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The Different Types of Heat Pump: A 2024 Guide for the UK
To understand heat pumps we need to know a little about the laws of thermodynamics. Don’t worry, the key principle is pretty simple, and we won’t stray too far into complex science. In a nutshell, thanks to the laws of thermodynamics we know that in our world heat flows from a warm location to a cooler one.
At their core, heat pumps use this phenomenon to move heat around. Remember, although they’re often designed for a single function, heat pumps can use this reaction in either direction. I.e. in theory, heat pumps can make a location hotter or colder depending on how they’re used. If you’d like to know more about the field of thermodynamics, here’s a great free resource from the BBC.
On this page we will look at the types of heat pump available in the UK. There are many options available including air-source heat pumps, ground-source, water-source, hybrid heat pumps and the increasingly popular, high temperature heat pumps.
What are Heat Pumps?
In essence, a heat pump is any device that allows the transfer of heat from a lower temperature area to a higher one, or the other way round. These machines or systems exist in many forms in the modern world. Here are some examples:
- Refrigerators
- Air conditioning units
- Air/ground/ water-based heating systems
Now, the first two examples above perform the opposite function and extract heat, but the principles are the same. Indeed, air-conditioning units can and often do provide heat too. However, heat pumps are designed to heat our homes and businesses rather than chill them.
Even here in our inclement climate, we can extract enough heat from the surrounding air, water, and ground to provide warmth for homes.
Are heat pumps renewable energy?
This is a complicated question, because most heat pumps need electricity to operate, they don’t count as a true renewable. Although the jury is out according to some organisations like the EU, it’s safer to refer to them as sustainable, low carbon, or green. That said, the amount of electricity needed is less than the heat provided. Therefore, regardless of their status, most heat pumps are eligible for the government’s Boiler Upgrade Scheme (BUS).
The Types of Heat Pumps Available in the UK
The term heat pump is a catch-all for many devices. Each unit in these sub-categories works in a similar fashion. The common difference that separates them, is the source of the heat they provide. As with other phenomenon in the natural world it’s possible to file these systems under earth, air, and water.
Air Source Heat Pumps
If you live in a moderate or settled climate, an air source heat pump can provide heating, or cooling in some cases, for your home or business. This makes the UK, the ideal place for air-sourced heat pumps. It may surprise you to know that even in the UK, the external temperature means air-sourced systems can heat most of our homes or businesses with ease.
Fitted to the outside of a building, heat pump units draw in the air from outside. Heat is then extracted before the system transfers it using a compressor, made from two coils of conductive copper tubing. When needed, heat is provided via a liquid refrigerant in the outside coil. The system extracts the heat from the air before funneling it into the inside coil. Here the gas returns to a warm liquid form that runs through your household heating system.
In recent years, air-source heat pumps have become much more efficient. Today, these air-based heating units provide significant savings over traditional central heating options. As we’ll discuss later though, these savings come with some caveats.
Follow this link to discover more about Air Source Heat Pumps and how they work.
There are two main varieties of air-source heat pumps:
Ducted air-source heat pumps
These larger systems use a network of vents and ducts to provide heat throughout a building. A ducted air-source heat pump can heat an entire home or business.
Duct-less air-source heat pumps, also known as mini-split
Common in business premises or where it’s tricky to install a full air-sourced heat pump system. These smaller units often heat or cool an individual room. Mini-splits or ductless heat pumps as they’re also called, use a single unit to transfer heat through a single wall. As they don’t need a lot of extraneous infrastructure like ducts and pipes, these systems are often the cheapest option.
Installing these ductless air-sourced heat pumps doesn’t take a great deal of effort. You can find them mounted on walls in specific rooms like larders, dormitories, and offices. In short, duct-less air-source heat pumps suit any single room where temperature matters.
Discover more about Air Source Heat Pumps and how they work.
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Ground Source Heat Pumps
The outside air isn’t the only place we can draw valuable heat from to keep our houses warm. Every day the sun warms our planet and every day the ground under our feet soaks up that power. This solar energy stored in the ground is the perfect resource to provide the heat needed for a heat pump system. This is the principle of a ground-sourced heat pump system.
Unlike air-source systems, ground-based heat pumps rely on a network of pipes laid into the earth. Also called geothermal heat pumps, they boast better efficiency than air-source heat pumps. Ground-sourced heat pumps work better because the average ground temperature is warmer than the air. In the UK, two main types of ground-source heat pumps exist:
- Horizontal arrays laid beneath garden surfaces.
