Heat pumps

2021-02-01

in Economics, The environment

David Mackay’s Sustainable Energy — Without the Hot Air emphasizes heat pumps as a decarbonization tool:

Notice that heat pumps offer a system that can be “better than 100%- efficient.” For example the “best gas” power station, feeding electricity to heat pumps can deliver a combination of 30%-efficient electricity and 80%- efficient heat, a “total efficiency” of 110%. No plain CHP [combined heat and power — where waste heat from energy production is used for heating] system could ever match this performance.

Let me spell this out. Heat pumps are superior in efficiency to condensing boilers, even if the heat pumps are powered by electricity from a power station burning natural gas. If you want to heat lots of buildings using natural gas, you could install condensing boilers, which are “90% efficient,” or you could send the same gas to a new gas power station making electricity and install electricity-powered heat pumps in all the buildings; the second solution’s efficiency would be somewhere between 140% and 185%. It’s not necessary to dig big holes in the garden and install underfloor heating to get the benefits of heat pumps; the best air-source heat pumps (which require just a small external box, like an air-conditioner’s) can deliver hot water to normal radiators with a coefficient of performance above 3.

There is also some evidence now that US house owners are sufficiently mindful about long-term energy costs to see their economic advantages reflected in house prices. In Nature Energy Xingchi Shen et al. conclude: “Residences with an air source heat pump enjoy a 4.3–7.1% (or US$10,400–17,000) price premium on average.” (See also)

Some of the usual impediments to environmental retrofits apply here. You generally need to pay for the system up front and then recoup savings over a long period, which means you need to be able to finance it initially. Also, there can be a lack of coordination between renters, landlords, and building owners. Still, technologically heat pumps are promising and we need non-fossil alternatives for building heating and cooling.

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