Understanding & DesigningDedicated Outdoor AirSystemsy(DOAS)ASHRAE Short CourseMarch 23, 2010Stanley AA. MummaMumma, PhPh.D.,D PP.E.EProf. Emeritus, Architectural EngineeringPenn State University, Univ. Park, [email protected]: http://doas-radiant.psu.edu1Copyright Materials Copyright 20010 by the American Society ofHeating Refrigerating and AirHeating,Air-ConditioningConditioningEngineers (ASHRAE). All rights reserved. No part of this presentation may be reproducedwithout written permission from ASHRAE, nory anyyppart of this ppresentation be reproduced,p,maystored in a retrieval system or transmitted in anyform or by any means (electronic, photocopying,recording or other) without written permissionfrom ASHRAE.2

AIA/CES Registered Provider ASHRAE is a Registered Provider with The American Instituteof Architects Continuing Education Systems.Systems Credit earned oncompletion of this program will be reported to CES Records forAIA members. Certificates of Completion for non-AIA membersare available on request. This program is registered with the AIA/CES for continuingprofessional education. As such, it does not include content thatmay be deemed or construed to be an approval or endorsementby the AIA of any material of construction or any method ormanner of handling, using, distributing, or dealing in anymaterial or product. Questions related to specific materials,methods, and services will be addressed at the conclusion ofthis presentation.3Presentation Outline &Learning Objectives Quick review of current leading building HVAC system issues.Define DOAS.Explain terminal equipment choices and issues.Describe Air Side Economizer lost—implications. Break #39Describe DOAS equipment choices and Psychrometrics.Explain design steps for DOAS and provide example30% surplus OA, why and does it use more energy? Break #75Explain relevance of DOE and ASHRAE Research findings.Describe field applications.Conclusions.4

Current HVAC system of choice:VAVOAStd. VAV AHUVAVSpace 1,VAV w/ single airdelivery path5Why VAV is system of choice. Eliminates bucking: a characteristic ofpredecessor systems such as dual duct, multizone and terminal,RH At off design conditions, the majority of thetime, fan power is reduced, i.e. at 50% flow, fanpower is 0.53—or 12.5%. Huge improvementover previous systems. Single duct,duct and easy to design for tenant fit outout. Often thought to be simple to control—but thatis not a fact—especially with ventilation needs,SAT reset, economizer, and buildingpressurization.6

Inherent Problemswith VAV SystemsPoor air distributiony controlPoor humidityPoor acoustical propertiesPoor use of plenum and mechanical shaft spaceSerious control problems, particularly withtracking return fan systems Poor energy transport medium: air Poor resistance to the threat of biological andchemical terrorism Poor and unpredictable ventilation performance 7. vent’n performance.Poor & unpredictableOAB 3,600 cfmOA ?AHU6,000 cfm% OAB ?601,500 cfmOA 2,250? (900 1,350) No!Eq. for OA? No! Why not? OAreq’d 900 cfmOA 3,600?OA (6,000-OA)*0.225 3,600 based on table 6-1OA 2,903, 30% more, but no Z 900/1,5001LEED pointi tZ1 0.62,903-(900 1,350) 653more than table 6-1 valueWhere does the 653 cfm go?Unvit ratio 0.2251,350/6,0004,500 cfmOAreq’d 1,350 cfmOver vent ?,cfm,, Unvit1,350Z2 0.38

Can VAV limitations be overcome?OA 2,250AHU2,250 cfmHow is thespace loadhandled,when 6,000cfm requiredfor say aVAV?Condition of supply air, DBT & DPT?% OAB 100900 cfm1,350 cfmOAreq’d 900 cfmOAreq’d 1,350 cfmZ1 1Z2 19DOAS Defined for This Presentation20%-70%less OA,than VAVDOAS Unitw/ EnergyRecoveryP ll lParallelSensibleCooling SystemCool/DrySupplyHighInductionDiffuserBuilding withSensibleand LatentCoolingDecoupled10

Key DOAS Points1. 100% OA delivered to each zone via itsown ductwork2. Flowlrate generallyll as spec. bby Std.d 62.12007 or greater (LEED, Latent. Ctl)3. Employ TER, per Std. 90.1-20074. Generally CV5 Use5.U to decoupledl space S/L loads—Dryl d D6. Rarely supply at a neutral temperature7. Use HID, particularly where parallelsystem does not use air11TotalEnergyRecovery(TER)Wheel12

High Induction Diffuser Provides completepair mixinggEvens temperature gradients in the spaceEliminates short-circuiting between supply & returnIncreases ventilation effectiveness13Parallel Terminal SystemsDOAS airInduction NozzleS CSenCoolingli CCoililRadiant Cooling PanelsRoom airChilled BeamsFan Coil UnitsAir Handling UnitsCV or VAVVRVMulti-SplitsUnitary ACsi.e., WSHPs14

