Performance of a Transcritical CO2 Heat Pump for Simultaneous Water Cooling and Heating

Authors: J. Sarkar, Souvik Bhattacharyya, M. Ramgopal

Abstract:

This paper presents the experimental as well as the simulated performance studies on the transcritical CO2 heat pumps for simultaneous water cooling and heating; effects of water mass flow rates and water inlet temperatures of both evaporator and gas cooler on the cooling and heating capacities, system COP and water outlets temperatures are investigated. Study shows that both the water mass flow rate and inlet temperature have significant effect on system performances. Test results show that the effect of evaporator water mass flow rate on the system performances and water outlet temperatures is more pronounced (COP increases 0.6 for 1 kg/min) compared to the gas cooler water mass flow rate (COP increases 0.4 for 1 kg/min) and the effect of gas cooler water inlet temperature is more significant (COP decreases 0.48 for given ranges) compared to the evaporator water inlet temperature (COP increases 0.43 for given ranges). Comparisons of experimental values with simulated results show the maximum deviation of 5% for cooling capacity, 10% for heating capacity, 16% for system COP. This study offers useful guidelines for selecting appropriate water mass flow rate to obtain required system performance.

Keywords: CO2 heat pump, experiment, simulation, performance characteristics.

Digital Object Identifier (DOI): doi.org/10.5281/zenodo.1077255

References:

[1] P. Neksa, "CO2 heat pump systems," Int. Journal of Refrigeration, vol. 25, no. 4, pp. 421-427, June 2002.
[2] M. H. Kim, J. Pettersen, and C. W. Bullard, "Fundamental process and system design issues in CO2 vapor compression systems," Progress in Energy and Combustion Science, vol. 30, no. 2, pp. 119-174, 2004.
[3] P. Neksa, H. Rekstad, G. R. Zakeri, and P. A. Schiefloe, "CO2 heat pump water heater: characteristics, system design & experimental results," Int. Journal of Refrigeration, vol. 21, no. 3, pp. 172-179, May 1998.
[4] S. D. White, M. G. Yarrall, D. J. Cleland, and R. A. Hedley, "Modelling the performance of a transcritical CO2 heat pump for high temperature heating," Int. Journal of Refrigeration, vol. 25, no. 4, pp. 479-486, June 2002.
[5] M. G. Yarral, S. D. White, D. J. Cleland, R. D. S. Kallu, and R. A. Hedley, "Performance of transcritical CO2 heat pump for simultaneous refrigeration and water heating," XX Int. Congress of Refrigeration, Sydney, 1999, Paper no. 651.
[6] W. Adriansyah, "Combined air conditioning and tap water heating plant using CO2 as refrigerant," Energy and Buildings, vol. 36, no. 7, pp. 690- 695, July 2004.
[7] J. Stene, "Residential CO2 heat pump system for combined space heating and hot water heating," Int. Journal of Refrigeration, vol. 28, no. 8, pp. 1259-1265, Dec. 2005.
[8] H. Cho, C. Ryu, Y. Kim, and H. Y. Kim, "Effects of refrigerant charge amount on the performance of a transcritical CO2 heat pump," Int. Journal of Refrigeration, vol. 28, no. 8, pp. 1266-1273, Dec. 2005.
[9] S. G. Kim, Y. J. Kim, G. Lee, and M. S. Kim, "The performance of a transcritical CO2 cycle with an internal heat exchanger for hot water heating," Int. Journal of Refrigeration, vol. 28, no. 7, pp. 1064-1072, Nov. 2005.
[10] J. Sarkar, S. Bhattacharyya, and M. Ramgopal, "Simulation of a transcritical CO2 heat pump cycle for simultaneous cooling and heating applications," Int. Journal of Refrigeration, vol. 29, no. 5, pp. 735-743, Aug. 2006.
[11] R. Yokoyama, T. Shimizu, K. Ito, and K. Takemura, "Influence of ambient temperatures on performance of a CO2 heat pump water heating system," Energy, vol. 32, no. 4, pp. 388-398, Apr. 2007.
[12] R. Cabello, D. Sa'nchez, R. Llopis, and E. Torrella, "Experimental evaluation of the energy efficiency of a CO2 refrigerating plant working in transcritical conditions," Applied Thermal Engineering, vol. 28, no. 13, pp. 1596-1604, Sep. 2008.
[13] J. Sarkar, S. Bhattacharyya, and M. RamGopal, "Optimization of a transcritical CO2 heat pump cycle for simultaneous cooling and heating applications," Int. Journal of Refrigeration, vol. 27, no. 8, pp. 830-838, Dec. 2004.
[14] S. S. Pitla, E. A. Groll, and S. Ramadhyani, "New correlation to predict the heat transfer coefficient during in-tube cooling of turbulent supercritical CO2," Int. Journal of Refrigeration, vol. 25, no. 6, pp. 887- 895, Sep. 2002.
[15] X. Fang, C. W. Bullard, and P. S. Hrnjak, "Heat transfer and pressure drop of gas coolers," ASHRAE Transactions, vol. 107, pp. 255-266, 2001.
[16] V. Gnielinski, "New equations for heat and mass transfer in turbulent pipe and channel flow," Int. Chemical Engineering, vol. 16, pp. 359- 366, 1976.
[17] S. H. Yoon, E. S. Cho, Y. W. Hwang, M. S. Kim, K Min, and Y. Kim, "Characteristics of evaporative heat transfer and pressure drop of carbon dioxide and correlation development," Int. Journal of Refrigeration, vol. 27, no. 2, pp. 111-119, Mar. 2004.
[18] D. S. Jung, and R. Radermacher, "Prediction of pressure drop during horizontal annular flow boiling of pure and mixed refrigerants," Int. Journal of Heat Mass Tran., vol. 32, no. 12, 2435-2466, Dec. 1989.