83 homes participated in the study, which investigated the factors that impact heat pump performance and how performance could be improved.
The Energy Saving Trust’s (EST) heat pump field trial, conducted as two phases between 2008 and 2013, presents reliable data on the in-situ performance of both air and ground-source heat pumps in UK homes.
Comprehensive monitoring was carried out at 83 households for Phase I. Detailed analysis investigated the factors that affect performance was published in March 2012. As a result of this detailed analysis, the Microgeneration Certification Scheme installation standards for heat pumps were improved and the new version came into force in March 2012.
For Phase II of the trial, 38 of the heat pumps from Phase I were selected for a range of interventions, from major (for example, re-sizing the heat pump) to minor (for example altering control parameters). Six new heat pumps, sized and designed according to the new MCS MIS 3005 Issue 3.1 standards, were also monitored.
There are many different definitions of “performance” depending on which electrical components are included; where possible, data from the second phase has been examined in detail to provide as many of these different metrics as possible, denoted SPFH1-H4 and “system efficiency”).
The results show that:
- There were significant improvements in performance at all but three of the sites which received major or medium interventions. Minor interventions had little effect on performance.
- 20 out of 21 ground-source heat pumps in the trial met or exceeded the performance criterion to be considered “renewable” under the EU Renewable Energy Sources Directive The figure for air-source was 9 out of 15. It is important to remember that many of these heat pumps were installed before the new MCS standards came into force; five of the six new air-source heat pumps, installed and designed to these standards, met the renewability criterion.
- DECC considers the most useful measure of performance for the householder to be SPFH4, weighted over both space and water heating. This is a comprehensive metric that takes account of all electricity used by the heating system including the auxiliary heater, domestic hot water immersion and building circulation pumps. According to this metric, the average performance was 2.82 for the ground-source heat pumps in the trial and 2.45 for the air-source heat pumps in the trial.
As a result of the Phase II analysis, DECC and EST are continuing to work with industry and the Microgeneration Certification Scheme to further improve standards and training. DECC has also incorporated lessons learned from this trial into its design of the domestic Renewable Heat Incentive policy - for example, by providing an additional incentive for householders to install metering and monitoring packages so that they know how much energy their heat pump is consuming.
The Energy Saving Trust’s report can be found on the EST website