guideline 36: best in class hvac sequences library/professional development/learning... · • 5.1...

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Guideline 36: Best in ClassHVAC Control Sequences

Steven T. Taylor, P.E., Fellow ASHRAETaylor, P.E., Fellow ASHRAE

TaylSteven T. Taylor, P.E., Fellow ASHRAETaylor Engineering LLP

staylor@taylor‐engineering.com

© 2020 ASHRAE (www.ashrae.org). For personal use only. Additional reproduction, distribution, or transmission in either print or digital form is not permitted without ASHRAE's prior written permission.

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Copyright

Copyright © 2019, 2020 by ASHRAE. All rights reserved. No part of this presentation may be reproduced without written permission from ASHRAE, nor may any part of this presentation be reproduced, stored in a retrieval system or transmitted in any form or by any means (electronic, photocopying, recording, or other) without written permission from ASHRAE.

ASHRAE has compiled this presentation with care, but ASHRAE has not investigated and ASHRAE expressly disclaims any duty to investigate any product, service, process, procedure, design or the like, that may be described herein. The appearance of any technical data or editorial material in this presentation does not constitute endorsement, warranty or guaranty by ASHRAE of any product, service, process, procedure, design or the like. ASHRAE does not warrant that the information in this publication is free of errors. The user assumes the entire risk of the use of the use of any information in this presentation.


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Course ID: 920019171

Guideline 36: Best in Class HVAC Control Sequences

By ASHRAE

Approved for:

3General CE hours

0LEED-specific hours


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• Explain the advantages of using standardized advanced sequences to designers, contractors, and owners

• Understand the key innovative sequences in ASHRAE Guideline 36, High-Performance Sequences of Operation for HVAC Systems

• Recognize the ASHRAE research behind Guideline 36 sequences and how current research will be used for future enhancements

• Distinguish how to implement Guideline 36 sequences in new and existing buildings for engineers and contractors

Learning Objectives

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• General Organization• 5.1 General Control Logic• 5.2 Generic Ventilation Zone Logic• 5.3 Generic Thermal Zone Logic• 5.4 Zone Groups• 5.5 to 5.14 Variable-Air-Volume Terminal Units• 5.15 to 5.16 Variable-Air-Volume Air Handlers Serving Multiple Zones• 5.18 Single Zone Variable-Air-Volume Air Handlers• Automatic Fault Detection and Diagnostics (AFDD)• Implementing Guideline 36• Related Research and Future Enhancements

Agenda

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• Title: High-Performance Sequences of Operation for HVAC Systems

• Purpose: Provide uniform sequences of operation for heating, ventilating, and air-conditioning (HVAC) systems that are intended to maximize HVAC system energy efficiency and performance, provide control stability, and allow real-time fault detection and diagnostics.

• Scope: • This guideline provides detailed sequences of operation for HVAC

systems.• This guideline describes functional tests that, when performed, will

confirm implementation of the sequences of operation.

Guideline 36 Title, Purpose, and Scope (TPS)


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• Configurable controllers• Control logic is preprogrammed, allowing only a few configuration

points and set points to be adjusted by the user• Fully programmable controllers

• Users can program whatever sequences they want into the controller

Configurable Versus Programmable


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• Pro: Preprogrammed, pretested, and debugged control logic, almost plug-and-play

• Reduces installation time• Reduces commissioning time• Improves reliability

• Con: Simplistic control logic • Poor flexibility• Poor energy efficiency • May not even meet energy and indoor air quality

(IAQ) codes

Typical Configurable Controllers


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• Can be programmed to do almost anything, including high-performance sequences

• But they seldom are, due to…• Poor sequences by engineer• Poor programming by contractor• Market pressures• Poor commissioning (if any) by

commissioning authority (CxA) • Poor training of building engineer

Programmable Controllers


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• We keep reinventing the wheel!• Same application, different sequences

• We don’t keep up with codes!• Title 24, ASHRAE/IES Standard 90.1, ASHRAE Standard 62.1…

• We don’t keep up with research• ASHRAE RP-980, 1455, 1515, 1547, 1587, 1747, 1711, etc. …

• Poor alarms and diagnostics• No alarms or too many alarms!• No advanced diagnostics

Other Issues


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• Old paradigm:• Building engineer will disable things until it gets

down to his/her level of understanding.• So, keep control sequences simple.

• New paradigm:• We cannot afford KISS in modern world.• Make the interface simple….• But make the engine high performing.

