The energy performance of air source heat pump water heaters decays with increasing time due to improper operation and maintenance. In this paper, a quantitative study is conducted on the energy performance decay of air source heat pump water heaters and the potential improvement of long-term energy performance. First, the energy performance decay of five heating systems in Shanghai was studied on site. The results showed that the Annual Performance Factor of the air source heat pump water heaters
decayed by 5%-6% per year during the first six years of operation. Then, a Service Life Cycle Performance Factor model was proposed for further evaluation of the long_x0002_term energy performance. Case studies combined with simulations showed that the Service Life Cycle Performance Factor could be improved by 8.0% to 12.2%.
Keywords Air source heat pump water heaters, Long_x0002_term energy performance, Energy performance decay, Field test, Optimization