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Homeowners looking for a renewable solution to heat their home and provide hot water have several technologies open to them. Potential options include solar thermal, solar PV, ground source heat pumps and even wood-burning stoves. But air source heat pumps could provide another option – should your property be suitable.
However, as with all renewable technologies, air-source heat pumps have their pros and cons. So in this article, we are going to look at the technology in more detail so that you can make an informed decision about whether air source heat pumps are the right solution for your home.
What is an air source heat pump?
Air source heat pumps absorb heat from the air outside before increasing its temperature so that it can be used to heat water or the air around your home. They work in a similar way to ground source heat pumps, which absorb heat from the ground. The advantage of air source heat pumps is that they don’t require a large garden space to lay the ground loop.
Types of air source heat pump
There are two main types of air-source heat pump:
Air-to-air heat pumps
With this type of system, heat is absorbed from the air outside before being amplified in the same way as an air-to-water system. But instead of being transferred to the water through a heat exchanger, the superheated refrigerant is distributed directly through a network of ducts heating the air around your home.
Air source heat pumps are also reversible and can be easily switched to a ‘cooling’ mode, acting as an air conditioning unit inside your home.
The advantage of this type of system is that they are extremely efficient. The downside is they do not generate hot water so a separate water heater will need to be installed.
Air-to-water heat pumps
With this type of system, heat is transferred from outside into a refrigerant fluid which boils at a low temperature. The refrigerant vapour is then passed to a compressor to increase its temperature. The now superheated vapour is then passed through a heat exchanger which transfers the heat around the home via a conventional wet central heating system.
Air-to-water heat pumps run more efficiently at lower temperatures too, when compared to a standard boiler system – this makes them an ideal solution for underfloor heating systems or larger radiators, which emit heat at lower temperatures over longer periods of time.
Air source heat pump pros and cons
Air source heat pumps are extremely efficient and have several advantages over conventional gas and electricity-powered heating systems. But they are not necessarily the right choice for everyone. So it’s a good idea to know the pros and cons of this type of system before making a decision.
Pros
- Energy-efficient – Air source heat pumps are more efficient than conventional gas or electricity-powered heating systems.
- Easy to install – They are much easier and cheaper to install than ground source heat pumps and do not require a large garden area to lay the ground loop.
- Heat generation all year round – Air source heat pumps can extract heat from the air, even when the temperature outside is as low as -15°C.
- Lower energy bills – Switching to an air source heat pump could help you lower you’re energy bills, especially if you’re switching from conventional electric heating or an old oil or LPG boiler.
- Lower carbon footprint – Help our planet by lowering your carbon emissions by using Air Heat Pump technology.
- Reversible – Air source heat pumps can be switch to a ‘cooling’ mode, acting as an air conditioning unit in your home.
Cons
- Requires space – You will need to ensure you have enough room outside for the external condensing unit. These vary in size depending on the system but a typical domestic condenser will be similar in size to an air conditioning unit.
- Can be noisy – The fan and condensing unit can be noisy and blow cold air out. So you will need to position these carefully so as not to upset neighbours.
- Requires separate electricity source – Both air-to-air and air-to-water systems require a separate electricity source to power the compressor. So this type of system is not considered zero-carbon unless the electricity is provided from a renewable source such as solar PV panels.
Air source heat pump efficiency
Air source heat pumps are an extremely efficient source of energy and can help to lower your carbon footprint. The exact amount of CO2 you’ll save will depend on the type of system you are replacing and where the electricity is coming from to power to the pump.
However, even the most efficient conventional boiler uses the same volume of fuel to produce a single unit of heat. This gives them a seasonal coefficient of performance (SCOP) rating of 1.
Air source heat pumps, on the other hand, are extremely efficient. Most modern air-to-water heat pumps have a SCOP of 3. Which means they can generate at least 3 units of heat per single unit of energy. So air source heat pumps are at least three times more efficient than any mains gas, LPG or oil-fired heating system.
Installing an air source heat pump
One of the best things about air source heat pumps is the ease of installation compared to other types of renewable heating system. The condensing unit is self-contained and about the same size as an air conditioning unit. So there is no need to dig up the garden to install the ground loop needed for a ground source heat pump.
This also makes them much cheaper to install. Energy Saving Trust estimates that the cost of installing a typical air-to-water type system is between £6,000 and £8,000. If you want to create a zero-carbon system you will need to factor in the cost of installing solar PV panels to generate electricity for the pump.
How much will an air source heat pump save you?
The time to recoup the initial outlay of your ASHP (in energy savings) depends on its efficiency and the type of system it’s replacing – you’ll also recieve a nice helping hand from Renewable Heat Incentive (should you choose to install an air to water heat pump).
The table below details the types of savings that could be made by replacing your current system (data courtesy of Energy Saving Trust website).
| Existing system | Fuel saving (per year) | Carbon saving (per year) |
|---|---|---|
| Existing system: Old (G-rated) gas boiler | Fuel saving(per year): £395 to £425 | Carbon saving(per year): 4,450 to 4,750 kg |
| Existing system: Old electric storage heaters | Fuel saving(per year): £920 to £1,000 | Carbon saving(per year): 3,450 to 3,750 kg |
| Existing system: Old (G-rated) oil boiler | Fuel saving(per year): £500 to £550 | Carbon saving(per year): 7,100 to 7,600 kg |
| Existing system: Old (G-rated) LPG boiler | Fuel saving(per year): £1,200 to £1,300 | Carbon saving(per year): 5,400 to 5,800 kg |
Energy Saving Trust also estimates annual Renewable Heat Incentive payments between £1,100 to £1,500.
Conclusion
Air source heat pumps are a cost-effective and energy-efficient option for replacing existing mains gas, LPG or oil-fired heating systems – especially if they’re old systems. They are relatively easy to install and require little on-going maintenance. And unlike ground source heat pumps, a large garden area is not needed to install the ground loop.
They are not considered zero-carbon solutions however because a separate electricity source is required to power the compressor. They are also less efficient than ground source heat pumps. So if you have space, ground source heat pumps represent the better option.
But if space and budget are limited, air-source heat pumps are a great way of reducing your energy bills and C02 emissions.