Kiss Principle

K I S SKEEP IT SIMPLE, STUPIDINTERFACE


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• Desired implementation• ASHRAE experts create and maintain advanced sequences• Manufacturers preprogram, test, and debug all the sequences for their dealers• Engineers simply spec: “Use ASHRAE Guideline 36 sequences”• Control contractors simply use the preprogrammed sequences• Commissioning agents use the functional performance tests (FPTs) (eventually)

included with ASHRAE Guideline 36• Perhaps even forgo FPTs once they are comfortable that manufacturers have programmed them correctly

ASHRAE Guideline 36: Best of Both Worlds

CONFIGURABLE PROGRAMMABLE

Preprogrammed, fully debugged

Advanced sequences and real‐time diagnostics


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• Reduce cost• Writing sequences, programming,

and commissioning• Reduce errors

• Unambiguous sequences• Algorithms pretested and

standardized• Ensure relevant code and standard

compliance• ASHRAE/IES Standard 90.1 and

Title 24 (energy)• ASHRAE Standard 62.1 and Title 24

(ventilation)• ASHRAE Standard 55 (comfort)

ASHRAE Guideline 36 Goals

• Improve energy efficiency and IAQ

• Improve reliability and ease of operation• Hierarchal alarms• Automatic fault detection

and diagnostics• Consistent pretested and

proven sequences of operations (SOOs)


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• First published June 2018• Addenda published 2019

• Addendum a – Controllable Minimum Revisions• Addendum b – Trim & Respond Revisions• Addendum c – Variable Speed Drive Minimum Speed Revisions• Addendum d – VAV Reheat Revisions• Addendum e – Automatic Vmin Determination

• Addenda published 2020• Addendum f – Return Fan Tracking Offset Revisions• Addendum g – Alarm Revisions• Addendum h – Set Point Clarifications• Addendum i – Variable Speed Series Fan-Powered Box Revision• Addendum j – Title 24 Occupied Standby

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Guideline 36 Status


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General Organization


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Contents

3.3 Information Provided by Control Contractor (Addendum a)

Zone temperature set points, ventilation rates, CO2 set points, terminal unit set points, economizer high limit type and climate zone, etc.

Maximum DP set points, minimum speeds, etc.

VAV box controllable minimum (relocated)


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Sequences of Operation—to Date


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5.1General Control Logic


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• Examples• Trim and respond (T&R) logic• Hierarchical alarm suppression

General Logic: Applies to Entire System


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• Used to reset set points based on zone demand, e.g., • Static pressure • Supply air temperature• Hot water (HW) and chilled water (CHW) supply temperature

• Zones issue “requests” based on zone temperature or damper/valve position• E.g., “Generate 1 request when damper position exceeds 95%”• Extra requests can also be generated based on error from set point

• Multiply “requests” by zone Importance Multiplier (IM)• IM=0 means zone does not contribute to reset• IM=1 default• IM>1 for critical zones to get past “Ignores”

• Send to air-handling unit (AHU) controller to adjust set point• Every time-cycle set point is reduced (“trim”)

• With Addendum b, trim only occurs if there is no respond• But set point is increased (“respond”) proportional to number of zone

“requests” (up to a maximum change)

General Logic: T&R Set Point Reset


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General Logic: T&R Parameters


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General Logic: T&R Example

trim

respond

trim

respond

trim

2 IGNORES


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• A rogue zone is one that is always requesting more (more static pressure, colder CHW, or hotter HW)

• Example causes• Load larger than anticipated in design• Poor duct design/construction• Extreme set point adjustments• Equipment failure (broken damper, valve)

• Rogue zones drive the reset loop to extremes and prevent energy savings

• Once identified (discussed later), rogue zones can be • Repaired • Locked out of the T&R control loop if noncritical

• Importance Multiplier set to 0

General Logic: T&R Rogue Zones


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General Logic: T&R Rogue Zones (cont.)

0

20

40

60

80

100

6/27/06 3:00 6/27/06 6:00 6/27/06 9:00 6/27/06 12:00 6/27/06 15:00 6/27/06 18:00 6/27/06 21:00

Cool

ing

Loop

Out

put (

%)

VAV2-20 VAV2-21 VAV2-11 VAV2-22 VAV2-23 VAV2-24 VAV2-25VAV2-27 VAV2-30 VAV2-31 VAV2-6 VAV2-7 VAV2-28 VAV2-9

VAV2-9 is a rogue zone


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• BAS calculates Request-Hours for each zone, and alarms on high cumulative %-Request-Hours.

• Decision to set IM=0 for rogue zones up to operator (not automatic)

General Logic: T&R Rogue Zones (cont.)


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Operating Mode

Airflow (CFM)

Airflow SP

(CFM)

Zone Temp (°F)

Htg SP(°F)

Clg SP(°F)

Damper Pos

(% Open)

HW Valve Pos

(%Open)

DA Temp (°F)

DA Temp SP (°F)

CO2 Level (PPM)

RequestsCumulative Req Hrs

(%‐req‐hrs)

