Heat Pumps - Pros and Cons

bernithebiker

We have 6 holiday houses to heat.

In 2010, 2 on LPG, 2 pure elec., 2 heating oil.

End 2011, 1 LPG goes to 1 full air/water heat pump (Sdeec) to take advantage of UFH.

1 LPG gets an electric immersion tank, and a cheap air/air heat pump as supplements.

Both pure elec. get cheap air/air heat pumps as supplements.

1 heating oil gets a wood stove as a supplement.

1 heating oil get s a 44kW wood boiler as prime source with HO as backup. (Chateau).

The air/air heat pumps are new and the source of my question. They are £650 each, all in, fitted by myself, very easy to do. COP of 4 at 7'C. Noise of 22dB inside, 38 out.

The idea is that whilst these are running, they are taking load off the LPG or pure elec heaters. In theory, for 1kW used, they are putting an extra 3 into the house. The thermostatic radiator valves in the sitting room of the LPG house for example, close off when the heat pump is running.

My back of a fag packet calcs. show that if the heat pump runs 24 hours a day, I'm paying for roughly 24kW of elec. (£2.50). But I'm getting another 72kW free.

As elec prices are pretty close to that of LPG, kw for kw, I reckon I could be saving as much as £8 a day.

I realise that COP will be less than 4 when it's colder (I estimate 3 at 0'C), and that the heat pump will not necessarily be at full output all the time, but worst case I hope to save £2.50 per day.

In this case the pump is paid for in 10 months of running, rather better than any other project I've done, like double glazing, wood boiler, solar, etc.

I reckon the downsides are; reliability - how long will it last? Low temps. How well will it work at -5'C (we rarely get below 0'C where we are). Will it ice up?

So far so good - it has been mild (10-12'C ish) and monitoring the pump shows it using between 500 and 1500W (DC inverter). It provides a nice strong flow of warm air, and noise is very low.

It almost sounds too good to be true. Am I missing something?!

lovesgshp

bernithebiker wrote: »

We have 6 holiday houses to heat.

In 2010, 2 on LPG, 2 pure elec., 2 heating oil.

End 2011, 1 LPG goes to 1 full air/water heat pump (Sdeec) to take advantage of UFH.

1 LPG gets an electric immersion tank, and a cheap air/air heat pump as supplements.

Both pure elec. get cheap air/air heat pumps as supplements.

1 heating oil gets a wood stove as a supplement.

1 heating oil get s a 44kW wood boiler as prime source with HO as backup. (Chateau).

The air/air heat pumps are new and the source of my question. They are £650 each, all in, fitted by myself, very easy to do. COP of 4 at 7'C. Noise of 22dB inside, 38 out.

The idea is that whilst these are running, they are taking load off the LPG or pure elec heaters. In theory, for 1kW used, they are putting an extra 3 into the house. The thermostatic radiator valves in the sitting room of the LPG house for example, close off when the heat pump is running.

My back of a fag packet calcs. show that if the heat pump runs 24 hours a day, I'm paying for roughly 24kW of elec. (£2.50). But I'm getting another 72kW free.

As elec prices are pretty close to that of LPG, kw for kw, I reckon I could be saving as much as £8 a day.

I realise that COP will be less than 4 when it's colder (I estimate 3 at 0'C), and that the heat pump will not necessarily be at full output all the time, but worst case I hope to save £2.50 per day.

In this case the pump is paid for in 10 months of running, rather better than any other project I've done, like double glazing, wood boiler, solar, etc.

I reckon the downsides are; reliability - how long will it last? Low temps. How well will it work at -5'C (we rarely get below 0'C where we are). Will it ice up?

So far so good - it has been mild (10-12'C ish) and monitoring the pump shows it using between 500 and 1500W (DC inverter). It provides a nice strong flow of warm air, and noise is very low.

It almost sounds too good to be true. Am I missing something?!

The COP @ 7c is usualy based on a 20C room temp. If your tenants increase this to 23c, then running costs will be higher. It is a question that could never be specificaly answered, as to many variables.
Reliability depends on the manufacturer and the guarantee they are prepared to give, plus how long they have been making the units.
Sorry that I cannot be more helpfull, but there are too many variables that could affect the performance.