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Heat Pumps

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ROI
4 to 30 -Years




For those interested it operates in a similar way to a refrigerator working in reverse, it works on the principle of the vapour compression cycle within the pump.  There is a volatile fluid known as a refrigerant. The refrigerant in the evaporator is heated by the heat source this causes it to turn into a gas. The gas then passes through the compressor; the compressor increases its pressure and causes its temperature to rise. The hot gas then moves to the condenser where it is condensed back into a liquid and in doing so it releases heat into the house via a distribution system. The refrigerant is then allowed to expand back to a low pressure through the expansion valve and pass back to the evaporator where it repeats the cycle in a closed loop.

What are they?

There are three main types, these are:-

  • Ground Source Heat Pump (GSHP),
  • Water Source Heat Pump (WSHP), and
  • Air Source Heat Pump (ASHP)

They function by extracting heat from the ground the water or the air respectively and releasing that heat energy at a higher temperature within a building.   All heat pumps consume energy usually in the form of electricity to operate the pump that is required to transfer the heat.  They can supply all the heating you would require, and ground source systems are the most effective.  To compare the performance of heat pump the term coefficient of performance is used (COP) and it described the ratio of heat movement to energy input.  In the table below the Best Average COP is used.  This a seasonal average, since air source and water source vary in performance with the temperature of the environment.  For ground source the underground temperature is however remarkably constant all year.

It should also be noted that you will need a reasonable amount of land for an effective GSHP, unless you drill down, and for a water source heat pump a body of water is essential!

Energetically are they worth it?

According to manufacturer information heat pumps provide between 2.5 and 5 times (or they have a COP of between 2.5 to 5) the energy they consume and by energy consumption they usually mean energy in the form of electricity.  Electrical power generation and distribution is covered in another article, however when trying to compare like for like and come to conclusions regarding total energy consumption, the inefficiency of power generation must be factored in, and it never is!  So here are the main points:-

  • 1kWh of electrical energy consumed by the pump should deliver 4kWh of heat energy, and it would have a COP of 4.
  • For a gas fired power station for example 1kWh in your house requires about 2.2kWh of gas energy to generate it, so in reality 2.2kWh is required to deliver 4kWh of heat energy, so should the COP value really be 1.8?

You decide!

Financially are they worth it?

The answer to this question is depends.   It simply depends on the form of heating you have currently, if you are mains gas heated this technology make no sense on financial grounds, since one unit of gas energy is four times cheaper than one unit of electrical energy; the system will be cash neutral and will never pay for itself.  If your only source of alternative heating is electrically powered at the standard rate, then it could be well worth the investment and pay back in about 8 years.

Data table

Heat Pump Best Average COP

Very Rough Equipment and Installation Cost

Grant are available to reduce this cost

Annual Electrical Energy Requirement

(16,000kWh/COP)

Cost of Electrical Energy

Cost of "Replaced" Energy

Payback Time
          Gas LPG Electrical Gas LPG Electrical
Ground Source 4 £ 12000 4000 kWh £ 580 £ 720 £ 1232 £ 2320 86 Years 18 Years 8 Years
Water Source 2.8 £ 8000 5700 kWh £ 827 £ 720 £ 1232 £ 2320 Never 20 Years 5 Years
Air Source 2.8 £ 6000 5700 kWh £ 827 £ 720 £ 1232 £ 2320 Never 15 Years 4 Years
This table gives the potential payback times for a various heat source pumps assuming that the total household heat requirement is satisfied. The requirement is assumed at slightly above the average at 16,000kWh each year.


 
Comments (8)
ASHP
8 Thursday, 06 December 2012 13:52
Grant
Putting Oil into the data table would be useful.
Thanks
7 Monday, 19 March 2012 14:26
Marco Brown
I am very happy to be here because this is a very good site that provides lots of information about the topics covered in depth. Im glad to see that people are actually writing about this issue in such a smart way, showing us all different sides to it. Please keep it up. I cant wait to read whats next.
Monday, 19 March 2012 21:59
Richard
thanks very much for the comment, we are planning quite a lot more over the next few months, and are happy to take suggestions if you have any thoughts
many thanks
Richard
6 Monday, 23 January 2012 20:53
Richard
re. oil, I can put oil in easily if useful on the heat pump page. The point was to just put a few indicative option in, to give people a feel for what they are doing to make sensible choices. There are lots of fuel types in use.

re. not replacing an old boiler, you are correct of course, the cost should be deducted. So if you get a quote and you intend not to replace an old boiler, then yes use this number will be the total investment cost, I think this is a very useful point. And I will try to make the point clearer on the site, particularly true for GSHPs.

re. relative efficiency gains, there it goes away from the spirit of simple digestible data, for example we could include heat pump life-cycle, relative maintenance costs (boiler, vs pump) and indeed if its better to invest the money in Greek bonds (I jest). How complicated should the comparison be, and at what point does it become over complicated is the problem here. Since every situation will be very different, it is difficult for a general site like this to cover all eventualities.

cheers

Richard
5 Monday, 23 January 2012 15:17
max
OK, I'm numerate, I CAN work it out for myself, but it would be nice to simply see the trade off of heat pumps against oil fired heating.
Surely the calculation should also consider the efficiency of and at what point in the replaced appliance lifecycle the change takes place. If you replace an inefficient oil boiler at the end of it's expected life span the the cost of replacing like for like (a new boiler) should be deducted from the cost of the heat pump, and the efficiency gains of a like for like replacement should be factored in to the pay back time.
Great
4 Thursday, 15 December 2011 06:23
Maxx Brown
Great share it is surely. My mother has been waiting for this tips pozycjonowanie
3 Thursday, 07 April 2011 11:22
Forgot to mention.
The air flow forces cold air out of the system.
If you have a small garden and the washing line is anywhere near in line with the fan - then your wet washing will be froozen like a board.
Any plants in line with the air being forced out of the fan (which is through a wide angle) will be killed by frostbite.
price
2 Saturday, 05 February 2011 19:34
Well thanks for that they look loverly. thought of putting the prices on your website?
1 Saturday, 29 January 2011 19:32
We've got air heat pumps here - for hot water and central heating wet radiators . We find that the radiators take a very long time to warm up compared to say a gas boilered central heating system.
We also find the system regularly flushes itself with freezing cold water, thus cooling the hot water and radiators.
And the Mitsubishi fans are noisy, especially when mounted next to the building - as vibration sound comes through the foundation, and where it's bolted to the wall.
Thursday, 25 October 2012 05:31
stretch
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Monday, 24 September 2012 20:59
Jonathan
Of course the radiators take longer to heat up than a gas boiler, thats why a heat pump is more efficient than a gas boiler, its like putting your foot on the accelerator pedal of a car, you shouldnt be switching it off at all they run on a constant trickle of heat controlled by your thermostat, and the rads sit at a constant temp.
Wednesday, 25 April 2012 16:01
Michael Smith
More likley to be poor installation/commissioning. The outside unit should be installed on semi flexible feet and attached, if necessary, to the wall with a non rigid connection.

Yes the flow temperature from a Heat Pump is lower than from a conventional boiler and this should have been made clear to you and factored in to the sizing calculation by your installer. Sometimes this means that some radiators may have to be increased in size and usually the pump is operated for longer periods than conventional high temperaturel fuel boilers. This increases effiiciency. Lastly, the initial setup of the flow controller is critical and if the installer has just left it at factory settings without taking into account your requirements it is unlikely to be working correctly.

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