Importance Multiplier

VR‐19‐1 Deadband 342 330 73.3 71.0 74.0 29 0% 56.9 55.0 na 0 10% 1VR‐19‐2 Cooling 278 280 73.9 71.0 74.0 31 0% 57.2 55.0 na 0 2% 1VR‐19‐3 Cooling 275 279 73.1 70.0 73.0 24 0% 57.2 55.0 na 0 1% 1VR‐19‐4 Deadband 245 235 72.9 71.0 74.0 16 0% 57.2 55.0 565 0 6% 1VR‐19‐5 Deadband 184 180 72.3 71.0 74.0 25 0% 58.7 55.0 na 0 3% 1VR‐19‐6 Cooling 1147 1144 70.8 68.0 71.0 45 0% 57.2 55.0 na 0 6% 1VR‐19‐7 Deadband 102 100 73.0 71.0 74.0 32 0% 59.1 55.0 na 0 1% 1VR‐19‐8 Deadband 252 250 72.9 71.0 74.0 41 0% 57.5 55.0 na 0 6% 1VR‐19‐9 Deadband 508 500 73.1 72.0 75.0 15 0% 58.4 55.0 na 0 1% 1VR‐19‐10 Deadband 308 300 72.4 71.0 74.0 31 0% 57.2 55.0 na 0 9% 1VR‐19‐11 Deadband 290 270 73.5 71.0 74.0 32 0% 58.1 55.0 na 0 1% 1VR‐19‐12 Deadband 368 360 74.3 72.0 75.0 11 0% 57.1 55.0 na 0 3% 1VR‐19‐13 Deadband 512 500 73.7 71.0 74.0 32 0% 58.6 55.0 505 0 14% 1VR‐19‐14 Cooling 673 675 73.8 71.0 74.0 54 0% 56.0 55.0 na 0 35% 1VC 19 15

Static Pressure Reset

General Logic: T&R Rogue Zones

VAV Box Table Graphic %‐Request‐Hours

Importance Multiplier


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General Logic: Example T&R Block

Active Duct Setpoint 0.4 in. H2O Status

Setpoint Start (SP0) 0.5 in. H2O # of Ignored Requests (I) 2

Setpoint Min (SPmin) 0.1 in. H2O # of Active Requests (R) 4

Setpoint Max (SPmax) 1.5 in. H2O Trim (SPtrim) ‐0.05

Delay Timer (Td) 10 min Respond (SPres) 0.06

Time Step (T) 2 min Max Response (SPres‐max) 0.13

Optimized Duct Static Pressure SetpointResponding


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• More stable and easier to tune than PID• But long, slow cycles still result

• Can trim slowly and respond quickly• PID goes up or down at the same rate

• Easy to track and nullify rogue zones • Set zone “importance” = zero

• Can increase importance of critical zones• Set zone “importance” ≥ 1

• Can generate extra requests nonlinearly as difference from set point increases and if zone is in alarm

General Logic: Advantages of T&R Versus PID


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• Intended to minimize nuisance alarms from failure of upstream (“source”) equipment

• Example: If a fan fails at an AHU, the zone alarms served by the fan will be suppressed

• Without alarm suppression, the variable-air-volume (VAV) boxes served by the failed fan would also alarm due to lack of flow and out of range temperatures

• Source/dependent relationships are defined separately for heating, cooling, and airflow

• E.g., a boiler plant failure will suppress low zone temperature alarms, but will not suppress high zone temperature alarms

• Upstream equipment passes “OK” token to downstream equipment when it’s working correctly.

• Until getting “OK,” downstream alarms are suppressed

General Logic: Hierarchical Alarm Suppression


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5.2Generic Ventilation Zone

Logic


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• Calculate zone minimum outdoor air requirements per ASHRAE Standard 62.1 (ventilation rate procedure)

• Area (Vbz-A) and Occupant (Vbz-P) outdoor air rates components entered by designer

• Zero all ventilation if window switch open• Adjust occupant component based on CO2 demand-controlled ventilation (DCV)

(next slide)• Zero occupant component (and building component where allowed by 62.1) if

occupancy switch open• Adjusts for zone air distribution effectiveness based in discharge air temperature

(DAT)• Dynamic calculation of zone ventilation rate Voz:

Voz = (Vbz-A* + Vbz-P*) / Ez• Zone outdoor air and primary airflow data sent to AHU controller

• Only for zone groups in Occupied Mode• Ensures AHU provides no more outdoor air than needed when building is partially occupied

• Outdoor air intake adjusted dynamically per multiple spaces equation

Generic Ventilation Zone Logic: Minimum Outdoor Air (OA)


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• P-only loop ranging from 0% at (CO2 set point—200 ppm) to 100% at CO2 set point

• Active minimum set point Vmin* reset from design minimum (Vmin) at 0% CO2 loop signal to design cooling maximum (Vcool-max) at 100%

• Occupant component similarly reset from 0 to design occupant outdoor air rate

Generic Ventilation Zone Logic: CO2 DCV per 62.1

Not recommended for cooling‐only zones − may be over‐cooled


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• ASHRAE Standard 62.1-2019 includes the Simplified Procedure

• ASHRAE/IES Standard 90.1-2019 mandates that the primary airflow minimum must be equal to the minimum, per the Simplified Procedure

• ASHRAE Guideline 36 Addendum e automatically calculates Vmin dynamically• Adjusts for dynamic changes to ventilation rate and if AHU is 100% outdoor air

Generic Ventilation Zone Logic: G36 Addendum e


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ASHRAE Standard 62.1 Simplified Procedure Example Minimum Outdoor Air (cfm/ft2)

VAV BOX SCHEDULE

TAG INLET SIZE

DESIGN CFM MIN OA CFM ZONE Ez CO2 DCV? COOL MIN HEAT AREA PEOP COOL HEAT

VR-101 6 300 102 120 18 50 1.0 0.8 Y VR-102 8 540 90 270 16 44 1.0 0.8 Y VR-103 12 1200 255 255 120 50 1.0 0.8 N

Addendum e: Just put “AUTO” in this minimum column and G36 sequences will dynamically determine minimum


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Can minimum setpoints really be that Low?

