Understanding the drivers affecting the in-situ performance of domestic heat pumps in the UK.
Doctoral thesis (Ph.D), UCL (University College London).
The UK Government views heat pumps (HPs) as an increasingly important technology able to contribute significantly towards the decarbonisation of domestic stock, with the Government committing to the annual installation of 600,000 HPs by 2028. However, there appears to be a performance gap between predicted and real-life HP performance. A number of studies have highlighted several possible causes of the performance gap but have not investigated these in a structured way. Given the important role of HPs in a Net Zero future and the potential to improve their performance, the aim of this study is to characterise the socio-technical parameters affecting heat pump performance in the field and discuss the implications for their future take up in the UK.
A sample of 21 case studies were selected from 700 domestic HPs monitored across the UK via the government’s Renewable Heat Premium Payment Scheme for the collection of qualitative and quantitative socio-technical data. The data collection process involved in-depth interviews and direct observational methods. The collected material was inductively analysed and corroborated with pre-visit material, including monitored HP performance data. Using systems thinking as an integrating framework, the results were fed into a series of interlinked causal loop diagrams, specifically focusing on the parameters and feedback processes that are likely to be linked to poor HP performance.
The systems model revealed complex mechanisms that are likely to influence HP performance in seven interconnected areas relating to the (i) household space heating practices (ii) household domestic hot water heating practices, (iii) bill affordability, (iv) ventilation patterns and indoor humidity, (v) building thermal characteristics, (vi) technical characteristics of the installation and (vii) technical problem resolution and control optimisation processes. These impact HP performance through different, direct, and indirect paths, the majority of which converge at two points, namely HP space heating demand and continuity of HP operation. The systems analysis identified four leverage points, i.e., places to intervene within a complex system, where small shifts can cause a big impact: ensuring both quality installations and appropriate control through behavioural change, allowing the incorporation of smart controls, carefully reconsidering the rules governing the HP installations and enabling system feedback.
The findings have important implications for policy makers, HP manufacturers and installers by identifying barriers to the performance of domestic HPs in the field. This work can inform future HP related government schemes and incentives, installer, and manufacturer standards, as well as the installation and monitoring practices of future field trials.
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