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Is a heat pump suitable for my home? 3 key checks

Posted by John Barker-Brown on 15 March 2010 at 9:59 am

Heat pumps are one of the most talked about renewable technologies - on television, in newspapers and magazines. The way they are portrayed they seem to be the answer to all our problems and will suit all properties. But is this true?

Heat pumps (ground, air or water) suit only certain applications and it is important to cut through the marketing spiel and realise this. These units can have large capital costs and can cost you more to run than the system you are replacing if installed in the wrong place.

Three of the key issues to check out before you install are as follows:-

1) Well insulated buildings

As heat pumps are a low temperature device, it is important that buildings that they are installed in are well insulated. Un-insulated buildings require high flow temperatures (the maximum from a heat pump is approx 55 degrees C). Heating to this temperature reduces the efficiency of the heat pump, as the compressor has to work harder to produce the higher temperatures. Add to this, the fact that in a poorly insulated building the heat emitting device, radiators or underfloor, may not be able to provide heat into the building at the low temperatures, so not only are the running costs high, but you also feel cold!

Insulating the building well also reduce the size of the heat pump needed, and the initial capital costs and, in the case of ground source, the amount of ground required.

2) Heating distribution systems

Most existing houses have radiators installed as their heat emitting device. A lot is made of the fact that heat pumps should only be used with underfloor heating. This is not strictly true. However, as radiators require the water to be heated to a high temperature, a heat pump will run up to 25% less efficiently with radiators. In addition, you may need to install larger radiators, to keep warm enough.

3) The fuel you are replacing

Many companies indicate savings can be achieved of up to 50% of your current fuel bills. However what they don’t tell you is that the amount you save depends on the fuel you are replacing and the installation, as we saw above. Different fuels have different costs associated with them. Direct electricity is the most expensive and gas the cheapest. While heat pumps use electricity to drive them, because of their high efficiencies the cost per kWh used can be as much as quartered, if you are currently heating with electricity.

If you have mains gas, the running cost of a well installed heat pump is similar, but as soon as you add radiators or a poorly insulated building into the equation, it pays to stay on gas. However this is likely to change next year if the Renewable Heat Incentive is introduced.

Heat pumps do not suit all applications. You can see that a rambling 17th Century listed building on radiators is not an ideal candidate, neither is an un-insulated building on radiators and the gas main. Do not install a heat pump in a poorly insulated building. However, where the application is correct heat pumps can significantly reduce running costs and carbon emissions making them a worthwhile investment and with the renewable heat incentive the growth of the heat pump market is about to explode.

Photo by mfeingol

About the author: John Barker-Brown is special projects manager at British heat pump manufacturer Kensa Engineering.

If you have a question about anything in the above blog, please ask it in the comments section below.

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Comments

6 comments - read them below or add one

Kensa Engineering Ltd

Kensa Engineering LtdComment left on: 27 April 2010 at 2:20 pm

At Kensa we have always sized on the heat load as required by the building and this is how it should be. We have been doing this since we started manufacting in Cornwall over ten years ago.

We are aware that a number of companies are limited by the size of the heat pump that they can offer on single phase, usually around 11kW (24kW is the largest heat pump Kensa manufacture on single phase) and therefore these companies undersize the heat pump. Basing the heating distribution system on the heat pump then, as you say, is a problem and without supplementary heating clients can feel cold.

The knowledge of some companies and the claims they make are laughable, but unfortunately with large marketing budgets, clients tend to believe them and the industry, if not careful, will suffer. The REAL Association have already mentioned to me that they are concerned with the amount of complaints they are receiving from clients who have been sold heat pumps for uninsulated buildings and now have large energy bills and even feel cold. 

I'll talk more about COP's and underfloor in another blog, as even with underfloor COP's are not always 4.0

 

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DB Heating Ltd

DB Heating LtdComment left on: 27 April 2010 at 12:38 pm

I was also at Ecobuild & at the NEC representing a Devon based heat pump manufacturer.(yes made in England) ....COP's of 4 & over are acheivable and have been acheived, however, only with a particular heat pump & correctly designed underfloor heating system. With regard to the underfloor heating design, I find that a lot of GSHP suppliers will base the underfloor output on the GSHP's output, leaving back up heating required when it gets cold !!! ...The correct way is to calculate the requirement of the dwelling/ building, then choose a GSHP to suit, not the other way around. this is now becomming less of a problem as some suppliers have now sourced larger units.  The stories, claims & ideas discussed at the show(s) was at times, nothing short of funny! 

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Kensa Engineering Ltd

Kensa Engineering LtdComment left on: 20 April 2010 at 2:41 pm

Phil,

I'm not an underfloor specialist, however I'm aware that studies on underfloor systems are generally limited to 3m due to the radiant nature of underfloor. Having said that heat will always migrate from hot to cold areas so it is important to insulate well otherwise any heat produced will simply be lost to the atmosphere.

Barns generally provide an ideal application for heat pumps particular ground source due to the associated land available.

Probably the best option is to talk to your underfloor specialist regarding underfloor and high buildings.

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philhatswell

philhatswellComment left on: 19 April 2010 at 5:54 pm

I am considering installing underfloor heating and a ground source heat pump in a barn conversion that I am planning. Even if I highly insulate the roof, due to the high roof heights I still have a large area to heat. I thought that the advantage of UFH in a barn was that it heats only the lowest few metres of air, unlike radiators where all the heat rises to the roof. I am I wasting my time using UFH and heat pumps in this situation, or I am I wasting my time insulating the roof!

Thanks

Phil

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Kensa Engineering Ltd

Kensa Engineering LtdComment left on: 29 March 2010 at 8:23 pm

Thanks Barry, Kensa were also at the National Homebuilding and Renovating show and the level of mis-selling certainly had us worried. I had one major boiler maker (new to heat pumps, but with a very large marketing budget), tell me I needed boreholes, even though I told them I had three acres of fields. Reason was the cost of landscaping! Landscaping a field????

The last thing we want is the technology getting a bad name due to incorrect application. 

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Barry Nutley

Barry Nutley from Viridis Energie ConsultantsComment left on: 25 March 2010 at 11:23 pm

Well done John for giving this honest appraisal of heat pumps ,especially from a heat pump manufacturer (please don't take it the wrong way?!).. Having spent last week exhibiting at the NEC (Homebuilding and renovations), if I had a £1 for every person that came to us asking us to clarify the claims being made by some installers, that their heat pump will work at a COP of 4:1, regardless. We'd have paid for our stand! The worst case I heard from one visitor, was that the "salesman" actually made that claim, sized the pump, and gave the guy an installation cost, without even asking him anything about his house! 

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