Heat demand characterisation for heat pump retrofit

Utilising heat pump technology is one of the main recognised solutions for transition to cleaner heat in the UK (DESNZ, 2023). By switching from natural gas boilers to electrical heat pump technologies, questions of performance (e.g., efficiency, comfort expectations, lifespan) are raised. Current practices associated with gas boiler driven heat systems undermine some of these performance issues. Oversizing of the gas boilers is, for example, a well noted practice (Bennett G, and Elwell C., 2020) that whilst having limited detrimental impact on these ’traditional’ heating systems, it can significantly undermine heat pump system performances. Therefore, a simple ‘like-for-like’ sizing of heat pumps during boiler replacement can lead to oversizing issues that would mean unnecessary financial investment, lower system efficiency and short cycling behaviours that reduce heat pump life expectancy. Correct sizing, through detailed examination of real heat demand, is a fundamental requirement for the success of transition from boilers to heat pumps.

Despite the availability of Energy Performance Certificates (EPCs), the estimated annual energy performance expressed in the EPCs cannot be used for sizing of the heating systems. The dynamics of heat demand must be understood so that a range of heat demand characteristics can be used to evaluate system options (e.g., peak load, heat storage potential, diurnal profile, etc.). This study aims to critically evaluate the application and robustness of existing heat demand estimation approaches and propose a roadmap for estimation of heat demand for replacement of gas boilers with heat pump technologies.

References:
DESNZ (2023). Heat Pump Investment Roadmap. The Department for Energy Security and Net Zero. London.
Bennett G, Elwell C. (2020). Effect of boiler oversizing on efficiency: a dynamic simulation study. Building Services Engineering Research & Technology.;41(6):709-726.