Very confused about Air Source Heat Pump

baxie

Hello,

My Mother has qualified for a grant to have Air Source Heat Pump installed with new radiators and solar panels with battery backup.

Unfortunately, due to having existing passive solar water heating panels, the installer says they cannot install the pv solar panels, but can do the Air Source Heat Pump.

On the leaflet they gave her it says that the "Net Energy required to heat property" is 16521kWh, which is the consumption for the existing system.

They say they are going to install a Vaillant aroTHERM Plus 5kWh VWL 55/6 A 230V S2 Air Source Heat Pump.

The figures for this say it will consume 6221Kwh.

My Mother has emailed the installer to ask if this means that when the heat pump is installed that it is going to use almost 1/3 of the energy as the current system.  Or, does it mean that the heat pump system will only provide about 1/3 of the heating?

The response was "16521kWh- heat kwh required

6221kWh- electrical kwh units

For the heat pump system performance estimate has estimated that you will use 6221kwh of electricity per year to heat the hot water and heating for the property. "

What does this mean?

Will 6221 kWh of electricity from the pump produce 16521 kWh of heat for the house?

Can any one help, please?

koru

The high figure is the heat needed over the year, to keep the house warm, measured in kWh. The lower figure is the electricity that they project will be required to produce this. (The difference is the heat extracted from the air outdoors.)

The ratio is 2.65, which is pretty low. At that level, a heat pump is likely to cost more to run than a gas boiler. Unless the house is poorly insulated, the ratio really ought to be more like 3.5 or higher.

Netexporter

That is a SCOP (seasonal coefficient of performance) of 2.66 which is fairly conservative. With luck/good management it should do better than that and use less electricity.

Netexporter

I'd pay to have the solar thermal removed and get the free solar PV. Much more useful. Also the thermal panels almost certainly won't work with the new hot water cylinder fitted with the heat pump.

Nick_Dr1

Basically because of how a heat pump works, 6221kWh- electrical kwh units is turned into 16521kWh- heat kwh required.
Heatpumps are efficient that way. As others have said, they are being a bit pessimistic as normally you would expect at least a 300% gain, but no-one really knows until the system is installed.

The actual cost of heating the house will depend completely on the tariff you are on. As a rough rule of thumb, it should cost about the same as a good gas system to run, all things being equal. If you get a good price for electricity it could well be cheaper. If you stay on a standard tariff it will be more expensive.

Reed_Richards

It's almost like magic but actually it's physics, you can get 16521 kWh of heat from 6221 kWh of electricity.  In fact for a heat pump that's not very good.  BUT how is your mother heating her house at present?  If she uses gas or oil then because of the high cost of electricity by comparison with either of these fuels she could well end up paying more than she is at present.  To match a gas or oil boiler that is reasonably modern you would need to get at least three times the kWh of heat per kWh of electricity.

Nick_Dr1

Oil (as an example) contains 10kWhr energy per litre and let’s say it costs 75p a litre. That’s 7.5p/kwhr of actual heat assuming 100% efficiency. 

So assuming a heat pump efficiency of 300% you’d need 1/3 kwhr electricity for 1kwhr heat. Let’s say a unit of electricity is 21p. 1/3 of a kwhr costs 7p. 

So the heat pump is marginally better. 

If you can get electricity for 12p a unit then you are paying 4p per kwhr of heat. 

If you can get the efficiency up to 400% then you only pay 3p kwhr. 

If you pay 32p unit it costs you between 10.6 and 8p kwhr. This is more expensive than oil. 

Of course the price of oil (or gas) can go up and down so the comparison is always changing. 

It’s basically all about the tariff!

Exiled_Tyke

If the installer isn't being as helpful as they could be answering questions then I'd look for some other installers to quote.  From the little information we have it does feel like they are looking for an easy journey for themselves.  Also note that it is relatively easy to qualify for the government grant (£7,500) for a heat pump installation, many providers are capable of applying for this. 

FreeBear

Exiled_Tyke said:

If the installer isn't being as helpful as they could be answering questions then I'd look for some other installers to quote.

If the work is being done under the ECO4 or similar scheme, you don't really get much choice about which installer does the job.

NedS

FreeBear said:

Exiled_Tyke said:

If the installer isn't being as helpful as they could be answering questions then I'd look for some other installers to quote.

If the work is being done under the ECO4 or similar scheme, you don't really get much choice about which installer does the job.

You can get multiple quotes for ECO4 - I had 6 surveys before I found a company/package I was comfortable with. There isn't much choice or flexibility in what an individual company will be offering, but the various offers varied significantly between companies.

baxie

Thank You all very much for your replies.

The scheme is ECO4 through the Scottish Government, and as such we have no option in installers.

The current system is a tank where the water is heated by electricity with the solar thermal panels assisting.  During the initial visit she was told it was essentially an immersion heater system.

She was quoted as getting something that would be 300% more efficient.  I will be quite !!!!!! off if this ends up costing more than she pays at the moment.

The company have said it is not economically viable for them to remove the solar thermal panels and retile that part of the roof, and that the roofer they use would estimate it would cost about £1000 to have them removed, but a proper quote would have to be done.

I am going to get in touch with Warmworks Scotland, the people running the scheme to see if there is anything they can do to help.

Thank You for all your advice.