We all know that when it gets cold you pop your heating on and the radiators get hot. Hey presto, your house is warm. It’s just a case of switching it on!
Heat pumps don’t work in the quite same way as conventional gas boilers. Part of understanding how they work will determine how we understand heating our homes in the future.
Whereas conventional boilers generate heat by burning natural gas, heat pumps use a slightly less intuitive, but just an effective process.
Heat pumps harvest energy from their surrounding environment – be it the ground, water or more commonly the air. Even when the outside temperature drops below zero, the air still contains energy. All particles contain energy, all the way down until absolute zero |or -273.15 degrees Celsius). Fortunately, we don’t experience winters that cold and heat pumps are effective down to temperatures between -10 and -25, depending on the model.
Heat pumps use a fan that draws ambient air across an evaporator – or grill. Inside the evaporator is a gas that boils at very low temperatures. The energy from the air is given up to the gas, which boils and evaporates. The gas is then compressed which greatly increases its temperature. It is this heat that is exchanged with water in your heating system, heating your radiators and hot water.
It’s a very clever use of physics. So clever that a heat pump is capable of delivering 3 or 4 kilowatts of heat energy for every 1 kilowatt of electrical energy used to run its internal parts. So where a gas boiler may be 80-90% efficient, a heat pump can be 300-400% efficient.
Well installed heat pumps use a combination of weather compensation and modulating output to control and deliver the precise amount of heat required to keep your house warm. The aim is to keep them gently ticking over and not switching on and off frequently.
A fridge is often used as an analogy for a heat pump. They use the same principles to remove heat and distribute it somewhere else…in a fridge’s case, out the back of the unit. The point being we do not ever turn our fridges off. Likewise, heat pumps are designed to run for as long as possible.
Most of the electrical energy consumed by a heat pump is used during start-up. So it is critical that a heat pump is correctly sized for the property. This avoids cycling, where the pump runs on and off multiple times an hour.
It is also critical that the internal heating system is well installed and commissioned. Often when we hear stories about heat pumps not working it’s usually down to poor installation, and not the heat pump itself.
So, in a nutshell, heat pumps employ a compression and evaporation cycle drawing energy from the air, converting it to useful heat for our homes. In future, it will no longer be a case of popping on the heating when it’s a bit chilly. The heating would have gently been ticking away in the background! The future of domestic heating is ‘low and slow’ and no longer a case of scalding hot radiators, and boilers switching on and off frequently.