- Vertical heat pump systems with a single long pipe bored many metres into the ground.
Where possible opting for a horizontal array is the better choice as it’s expensive to drill deep boreholes. To give you an idea of costs; for a four bedroom residential property, you would usually need three bore-holes at around £5,000 per hole, and that's before you add any technology in! For this reason, vertical ground-source heat pumps are best installed in areas without space for horizontal pipes. Both ground-source versions offer improved functionality over air-source heat pumps though.
The trade-off with ground-source systems’ greater efficiency over air-source heat pumps comes at a price though, and a high one at that. They are more expensive to install because they need significant excavation to lay the piping.
Find out more about how ground source heat pumps work.
Water-sourced Heat Pumps
As you’d expect from the name, water-based heat pumps extract their heat from an external source of water. Water, like the ground, stores heat from the sun and keeps a consistent temperature. Unlike ground-based systems though, water-soured heat pumps don’t rely on a vast network of pipes to function. A water source heat pump (WSHP) utilizes water from a lake, river, or underground source to heat and cool buildings. The system extracts heat from the water transferring it indoors via a refrigerant.
Like other heat pumps, the cycle relies on a heat exchanger, compressor, and expansion valve to move the refrigerant and manage temperature changes efficiently.
In theory, any accessible body of water is usable given the appropriate permissions. In the UK, the most common sources are as follows:
- canals
- lakes
- docks
- ponds
- rivers
The obvious drawback about water-sourced heat pumps is that they need a suitable existing water source. Unless a developer has the means to create this kind of resource then installing a water-source heat pump comes down to location. If you’re interested you can read more about water-based heat pumps here.
Hybrid Heat Pumps
Not all heat pumps work in isolation. Some units work alongside another system. A hybrid or bivalent system is a heat pump working in conjunction with another energy source, like a gas boiler. Together, these systems provide a more constant source of warmth at a higher level of efficiency. The advantage of a hybrid heat pump system is that anyone with a gas or oil boiler won’t need to change their radiators after it’s installed.
A hybrid system could be a single unit installed by one company or it might compose two systems installed by two different companies. A hybrid system is a best-of-both world’s scenario where the shortcomings of one system are overcome by the other. You might use your gas system to heat a cold home fast, before switching to the heat pump system and save on the cost of energy. Hybrid systems feature either air, ground, or water-sourced heat pumps alongside an oil or gas-fired boiler.
Another hybrid configuration is a mix of ground/water and air-source heat pumps. This combo can then operate at full efficiency at different times of the day or the year. Therefore, in the winter, when the air is colder outside, the system uses the ground source heat pump. In the summer, though, when the air is warmer, it does the reverse.
Absorption Heat Pumps
An absorption heat pump is a system driven by another heat source such as solar-heated water or geothermal-heated water. These systems use alternative power sources over electricity. Some systems use natural gas. These gas-fired heat pumps, so-called because of their fuel source, are more common in industrial or commercial units.
High Temperature Heat Pumps for the UK
If you’re on a tight budget, then you may want to skip over high temperature heat pumps. More complex than other systems, they offer comparable performance to traditional central heating. At their core they work like other heat pumps, but with additional components to amplify the temperatures they provide.
High temperature heat pumps reach higher temperatures and do so faster than traditional heat pump systems, overcoming the need for lots of insulation or oversized radiators. This makes them ideal for older properties where other heat pumps can prove ineffective.
These systems can reach temperatures of 60-80°C, but their efficiency comes at a price. An average householder should expect to pay 25% more for a high temperature heat pump and the systems cost more to run too.
Although, they’re ‘greener’ than traditional combustion boilers and as capable, don’t expect lower energy bills when switching from a conventional gas boiler.
They work by adding more elements to the standard heat pump circuit. These include heat sinks and complicated heat exchangers. These devices use more hazardous fluids like propane or hydro-fluorocarbons as refrigerants. These chemicals are not only flammable they’re also toxic to humans. If the term hydro-fluorocarbon rings a bell, that’s because you might remember it from all warnings about global warming.
So, while the system itself is pretty green, its constituent parts are anything but. To function, high temp heat pumps add a couple more stops to the usual heat pump system.
