Ventilation Requirements & Dynamic Reset...intake flow using either VRP or IAQP 6.2 Ventilation Rate Procedure Prescribes minimum rates for “typical” zones Prescribes calculations

Multiple-Zone Ventilation© 2007 American Standard Inc. All rights reserved

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© 2006 American Standard Inc.

complying with Std 62.1-2007:

Ventilation Requirements & Dynamic Reset



Dennis Stanke

February 2008

© 2008 Trane

ASHRAE Standard 62.1

What Is It?

� Title: “Ventilation for Acceptable Indoor Air Quality”

� Purpose: “… to specify minimum ventilation rates and other measures intended to provide indoor air quality that is acceptable to human occupants and that minimizes adverse health effects.”

� Scope: All commercial, institutional, and high-rise residential buildings


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© 2008 Trane


Why Care?

� The Std 62.1 Ventilation Rate Procedure (VRP) is now the basis for both US ventilation model codes (UMC and IMC)

� VRP more stringent than some local codes(helps establish “standard-of-care”)

� VRP less stringent than some local codes(helps designer pursue code variance)

� VRP is a prerequisite for any LEED credits

© 2008 Trane

what does Std 62.1 require?

Must Comply With …

� General requirements (Sect 4 and 5)

� To reduce generation of indoor contaminants and introduction of outdoor contaminants

� Ventilation requirements (Sect 6)

� To dilute and remove indoor contaminants

� Construction, startup, operation and maintenance requirements (Sect 7 and 8)

� To assure installation/operation as designed


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© 2008 Trane

ventilation requirements

6.0 Procedures

� 6.1 General. For mechanical systems, find OA intake flow using either VRP or IAQP

� 6.2 Ventilation Rate Procedure

� Prescribes minimum rates for “typical” zones

� Prescribes calculations for minimum intake rate

� 6.3 IAQ Procedure

� It’s performance-based

� Must ventilate as necessary to achieve specific concentration targets for contaminants of concern

© 2008 Trane

Std 62.1-2007 Section 6.2

Ventilation Rate Procedure

� 6.2.1 Outdoor air treatment

� 6.2.2 Zone calculations

� 6.2.3 Single zone systems (intake calculations)

� 6.2.4 100% OA systems (intake calculations)

� 6.2.5 Multiple-zone systems (intake calculations)

� 6.2.6 Design for varying operating conditions

� 6.2.7 Dynamic reset

� 6.2.8 Exhaust ventilation

� 6.2.9 Ventilation in smoking areas


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© 2008 Trane

Std 62.1-2007 Section 6.2.2

Zone Calculations

1. Calculate breathing-zone outdoor airflow, using Table 6-1 rates (cfm/per, cfm/ft2)

Vbz = Rp × Pz + Ra × Az (6-1)

2. Find zone air distribution effectiveness, Ez

Look up Ez (typically 1.0) (Tab 6-2)

3. Calculate zone outdoor airflow

Voz = Vbz/Ez (6-2)

© 2008 Trane

6.2.2 zone calculations

Minimum Ventilation Rates

Table 6-1: Minimum breathing-zone rates for 63 categories

Office 20 0.0 5.0 0.06

Classroom (ages 5-8) 15 0.0 10.0 0.12

Lecture classroom 15 0.0 7.5 0.06

Retail sales 0 0.3 7.5 0.12

Auditorium 15 0.0 5.0 0.06

Std 62-2001 Std 62.1-2007

Rp Ra Rp RaOccupancy category cfm/p cfm/ft² cfm/p cfm/ft²

Prescribes both per-person, per-area rates


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Office (5p) 100 20.0 85 17.0

Classroom (ages 5-8) (25p) 375 15.0 370 15.0

Lecture classroom (65p) 975 15.0 550 8.5

Retail sales (20p) 300 15.0 270 14.0

Auditorium (150p) 2250 15.0 810 5.4

Occupancy category(default density/1000 ft²)

Std 62-2001

Vbzcfm

Effectivecfm/p

6.2.2 zone calculations

Effective Minimum Rates

Std 62.1-2007

OA flow rates go down in 70% of occupancies

Vbzcfm

Effectivecfm/p

© 2008 Trane













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© 2008 Trane

Single-Zone CV System

SAOA

RAEA

space

© 2008 Trane

Std 62.1-2007 Section 6.2.3

Single-Zone Systems

For single-zone systems

� Complete first three steps for zone

� For system, find outdoor air intake flow, Vot:

Vot = Voz (6-3)

Compared to 62.1-2001, reduced zone airflow reduces design intake OA in many

single-zone systems

But … intake flow (Vot) equals zone OA (Voz), that is, no credit available for system

occupant diversity


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© 2008 Trane

six-zone school example

Design Zone Calculations Example School Rp Pz Ra Az Ez Voz

cfm/per people cfm/ft2 ft2 -- cfm

South classrms (9+) 10 140 0.12 4,000 1.0 1,880

West classrms (9+) 10 140 0.12 4,000 1.0 1,880

North lecture class 7.5 260 0.06 4,000 1.0 2,190

East lecture class 7.5 260 0.06 4,000 1.0 2,190

Interior offices 5 5 0.06 1,000 1.0 85

North art classrm 10 32* 0.18 2,000 1.0 680

* Average (81% of 40 peak)

Step 1: Vbz = Rp*Pz + Ra*AzStep 2: Look up EzStep 3: Voz = Vbz/Ez

Step 7: Vot = ΣΣΣΣVoz

© 2008 Trane

Single-Zone Systems

� OK, for design.

� But … What about operation?

� Does 62.1-2007 allow intake airflow to vary during operation?

� Of course.


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operation for varying conditions

6.2.7 Dynamic Reset

Optional controls may reset zone or system settings based on changing conditions, including:

� Variations in occupancy (TOD, OCC, COU) or ventilation airflow (CO2)

� May reset zone OA flow in any system

� Variations in efficiency

� May reset system OA intake in VAV systems

� Reset VAV box minimums when economizing

� May reset minimums in some VAV-reheat systems

Std 62.1 allows zone-level dynamic reset based on “demand” (Demand Controlled Ventilation: DCV)

part load

© 2008 Trane

Single-Zone CV System

SAOA

RAEA

space

Variations in occupancy:

� Time-of-day (TOD) schedule

� Occupant count/detection

� CO2-based DCV

Variations in occupancy:

� Time-of-day (TOD) schedule

� Occupant count/detection

� CO2-based DCV

part load


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6.2.7 dynamic reset

Variations in Occupancy

May reset zone OA requirement to match it to current population (that is, demand), based on:

� Time-of-day (TOD) schedules… number of people expected in zone at a given time

� On/off occupancy (OCC) sensors … design population or no people in zone

� People-counters (COU)… “accurate” real-time count of people in zone

� Carbon dioxide sensors (CO2)… estimate of OA flow (cfm/person) within zone

part load

© 2008 Trane

CO2-based demand-controlled ventilation

How Concentrations Work

Ci = Co + N/Vo

where

Co = CO2 concentration inoutdoor air, ppm

N = CO2 generation rate,cfm/person

Vo = outdoor airflow rate,cfm/person

� When OA flow Vo = 15 cfm/p, 80% of visitors deem human bioeffluent odors as acceptable

� Sedentary people generate CO2

at about 0.0105 cfm/p

� If Co = 300 ppm,Ci = 300 + 10500/15

= 1000 ppm

� So, maintaining Ci – Co = 700 ppm indirectly maintains to 15 cfm/p

At Steady State

part load


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40 80

800

1600

2400

3200

4000

zone population, Pz

breath

ing zone O

A, Vbz

120 160 220 240

diffe

rentia

l CO

2 , ppm

200

400

600

800

1000

1200

000

4800

Now ∆∆∆∆CO2 varies,so DCV isn’t as easy

CO2-based DCV

ASHRAE Std 62.1-2007

Fixed ∆∆∆∆CO2 setpoint no longer works as well

62.1-2007


What about CO2 levels?

∆∆∆∆CO2 = 700 ppm(Std 62-2001)

∆∆∆∆CO2 varies(Std 62.1-2007)

Vbz = 2190 cfm

Vbz = 3900 cfm

lecture classrmsdesign Pz = 260 p

part load

© 2008 Trane

How to Use CO2?