• Minimum controllable setpoint is much higher according to VAV box manufacturers

Equates to ~0.03” minimum VP and about 30% of design CFM for typical box selections

NOT “typical” at all. Way too conservative!


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Can minimum setpoints really be that Low?

Most VAV controllers are highly accurate down to about 0.003”VP. Controllable setpoints possible at 0.004”VP

“A”“B”

PG&E RP and ASHRAE RP‐1353

YES!

8” VAV Box


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Sample Controllable Minimum

FVPFPM min

min 4005

3.2004.04005170

Box Inlet Diameter

Maximum CFM at 0.5 in.w.g.

pressure drop

Minimum CFM at 0.004 in.w.g. sensor

reading

Minimum Ratio at Highest

Maximum, %

Minimum Ratio at lowest Maximum, %

6 425 33 7.8% ‐8 715 58 8.1% 13.6%

10 1,100 91 8.3% 12.7%12 1,560 130 8.3% 11.8%14 2,130 177 8.3% 11.3%16 2,730 232 8.5% 10.9%

4

2

minminDFPMCFM


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• What happens if ventilation minimum is less than controllable minimum? • ASHRAE Standard 62.1 allows time averaging over the room time

constant (typically 1 to 6 hours)• TAV pulses the minimum from zero to the controllable minimum to ensure

average minimum is maintained over a 15-minute window

Generic Ventilation Zone Logic: Time‐Averaged Ventilation (TAV)


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5.3Generic Thermal Zone Logic


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• Temperature set points• Zone (scheduling) groups• Zone group modes

Generic Thermal Zone Logic: Applies to All Zones


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• Every zone has occupied and unoccupied set points • Active set point based on zone group mode

• Every zone has separate heating and cooling set points• 1°F minimum dead band• Adjustable set point limits: 65°F–72°F heating, 72°F–80°F cooling

• Setback of ±1°F with occupancy sensors• Mild, so warm-up/cool-down is short when reoccupied

• Extreme setback (40°F/120°F) with window switches• Up to ±4°F setback based on demand response signal

Generic Thermal Zone Logic: Zone Set Points


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• Zone group: A collection of zones that operates on a single time schedule

• All zones belong to exactly one zone group• All zones in a zone group are served by the same AHU

• ASHRAE/IES Standard 90.1 and Title 24 call these isolation areas• Purpose is to allow some zones to be occupied while others are shut off• Required for systems serving over 25000 ft2 area or more than one floor

Zone Groups


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• Zone group modes• Determines zone set points and AHU control responses

• Hierarchy of modes:• Occupied mode• Cool-down mode• Setup mode• Warm-up mode• Setback mode• Freeze protection setback mode• Unoccupied mode

• Zone modes flow “upstream”• Highest zone mode sets mode of zone group• Highest zone group mode sets mode of AHU

Zone Group Modes


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3 Minute Break


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5.5 to 5.14Variable‐Air‐Volume Terminal

Units


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• Points lists, control diagrams and sequences of operations for• Single-duct VAV

• Cooling-only or reheat• Dual-duct VAV

• Snap acting control, with inlet or discharge sensors• Mixing control, with inlet or discharge sensors• Cold duct minimum control

• Parallel Fan VAV• Constant or variable-volume fan

• Series Fan VAV• Constant or variable-volume fan

VAV Terminal Units


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Single‐Duct VAV Reheat: Control Diagram

DA


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Single‐Duct VAV Reheat: Points List

R = Required pointA = Required for some applicationsO = Optional monitoring points


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• Minimum and maximum airflow set points depend on the mode of the zone group

• Vheat-max and Vcool-max are specified on schedule• Vmin* is specified on schedule (or automatically calculated by Addendum e)

• Reset by DCV, window switch, and occupancy sensor status• Heating maximum is Vcool-max in warm-up and setback modes, to allow space to be

heated more quickly

Single‐Duct VAV Reheat SOO: Min and Max Airflows


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Single‐Duct VAV Reheat SOO: Dual Maximum Logic


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Single‐Duct VAV Reheat SOO: Actual Dual Maximum Logic—Allows for Zero Minimum


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Dual Maximum Logic in Action

Start heating, increase DAT set point

At 50% Heat, start increasing airflow


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Dual Maximum VAV Logic: RP‐1515 Results


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• Requires discharge temperature sensor • This is helpful for diagnostics anyway

• Ability to measure and control low airflow rates• Proven not an issue by RP-1353 and PG&E• ~10%–15% minimum possible in most cases

• Maintaining ventilation • No issue with Title 24• No longer an issue with ASHRAE Standard 62.1 using Simplified

Procedure• Air diffuser performance and thermal comfort at low airflows

• Proven not to be a comfort issue by RP-1515• In fact, comfort was improved (as explained in the next slide)

Dual Maximum VAV Logic: Potential Issues


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What Happens When Load is Less than Airflow Minimum?

