Evaluation of the coefficient of performance of an air source heat pump unit and an air to water heat pump

  • S. Tangwe Department of Electrical, Electronic and Computer Engineering, Faculty of Engineering, Built Environment and Information Technology, Central University of Technology, Free State, South Africa https://orcid.org/0000-0002-6936-9629
  • K. Kusakana Department of Electrical, Electronic and Computer Engineering, Faculty of Engineering, Built Environment and Information Technology, Central University of Technology, Free State, South Africa https://orcid.org/0000-0001-7663-4614
Keywords: vapour compression refrigeration cycle, coefficient of performance, energy optimisation, data acquisition system

Abstract

Air source heat pump (ASHP) water heaters are efficient devices for sanitary hot water heating. The coefficient of performance (COP) of the air to water heat pump (AWHP) is constantly lower than that of the corresponding ASHP unit. The study focused on determining the COP of both the ASHP unit and the AWHP. This was achieved by the implementation of both experimental and simulation methods, with the help of a data acquisition system and the REFPROP software. The system comprised of a 1.2 kW split type ASHP unit and a 150 L high pressure geyser. A power meter, flow meters, temperature sensors, pressure sensors, ambient temperature and relative humidity sensor were installed at precise locations on the split type AWHP. Controlled volumes of 150, 50 and 100 L were drawn off from the AWHP during the morning, afternoon and evening for a year. The average COP for the summer and winter, in terms of the input electrical and output thermal energies of the AWHP were 3.02 and 2.30. The COPs of the ASHP unit, in terms of the change in the enthalpies of the refrigerant at the inlet and the outlet of the condenser and the evaporator, were 3.52 and 2.65 respectively. The study showed that the difference between the COP of the ASHP unit and that of the AWHP could be ascribed to the electrical energy consumed by the fan and the water circulation pump during the vapour compression refrigeration cycles. The work provides an energy optimisation opportunity to the manufacturers of this technology, helping to enhance the efficiency and COP of ASHP water heaters.

Highlights
  1. The COPt of the ASHP unit was higher than the COPe of the AWHP.
  2. The COPe of the AWHP was the ratio of the input electrical energy consumed and the output thermal energy gained by the stored water.
  3. The COPt of the ASHP unit was enthalpies-dependent and a function of inlet and outlet enthalpies of the evaporator and condenser.
  4. The inlet and outlet refrigerant temperatures profiles of the condenser confirmed thermal energy dissipation.

Author Biographies

S. Tangwe, Department of Electrical, Electronic and Computer Engineering, Faculty of Engineering, Built Environment and Information Technology, Central University of Technology, Free State, South Africa

Dr  Stephen Tangwe  is a postdoctoral research fellow at the department of Electrical, Electronic and Computer Engineering, faculty of Engineering Built Environment and Information Technology, Central University of Technology. He is a Chartered Engineer and a Member of the Institution of Mechanical Engineers (CEng MIMechE) and also a CMVP and an energy expert. He holds a PhD in Engineering from the  University of Sunderland in the United Kingdom at the  faculty of Technology, school of Engineering and Advanced Manufacturing. He also holds a Postgraduate Diploma in Renewable energy from Teri School of Advanced Studies in New Delhi, India. He is an IEEE, AEE, SAEE and also an IEEE Power and Energy society member. He is an  adhoc Eskom M&V Engineer with the UFH team. He is also a researcher in energy efficiency and a MATLAB application Engineer. He is a seasoned author and reviewer in accredited peer review Journals. Email: lstephen@cut.ac.za; Tel: 0783076922

K. Kusakana, Department of Electrical, Electronic and Computer Engineering, Faculty of Engineering, Built Environment and Information Technology, Central University of Technology, Free State, South Africa

Prof K. Kusakana (DTech, Pr.Eng, and CEM) is a NRF rated researcher. His research interests are power and energy systems, energy management, renewable and alternative energies. He is currently a Professor and Head of the Electrical, Electronic and Computer Engineering Department at Central University of Technology. He is a seasoned Author and reviewer in a series of DHET accredited peer review journals and conference proceedings with high impact factors.