� Reminder: This is zone-level DCV for a single-zone system

� Here’s some example approaches:

� Follow the Users Manual

� Modify the UM using a minimum non-zero population

� Use a fixed ∆CO2 set point combined with a minimum OA intake (Vot) setting

part load


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one way to implement SZS DCV …

62.1 User’s Manual

� Find breathing zone OA (Vbz) range

Vbz = (Rp × Pz + Ra × Az)Vbz-des = (7.5 × 260 + 0.06 × 4000)/1.0 = 2190 cfmVbz-min = (7.5 × 0 + 0.06 × 4000)/1.0 = 240 cfm

� Find target indoor CO2 (Crz) range

Crz = Co + N/(Vbz/Pz)Crz-des = 0.000350+0.0105/(2190 cfm/260 p) � 1600 ppmCrz-min = 0.000350 � 350 ppm

� The Controller: Set Vot (= Vbz/Ez) signal range to match Crz range

� Adjust OA damper to deliver Vbz-des at max signal, Vbz-min at min signal

part load

© 2008 Trane

DCV for single-zone CV systems


Crz (CO2, ppm)

Vbz(cfm)

240

2190

350 1600

The Controller

part load


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© 2008 Trane



� Using this controller, sensing CO2 and adjusting OA damper position, results in Vot equal to or greater than the required minimum Vot

� Incidentally, to make the following plots, at each zone population, we assumed a zone-CO2 level (Crz-guess), then found breathing zone OA (Vbz) needed using The Controller, solved for Crz at that Vot, and compared. We repeated the process until Crz matched Crz-guess.

� Assume Cr-guess

� Vot = (1.56 � (Crz-guess – 350) + 240)/1.0

� Crz = 350 + Pz � k � m / Vbz

� Repeat until Crz = Crz-guess

part load

© 2008 Trane



40 80

800

1600

2400

3200

4000

zone population, Pz

120 160 200 240

indoor C

O2 , C

rz, p

pm

300

600

900

1200

1500

1800

000

4800

Vot-min

Vot-design

outd

oor-a

ir inta

ke flo

w, Vot, cfm

part load


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© 2008 Trane

another way to implement SZS DCV

62.1 UM Modified

zone population, Pz

300

600

900

1200

1500

1800

0

Vot-design

Vot-min

Cs-design

Pz-min

Cs-min

indoor C

O2 , C

rz, p

pm

outd

oor-a

ir inta

ke flo

w, Vot, cfm

40 80 120 160 200 2400

800

1600

2400

3200

4000

0

4800

part load

© 2008 Trane

another way to implement SZS DCV

Single CO2 Setpoint

zone population, Pz

300

600

900

1200

1500

1800

0

Cs-min

Vot-min

indoor C

O2 , C

rz, p

pm

outd

oor-a

ir inta

ke flo

w, Vot, cfm

40 80 120 160 200 2400

800

1600

2400

3200

4000

0

4800

part load


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© 2008 Trane

Implementation Issues

� Sensor location

� Wall-mounted (in the breathing zone)

� Duct-mounted (not so good)

� Economizer operation may override DCV minimum OA intake

� Don’t forget about building pressure control! Can only reduce intake so much.

part load

© 2008 Trane

DCV approaches

Resources

� ASHRAE Journal

� May 2006: CO2-based DCV Using 62.1-2004

� Dec 2006: System Operation: Dynamic Reset Options

� Std 62.1-2007 User’s Manual, Appendix A (for single-zone systems only)

part load


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© 2008 Trane

100% OA Systems

CA

OA

EAEA

space

space

SA

RA

SA

RA

design


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© 2008 Trane

Std 62.1-2007 Section 6.2.4

100% OA Systems

For 100% OA systems

� Complete first three steps for zone

� For system, find outdoor air intake flow, Vot:

Vot = ΣΣΣΣVoz (6-4)

Compared to 62.1-2001, reduced zone airflow reduces OA energy in many

100% OA systems

But … intake flow (Vot) must be sum-of-zone OA at design (Voz), that is, no credit available for system occupant diversity

design

© 2008 Trane

system calculations

100% OA SystemsExample School Rp Pz Ra Az Ez Voz


South classrms (9+) 10 140 0.12 4,000 1.0 1,880

West classrms (9+) 10 140 0.12 4,000 1.0 1,880





OA intake flow (Vot) 8,900

*Average (81% of 40) Step 7: Vot = ΣΣΣΣVoz


design


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© 2008 Trane

100% OA Systems

� OK, for design.