Conventional Logic Dual Max Logic

Actual Required Airflow

Resulting Loop Output


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• Lower fan energy• Lower heating energy: avoids high minimums, which can drive zone

into heating• Lower reheat energy• Control of supply air temperature reduces stratification• Better modulation of HW valve and less supply air temperature (SAT)

overshoot• HW circuit is self balancing with two-way valves• Improved comfort per ASHRAE RP-1515

• High minimums push zone into heating even in summer• Meets ASHRAE/IES Standard 90.1 and Title 24!

Dual Maximum VAV Logic: Advantages


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Dual‐Duct VAV: Control Diagram (Inlet Sensors)


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Dual‐Duct VAV: Control Diagram (Discharge Sensor)


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Dual‐Duct VAV: Snap Acting SOO

Hot Duct Airflow

Heating Maximum

Heating Loop Signal Cooling Loop Signal

Cold Duct Airflow

Minimum Airflow Setpoint

Cooling Maximum

Transition from Cooling towards Heating

Deadband

Hot Duct Airflow

Heating Maximum


Cold Duct Airflow


Cooling Maximum

Transition from Heating towards Cooling

Deadband

• Most recently used duct (heating or cooling) is used for dead band ventilation

• Advantages• Energy efficient

• No mixing section (high ΔP)

• Can use two standard single‐duct VAV boxes

• Issues• The room is the mixing box. High ventilation minimums

may cause comfort issues

• Not ideal for DCV

• If no direct OA from hot duct; analysis needed to show ventilation will be maintained


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• Preferred dual-duct control logic for DCV

• Mixing section required if serving multiple zones

• Can be used with dual inlet or single discharge airflow sensor

• No direct OA from hot duct; analysis needed to show ventilation will be maintained

Dual‐Duct VAV: Mixing SOO


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• Most conventional, least efficient dual-duct control strategy

• Constant minimum ventilation from cold duct

• Easiest to demonstrate ASHRAE Standard 62.1 compliance

• Uses dual inlet airflow sensors

Dual‐Duct VAV: Cold Duct Minimum SOO

Hot Duct Airflow

HeatingMaximum


Cold Duct Airflow

Cooling Maximum


Deadband


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Parallel Fan Powered VAV Box, VAV Fan


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Parallel Fan Powered VAV Box: SOO for CAV Fan

• Fan start/stop depends on current OA-min.

• If Vmin < Zone OA-min, use fan to maintain airflow. Circulates “unused” OA from adjacent zones.

• If Vmin > Zone OA-min, parallel fan is used only in heating.


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Parallel Fan Powered VAV Box: SOO for VAV Fan

Variable fan runs to maintain total airflow > OA-min ECM fans are very

quiet and efficient. Better for noise than CAV parallel fan


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Series Fan Powered VAV Box , VAV Fan


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Series Fan Powered VAV Box: CAV Fan SOO

• Fixed-speed fan runs continuously to maintain outlet velocity

• Other control logic is like a standard VAV box


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Series Fan Powered VAV Box: VAV Fan SOO

• ECM fan runs continuously, first tracking primary cooling air, then as required for ventilation, then ramp up for second stage heating

• Other control logic is like a standard VAV box


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5.15 to 5.16Variable‐Air‐Volume

Air Handlers Serving Multiple Zones


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• Outdoor air measurement/control options • Differential pressure on dedicated minimum OA intake• Airflow measuring station (AFMS) on dedicated minimum OA intake• AFMS on combined economizer/OA intake

• All minimum OA control options support both Title 24 and ASHRAE Standard 62.1 ventilation rules

• Building pressure options• Barometric relief• Relief fans• Return fans: controlled by direct building pressure or airflow tracking

VAV AHU: Options


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VAV AHU Return Fan with Direct Building Static Pressure Control Minimum OA AFMS


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Relief Fan Minimum OA with Differential Pressure (DP) SensorVAV AHU


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• Uses same mode hierarchy as Zone Groups• Occupied mode• Cool-down mode• Setup mode• Warm-up mode• Setback mode• Freeze protection setback mode• Unoccupied mode

• AHU operates in the highest mode of any of its zone groups• Operating mode may determine set points. Examples:

• SAT set point = 95°F in warm-up mode, but is reset by T&R in occupied mode• Minimum outdoor air set point = 0 in all modes but occupied mode

VAV AHU SOO: Modes


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VAV AHU SOO: Supply Fan Duct Static Pressure (DSP) Control

Supply fan static pressure set point is reset by requests from zone damper position


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VAV AHU SOO: Supply Fan DSP Control: VFD Power at Varying SP Set Points

0%

20%

40%

60%

80%

100%

120%

0 10% 20% 30% 40% 50% 60% 70% 80% 90% 100%

Percent Fan CFM

Perc

ent F

an k

W SP setpoint = TSPSP setpoint = TSP*.75SP setpoint = TSP/2SP setpoint = TSP/3SP setpoint = 0

