Air Source Heat Pump - advice

Catbells

I am hoping to have an air source heat pump installed early next year. I understand from one company I spoke to yesterday that the Government are bringing in new incentives in June next year to encourage people to buy them by paying them back annually for 18 years, the money spent on them - around £7-8k in my case. This sounds great.

The person I spoke to said to turn down the regulator on the central heating boiler to number 1 and keep the CH running for 24 hours to see what the temperatures were like in the house. This would give us an idea of what an air source heat pump would feel like and also be an indication of the insulation level of the house - windows, walls etc. If anyone has had experience of this kind I would be glad to hear if the advice I was given is consistent with theirs. Thanks.

zeupater

Catbells wrote: »

I am hoping to have an air source heat pump installed early next year. I understand from one company I spoke to yesterday that the Government are bringing in new incentives in June next year to encourage people to buy them by paying them back annually for 18 years, the money spent on them - around £7-8k in my case. This sounds great.

The person I spoke to said to turn down the regulator on the central heating boiler to number 1 and keep the CH running for 24 hours to see what the temperatures were like in the house. This would give us an idea of what an air source heat pump would feel like and also be an indication of the insulation level of the house - windows, walls etc. If anyone has had experience of this kind I would be glad to hear if the advice I was given is consistent with theirs. Thanks.

Hi

Well firstly, 7k-8k for an ASHP seems a little high ..... secondly, I'd look at the temperature of the boiler feed and/or the radiators when the CH is set to number 1 on your boiler, it could still be far above the efficient running temperature of a heat pump system.

The ASHP will become far less efficient both as the temperature outside drops (when you need it most) and when you increase the feed temperatures to the radiators. It would seem to be the norm to say that, if you are not considering installing underfloor heating loops, you should at least double, or possibly even tripple, the surface area of your radiators. At 7k to 8k for the installation I would hope that a good proportion of your radiators are being upgraded/replaced and I do hope that the company which has provided the guide price has done a heatloss calculation for your house and isn't just considering the bottom line for the sale.

Catbells

Many thanks. I'll keep your comments to hand when I next speak with the company. He mentioned the Mitsubishi model as being the most appropriate.

Also having turned the boiler down to 1 - the radiators seem just as hot as before so am not sure why it was up to 4 in the first place??!!

Cardew

Catbells wrote: »

Many thanks. I'll keep your comments to hand when I next speak with the company. He mentioned the Mitsubishi model as being the most appropriate.

Also having turned the boiler down to 1 - the radiators seem just as hot as before so am not sure why it was up to 4 in the first place??!!

Firstly make sure that the boiler being turned down to 1 isn't for the Hot Water(for taps).

Most boilers - but not all - can control the temperature of the water in the Radiators mine is in 8 steps from 50C to 82C.

There are two basic facts to be considered when contemplating an ASHP system.

Firstly that they are more efficient when producing hot water at far lower temperatures than conventional central heating. 35C to 40C is when they at their most efficient, which is why they are ideally suited to underfloor heating. If you stick to radiators they will need to be much bigger or make the water hotter and lose efficiency.

Secondly, as ambient temperatures reduce the efficiency falls off.

If you have gas at present, I would personally never consider an ASHP especially at the sort of prices you quote.

The problem is there are a lot of heat pump enthusiasts and having fitted a system, people are loath to admit that they are disappointed.

Catbells

Cardew wrote: »

ASHP system.

Firstly that they are more efficient when producing hot water at far lower temperatures than conventional central heating. 35C to 40C is when they at their most efficient, which is why they are ideally suited to underfloor heating. If you stick to radiators they will need to be much bigger or make the water hotter and lose efficiency.

Secondly, as ambient temperatures reduce the efficiency falls off.

.

Thanks. Am trying to understand your first point that they are more efficient at producing hot water at far lower temperatures than conventional central heating. Do you mean that hot water is never as hot with ASHP as it is with gas CH (which I have). Also how would having bigger radiators increase temperatures? Or is that bigger surface areas radiate the same temperatures - only more of it? If I have understood correctly.

Your second point suggests to me that the colder it is outside (like now) the less heat is produced - which is when you need it the most. Right?

zeupater

Catbells wrote: »

Thanks. Am trying to understand your first point that they are more efficient at producing hot water at far lower temperatures than conventional central heating. Do you mean that hot water is never as hot with ASHP as it is with gas CH (which I have). Also how would having bigger radiators increase temperatures? Or is that bigger surface areas radiate the same temperatures - only more of it? If I have understood correctly.

Your second point suggests to me that the colder it is outside (like now) the less heat is produced - which is when you need it the most. Right?

Hi

What Cardew means is that the higher the temperature the ASHP feeds water into the heating circuit, the lower the efficiency of the ASHP becomes. Heat pump efficiency is measured as being the heat output (kW) over the electricity input (kW), this provides a ratio known as the COP (Coefficient Of Performance). The problem with heat pumps is that as the feed temperature of water increases, they need more kW of energy to produce each kW of heat.

