Analysing te energy consumption of air andling units by Hungarian and international metods László Kajtár 1, Miklós Kassai 2,* 1,2 Budapest University of Tecnology and Economics (BUTE), Budapest, Hungary * Corresponding email: kas.miklos@gmail.com SUMMARY According to te 2002/91/EC, te Directive on te energy performance of buildings it is important to determine te expected energy consumption of te building in te step of te designing. Tere are imperfections in te actual available national and international regulations as for te metods to calculate te energy consumption of te air andling units. Te actual calculation metods caracterise te montly energy consumption only wit te average temperature or average entalpy wic takes into account te canging of te ambient air state only approximately. Te most actual calculation procedures also not consider te systems tat operate not continuously (only at nigt or in daytime). Based on te calculation procedure tat uses te ambient temperature and entalpy duration curves tese problems can be solved. A new calculation metod was worked out tat takes into consideration te air andling energy consumption wit te ambient temperature and entalpy duration curves. KEYWORDS Energy performance, HVAC and mecanical systems, Models, Modeling 1 INTRODUCTION Making a study of te international scientific literature, Erik Reicert worked out a calculation procedure in is P.D. tesis at te University of Applied Sciences Stuttgart, wit wic te net energy consumption of te air andling unit can be calculated (Erik Reicert, 2000). Te metod sepatares te Mollier -x cart into 4 parts in accordance wit te main canging processes of te air state (air umidification, cooling). Wit tis procedure te energy consumption of te air andling units can be calculated wit te elp of statistical, meteorological database suitable for te geograpic area of te analysed space. Similarly in Germany wit te leading of Professor Bert Oscatz a calculation metod was developed to determine te energy consumption of te air-conditioning systems. Tis metod uses specific values [W/m 3 ] to calculate te eating and cooling energy consumption of te air andling units also in montly period (Bettina Maria Scmidt, 2007). Claude-Alain Roulet as also developed a calculation procedure to determine te annual energy consumption of te air andling systems (Claude-Alain Roulet, 2002). From te developed metods also standards were made: VDI 2067 (Blatt 21) based on te researc work of Erik Reicert, DIN V 18599-7/3/5/10 based on te researc work of Professor Bert Oscatz and EN ISO 13790 based on te researc work of Claude-Alain Roulet. Te timeliness of tis researc teme sows tat te current available calculation procedures enable te only te roug estimate of te energy consumption of air andling units. Te mentioned metods do not take into account of te eat and moisture load of te air andled space (L. Kajtár, M. Kassai, 2010).
During our researc our objective was to work out a calculation procedure wic is suitable for te analysis of te energy consumption of air andling units taking into account te different and complex air andling processes and te above mentioned inadequacies. 2 THE YSICAL MODEL Te developed calculation procedure is introduced in te article by a fres air supply air andling unit (AHU). Te connection diagram can be seen of fres supply air andling system on Figure 1. Te signs of te figure are te following: Pre-eater (), adiabatic umidifier (AH), Cooler (C), Re-eater (RH), Ventilator (V), Filter (F), Sutter against te rain (SH). Figure 1. Te connection diagram of te AHU During te cange of te ambient air state te pre-eater eats up te air up to a constant entalpy line tat is determined by te adiabatic umidifier, terefore te ambient entalpy duration curve as to be used to define te energy consumption of eating. On te ambient entalpy duration curve (Figure 2.) te air state parameters in te dimensioning pase are also sown as well as teir canges as te ambient air entalpy varies during te eating season. Te areas of te ambient entalpy duration curve tat represent te energy consumption of te pre-eater and te re-eater can be accordingly drawn. Trougout te calculation of te energy consumption of eating te supply and outgoing air parameters were assumed to be constant during te eating season. Tis approximation was also applied for te supply and outgoing parameters in te dimensioning pase for te cooling season in te summer. Figure 2. Te areas on te ambient entalpy duration curve
On Figure 2. can be seen te areas tat proportional to te daytime eating energy consumption of te air andling unit (07-19 ours). In compliance wit it te pysical and matematical equations were determined to calculate te energy consumption of te eaters in te fres air supply air andling unit. Te energy consumption of te pre-eater: ( ) Q = ρ V& F d [kj/year] (1) OS O were ρ is te air density in kg/m 3, V & is air volume flow in m 3 /, F O () is te ambient entalpy duration curve (07-19 ours), OS is te ambient entalpy in sizing state in te winter time in kj/kg, is te entalpy of te air after te pre-eater, wic is equal wit te entalpy by te adiabatic umidifier in kj/kg. Te energy consumption of te re-eater: RH ( ) Q = ρ V& F d [kj/year] (2) RH O were RH is te entalpy of te air after te re-eater, wic is equal wit te entalpy of supply air in kj/kg. Analyzing te cooling energy consumption te calculation procedure is similar in te summer time. Te dimensioning pase for te summer period is specified by te regulations (Figure 3.). Te average temperature of te surface of cooling coil ( t SA ) is about 11-12 C wen te cooling water temperature is 7/12 C. Figure 3. Cooling process on te Mollier -x cart In ligt of te above mentioned data te area proportional to te energy consumption of te cooling coil can be drawn in te ambient entalpy duration curve. In consideration of te fact tat tere is condensation on te surface of te cooling coil, te ambient entalpy duration curve was used to determine te annual energy consumption of te cooling coil (Figure 4.).
