Heat pumps are an extremely effective and efficient way to heat your home and also to produce all your household hot water needs. Heat Pumps work by drawing heat from the environment using the conventional refrigeration cycle to produce more energy than they consume.
Daly Renewables has been installing the innovative Ecoforest and Hitachi air source heat pumps for several years. We are proud to be approved suppliers and installers for both market-leading manufacturers. Having the choice of both companies ASHP products means that we can advise on which heat pump model is best suited to your needs.
The science – how they generate heat
ASHP work using similar technology as the ground source heat pumps (GSHP) but using the outside air as its energy source. In the UK and Ireland, the outside air temperature rarely goes below -3°C. The heat, or energy, moves from hot to cold (2nd law of thermodynamics) and the refrigerant in the heat pump boils at very low temperatures of -30°C so the difference between the outside air and refrigerant create the energy that flows into the heat pump.
How does an ASHP work?
An Air Source Heat Pump uses a fan to draw the outside air across the evaporator and this heat transfer process is converted to useful heat using a refrigeration circuit similar to your fridge or freezer at home. The electricity used to run the fan and compressor is typically one quarter of where the energy is required, with the other three quarters coming from the air outside. The refrigerant in the heat pump boils at very low temperatures, as low as -30°C so the difference between the outside air and refrigerant create the energy that flows into the heat pump. The heat produced inside the unit is transferred to the building via a built in circulating pump and there will be seperate heating and hot water control which means the heat pump can provide hot water all year round when the heating is off in the summer.
The difference in ASHPs and GSHPs
Our findings on reviewing both ASHP and GSHP systems that we have installed in similar sized houses with similar insulation specifications, is that a typical ASHP will have a 15-20% higher running cost than GSHP system. This is still significantly better than a fossil fuel system as there is a 400% efficiency with an ASHP compared to an oil or gas boiler which is around 90% efficient. ASHP systems are less expensive to install than GSHP systems with the main difference being that the unit will have to be mounted at the side of your property or garage whereas the GSHP unit is internal in the house.
Hot Water needs met with a heat pump
A heat pump can provide a typical family’s hot water requirements without the need to use a back-up immersion heater. The back-up immersion should only be
required to assist with carrying out Legionella Cycles.
Typical running costs of an ASHP
Based on feedback from previous clients, typical running costs for heating and hot water for a full year tend to be between £350 – £800 for an average 2,500 square foot house.
The Air Source Heat Pump unit is more efficient when positioned at the rear of the property backing directly onto the house, and it has to sit at least 300mm out from the wall. With the split models available, the outdoor unit can be positioned up to 75m from the dwelling if location is an issue. This will however increase the capital cost and result in a slightly higher running cost.We advise all our clients to work closely with their architect in order that they specify low U-values and come up with an air tightness brief to make the house a low energy dwelling from the outset. In our experience, our systems work really well in timber frame houses as they are well insulated and air tight but they can also perform as well in masonry houses as long as the air tightness measures are applied correctly during the build.
The maintenance requirements for an ASHP systems is minimal. The filters can be removed and cleaned and after this is done at commissioning stage it should not have to be done on a repeated basis. Other external factors such as ensuring the pressure in the heating and/ or brine circuits is regularly checked and the quality of the water will have an impact on the performance and longevity of these systems but this is no different to a conventional heating system.
We recommend that a service is undertaken of the heat pump between every 3 and 5 years.