Surge Region


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VAV AHU SOO: Supply Fan DSP Control: Reset Trends

TAB SP=1.25”


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• Cooler temperature• Decreases fan energy

• Warmer temperature• Extends economizer operation (more hours with cooling system off)• Reduces reheat at zone level

• Need to optimize the two

VAV AHU SOO: SAT Set Point Reset


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• To find balance between fan and cooling energy, sequence uses both:

• Zone reset based on T&R from zone cooling loops• OAT to reduce SATsp in warmer weather

• Result:• In cold weather, SATsp is high, so economizer is maximized,

reheat is minimized• In warm weather, SATsp is low to reduce fan energy

• Default set points intended for VAV reheat system serving offices in mild or dry climate

VAV AHU SOO: SAT Set Point (cont.)


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VAV AHU SOO: SAT Set Point: Net Result


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VAV AHU SOO: SAT Set Point: Actual Performance

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54

56

58

60

62

64

52 54 56 58 60 62 64

Outdoor Air Temperature (oF)

Supp

ly A

ir Te

mpe

ratu

re S

etpo

int (

oF)

52

54

56

58

60

62

64

52 54 56 58 60 62 64 66 68

Outdoor Air Temperature (oF)

Supp

ly A

ir Te

mpe

ratu

re S

etpo

int (

oF)

Oversized Zones

At Least One Rogue Zone


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• Cost‐based reset (Raftery 2018 )• Estimate fan, reheat, and cooling energy cost at current, slightly higher, and slightly lower SAT

• If no cooling requests, reset set point in direction of lower cost• If any cooling requests, that takes priority

Latest Research from Center for Built Environment


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3 Minute Break


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VAV AHU SOO: Economizer Control

Economizer (not min OA) dampers are sequenced, rather than complementary, to save fan energy (reduced ΔP) when using relief fans

At 50% open, both dampers are wide open rather than half closed

Return Air Damper

Outdoor Air Damper

Return Air Damper

Outdoor AirDamper

Closed

Open

Closed

OpenTraditional Control G36 Control

Mixing BoxDP

Mixing BoxDP

PBD

OBD


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SAT Loop Mapping—Relief Fans


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SAT Loop Mapping—Return Fans


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VAV AHU SOO: Economizer High Limit Lockout

• Supports economizer lockout per ASHRAE/IES Standard 90.1 and Title 24• Set points based on climate zone, e.g. for ASHRAE/IES Standard 90.1

• Set automatically based on climate zone specified by engineer to ensure compliance


87

• ASHRAE Standard 62 logic calculates the uncorrected OA volume Voudirectly from zone ventilation rates with people component adjusted for occupancy sensors and CO2, but no larger than design uncorrected outdoor air rate (user input)

• Find “critical zone” from zone outdoor air and primary air rates:

• Ventilation efficiency (Ev) is dynamically calculated from Vou and maximum Z

• Then divides by system ventilation efficiency Ev to get OA set point but not to exceed design outdoor air rate (user input):

VAV AHU SOO: Standard 62 OA Set Point


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• The sequences support three methods for controlling MinOA AHUs:• Differential pressure on dedicated minimum OA intake

• Two‐position MinOA damper• Control OA rate with return damper

• AFMS on dedicated minimum OA intake• Modulating MinOA damper• Control OA rate with MinOA damper and return damper in sequence

• AFMS on total economizer/OA intake• Control OA rate with OA damper and return damper in sequence

VAV AHU SOO: OA Volume Control


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Fixed Minimum OA Damper with Plenum Pressure Control

Outdoor Air

Return Air

Signal from SAT Controller

DDC


90

Dedicated Minimum Outdoor Air Section with AFMS

Signal from SAT Controller

Outdoor Air

Return Air DDC


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Airflow Measurement of 100% OA

Signal From SAT Controller

AFMS must be accurate at low flow

Outdoor AirAF

MS

DDC

Return Air


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• ASHRAE Guideline 36 does not support any of these methods for controlling OA dampers at the AHU:

• Fixed minimum position• Dual minimum position (except for single-zone variable-air-volume

[SZVAV])• Energy balance• CO2 balance• Return fan airflow tracking

• These methods do not provide adequate accuracy per ASHRAE RP-980

VAV AHU SOO: MinOA Volume Control


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• Pressure control with building pressure sensor • Set point typically 0.05 in.