Have a look at this wiki ... http://en.wikipedia.org/wiki/Heat_pump#Efficiency

What needs to be remembered is that gas is generally around a third the price of electricity, therefore the operating COP needs to be over 3.0(ish) to break even on operating costs, unless you are operating the heatpump on cheaper nighttime electricity, when the breakeven is closer to a COP of 1.5, which is possibly all you would (optomistically) achieve whilst the nighttime temperatures are where they are at the moment !

Also remember the hot water requirement will be produced at a very low COP and will most likely need to be supplimented by direct heating coils/immersion heaters (ie a COP of 1.0) on a regular basis.

Regarding the radiator upsizing .... because the heating circuit water temperature is lower the current radiators will be less efficient at heating the air per m2 of panel size, therefore you will need to substantially increase the surface area in order to compensate for this.

Regarding the question "the colder it is outside (like now) the less heat is produced - which is when you need it the most. Right?" ... this is correct, many (most ?) heat pumps (/installations) will have an option (optional extra ?) to suppliment the heat supplied by switching on direct electric heating coils when they cannot generate enough heat from the HP , the COP therefore being 1.0, or three times the cost of gas !

HTH

Catbells

Thank you both. I'm coming round to thinking its not going to be viable from both cost and efficiency standpoints. I would definitely need bigger and possibly more radiators - so more cost. Its disappointing not to be able to use green energy to heat my new home but no point in going green just for the sake of it. I may get a new type of wood/solid fuel stove which I know are very warm. Hopefully there will be ways of purifying the emissions from these by now.

zeupater

Catbells wrote: »

Thank you both. I'm coming round to thinking its not going to be viable from both cost and efficiency standpoints. I would definitely need bigger and possibly more radiators - so more cost. Its disappointing not to be able to use green energy to heat my new home but no point in going green just for the sake of it. I may get a new type of wood/solid fuel stove which I know are very warm. Hopefully there will be ways of purifying the emissions from these by now.

Hi

There are a number of stoves which 'clean burn', this is done by pre-heating air before entering the combustion chamber, usually done as a preheated air-wash down the glass door to keep the glass clean.

My stove is running at the moment .... it's very cosy sitting here , logs are local, either my own or from managed woods about 2-3 miles away delivered by the tractor load, can't get much greener, what I burn gets replaced on a totally sustainable basis, so effectively it's a carbon/CO2 closed loop.

HTH

Catbells

Which make is it?

What's a worry is that energy said to be going to rise massively over the next 10-20 years so maybe getting an ASHP, even if it isn't totally efficient, isn't a bad idea after all. You can always supplement it with solid fuel. Decisions, decisions...

zeupater

Catbells wrote: »

Which make is it?

What's a worry is that energy said to be going to rise massively over the next 10-20 years so maybe getting an ASHP, even if it isn't totally efficient, isn't a bad idea after all. You can always supplement it with solid fuel. Decisions, decisions...

Hi

Mine's a Clearview .... when I bought it it was the best around, some others are probably just as good now, but many swear by the Clearview build quality and strength. I had mine in the early 90's and it looks as good as new .... mind you they're not cheap !!

Regarding fuel costs ... you'll find that the cost ratio between the cost of different fuels will probably remain constant for a good while so gas will still remain cheaper than ASHP/Radiators in mid winter.

In your case, you need to consider the RHI scheme which should be introduced next year. This is the only way that you would make cost savings on ASHP v Gas, however, you will be cold in the winter unless you seriously upsize the radiators or install underfloor heating loops ...

Have you considered GSHP ? .... ground source heat is more consistant and stable than air source ... when the outside temperature drops the ground temperature at depth doesn't, so efficiency is maintained better. If you don't have enough space for a horizontal ground loop (very big garden required !), you can use vertical boreholes .... at the £7k-£8K guide price you have been given you'll probably not be that far off the cost of a competitively priced ground source system ... you'll still need really big radiators or U/F heating though !

HTH

Catbells

zeupater wrote: »

Hi

Mine's a Clearview .... when I bought it it was the best around, some others are probably just as good now, but many swear by the Clearview build quality and strength. I had mine in the early 90's and it looks as good as new .... mind you they're not cheap !!

Regarding fuel costs ... you'll find that the cost ratio between the cost of different fuels will probably remain constant for a good while so gas will still remain cheaper than ASHP/Radiators in mid winter.

In your case, you need to consider the RHI scheme which should be introduced next year. This is the only way that you would make cost savings on ASHP v Gas, however, you will be cold in the winter unless you seriously upsize the radiators or install underfloor heating loops ...

Have you considered GSHP ? .... ground source heat is more consistant and stable than air source ... when the outside temperature drops the ground temperature at depth doesn't, so efficiency is maintained better. If you don't have enough space for a horizontal ground loop (very big garden required !), you can use vertical boreholes .... at the £7k-£8K guide price you have been given you'll probably not be that far off the cost of a competitively priced ground source system ... you'll still need really big radiators or U/F heating though !

HTH

I initially wanted GSHP but was informed the air pump was more suitable for my property - semi detached 4 bed (inc loft extension) with a 50ft garden - in London.

Sorry - what does RHI stand for?