperatureshall be boosted from 60°C (140ºF) to 82°C (180°F). Heatpump hot water heaters shall be used where possible tosave energy. For incidental use, the use of instantaneoushot water heaters is permitted.

Distribution system shall consist of a piping system,which connects water heater or heaters to all plumbingfixtures as required. Circulation systems or temperaturemaintenance systems shall be included. Hot water shall beavailable at the furthest fixture from the heating sourcewithin 15 seconds of the time of operation.

Domestic Water Supply Equipment. Domestic watersupply equipment shall include, but not be limited to, thefollowing equipment:

• Water heaters• Pressure booster systems• Pressure regulating valves• Circulating pumps• Back flow preventers• Balancing valves• Isolation valves• Hangers and supports• Thermal insulation

Water hammer arrestors shall be provided at every branchto multiple fixtures and on every floor for both hot andcold water.

Domestic cold and hot water distribution systems shall be insulated per ASHRAE 90.1 and all exposed piping shallhave PVC jacketing.

Sanitary Waste and Vent SystemWaste Pipe and Fittings. A complete sanitary collectionsystem shall be provided for all plumbing fixtures, floordrains and kitchen equipment designed in compliancewith applicable codes and standards. Piping shall be castiron soil pipe with hub and spigot joints and fittings.Above ground piping may have no-hub joints and fittings.

Vent Piping and Fittings. System shall be the same as thewaste piping above.

Floor Drains. Floor drains shall be provided in multi-toilet fixture restrooms, kitchen areas, mechanicalequipment rooms, locations where condensate fromequipment collects, and parking garages and ramps. Singlefixture toilet rooms do not require floor drains.

In general, floor drains shall be cast iron body type with 6 inch diameter nickel-bronze strainers for public toilets,kitchen areas and other public areas. Equipment roomareas will require large diameter cast iron strainers andparking garages will require large diameter tractor grates.Drainage for ramps will require either trench drains orroadway inlets when exposed to rainfall. Trap primersshall be provided for all floor drains where drainage is notroutinely expected from spillage, cleaning, or rainwater.


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Sanitary Waste Equipment. Specific drains in kitchenareas shall discharge into a grease interceptor beforeconnecting into the sanitary sewer in accordance with therequirements of the state health department and localauthorities will determine which drains. Floor drainsand/or trench drains in garage locations are to dischargeinto sand/oil interceptors.

Automatic Sewage Ejectors. Sewage ejectors should onlybe used where gravity drainage is not possible. If they arerequired, only the lowest floors of the building should beconnected to the sewage ejector; fixtures on upper floorsshould use gravity flow to the public sewer. Sewageejectors shall be non-clog, screenless duplex pumps, witheach discharge not less than 100 mm (4 inches) indiameter. They shall be connected to the emergencypower system.

Rainwater Drainage SystemPipe and Fittings. Piping system shall be in compliancewith local codes and sized based upon local rainfallintensity.

Roof Drains. Roof drains shall be cast iron body typewith high dome grates and membrane clamping rings,manufactured by any of the major foundries. Each roofdrain shall have a separate overflow drain located adjacentto it. Overflow drains will be the same drains as the roofdrains except that a damming weir extension will beincluded.

Rainwater Drainage Equipment. Foundations drainagesystem with perforated drain tile collecting into a sumpcontaining a pumping system as required by theapplicable codes shall be provided.

National Building Museum, Washington, D.C.


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Plumbing FixturesGeneral. Provide all required plumbing fixtures includingthose that are indicated in the U.S. Courts Design Guidesand all penal types. Fixtures shall be manufactured bycompanies that are approved by General ServicesAdministration or their representatives.

All fixtures shall have sensing devices for saving water.

Natural Gas SystemsService Entrance. Gas piping entering the building must be protected from accidental damage by vehicles,foundation settlement or vibration. Where practical, theentrance should be above grade and provided with a self-tightening swing joint prior to entering the building. Gaspiping shall not be placed in unventilated spaces, such astrenches or unventilated shafts, where leaking gas couldaccumulate and explode.

Gas Piping within Building Spaces. Gas shall not bepiped through confined spaces, such as trenches orunventilated shafts. All spaces containing gas-firedequipment, such as boilers, chillers and generators, shallbe mechanically ventilated. Vertical shafts carrying gaspiping shall be ventilated. Gas meters shall be located in agas meter room, thus avoiding leakage concerns andproviding direct access to the local gas utility.

All gas piping inside ceiling spaces shall have plenumrated fittings.

Diaphragms and regulators in gas piping must be ventedto the outside.

Fuel Oil SystemsFuel Oil Piping. Fuel oil piping system shall use at leastSchedule 40 black steel or black iron piping. Fittings shallbe of the same grade as the pipe material. Valves shall bebronze, steel or iron and may be screwed, welded, flangedor grooved. Double-wall piping with a leak detectionsystem shall be used for buried fuel piping.

Duplex fuel-oil pumps with basket strainers and exteriorenclosures shall be used for pumping the oil to the fuelburning equipment.

Underground Fuel Oil Tanks. Underground fuel oilstorage tanks shall be of double wall, non-metallicconstruction or contained in lined vaults to preventenvironmental contamination. Tanks shall be sized forsufficient capacity to provide 48 hours of systemoperation under emergency conditions (72 hours forremote locations such as border stations). Forunderground tanks and piping a leak detection system,with monitors and alarms for both, is required. Theinstallation must comply with local, State and Federalrequirements, as well as EPA 40 CFR 280 and 281.

Fire ProtectionRefer to Chapter 7: Fire Protection Engineering.


