implementing demand-controlled ventilation...

Implementing Demand-Controlled Ventilation Strategies© 2016 Trane, a business of Ingersoll-Rand.

ImplementingDemand-Controlled Ventilation Strategies

John Murphy, ASHRAE Fellow, LEED® AP BD+CApplications EngineerTraneIngersoll RandLa Crosse, Wisconsin

29 April 2016ASHRAE Region VI CRCMadison, Wisconsin

Implementing Demand-Controlled Ventilation Strategies2

ASHRAE Standard 62.1-2013

Section 6.2.7

6.2.7 Dynamic Reset. The system may be designed to reset the outdoorair intake flow (Vot) and/or space or ventilation zone airflow (Voz) asoperating conditions change.

6.2.7.1 Demand Control Ventilation (DCV)…

6.2.7.2 Ventilation Efficiency…

6.2.7.3 Outdoor Air Fraction…

Examples mentioned include:

• Variations in zone population(“demand-controlled ventilation” or DCV)

• Variations in ventilation efficiency due to changes in airflow(“ventilation optimization” or “ventilation reset”)

• Variations in OA fraction due to airside economizer operation(“VAV box minimum reset”)



implementing DCV strategies

Agenda

• Requirements of ASHRAE Standard 90.1

• Common DCV technologies

• Implementing DCV is various types of systems

– Single-zone systems

– Dedicated (100%) outdoor-air systems

– Multiple-zone recirculating systems


ASHRAE Standard 90.1-2010 (mandatory requirement)

Demand-Controlled Ventilation

6.4.3.9 Ventilation Controls for High-Occupancy Areas.Demand control ventilation (DCV) is required for spaces larger than 500 ft2

and with a design occupancy for ventilation of > 40 people per 1000 ft2 offloor area and served by systems with one or more of the following:

a. an air-side economizer,

b. automatic modulating control of the outdoor air damper,

or

c. a design outdoor airflow > 3000 cfm.

Exceptions:

a. Systems with exhaust air energy recovery complying with Section 6.5.6.1.

b. Multiple-zone systems without DDC of individual zones communicating with acentral control panel.

c. Systems with a design outdoor airflow < 1200 cfm.

d. Spaces where the supply airflow rate minus any makeup or outgoing transfer airrequirement is less than 1200 cfm.



• Correctional waiting room

• Lecture classroom

• Lecture hall

• Multi-use assembly

• Restaurant dining room

• Cafeteria / fast food dining

• Bars, cocktail lounge

• Conference / meeting

• Break room

• Telephone / data entry

• Transportation waiting

• Auditorium seating area

• Place of religious worship

• Courtroom

• Legislative chambers

• Lobby

• Spectator area

• Disco / dance floor

• Gambling casino

• Stage / studio

>40

peo

ple

/1000

ft2


ASHRAE Standard 90.1-2013 (mandatory requirement)


6.4.3.8 Ventilation Controls for High-Occupancy Areas.Demand control ventilation (DCV) is required for spaces larger than 500 ft2

and with a design occupancy for ventilation of ≥ 25 people per 1000 ft2 offloor area and served by systems with one or more of the following:

a. an air-side economizer,

b. automatic modulating control of the outdoor air damper,

or

c. a design outdoor airflow > 3000 cfm.

Exceptions:

1. Systems with exhaust air energy recovery complying with Section 6.5.6.1.

2. Multiple-zone systems without DDC of individual zones communicating with acentral control panel.

3. Systems with a design outdoor airflow < 750 cfm.

4. Spaces where > 75% of the space design outdoor airflow is required formakeup air that is exhausted from the space or transfer air that is requiredfor makeup air that is exhausted from other space(s).

5. Correctional cells, daycare sickrooms, science labs, beauty and nail salons,and bowling alley seating.



impact of90.1-2013



• Lecture hall






• Break room





• Courtroom


• Lobby

• Spectator area


• Gambling casino

• Stage / studio


• Daycare

• Classroom (ages 5-8)

• Classroom (age 9+)


• Lecture hall

• Computer lab

• Media center

• Music / theater / dance






• Lobby / pre-function

• Break room

• Reception area





• Courtroom


• Lobby

• Museum / gallery

• Spectator area


• Health club / aerobics room

• Gambling casino

• Stage / studio

≥ 2

5p

eo

ple

/1000

ft2

>40

peo

ple

/1000

ft2


ASHRAE Standard 90.1-2010 (prescriptive requirement)

Ventilation Optimization

6.5.3.3 Multiple-Zone VAV System Ventilation Optimization Control.Multiple-zone VAV systems with DDC of individual zone boxes reporting to acentral control panel shall include means to automatically reduce outdoor airintake flow (Vot) below design rates in response to changes in systemventilation efficiency (Ev) as defined by ASHRAE Standard 62.1, Appendix A.