• Three options• Relief dampers (aka nonpowered or barometric relief) • Relief fans (aka powered exhaust fans)• Return fans (aka return/relief fans) with

• Direct pressure control• Return fan tracking control

• AHUs serving “coupled” spaces use common PID loop• Details in ASHRAE Guideline 16

VAV AHU SOO: Building Pressure Control


VAV AHU SOO: Relief Damper


VAV AHU SOO: Relief Fan


VAV AHU SOO: Return Fan (Direct Building Pressure)


VAV AHU SOO: Return Fan (Airflow Tracking)


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• Relief system may be enabled with economizer or always enabled, depending on designer’s judgment of building tightness and minimum outdoor air rates:

• Disabling prevents integral wind‐up

• Passive relief dampers:• Relief dampers modulate to maintain building pressure set point

• Relief fans with dampers:• Relief dampers open to provide first stage of relief passively• Relief fans staged to keep fans operating near minimum speed to minimize noise and pressure drop through dampers, minimizing fan energy

• All relief fans run at same speed

VAV AHU SOO: Relief Damper and Fan


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VAV AHU SOO: Relief Fan Control

0% 5% ~20% 100%

Relief Damper

0%/Off

100%/On

Fan Speed

Two position control uses a differential

Open Relief Damper

Relief fan starts when pressure loop equals fan minimum speed + 10%


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• Return fan (RF) speed controlled by discharge static pressure

• Loop must be faster than building static pressure loop to avoid fighting

VAV AHU SOO: Return Fans (Direct Building Pressure Control)

• Building pressure set point is maintained by

• First modulating exhaust damper open • Then resetting RF DP set point very low value to that required to exhaust design return fan airflow (return

damper closed). These set points determined by testing, adjusting, and balancing (TAB) per Section 3


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5.17 Dual‐Fan Dual‐Duct Heating VAV Fan

Logic similar to VAV AHU but without economizer; assumes 100% return air. SAT reset based on zonal heat requests.


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5.18Single Zone Variable‐Air‐Volume

Air Handlers


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Single Zone VAV


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• Complex cooling sequence designed to balance • Mechanical cooling energy by maximizing economizer use• Fan energy by reducing supply air temperature

• All while ensuring space humidity is not excessive

SZVAV SOO: SAT and Fan Speed Control


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SZVAV SOO: Fan Speed Control Component


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SZVAV SOO: SAT Control Component


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• CHW valve controlled to SATsp‐C• HW valve and economizer controlled to SATsp

SZVAV SOO: SAT Control


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SZVAV SOO: Minimum Outdoor Air Control

• Assumes no outdoor AFMS, which is typical of small, single‐zone (SZ) units due to cost and physical limitations

• Must use overlapping parallel blade dampers for constant flow versus pressure drop


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Automatic Fault Detection and Diagnostics (AFDD)


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• Detects faults based on sensor inputs and suggests likely cause(s) based on fault condition

• Based on NIST research, which was tested at several field sites• RP-1455 and ASHRAE Guideline 36 includes AFDD for air

handlers (APAR [AHU Performance Assessment Rules])• RP-1455 investigated AFDD for terminal units, but it requires

too much tuning, pushes zone controller memory limits, and was not included

AFDD


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• There are 13 rules (“fault conditions”) evaluated• Most rules are mass/energy balance equations• Not all rules apply at all times• Rule application depends on the AHU operating state (OS):

• OS #1: Heating• OS #2: Free cooling with modulating OA• OS #3: Mechanical cooling with economizer• OS #4: Mechanical cooling with minimum OA• OS #5: None of the above

AFDD: AHU Performance Assessment Rules (APAR)


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APAR AFDD: AHU Operating State

OS#4

CHW Valve

HW Valve

100%

0%

Dam

per/V

alve

Pos

ition

, % O

pen

Outdoor Air Damper

OS#2 OS#3 OS#1

Operating State

Heating Valve

Position

Cooling Valve

Position Outdoor Air

Damper Position #1: Heating > 0 = 0 = MIN #2: Free Cooling, Modulating OA = 0 = 0 MIN < X < 100% #3: Mechanical + Economizer Cooling = 0 > 0 = 100% #4: Mechanical Cooling, Min OA = 0 > 0 = MIN #5: Unknown or Dehumidification No other OS applies


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• Each fault condition specifies• Performance assessment equation: if equation is true, there is a fault• Operating state(s) when fault condition may be evaluated• Likely causes of fault

• Intended to minimize false alarms• Assumes typical sensor error• Uses rolling averages to smooth input spikes• Suspends evaluation after change in operating state• Fault condition must be true for a user‐specified period before alarm is reported

APAR AFDD: Fault Condition Equations


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APAR AFDD: Example Fault Condition Equations


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APAR AFDD: Typical Sensor Error Assumptions


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Implementing Guideline 36


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• Chicken and egg• Engineers don’t want to specify it if the cost of implementation is solely funded by

their project• Local dealers won’t use ASHRAE Guideline 36 SOOs until engineers demand it

and/or their product manufacturer programs the sequences for them• Manufacturers won’t program sequences until their dealers and direct building

customers demand it• Key may be the manufacturers

• Some have already programmed (or are in the process) to be the “first on the block”• California Energy Commission (CEC) is funding programming for a few projects in California

• But engineers can get the ball rolling with little concern for cost if we all specify ASHRAE Guideline sequences right now, together

How to Get ASHRAE Guideline 36 Ball Rolling


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• Cut and paste into specs, then edit per the instructions built into the guideline

• Pros:• Desired (and, with minor edits, as-built) SOOs written • Engineer hopefully understands what SOOs he/she is specifying

