ANALYTICAL MODEL BASED INVESTIGATION OF VENTILATION SYSTEM ENERGY CONSUMPTION

Transcription

1 Topic B4: Venilaion ANALYTICAL MODEL BASED INVESTIGATION OF VENTILATION SYSTEM ENERGY CONSUMPTION Miklos KASSAI *, Laszlo KAJTAR Deparmen of Building Service Engineering and Process Engineering, Budapes Universiy of Technology and Economics, Budapes, Hungary * Corresponding kas.miklos@gmail.com Keywords: energy saved, venilaion sysem, hea recovery uni SUMMARY (12 p, Bold, leave a blank line before and afer he main level headings) In our ime he explosive spread of he air condiioning sysems herein he air handling unis is a global phenomenon (Jaff B, 28). Based on he 22/91/EC, he Direcive on he energy performance of buildings (EPBD) i is imporan o deermine he expeced energy consumpion of he building during he designing period of he HVAC sysems. The energy consumpion of air handling unis and he energy saved by hea recovery unis can be deermined by wo mehods. In he case of operaing venilaion sysems he acual consumpion daa can be exacly deermined by measuremen. There are imperfecions in he acual available naional and inernaional regulaions for calculaing he energy consumpion of venilaion sysems. Our research focuses o work ou a deailed mehod o calculae he saved energy of he hea recovery unis inegraed in venilaion sysems. INTRODUCTION In our ime he explosive spread of he air condiioning sysems herein he air handling unis is a global phenomenon. Wih he help of hem such air parameers can be supplied in he spaces of he building which can provide he pleasan comfor sensaion of he people or he easy operaion of he insalled echnology. Previously he main consideraion of he enders for he reviewing of air-condiioning sysem designs and consrucing was he invesmen cos. The imporance of energy efficien operaion and qualiy managemen is higher and higher. One of he ways o decrease he invesmen cos is he neglecing of he accessory coss, and he low qualiy of he maerial. All hese raise he energy consumpion and he opporuniy of he uneconomical operaion. To supplan hese disadvanageous effecs, he Life Cycle Cos principle is aken ino consideraion during he reviewing of he enders. On his wise he invesmen and operaion coss are ogeher aken ino consideraion for he whole operaion period of he equipmen (Magyar T, 23). The operaion coss include he energy consumpion of he air handling uni, he mainenance cos, he cos of he preservaion and he annuiy cos. In his case he imporance of he qualiy managemen and he energy efficien operaion is higher han focusing only for he invesmen cos. The spread of his aiude is especially imporan, because he low energy buildings, he super low energy buildings and he passive buildings are coming o force in he immediae fuure. (Mikko N, Carey JS 25; Yaw A, Rober W B, Carey JS, 25). In addiional he saisical daa aes ha he acive cooling is applied by residenial and public buildings more and more. By hese buildings he venilaion proporion is significanly

2 increased in he whole energy consumpion. There are similar problems by he operaion of hermal insulaed buildings. In his case he energy consumpion of he venilaion sysem is a major proporion of he energy consumpion of whole building services (Kjell F, William L, 25). METHODOLOGIES Calculaion of heaing and cooling energy consumpion i is necessary o ake accoun of variaion of ambien air parameers (emperaure, humidiy and enhalpy) ha vary in daily and season period. The developed calculaion procedure is inroduced in he aricle by a fresh air supply air handling uni (AHU). The connecion diagram can be seen of a fresh supply air handling sysem wih hea recovery on Figure 1. The signs of he figure are he following: HR: Hea recovery uni, PH: Pre-heaer, AH: Adiabaic humidifier, C: Cooler, RH: Re-heaer, V: Venilaor. OG V 2 SPACE h h OG HR I HR h HR PH PH h PH AH AH h AH C RH RH h RH V 1 S h S Figure 1. The connecion diagram of he venilaion sysem PH 1,16 1,18 RH=S Air emperaure [ 癈 ] ,2 1,22 1,26 1,28 1,3 1,32 1,34 1,36 HRS=O' OG' OG=I H h x h RH h PH Mollier diagram Figure 2. Air handling processes a Mollier diagram in he dimensioning sae in winer ime.

