MODELING OF VENTILATION AIR HEAT RECOVERY AND ITS IMPACT IN HIGH-PERFORMANCE GREEN BUILDINGS Sa Nuenbege and Andew Lau College of Engineeing, Te Pennylvania State Univeity, Univeity Pak, PA ABSTRACT A uto-develoed eadeet tool wa ued to analyze te efoane of a ontant volue HVAC yte, wit otion of ventilation ai eat eovey (VAHR), ai-ide eonoize (ASE) yte, o a obination of VAHR and ASE, fo a tyial offie e and laoo e, in five diffeent liate in te U.S. Fo all but one of te ae tudied, te eult ow tat VAHR ued te ot enegy on an annual bai. INTRODUCTION Reent exeiene wit eveal geen building ojet indiated tat tee ae tie wen VAHR yte ay not ve enegy. It i tue tat VAHR yte edue te intalled aaity of eating and ooling euient, eeially fo building euiing lage aount of ventilation ai, like ool. Ti an ignifiantly edue te fit ot of te eating and ooling yte by eduing te eating and ooling ld due to outide ai. In vey ot and vey old weate VAHR tyially edue te HVAC enegy uge a well. Tee ae two eaon toug, wy a VAHR yte an ineae annual enegy uge. One i te ubtantial fan owe euied to ove te ai toug te eat eovey eat exange. In ti tudy fan owe tyial of eat eovey weel wa ued (1.5 /f). Te ote i tat at tie wen ventilation ai ould be ued to ool te building (like an ai-ide eonoize), VAHR yte often ontinue to oeate in eat eovey ode. Beaue geen building tyially ave bette inulated building kin, tey alo ave elatively low balane teeatue. Balane teeatue i te outide teeatue at wi te e eat gain balane te kin loe. Fo oden geen building balane teeatue wen ouied an be below 20 F. Teefoe, beaue tee geen building tyially need e ooling down to eaonably old outdoo ai ondition, ASE oeation an ubtantially edue o eliinate te ooling ld on te HVAC yte. It i wotwile to note tat ASHRAE Standad 90.1-1999 euie VAHR yte fo HVAC yte wit a uly flow geate tan 5,000 f, and wit iniu outide ai of 70% o geate of te deign uly ai uantity (ASHRAE 1999). Futeoe, if tee i a VAHR yte, Standad 90.1-1999 tate tat Poviion all be ade to bya o ontol te eat eovey yte to eit ai eonoize oeation a euied by 6.3.1.1. Many of te ojet in te auto exeiene did not ave ti bya aability, but ould ave benefited geatly if tey ad. Ti tudy will ow te otential enegy ving fo yte tat obine VAHR and ASE. A liteatue uvey of te lat 20 yea evealed vey little ublied infoation on te efoane of VAHR yte, eeially toe wit eat eovey weel. One elevant and eent tudy foued on ventilation ai fo gound oue eat u yte (Kavanaug and Xie, 2000). Te auto tudied even diffeent ventilation ai teatent otion in 3 diffeent liate uing a uto eadeet, u like tat ued in ti tudy. One of tei onluion i Heat eovey unit, wi ay be effetive at eduing enegy ue wen outdoo ondition ae extee, an onue oe enegy on an annual bai tan onventional euient if anillay euient (fan, u, et.) enegy ue i ig. SIMULATION Ti tudy extend te wok of Kavanaug to five liate, wit te fou on tee HVAC yte. Te bae ae yte i a ontant volue ai-to-ai eat u yte fo eating and ooling. Two otion ae onideed fo ventilation ai. One i a eat weel VAHR yte, and te ote i an ASE yte. A tid otion i alo onideed tat utilize bot VAHR and ASE, auing tat wieve eult in iniu enegy ue will be utilized at tat outdoo ondition. Beaue te fou of ti tudy i ventilation ai, two bai building tye wee onideed. One i an offie building wit elatively low ootion of ventilation
