Simulation study on the thermal performance of a direct-expansion solarassisted heat pump for water heating in Kermanshah climate

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1 -3539 mme.modares.ac.ir * - - hsafarzadeh@razi.ac.ir 7973 * R3a : 39 7 : 39 9 : Simulation study on the thermal performance of a direct-expansion solarassisted heat pump for water heating in Kermanshah climate Sobhan Fathollahi, Habibollah Safarzadeh * Department of Mechanical Engineering, Razi University, Kermanshah, Iran * P.O.B Kermanshah, Iran, hsafarzadeh@razi.ac.ir ARTICLE INFORMATION Original Research Paper Received August 5 Accepted 9 October 5 Available Online 3 November 5 Keywords: Heat pump Solar collector Compressor Coefficient of thermal performance Solar radiation ABSTRACT Direct-expansion solar-assisted heat pumps (DX-SAHP) have been used widely to heat the water consumed by buildings and industrial facilities, domestic and industrial space heating and also, air conditioning. These systems transfer energy from lower temperature source to a higher temperature source. In DX-SAHP systems, in order to optimize the heat transfer of solar radiation to the refrigerant, the flat plate solar collector is used as the evaporator. In this paper, the effect of the number of collector cover has been studied on the thermal performance of the DX-SAHP system using numerical simulation and also the thermal performance of the system has been analyzed for heating the water of a house in Kermanshah. The system mainly employs a bare at-plate solar collector with a surface area of m, a hot water tank with the volume of 5 L, a rotary-type hermetic compressor, a thermostatic expansion valve and R-3a are also used as working uid in the system. The results show that the hours of system operation, during different months in the climate of Kermanshah vary between 37 to 3 hours and the monthly average and the solar collector efficiency vary between 3.9 to.7 and to 99 percent respectively. The effect of various parameters, including solar radiation, ambient temperature, evaporating and condensing temperature, collector area, compressor speed and wind speed have been analyzed on the thermal performance of the system. - Pleasecitethisarticleusing: : S.Fathollahi,H.Safarzadeh,Simulationstudyonthethermalperformanceofdirect-expansionsolar-assistedheatpumpforwaterheatinginKermanshahclimate,Modares MechanicalEngineeringVol.5,No.,pp.3-,5(inPersian)

2 [] [5]... [] [7]. 9. [] [9] [].[]. []. [3].. [] [] [] [3] - Lord Kelvin

3 Compressor Collector/evaporator Expansion valve 3 5. EES Hot Water Tank :[7] = [ ( )] = [ ( )] ( ) = ( ) ( ) h () () h F ' T e r A C T a T wo T wi T P I T =. Fig. Schematic diagram of the DX-SAHP system - Polytropic [5] R3a.() () ().(3).() [] hermetic 539 3

4 = + + ( + ) +. + ( + ) +. ( 3) = ( +.9. ) +.7 ( ) =.3 ( 5) = 5(.5 ); 7 ( ) u W h W [9] =. + 3 ; 5 ( 7) = = [7] + + [+()] ( ) tanh () () ( 9) = ( ) W D F k P (). h fi [] =. Re. P ( ) = ( ) x. 77 j() Re L. tp. h fg = + ( ) ( 3) () () k r = + ( ) ( ) T 3 Fig. T S diagram for the DX-SAHP system - S Table Main parameters used in the simulation of the system 3( rpm 3.(cm 3 rev) ( C ( m 3(W/mK) (mm) 9.(mm).(mm).9(m) (mm).9.. 3) 5(L) () 5( C) 7(W/m ) ( 3(m/s n V d v cm k T cond A C k P P D D i L W p g V w T wi T wo I T T a u W U L [] P (3) g N g

5 R3a [] = exp () R3a = ; 7 (3) = ; 7 () R3a 9. = exp ( (5) ); 7 =.75( ) ( ) () R3a EES [] R[] R R3a ASHRAE. ODP [] = (7) = ().55RGWP 3R3a 7 3 [] - Ozone Depletion Potential - Global Warming Potential :[7] = + ( ) + ( 5) :[] = ( ) V d n i = ( 7) k P P. cm / ( ) = = () ( ) (5 ) =. = (9) ( ) C w M w (). T wo T wi h T wi =T a. 5. h 3 t = ( 3 ). (5 ) () = () 3

6 T a (C) Fig. 3 Effect of ambient air temperature on the system performance n=3(rpm);i T =75(W/m A C.(m );T cond =5 (C) Simulated [] Measured Simulated C [] Measured C n=3 (rpm);t a =5.7 (C) A C. (m );T cond =5 (C) Simulated [] Measured Simulated C [] Measured C I T (W/m ) Fig. Effect of solar radiation intensity on the system performance C.5 C [] R R3a.[].. []. [].9. () ()

7 I T =7(W/m ); A C (m ) T a =( C);N g =.. C. C.. n=3(rpm);i T =7(W/m ) A C (m );N g = (rpm) Fig. Effect of compressor speed on the system performance C... C (W/m K).(W/m K) T e (C) Fig. 5 Effect of evaporating temperature on the system performance 5 I T =7(W/m ); A C (m ) T a =( C);n=3(rpm)N g = C T cond C) Fig. Effect of condensing temperature on the system performance..... C n=3 (rpm); I T =7 (W/m ) A C = (m ); T a = ( C) I =7(W/m ); T a =( C) n=3(rpm);n g =.. U L (W/m K) 3 Fig. 9 Effect of number of solar collector covers on the total heat loss coefficient of the collector 9 N g 3 5 A C (m ) Fig. 7 Effect of collector surface area on the system performance 7 C... C 539 3