� For CV AHU, dynamic reset (zone level DCV) can’t be implemented – no dampers

� For VAV AHU, it seems reasonable to apply single-zone DCV concepts to find and control Voz zone-by-zone

© 2008 Trane

100% OA Systems - CV

CA

OA

EAEA

space

space

SA

RA

SA

RA

No DCV possible

part load


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© 2008 Trane

100% OA Systems - VAV

CA

OA

EAEA

space

space

SA

RA

SA

RA

VFD

VFD

CO2

OCC

DCV at zones resets Voz,AHU control resets Vot at

system

part load

© 2008 Trane

DCV for 100% OA systems

100% OA Systems - VAV

� If you calculate Voz set point

� For TOD, OCC, and COU zones, find Voz = Rp*Pz + Ra*Az using estimated or actual population

� For CO2 zones, find Voz = [Rp*Pz + Ra*Az]/Ev, using sensed CO2 and differential controller

� If you don’t calculate Voz

� For occ/unocc TOD, OCC zones, simply open/close damper – we don’t know Pz so we can’t modulate

� For estimated pop (TOD, COU) and CO2 zones, use “trim/respond” logic to modulate damper

part load


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100% OA Summary

� To comply at design, Vot = Voz. No diversity credit possible … must assume full system population to size AHU

� Optional control at part load,

� For CV OA AHU, no way to use DCV in zones … nothing to adjust!

� For VAV OA AHU, use zone DCV to estimate current Voz and adjust zone damper

� Control OA AHU to modulate intake airflow, based on duct pressure or ventilation damper positions (Std 90.1 might require this)

© 2008 Trane













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© 2008 Trane

Multiple-Zone Systems

SAOA

RA

EA

space

space

© 2008 Trane

Std 62.1-2007 Section 6.2.5

MZ Recirculating Systems

For multiple-zone recirculating systems, complete first three steps for zone, then:

4. Find primary (or discharge) outdoor air fraction

Zp = Voz/Vpz-min (6-5)

5. Find uncorrected outdoor airflow

Vou = D*ΣΣΣΣ(Rp×Pz) + ΣΣΣΣ(Ra×Az) (6-6)

6. Find system ventilation efficiency

Look up default Ev, or (Table 6-3)

Or, calculate Ev per equations (App A)

7. Find outdoor air intake flow, Vot:

Vot = Vou/Ev (6-8)

design


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© 2008 Trane

Std 62.1-2007 Section 6.2.5

MZ Recirculating Systems

For multiple-zone recirculating systems, complete first three steps for zone, then:

4. Find primary (or discharge) outdoor air fraction

Zp = Voz/Vpz-min (6-5)

5. Find uncorrected outdoor airflow

Vou = D*ΣΣΣΣ(Rp×Pz) + ΣΣΣΣ(Ra×Az) (6-6)

6. Find system ventilation efficiency

Look up default Ev, or (Table 6-3)

Or, calculate Ev per equations (App A)

7. Find outdoor air intake flow, Vot:

Vot = Vou/Ev (6-8)

Compared to 62.1-2001, reduced zone airflow (Voz) reduces design OA (Vot) and

energy in many multiple-zone systems

Compared to single-zone and 100% OAsystems, accounting for occupant diversity

reduces design OA (Vot) and energy

design

© 2008 Trane

six-zone school example

Zone-Level Calculations Example School Rp Pz Ra Az Ez Voz


South classrms (9+) 10 140 0.12 4,000 1.0 1,880

West classrms (9+) 10 140 0.12 4,000 1.0 1,880







design


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multiple-zone system calculations

Single-Path VAV: Calc EvExample School Pz Vdz Voz Vdzm Zd Evz

people cfm cfm cfm -- (5,6,7)

South classrms (9+) 140 6,500 1,880 4,000 0.47

West classrms (9+) 140 6,700 1,880 4,000 0.47

North lecture class 260 5,500 2,190 4,000 0.55

East lecture class 260 7,900 2,190 4,000 0.55

Interior offices 5 500 85 300 0.28

North art classrm 32* 1,700 680 1,300 0.52


Step 4: Find outdoor air fraction for each zone:Zd = Voz/Vdzm = 1880/4000 = 0.47

design

© 2008 Trane




South classrms (9+) 140 6,500 1,880 4,000 0.47 --

West classrms (9+) 140 6,700 1,880 4,000 0.47 --

North lecture class 260 5,500 2,190 4,000 0.55 --

East lecture class 260 7,900 2,190 4,000 0.55 --

Interior offices 5 500 85 300 0.28 --

North art classrm 32* 1,700 680 1,300 0.52 --

Uncorrected OA flow -- -- -- Step 5 Vou 6,500


Step 5a: Find occupant diversity:D = Ps/ΣΣΣΣPz = 550/837 = 0.66

Step 5b: Find uncorrected outdoor air intake:Vou = D*ΣΣΣΣ(Rp*Pz) + ΣΣΣΣ(Ra*Az)

