Heat pumps#
Heat pumps can take heat from the ground or the air and heat your building by using the same kind of technology as refrigerators, but in reverse. Ground source heat pumps always heat water and use that to heat the building. Air source heat pumps can heat water, but they can also heat the air in the building directly. Because they produce a lower temperature than a boiler, they are usually run for long periods. That means they suit buildings in high occupancy, although long slow heating is also good for using thick stone walls as a store of heat, and, for instance, the Church of England has case studies showing a heat pump used for a church in less frequent use.
The upfront costs of installing a heat pump are relatively high. The UK Government aspires to help industry make heat pumps cost the same as boilers by 2030. Meanwhile, there are often generous grants available to those who want to install them now.
Unlike public perceptions, heat pumps do work (even in Scotland!) but they have to be designed for the building and installed and configured correctly. There is a skills shortage for installing them, so many installers don’t have much experience. At a bare minimum, you want to be dealing with people who are MCS accredited. Community buildings are trickier than most homes, so you also want people who have been around for a while and have experience with buildings like yours and case studies or clients who can vouch for them. The good installers tend to monitor the performance of the systems they put in so they can learn from experience. Really good installers often manage to make installs 4-5 times as effficient as using electricity directly to heat the building. This is important because gas is so much cheaper than electricity. With a poor installer, your running costs could be higher with the heat pump, especially if you still have a gas supply so have to pay the standing charge still.
Ground source heat pumps are relatively expensive and require a reasonable amount of space to install - either several hundred square meters of land or the right underlying geology and access for drilling equipment that can lay pipes vertically. It can be expensive to fix if anything goes wrong with the pipes.
Air source heat pumps (ASHP) designed for commercial premises can also be very expensive. That means larger community buildings often need to install 2 or 3 domestic models, each about the size of a large suitcase, or to combine an ASHP with another source of heating, either temporarily or permanently. This is not practical in some buildings but has some advantages. If an air source heat pump happens to run its defrost cycle when the space is in use, the building might cool and take a while to come back to temperature - but with more than one pump, it’s unlikely to happen to both at the same time. Also, if one pump breaks down, at least there’s still some heat.
How easy it is to put a heat pump in depends on the building.
For pumps that heat water, if your radiators are big enough, you might be able to get away with using them, but often venues need bigger ones. Even if your radiators will work, your pipework might be too narrow to deliver the water fast enough. Changing to underfloor heating gives better results and better comfort for lower energy input, especially for lossy buildings in high use. Everyone likes warm feet!
It’s best to address heat loss first because then you can get away with a smaller heat pump, but you can think about staging works instead of doing everything in one go if that helps. You might, for instance, put in an air-to-air heat pump and use it most of the time, topping up with the old gas system when it’s really cold or until you’ve addressed heat loss better. This might help if you’re unsure whether you want to use radiant heating or another pump for the rest of the heating. Or if you’ll need it, you could put in underfloor heat distribution (and insulation!) when your floors need renewing anyway, and the heat pump later on.
The industry’s understanding of how to deal with older buildings is changing all the time. Some of the best performing heat pumps are in buildings with massive stone walls and roof insulation, but missing wall insulation, which used to be considered a must.
More information
The air to air case studies uses relatively large pumps to heat the air just enough to make people comfortable for an hour of use without running the pumps all the time. As a community we need a better understanding of when to choose radiant heating or heated seated versus when to take this approach.