8 Fig. Effect of number of solar collector covers on the system performance U L (W/m K) u (m/s) Fig. Effect of wind speed on total heat loss coefficient of the collector C 3 N g n=3(rpm);i =7(W/m ) A C (m );T a =( C);N g = n=3(rpm);i =7(W/m ) A C (m );T a =( C);N g = C u W (m/s) Fig. Effect of wind speed on the system performance C C (W/m K)

9 Fig. The average values of solar radiation and ambient temperature for the months of the year Q load (kwh) Fig. 5 The values of monthly required heat load and the system performance hours for the months of the year n=3(rpm);a C (m );N g.. C Months Requiredheat Systemperformance hours n=3(rpm);a C (m )N g Months..... C t(hr) Table Average monthly weather data for the Kermanshah u I T (W/m W (m/s) ) T a ( C) I T (W/m ) Solar radiation Ambient temperature Months Fig. 3 The values of solar radiation and ambient temperature for the months of the year T a (C) 539

10 (m 3 ) (cm 3 /rev) (m 3 /kg) (mm) (W) ) (mm) (kg/ms) (W/m K ) - cm Cond sat tp - [] P. Sporn, E. R. Ambrose, The heat pump and solar energy, Proceedings of the world symposium on applied solar energy, Phonix, Arizona, 955. [] W. W. S. Charter, L. E. Taylor, Some performance characteristics of a solar boosted heat pump, Proceeding of the International Institute of Refrigeration conference, Melbourne, Australia, 97. [3] H. L. Franklin, E. W. Saaski, A. Yamagiwa, A high efficiency direct expansion solar panel, Proceeding of flat plate solar collector conference, Orlando, Florida, 977. [] G. L. Morrison, Simulation of packaged solar heat-pump water heaters, Solar Energy, Vol. 53, No. 3, pp. 9-57, 99. [5] E. Torres Reyes, M. Picon Nuñez, de. GJ. Cervantes Exergy analysis and optimization of a solar-assisted heat pump, Energy, Vol. 3, No., pp , 99. [] S. K. Chaturvedi, D. T. Chen, A. Kheireddine, Thermal performance of a variable capacity direct expansion solar-assisted heat pump, Energy, Conversion and Management Vol. 39, No. 3-, pp. -9, 99. [7] B. J. Huang, J. P. Chyng, Performance characteristics of integral type solarassisted heat pump, Solar Energy, Vol. 7, No., pp. 3-,. [] Y. H. Kuang, R.Z. Wang, Performance of a multi-functional directexpansion solar-assisted heat pump system, Solar Energy, Vol., No. 7, pp , R3a (m ) (kj/kgk) (mm) (W/m K) /(kj/kg) (kj/kg) (W/m ) /(W/mK) (m) (kg) (kg/s) (rpm (kpa) (kwh (W (kj/kgk) ( C) (hr) (W/m K) (m/s) - 7 Re S 539

11 heat pump system, Applied Thermal Engineering, Vol. 73, No., pp. 5-5,. [] X. Q. Kong, D. Zhang, Y. Li, Q. M. Yang, Thermal performance analysis of a direct-expansion solar-assisted heat pump water heater, Energy, Vol. 3, No., pp. 3-3,. [7] J. A. Duffie, W. A. Beckman, Solar Engineering of Thermal Processes, th Edition, pp. 5-, New York: Wiley, 99. [] S. A. Klein, Calculation of flat plate collector loss coefficients, Solar Energy, Vol. 7, No., pp. 79-, 975. [9] J. H. Wattmu, W. W. S. Charters, D. Proctor, Solar and wind induced external coecients for solar collectors, Conference of the Mediterranean Cooperation for Solar Energy, Paris, Farance, 977. [] M. Altman, R. H. Norris, F. W. Staub, Local and average heat transfer and pressure drop for refrigerants evaporating in horizontal tubes, Heat Transfer, The American Society of Mechanical Engineers, Vol., No. 3, pp. 9-9, 9. [] A. C. Cleland, Polynomial curve-fits for refrigerant thermodynamic properties: extension to include R3a, Refrigeration, Vol. 7, No., pp. 5-9, 99. [] ASHRAE handbook refrigeration, Inch-Pound Edition ed., Atlanta, GA: the American Society of Heating, Refrigerating and Air-Conditioning Engineers,. [9] G. Xu, X. Zhang, S. Deng, simulation study on the operating performance of a solar air source heat pump water heater, Applied Thermal Engineering, Vol., No. -, pp. 57-5,. [] S. Ito, N. Miura, A comparison of heat pump systems using different types of direct expansion solar collectors, Proceeding of biennial congress of the International Solar Energy Society, Denver, Colorado, USA, 99. [] S. Ito, N. Miura, K. Wang, Performance of a heat pump using direct expansion solar collectors, Solar Energy, Vol. 5, No. 3, pp. 9-9, 999. [] H. Azarkish, A. Behzadmehr, M. H. Sarvari, Effect of dierent refrigerands on the performance of a solar assisted heat pump for heating a residential unit, Proceeding of th Annual Conference of Mechanical Engineering, Tehran, Iran,. (in Persian ) [3] M. Moradali, F. Jafarkazemi, Simulation study on the performance of a solar-assisted heat pump compared to a conventional heat pump, Proceeding of the th International Conference Heating Ventilation and Air Conditioning, Tehran, Iran,. (in Persian) [] A. Moreno-Rodriguez, N. Garcia-Hernando, A. González-Gil, M. Izquierdo, Experimental validation of a theoretical model for a direct-expansion solarassisted heat pump applied to heating, Energy, Vol., issue C, pp. -53, 3. [5] D. Zhang, Q. B. Wu, J. P. Li, X. Q. Kong, Effects of refrigerant charge and structural parameters on the performance of a direct-expansion solar-assisted 539