Air Source Heat Pumps
An air source heat pump is usually placed outside at the side or back of a property, and takes heat from the air and boosts it to a higher temperature using a heat pump. Air source heat pumps (ASHP) look similar to air-conditioning units. The main components of an ASHP are a heat exchanger, a compressor just like your fridge.
This heat is then used to heat radiators,underfloor heating system and hot water in your home.
The pump needs electricity to run, but the idea is that it uses less electrical energy than the heat it produces.
Ground source heat pumps are also available. They draw heat from the ground via a network of water pipes buried underground, usually in your garden, but can also use bore holes and be laid on the bottom of ponds and lakes.
How it works
An ASHP works a bit like a refrigerator in reverse. The process consists of an evaporator, a compressor and a condenser. It absorbs heat from the outside air and the heat pump compressor then increases the temperature of that heat further to create useful heat.
There are two main types of ASHP:
- Air-to-water systems take heat from the outside air and feed it into your wet central heating system. As the heat produced is cooler than that from a conventional boiler, you may need to install larger radiators or underfloor heating in your home to make the most of it.
- Air-to-air systems take heat from the outside air and feed it into your home through fans. This type of system cannot produce hot water.
- In the summer, the ASHP can be operated in reverse, like an air-conditioning unit, to provide cool air for your home.
Heating bill savings?
How much money you'll save on your heating bills depends not just on the factors listed above, but also on whether the system is the right size, installed correctly and used correctly by householders.
The Energy Savings Trust says that a 'typical' air source heat pump could save you up to £380 (replacing electric heating) a year. It found wide-ranging variations in performance, with the biggest heating bill reductions for households off the gas grid. However, the trials found that, without the RHI, an ASHP could actually cost you more if you are currently using gas to heat your home.
But, as of 2013, payback time for heat pumps will be reduced thanks to the Renewable HeatIncentive which will pay householders who generate heat using renewable technologies like heat pumps.
Air source heat pump costs and payback
The Energy Saving Trust (EST) estimates that the cost of installing a typical ASHP system into a detached home ranges between £6,000 and £10,000.
The payback period (the time it takes for the cost of the system to be recouped in energy savings) depends on how efficiently your system works, the type of system you're replacing and how you'll be using the heat generated from the pump. Here are some general rules of thumb to bear in mind:
- Air-to-water ASHP work better with underfloor heating systems. If underfloor heating is not possible, large radiators should be used. This is because the heat generated by the heat pump is not as high as that produced by a conventional gas boiler, so a larger surface area is needed to achieve similar temperatures in your home.
- Air-to-water heat pumps could be better suited to new-build properties than retrofit - this is because costs could be reduced if the heat pump is included as part of the building specification, rather than have