DOAS with Parallel VAVStd. VAV AHUOAEconomizerOAOutdoor air unit with TERVAVSpace 2,DOAS inparallel w/VAV15VAV Problems Solved withDOAS/Parallel VAVPoor air distributionPoor humidity controlPoor acoustical propertiesPoor use of plenum and mechanical shaft spaceSerious control problems, particularly withtracking return fan systems PoorPenergy transporttt medium:diairi Poor resistance to the threat of biological andchemical terrorism Poor and unpredictable ventilation performance 16

DOAS with Parallel FCUOther ways tointroduce OA at FCU?Implications?OAOutdoor air unit with TERFCUSpace 3,DOAS inparallel w/FCU17Parallel vs. Series OA introduced forDOAS-FCU applications?Parallel, GoodSeries, Bad18

Common arrangement of FCU inseries with DOAS--BADDOASOAEAOAOARASARASA19Usual concept of ceiling FCU in parallelwith DOAS—a false paradigmDOASOAEARASAOAOASARA20

Reasons given by series camp for usingseries arrangement of FCU with DOAS overthe false paradigm parallel arrangementSuperior thermal comfortSSuperiori IAQSuperior energy efficiency and performanceSimpler arrangementReduced 1st , labor and materialsIdeal for constant volume systemsBest for low occupancy density spacesSimpler controlsEliminates the need for DOAS terminal reheatSimplifies the selection, performance and placement ofdiffusers Eliminates the distribution of cold DOAS air to perimeterspaces in the winter. 21The correct paradigm of ceiling FCU inparallel with DOASDOASOAEARAOASASARA22

Advantages of the correct paradigmparallel FCU-DOAS arrangement At low sensible cooling load conditions, the terminalequipment may be shut off—saving fan energy The terminal device fans may be down sized since they arenot handling any of the ventilation air, reducing first cost The smaller terminal fans result in fan energy savings The cooling coils in the terminal FCU’s are not derated sincethey are handling only warm return air, resulting in smallercoils and further reducing first cost. Opportunity for plenum condensation is reduced since theventilation air is not introduced into the plenum near theterminal equipment, for better IAQ Is not inferior to the series arrangement in any of the 11categories sited above as advantages by the series camp,when configured with the correct parallel paradigm23VAV Problems Solved withDOAS/Parallel FCUPoor air distributionPoor humidity controlPoor acoustical propertiesPoor use of plenum and mechanical shaft spaceSerious control problems, particularly withtracking return fan systems PoorPenergy transport medium:dair Poor resistance to the threat of biological andchemical terrorism Poor and unpredictable ventilation performance 24

DOAS with Parallel Radiant, orChilled BeamOAOutdoor air unit with TERRadiantPanelSpace 3,DOAS inparallel w/CRCP25VAV Problems Solved withDOAS/Radiant-Chilled BeamPoor air distributionPoor humidity controlPoor acoustical propertiesPoor use of plenum and mechanical shaft spaceSerious control problems, particularly withtracking return fan systems Poor energy transport medium: air Poor resistance to the threat of biological andchemical terrorism Poor and unpredictable ventilation performance 26

Additional Benefits ofDOAS/Radiant-Chilled BeamBeside solving problems that have goneunsolved for nearly 35 years withconventional VAV systems, note thefollowing benefits: Greater than 50% reduction in mechanicalsystem operating cost compared to VAV Equal or lower first cost Simpler controls Generates up to 80% of points needed forbasic LEED certification27Role of Total Energy Recovery28

DOAS & Energy RecoveryASHRAE Standard 90.1-2007 in section Air Energy Recovery requires thef ll ifollowing:“Individual fan systems that have both a designsupply air capacity of 5000 cfm or greaterand have a minimum outside air supply of70% or greater of the design supply airquantitytit shallh ll havehan energy recoverysystem with at least 50% total energyrecovery effectiveness.”Std 62.1-2007 allows its use with class 1-3 air.29Merits of Using a TER(Enthalpy Wheel) with DOAS A significant reduction in the design OA coolingl d reducingload,d i bothb th ththe chillerhill sizei & ththe peakkdemand A reduction in the annual OA cooling anddehumidify energy consumption A significant reduction in the OA heating andhumidification energy consumption (in the N) Conforms to ASHRAE Standard 90.1-2007 A major reduction in the variability of the OAconditions entering the CC (critical w/ pkg.equip.)30

Atlanta Data, 12 hr/day-6 day/wkh 43.1 Btu/lb160150 h 26.0 Btu/lb140130h 31 1 Bth 31.1Btu/lb/lb120W, grains/lb110 h 3.5 Btu/lb10090h 27.6 Btu/lb8070h 17.1 Btu/lb605040Conditions afterthe TERequipment &entering the CC302010005101520253035404550556065707580859095 100DBT, F31Implications of the SmallArea on the PsychrometricChart Entering the CC Variation in the OA load on the CCranges by only 25% (from a low of 75%to a max of 100%) At peak design load conditions, theenthalpy wheel reduces the OA load onthe chiller by 70-80%. Often 40-50% ofthe total design load on the chiller.32

