ESTIMATION OF EXCESSIVE HVAC ENERGY CONSUMPTION DUE TO FAULTY VAV UNITS. Department of Urban and Environmental Engineering, Kyoto University 2

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1 Ninh Inenaional IBPSA Coneence Monéal, Canada Augus -8, STIMATION OF XCSSIV HVAC NRGY CONSUMPTION DU TO FAULTY VAV UNITS Masao Miyaa, Haunoi Yoshida, Masahiko Asada, Kena Fujii 2, and Shio Hashiguchi 3 Deamen o Uban and nvionmenal ngineeing, Kyoo Univesiy 2 Kansai lecic Powe Co., Inc 3 Yamaake, Co., Ld ABSTRACT The esen ae invesigaes, boh exeimenally and by simulaion, he inluence o auly VAV unis ha do no aec he zone emeaue on oal enegy consumion o a VAV sysem. In an exeimenal oom, he esecive oal enegy consumions o boh nomal oeaion and auly oeaion wee measued. The esuls indicae ha a auly uni aecs ohe nomal unis, causing an enegy wase o aoximaely 2-%. In addiion, he esen ae also discusses whehe he addiional enegy consumion can be calculaed via he simulaion o he VAV sysem in he exeimenal oom. The esuls indicae ha he simulaion can be used o esimae he addiional enegy consumion caused by he auls. INTRODUCTION Vaiable ai volume (VAV) ai-condiioning sysems ae enegy eicien and ae widely used in many counies. Howeve, he ossibiliy o aul occuences has been eoed o be high [Yoshida, 996], and many auly VAV unis have been eoed in eal buildings [Qin, ]. The auhos have eviously oosed aul deecion and diagnosis mehods o mulile VAV eminal unis [Miyaa, ]. Howeve, because some auly unis do no aec he zone emeaue, i is also necessay o analyze how he auls aec he enie sysem and analyze he cos benei o mainenance. The esen ae invesigaes, boh exeimenally and by simulaion, he inluence o auly VAV unis ha do no aec he zone emeaue. Fis, he oeaional daa o nomal and auly saes ae measued unde he same hemal condiions in an exeimenal oom, and dieences in he oal enegy consumion ae analyzed. Nex, in ode o examine he ossibiliy o alying he esuls o he exeimen o ohe sysems, he ossibiliy o esimaing he addiional enegy consumion by simulaion is discussed. XPRIMNT xeimenal Room The exeimens wee conduced in an exeimenal oom in which he indoo and oudoo condiions can be se abiaily. Figues and 2 and Table descibe he exeimenal oom and he ai condiioning sysem o he oom. The oom is ai-condiioned by one ai-handling uni (AHU-) and has ou VAV eminal unis (Unis hough 4). The maximum and minimum ai volumes o each uni ae m 3 /h and 4 m 3 /h, esecively. The oom is enveloed by six chambes. Chambes hough 4 ae shown in Figue, and Chambes and 6 cove he ceiling and loo, esecively. The hemal condiions in each chambe can be conolled eely by using a seaae ai-condiioning sysem. The suly ailow ae o each VAV uni and he wae low ae o he coil ae conolled by a PI conolle. The se oin o he suly ai emeaue is also calculaed auomaically by a conolle. I he demand ailow ae eaches he maximum value in any uni, hen he se oin will be deceased by degee. I he demand ailow ae eaches he Table Design caaciy o he sysem Ai Flow Rae 4 m 3 /h Ai Handling Uni (AHU-) Suly Fan Reun Fan Coil Pessue Head 923 Pa Roaion Seed 3 s Powe 2.2 kw Ai Flow Rae 4 m 3 /h Pessue Head 42 Pa Roaion Seed 8 m Powe. kw Cooling Caaciy 6.98 kw Wae Flow Rae 3 l /min Roaion o Seed 3 m Pum (P-2) Wae Flow Rae 2 l /min Toal Pessue Head m Powe. kw Figue Plan o he exeimenal oom Figue 2 Pimay sysem Reigeaion Sysem Sysem COP

