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

Authors

  • 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

DOI:

https://doi.org/10.17159/2413-3051/2021/v32i1a7935

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.

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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.

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Published

2021-02-18

Issue

Vol. 32 No. 1 (2021): Journal of Energy in Southern Africa

Section

Articles

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Copyright (c) 2021 S. Tangwe, K. Kusakana

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This work is licensed under a Creative Commons Attribution-ShareAlike 4.0 International License.

How to Cite

Evaluation of the coefficient of performance of an air source heat pump unit and an air to water heat pump. (2021). Journal of Energy in Southern Africa, 32(1), 27-40. https://doi.org/10.17159/2413-3051/2021/v32i1a7935