Evaluating the Performance of Individual vs. Communal Domestic Ground Source Heat Pumps

As the UK government moves toward decarbonizing heat, Ground Source Heat Pumps (GSHPs) have emerged as a promising yet under-researched technology, offering cleaner heat than gas boilers and potentially more efficient heat compared to Air Source Heat Pumps.

In the UK, two main types of GSHP systems are used to heat homes: individual GSHPs, where each home has its own ground loop, and communal GSHPs, where multiple homes share a single ground loop. This article presents the findings of an analysis comparing the performance of these two types of GSHP systems based on monitored data from 27 sites provided by Energy System Catapult. Here we define performance as the Seasonal Performance Factor (SPF) calculated over the period December 2021 to February 2022. The analysis, based on data, focused on the an indicator of system efficiency equals to energy generated divided by electricity input. Although the sample size is small some useful insights were obtained as follows:

Key Findings

1. Superior Performance of Individual GSHPs: In this sample, individual GSHPs generally outperformed communal GSHPs. The mean SPFH4 for individual GSHPs is 3.5 which means that for every unit of electricity used, the system can generate 3.5 units of heat, reflecting its high efficiency.
2. Communal GSHPs have lower mean SPFH4 of 2.8, which means they generally perform worse compared to Individual GSHPs. However, two blocks of communal systems are present in the dataset showing a significant performance difference to each other, with the better performing block (in the postcode NE3) achieving an SPFH4 of up to 3.1. Therefore, although communal GSHPs generally perform worse, there is considerable potential for improvement.
3. Lower flow temperature, better performance. This applies to both space heating flow temperature and water heating flow temperature. 
4. The refrigerants used in the heat pumps may also have played a crucial role in performance. Systems using R410A refrigerant outperformed those using R134A. This suggests that R410A’s higher critical pressure enables the system to maintain a larger pressure difference between the evaporator and condenser, resulting in more efficient heat transfer. However, R410A has a higher Global Warming Potential (GWP). Thus, the balance between efficiency and environmental impact still requires further research.
5. Heat pumps operating for less than 14 hours per day show better performance, with an average SPFH4 of 3.30. In contrast, those running for more than 14 hours per day have a lower performance, with an average SPFH4 2.81. (In this context, a heat pump is considered to be working whenever its energy output is greater than zero.). There could be several reasons for this finding, as the interaction between heat pump sizing, demand, operation mode and efficiency is complex.

Our recommendations

Given the performance difference between individual and communal systems, heat pump manufacturers should focus on several key areas for improvement. They could invest more in refrigerant replacement to improve both environmental impact and heat transfer efficiency. Binary refrigerants, which combine the thermodynamic advantages of two refrigerants, may be a promising option. More accurate MCS estimations would also help ensure the installation of appropriately sized heat pumps, further improving efficiency. Other factors, such as optimizing flow temperature and adjusting working hours to reduce energy consumption without compromising performance, needs to be further investigated. Finally, exploring innovations in ground loop design and improving insulation can also contribute to closing the performance gap between communal and individual GSHP systems.

Images and additional information

• SPF is defined as the ratio of heat output to electricity input. This article presents the findings at the H4 boundary, which includes heat and electricity from sources other than the heat pump compressor
• NE3 and KT18 are two subgroups of communal GSHPs named by their postcodes.

Authors

• Dr. Jenny Crawley, Senior Research Fellow, UCL Energy Institute
• Winston Zhang, Undergraduate Student, UCL Energy Institute