2 xeimen Numbe minimum value in any uni, he se oin will be deceased by. degees. Ae he se oin is changed, he value will be mainained o a leas minues. Desciion o he xeimen Table 2 shows a lis o he auls we invesigaed. In ode o measue he oeaional daa unde he same hemal condiions in each exeimen, he ai emeaue o Chambe 2 was se a 4 o C and he ai emeaue o he ohe chambes was se a o C. The lighs wee swiched o and ouside ai was no sulied. The inenal hea was geneaed by an elecic heae a a ae o 3 W/m 2. The se oin o he oom ai emeaue was o C. In all exeimens, he AHU was saed ae he zone ai emeaue became sable, and he oeaional daa wee measued o 2 hous. The samling ime was 6 seconds. The accuacy o he emeaue senso, he wae low senso and he enegy consumion mee ae ±. K, ±.%, and ±.%, esecively. Figue 3 shows he measuemen esuls o zone ai Zone Ai Temeaue (Zone) [ o C] Zone Ai Temeaue (Zone3) [ o C] 3 3 Table 2 Fauls o analysis x. 9 Faul x. x. 7 x ime [min] Analyzed Peiod Analyzed Peiod x. 7 x. x. 8 (a) Temeaue o Zone x. x. 3 x. 6 x. 9 x ime [min] (c) Temeaue o Zone 3 Fauly Uni, 2 None - 3, 4, Fully-closed dame aul Uni 4 6 Fully-oened dame aul Uni 4 7 Fully-oened dame aul Uni 2 8 Minimum ai volume o he ineio is 6% o maxmum ai volume Uni, Uni 2 9 Se oin o suly ai emeaue is o C - Se oin o suly ai emeaue is 22 o C - x. 6 x. 3 emeaue o all o he exeimens exce x. 2, x. 4, and x.. In he gahs o Figue 3, he AHU was saed a =. The daa colleced in x. 2 was aoximaely equivalen o hose colleced in x.. The behavios o x.4 and x. ae no much dieen om ha o x.3 and heeoe he cuves o x. 4 and ae no shown in hese igues. The igue shows ha none o he auls aec he oom ai emeaue gealy. Analysis o Daa The enegy consumion o he enie sysem [kw] is deined as ollows: = + + () w AHU = 2 (2) w 2 Q cahu, = (3) Cs Since um (P-2) delives wae o no only AHU- bu also o he ohe sysems, he enegy consumed by AHU- is esimaed using quaion (2). The enegy consumion o he eigeaion sysem is esimaed using quaion (3) because i is diicul o measue he enegy consumion o he ice soage sysem. The analysis eiod sas a = 4 minues and lass o hou, and he values o he aveage enegy consumion duing he analysis eiod ae comaed. In ode o evaluae he enegy consumion dieence beween nomal oeaion and auly oeaion, he ollowing value d [%] is deined. Zone Ai Temeaue (Zone2) [ o C] Zone Ai Temeaue (Zone4) [ o C] 3 x. 9 x ime [min] 3 x. x. 7 x. x. 3 x. Analyzed Peiod (b) Temeaue o Zone 2 Analyzed Peiod x. 7 x. 6 x. 9 x ime [min] (d) Temeaue o Zone 4 x. x. 6 x. 3 Figue 3 Zone ai emeaue in each exeimen

3 aul nomal d = (4) nomal Figue 4 shows he aveage o,,, and in he analysis eiod. Table 3 shows he aveage o he oeaional daa o each exeimen in he analysis eiod. The esuls ae summaized as ollows. a) xeimens and 2 Nomal oeaion was measued wice, and he similaiy o he daa indicaes ha he measuemens wee accuae enough. The aveage o he enegy consumions is used as he no aul eeence value. b) xeimens 3, 4, and When a ully-closed dame aul was inoduced in Uni 4, he ollowing henomena wee obseved: Because he ai emeaue o Zone 4 could no each he emeaue se oin, he demand ailow ae o Uni 4 became maximum and he suly ai emeaue se oin was deceased. Zones and 2 wee ovecooled because hese unis could no suly an ailow ae lowe han he minimum low ae. As a esul, alhough he values o wee smalle han hose unde nomal oeaion by aoximaely %, and wee aoximaely % lage. Fo he enie sysem, he ully-closed dame aul consumed % moe enegy han nomal oeaion. c) xeimens 6 and 7 When a ully-oened dame aul was inoduced in Uni 4, he