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Displacement Ventilation

Displacement Ventilation

• Displacement Ventilation vs. Dilution Ventilation

• Characteristics• Design Considerations• Layout and Selection• Product Overview• Casino Case Study

Dilution Air Distribution• Induce as much as possible

• Ensure maximum 50 fpm within Occupied Zone

• High velocity jets at diffusers

• Diffuser Performance aerodynamic dependant

• Supply air used to dilute pollution in space

• Diffuser located Outside OZ

• Complete Mixing in Entire Space

• Minimal Temperature Stratification

• Uniformity is Sought

• Supply of 55°F - < 0 > +Temperature

9 FT

Dilution Air Distribution

Displacement Air Pattern

• Low Velocity Supply

• Low Induction

• Uniform Distribution

• Often Located in the Occupied Zone

• Supply between 65°F and 75°F

Body’s Thermal Plume

Air Distribution Characteristics

• 5-10 deg F Cooling Differential

• Supply Air Flows Along Floor

• Rises When Heat Source is Contacted

• Displaces Room Air Upward

Air Pattern Cooling

2-10 oF Cooling Differential 0-5 oF Heating Differential 5 oF+ Heating DifferentialMorning Warm-up

Heating Options• Perimeter Radiation

• Radiant Ceiling Panels

• Fan Coil Units

Air Distribution Characteristics

• Stratified Room Temperature

• Maximum 5 deg F in Occupied Zone*

• 80-85 deg F Return Air

*Based on ASHRAE 55. Current research is showing that occupants may becomfortable with a larger temperature gradient

Air Distribution Characteristics

• Warm Air at Top

• Pollutants at Top

• High Level Return

Ventilation Effectiveness

• How effectively airborne contaminants are removed from a room.

Mix air Systems DV SystemsEc= 0.8 – 1.0 Ec=1.2 - 1.4

Occupant

Exhaustc C

CE =

Limitations

• Pollutants Need to be Buoyant in Air – Warmer/lighter

• Ceiling Height of at least 9 ft Recommended• Large Drafts Cause Unwanted Mixing• Limit in Cooling of 38 BTU/Hr/ft^2

– Radiant cooling systems• Chilled Beams/Sails• Radiant Panels/Floors

– Limit Loads into Space• Higher R walls• Low E windows

Humidity Control

Side-Stream Bypass

RETURNAIR

SUPPLYAIR 65 F

PRIMARYAIR 55 F

EXHAUST AIR

OUTSIDE AIR

COOLING COIL

Layout and Selection

Performance Data

• Sound - NC Level

• Pressure Drop -Inches W.G.

• ASHRAE Test Standard

• Throw Not Applicable

Performance Data

• Supply air is injected directly into occupied zone

• Designers must be cautious to limit the velocities near occupants

• The aspect ratio or the diffusers is important– Taller diffusers have higher velocities in the

near zone

Displacement Ventilation and Comfort

Effect of Air Motion on Comfort

Ankle Region Neck Region

Percentage of Occupants Objecting to Drafts in Air-Conditioned Spaces

Feeling ofCoolness

Feeling of Warmth

Feeling of Warmth

Feeling Of

Cool-ness

TEMPERATURE DIFFERENCE, °F TEMPERATURE DIFFERENCE, °F

AIR

VEL

OC

ITY,

FPM

AIR

VEL

OC

ITY,

FPM

Comfort Criteria

• Maximum 40 FPM Face Velocity* per ASHRAE Research Project RP-949

• Based on Commercial Applications

• Velocity can be increased for Transient Spaces

• Higher airflow rates are acceptable for Industrial Applications.

Selection

• Outlet Type Determined by Room Layout and Architecture

• Outlet Quantity Determined by Air Volume and Room Layout

• Outlet Size Based on Performance

• Maximum 40 FPM Face Velocity• Sound and Pressure Drop not Significant

Layout Considerations

• Heat sources pull supply air to region

• Easily moves along walls to source entire room

Layout Considerations

Layout Considerations

• For large open spaces, diffuser can be located in the space

• Areas of high load should have more diffusers

Layout Considerations

• Diffusers should be located at least 2 ft from occupants

• Diffusers should not be located behind large objects that might restrict air flow to the zone