= 0.66*7,000 + 1,900 = 6,500 cfm

design


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© 2008 Trane




South classrms (9+) 140 6,500 1,880 4,000 0.47 0.85

West classrms (9+) 140 6,700 1,880 4,000 0.47 0.85

North lecture class 260 5,500 2,190 4,000 0.55 0.77

East lecture class 260 7,900 2,190 4,000 0.55 0.77

Interior offices 5 500 85 300 0.28 1.04

North art classrm 32* 1,700 680 1,300 0.52 0.80


Uncorrected OA frac Step 6 Xs 0.32

Sys vent eff -- -- -- Ev 0.77


Step 6a: Find system primary airflow:Vps = LDF*ΣΣΣΣVpz = 0.70*28,800 = 20,200

Step 6b: Find average outdoor air fraction:Xs = Vou/Vps = 6,500/20,200 = 0.32

Step 6c: Find ventilation efficiency for each zone:Evz1 = 1+Xs–Zd = 1+0.32–0.47 = 0.85

Step 6d: Find system ventilation efficiencyEv = min(Evz) = 0.77

design

© 2008 Trane




South classrms (9+) 140 6,500 1,880 4,000 0.47 0.85

West classrms (9+) 140 6,700 1,880 4,000 0.47 0.85

North lecture class 260 5,500 2,190 4,000 0.55 0.77

East lecture class 260 7,900 2,190 4,000 0.55 0.77

Interior offices 5 500 85 300 0.28 1.04

North art classrm 32* 1,700 680 1,300 0.52 0.80


Uncorrected OA frac Step 6 Xs 0.32

Sys vent eff -- -- -- Ev 0.77

Outdoor air intake -- -- -- Step 7 Vot 8,400


Step 7: Find outdoor air intake flow:Vot = Vou/Ev

= 6,500/0.77 = 8,400

design


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© 2008 Trane

VRP calculation details

Resources

� ASHRAE Journal

� Oct 2004 Single-zone and dedicated-OA systems

� Nov 2004 Ventilation for changeover-bypassVAV systems

� Jan 2005 Single-path, multiple-zone systems

� May 2005 Dual-path, multiple-zone systems

� Go to <ashrae.org>, Addenda to Std 62-2001, Addendum 62n, for one spreadsheet

� See Std 62.1-2007 User’s Manual for another

design

© 2008 Trane

Multiple-Zone Systems

� OK, for design.


� Can we use dynamic reset controls?

� Sure …


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© 2008 Trane

operation for varying conditions

6.2.7 Dynamic Reset

Optional controls may reset zone or system settings based on changing conditions, including:

� Variations in occupancy (TOD, OCC, COU) or ventilation airflow (CO2)

� May reset zone OA flow in any system

� Variations in efficiency

� May reset system OA intake in VAV systems

� Reset VAV box minimums when economizing

� May reset minimums in some VAV-reheat systems

Std 62.1 allows zone-level dynamic reset based on “demand” (Demand Controlled Ventilation: DCV)

part load

© 2008 Trane

multiple-zone system

Dynamic Reset Approaches

� No dynamic reset

� Easy to do, but doesn’t save any energy!

� System-level (DCV)

� Approach not developed … needs research

� Ventilation reset control (VRC) only

� Responds to changes in system vent efficiency

� Ventilation reset (VRC) combined with zone-level DCV

� Responds to changes in both zone population and system ventilation efficiency

part load

��


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© 2008 Trane

MZS dynamic reset approaches

Ventilation Reset Control

� Provides system-level reset

� Accounts for changes in ventilation system efficiency (Ev) due to zone/system airflow changes

� Solves MZS equations in real time to find current Vot set point required (assuming design population in zones)

part load

© 2008 Trane

dynamic reset

Ventilation Reset Control

� Current zone airflows

Vbz = entry (found using Pz-des)Voz = Vbz/Ez (calculated w/Ez)Vdz = sensed (discharge airflow sensor)

� Current ventilation fraction for each zoneZdz = Voz/Vdz (calculated)

� Current intake airflow Vot set point (solving MZS equations)

Vou = entry (found using Pz-des and Ps)

Ev = 1 + Vou/Vps – Zd (calculated)Vot = Vou/Ev (calculated)*

*Vot =< Vot-des

part load


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VAV ventilation reset control (no DCV)

Single-Duct VAV System

Design

VRP requires minimum Vot at design

8, 810

For each zone use:

