Nine factors that will affect the efficiency of your Heat Pump

March 15 2015

First of all, supplying and installing heat pumps throughout the UK and Ireland leads to a lot of questions regarding the efficiency of these renewable energy systems in terms of how much electricity they use. A heat pump more often than not will have a Seasonal Performance Factor (SPF) of 4.0 or higher, which compares favourably to an oil or gas boiler (0.7 – 0.9). The SPF is the average of the Coefficient of Performance (COP) of the Heat Pump over the whole year. This is put into perspective in our How much do Heat Pumps affect the Electricity Power Network blog post. All in all they’re pretty efficient source of renewable energy, but there’s always room for improvement right?

There are a number of factors which will affect the electricity consumption of a heat pump in your home. Identifying these factors is half the battle when you’re trying to increase its efficiency. So here are the nine factors that will affect the efficiency of your heat pump:

1) The standard of insulation and air tightness measures supplied and installed in the property (The most important)- Your heat pump will not have to work as hard to heat the air in your home if it is well insulated, which means a lower electricity bill.

2) The length of the drying out period- It can take up to 1 year for the house to “dry out” once it has been built because of all the moisture collected during the building process. The heating system is often left on for this period, which varies depending on the house.

3) The room temperature set by the home owner- Increasing the Room Temperature in the house by 1 degree can result in an increased running cost for the heat pump by up to 20%.

4) The Hot Water Temperature set on the Heat Pump- A lower water temperature results in a lower running cost for the heat pump.

5) The Hot Water Consumption in the House- For example, flat head showers will cause your home’s hot water requirements to increase.

6) The electricity tariff- The “Economy 7” tariff, available in the UK, where you get 7 hours cheap electricity at night will allow you to set your heating and hot water slightly higher at night, resulting in reduced running costs by up to 50%.

7) The use of Solar PV– A 4kw Solar PV System can offset the running costs of the heat pump by up to 40%. A heat pump which has an Inverter Compressor is better suited when a Solar PV System is installed as it uses less power once it reaches its target flow temperature in the heating system.

8) Windows and doors that haven’t been closed- The best insulation and air tightness measures are wasted if you leave doors and windows open. Heated air rushes out, which means your heat pump has to work to raise the temperature of your home again.

9) The use of a mechanical heat recovery ventilation system– A well designed and installed MHRV System can recover up to 85% of the heat in the house which would otherwise be lost if trickle vents and mechanical extract fans are used in the property.

Modern heat pumps make it easier for you to tell if your efforts to make them more efficient have worked with the inclusion of energy meters that tell you it’s COP. This can be viewed in the top image presented below, which was taken from an Ecoforest ground source heat pump in March. It will also tell you the daily, monthly and annual electricity consumption for added clarity. It is worth noting that the average SPF will normally be 4 or higher, which will depend on the energy requirements of the house. If for example the house is very well insulated the ratio of hot water production to space heating production will be higher, therefore the COP on the heat pump may actually be lower, but overall the electricity consumption will be low.

These factors are important, but none compare to the importance of buildings construction quality when it comes to running costs. Heat Pumps when designed and installed correctly are a very efficient form of heating especially in low energy homes. Unfortunately not all homes have been built as a low energy home. The bottom image below shows a rigid board insulation installed in a cavity wall. As you can see a 10mm gap has been left between the joints. This was taken on site on a new project we were working on. This can result in the U-value of the Wall being 5 times higher than the intended rating.

It is important to remember that modern heat pumps only produce heat and hot water that the house requires. By making some small changes you can drastically reduce the amount of heat that your home needs.

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