Caveat

So let’s begin with the normal Caveat. Before getting around to selecting the particular heat pump you want, check that all of the practical insulation measures that could have been taken on your property have been taken!

 

Let’s quickly slim the choice down!

The first thing you can do is to eradicate any heat pumps that are not certified under the Microgeneration Certification Scheme, or MCS as it has now become known as. Government and industry has worked hard over the past few years to develop a certification scheme with exacting standards to ensure that consumers get a product that meets high quality and performance standards.

 

So it’s MCS accredited, what’s next?

When comparing the performance of heat pumps I would recommend you should compare the performance in terms of heat output, normally quoted in kW, and efficiency, normally referred to as Coefficient of Performance or sometimes the abbreviated version CoP. Whilst I am sure you will be able to relate to heat output in kW, you may not be conversant with CoP. If you are, skip the next paragraph…!

 

CoP

Coefficient of performance basically compares the energy in, in terms of electricity, to the energy out, in terms of kW of heat.

If the unit producing a flow temperature of 35^oC produces 3kW of heat when the ambient (outside) condition is -1^oC and it consumes 1kW of electricity it’s CoP, at that condition, will be its output (3kW) divided by its electrical input 1kW, which in this example equals a CoP of 3.  If it was only producing 2.1kW at this condition it’s CoP at this condition would be 2.1!

 

Condition to Compare at…

When comparing duty and CoP, I would advise you compare them at the recommended design condition for your area and application.

 

I have listed below for your information the design temperatures specified in the Microgeneration Installation Standard: MIS 3005, for different areas of the UK which are as follows:-

• Belfast   -1.2^oC
• Birmingham   -3.4 ^oC
• Cardiff   -3.9 ^oC
• Edinburgh    -1.8 ^oC
• Glasgow   -3.9 ^oC
• London   -1.8 ^oC
• Manchester   -2.2 ^oC
• Plymouth   -1.2 ^oC

 

By application I’m referring to the type of heat emitters you are using. Under floor systems can be designed typically using flow temperatures between 35^oC and 40^oC, whilst radiator systems will use design flow temperatures of 50^oC+, so it is important when comparing heat pumps for your property to do so at the design flow temperature and design ambient condition. The headline outputs and CoP quoted by manufacturers are normally based on a European Standard of an outside condition of 7^oC and a flow temperature of 35^oC. Whilst one has to accept this is probably a good average condition for Europe as a whole, it is not much use when selecting equipment for the UK. You will consume most of your energy when the temperatures are close to or below 0^oC, not when they are 7^oC and above. Personally I would be suspicious if a manufacturer / supplier could not provide me with this information.

Some less scrupulous manufacturers for example, although none to my knowledge listed under MCS, quote their headline heat outputs and CoPs at 20^oC ambient conditions. Not much good to you given you are unlikely to require much heating at this condition!

 

Minimum Operating Temperature

Although this should not be an issue with MCS accredited units check at what temperatures the heat pump will continue to produce the flow temperature your system requires. It is obviously not much good, if, just when you need it, the unit can no longer produce flow temperatures which are adequate for your application. Most units continue to work down to -20^oC, but some will not produce flow temperatures any where near your design conditions.

 

Maximum Flow Temperature

If you intend to use your heat pump with radiators, there are models on the market which produce high flow temperatures 60^oC+ (including our Bwarm “i” range) and still provide good CoPs, but hopefully your comparison exercise will have revealed this to you.

 

Size

As well as the size of unit, from an output point of view it is worth considering the physical size of the product. Some units are much larger than others for the same output and some are much taller than others, which might be an important consideration if you are positioning the unit under a ground floor window.

 

Controls

You may wish to select a unit that can be operated with the type of controls you, or your family, are used to using. A unit can be the most efficient on the market, but if you don’t control it properly…!

 

Electrical Supply

When selecting your heat pump make sure the model you select is suitable for a single phase electrical supply and not three phase supply, which is only available on less than 1% of the UK’s domestic premises.

 

Sound Levels

Most modern heat pumps are very quiet but it is worth checking the sound levels between models. This detail may help you to finalise the choice between your selected products.

 

Have I missed anything?

Let me know if there is anything else you think I have forgotten, that should be considered, when selecting an Air Source Heat Pump.

 

Happy selecting!