Ceiling Diffusers• Ceiling mounted diffusers

– Supply air will gain someheat during fall

• Reduced if along a surface

• Reduced Ventilation Effectiveness

– Recommend to mount near walls to limit heat gain

– Ensure that space below diffuser is a transient space

Air Volume Calculations

• ASHRAE Design Guide

• Calculation Method

• Supply Air Volume

• Supply Air Temperature

• Exhaust Air Temperature

• Only suitable for zones with ~9ft ceiling height

• Need another calculation method for large volumes

Loads

• Two Components to loads– Convection

– Radiation

• ASHRAE handbook lists portions attributable to each

Room Load Calculations

• Room Load Coefficients– Occupants, Lamps,

Equipment (aoe) = 0.295*

– Overhead Lighting (al) = 0.132*

– Conduction and Radiation (aex) = 0.185*

• Remember: Building Loads are same as OH

*From ASHRAE Design Guide based on RP-949This methodology should only be used for typical office spaces

Energy / Airflow Modeling

• CFD Analysis Useful for Validation of Design

• Can Predict Airflow in Building

Why Use DV?

• IAQ– Efficient removal of smoke,

odors• Pollutants lighter than supply

air

– VE of 1.2 – 1.4 (typically)• Can be > 3

– Thermally comfortable environment

• Meet ASHRAE 55• Higher SAT• No Drafts

Why Use DV?

• Energy Efficiency– Reduced Room Cooling Load

– Extended Economizer Cycle

– Efficient System

• Load Flexibility– Cool supply air will find the heat load.

– As loads are reconfigured or move, the system will automatically compensate.

• Architectural Flexibility– DV is a robust system

– Diffusers can be mounted in various locations

• Ceiling

• In walls

• In furniture

• In the floor

• In architectural elements

Why Use DV?

Displacement Outlet Types• Flat 1 Way Diffuser• Flat 3 Way Diffuser• Flat Wall Diffuser• Flat Corner Diffuser• Flat Riser Diffuser• Linear Enclosures• Round Full Circular Diffuser • Round Half Circular Diffuser• Round Corner Diffuser• Floor Diffusers• Flat multi-way Industrial

Diffusers• Special Applications

Displacement Diffuser

• Low Velocity Supply

• Low Induction

• Uniform Distribution

• Dual Perforated face

Flat 1-way

• 1 way discharge• Side wall application where one

way discharge required• Square or rectangular• Mounted against wall inside of

occupied space• 3.6 to 14.2 ft2 face area• 100-700 CFM• Top, left, right, and rear ducted

options• Accessories

– Duct Cover– Base

1-Way Pattern

Flat 3- Way

• Square or Rectangular• Side wall application where

three way pattern is required• 3-way Air Pattern• 7.7 to 27.2 ft2 face area• 150-1300 CFM• Top and rear ducted

available• Accessories

– Duct cover– Bases

3-Way Pattern

Flat Corner Unit

• Square or Rectangular

• Mounted in Corner

• 90 Degree Air Pattern

• 3.8 to 17.6 ft2 face area

• 80-800 CFM

• Accessories– Duct cover

– Base

Corner Pattern

Wall Unit

• Square or Rectangular• Mounted in Wall• Provided with plenum• Square inlet• 1-way Air Pattern• 3.6 to 7.4 ft2 face area• 80-300 CFM

Recessed Unit

• Rectangular• Mounted in Wall / Stair Riser /

Integrated into baseboards• 1-way Air Pattern• 20-875 CFM• .19 to 17.5 ft2 face area• Snaps into mounting flange

flush with wall• Can be used in any wall

mounted application where a pressurized plenum can be provided

• Ideal for concealed look

Linear Enclosure

• Displacement Linear Enclosure

• Attractive Linear Grille

• Rigid Steel Construction – Heavy Duty

• Ducted from below, behind or from the side

• Ideal for:– Offices

– Boardrooms

– Classrooms

Available 2nd QTR 2006

Circular Unit• Round Face• Mounted Free Standing in

Interior Space• Can be ducted from above

or below• 360 Degree Air Pattern• 1.5 to 62.5 ft2 face area• 115-3100 CFM• Designed for large

capacities• Accessories

– Bases– Expansion Collars

Circular Pattern

Elevated Circular Unit

• Round Face

• Fastened directly to elevated ductwork

• 360 Degree Air Pattern

• 1.5 to 62.5 ft2 face area

• 115-3100 CFM

• Designed for large capacities

Elevated Circular Unit

Used where supply cannot be within the occupied zone

Large open space

Far from walls

Raised floor not an option

Valuable floor space

Half Round Unit

• Round Face• Side wall application• 180 Degree Air Pattern• 4 to 31 ft2 free area• 85 - 1550 CFM• Top or rear ducted option,

