Air Source vs Ground Source Heat Pump – Which is Best?
When choosing a heat pump, there are numerous factors that you should take into account.
While the first thought is to opt for the most affordable option, this is often not the best alternative.
You should consider the running costs, not just the installation costs of the heat pump.
You also need to take into account the efficiency that the particular system can offer you, and practical aspects such as the space in your property.
Here we will be trying to outline such key factors to help you make the best choice, while focusing on the two most common types of heat pump systems; the air source and the ground source.
How Do Air Source Heat Pumps Work?
Air source heat pumps are generally placed outdoors, either at the back or at the side of the property.
The heat is derived from the air, thus their name.
This air is then boosted to a higher temperature by means of the heat pump.
Such a pump requires electricity in order to run, but it should be using less electrical energy than the heat that it generates.
Most heat pumps in the UK are air source heat pumps.
They are the most sought after option by far.
Such heat pumps also work very well with underfloor heating systems.
Air source heat pumps can be of two main types:
Air to Water Systems
These take heat from the air outside and feed it into the central heating system.
Air to Air Systems
Take heat from the air outside the property and then feed it inside by directing it through fans.
In this case however, you will not get hot water.
How Do Ground Source Heat Pumps Work?
Ground source heat pumps are more modern, and considerably more efficient.
For every kilowatt of electricity that gets used by the heat pump, around 3 kilowatts of heat will be delivered to the property.
The efficiency of such a system depends on the quality of its design and installation.
This type of system is very popular in the USA, Canada, Germany and Sweden, but it is also gaining more popularity than before in the UK too.
In fact, all new buildings being constructed in the UK are being designed to meet the standards of having a ground source heat pump.
This is because they’ve been proven to be safe, environmentally friendly and cost effective systems.
In fact, the main aim is to increase the use of these systems as they can reduce heat loss and the reliance on fossil fuels.
Over time it is expected that modern buildings will need less heating as a result.
The following are the main differences between air source and ground source heat pumps.
Air Source Installation Cost
Air source heat pumps are considerably cheaper to install than ground source heat pumps.
You will only need to pay for the unit itself.
The size of the property will have an impact on the installation cost.
Newer houses tend to keep the costs even lower than existing houses.
The cost of an air source heat pump is in the range of £7000 and £13000.
Ground Source Installation Cost
There is a greater upfront cost when you opt for a ground source heat pump.
It could cost around £14,000 to £19,000, not to mention that there will be additional expenses relating to the external works that will need to be carried out to install such a system, slinkies or boreholes.
Air Source Installation Requirements
Air source heat pumps are somewhat easier to install.
The process is not complicated either as there is no need to dig up land as with ground source heat pump systems.
There is no need for any ground arrays like pipe trenches and boreholes.
However, you will need to check whether there will be the need for planning permission, especially if you live in a high density area.
This is due to the fact that such heat pump systems are relatively noisier and they may disrupt neighbours since they are fitted outdoors.
Ground Source Installation Requirements
There is much more planning and labour required to have a ground source heat pump system installed.
However, such a system is more efficient and there is also the advantage that there will not be any pipework visible.
Having said that, with a ground source heat pump you will need to carefully discuss with the installer whether you can opt for a horizontal or a vertical installation.
If you have to opt for the latter, it is going to be more costly.
With a ground source heat pump you will not need to seek planning permission in most cases.
As noted before, such a system is visually unobtrusive and not noisy.
However, there is plenty of groundwork involved, and you will need to hire a specialist subcontractor to complete the digging and related works.
But once this is completed, all that will be left is to install the pump inside the property.
This is just about the size of a fridge, and it can be placed in a utility room, or even a kitchen.
Air Source Space Requirements
An air source heat pump looks like an air conditioning unit, which is mounted outside the property, generally next to a wall.
Some systems also include an inside unit, and in this case they are referred to as split systems.
There are also systems that do not include an inside unit, and these are called monoblocs.
The size of an air source heat pump depends on the size of the property as well as the demand for heat.
Hence this will need to be discussed with the installer.
Even though such heat pumps do not take up much space, it is important to point out that they have some drawbacks.
This includes the fact that the unit will be visible on the exterior of the property, and while the pump is running the fans will generate some noise.
Ground Source Space Requirements
The main factor to take into consideration prior to installing a ground source heat pump is whether you have enough outdoor space to have such a system fitted.
A ground source heat pump will require what is referred to as the ground loop, which can be installed either vertically or horizontally.
Regardless of the choice, each will take up some space and you will also need to check whether it is possible to dig the ground as not all types of ground are suitable for digging.
In cases where there is not that much area, you may wish to consider using boreholes, but this will end up increasing the installation costs.
While a small or medium sized property will require one borehole only, bigger ones will need two or even three and there will need to be pipework installed as well.
A horizontal installation will be considerably cheaper, but it can only be done if there is sufficient space on the ground.
As a general rule of thumb you will need around 3 times as much free land as the floor area of the property, and the land will need to be unobstructed, that is, free from any trees.
You will also need indoor space to place the heat pump unit, which is like a fridge in terms of its dimensions.
Some models will include an integrated hot water cylinder in this unit.