ai. Te ote i a ool building wit elatively ig ootion of ventilation ai. Te oe of te odeling effot i to do eliinay analyi wit a uto eadeet, and ten to efo oe igoou analyi wit DOE2.2. Ti ae eot te eult of toe eliinay analye. One of te advantage of ti eadeet i it allow one to ee te effet of outide ai teeatue on yte efoane, illuinating te eaon fo te diffeene in annual eult. Fo ti eadeet analyi, only one eeentative e, euivalent to an eleentay ool laoo ize, wa ued. Te five diffeent itie ued in te analyi wee Atlanta, Detoit, Houton, Lo Angele and New Yok. Tee itie wee defined by an ealie tudy to eeent te diffeent liate in te United State (B. Andeon,.L. Caoll, M.R. Matin 1982). eate data fo ea ity, in te fo of bin teeatue data, wit ean oinident wet bu teeatue, wa ued (Deatent of te Ai Foe, te Ay, and te Navy, 1978). Only te data fo te eigt-ou eiod fo 8 a.. to 4.. wa ued beaue te analyi wa only fo te ouied eiod of te building. Ti aue tat no ventilation ai i ued wen te building ae unouied. Tu te eult only eeent te HVAC enegy ue duing te ouied eiod. Standad aution ued in te iulation fo bot building an be een in Table 1. Table 2 eeent aution ade eifi to ea building tye. Ote aution ade inlude: Te denity and eat aaity of ai and wate vao ae ontant Steady-tate ondition In enible ld alulation we aue t Volue flow ate of uly ai i ontant Btu fg @ t kin 1044 indow ola gain i baed on aveage ouly gain fo a Not-faing window wit a ading oeffiient of 0.4. at follow i an exlanation of te analyi ontained in te eadeet. Te deied outut i te enegy ue fo HVAC. Te yte odeled ee i an all-eleti eat u yte wee eleti uge inlude oeo enegy fo eating, oeo enegy fo ooling, fan enegy, and VAHR fan enegy. Te analyi tat by finding te e ld at a given outide ai ondition, deteining te outide ai ld, and te ubeuent ooling o eating oil ld. Coil ld ae onveted to eleti uge uing outide ai teeatue-deendent eat u effiienie. Bot enible and latent ld ae onideed. e tat by olving fo te ouied e ooling enible ld, eentially by auing teady-tate, and uing u te intenal and extenal ld oonent. Te analyi i eaated into enible ld and latent ld. Senible ld ae deibed fit; latent ld ae deibed nea te end of ti etion (a oitive ld eflet a ooling ld). wee int, +, int, ext, (1) i te u of te ligting ld, euient ld, and eole ld: and int, wee and i: ext, win ( LPD + EPD) A + ( N ) floo + +, 1 Btu 3.413 (2) ext, ol win (3) + ol ( SC) A win SHGF (4) [( U A + U A )( t t )] win Cooling oil enible ld, win oil, o (5) i te u of te e ld and te outide ai ld: + (6) oil,,, (7) ( t t,, Sine V i in f, and we aue tandad ai, ten we get te enible ooling oil ld witout eat eovey: + 1.10V ( t t ) (8) oil,, )
If eat eovey i being ued, V and te V, in net outide ai ld i edued by te effetivene of te eat eovey yte.,, VAHR 1 ε ), (9) ( Fo te ASE, we need to deteine ow u outide ai i being bougt into te yte. To do ti, we tat wit te ixing euation i: ( a ) aa + (10) Beaue we aue tandad ai denity, we an elae wit V. Fo, we an ubtitute t, eduing euation 10 to: V t ( V a V ) t V ata + (11) Fation of outide ai, f, an be defined a V f (12) V a 1 Multilying Euation (11) by V we get f t Ten olving fo a ( f ) t ta + 1 (13) f we get: t ta f (14) t t Fo an ASE, te f i ontolled a follow. en t i geate tan a etain teeatue tat i a few degee oole tan te oo teeatue (to event ig uidity ai fo being intodued), in ti ae 65 F, iniu outide ai i ued. en t i le tan 65 F, and geate tan te deied ixed ai etoint, 100% outide ai i ued. en t t a et te oo ai i ixed wit outide ai to aintain t. a et e odify euation 14 to allow te deteination of f : t ta f t t et (15) If f fall below in f ten f f in Latent ld due to eole and ventilation ai ae alo aounted fo and ued to deteine te oil latent ld wen ooling. Ti oil latent ld i added to te oil enible ld to get te total oil ld tat i ued in euation 16. Moitue alulation wee baed on algoit in te 1997 ASHRAE Handbook (ASHRAE 1997). In ode to olve fo te oitue geneated by eole, we tat wit latent eat given off by a eon,, l fo te ASHRAE Handbook fo a odeately ative offie woke, 200 Btu/. A ligtly lle value wa ued fo te laoo analyi a eeentative of ilden. Ten, Knowing, l (16) and l, fg @ t kin fg @ t kin. 200 Btu eon 0. 19 1044 Btu, we an ten olve fo eon An H 2 O a balane inide te oo give u: wee: + N (17) v, (18) Te ai a flow ate,, i deteined by an enegy balane on te oo at deign ondition: ( t t ) (19), Sine we aue tat wen te ooling oil i unning and tee i a latent ld, SA, we an olve Euation (19) fo. @90% φ Entaly weel latent effetivene ε l i defined a:, e ε l (20)