Pz = highest expected zone populationVdz = the peak zone discharge airflow Vdzm = minimum expected VdzVbz = Rp*Pz + Ra*AzZdz = Voz/Vdzm = Vbz/(Ez*Vdzm)

Votreq’d

@ design

population Pz 140 140 260 260 5 40disc airflow Vdz 6,500 6,700 5,500 7,900 500 1,700

Vdzm 4,000 4,000 4,000 4,000 300 1,300vent rate Vbz 1,880 1,880 2,190 2,190 85 760vent fract Zdz 0.470 0.470 0.548 0.548 0.283 0.585

Vou = D*ΣRp*Pz + ΣRa*Az = 0.65*7,125 + 1860 = 6,500Xs = Vou/Vps = 6,500/20,160 = 0.322Ev = 1 + 0.322 – 0.585 = 0.738Vot = Vou/Ev = 6,500/0.738 = 8,808

For the system use:

Ps = highest system pop = 550D = Ps/ΣPz = 550/845 = 0.650LDF = load diversity factor = 0.7Vps = LDF*ΣVdz-des

= 0.7*28,800 = 20,160

design

© 2008 Trane

8, 810

Votreq’d

(current)



100% Load (1)

8, 810

For each zone use:

Pz = use highest zone populationVdz = use current discharge airflow Vdzm = don’t needVbz = same as design (Pz = Pz-des)Zdz = Vbz/(Ez*Vdz) = current fraction

Votreq’d

@ design

population Pz 140 140 260 260 5 40disc airflow Vdz 4,960 5,400 4,000 4,000 500 1,300vent rate Vbz 1,880 1,880 2,190 2,190 85 760vent fract Zdz 0.379 0.348 0.548 0.548 0.170 0.585


For the system use:

Ps = use highest system popD = Ps/ΣPz = 0.650 (same as design)LDF = don’t needVps = ΣVdz = 20,160 = currentairflow

part load


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© 2008 Trane

8, 390

Votreq’d

(current)



100% Load (2)

VRC delivers Vot-des or less at 100% load

8, 810

Votreq’d

@ design

population Pz 140 140 260 260 5 40disc airflow Vdz 4,960 5,000 4,000 4,000 500 1,700vent rate Vbz 1,880 1,880 2,190 2,190 85 760vent fraction Zdz 0.379 0.376 0.548 0.548 0.170 0.447


part load

© 2008 Trane



100% Load (2)

8, 810

Votreq’d

@ design

population Pz 140 140 260 260 5 40disc airflow Vdz 4,960 5,000 4,000 4,000 500 1,700vent rate Vbz 1,880 1,880 2,190 2,190 85 760vent fraction Zdz 0.379 0.376 0.548 0.548 0.170 0.447

Vou = D*SRp*Pz + SRa*Az = 0.65*7,125 + 1860 = 6,500Xs = Vou/Vps = 6,500/20,160 = 0.322Ev = 1 + 0.322 – 0.548 = 0.775Vot = Vou/Ev = 6,500/0.775 = 8,390

8, 390

Votreq’d

(current)

population Pz 140 140 260 260 5 40disc airflow Vdz 4,000 3,700 4,200 4,300 300 1,700vent rate Vbz 1,880 1,880 2,190 2,190 85 760vent fraction Zdz 0.470 0.508 0.521 0. 509 0.283 0.447Vou = 6,500Xs = Vou/Vps = 6,500/18,200 = 0.357Ev = 1 + 0.357 – 0.521 = 0.836Vot = Vou/Ev = 6,500/0.836 = 7,780

90% System Load

8,810 7,780

VRC reduces Vot,saves energy

part load


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© 2008 Trane

multiple-zone system

Dynamic Reset Approaches

� No dynamic reset

� Easy to do, but doesn’t save any energy!

