Heat pumps
What are heat pumps?
There are two types of heat pump available to the home-owner, air source and ground source heat pumps.
Heat pumps are basically fridges in reverse. They use electricity to move outside heat – either from the air or from the ground – into your house. They are about three times more efficient than a normal electric bar heater, and can produce hot water as well as heating homes.
Heat pumps have not widely caught on in the UK, but they are common in many other countries, particularly Sweden, Switzerland and France.
They produce less heat than conventional boilers, so they’re only suitable for well-insulated houses.
As their names suggest air source heat pumps extract heat stored in the outdoor air and ground source heat pumps extract heat which is stored in the ground.
Generally, they are more efficient when heating things to a lower temperature, so they work best with large heating surfaces – which means either having underfloor heating or large radiators.
Air source is not always feasible at lower temperatures, especially since the times when you’re most likely to need them, i.e. In the morning and evening, the air temperature will be at its lowest. A higher efficiency can generally be achieved from a ground source heat pump as the average temperature underground is higher than the average air temperature.
Ground-source, air-source or hybrid?
Heat pumps come in different types. Air-source are less efficient than ground-source but are cheaper, easier to install and suitable for a wider variety of properties. You also get water-source heat pumps, but they aren’t used at a domestic level.
With air-source you just need an outside wall, so they can be installed on almost all properties, including flats. The pump itself is about the size of a fridge. All the companies make air source heat pumps.
Ground-source come in two types: horizontal or vertical. The horizontal ones require an outside area twice the size of the house. The vertical ones only require room to dig a borehole and access for the drilling machinery, but they are more expensive than the horizontal ones. Also, only some areas have suitable geology for a ground source heat pump, as they don’t work well in areas with sandy soils. On the score table, Vaillant, Ideal, Worcester, Viessmann and Mitsubishi Electric make ground-source heat pumps.
There are also hybrid systems, which combine a heat pump with a small backup gas boiler. For many people, this may be the easiest option.Vaillant and Glow-Worm make hybrid systems.
How good are they?
If they are running on renewable-powered electricity, heat pumps have greenhouse gas emissions of close to zero.
However, using the current general electricity grid mix, the carbon benefits of heat pumps in the UK are debated. Some people say that they are substantially better than gas boilers, while some people say there is no real benefit at all. The thing is, it all depends on what efficiency the heat pump achieves, and many in the UK are performing poorly. However, the best performers are doing much better than average, and so it is widely believed that the poor efficiencies have just been caused by bad installation.
Another reason to have faith in the potential performance of heat pumps is that in other countries they tend to manage much better efficiencies, and that should theoretically be replicable here.
Score table highlights
- All of the companies, apart from LG, got our worst rating for management of workers’ rights in supply chains.
- Seven of them – Remeha (Baxi), Groupe Atlantic, Panasonic, Samsung, Mitsusbishi Electric, Viessmann and Robert Bosch (Worcester) – had inadequate policies whilst Vaillant said nothing at all about workers’ rights.
- Most companies did better on reporting about their environmental impacts, with LG and Samsung scoring best in this category.
Conflict minerals policies
We rated all the companies for their policy on the sourcing of conflict minerals – tin, tantalum, tungsten and gold – because they use them in their electrical components. There is a risk that revenues generated from the sale of these minerals is being used to fuel conflict in a number of countries in central Africa, most notably the Democratic Republic of Congo.
Most of the companies get a worst rating. LG got a best rating and Panasonic scored a middle rating.
Ideal, Mitsubishi Electric and Samsung received our worst rating for not having adequate policies but they at least did better than the following companies which did not even mention conflict minerals – Viessmann, Vaillant, Baxi, Worcester Bosch.
Refrigerant gases
Heat pumps use refrigerants, and the most common are HFCs, such as R407 which has a global warming potential (GWP) of over 1,600 more than CO2. Any leakage can easily turn the heat pump from a friend of the climate into its worst enemy. However, it is generally considered possible to keep leakage levels low enough that this is not too much of an issue.
CO2 was one of the most widely used refrigerants alongside ammonia in the early 20th century and is now having a renaissance. As the Global Warming Potential values for HFC refrigerants are nearly two thousand times higher than for CO2, leakage of CO2 gas from a refrigeration system is consequently nearly two thousand times less damaging to the environment than the release of any HFC gas.
Plus CO2 is a more efficient refrigerant than HFC.
In terms of environmental impact, natural refrigerants are all deemed as having close to zero global warming potential in comparison to standard HFC refrigerants. Other natural refrigerants are:
√ R170 – Ethane √ R290 – Propane √ R600a – Isobutane √ R717 – Ammonia √ R744 – CO2
In 2011, Peter Bartley of CHB Sustainability had this to say about refrigerants:
"Heat pumps are designed as tightly sealed systems in order to minimise leaks; however there is always a chance of a leak of a chemical which can pose a significant contributory factor towards climate change (around 20% of the climate change effect of refrigeration is due to refrigerant leaks and the other 80% due to the energy used).
There are now alternative refrigerants which have a much lower, or in some cases no contribution towards global warming. However, these chemicals can pose their own risks in terms of safety and environmental impact. Common low GWP alternatives are ammonia, hydrocarbons (petrochemicals such as propane, isobutane and butane) and CO2. However, ammonia is very toxic and flammable. Hydocarbons are highly flammable and can contribute to pollution, and so ironically CO2 looks to have a future as the ‘green’ refrigerant alternative to HFCs!"
What do heat pumps cost?
Heat pumps are rather expensive. Air source are in the region of £6,000-£10,000 for the whole system including installation. Ground source are about £9,000-£16,000. Gas boilers cost between £500 and £2500. See our guide to gas condensing boilers.
Unfortunately, while heat pumps save energy, electricity is a much more expensive fuel than gas, so their running costs may not be much lower than a gas boiler.
You can get some help with the cost. Heat pumps are one of the technologies now supported under the Renewable Heat Incentive (RHI). The RHI gives regular payments for the first seven years of running your pump, at the rate of 10.49p per kWh heat generated for air-source, and 20.46p for ground-source (from 1st April 2018).
This will help you pay back the capital cost, although you may not make all of it back.
If you aren’t on the gas grid, a heat pump is a great heating option, as in this instance you may well save money as well.
If you are on the gas grid, they are less financially attractive. But if you have some spare cash and you care about the climate, there is good reason to consider one.
There is an urgent need to help the industry here get going. If we were all using heat pumps there would still be the issue of decarbonising the electricity they run on, but it would, nonetheless, be a massive step towards decarbonising our heating. And if consumers support heat pumps, they can be expected to get better with time.
The efficiency measure for heat pumps
The Coefficient of Performance (CoP) is the unit by which the performance of heat pumps is measured. Basically, it measures the amount of heat produced, as compared to the amount of electrical energy required to produce it. The less electricity required, the higher the CoP, and the more efficient the heat pump.
So for example, at a CoP of 3, you put in 1 unit of electricity and you get out 3 units of heat.