Using statistical tests to compare the coefficient of performance of air source heat pump water heaters




Air source heat pump (ASHP) water heater, Coefficient of performance (COP), p-value, Significance level, one-way ANOVA test and Kruskal-Wallis test


The study compared the coefficient of performance (COP) of two residential types of air source heat pump (ASHP) water heaters using statistical tests. The COPs were determined from the controlled volume of hot water (150, 50 and 100 L) drawn off from each tank at different time of use (morning, afternoon and evening) periods during summer and winter. Power meters, flow meters, and temperature sensors were installed on both types of ASHP water heater to measure the data needed to determine the COPs. The results showed that the mean COPs of the split and integrated type ASHP water heaters were 2.965 and 2.652 for summer and 2.657 and 2.202 for winter. In addition, the p-values of the groups COPs for the split and integrated type ASHP water heaters during winter and summer were 7.09 x 10-24 and 1.01 x 10-11, based on the one-way ANOVA and the Kruskal-Wallis tests. It can be concluded that, despite the year-round performance of both the split and integrated type ASHP water heaters, there is a significant difference in COP at 1% significance level among the four groups. Furthermore, both statistical tests confirmed these outcomes in the comparisons of the mean COPs among the four groups based on the multiple comparison algorithm.



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Author Biographies

S. Tangwe, 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:; Tel: 0783076922

K. Kusakana, Central University of Technology, Free State, South Africa

Author: 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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How to Cite

Tangwe, S., & Kusakana, K. (2022). Using statistical tests to compare the coefficient of performance of air source heat pump water heaters. Journal of Energy in Southern Africa, 33(1), 40–51.