In-Use Performance of Air-to-Water Heat Pumps: are the Standards robust?

Abstract

This paper presents an energy performance comparison of air to water heat pump manufacturer quoted values, calculated seasonal performance values from standards and actual in-use values for space heating mode only. Within this, the paper determines whether an in-use factor would be suitable to correct performance predictions where differences exist. The paper also presents an in-use Carnot efficiency. Over five weeks of high-resolution data during winter and shoulder season conditions were collected and analysed for three different systems. The average in-use Carnot efficiency was found to vary largely from system to system (0.19 to 0.42). All heat pumps were found to underperform on average with respect to their standardised energy performance certificate values. The difference between standardised values and in-use values was between 11% and 53% in relative terms. The gap in performance is thought to be due to oversized or under-utilised systems. Standardised methodologies appear unable to capture potential under-performance in these types of systems. An in-use factor appeared to be an inappropriate approach in reflecting this difference. Further investigations are required to incorporate these risks into standards.