3 During he energy calculaions i is imporan o ake ino consideraion he order of he air handling elemens and he air handling processes. During he operaion of he air handling unis he air handling processes can be bes demonsraed by he Mollier h-x char (Heinz E, 1998). Some parameers are given such as he emperaure and relaive humidiy of ambien air in he dimensioning phase ( ; ϕ ), he supply air ha eners he room ( S ; ϕ S ) and he ougoing air ha leaves he room ( OG ; ϕ OG ). To perform he energy calculaions i is necessary o know he supply air volume flow and he densiy of he supply air. The values of indoor air parameers depend on he air disribuion of he room and are shown beween he supply air and ougoing parameers. The energy analysis is no influenced by he indoor air parameers. Figure 2. shows in Mollier h-x char (25; Heinz E, 1998) he process of hea recovery ( - HRS ) pre-heaing ( HRS-PH secion), he adiabaic humidifier ( PH-H secion) and he reheaing ( H-RH secion) in he dimensioning phase in winer ime. During he change of he ambien air sae he pre-heaer heas up he air up o he consan enhalpy line ha is deermined by he adiabaic humidifier, herefore he ambien enhalpy duraion curve has o be used o define he energy consumpion of heaing (Róber Kiss, 198). On he ambien enhalpy duraion curve (Figure 3.) he above menioned air sae parameers in he dimensioning phase are also shown as well as heir changes as he ambien air enhalpy varies during he heaing season. The areas of he ambien enhalpy duraion curve ha represen he energy consumpion of he pre-heaer and he re-heaer can be accordingly drawn. Throughou he calculaion of he energy consumpion of heaing he supply and ougoing air parameers were assumed o be consan during he heaing season. This approximaion was also applied for he supply and ougoing parameers in he dimensioning phase for he cooling season in he summer. τ o hours HR RH τ, [hour] F O HV η 1-η HR HR PH F HR Disribuion [%] -2 HRS H OG S 4, [ 癈 ] Figure 3. The areas on he ambien enhalpy duraion curve ha represen he energy saved of hea recovery uni in winer.

4 On Figure 3. can be seen he areas ha proporional o he dayime (7-19 hours) heaing energy saved of hea recovery uni in he venilaion sysem. In compliance wih i he physical and mahemaical equaions were deermined o calculae he energy saved of hea recovery for he heaers. Energy saved of he hea recovery for he pre-heaer: H H Q HR PH = cpa ρ V Fo ( ) d FHR( ) d [kj/year] (1) HRS where cpa specific air capaciy of he air in kj/kg C, ρ is he air densiy in kg/m 3,V is he air volume flow in m 3 /h, F O is he ambien emperaure duraion curve (7-19 hours) in h C, H is he air emperaure afer he adiabaic humidifier in C, is he ambien emperaure in sizing sae in winer in C, F HR is emperaure duraion curve based on he hea recovery efficiency in h C, HRS is he air emperaure afer he hea recovery uni in C. Energy saved of he hea recovery for he re-heaer: OG OG Q HR RH = cpa ρ V F ( ) d FHR( ) d [kj/year] (2) H H where OG is he ougoing air emperaure he leaves he space in C. Analyzing he cooling energy consumpion he calculaion procedure is similar in he summer ime. The dimensioning phase for he summer period is specified by he regulaions (Figure 4.). The average emperaure of he surface of cooling coil ( ST ) is abou C. Air emperaure [ C] ,16 1,18 1,2 1,22 1,24 OG' OG S ST h x HRS=' h C h HR Figure 4. Cooling process on he Mollier h-x char in he dimensioning phase in summer ime.

