Earth Notes: To Zone or Not to Zone When Retrofitting a UK Heat Pump (2024)

TL;DR

Paper Abstract

Domestic heating systems across northern Europe are responsible for a substantial fraction of their countries' carbon footprints. In the UK, the vast majority of home space heating is via natural gas boilers with 'wet' hydronic radiator systems. Most of those use TRVs (thermostatic radiator valves) for micro-zoning, to avoid overheating, improve comfort and save energy. To meet Net Zero targets, 20 million such UK gas systems may be retrofitted with heat pumps. Heat pump system designers and installers are cautious about retaining TRVs in such systems in part because of worries that TRV temperature setbacks that lower heat demand may raise heat pump electricity demand in a "bad setback effect", thus wasting energy. This paper presents a new view of heat pump control and provides the first exploration of this issue through the development of a simple physics-based model. The model tests an installation industry claim about the negative effect of TRVs, and finds that though real it should not apply to typical UK retrofits with weather compensation. The energy efficiency benefits of TRVs for older and partly occupied homes, and to keep bedrooms cooler, remain valid. Comfort-seeking householders and installers should know that setting 'stiff' temperature regulation may invoke the bad setback effect and cost dearly in energy and carbon footprint.

Read the Paper

Online free To Zone or Not to Zone When Upgrading a Wet Heating System from Gas to Heat Pump for Maximum Climate Impact: A UK View and PDF [hart-davis2024zone].

Read the Press

• 2025-01-10: Heat Pumps and TRVs — What installers need to know: A recent study by Damon Hart-Davis, Lirong Liu and Matthew Leach found that in most cases where installers are retrofitting heat pumps in UK properties, TRVs can offer significant comfort benefits, and the risk of increased energy consumption can be managed with proper control strategies in place. [sharpe2025TRVs].
• 2024-05-31: The rise of Heat Geek — a startup hell-bent on bringing heat pumps to the Brits: Among those impressed by his understanding of heating system technology is Damon Hart-Davis, a PhD candidate at the University of Surrey. He recently wrote a research paper on something occasionally discussed by Chapman in some of his videos — briefly, that turning off the heating in one room in a house can, in some scenarios, be less efficient overall than if you just heat every room. "I thought, ‘Oh, this can't be right, I shall prove him wrong'," recalls Hart-Davis. But the modelling instead validated Heat Geek's analysis, given certain conditions. "That is really surprising," says Hart-Davis. [baraniuk2024HeatGeek]