welshboy454
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Heat Pumps - Maximising EfficiencyHeat pumps work by moving heat from one place(normally a ground loop) to another place underfloor heating.
The amount of work they have to do(and therefore the amount of electric they use) depends on the difference in the temperature between the groundloop and the underfloor receiver.
Think of it as little men carrying btu's up a ladder- the ladder gets taller by one rung for every one degree rise in temperature.It follows that taller the ladder(diff in temps) the harder the little men are working.
What you have to remember is that the steps on the ladder get progressively further and further apart as the temperature difference rises.So not only are there more rungs to climb but the higher ones are further apart.
So a heat pump might give a 5 to 1 ratio of heat delivered compared to electric used at low lift temperatures but approach 1 to 1 when a high lift of temperature is asked of the heat pump.
What can you do to maximise efficiency
1 set the temperature you want to be about 32c
2 when placing the u/f pipes set them close together
3 design your output to preheat the hot water feed .I have two hw cylinders - one has an internal coil which the heatpump warms the water which feeds the second main hw cylinder now already at 30c ish so you only have to lift that one a bit more.
4 Think about designing a preheat of the ground loop temperature
either by dumping summer excess solar into the ground loop or have a switched gloop through pipes in tarmac on the drive etc to raise the temp of the source up to in my case 20c as that is the maximum my heat pump can accept.
Although Heat pumps can raise the temperature to 55c you pay for that dearly and even more so at 65c as some heat pumps ar4e capable of by effectively attaching an immersion heater.
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JB
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A couple of other options to maximise efficiency ...
Use heat pumps to run piped underfloor heating which requires a lowre temperature of water than raditors.
Avoid air source heat pumps if there is a high temperarture difference. This is less of a problem in the UK but in places which have climate rather than weather it means that ground source heat pumps are better.
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vegplot
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If considering air source heat pumps also bear in mind that as the temperature outside drops so does efficiency - just when you need don't want it to.
Air source heat pumps suffer from dicing issues in cold weather (start at around 5C) and the normal method to de-ice is to put the system in reverse thus using precious heat to de-ice the external system. This creates noise and lowers overall efficiency.
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