References

[1] Swan, L.G. and Ugursal, V.I., 2009. Modeling of end-use energy consumption in the residential sector: A review of modeling techniques. Renewable and Sustainable Energy Reviews, 13(8): 1819-1835.
[2] Rousseau, P.G. and Greyvenstein, G.P., 2000. Enhancing the impact of heat pump water heaters in the South African commercial sector. Energy, 25(1): 51-70.
[3] Tangwe, S., Simon, M. and Meyer, E., 2014. Mathematical modeling and simulation application to visualize the performance of retrofit heat pump water heater under first hour heating rating. Renewable Energy, 72: 203-211.
[4] Chua, K.J., Chou, S.K. and Yang, W.M., 2010. Advances in heat pump systems: A review. Applied Energy, 87(12): 3611-3624.
[5] Hepbasli, A. and Kalinci, Y., 2009. A review of heat pump water heating systems. Renewable and Sustainable Energy Reviews, 13(6-7): 1211-1229.
[6] Morrison, G.L., Anderson, T. and Behnia, M., 2004. Seasonal performance rating of heat pump water heaters. Solar Energy, 76(1-3): 147-152.
[7] Bodzin, S., 1997. Air-to-water heat pumps for the home. Home Energy, 14(4):1-120 .
[8] Xu, G., Zhang, X. and Deng, S., 2006. A simulation study on the operating performance of a solar–air source heat pump water heater. Applied Thermal Engineering, 26(11-12): 1257-1265.
[9] Peng, J.W., Li, H. and Zhang, C.L., 2016. Performance comparison of air-source heat pump water heater with different expansion devices. Applied Thermal Engineering, 99: 1190-1200.
[10] Tangwe, S.L., Simon, M. and Mhundwa, R., 2018. The performance of split and integrated types air-source heat pump water heaters in South Africa. Journal of Energy in Southern Africa, 29(2): 12-20.
[11] Kamel, R.S., Fung, A.S. and Dash, P.R., 2015. Solar systems and their integration with heat pumps: A review. Energy and Buildings, 87: 395-412.
[12] Staffell I, Brett D, Brandon N, Hawkes A., 2012. A review of domestic heat pumps. Energy & Environmental Science. 5(11): 9291-306.
[13] Vieira, A.S., Stewart, R.A. and Beal, C.D., 2015. Air source heat pump water heaters in residential buildings in Australia: Identification of key performance parameters. Energy and Buildings, 91: 148-162.
[14] Guo, X. and Goumba, A.P., 2018. Air source heat pump for domestic hot water supply: Performance compari-son between individual and building scale installations. Energy, 164: 794-802.
[15] Ashdown, B.G., 2004. Heat pump water heater technology: Experiences of residential consumers and utilities (No. ORNL/TM-2004/81).
[16] Sinha, S.K. and Dysarkar, A., 2008. United States patent application: Heat pump liquid heater. Available on http://appft1. uspto. gov/netacgi/nphas on: 19-04.
[17] Lemmon, E.W., Huber, M.L. and McLinden, M.O., 2010. NIST Standard Reference Database 23, Reference Fluid Thermodynamic and Transport Properties (REFPROP), version 9.0, National Institute of Standards and Tech-nology. R1234yf. fld file dated December, 22: 2010.
[18] De Monte, F., 2002. Calculation of thermodynamic properties of R407C and R410A by the Martin-Hou equa-tion of state — Part II: Technical interpretation. International Journal of Refrigeration, 25(3): 314-329.
[19] De Swartdt, C.A., Meyer, J.P. 2001. A performance comparison between an air source and a ground source reversible heat pump. International Journal of Energy Research, 25: 899–910.
[20] Urchueguía, J.F., Zacarés, M., Corberán, J.M., Montero, A., Martos, J. and Witte, H., 2008. Comparison between the energy performance of a ground coupled water to water heat pump system and an air to water heat pump system for heating and cooling in typical conditions of the European Mediterranean coast. Energy Conversion and Management, 49(10): 2917-2923.
[21] Congedo, P.M., Baglivo, C., Bonuso, S. and D’Agostino, D., 2020. Numerical and experimental analysis of the energy performance of an air-source heat pump (ASHP) coupled with a horizontal earth-to-air heat exchanger (EAHX) in different climates. Geothermics, 87: 101845.
[22] Wang, X., Xia, L., Bales, C., Zhang, X., Copertaro, B., Pan, S. and Wu, J., 2020. A systematic review of recent air source heat pump (ASHP) systems assisted by solar thermal, photovoltaic and photovoltaic/thermal sources. Renewable Energy, 146: 2472-2487.
Views
  • Abstract 72
  • pdf 53
Views and downloads are with effect from 11 January 2018
Published
2021-02-18