How Air Source Heat Pumps Work
The effiiciency will be sssssWhat is an Air Source Heat Pump and how does it work?
An Air Source Heat Pump (ASHP) is a very efficient way of heating your home, providing more energy than it consumes in operation. Whilst that might initially sound like magic and witchcraft, the way it does it is both very clever and very simple… and yet strangely familiar.
The reason why an ASHP will be familiar to you is because it works by using the process of refrigeration, it is essentially an inside out fridge. You may well have noticed that whilst a fridge is cold on the inside, it has a load of pipework on the back of it that can get very warm. Such pipework is known as the condenser coil – an ASHP uses the heat produced by it’s condenser coil to heat your home.
But how does it actually do that?
It all comes down the expansion and compression of liquid and gas. A really good example of this is deodorant body spray! You will have noticed that even if the can is warm to the touch, when you spray your body, the spray is cold. This is because the small amount of liquid sprayed from the can rapidly expands into a gas filling a much larger volume. That gas still has the same amount of heat energy as the liquid but it’s now having to fill a much larger volume, which means the temperature drops. If you were to contain that gas in a sealed network of pipes and allowed the gas to increase in temperature by warming to its environment, and then compressed the gas back into a liquid, the opposite process would happen. When the warm gas is compressed it turns into a hot liquid.
The diagram below shows how this process works on a heat pump.
So, does it not use electricity?
A Heat Pump provides heat to you home through a refrigeration process and not by electricity. However, you will still need electricity to power the pump itself. It only takes around 1kW of electricity to power the pump to make around 3kW of heat. This is what is known as the Coefficient of Performance (CoP) and it’s how the efficiency of ASHP is measured.
However, an ASHP gets its energy from the air outside. Therefore, when the temperature drop, the efficiency drops too. This leads to a separate measure known as the Seasonal Coefficient of Performance (SCoP). The efficiency will be lower when there is a big difference between outside air temperature and the desired temperature inside. “Heat Load” calculations are therefore required of your home to ensure the most efficient size of ASHP is specified. However, a heat pump will only stop being as effective when the temperature reaches below -28 degrees. Most importantly, the UK has not seen such a drop since 1982!