Exceptions:

a. VAV systems with zonal transfer fans that recirculate air from other zoneswithout directly mixing it with outdoor air, dual-duct dual-fan VAV systems,and VAV systems with fan-powered terminal units.

b. Systems required to have the exhaust air energy recovery complying withSection 6.5.6.1.

c. Systems where total design exhaust airflow is more than 70% of totaldesign outdoor air intake flow requirements.




Agenda








Demand-Controlled Ventilation (DCV)

An energy-saving control strategy that responds to theactual “demand” (need) for ventilation in a zone by varyingthe rate at which outdoor air is delivered to that zone.

cfm required = cfm/person number of people

local code,ASHRAE 62.1



ASHRAE Standard 62.1-2013, Section 6.2.7.1


6.2.7.1 DCV shall be permitted as an optional means of dynamic reset.Exception: CO2 -based DCV shall not be applied in zones with indoor sourcesof CO2 other than occupants or with CO2 removal mechanisms, such asgaseous air cleaners.

6.2.7.1.1 The breathing zone outdoor airflow (Vbz) shall be reset in response tocurrent occupancy and shall be no less than the building component(Ra × Az) of the DCV zone. Note: Examples of reset methods or devices includepopulation counters, carbon dioxide (CO2) sensors, timers, occupancyschedules, or occupancy sensors.

6.2.7.1.2 The ventilation system shall be controlled such that at steady-state itprovides each zone with no less than the breathing zone outdoor airflow (Vbz)for the current zone population.

6.2.7.1.3 The current total outdoor air intake flow with respect to the coincidenttotal exhaust airflow for the building shall comply with Section 5.9.2.


Time-of-Day (TOD) Schedule

• Scheduling function of the BAS is used to define theamount of outdoor air required in a zone for each hour… based on estimated population



0

50

100

150

zo

ne

po

pu

lati

on

,P

z

midnight 6 a.m. noon 6 p.m. midnight

example: high school cafeteria

Occupancy/Ventilation TOD Schedule

200 estimated Pz

each hour


People Counters



Occupancy Sensor / Motion Detector

• Sensor is used to determine if people are present

– Simple, binary input

• When a zone is occupied:

– Zone ventilation setpoint is set to design outdoor airflow

• When a zone is unoccupied:

– Zone ventilation setpoint is reduced to“building” ventilation airflow (Ra × Az)


example: conference room

Occupancy Sensor

• Floor area (Az) = 300 ft2

• Design population (Pz) = 10 people

• Required outdoor airflow at design population

Vbz-design = Rp Pz + Ra Az

= 5 cfm/p 10 people + 0.06 cfm/ft2 300 ft2

= 68 cfm

• Required outdoor airflow at zero population

Vbz-standby = 5 cfm/p 0 people + 0.06 cfm/ft2 300 ft2

= 18 cfm

6.2.7.1.1 The breathing zone outdoor airflow (Vbz) shall be reset in response tocurrent occupancy and shall be no less than the building component (Ra × Az) of theDCV zone.

8.3 Systems shall be operated such that spaces are ventilated in accordance withSection 6 when they are expected to be occupied.

ASHRAE Standard 62.1-2013 (see official interpretation 62.1-2010-4)



“occupied-standby” mode

Addendum P to ASHRAE 62.1-2013

6.2.7.1.1 For DCV zones in the occupied mode, breathing zone outdoor airflow(Vbz) shall be reset in response to current population.

6.2.7.1.2 For DCV zones in the occupied mode, breathing zone outdoor airflow(Vbz) shall not be less than the building component (Ra x Az) for the zone.

Exception: Breathing zone outdoor airflow shall be permitted to be reducedto zero for zones in occupied-standby mode for the occupancy categoriesindicated in Table 6.2.2.1 provided that airflow is restored to Vbz wheneveroccupancy is detected.

Section 3 Definitions

occupied mode: when a zone is scheduled to be occupied

occupied-standby mode: when a zone is scheduled to be occupied andan occupancy sensor indicates zero population within the zone

addendum P to ASHRAE Standard 62.1-2013


physical activity level, MET

0 1 2 3 4 5

0.5

0

1.0

1.5

2.0

CO

2p

ro

du

cti

on

,L/

min off

ice

work

sle

epin

g

walk

ing

lightm

achin

ew

ork

very light moderatelight

Source: ASHRAE Standard 62.1-2013, Figure C-2

CO2 Sensor

• Production of CO2 isrelated to the person’slevel of activity (MET).

• Therefore, CO2 can beused as a "tracer gas"for occupancy.



