SR414 Heat pump performance (November 2018)

Heat pumps started to become popular in the mid-2000s, and around 38% of homes had a heat pump by 2015. Heat pump technology has been promoted as being highly energy efficient, but there is often conflicting advice on how best to operate a heat pump and variable information on how much electricity it will use.

Heat pump performance is not a fixed factor and depends on:

• indoor and outdoor temperatures when it is operating
• what additional energy use is involved, such as use of the defrost system
• system loading – performance will be reduced if the heat pump only operates in demanding conditions, such as being used to heat cold rooms on cold mornings.

A household from the earlier heat pumps study (SR329) was examined. This household changed how they used their heat pump half-way through winter, going from intermittent use (turning on for an hour in the morning and evening) to leaving the heat pump on continuously. The amount of time the room was cooler than 16°C fell from 38% of the time to less than 4% and required no additional electricity to run the heat pump.

Whether it is favourable in general to leave a heat pump on continuously is not well understood. There is a trade-off between improved operating efficiency from continuously operating a heat pump and the additional heat losses from having a warm room for a greater proportion of the time. This type of trade-off is well suited to being examined using simulation tools that allow for many variations of climate, household insulation level and heat pump scheduling to best understand how to operate a heat pump efficiently. Simulation tools promise to be an important technique to examine heat pump performance, and further work in this area would be beneficial.