...AND CHEAPER...:

Yu's idea is one of several recent innovations that aim to make 200-year-old heat pump technology even more efficient than it already is, potentially opening the door for much greater adoption of heat pumps worldwide. To date, only about 10 percent of space heating requirements around the world are met by heat pumps, according to the International Energy Agency (IEA). But due to the current energy crisis and growing pressure to reduce fossil fuel consumption in order to combat climate change, these devices are arguably more crucial than ever.

Since his 2020 lockdown brainstorming, Yu and his colleagues have built a working prototype of a heat pump that stores leftover heat in a small water tank. In a paper published in the summer of 2022, they describe how their design helps the heat pump to use less energy. Plus, by separately rerouting some of this residual warmth to part of the heat pump exposed to cold air, the device can defrost itself when required, without having to pause heat supply to the house.

The idea relies on the very principle by which heat pumps operate: If you can seize heat, you can use it. What makes heat pumps special is the fact that instead of just generating heat, they also capture heat from the environment and move it into your house -- eventually transferring that heat to radiators or forced-air heating systems, for instance. This is possible thanks to the refrigerant that flows around inside a heat pump. When the refrigerant encounters heat -- even a tiny amount in the air on a cold day -- it absorbs that modicum of warmth.

A compressor then forces the refrigerant to a higher pressure, which raises its temperature to the point where it can heat your house. It works because an increase of pressure pushes the refrigerant molecules closer together, increasing their motion. The refrigerant later expands again, cooling as it does so, and the cycle repeats. The entire cycle can run in reverse, too, allowing heat pumps to provide cooling when it's hot in summer.

The magic of a heat pump is that it can move multiple kilowatt-hours of heat for each kWh of electricity it uses. 

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