• Cons:• ASHRAE Guideline 36 not (yet) available in word-processor software

format• Very time consuming and prone to editing errors• Many engineers will not fully edit—no better than just referencing

ASHRAE Guideline 36 • Dealer does not know if some SOOs may have been changed from

ASHRAE Guideline 36

#1 How Engineers Can Specify ASHRAE Guideline 36 SOOs


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• Specify G36 by section number, e.g.,

• And require contractor to compile as‐built SOOs, e.g.,

• Pros• Easier for engineer• Changes from G36 standard SOOs very clear• Includes addenda inherently

• Cons• Burden for compiling as‐built SOOs shifted to dealer (but we expect manufacturers will soon develop tools to automate English SOO and control code with menu‐based interface)



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• Just say “Control sequences shall fully implement and be in accordance with ASHRAE Guideline 36”

• Pros• Easiest for engineer

• Cons• Changes from ASHRAE Guideline 36 standard SOOs not possible (but not usually necessary)

• Requests for information (RFIs) will be required to have engineer choose the desired option where ASHRAE Guideline 36 has multiple choices

• e.g., control of return fans• Burden for compiling as‐built SOOs shifted to dealer (but we expect manufacturers will soon develop tools to automate English SOO and control code with menu‐based interface)



121

Related Research and Future Enhancements


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• RP-1587 control loop performance assessment• Defines “control quality factor (CQF)” that dynamically assesses how

well a control loop is performing, 0% to 100%• Maintain controlled variable close to set point• Without excessive dithering

• Designed to be able to continuously monitor all control loops• Compact math to fit into compact controllers but not all manufacturers can

support it• Allows designers and commissioning providers to objectively specify

tuning• e.g., system acceptance only if all loops average a CQF over 80% for two weeks

• RP complete but not yet incorporated in ASHRAE Guideline 36

Related Research


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• CO2-based demand-controlled ventilation • RP-1547, CO2-Based Demand Controlled Ventilation for Multiple Zone HVAC

Systems• RP-1747, Implementation of RP-1547 CO2-based Demand Controlled Ventilation for

Multiple Zone HVAC Systems in Direct Digital Control Systems• RP-1819 CO2 Demand Controlled Ventilation in Multiple Zone VAV Systems with

Multiple Recirculation Paths• Complex logic for optimizing energy efficiency while ensuring ASHRAE

Standard 62.1 compliance by dynamically solving the multiple spaces equation

• Requires additional sensors• Very accurate supply air CO2 sensor• Occupancy sensor or CO2 sensor in each zone

• RPs complete but not yet incorporated in ASHRAE Guideline 36• But ideal application because it is complex enough it would be difficult for designers

to spec and dealers to implement

Related Research (cont.)


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• RP-1711 Advanced Sequences of Operation for HVAC Systems—Phase II Central Plants and Hydronic Systems

• SOOs for almost every possible design of hot-water and chilled-water plants

• Published February 2020• Submission to SGPC 36 expected in June 2020

• TRP-1865 Optimizing Supply Air Temperature Control for Dedicated Outdoor Air Systems

• To determine optimum SAT logic for most popular configurations of DOAS units to balance DOAS energy use with zonal energy use

• Awarded April 2020

Related Research (cont.)


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Some Early ASHRAE Guideline 36 Implementation Results

EPIC Best in Class555 County Center


126

• ASHRAE Guideline 36 combines the best of both the configurable and programmable worlds:

• Plug and play • Advanced sequences and diagnostics

• Long term goal• Engineers no longer write sequences

• Just specify “Control sequences shall fully implement and be in accordance with ASHRAE Guideline 36”

• Sequences all preprogrammed and debugged by control system manufacturer

• Some manufacturers have already done so• Controls contractors no longer program sequences• Commissioning agents no longer test sequences

• You can specify the sequences right now!

Conclusions


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• ASHRAE. 2018. ASHRAE Guideline 36-2018, High-Performance Sequences of Operation for HVAC Systems. Atlanta: ASHRAE.

• ASHRAE. 2015. RP 1515, Thermal and Air Quality Acceptability in Buildings that Reduce Energy by Reducing Minimum Airflow from Overhead Diffusers. Atlanta: ASHRAE.

• ASHRAE. 2012. RP-1353, Stability and Accuracy of VAV Box Control at Low Flows. Atlanta: ASHRAE.

• ASHRAE. 2003. ASHRAE Guideline 16-2003, Selecting Outdoor, Return, and Relief Dampers for Air-Side Economizer Systems. Atlanta: ASHRAE.

• Raftery, P., S. Li, B. Jin, M. Ting, G. Paliaga, and H. Cheng. 2018. Evaluation of a cost-responsive supply air temperature reset strategy in an office building. Energy and Buildings 158(1):356-370.

Bibliography


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Steve [email protected]

Questions?


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• If you have any questions about ASHRAE Certificates, please contact Kelly Arnold, Coordinator Professional Development at [email protected].

• If you have any questions about ASHRAE courses, please contact Tiffany Cox, Professional Development Course Administrator, at [email protected].


130

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