What is an air to water heat pump and how does it work?
What are heat pumps?
Heat pumps are machines that extract heat from one place, upgrade it to a higher temperature and move it to another place. Heat pumps work by circulating refrigerant liquids between two heat exchanger’s with a compressor pump.
The most common everyday items that use heat pump technology are fridges and freezers. Warm air is extracted from inside these appliances and vented outward. Heat pumps are also used for home heating. They extract heat from a heat source but instead of releasing it into the air, like fridges and freezers, they put it into water that circulates through radiators or under-floor heating.
The remarkable thing about heat pumps is that they can extract useful heat from low temperature sources, even down to 20 degrees below freezing.
Which heat pumps are used for home heating?
1. Air to water heat pumps, as their name suggests, extract heat from the air.
They are increasingly popular throughout Ireland and Europe.
2. Ground source heat pumps extract heat through pipes that are buried horizontally or drilled vertically into the ground.
In the early 2000’s ground source heat pumps were the most common type of heat pump installed in Ireland.
3. Water source heat pumps take heat from a water source such as a well.
What do air to water heat pump systems look like?
Homes heated in this way have an air source heat pump fitted on the ground or on a wall outside the house. The pumps are powered from the electricity supply. Air to water heat pumps look very like air conditioning units that are often seen on the outside of commercial buildings.
One homeowner who retrofitted his home under the SuperHomes scheme recalls: ‘When the contractors came to fit the heat pump they literally took the oil boiler out, put the heat pump in its place, and connected up.’ Read more of what our homeowners had to say here.
Unlike oil boilers, which heat water to 60 or 65 degrees, heat pumps heat the water to 30 or 35 degrees over a longer time frame/ more consistent basis. Heat pumps therefore work well with under floor heating and large radiators. If a house is being retrofitted larger radiators may need to be installed but often this is not necessary. Heat pumps can also be used to heat the hot water tank using a special low temperature coil.
Do heat pumps work when it’s very cold outside?
Yes. Proof of this is the fact that 20% of Swedish homes are heated by heat pumps!
In theory heat pumps can extract heat from any source, no matter how cold, but a warmer source allows a higher efficiency.
The relationship between the amount of energy used to run a heat pump and the amount of energy it produces is called the COP. This stands for Coefficient of Performance.
If a heat pump uses 2kW of electricity to produce 8kW of energy it has a COP of 4. Air to water heat pumps in Ireland typically achieve a COP of 3 to 4. This means a home uses 1 unit or kWh of electricity for 4 units of heat produced.
What are the advantages of air source heat pumps?
Cost: Running costs are much less. Typically they cost one third to half as much to run for each unit of energy produced.
One homeowner who replaced her oil boiler with an air source heat pump under the SuperHomes scheme saved over €2500 euro in energy costs after one year – while her electricity bill increased by €700, she didn’t have to pay for oil.
If homeowners install solar electricity PV panels they can reduce running costs even further.
Comfort: Heat pumps are generally fitted with sophisticated controllers that maintain a chosen set point in temperature in the home.‘We don’t have the peaks and troughs of temperature that we had with our oil boiler system,’ says one householder.
If heat pumps are also connected to the hot water tank they bring added home comfort.
‘We have constant hot water because the heat pump automatically tops it up,’ says another homeowner.
Environment: Heat pumps are environmentally friendly reducing harmful particulate and carbon dioxide emissions by over 60% – 80%.
Are heat pumps classified as renewable energy?
Yes, both the EU and the International Energy Agency classify heat pumps as providers of renewable energy.
This is because the pumps extract free heat from the environment.
Heat pumps are especially clean sources of energy if the electricity used to power them is generated from renewable sources such as solar PV panels or wind turbines.
They are one of the main ways of producing heat without releasing climate-changing carbon into the atmosphere. Some of the energy for your home will come from non-renewable energy, and over time this will decrease to near zero over the next 30 years.