In light of the urgency to phase out the use of fossil fuels by 2050 the search is on for alternative effective and ecologically sound methods to provide heat and hot water to our homes.
One of the methods being strongly encouraged by the government is the use of heat pumps. These systems transfer heat from the air or ground or water into a liquid (usually water with antifreeze) which is then compressed to increase the temperature to a level warm enough to provide heat and hot water to a property. It may help to think of them as reverse refrigerators.
Air source heat pumps take warmth from the external air and ground source heat pumps take warmth out of the ground. The more consistent temperatures underground or in water enable ground source heat pumps to be more efficient whereas air source heat pumps must work harder in cold weather. Both forms of heat pump use electricity to operate meaning you no longer need to burn fossil fuels to produce heat and hot water in your building. This means they can be carbon neutral in operation if the electricity used is from renewable sources.
The compression of the liquid to increase its temperature requires electricity and the colder the liquid is the more electricity is required – this is referred to as the Coefficient of Performance (COP). The issue of course is that we generally need more heat when it is cold outside which is when the heat pumps are at their least efficient. It is generally recognised that air source heat pumps work between 3 and 4 COP – meaning broadly that one unit of electricity used in compression provides 3 to 4 units of heat. The COP for ground source heat pumps is usually slightly better plus they can be used to cool when it is hot. It is worth pointing out that electricity is 4-5 times more expensive than gas and so your energy bills are possibly going to be higher using heat pumps when compared with a new gas boiler.
Standard heat pumps only raise the temperature of the liquid to 55 degrees Celsius which is well suited to underfloor heating but not for conventional radiators. As such you cannot simply install a standard heat pump without either replacing your radiators with larger ones or installing underfloor heating. Alternatively, there are high temperature heat pumps, but they use more electricity to raise the temperature of the liquid to approximately 80 degrees Celsius and hence are more costly to operate.
Heat pumps rely on a building being well insulated and reasonably airtight so are a good option for a newer property but do not work in older draughty non insulated properties. To be able to use heat pumps economically in an older property will require significantly improving its thermal performance by substantially insulating the roof, floors and walls, draft proofing and installing double glazing. They will ‘work’ in an older building, but the efficiency will be significantly lower in cold weather which can lead to exorbitant electricity bills.
Air source heat pumps require an external condenser unit (like those used for air conditioning) which might require planning approval and might also require an acoustic housing as they can be noisy. Ground source heat pumps require an amount of land (or water) in which the pipes can be located either horizontally or vertically and as they do not require an external condenser, they are generally quieter.
It is worth noting that air source heat pumps are roughly four times (or more) the cost of a conventional boiler and are more expensive to service and maintain. Ground source heat pumps cost even more. However, there are government incentives to potentially assist in funding.
We strongly recommend taking proper independent professional advice (from an experienced mechanical consultant) if you are considering a heat pump to ensure it is the right solution for your home.