Ti allow u to olve fo, e wi i te oitue ontent of te exaut ai afte te entaly weel. If tee i no VAHR,, e. Te ooling oil latent ld i found by finding te flow ate of ondente leaving te ooling oil. An H 2 O a balane on te wole yte (HVAC lu e) give: v v e, +,, + (21) Auing tat 4. 5V, a, a,, e 4.5V (, e ) + N P0. 20 e (22) Fo te flow ate of ondente, we an etiate te latent ooling oil ld a: Btu oil, l fg @ 55F 1062 (23) Ti latent ooling oil ld i added to te enible ld to get te total ooling oil ld. To deteine te eletiity ue by te eat u: oil COP (24) E Te vaiation of COP fo ooling and fo eating i aounted fo in te eadeet uing te default efoane uve in DOE 2.2 (J. Hi 2004). RESULTS Ti etion will begin wit an oveview of te eult fo annual enegy uge. Ten we will look in oe detail at eifi ae, utilizing te aability of te eadeet to ow ow ea yte efo a a funtion of outide teeatue. Finally, we will exaine te effet of eat eovey fan owe on VAHR annual enegy ue. Te ga of bot te ool and offie annual eleti uge, Figue 1 and 2, ow tat ove a total yea in all five liate, VAHR onitently ue te ot enegy. Out of te tee HVAC yte odeled (not inluding te otiu), te ASE onitently ued te leat aount of annual enegy. Te otiu ba eeent a obination of te ASE lu te VAHR. Ti otiu yte ue wieve yte deand le eleti owe at a given outide teeatue. Fo exale, in Figue 3, a lot of eletiity deand veu outide teeatue in a Detoit ool, ow tat uing eat eovey ould ve a onideable aount of enegy ove an ASE duing tie wen outide teeatue i below about 40 o F. Likewie, above teeatue of 40 o F an ASE (o te bae ae wit no VAHR o ASE) ue le enegy. Te otiu yte would ue te VAHR fo outide teeatue of unde 40 o F, and te ASE fo teeatue above 40 o F (o ily utting down te VAHR and byaing it). It i inteeting to note tat in te annual enegy ue in Figue 1 tee wa little ving fo eite te VAHR o te ASE alone. Tat i beaue te ving fo te VAHR below 40 o F i ougly euivalent to te ving of te ASE above 40 o F. By eleting te ot enegy effiient otion at any given ondition, enegy ving i geatet. One an alo obeve fo tee lot, Figue 3 to 6, tat an ASE on a ig ouany ool a little ving beaue te yte i aleady binging in a ig ootion of outide ventilation ai (aound 67%). Looking at te total annual eleti uge fo an LA ool, own in Figue 1, it an be een tat te tee i a lage diffeene between te enegy needed fo a VAHR yte oaed to an ASE yte. Ti an be eaily exlained by Figue 4, wi illutate te eletiity deand at a given teeatue. Toug it i een tat te VAHR ve enegy below about 40 o F, tee ae no bin ou in tat teeatue ange. Ti i alo te eaon tat te ASE i eual to te otiu. Alo notewoty fo te LA ool i tat fo teeatue above about 72 o F, te ooling ld i le fo te VAHR yte tan an ASE yte, a een in Figue 5. Ti doe not eult in a ving a would be een on Figue 4, beaue of te owe needed fo te fan in te VAHR yte. If we edue te fan ue fo 1.5/f to 0.75 /f, a een in Figue 6, a ll ving an be een fo teeatue above about 83 o F. One aet of a VAHR yte tat ignifiantly iat te annual enegy ue i te fan owe. Te value of 1.5 /f wa baed on atual geen building ojet. It i oible to edue te fan owe, fo exale, by intalling a lage eat eovey weel. Ti would edue te fae veloity and teefoe edue te fan owe. To exaine te effet of eduing fan owe we an te odel wit VAHR fan owe of 0.75 /f. Te eult ow tat wit one exetion te VAHR till onitently ued te ot enegy. Te exetion wa te Detoit ool ae, a een in Figue 7. Te ain eaon VAHR ve enegy in ti Detoit ae i te Detoit liate a onideable ou at olde teeatue wee te VAHR yte ue u le enegy tan te ote yte.