� Demand controlled ventilation (DCV) only

� Approach not developed … needs more work

� Ventilation reset control (VRC) only

� Responds to changes in system vent efficiency

� Ventilation reset (VRC) combined with DCV

� Responds to changes in both zone population and system ventilation reset

part load

© 2008 Trane

VRC calculations with DCV zones


� If you calculate Vot set point

� For non-CO2 zones, find Vbz = Rp*Pz + Ra*Az using estimated (TOD, OCC) or actual (COU) Pz

� For CO2 zones, find Vbz = [Rp*Pz + Ra*Az], using a CO2 Controller (relates sensed CO2 to Vbz required)

� Use current Vbz and Voz values to solve MZS equations for current Vot set point

� If you don’t calculate Vot set point

� I’m not sure what to do … this type of “trim and respond” approach with zone or system-level DCV needs study

part load


30

© 2008 Trane

8, 810

Votreq’d

@ design

VAV vent reset control with DCV zones


Design

Same Vot-des, with or w/o DCV zones

For each zone use:

Pz = highest expected zone populationVdz = the peak zone discharge airflow Vdzm = minimum expected VdzVbz = Rp*Pz + Ra*AzZdz = Voz/Vdzm = Vbz/(Ez*Vdzm)

population Pz 140 140 260 260 5 40disc airflow Vdz 6,500 6,700 5,500 7,900 500 1,700

Vdzm 4,000 4,000 4,000 4,000 300 1,300vent rate Vbz 1,880 1,880 2,190 2,190 85 760vent fract Zdz 0.470 0.470 0.548 0.548 0.283 0.585


For the system use:

Ps = highest system population = 550D = Ps-des/ΣPz-des = 550/845 = 0.650LDF = load diversity factor = 0.7Vps = LDF*ΣVdz-des

= 0.7*28,800 = 20,160

CO2 OCC

design

© 2008 Trane



100% Load (1)

8, 810

For each non-dcv zone use:Pz = highest zone pop (Pz = Pz-des) Vbz = same as design

For each non-CO2 dcv zone use:Pz = estimated pop (Pz = Pz-est)Vbz = Rp*Pz-est + Ra*Az

For each CO2 dcv zone use:Pz = ??? (don’t know current pop)Vbz = Vbz-est (from CO2 Controller)

Votreq’d

@ design

population Pz 140 140 ??? 260 5 0disc airflow Vdz 4,960 5,400 4,000 4,000 500 1,300vent rate Vbz 1,880 1,880 1,300* 2,190 85 360vent fract Zdz 0.379 0.348 0.325 0.548 0.170 0.277

Vou = D*Σnon(Rp*Pz)+Σnon(Ra*Az)+Σnon-co2(Rp*Pz-est+Ra*Az)+Σco2[Vbz-est]

= 0.65*4,780 + 1,260 + 360 + [1,300] = 6,030Xs = Vou/Vps = 6,030/20,160 = 0.299Ev = 1 + 0.299 – 0.548 = 0.751Vot = Vou/Ev = 6,030/0.751 = 8,030 (but no more than 8,808)

For the system use:D = Ps-des/ΣPz-des = 0.650Vps = current airflow = ΣVdz = 20,160Vou = D*Σnon (Rp*Pz-des) + Σnon (Ra*Az)

+ Σnon-co2 (Rp*Pz-est + Ra*Az)+ Σco2 [Vbz-est]

CO2 OCC

part load

8, 810

Votreq’d

(current)

8, 030

For all zones:Vdz = current discharge airflowZdz = current OA fraction = Vbz/Ez*Vdz


31

© 2008 Trane



100% Load (1)

8, 810

For each non-dcv zone use:Pz = highest zone pop (Pz = Pz-des) Vbz = same as design

For each non-CO2 dcv zone use:Pz = estimated pop (Pz = Pz-est)Vbz = Rp*Pz-est + Ra*Az

For each CO2 dcv zone use:Pz = ??? (don’t know current pop)Vbz = Vbz-est (from CO2 Controller)

Votreq’d

@ design




For the system use:D = Ps-des/ΣPz-des = 0.650Vps = current airflow = ΣVdz = 20,160Vou = D*Σnon (Rp*Pz-des) + Σnon (Ra*Az)

+ Σnon-co2 (Rp*Pz-est + Ra*Az)+ Σco2 [Vbz-est]

CO2 OCC

part load

8, 810

Votreq’d

(current)

8, 030

For all zones:Vdz = current discharge airflowZdz = current OA fraction = Vbz/Ez*Vdz

VRC w/DCV reduces Vot,saves energy (even at 100% load in some

cases)

© 2008 Trane



100% Load (1)

8, 810

Votreq’d

@ design




CO2 OCC

part load

8, 810

Votreq’d

(current)

8, 030

population Pz 140 140 ??? 260 5 0disc airflow Vdz 4,000 3,700 4,200 4,300 300 1,700vent rate Vbz 1,880 1,880 2,190 2,190 85 760vent fraction Zdz 0.470 0.508 0.521 0. 509 0.283 0.447 Vou = 0.65*4,780 + 1,260 + 360 + 1,300 = 6,030Xs = Vou/Vps = 6,030/18,200 = 0.331Ev = 1 + 0.331 – 0.521 = 0.810Vot = Vou/Ev = 6,030/0.810 = 7,440

90% System Load

8,810 7,780

VRC w/DCV reduces Votsaves more energy

7,440


32

© 2008 Trane

VAV vent reset control (with DCV zones)


� So, if you had a way to relate zone CO2

sensed to zone OA required, you could use MZS equations to find Vot-set

� One simple way uses a linear controller to relate zone CO2 to require Vbz, like we did for SZS

� Can this be implemented? Yes.