round or rectangular inlets available

• Accessories– Duct cover– Base

Half Round Pattern

Corner Round Unit

• Round Face

• Mounted In Corner

• 90 Degree Air Pattern

• 2 to 15.5 ft2 face area

• 40-775 CFM

• Accessories– Duct Cover

– Base

Floor Displacement Outlet

• 8” Round Aluminum Face

• Mounted In The Floor • Horizontal Air Pattern• 50-80 CFM• Compatible with

underfloor products• Used with raised floors

or can be installed directly in floor slab

Specials• Sizes• Shapes• Face Types• Colors• Material

Displacement Diffuser Accessories

• Duct Covers– Conceal Duct work

• Bases– Match room features

– Protect diffuser while cleaning

• Expansion Collar

Application of Displacement Ventilation in a Casino

Edgewater Casino, Vancouver, BC

Major Project Challenges

• Retrofit of Existing Building

• Must Maintain Transparency –Heritage Requirement

• Owner Demanded High Level of Comfort & IAQ

• Central Atrium

• 24 Hour Occupancy

• Fast Track Project

CFD ModelingTemperature Contour

Design Solutions

• Double Skin System

• New Air Handlers on Main Floor

• Utilized Existing Air Handlers on Second Floor

• Raised Floor Added to Main Level

• Under Floor Air Delivery on Main Floor

• Displacement Delivery on Main Floor

• Generates Twist Effect Using Linear Slots in Combination With Inclined Discharge

• Produces Angular Vertical Pattern

• High Induction Turbulent Flow for Rapid Temperature Equalization

• Mixing Within Occupied Zone (6 ft from floor)

• Projects Air Upwards 3-6 Feet

Turbulent Floor Outlet

• Radial Slots With Inclined Discharge

• Produces Horizontal Pattern Close to Floor

• Low Turbulence

• Low Velocity

• Minimal Mixing

• Air Buoyancy Carries Heat and Pollutants to Ceiling for Exhausting.

Displacement Floor Outlet

Lab Mockup

• Attended by Design Team and Owner

• 6 Slot Machines Simulated

• Floor Outlets Located Below Each Chair

• Measured Velocity and Temperature at Several Flows

• Opportunity to “Feel” the System

Lab Mockup

Various Wall Mounted Displacement Outlets Were Also Demonstrated

Displacement Benefits

• Low Velocity/High Comfort

• Heat Sources Pull Supply Air to Region

• Ideal for Variable Occupancy

• Minimal Impact by Furnishings

• Easily Moves Along Walls to Fill Entire Room

HVAC System Details

• 36,000 CFM Supply Air Capacity

• Constant Volume with Reheat

• 67 Deg F Supply Air Temperature

• 3 CFM per Sq Ft in General Areas

• Demand Control Ventilation

• Return Through Top of Atrium

Main Floor HVAC

Main Floor HVAC

• Displacement Floor Air Outlets in Gaming Area – 1300 Units

• Displacement Wall Outlets in Lobby and Eating Area

Second Floor HVAC

Second Floor HVAC

• Displacement Wall Outlets Throughout

Displacement Wall Outlets

• Diffuser Face Recessed into Millwork

• Coordination with Architect Critical

• Air Delivered Through Pressurized Plenums

• Self Balancing System

• Diffuser Face Sized for Maximum 40 FPM Face Velocity

• Sizes up to 36” x 72”

• 220 Units

Results

• Open Since February 05

• Minimal Balancing Required

• Passed Opening Day Test

• No Draft Complaints

• Excellent Temperature Control-Within 1 Deg F

Results

• Supply Air Drawn to Occupants for High IAQ and Comfort

• Flexible System

• Extended Hours of Free Cooling

• Lower Fan HP

• Two New BC Casino’s Under Design with Displacement

Conclusions

• Casino’s are a Good Application for Displacement Delivery

• Comfort ,IAQ and Energy Efficiency are Benefits

• CFD is a Valuable Design Tool

• Lab Mock Ups are Extremely Beneficial

• Coordinated Effort by Entire Design Team and Owner Ensures Success

Questions?