Still trying to make the numbers work for a heat pump 11 September 2020 at 4:36PM in Green & ethical MoneySaving 35 replies 930 views

michaels

Our deemed heat usage on the EPC is about 13k heat and 2.5k hot water.  Our actual usage (high efficiency Gas boiler) is about 17k heat (we heat 24/7) and 14k hot water (we like to keep clean).  This means that what we can get form the RHI is much lower than the cost of installing a GSHP or ASHP.

However we can probably get up to 10k from the Green Home Grant.

So I am thinking for 10k could we get a system that did the space heating whilst leaving the hot water heating to gas.

My understanding is that DHW heating using a heat pump is particularly inefficient due to having to achieve higher water temperatures.

So what are the ASHP options?
How about air to air?  Is this covered by the green home grant - there is no mention of it not being covered unlike the RHI.  How does a typical air to air system work?  Do you have a single compressor and then a refrigerant circuit to multiple heat emitters?  Presumably it has the advantage or providing cooling too.  Are the SCOP better for air to air than air to water?  What values could be expected?  Presumably air to air gets round any problems with undersized rads (which could even be removed to increase interior space?
alternatively how about air to water?  What size system would be need to provide this sort of annual level of heat?  Could this be installed for 10K all in?

Thanks for your thoughts

gefnew

Hi
this may help you a bit.
https://www.homeheatingguide.co.uk/renewables-advice/air-source-heat-pumps-a-sizing-guide

michaels

Thanks
I can't find little info on air to air heat pumps, probably because they were not eligible for rhi so are not very common in the UK..  I think some on here may have experience?
There is no clarity (no info at all on) on whether air to air might come under the green home grant.

shinytop

michaels said:

Thanks
I can't find little info on air to air heat pumps, probably because they were not eligible for rhi so are not very common in the UK..  I think some on here may have experience?
There is no clarity (no info at all on) on whether air to air might come under the green home grant.

Yes there is and they and unfortunately are not included. I had my eye on one too. 
https://www.simpleenergyadvice.org.uk/measures/meta_air_source_heat_pump
Paragraph 6 of 'What is is?'

Cardew

shinytop said:

michaels said:

Thanks
I can't find little info on air to air heat pumps, probably because they were not eligible for rhi so are not very common in the UK..  I think some on here may have experience?
There is no clarity (no info at all on) on whether air to air might come under the green home grant.

Yes there is and they and unfortunately are not included. I had my eye on one too. 
https://www.simpleenergyadvice.org.uk/measures/meta_air_source_heat_pump
Paragraph 6 of 'What is is?'

Does not paragraph 6 refer only to RHI not the 'Green home Grant'

michaels

Mickey666 said:

As the OP has gas to the property (I’m assuming mains gas) then the numbers for a heat pump will never ‘work’ - at least not for the foreseeable future.  

I went through a similar exercise a little over 10 years ago when I didn’t even have mains gas.  It worked out cheaper to have mains gas installed and a new boiler installed than having a heat pump installed.  In short, mains gas is about 3x cheaper than electricity (per kWh) and a heat pump is about 300% efficient.  In other words a heat pump will cost about the same for heating as using mains gas.  Even if you can get a grant for a heat pump, it won’t be 100% so you’ll still have to fork out a few thousand pounds and after that expenditure your heating costs will remain roughly the same anyway.
Ten years ago, I decided to wait until the numbers for a heat pump ‘worked’ when compared with mins gas . . . and I’m still waiting.

If it was 3x it would be ok - problem is currently it is more like 4x - 5x cheaper for gas than electricity and either you get an ashp with a max scop of 3 and a reasonable install cost (after RHI) or a gshp with a better scop but an unaffordable install cost for a vertical loop system

Hence wondering whether it might be possible to get an air to air which has a reasonable scop and provides AC as well and keeping the gas boiler for hot water.

joefizz

michaels said:

Hence wondering whether it might be possible to get an air to air which has a reasonable scop and provides AC as well and keeping the gas boiler for hot water.

Wee quick update with my ashp. Ive had the oil heating disconnected for a couple of weeks now (building small sunroom on so needed to move the boiler) so been relying on battery, ashp and immersion for heating and hot water.

Apart from the sun not shining enough to fully charge the battery for a couple of weeks (until yesterday), we had a cold snap in the last couple of days with the air outside touching 7C. Thats close to the min 'optimum' operating temp of the ASHP (It can go much lower but uses some energy to keep the outside unit frost free) and wasnt enough to put enough heat in the house overall.

Ended up lighting the fire a couple of nights (used the first of the wood from our woodlands) and believe it or not electric blankets and hot water bottles!

Now I went for a cheap chinese install myself ASHP and in retrospect should have went for the two output units and piped them up myself but it was an experiment and has worked well. I suspect by the end of play today I'll be using it as air con at some point!

Certainly in my case, the 'numbers dont work' but if you tie in that usage above with my annual oil usage it has allowed me to drop oil usage by around 300 litres a year (coupled with the battery for immersion etc). With two tanks now installed Ive now something like 2200 litres capacity which is just a little over 3 years worth so I dont give a monkeys if oil goes to 100-200 usd a barrel because Im locking most of it in at todays prices. Not possible with gas of course but you get the idea, its not really the direct numbers but playing the long game it can add up to savings elsewhere. (just dont ditch the hot water bottles ;-))

shinytop

Cardew said:

shinytop said:

michaels said:

Thanks
I can't find little info on air to air heat pumps, probably because they were not eligible for rhi so are not very common in the UK..  I think some on here may have experience?
There is no clarity (no info at all on) on whether air to air might come under the green home grant.

Yes there is and they and unfortunately are not included. I had my eye on one too. 
https://www.simpleenergyadvice.org.uk/measures/meta_air_source_heat_pump
Paragraph 6 of 'What is is?'

Does not paragraph 6 refer only to RHI not the 'Green home Grant'

Oops, yes sorry. 

michaels

Spoke to someone in the industry who ws also unsure if air to air heat pumps were included in the green energy grant.

Found out something interesting, under some circumstances it may be possible to use metered heat demand rather than deemed demand from the EPC - relevant to us as our EPC is fairly low but our actual demand (based on excessive hot water usage and heating 24/7 compared to epc 9 hours per day) is about twice as much.

Martyn1981

I don't understand that. In the case of RHI I thought they used the metered heat demand for subsidy payments, but it's limited to 20,000kWh or the EPC whichever is lower.
So I'm just guessing that the green grant would have similar strings, or are you saying you might be able to get an exemption (or something) from the EPC estimate?

Just a thought, and might not work in the UK, but could you use one (or three) heat pump hot water cylinders and locate them in a semi-vented structure like a garage? This probably makes no sense, and I'm thinking of loads of problems, but happy to think out loud and look a bit stupid? I think this is done in the US, but probably in states which have, compared to the UK, higher average air temps.

michaels

My understanding was that in general it uses deemed (via EPC) heat useage and generally only has a meter installed if there is some other factor in play like a combined heat pump/boiler system.  For us the deemed usage is much lower than actual usage so we woudl get a much higher RHI payment if it were able to be based on actual usage.