enegy consumion was aoximaely equal o ha o nomal oeaion because he load o Zone 4 was high and he dame oening in no-aul oeaion is nealy ully-oened. When a ully-oened dame aul was inoduced in Uni 2, he ollowing henomena wee obseved: In ode o ensue ha he ai emeaue o Zone 2 Zone Ai Temeaue [ o C] Demand o Ai Volume [m 3 /h] Cooling Coil xeimen Numbe Fan INV [%] Table 3 Suly Ai Temeaue [ o C] Se Poin o Suly Ai Temeaue [ o C] x. x. 2 Ave. o Nomal Saes x. 3 x. 4 x. x. 6 x. 7 x. 8 x. 9 x. Fan Pum Reigeao was no lowe han he se oin, he se oin o suly ai emeaue was aised. The ai volume demands o all unis wee lage, and he an invee values wee lage han hose unde nomal oeaion. As a esul, alhough did no change, was % geae and was 3% geae, and o he enie sysem, was 3% geae negy Consumion [kw] d) xeimen 8 Because he ailow aes o Uni and 2 can no all below he auly minimum value, Zones and 2 wee ovecooled and and wee lage. Howeve, because he ai om Unis and 2 lowed o Zones 3 and 4, he oal suly ailow ae was smalle and was 6% lowe, and o he enie sysem was aoximaely % geae. Aveage oeaional daa duing he analysis eiod 2 Ave. o x. & Ave. o Nomal Saes Figue 4 Measuemen esuls Zone Zone Zone Zone Uni Uni Uni Uni Wae Flow Rae [l /min] Temeaue Dieence Beween Inle and Oule [ o C] Tanseed Hea [kw]

4 e) xeimen 9 Because he suly ai emeaue se oin was low, he oal suly ailow ae was lowe han ha unde nomal oeaion and was also lowe. Howeve, and wee % geae, and o he enie sysem, was aoximaely 2% geae. ) xeimen Because he suly ailow ae was lage due o he highe se oin o he suly ai emeaue, was 9% geae. Alhough did no change, was aoximaely 3% geae, and o he enie sysem, was aoximaely % geae. Fom he measuemen esuls, i is clea ha, exce o x. 6, he auls aeced he enie sysem and caused a 2% o % incease in enegy consumion. Fuhemoe, he auly VAV uni can also aec he ohe nomal unis, esuling in addiional enegy consumion. SIMULATION This secion descibes he mehod by which o esimae he incease o he enegy consumion caused by he auls hough simulaion. I is imoan o oose a mehod o edic he addiional enegy consumion by simulaion in ode o aly he measuemen esuls shown in he evious secion o ohe buildings. In he esen ae, he simulaion o he VAV sysem in he exeimenal oom is consuced by connecing he models o he mechanical comonens and conolles o he oom model. The eomances o he VAV sysem unde boh nomal oeaion and auly oeaion ae simulaed, and he addiional enegy consumion is esimaed. Ai-condiioning Sysem Model The ai-condiioning sysem model consiss o he models o mechanical comonens and he models o conolles. Figue shows a schemaic diagam o he ai-condiioning sysem model. Table 4 is a lis o he models used o he ai-condiioning sysem model. The an model used heein is ha oosed by Wang e al. [Wang, ], and he coil model is aken om SIMBAD [CSTB, 2]. The eigeao enegy consumion is esimaed using quaion (3). The VAV uni model, he valve model and he um model ae given by he ollowing equaions: V = av () v d w w v w v w v w = a + a O + a O + a O (6) = a + a w + a w + a w (7) In ode o accuaely simulae he acual behavio, he aamees o he models o he ai-condiioning sysem ae deemined using he daa measued unde nomal oeaion (x. and 2). The aamees o he conolle models ae also deemined using he measued daa. Then, he aamees o he coil model canno be esimaed by he measued daa because hee ae oo many aamees in he coil model. The aamees o he coil model used in he esen ae ae aken om he seciicaion daa given by he manuacue. The inus o he Figue Schemaic diagam o he ai-condiioning sysem model