5 In ligh of he above menioned daa he area proporional o he energy consumpion of he cooling coil can be drawn in he ambien enhalpy duraion curve. In consideraion of he fac ha here is condensaion on he surface of he cooling coil, he ambien enhalpy duraion curve was used o deermine he annual energy consumpion of he cooling coil (Figure 5.). τ τ, [hour] o hours F O F HR 1-η HR ηhr HR 1 Disribuion [%] S OG HRS 36, [ C] Figure 5. The area on he ambien enhalpy duraion curve ha represens he energy consumpion of he cooling coil. Energy saved of he hea recovery for he cooling coil: HRS Q C = c pa ρ V [ 1 FO ( ) ] d [ 1 FHR ( ) ] d [kj/year] (3) OG OG By his manner energy consumpion of oher consruced air handling unis were also deermined. RESULTS AND DISCUSSION Good agreemen beween he experimenal and developed deailed analyical resuls is archived. For proving righ of he heoreical mehod, measured energy consumpion daa of separaed years (22, 25 and 26) were used in he case of wo hoel building complexes and an office building. In he seleced years he operaion characericic and he caseload of he buildings was average correlae wih he building ype. On he basis of he underlying six independen measured energy consumpion daa he difference of he calculaed and he measured energy consumpion values was beween -11,7 and +11,7 % (Table 1). During our research he daa of 3 pieces of various consruced air handling unis were used. Furhermore, in our research work a heoreical comparaive analysis was made beween wo cases oo. During our analysis he saved energy of wo air handling unis were deermined for heaing and cooling seasons and he volume flow rae of he air was 3 m 3 /h and he efficiency of he hea recovery was 7%. The reference model was a model for fresh air supplied air handling uni. The energy analysis was fulfilled using meeorological daa for Budapes. The elemens of he AHUs are presened in Table 2.

6 Table 1. The measured and he calculaed energy consumpion Measured value Calculaed value Difference [(C-M)/M] [kwh/m 2 year] [kwh/m 2 year] [%] Office building (22) ,7 476 Office building (25) ,7 Hoel 1 (25) 437 4,1 455 Hoel 1 (26) 444 2,4 Hoel 2 (25) 441-4,3 422 Hoel 2 (26) 418,9 Table 2. Elemens of he AHUs. HR PH AH RH C AHU 1 X X X X AHU 2 X X X The annual energy saved by he hea recovery uni for heaing and cooling seasons has been calculaed wih he developed mehod. The saved energy in he case of AHU 2 in heaing case is abou 23 kwh/year and for cooling season was 11 kwh, comparing he resuls wih AHU 1 which does no include hea recovery uni. CONCLUSIONS The resuls show ha he saved energy wih he hea recovery uni in heaing case was abou 23 kwh/year and for cooling season was 11 kwh. The annual energy saved is a significance proporion. The developed mehod is suiable for analysing he energy saving of he various consruced air handling unis. In his manner an opimal decision can be made in he design phase. By choosing he lowes energy consumed air handling uni, a significan energy saving (3-6%) can be achieved during he whole lifeime of he sysem. ACKNOWLEDGEMENT This research was financially suppored by Susainable Energy Program of BUTE Research Universiy, Budapes, Hungary. REFERENCES Jeff B, Explaining he spread of residenial air condiioning, , Exploraions in Economic Hisory 45 (28) Magyar T (23) Principle of air duc design and applicaion. Budapes, Hungary p. 3./ Mikko N, Carey JS (25) Life cycle assessmen of residenial venilaion unis in a cold climae, Building and Environmen, p Yaw A, Rober W B, Carey JS (25) Cos-Effecive Design of Dual Hea and Energy Recovery Exchangers for 1% Venilaion Air in HVAC Cabine Unis, ASHRAE Transacions, Volume 111, Par 1, ISSN 1-255, p Kjell F, William L (25) Calculae venilaion Life Cycle Cos and Coun on Savings, Business Briefing: Hospial Engineering & Faciliies Managemen.

7 Heinz E (1998) Einführung in die Klimaechnik, Erläuerungen zum h-x Diagramm, ISBN , p.1. Rober Kiss (198) Daa for venilaion, Technican Publisher. Budapes, ISBN , p