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24 Aug 2020

The most efficient way to run an air source heat pump

By Oliver
  • Read time: 4 minutes
Air source heat pumps are a great source for renewable energy but they need to be used correctly to receive the maximum levels of efficiency and the highest savings on energy bills. Used correctly they can often pay for themselves along with the RHI repayments.

For many renovators and self-builders, an air source heat pump is often the most viable alternative to gas boilers. As its name suggests, it needs air to run, meaning it has to be positioned where there is enough supply of ambient air. This is a popular renewable heat technology which is an ideal solution when you want to generate your heat and save on energy bills. However, your home has to be well-insulated. Otherwise, the heat generated will end up escaping. Here, we bring you the most efficient ways of running your heat pump.

How an air source heat pump works

Some air source heat pumps (ASHP) can also be used to keep a home cool during summer and warm in winter such as the Vaillant aroTHERM. The process uses the principle of vapour compression to transfer hot air from one place to another, the same way a refrigerator does. The air source heat pump is placed outdoors. It then sacks heat from the air and raises it to a higher temperature using the heat pump. For it to run, it has to use electricity but should consume less energy than the heat it produces.

How ASHPs work

How to run your heat pump efficiently

The key to achieving air source heat pump efficiency is by ensuring that you have an insulated home. Given that the heat pump will operate at a low temperature, the state of insulation must be addressed before installation. This will ensure that heat-loss through the floor, walls and the roof is minimised. Now is a great time to look at getting these improvements made to your home with the Government's Green Home Grant offering funding towards all of the below measures. Here are areas to look into:

Loft insulation
At least a quarter of the heat generated is lost through the roof. Insulating the loft and the attic is an excellent way for reducing the heat loss to help you save on energy bills. It will mean installing about 270mm in the loft to achieve the u-value of 0.16W/m2k. The insulation can be laid between joists or the rafters. Lost insulation lowers the heating bills, reduces the carbon footprint, improves the energy efficiency rating and increases the home value.

Cavity wall insulation
The cavities on your walls should be filled with insulation to keep in as much heat as possible and save on your energy bills. Consider cavity wall insulation if:

  • The bricks are in good condition

  • The cavities are about 2 inches wide

  • The external walls are accessible

  • The internal walls are dry

  • The construction is not timber or steel-framed

A registered installer should fill the cavities with polystyrene granules, polyurethane foam or mineral fibre wool.

Double glazed windows
Windows are responsible for heat gain and heat loss of about 25-30%. Double glazed windows improve efficiency and can increase the comfort of your home. Energy-efficient windows reduce the carbon footprint and energy bills.

Correct sizing
Although air source heat pumps have a lower kW output than the conventional ones, they are limited by the electrical supply, meaning that you need to install the right size against your property’s heat loss. The wrong size, both oversize and undersize, will mean running high electricity costs and even system failures. Before installation, have the heat loss calculation of your building collected based on your location. It is crucial to ensure that the heat pump can offer the energy needed in line with the outdoor temperature.

Intelligent control
Intelligent control keeps your system running efficiently. It consists of a water freezing system, a cooling apparatus, a fan, compressor and a flow capacity observation apparatus. You can purchase a digital thermostat and timers to easily adjust to your needs. The right control will optimise your running costs and keep your home comfortable. In the event of a breakdown, these controls make it easy to check and diagnose faults as well as ensure that the correct parts are sourced.

Vaillant GSHP

Should you consider a high temperature heat pump?

If you are looking to achieve a high temperature, you can take advantage of systems which are built for that purpose. These are built in a cascade system to release a temperature flow of up to 80°C. Note, however; they should not be used in the place of a high temperature boiler unless proper calculations of the lower efficiency have been done to ensure they are right for your property. This is because they are purely created for hot water. One of the most outstanding benefits of this system is its ability to reduce the heat pump’s complexity. Other technological advances have also featured in the market, such as compressors built to allow compressed air to be re-sacked by the compressor for higher temperatures. They include systems such as the Mitsubishi Ecodan, and can to get temperatures of about 65°C.

Is an air source heat pump right for you?

Before answering this question, there are a few aspects you need to consider, and they are as follows:

Be sure you have enough space to put the system outside your house. The system can be either placed on the ground or fitted to your wall. For optimal air-flow, the unit will need plenty of space.

The type of heating system you intend to use
These units operate at low temperatures, meaning they are best suited for warm air heating. If you do not have a central air conditioning system, have one installed for your heat pump to work.

How well is your home insulated? Note; air source heat pumps operate well when left to produce heat at low temperatures. It means that you can only minimise heat loss by draught-proofing and insulating your home.

Type of fuel being replaced
If you are replacing an expensive fuel source such as electric heating, you will save a lot in terms of monthly heating bills. However, when switching from mains gas, you may not save much.

Heat pumps, unlike gas or oil boilers, deliver their heat at much lower temperatures for longer periods. Should you choose an ASHP, consider upgrading your insulation for optimal performance and also save on your energy bills. Air source heat pumps work best with underfloor heating. If you are looking to get the most out of your system, consider underfloor heating.


Written by Oliver

Oliver is a Content Specialist for 50five UK