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5.25 Alterations in ExistingBuildings and Historic Structures

The goal of alteration projects is to meet the samestandards described in this document for new projects.Equipment/systems at 20 years life or older must bedemolished and new systems designed to meet the currentusage of the facility. Renovation and rehabilitation designsmust satisfy the immediate occupancy needs andanticipate additional future changes. Remodeling shouldmake building systems become more flexible, not less.Parameters of reuse and disruption of service must beclearly specified in construction documents.

Alteration projects can occur at three basic scales:refurbishment of an area within a building, such as a flooror a suite; major renovation of an entire structure; andup-grade/restoration of historic structures.

In the first instance, the aim should be to satisfy the newrequirements within the parameters and constraints of theexisting systems. The smaller the area in comparison tothe overall building, the fewer changes to existing systemsshould be attempted. In the second case, the engineer hasthe opportunity to design major upgrades into themechanical, electrical and communications systems. Themechanical services can come close to systems that wouldbe designed for a new building, within the obvious limitsof available physical space and structural capacity.

Where a historic structure is to be altered, specialdocuments will be provided by GSA to help guide thedesign of the alterations. The most important of these isthe HBPP that identifies zones of architecturalimportance, specific character-defining elements thatshould be preserved, and standards to be employed. SeeChapter 1: General Requirements, General DesignPhilosophy, Historic Buildings.

Modern standards for climate control developed for newconstruction may not be achievable or desirable forhistoric buildings. In each case, the lowest level ofintervention needed to successfully accomplish the projectshould be selected. When a system is designed, it isimportant to anticipate how it will be installed, howdamage to historic materials can be minimized, and howvisible the new mechanical system will be within therestored or rehabilitated space.

The following guidelines should be followed for HVACwork in historic buildings:

• Reduce heating and cooling loads to minimize size andother impacts of modern equipment.

• Calculate the effect of historic building features suchas wall thickness, skylights, and porticos, interiordesign features such as draperies, shutters andwindow shades, and existing site features such aslandscaping.

• Add insulation where not visible and intrusive, such asattics or basements. Insulate walls only where it can bedone without removal or covering of original visibleelements.


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• Add storm windows where they can be installed in amanner that will not detract from original visibleelements.

• Use new replicated thermal windows only where it isnot economically feasible to repair existing windows.

• Select system types, components, and placement tominimize alteration of significant spaces. In previouslyaltered spaces, design systems to allow historicsurfaces, ceiling heights, and configurations to berestored. Consider reuse of existing components whenreuse will reduce architectural intrusion and achievesavings, without compromising overall performanceand life cycle requirements. Reuse of HVAC systemelements is only permitted with written documentationobtained from GSA Property Management by the A/E.Retain decorative elements of historic systems wherepossible. Ornamental grilles and radiators and otherdecorative elements shall be retained in place.

• Retain the original type of system where a new onecannot be totally concealed. For example, reuseexisting radiators with new distribution piping orreplace with modern heating-cooling units, rather thanadding another type of system that would require theaddition of new ceilings or other non-original elements.

• Use a number of smaller units in lieu of a few largeones. Insure that room is available to maintain andreplace equipment without damaging significantfeatures to the greatest extent possible, selectingcomponents that can be installed without dismantlingwindow or door openings.

• Place new distribution systems out of sight wheneverpossible by using closets, shafts, attics and basements.

• Use custom rather than commercial standard productswhere elements are exposed in formal areas.

• Select temperature and humidity conditions that willnot accelerate deterioration of building materials.

• Where equipment is near significant features, insurethat leakage from pipes and HVAC units will not causedeterioration. Use deeper condensate drain pans, linedchases and leak detectors.

• Design HVAC systems to avoid impacting other systemsand historic finishes, elements and spaces.

• Place exterior equipment where it is not visible. Beparticularly careful with new chimneys or vents andcondensers, towers, solar panels and air intakes anddischarges. Recess equipment from the edge of theroof to minimize visibility of the equipment from grade.Alternatively, explore creating a vault for easier accessto large mechanical equipment. If equipment cannot beconcealed, specify equipment housings in a color thatwill blend with the historic face. As a last resort,enclose equipment in screening designed to blendvisually with the facade.

• Locate equipment with particular care for weight andvibration on older building materials. These materialsmay not accept the same stress as when theequipment is used in newer construction.


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• If new ceilings must be installed, insure that they do notblock any light from the top of existing windows or alterthe appearance of the building from the outside. This isthe area of highest natural illumination, and it can beused to reduce the need for artificial illumination, whichwill in turn reduce the size of HVAC systems. Originalplaster ceilings in significant spaces such as lobbiesand corridors should be retained, to the extent possible,and modified only as necessary to accommodatehorizontal distribution. Use soffits and false beamswhere necessary to minimize alteration of overallceiling heights.

• Locate pipes so that they do not damage or visuallyinterfere with character-defining elements in historicstructures such as windows, doors, columns, beams,arches, baseboards, wainscots, paneling, cornices,ornamental trim, decorative woodwork and otherdecorative treatments of doors, walls and ceilings.

• Vertical Distribution. If new risers are required, theyshould preferably be located adjacent to existingshafts.

• Horizontal Distribution. Many older buildings have highfloor-to-floor heights, which permit an option to use anexisting ceiling space.

• In buildings containing ornamental or inaccessibleceilings, piping and ductwork may have to be routed infurred wall space or exposed in the occupiable buildingarea. Exposed ducts must be designed to complementthe building architecture in forms and materials used.Use of exposed ducts is encouraged in locations whereconcealing ducts would obscure significantarchitectural surfaces or details, such as vaultedceilings. Exposed ducts should also be considered inhistoric industrial buildings and open plan, tall ceiling,high window spaces suited to flexible grid/flexibledensity treatments.

21119 gpo chapter 5

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