Air Source Energy Efficiency
Air source heat pumps make use of heat energy from the air so as to offer a higher temperature indoors.
As a result the efficiency of such a heat pump depends considerably on the time of day and the seasons.
During winter, for instance, the air will be cold, and so the unit will need more electricity to operate efficiently.
It is also worth mentioning that the air temperature fluctuates
Ground Source Energy Efficiency
It is a known fact that ground source heat pumps fare better in terms of their efficiency.
The ground generally maintains a constant temperature all year round, and so the average ground temperature during the winter months will be considerably higher than the temperature of the air.
Hence there will not be any unexpected spikes in the usage of electricity.
Such a pump will not need to work as hard as an air source heat pump in order to upgrade the source energy into usable indoor heat, thereby making it more efficient.
Moreover, with the smart controls featured on such systems, and time-of-use tariffs, ground source heat pumps are operationally efficient as well as they undertake load shifting.
Air Source Running Costs
When it comes to running costs, air source heat pumps do not fare as well as ground source heat pumps as they are not as efficient.
One will need to pay for more electricity in order for the pump to bring cold air to the desired temperature level.
So in the long run, even though the initial installation costs are lower, one will end up spending more if the running costs are factored in.
Air source heat pumps also have another disadvantage in this respect.
This is because such heat pumps will not be able to make the most of time-of-use tariffs since the air temperature will be cooler during off peak times.
Hence such a system will be operating at its lowest efficiency when the electricity tariffs are cheaper.
Ground Source Running Costs
Ground source heat pumps are efficient and this can be demonstrated in the lower running costs.
Indeed, ground source heat pumps can provide significant savings over traditional heating systems, as well as over air source heat pumps.
While the running costs depend on current temperature and the amount of heat that the system will need to generate, such pumps operate more efficiently, especially since they can make the most of time-of-use tariffs.
Adequate insulation can also help in ensuring that the heat the pump generates does not escape through walls, windows and doors, to keep running costs even lower.
The COP, Coefficient of Performance, is the way in which the efficiency of a heat pump is measured.
This is done by measuring the amount of power input in relation to the power output that is produced by the system.
The higher the value of this coefficient, the more efficient the system is said to be.
In the case of a ground source heat pump system, the COP is in the range of 3.5 to 4.5, whereas for an air source heat pump system it is typically in the range of 2.5 to 3.5.
This is mainly due to the fact that the ground source heat system will need to work less since the difference between the temperatures is less than that between the air and the required indoor temperature.
A ground source heat pump will also not be affected that much by the weather conditions.
We are all well aware of the climate emergency that is facing us all.
The UK has committed to reaching zero carbon emissions by the year 2050.
Considering the emissions resulting from domestic heating systems and hot water systems constitute around 77% of total emissions by households, it goes without saying that there needs to be a huge change in the way UK households heat up their homes.
Both air source and ground source heat pumps are going to help in replacing the high carbon fuels that are used to heat up many buildings in the UK.
Based on the fact that ground source heat pumps are more efficient, they have the lowest carbon footprint.
However, even air source heat pumps are considered to do well in this regard.
The design and the installation of the system will have an important impact on how carbon intense it can be.
Hence, it is important to ensure that the heat distribution system, and the installation and design are carried out in a way that takes this into consideration to ensure the optimal efficiency and the lowest carbon emissions possible.
Air source heat pumps are said to last around 10 years.
This is mainly due to the fact that they are exposed to the external elements, and this will take its toll over time.
Moreover, if the property is very close to the sea, and hence saltwater can cause rust to develop on internal components, the lifespan will be much lower.
Ground source heat pumps on the other hand fare better in terms of their longevity.
Since this is a closed system which is installed inside the property, there is no need to worry about environmental damages.
There is also no need to worry about the risk of theft.
The unit does not require much maintenance either and many state that the lifetime of such systems is around 20 years.
The ground array on the other hand is completely unobtrusive and it can last for several decades.
Which Type of Heat Pump is Best?
By now you probably have come to the conclusion that both types of heat pumps have their respective pros and cons.
You cannot really compare them to one another, unless you take into account several underlying factors.
These systems have a number of similarities, but they have different setups, requirements and costs.
The best thing is that they both offer energy savings and can help you to support the greener alternative to reduce carbon emissions.
You can also benefit from lower running costs on both systems, although the ground source systems are much more efficient.
However, one would need to consider the installation and space requirements for ground source systems.
As explained earlier, in some cases it is not possible to opt for such a system especially in cases of space limitations.
At the end of the day, the main decision will depend on your property, your requirements and your budget.
As a general rule, if you have the space to accommodate a ground source heat pump, then definitely go for it.
Even though it is more expensive to install, it will offer energy savings and lower running costs in the long run.
Moreover, it requires less maintenance and it has a longer lifespan too.
We hope that this overview of these two types of heat pump systems has helped you to get a better idea of whether you should choose one or the other.
Both have their pros and cons, and it will depend on the property as well as your heating requirements which one you choose.
All in all, a ground source heat pump has more advantages than an air source heat pump, so if you have the space and the budget for the former, it’s best to go down that route.