5 Table 4 Ai-condiioning sysem models Mechanical Conolle Model VAV Uni Model Valve Model Demand o ailow ae Demand o valve oening Inu Coil Model Inle ai emeaue Inle ai humidiy Ai low ae Oule ai emeaue Oule ai humidiy Inle wae emeaue Wae low ae Oule wae emeaue Tanseed hea Pum Model Wae low ae Pum enegy consumion Fan Model Fan oaion seed Ai low ae Fan enegy consumion Chille Model Coil anseed hea Chille enegy consumion VAV Demand Ailow Zone emeaue Se oin o zone emeaue Demand ai low ae Suly Ai Temeaue Se Poin Demand ai low ae Se oin o suly ai emeaue Fan Invee Demand ai low ae Fan invee value Valve Oening Suly ai emeaue Se oin o suly ai emeaue Demand o valve oening Ouu Suly ailow ae Wae low ae ai-condiioning sysem model ae ai emeaue o each zone, se oin o he ai emeaue, eun ai emeaue, eun ai humidiy, and coil inle wae emeaue. The ouus ae suly ai emeaue, suly ai humidiy, suly ailow ae, and he enegy consumions o he an, um and eigeao. Room Model (One-Zone Model) The zone model oosed in SIMBAD is used as he oom model [Riedee, 2]. The model is descibed by he volume o he zone, he suace o walls, he comosiion o walls, and he hea anse coeiciens. Fom hese daa, ive esisances and hee caaciances ae calculaed in ode o eesen he zone model in an elecical scheme based on he sae sace aoach. Alhough he exeimenal oom is divided ino ou zones, he model canno exess mulile zones. Theeoe, one zone is assumed o he simulaions. The inus o his model ae suly ai emeaue, suly ai humidiy, and suly ailow ae, and he ouus ae oom ai emeaue and humidiy. The model aamees ae deemined om he design inomaion. The line labeled (Beoe) in Figue 6 indicaes he simulaion esul o he oom model obained using he daa measued Zone Ai Temeaue [ o C] 33 3 (Aveage o all zones) (Ae) (Beoe) 2 Figue 6 Veiicaion esul o he oom model unde he nomal oeaion (x. ). The esul shows ha he behavio o he simulaed emeaue is quie dieen om ha o he measued emeaue. In ode o moe accuaely simulae he oom ai emeaue, he hea caaciy o he uniue is aken ino consideaion and is added o he oom model as a viual inenal wall. The line labeled (Ae) in Figue 6 shows he simulaion esul when he hea caaciy is se a 7. kj/(m 3 K). The esul shows ha he model can accuaely simulae he acual behavio o oom emeaue. VAV sysem simulaion (One-Zone Model) By combining he ai-condiioning sysem model and he oom model, he behavio o he VAV sysem in (Uni3) 8 6 (Uni4) 4 (Uni) 2 (Uni2) (Se Poin) (Se Poin).2 Figue 7 Simulaion esuls <one-zone model> (nomal oeaion, x. )

6 Figue 8 Room model (wo-zone model) he exeimenal oom is simulaed. Hee, because he simulaion does no include he eigeaion sysem model, he measued daa o he coil inle wae emeaue mus be inu ino he simulaion. Figue 7 shows he simulaion esuls unde nomal oeaion. The igue shows ha he simulaed enegy consumion o he an, um and eigeao ae quie dieen om he measued values, aiculaly he an enegy consumion. The eason o he dieence lies in he assumion ha he oom has only one zone. The assumion causes he dieence in he demand values o he VAV ailow ae beween simulaion and measuemen and causes he dieence in he se oin o he suly ai emeaue and he dieence in he an enegy consumion. Room Model (Two-Zone Model) In ode o eom a moe accuae simulaion, he oom model is divided ino wo zones, an ineio zone (Zone /2) and a zone acing he ouside (Zone 3/4), as shown in Figue 8. A he cene o he