A method for the seasonal performance rating of a residential water heating heat pump

Abstract

To save electricity in the South African residential market, energy efficient air source water heating heat pumps have been widely implemented in combination with conventional hot water storage vessels, also known as geysers. The performance of these heat pump installations are significantly influenced by seasonal changes in the surrounding ambient conditions as well as the municipal water supply temperature. As heat pumps are designed and built by different manufacturers, differences in terms of the sub-components used and their specifications are common. As a result, each heat pump model must be tested to determine its energy saving capabilities. From the literature review it became evident that very little research has been done world-wide on the performance verification of residential heat pump water heaters. It was further found that there are currently no standard for the performance testing of a residential heat pump water heater in South Africa. The aim of this study was therefore to research and develop a laboratory testing methodology that will accurately represent a residential heat pump’s in-field performance taking into account the seasonal influences on these systems. In order to reach this objective, the seasonal performance of air source water heating heat pumps were measured and reviewed for different climate regions in South Africa. The measured data was then used to generate general performance curves at different ambient conditions. The performance curves were verified and validated with laboratory tests as well as a Flownex® SE simulation model. The results were then used to determine which factors must be included in a laboratory test to accurately represent the in-field performance. Based on this a proposed laboratory testing methodology was developed.