It might seem strange that on a cold winter’s day, the air outside your home can be used to heat the inside of it.
But that’s exactly what an air source heat pump does.
The important thing to understand is that cold air still contains thermal energy. Even when the temperature outside drops below 0°C, there is still energy available for a heat pump to capture.
So, how does it turn that into useful heat for your home?
Step 1: Capturing heat from the outside air
An air source heat pump has an outdoor unit containing a heat exchanger. A fan within the unit draws in outside air, from which heat can be absorbed due to a special fluid called a refrigerant.
The refrigerant is able to boil at a very low temperature, so it can absorb heat from outside air even when that air feels very cold to us.
As it absorbs this energy, the refrigerant evaporates and changes from a liquid into a gas.
Step 2: Raising the temperature
At this stage, we’ve captured some heat, but it isn’t yet at a high enough temperature to heat your home.
This is where the compressor comes in. The refrigerant is compressed, increasing its pressure and temperature considerably.
This is also where most of the electricity used by the heat pump comes into the process: electricity powers the compressor and other components that allow heat to be moved from the lower-temperature outside environment to the warmer heating system inside.
Step 3: Transferring that heat into your home
The now hot refrigerant travels to another heat exchanger, where its heat can be transferred into the water circulating around your home’s heating system.
That heated water can then travel to your radiators or underfloor heating, beginning the journey around your home.
As the refrigerant gives up its heat, it cools and condenses back into a liquid. Its pressure is then reduced and the cycle begins again.
But what happens when it's freezing outside?
This is probably the part that seems most surprising. If it’s freezing outside, how can there possibly be enough heat in the air to warm your home?
Even when outside temperatures drop below 0°C, the air still contains thermal energy. A heat pump uses a refrigerant that is even colder than the outside air.
Because heat naturally moves from warmer to colder areas, heat from the outside air can transfer into the colder refrigerant.
The heat pump then raises the temperature of that refrigerant, allowing the captured heat to be transferred into your home’s heating system.
So, even when the air feels freezing to us, there’s still heat there for the heat pump to use.
So, where does the heat actually come from?
A significant proportion of the useful heat delivered by an air source heat pump is transferred from the outside air.
Electricity is used to power the heat pump, particularly the compressor, which compresses the refrigerant and raises its temperature so that the heat it has absorbed can be transferred into your home’s heating system.
Because the system is using electricity to transfer and raise the temperature of existing heat, rather than relying solely on burning fuel or converting electricity directly into heat, it can deliver more heat energy than the electrical energy it consumes.
For example, if a heat pump is operating at a COP of 4, 1 unit of electricity helps it deliver around 4 units of heat, with much of that energy having been transferred from the outside air.
And once that heat reaches your heating system, another journey begins.
From outside air to heating your home
You’ve seen how the technology works. Now find out how it could work for your home. Our surveys help us understand your property’s heating needs and design a heat pump system around them.
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