CO2-Based DCV

0

200

400

600

800

1000

1200

1400

1600

CO

2co

ncen

trati

on

,p

pm

steady state conditions

time

CO2 outdoors

15 cfm/p

20 cfm/p

10 cfm/p

CO2 indoors


Mass Balance: CO2-Based DCV

CO

2co

ncen

trati

on

,p

pm

time

CO2 indoors

COA = 350 ppm

Cspace = 1050 ppm

Cspace – COA = N / VOA

N = CO2 generation rate, cfm/personVOA = ventilation rate, cfm/person

0

200

400

600

800

1000

1200

1400

1600



CO2-based DCV

Setpoints Vary by Application

• CO2 generation rate (N) varies with activity level– Refer to Appendix C of ASHRAE 62.1

• Ventilation rate (VOA) differs by space type andcfm/person varies as zone population changes

• Outdoor CO2 concentration (COA) varies by location

– Most designers use a one-time reading from the site ora conservative value from historical local data

"Unless combustion fumes are present, the outdoor CO2

concentration in most locations seldom varies more than 100 ppmfrom the nominal value."

ASHRAE Transactions, 1998



Agenda









DCV in a Single-Zone System

SASAOAOA

RARAEAEA

space

CO2


implementing DCV in a single-zone system

ASHRAE 62.1 User’s Manual (Appendix A)

Example: University lecture classroom• Floor area (Az) = 1000 ft2

• Peak population (Pz) = 65 people

• CO2 generation rate (N*) = 0.0105 cfm/person(light desk work)

• Outdoor CO2 concentration (COA) = 350 ppm

For this occupancy classification, Table 6.2.1.1of ASHRAE Standard 62.1-2013 requires:

• Rp = 7.5 cfm/person

• Ra = 0.06 cfm/ft2

* N, cfm/person = MET 0.0084 for average adult population(Standard 62.1-2010 User’s Manual, p. 158)




Example: University Lecture Classroom

1) Calculate breathing-zone outdoor airflow (Vbz)for both design population and with zero people

Vbz = Rp × Pz + Ra × Az

Vbz-design = 7.5 × 65 + 0.06 × 1000 = 550 cfm (8.5 cfm/p)

Vbz-DCVmin = 7.5 × 0 + 0.06 × 1000 = 60 cfm (>68 cfm/p)




2) Calculate steady-state indoor CO2 concentration (Cs)for both design population and with zero people

Cs = COA + N / ( Vbz / Pz )

Cs-design = 350 + 0.0105 / (550 cfm / 65 people) = 1600 ppm

Cs-DCVmin = 350 + 0.0105 / (60 cfm / 0 people) = 350 ppm





Vbz-design = 550 cfm

indoor CO2 concentration, ppm

Vbz-DCVmin = 60 cfm

ou

tdo

or

air

flo

w,cfm

set position of OA damper to bring in60 cfm when indoor CO2 equals 350 ppm

set position of OA damper to bring in550 cfm when indoor CO2 equals 1600 ppm

For single-zone systems, Vot = Voz = Vbz/Ez (assumes Ez = 1.0)

Cs-design = 1600 ppmCs-DCVmin = 350 ppm



Control Coordination Issues

SAOAOA

EAEA RA

1. Economizer operation should override DCV2. Don’t forget about building pressure control

space

CO2P




Agenda








implementing DCV in a dedicated OA system

OA Delivered Directly to Each Zone

SAlocalHVAC unit

CACA

EA

VAV

dedicatedOA unitOA

VFD

CO2

RA CA

SA

CO2

RA



implementing DCV in a dedicated OA system

Control Coordination Issues

• Requires pressure-independent OA dampers forany non-DCV zones also

• Requires variable airflow at the dedicated OA unit(added benefit of fan energy savings)

• Don’t forget about building pressure control!



Agenda









implementing DCV in a multiple-zone recirculating system

1) CO2 Sensor in Every Zone?

SASA

OAOA

RARAEAEA

space

space

CO2

CO2



1) CO2 Sensor in Every Zone?

• Requires a CO2 sensor in every zone– CO2 level doesn’t change much in many of the zones

– Non-critical zones will always be over-ventilated

– Increases installed cost, maintenance, and risk of energy waste

• Requires BAS to poll all sensors and then determinerequired OA damper position

• Requires method to ensure minimum outdoor airflow

6.2.7.1.1 The breathing zone outdoor airflow (Vbz) shall be reset in responseto current occupancy and shall be no less than the building component(Ra × Az) of the DCV zone.





2) CO2 Sensor in Common Return Duct?

SASAOAOA

RARAEAEA

space

space

Under-ventilates some zones while over-ventilating others

CO2



2) CO2 Sensor in Common Return Duct?

6.2.7.1.2 The ventilation system shall be controlled such that at steady-state itprovides each zone with no less than the breathing zone outdoor airflow (Vbz)for the current zone population.