Figure 4. Te area on te ambient entalpy duration curve tat represents te energy consumption of te cooling coil Te energy consumption of te cooling coil: OS [ 1 F ( ) ] Q C = ρ V& C O d [kj/year] (3) S were V & C is te air volume flow in te cooling coil in m 3 /, air in kj/kg. S is te entalpy of te supply In ligt of te energy consumption of te cooling coil te electricity consumption of te compressor can be calculated as follows [Carson Dunlop, 2003]: W = Q C /(SEER 3600) [kw/year] (4) C were SEER is te Seasonal Energy Efficiency Ratio. By tis manner energy consumption of oter constructed air andling units were also determined. 3 THE MATHEMATICAL MODEL Te ambient temperature and entalpy duration curves are not known analytically, in tis manner te integral values tat we developed were determined wit appreciative numerical computing. We digitalized te duration curves from te scientific literature tat were fixed in tree ours period during te meteorological monitoring ten we placed points to te functions (Figure 5.). For tis task Autodesk AutoCAD 2006 program was rigt. Wittingly te scale of te duration curves te areas (te values of te integrals) could be computable numerical.
Figure 5. Application of spline interpolation wit Autodesk AutoCAD 2006 program In te matematical sciences te spline is a special function tat consists from more polynomial. Autodesk AutoCAD 2006 uses rational B-spline curbes (NURBS) (Joe Sutpin, 2005) 4 RESULTS In our researc work a comparative analysis was made between te new calculation procedure we ad developed and te existing international calculation metods. During our analysis te net energy consumption of tree air andling units for eating and cooling was determined and te volume flow rate of te air was 3000 m3/. Te energy analysis was performed using meteorological data for Budapest. Te elements of te AHUs are presented in Table 1. Te symbols are te following: eat recovery unit (HR), energy recovery unit (ER), pre-eater (), cooling coil (C), adiabatic umidifier (AH), steam umidifier (SH), Re-eater (RH). Table 1. Elements of te AHUs HR ER C AH SH RH AHU 1. X X X X X AHU 2. X X X X X AHU 3. X X X X Te annual net energy consumption of te analysed air andling units for eating and cooling can be seen in Tables 2-3. Table 2. Annual net energy consumption of te AHUs for eating Q H [kw/year] New metod Erik R. Bert O. Claude-A. R. 1. 15 667 15 080 8 514 26 899 2. 28 158 17 150 12 435-3. 38 865 24 927 34 264 42 648
Table 3. Annual net energy consumption of te AHUs for cooling Q C [kw/year] New metod Erik R. Bert O. Claude-A. R. 1. 4 773 4 900 5 726 5 832 2. 4 344 4 900 5 412-3. 5 873 6 022 5 785 6 374 5 DISCUSSION Te new developed calculation procedure is also suitable for comparative energetic analysis of various constructed air andling units also in te design pase, considering te cost of te investment, te possibilities of te energy saving and te amount of te saved energy. By tis manner tere is also possibility to cose te lowest energy consumed system in te design pase. Te results tat are determined by te new calculation metod are important not only for te designing engineers wit respect to te energy conscious designing and te making of te energy performance certificate of buildings, but also for te investor, because te operating cost influences te rent cost. 6 CONCLUSIONS Te tables sow tat te results of te energy consumption different if calculated using te new procedure or te metod by Erik Reicert, Bert Oscatz, Calude-Alain Roulet. But in eac examined case (AHU 1-3.) te result of te international calculation metods is almost te same as te figures obtained troug te new calculation procedure. In te case of AHU 2 equipped wit an adiabatic umidifier tere is a larger difference wit regard to energy consumption for eating. In our view te present international metods do not take into consideration te iger energy consumption of te re-eater, caused by te adiabatic umidifier. Anoter reason for te different results is tat effective regulations define te montly energy consumption by a single figure only, e.g. average temperature or average entalpy wic only approximately takes into account te canging of te ambient state of te air. ACKNOWLEDGEMENT Te researc work was supported by Sustainable Energy Program of BUTE Researc University. 7 REFERENCES Erik R.. 2000. Ein Verfaren zur Bestimmung des Energie- und Stoffaufwands zur Luftbeandlung bei raumlufttecniscen Anlagen, P.D. Tesis, ISBN 3-9805218-4-2, Universität Stuttgart, p. 25-29. Bettina M. Sc., Tomas H., Daniel F. 2007. Der einface Weg zur DIN V 18599 (Teil 3.), IHKS Fac.Journal - Faczeitscrift für Planungsbüros, Anlagenbau, Öffentlice Hand und Facandel, p. 24-31. Claude-A. R. 2002. pren-isp 13790-A Simplifield Metod to Assess te Annual Heating Energy Use in Buildings, ASHRAE Transactions, ISSN 0001-2505, Volume 108, Part 2, p. 911-918. L. Kajtár, M. Kassai. 2010. Energy Consumption of Air Handling Units. Clima 2010 10t REHVA World Congress, Antalya, ISBN 978-975-6907-14-6, p. 37-39. Carson D. 2003. Air conditioning & Heat Pumps, IL 60606-7481, p.126. Joe S. 2005. AutoCAD 2006 VBA, A Programmer s Reference, ISBN 1-59059-579-3, p. 593.