� Does it work? Probably, but how well? This needs ASHRAE research.

© 2008 Trane

one way to implement DCV-zone …

CO2 DCV for VAV

� Find breathing zone outdoor airflow range

Vbz = (Rp × Pz + Ra × Az)Vbz-des = (7.5 × 260 + 0.06 × 4000) = 2190 cfmVbz-min = (7.5 × 0 + 0.06 × 4000) = 240 cfm

� Find target indoor ∆∆∆∆CO2 range

Crz = Cd + N/(Vbz/Pz)Crz-max = (after some math) = 1500 ppmCrz-min = (after some math) = 500 ppm

� Set CO2 signal range to match Cr range

� Adjust The Controller to require Vbz-design at max CO2

signal, Vbz-min at min CO2 signal

part load


33

© 2008 Trane

one way to implement DCV-zone …

CO2 DCV for VAV

CO2 (Crz), ppm)

Vbz(cfm)

240

2190

500 1500

The Controller

part load

© 2008 Trane

DCV for multiple-zone systems


� In operation we could:

� Sense CO2 in the zone (Crz)

� Adjust OA required (Vbz) per The Controller

� Solve use current Vbz values to solve the MZS equations and find the current set point for OA intake, provided Vot-set <= Vot-des

� Actual OA delivered to the CO2-zone would always equal or exceed the minimum Vbz required by Std 62.1

� But this control approach must be refined and the results analyzed before we go too far with it

part load


34

© 2008 Trane

Implementation

� For VRC alone or combined with zone-level DCV, design usually includes:

� Communicating DDC VAV boxes

� A communicating BAS with equation-solving capability

� Intake airflow sensing and control at the AHU

part load

© 2008 Trane

OA

RA

SA

central station air handlerwith controls

communicatingBAS

• Reset outdoor airflow(TRAQ™ damper)

For VRC: Need DDC/VAV, a BAS, OA flow sensor

DDC/VAV terminals

• Req’d ventilation (Vbz, Voz)• Actual discharge flow (Vdz)• Current ventilation fraction(Zdz = Voz/Vdz)

• Totals (Vou, Vps)• “Used” OA fraction (Xs)• Sys vent efficiency (Ev)• New OA setpoint (Vot)

VAV ventilation optimization


OCCCO2 TOD

part load


35

© 2008 Trane

Some Things To Consider

� Can the BAS solve the MZS equations dynamically? If so:

� Do you want system-level VRC only, or using both VRC and zone-level DCV?

� If VRC and DCV, do you want use CO2, TOD, OCC, COU or some combination?

� Without solving MZS equations, is there a reasonable “trim/respond” approach based on DCV zones? (Don’t know, now)

part load

© 2008 Trane

incidentally, if you reduce intake airflow…

Building Pressure Control

At minimumintake, exhaust must be less than intake airflow

(Positive building pressure reduces infiltration)

++++

exhaustintake


36

© 2008 Trane

incidentally, if you reduce intake airflow…

Building Pressure Control

If DCV reduces intake, exhaust airflow may not exceed intake

(Negative building pressure causes infiltration)

––––

exhaustintake

© 2008 Trane


Quick Summary

� Compared to 1989, 1999, 2001, the 2007 version of the Ventilation Rate Procedure:

� At design

� Lowers many breathing zone OA flows

� Ventilates for two zone sources (people and building), which make zone-level DCV more difficult

� Requires OA intake dependent upon system type

� For operation, makes DCV more difficult, but it allows OA intake reset based on:

� Zone-level demand (DCV)

� System-level ventilation efficiency (VRC)


37


Questions?

Dennis Stanke





Documents

Ventilation Requirements & Dynamic Reset...intake flow using either VRP or IAQP 6.2 Ventilation Rate Procedure Prescribes minimum rates for “typical” zones Prescribes calculations