What is a Heat Pump & Why do I Need One?
As the UK government works toward its nett zero target for carbon emissions, we are being encouraged to make radical changes to our lifestyles. We are being asked to replace petrol and diesel fuelled vehicles with electric ones and as of 2025, it seems that we will be unable to install gas central heating boilers in new build homes and by 2035 we may be unable to retrofit gas boilers, with heat pumps seemingly the government’s favoured alternative. But what is a heat pump, how does it work and why does the government want us all to replace our trusted gas combi boiler with one?
There are a number of different variations of heat pumps, the main two in terms of probable usage being air source and ground source heat pumps and they basically extract heat from a source, boost it and use the heat produced for your central heating.
An air source or ground source heat pump uses the same technology as an air conditioning unit. It takes heat from the outside air or warmth from the ground and passes it over a heat exchanger on the exterior section of the heat pump. This heat causes a liquid refrigerant in the heat pump to evaporate and turn into a gas. This is then passed through a compressor, thus increasing the pressure, which causes the temperature to rise further. The warm gas is passed over the internal heat exchange surface and as it passes into the property a slight fall in temperature sees it convert to warm water which can be used in the house for heating the property or domestic hot water.
The heat source for an air source heat pump is the air surrounding the property. Even on cold days there is sufficient heat in the ambient air for the heat pump to extract and begin the above process.
A ground source heat pump extracts heat from a series of underground pipes filled with a mix of water and anti-freeze. This mixture is compressed and goes through a heat exchanger, which extracts the heat and transfers it to the heat pump in the same way as an air source heat pump.
The hot water produced by a heat pump can then be used in radiators, an underfloor heating system or for domestic hot water. The provision of domestic hot water however, means that a hot water storage tank becomes a requirement, unlike with a combi boiler. Certain types of properties, such as flats, may not easily accommodate a water tank.
It is also worth bearing in mind that a domestic gas fired boiler will provide hot water at a temperature of around 75’C, whereas a heat pump will deliver water heated to around 65’C. This means that you might want to look at reconfiguring your central heating to compensate for this difference in temperatures. To heat an area such as a room, you either need to have a small heat source radiating heat at a very high temperature or a large heat source at a lower temperature. In a domestic property, the most efficient heating system to use with a heat pump is underfloor heating, which distributes the slightly lower temperature over a larger area. Underfloor heating tends to be a ground floor heating solution, so there may be an argument to utilise this on the ground floor and to possibly use slightly larger, thermostatically controlled radiators in all other floors of the property.
If you think all of this sounds as if it might be getting rather expensive, you would be right, heat pumps are not cheap. An air source heat pump they can cost anywhere between £8,000 and £15,000 to install, while a ground source heat pump needs an investment of between £20,000 and £35,000 to buy and install, because of the extra groundworks involved in installing underground pipework. There is at present a government scheme called the Boiler Upgrade Scheme which will contribute a grant of £5,000 towards an air source heat pump and £6,000 to offset the cost of a ground source heat pump. Funding allocated to this scheme by government is limited, and will eventually run out if not topped up to further incentivise potential buyers and the system would require to be installed by a Microgeneration Certification Scheme (MCS) certified installer.
It is almost impossible to put a figure on the potential savings you will accrue after installing a heat pump, as there are so many variables to the cost of running your present system. Old gas boilers can run at less than 70% efficiency, newer ones should achieve 90+% and there are a number of variables in electricity tariffs with price caps and uncertainty over future energy costs. Installing a heat pump could potentially save you somewhere between £200 and £1,000 per annum and would arguably increase the value of your property and certainly make it more marketable.
The real benefits of installing a heat pump are not financial but are in the savings achieved in lowering your carbon emissions, which is why the government is keen to see the use of alternative fuel sources. Heat pumps burn no fossil fuel, they get their energy from naturally existing heat in either the air or the ground surrounding the property and use only a small amount of electricity to power the compressor. Provided you ensure that your energy supplier offers 100% renewable energy, you will be able to heat your home with zero carbon emissions.
Heat pumps are more efficient than almost any other form of heating. The amount of heat they produce is more than the amount of electricity they use. The amount of heat produced per unit of electricity used is referred to as the Coefficient of Performance or CoP. A heat pump CoP should be somewhere between 2.5 and 4.5 which means that for every unit of energy it uses it will generate between 2.5 and 4.5 units of heat energy.
As with any new technology, heat pumps will evolve and improve and as they are deployed more widely the unit cost will reduce. Replacing gas boilers in existing properties with heat pumps is unaffordable for many households at present day prices. Some major energy suppliers are already offering special deals but the real price break through will come when heat pumps become the normal heat source for central heating and hot water in new build developments.