The first three steps are the same. The real difference between the two systems is that a high temperature heat pump is likely to have two sets of compressors. The second of which amplifies the heat extracted by the first. Apart from that, they work in a similar way.
First it absorbs the heat through evaporation and turns it into a low-pressure gas. Next it compresses this gas, increasing its temperature and its pressure. After that, the compressed gas is re-compressed making it hotter still. It’s at this stage that high temperature heat pump passes the gas through a heat sink.
The heat sink device the heat via the refrigerant. This fluid then meets a heat exchanger where the heat passes to water. This fluid then circulates around a network of pipes and radiators like a traditional central heating system.
At the end of the cycle the refrigerant returns to the expansion chamber where it evaporates and the whole process starts again.
The cost of a high temperature heat pump system is higher than the alternatives. However, if you meet the criteria, it’s possible to claim up to £7,500 from Government’s Boiler Upgrade Scheme (BUS).
Because of the high prices and increased running costs of high temperature heat pumps, there aren’t many good reasons to opt for one. However, if your property falls into one of the following categories, it’s worth a look.
- A Listed or protected building
- A property not connected to the gas mains
- An older building unsuitable or harder to insulate
On the plus side, if your home isn’t suitable for standard heat pumps, high speed/temp heat pumps are a green, efficient alternative to oil, LPG, and electric boilers.
The Drawbacks of Heat Pumps
Insulation
Regardless of the kind of heat pump you use, they all share a few common flaws. The most fundamental issue with all heat pumps is the fact they work best in well-insulated buildings. If you have a modern, well-insulated property then you can ignore this fact. If, however, you live in an older, poorly insulated house you may want to rethink adding a heat pump.
In the simplest terms, heat pump technology is best at achieving and maintaining lower general temperatures. Traditional gas-fired central heating or the like, by comparison, isn’t as good at keeping the temperature steady. If your house is harder to heat, then a heat pump system may struggle to heat it all. Of course, the remedy is to insulate your home if that’s an option, but for some of us that can be a tall order.
Aesthetics
The truth is, there are few people who might consider a heat pump installation a thing of beauty. Some systems are less obtrusive than others, but most air-sourced systems need a big white box on the outside of your house. These fridge-like structures are anything but subtle. While manufacturers strive to reduce their size, they're still around the size of a washing machine cut in half and put end-to-end.
Noise
The outside unit of an air-source heat pump does make some noise. Some are advertised as 'whisper quiet' and it's always worth checking the decibel rating of the unit your thinking of purchasing. It's important to consider the location where the heat pump is planned to be installed. Is it close to a window? Is there any natural sound proofing? Will your neighbours be able to hear it?
A good installation company will be able to show you the unit in action and sound-dampening techniques, can further reduce perceived noise. It's also worth noting that a well sized and maintained pump will produce less noise.
Cost
The price of installing heat pump systems is still high. Some systems offer better value than others and if you can factor in the potential future savings on your energy bills, they’re worth it.
Maintenance
Heat pumps are said to be low maintenance, but like any complex mechanical device, maintenance is essential for optimal performance and longevity. Regular maintenance includes checking and cleaning filters, coils, and fans to ensure efficient airflow and heat exchange. there may be a need to check refrigerant levels. Ensure that the outside has a good air-flow but removing any obstruction. An annual inspection by a qualified professional can ensure high efficiency, reduce energy costs, and extend the heat pump's lifespan.
The Future of Heat Pumps
The benefits of heat pumps already outweigh the drawbacks. In the years ahead it may well be the preferred heating choice for all of us. I mean, what’s not to love? For a little electricity, we can already extract heat from a low-temperature area outside and turn it into warmth indoors. Perhaps in next decade heat pumps will power radiators and heat water like a boiler. With the government banning the installation of combustion boilers in new build properties in 2025, the houses of the future may come with heat pumps installed as standard. Common sense tells us if research continues apace, future generations will make more efficient heat pumps.
The market is on the rise and trending in the right direction. As more home owners see it as a viable source of cheaper heating, the price will drop, and efficiency will rise. Even now the industry is booming because the UK Government added to its Boiler Upgrade Scheme (BUS).
If you’d like to learn how heat pumps can help reduce your carbon footprint and provide green heating for your home, then reach out to us today.
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How Does a Heat Pump Work? UK Guide 2024