3) DCV at Zone Level + Ventilation Reset

lounge restroom

storage office

office conference rm computer roomreception area ele

vato

rs

vestibule corridor

CO2

CO2

OCC

OCC

TOD TOD




• Use all zone-level DCV approaches,each where it best fits

– CO2 sensors: densely-occupied zones with highly-variable population

– Occupancy sensors: low-density offices or densely-occupied zones where population varies only minimally

– Time-of-day schedules: zones with predictable patterns





CO2 OCC

SA RA

CO2TOD TODOCC

• Current required outdoor airflow (Voz)(TOD schedule, OCC sensor, CO2 sensor)

• Current primary airflow (Vpz)• Current OA fraction (Zpz)

communicating VAV controllers

AHU or rooftop unit withflow-measuring OA damper

• Reset intake airflow (Vot)

Building Automation System• Find highest OA fraction (Zpz)• Calculate current system

ventilation efficiency (Ev)• Calculate current system

intake airflow (Vot)




• Saves energy during partial occupancy

• Lower installed cost, less maintenance, and morereliable than installing a CO2 sensor in every zone

– Use zone-level DCV approaches where they best fit(CO2 sensor, occupancy sensor, time-of-day schedule)

– Combine with ventilation reset at the system level

• Earn LEED EQc1: Outdoor Air Delivery Monitoring

• Monitor CO2 concentrations within all densely occupied spaces ...

• Provide a direct outdoor airflow measurement device capable ofmeasuring the minimum outdoor air intake flow ...

IEQ credit 1, LEED-NC (v2009)




4) DCV + VAV Box Reset + Ventilation Reset

CO2

SA RA

CO2TOD TODOCC

• Current required outdoor airflow (Voz)(TOD schedule, OCC sensor, CO2 sensor)

• Current primary airflow (Vpz)• Current OA fraction (Zpz)• OA fraction limit (max Zpz)

communicating VAV controllers

AHU or rooftop unit withflow-measuring OA damper

• Reset intake airflow (Vot)

Building Automation System• Find highest OA fraction (Zpz)• Calculate current system

ventilation efficiency (Ev)• Calculate current system

intake airflow (Vot)

OCC


CO2-Based DCV for Multiple-Zone HVAC Systems

ASHRAE Research Project 1547

• Compares various control sequences

• Further enhances control sequencesand setpoints for multiple-zonerecirculating ventilation systems



Implementation of RP-1547 CO2-Based DCV Control Sequences

ASHRAE Research Project 1747

“Valid logic was developed in RP-1547, but it is not readily implemented inreal control systems.”

“This project will develop practical control sequences, then test them in areal-world building environment with a commercial-grade DDC system.”

RFP for ASHRAE Research Project 1747

• Project began in September 2015… with expected completion by February 2017


Seventhwave (2015) field study of DCV in Minnesota

DCV Control Sequences Implemented




Measured/Calculated Energy Savings



Findings From Recommissioning




Most Critical DCV Commissioning Steps

• During design, verify that designer has defined:

1. Control sequence

2. CO2 setpoint(s)

3. OA flow limit(s)

4. Sensor location(s)

5. Airflow measurement

• During installation, verify CO2 sensors are calibrated

• After occupancy, verify that system performs accordingto the sequence, for at least a week of operation

• Ensure that the owner is trained, and understands whatthe sensors should do and why they do it



Summary

• ASHRAE Standard 62.1 allows dynamic reset ofventilation air as operating conditions change

• ASHRAE Standard 90.1 is requiring DCV in moretypes of spaces

• Consider CO2-based DCV in densely-occupied zoneswith widely-varying population

• Use other DCV technologies (occupancy sensors,time-of-day schedules) where they make sense

• Combine DCV with ventilation reset in a VAV systemto avoid the need to sense CO2 in every zone




Further Reading• American Society of Heating, Refrigeration and Air-Conditioning Engineers,

Inc. 2011. 62.1 User’s Manual. Atlanta, GA: ASHRAE.

– Appendix A: CO2-Based Demand-Controlled Ventilation

– Appendix B: Ventilation Reset Control

• Murphy, J. 2005. “CO2-Based Demand-Controlled Ventilation withASHRAE Standard 62.1,” Trane Engineers Newsletter (ADM-APN017-EN).

• Seventhwave. 2015. “Energy Savings from Implementing and EnergySavings from Implementing and Commissioning Demand Control Ventilation.”

• Stanke, D. 2006. “Standard 62.1 System Operation: Dynamic Reset Options”,ASHRAE Journal (December): pp. 18-32.

• Stanke, D. 2010. “Dynamic Reset for Multiple-Zone Systems,”ASHRAE Journal (March): pp. 22-35.

• ASHRAE Research Project 1547. CO2-Based Demand-Controlled Ventilationfor Multiple-Zone Systems. January 2014.

• ASHRAE Research Project 1747 (in progress). Implementation ofRP-1547 CO2-based DCV for Multiple-Zone Systems in DDC Systems.

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