Air side economizer lost:implications! This a frequent question, coupled with therealization that without full air sideeconomizer, the chiller may run manymore hours in the winter than owners andoperators would expect based on theirprior experiences. The following slides will address thisissue. For more details, please check the link: Econ Pt1 Pt2.pdf33100% Air Side Economizer Lost!6.5.1 Air (100% OA) or Water (via a cooling tower)Economizers: a prescriptive requirement11.1.1 Energy Cost Budget Method, an alternative totheh prescriptive provisions. It may beb employedld fforevaluating the compliance of all proposed designs.Requires an energy analysis.34

Air Side VAV Econ. Performance Vs. DOASAn example, assuming: Internally dominated cooling load building. Fullyoccupiedi d 6 daysdper week,k fromf6 am tot 7 pm (13hours per day, 4,056 hours per year). 100,000 cfm design supply air flow rate at 55 F Minimum ventilation air requirement: 20,000 cfm In the economizer mode, the OA flow canmodulate between 20,000 cfm and 100,000 cfm. Therefore, the only variability in chiller energyconsumption/demand is the economizer controland the geographic location.35ObjectiveShow that DOAS w/o economizer uses lessenergy thanh VAV withi h economizeriAssumes: 0.7 kW/ton coolingeff. 70%: Motor eff.eff 90% Fan eff Electricity: 0.08/kWh AHU internal P 3”, External P 4”36

Min OA Region if Enthalpy Ctl,or 100% OA if DBT90 Ctl:691 hrs, Miami, FL419 hrs, Columbus OH.193 hrs, Int’l Falls, MN.60ulb%)(F 70OA Design:Miami 311 TMiami,%40Columbus,290 TInt’l Falls, 271 TLoad if 100% OA, 560 Tby design or 120%Min OA RMiRegion:i2766 hrs, Miami, FL56.008008685 hrs, Columbus, OH.206 hrs, Int’l Falls, MN.28.004708090DRY BULB TEMPERATURE (F)100Humidity ratio (grains/lb)WBet196.028HUMIDITY RATIO (Lbv/Lba)Modulating OA Region:76 hrshrs, MiamiMiami, FL1894 hrs, Columbus OH.2771 hrs, Int’l Falls, MN.608080%100% OA Region:523 hrs, Miami, FL1058 hrs, Columbus OH.886 hrs, Int’l Falls, MN.120Economizers frequently experiencemalfunctioning problems, including stuckor improperly operating dampers.Malfunctions can be minimized as follows:1. quality components must be selected andproperly maintained.2. economizer dampers need to be testedtwice annually before entering each coolingand heating seasonseason.Item 2 is rarely done because of operationalpriorities and the frequent inaccessibility of thehardware.38

Industry advice when Economizersexperience repeated problems.Ref: 8.aspx ThThe electricl t i utilitiestiliti recommend,d iin orderd ttoplace a lid on high demand, “locking theeconomizer in the minimum outside airposition if an economizer repeatedly fails,and it is prohibitively expensive to repair it. Although the potential benefits of theeconomizer’s energy savings are lost, it is acertain hedge against it becoming asignificant energy/demand waster.”395060%168.0246080%Min OA Region:%Economizer40does notreduce the TH’s in thisregion compared toDOAS.2708090DRY BULB TEMPERATURE (F)100140.020020112.01684.0120%100% OA RRegioni vs. DOAS:DOAS59 vs. 88 kTH, Miami, FL94 vs. 171 kTH, Columbus75 vs. 144 kTH, Int’l Falls404080196.02812056.00800828.004Humidity ratio (grains/lb)50100% OA Region if DBT Ctl. vs,90Min OA if Enthalpy Ctl: (DOAS)234 vs. 150 kTH, Miami, FL122 vs. 87 kTH, Columbus OH.53 vs. 40 kTH, Int’l Falls, MN.HUMIDITY RATIO (Lbv/Lba)h Econ Savings over DOAS:Miami, 2,184Columbus, 16,000Int’l Falls, 18,760Fan Op. CostVAV fan energy: 41,500DOAS fan energy: 8,000DOAS FFan SSavings:i 33 33,500,500or 2-15 times Econ savings.)Modul’g OA Region vs. DOAS:(F 70ulbB0 vs. 10 kTH, Miami, FL etW0 vs. 209 kTH, Columbus OH.600 vs. 266 kTH, Int’l Falls,MN.

Economizer SummaryUsing water economizer with DOAS-hydronicsystems is a good idea, and can savemechanical cooling energy.energyIt is recommended for applications employingwater cooled chillers.However the DOAS-hydronic systems shouldnot need WSFC to comply with the EnergyCost Budget Method of StdStd. 9090.1.1That’s good, because many projects are too smallfor cooling towers, but are excellent candidatesfor DOAS-hydronic.41DOAS Equipment on the Market TodayI: Equipment that adds sensibl