To get oe ene of te eaonablene of te VAHR fan owe aution ued ee, we oaed two ote ublied value. In te wok of Kavanaug (Kavanaug and Xie, 2000), te owe fo te VAHR fan and weel oto wa euivalent to 1.40 /f. Ti i in te ange of te 1.5 /f ued fo te ajoity of te ae ee. In a eent ARI (Aionditioning and Refigeation Intitute) ubliation (ARI, 2003), tey eent an exale in Aendix C tat i euivalent to 0.61 /f. Ti value i low oaed to te value tudied ee. It would be ueful to uvey ote atual VAHR intallation to deteine te ange of fan owe euieent. Beaue te efoane of a VAHR yte i geatly affeted by te fan owe aoiated wit te yte, it i iotant fo deigne to elet yte tat tend to edue te fan owe, and to aefully onide te iat toug detailed enegy analyi. A tated ealie, in building wit lage ventilation euieent, like ool, yte wit VAHR ould alo ave te ability to bya te VAHR wen an ASE i advantageou. CONCLUSIONS/RECOMMENDATIONS Tee eliinay eult ow tat, fo te ontant volue HVAC yte and liate tudied ee, VAHR i not te bet otion fo te tandoint of effiient enegy ue. Beaue geen building ae well inulated and ave low balane teeatue, ASE yte an ignifiantly edue ooling enegy ue. If a VAHR yte i intalled in a building to edue te intalled yte aaitie, te yte ould ave te otion of byaing te VAHR yte and uing an ASE wen advantageou. Attention ould alo be given in te VAHR yte deign to eduing te fan owe euieent. REFERENCES ARI 2003. 2003 Guideline fo Calulating te Effiieny of Enegy Reovey Ventilation and it Effet on Effiieny and Sizing of Building HVAC Syte, Ai-Conditioning and Refigeation Intitute, Alington, Viginia. ASHRAE 1999. Enegy Standad fo Building Exet Low-Rie Reidential Building, ASHRAE/IESNA 90.1-1999. ASHRAE 1997. ASHRAE 1997 Handbook Fundaental, Aeian Soiety of Heating, Refigeating, and Ai-Conditioning Enginee, Atlanta, Geogia. Andeon, B., Caoll,., and Matin, M. 1982. Aggegation of U.S. Poulation Cente into Cliate Region, Poeeding of te 7 t National Paive Sola Confeene, Aeian Sola Enegy Soiety. Deatent of te Ai Foe, te Ay, and te Navy 1978. Engineeing eate Data, AFM 88-29. J.J. Hi 2003. www.doe2.o. Kavanug, S., and Xie, L. 2000. Enegy Ue of Ventilation Ai Conditioning Otion fo Gound- Soue Heat Pu Syte, ASHRAE Tantion 106: 543-550. NOMENCLATURE A aea of A win aea of window COP oeffiient of efoane EPD euient owe denity ε entaly weel enible effetivene ε entaly weel latent effetivene l fg @ t kin entaly of vaoization at kin teeatue a entaly of ixed ai entaly of outide ai entaly of oo ai LPD ligting owe denity a flow ate of outide ai enteing yte a, a,, e a flow ate of ai exiting yte a flow ate of ondente fo oil a flow ate of ixed ai a a flow ate of oitue fo eole a flow ate of uly ai a flow ate of vao exiting yte v,, e a flow ate of vao in outide ai v, v, wate vao flowate in uly ai N nube of eole ouied e enible ooling ld, ext extenal enible ld int intenal enible ld ate of latent eat gain fo ouant, l, ate of enible eat gain fo ouant ooling ld fo outide ai oil oil ooling ld