oom, Zone Ai Temeaue [ o C] 3 (Zone,2) (Zone,2) (Zone3,4) (Zone3,4) Figue 9 Veiicaion esul o he oom model a zeo hickness wall is assumed, and he oom is divided ino wo aeas by he wall. The behavio o each aea is simulaed by he zone model in SIMBAD. Howeve, he model canno evaluae he hea exchange beween hese wo zones. Figue 9 shows he veiicaion esuls o he oom model using daa measued unde nomal oeaion. This model also consides he viual inside wall in ode o accuaely simulae he acual behavio o he zone ai emeaue. The veiicaion esuls show ha he model can accuaely simulae he zone ai emeaue. VAV sysem simulaion (Two-Zone Model) Using he VAV sysem simulaion wih he wo-zone oom model, he behavio unde nomal oeaion is nex simulaed. The simulaion esuls ae shown in Figue. The igue shows ha he simulaion accuacy is imoved and ha he behavios o he enegy consumions duing he analysis eiod ae (Zone3,4) (Zone3,4) (Zone,2) (Zone,2) (Uni3) 8 (Zone,2) (Zone3,4) 6 (Uni4) 4 (Uni) 2 (Uni2) (Se Poin) (Se Poin) Figue Simulaion esuls <wo-zone model> (nomal oeaion, x. )

7 Table Simulaion esuls obained using he wo-zone oom model xeimen Numbe [kw] [kw] [kw] [kw] Incease o negy Consumion 2 Ave [kw] [%] 2.4% 2.9% 37.2% 8.2% 4.%.9%.2% 6.8% Table 6 Measuemen esuls obained in he exeimenal oom xeimen Numbe [kw] [kw] [kw] [kw] Incease o negy Consumion 2 Ave [kw] [%] 2.9%.3% 34.2% 4.6% 34.3% 22.9% 2.9% 2.7% Table 7 Dieence in he incease o enegy consumion beween simulaion and measuemen xeimen Numbe 2 Ave Dieence [kw] [%] % -8.4% 3.% 3.7% -2.2% 3.% -.7% 4.2% aoximaely he same as ha o he measued daa. The auls lised in Table 2 ae ceaed in he simulaion, and he behavios o he VAV sysem ae simulaed. Table shows he aveages o,,, and o each exeimen duing he analysis eiod esimaed by he simulaion. Table 6 shows he measuemen esuls o he enegy consumion, and Table 7 shows he dieence in he incease o he enegy consumion beween he simulaion and he measuemen. Table 8 shows simulaed value o he aveage oeaional daa in he eiod analyzed. The esuls o he simulaion eveal he ollowing. ) The simulaion can be used o esimae he incease in he enegy consumion o he enie sysem caused by he auls. The dieences beween simulaion and measuemen ae wihin %, exce o x. 7 and 9. 2) The simulaed incease in enegy consumion o x. 7 is aoximaely 2% lowe han he measued value because he simulaed demand ailow ae o Uni is smalle han he acual value, due o he assumion ha Zones and 2 ae in he same zone, and he an enegy consumion is esimaed o be somewha lowe. Table 8 values o he aveage oeaional daa duing he analysis eiod Zone Ai Temeaue [ o C] Demand o Ai Volume [m 3 /h] xeimen Numbe Fan INV [%] 2 Ave. o x. & Zone, Zone 3, Uni, Uni 3, Suly Ai Temeaue [ o C] Se Poin o Suly Ai Temeaue [ o C] Wae Flow Rae [l /min] Cooling Coil Temeaue Dieence Beween Inle and Oule [ o C] Tanseed Hea [kw]

8 The enegy incease o x. 9 is esimaed o be aoximaely % lowe han he measued value because he oom model does no conside he hea exchange beween Zone /2 and Zone 3/4 and he simulaed ai emeaue o Zone 3/4 is highe han he acual value, and he esimaed eigeao enegy consumion is low. 3) The emeaues o Zones and 2 o x. 3, 4 and ae esimaed o be somewha lowe han he measued value because he simulaion does no conside he inluence o hea exchange beween Zone /2 and Zone 3/4. These discussions indicae ha he VAV sysem simulaion can be used o esimae he incease in he enegy consumion o he enie sysem. Howeve, he simulaion canno