AIR SOURCE HEAT PUMPS

Air source heat pumps

Air source heat pumps (ASHP) are cheaper than ground source heat pumps, but less efficient. On the other hand, they’re much easier to install as they only take up a small space at the side of a building. This makes them ideal for retrofitting to existing properties.

Most ASHP installations qualify for the Renewable Heat Incentive (RHI). It’s very important to choose the right size of heat pump for the job you want it to do, but we can help you with this if required.

How they work

  1. The ASHP draws energy found in the air. At cold times of the year, the air temperature is only around 4 to 5oC, so the heat pump needs to increase the temperature, so it can be used to provide heating and hot water.
  2. It does this by first passing refrigerant gas through a heat exchanger called an evaporator, where it’s slightly warmed by the air.
  3. The refrigerant gas is then compressed to a liquid which dramatically increases the temperature.
  4. The heat then goes through a second heat exchanger called a condenser, which warms the water in the central or underfloor heating system.
  5. An expansion valve turns the refrigerant liquid back into gas, so the cycle can start again.

GET A QUOTE

Why choose Radiant Heating Solutions for your ASHP?

  • Experience and expertise. Our team have been supplying and installing ASHPs for over 25 years. We have the technical know-how to choose the right size of heat pump for any building and any heating requirements. We can also design a hybrid or integrated system that links to other energy sources, such as underfloor heating or solar PV panels, helping you save energy and money.
  • Quality products. We work with leading manufacturers to supply a wide range of high quality heat pumps that use the latest refrigeration technologies. All our products are perfectly suited for the UK climate and will work effectively in temperatures as low as -20o
  • Easy installation. Our heat pumps are easy to install by competent plumbing and heating engineers. You can also ask us to carry out your installation, to ensure full compliance with the Microgeneration Certification Scheme (MCS) and eligibility for RHI payments.

About our products

All our ASHPs use direct scroll or inverter driven compressors, R410a refrigerant gas, 316 grade stainless steel heat exchangers and micro-processor controls.

Some products feature auxiliary heaters that boost the heat pump’s performance in very cold weather and tray heaters to help clear water during the defrost cycle (see below).

Our smaller models are also fitted with water circulation pumps as standard.

Comparing heat pump performance

The output from our heat pumps is measured for an air temperature of -2oC and a heated water temperature of 35oC. This is the European standard measurement for air source heat pumps and will normally be displayed as A-2/W35. So when you’re comparing different heat pumps, it’s important to make sure the stated output refers to this standard.

A heat pump’s performance is referred to as the co-efficiency of performance (COP). This is the relationship between the amount of energy used and the amount generated. For example, if a heat pump uses 1kW of electricity and produces 3kW of heating water, the COP would be 3.

The performance of an ASHP will vary depending on the weather conditions. The variation is around 250 watts for every degree Celsius of change in the air temperature. However, the variation isn’t constant and depends on the actual air temperature and the desired water heating temperature.

ASHPs still maintain their output in very cold weather, enabling a consistent energy output. Despite this, it’s important to take this variation of performance into account when choosing the right size. As with any heat source, the place to start is to work out the true heat loss of the building. There are many ways to do this and we’ll be happy to help.

Once you know the heat loss level, you can then match this with a heat pump. You’ll also need to account for the defrost cycle when working out the correct size requirement.

The defrost cycle

An ASHP will automatically switch to defrost mode during normal operation. This happens because the air contains varying degrees of moisture. As the fan draws moist air across the evaporator, it will start to freeze on contact. This is because the refrigerant gas inside the evaporator is much colder than the air temperature.

This result is a slow build-up of frost or ice on the evaporator. This must be removed to prevent performance loss. Defrosting the evaporator can take quite a while depending on the air temperature. Whilst the heat pump is in defrost mode, there’ll be no heat output.

To compensate for this, the heat pump needs extra capacity. Our heat pumps take into account the defrost cycle in line with EN 14511.

Other things to consider

  • The best type of heating system to use with a heat pump is a low temperature delivery system such as underfloor heating, wall heating or fan-assisted radiators.
  • For areas with high ceilings that aren’t using underfloor or wall heating, the total volume of the space needs to be factored in when sizing your heat pump, as more kW capacity will be needed.
  • Underfloor or wall heating should always be installed with the pipes embedded in screed/plaster or a Fermacel type board, to give high thermal mass.

The underfloor or wall heating pipework must be spaced at the correct centres for the designed output and U values of the building. This can be complicated, so we recommend you ask us to quote for this.