latent ooling ld of oil oil, l ol eat gain fo un win eat gain toug window eat gain toug SHGF aveage ola eat gain fato t ai teeatue outide t ai teeatue of oo t teeatue of uly ai U oveall eat tanfe oeffiient of window U win oveall eat tanfe oeffiient of V volueti flow ate of outide ai V a volueti flow ate of ixed ai, uidity atio of ai exiting yte e uidity atio of ai outide uidity atio of uly ai at 90% elative uidity, and at t uidity atio of oo ai
APPENDIX Table 1 Roo and yte aution Roo Deition Roo Teeatue 74 F idt 28 ft Det 24 ft all Heigt 12 Floo Aea 672 ft 2 all Aea 336 ft 2 indow Fation 0.5 indow Aea 168 ft 2 all U-fato 0.10 Btu/-ft 2 -F indow U-fato 0.50 Btu/-ft 2 -F Fe Ai Aount 15 f/eon HVAC Paaete COP Heating 3 COP Cooling 3 Senible Effetivene 0.7 Latent Effetivene 0.7 Suly Fan Powe 1.0 /ft 2 City Table 2 Sool and offie aution Sool Offie Ligting Powe Denity (/ft 2 ) 1.2 1.0 Euient Powe Denity (/ft 2 ) 0.5 1.0 Nube of Peole 25 5 Peole Senible Gain (Btu/eon) 200 250 Table 3 Sool eleti uge Eleti Uge Sool All unit in (k/ft 2 ) HR No HR Eon Otiu Atlanta 9.09 7.11 6.94 6.77 Detoit 7.84 7.63 7.50 5.94 Houton 10.09 8.44 8.31 8.22 LA 8.93 5.76 5.37 5.37 New Yok 7.85 6.44 6.27 5.55 City Table 4 Offie eleti ue Eleti Uge Offie All unit in (k/ft 2 ) HR No HR Eon Otiu Atlanta 4.80 4.26 3.88 3.87 Detoit 4.01 3.60 3.27 3.11 Houton 5.31 4.95 4.68 4.66 LA 4.73 4.10 3.51 3.51 New Yok 4.06 3.44 3.02 2.98 Total Sool Eleti Uge (k/ft^2) Total Offie Eleti Uge (k/ft^2) 12.00 10.00 8.00 6.00 4.00 2.00 0.00 6.00 5.00 4.00 3.00 2.00 1.00 0.00 Atlanta Detoit Houton LA New Yok HR No HR Eon Otiu Figue 1 Total ool eleti uge Atlanta Detoit Houton LA New Yok HR No HR Eon Otiu Figue 2 Total offie eleti uge
10.0 300 10.0 800 HVAC Eletiity Deand (/ft 2 ) 9.0 8.0 250 7.0 200 6.0 5.0 150 4.0 3.0 100 2.0 50 1.0 0.0 0 0 20 40 60 80 100 Outide Teeatue (F) HR No HR Eon Bin Hou Bin Hou HVAC Eletiity Deand (/ft 2 ) 9.0 8.0 7.0 6.0 5.0 4.0 3.0 2.0 1.0 0.0 0 20 40 60 80 100 Outide Te eatue (F) 700 600 500 400 300 200 100 0 Bin Hou Figue 3 Detoit ool eletiity deand HR No HR Eon Bin Hou HVAC Eletiity Deand (/ft 2 ) 2 Cooling Ld (Btu/-ft ) 10.0 800 9.0 700 8.0 600 7.0 6.0 500 5.0 400 4.0 300 3.0 200 2.0 1.0 100 0.0 0 0 20 40 60 80 100 Outide Te eatue (F) HR No HR Eon Bin Hou Figue 4 LA ool eletiity deand 60 40 20 0 ` 0 20 40 60 80 100-20 -40 Bin Hou Figue 6 LA ool ooling ld wit alf te fan ue owe 2 ) Annual HVAC Enegy (k/ft 9.0 8.0 7.0 6.0 5.0 4.0 3.0 2.0 1.0 0.0 6.62 7.63 7.50 5.51 HR No HR Eon Ot Figue 7 Detoit ool enegy uge wit edued VAHR fan owe -60 Outide Teeatue (F) Sae (Btu/) Coil Coil w /HR Coil w /Eon Figue 5 LA ool ooling ld