accuaely esimae henomena caused by he auls. I he simulaion akes he inluence o he hea exchange among he zones ino consideaion, hen he simulaion can be used o esimae he henomena. CONCLUSIONS This ae invesigaes he inluence o a auly VAV uni on he oal enegy consumion o a VAV sysem boh exeimenally and by simulaion. Based on he above discussions, he ollowing conclusions ae obained. ) In he exeimenal oom, in which he indoo and oudoo condiions can be se abiaily, oeaional daa wee measued unde nomal and auly saes. The esuls show ha i he sysem has a uni wih a ully-closed dame aul, hen he enegy consumion o he enie sysem is aoximaely -3% geae han ha o he nomal sae. I he sysem has a uni locaed on he ineio side wih ully-oen dame aul, hen he enegy consumion is aoximaely 3% geae. I he minimum value o he demand ailow ae o he se oin o suly ai emeaue is suck a an abnomal value, hen he enegy consumion is aoximaely 2-% geae. 2) The measued daa indicaes ha he auly VAV uni can also aec ohe nomal unis in he same ai-condiioning sysem and heeby cause addiional enegy consumion. 3) A mehod is oosed by which o esimae he incease in enegy consumion caused by he auls using simulaion. The esuls o he veiicaion o he simulaion accuacy using he measued daa o he nomal sae eveal ha he oom model mus be divided ino seveal zones in ode o accuaely simulae he behavio o a VAV sysem. 4) I is veiied ha he simulaion can be used o esimae he incease in he enegy consumion o he enie sysem caused by he auls. The dieences in he enegy incease beween he simulaion and he measuemen ae aoximaely %. I he simulaion akes ino consideaion he inluence o he hea exchange among zones, hen he simulaion can accuaely esimae he henomena caused by he auls. NOMNCLATUR a v : Paamee o he VAV uni model [-] a wi : Paamees o he valve model [-] a i : Paamees o he um model [-] C s : Ai-condiioning sysem COP [-] 2 : negy consumion o um (P-2) [kw] : negy consumion o he enie sysem [kw] : negy consumion o he an [kw] : negy consumion o he um [kw] : negy consumion o he chille [kw] O v : Valve oening [-] QcAHU, : Hea anse o he coil in AHU- [kw] V d : Demand ailow o he VAV uni [m 3 /h] V : Real ailow o he VAV uni [m 3 /h] wahu : Wae low ae o AHU- [l/min] w : Wae low ae o um (P-2) [l/min] 2 RFRNC Clak, R.D.: HVACSIM+ Building Sysems and quimen Simulaion Pogam Reeence Manual, NBSIR 84-96, Januay 98,.. Gaihesbug: U.S. Deamen o Commece CSTB: SIMBAD Building and HVAC Toolbox, Vesion 3, Cene Scieniique e Technique du Baimen, Novembe 2. Husaunndee A., Riedee P., e Visie J.C.: Coil modelling in he Simbad oolbox - numeical and exeimenal validaion o he cooling coil model, SSB'98 Sysem Simulaion in Building Coneence, Liege, Decembe 4-6, 998 IA ANNX7: Simulaion and mulaion o HVAC Sysems, Cene Scieniique e Techmique, FRANC, Seembe, 992 Miyaa, M., Yoshida, H., Asada,M. e al. : Faul Deecion and Diagnosis Mehod o VAV Teminal Unis, Inenaional Coneence o nhanced Building Oeaion,. Qin, J., Wang, S.: Auomaic Commissioning o Mulile VAV Teminals, Inenaional Coneence o nhanced Building Oeaion,. Riedee, P. e.al: Building Zone modelling adaed o he sudy o emeaue conol sysems, ASHRA/ CIBS coneence, 2, Dublinm, Ieland. Wang, F., Yoshida, H., Miyaa, M.: Toal negy Consumion Model o Fan Subsysem Suiable o Coninuous Commissioning, ASHRA Tansacions, Volume, Pa, Yoshida, H.: Tyical Fauls o Ai Condiioning Sysems and Faul Deecion by ARX Model and xended Kalman File, ASHRA Tansacions, Vol.2, Pa,.7-64, Feb