ASHP for old house?

[ASHP newbie]

I am at the point of signing up for a ASHP for my old stone built almost renovated cottage and would much appreciate finding out whether it will actually work for a house like mine. I am concerned that I might end up using more electricity££ than I save on LPG££.  I am a very low energy user, less than £400 pa on LPG and just over £200 pa on electricity. I have solar PV. It's the hot water that I am so unsure about. Space heating will work as I use a woodburner a lot.

[ProDave]

Those are interesting figures.  I spend just under £250 pa heating my house with an ASHP but I spend double that powering all the other electrical "stuff" in the house so I am mighty impresses that you only spend £200 on electricity per year.

 

 

[ASHP newbie]

I don't have gadgets (except TV and laptop) and turn things off. Works wonders! Solar PV helps, esp when I remember to put the washing machine on when the sun is shining. I don't really want my electricity to go through the roof by heating a tankful of water every day, hence my quest for others' experiences.

[joe90]

Just remember the COP for the ASHP should be around 3 or 4 so a third or quarter of using direct electric heating!

[ASHP newbie]

The SCoP is 3.81 at 50degC. Don't know the CoP. How does it differ from the SCoP? Also heard that SPF matters but don't know what it is.

More info re the house follows (copied from "Introduce yourself" sub-forum):

The house is reasonably insulated for its age - roof insulated, all north-facing walls insulated internally, other walls maybe half insulated where appropriate. EPC D with solar PV, since it was done have added oak frame extension where double glazing manages to lose more heat than I am happy with but it is to 2015 regs. All windows and doors double glazed. About half of solid floor area also insulated. Most insulation is 4" of Kingspan as far as I remember. I've had the ASHP sizing done for 11.4kW system with heat loss factor 62 w/sq.m. floor area 148m2 (should be 167m2 - ignores hallway etc) heating energy req't 16,787kWh and hot water req't 2,606kWh. Tried doing the sums but got bogged down so thought I'd try see if some knows because they been there/done that. Also been thinking of noise levels (sound power 66dBA) as the unit will be below a first floor bedroom window (spare room). And what would have happened during The Beast from the East as the unit will face East. 

[ProDave]

If you have solar PV then you really DO want a hot water tank, with a solar PV diverter to send excess power to the immersion heater (rather than export it)

 

an ASHP will probably cost half to run compared to bulk LPG but remember they work best (highest COP) with low temperature water so that means under floor heating or hich capacity low temperature radiators.

 

I am still marvelling at your £200 electricity cost.  I have dome measurements when away on holiday.  With only a Fridge freezer, mvhr and waste treatment plant, and a sky box left on to record some stuff,  use 31kWh per week which works out at £230 per year.  Another test during a different holiday, with a second freezer running and two televisions left on standby pushed that up to 46kWh per week or just over £300 per year.

 

I really don't see how to get that base load down.  And that is with solar PV that will have offset most of the daytime use of those appliances.

[ASHP newbie]

I've worked out I use about 1kWh a day in the summer. It's actually 1073kWh a year. Whatever, it's low and I want to keep it that way. 

I did suggest a smart switch to the installers and they said to use the ASHP in summer as it's more efficient. I'd still like to dump any surplus electricity into the tank but it's another £500 or so. Maybe later.  My projected savings are pretty low as my usage is so low, hence the worry that any savings will be gobbled up by the extra electricity needed to run the ASHP for hot water and an immersion for hop water top ups. I do like a hot bath :-) Do you know how much elec your ASHP uses to heat your water each week say? For how many people?

[ProDave]

Winter ASHP usage for water heating is typically 25kWh per week.  In the summer that can drop to less than 10kWh as a lot of the hot water comes from the solar PV.

 

It's actually better than that, as my meter still measures how much the ASHP consumes but in many cases most of what the ASHP is using in the daytime is coming from the solar PV.

 

That is for 3 people.

[ASHP newbie]

Thanks for that! I've stuck it into my spreadsheet and bearing in mind that it's all approximate I should make some savings - at least I now feel more confident that my electricity bills shouldn't end up higher than my current bills +LPG.

[dpmiller]

Since when was a PV diverter £500?

[scottishjohn]

all I can comment on is switching from lpg to ASHP basically saved £1000 per year with no change to the house just swopping heat source

LPG is most expensive heat source there is

I am guessing you are using alot of logs for the fire in winter 

Edited August 10, 2020 by scottishjohn

[SteamyTea]

sCoP and SPF are basically the same thing, just measured in a different way.

The main thing is to get it sized correctly, which may mean it seems oversized.

This is to stop the inbuilt immersion heating coming on and reduce the chances of the unit frosting up.

Basically all you need to do is work out the different costs of running different systems.

[ASHP newbie]

On 10/08/2020 at 16:40, dpmiller said:

Since when was a PV diverter £500?

Since I asked the price from one of the companies quoting for ASHP. That included installation. What should I expect it to be?

[ASHP newbie]

On 11/08/2020 at 11:08, SteamyTea said:

sCoP and SPF are basically the same thing, just measured in a different way.

The main thing is to get it sized correctly, which may mean it seems oversized.

This is to stop the inbuilt immersion heating coming on and reduce the chances of the unit frosting up.

Basically all you need to do is work out the different costs of running different systems.

Thanks, I did more looking up of stuff and got it sorted. Amazing, what one  can find out in the internet :-)

I've been quoted SCoP values of 3.51 at 55degC and 3.81 at 50degC. Seemed reasonable.

[ASHP newbie]

On 10/08/2020 at 17:17, scottishjohn said:

all I can comment on is switching from lpg to ASHP basically saved £1000 per year with no change to the house just swopping heat source

LPG is most expensive heat source there is

I am guessing you are using alot of logs for the fire in winter 

Yes I do use the woodburner every evening in the winter, also sometimes Rayburn if I am going to be in all day. Guess this winter I'll be in most days - the way  Covid is making us live. I am lucky I have loads of wood from sorting seriously overgrown hedgerows etc. and a few dead trees as well. Not had to buy logs yet - been here almost 6 years.  My problem with my LPG savings is that they get wiped out by increased electricity consumption plus maintenance charges while under warranty (7 yrs). I think I've been quoted over-the-top maintenance, when I've searched the internet consensus seems to be once every couple of years - not every year.

[SteamyTea]

9 minutes ago, ASHP newbie said:

I've been quoted SCoP values of 3.51 at 55degC and 3.81 at 50degC. Seemed reasonable.

Probably only need to go up to 45°C, so should be a little higher.

There is also a quirk when the external air temperature is between 0° and 7°C, the CoP can reduce.  This is to do with frosting.  On a really cold, but dry, day, the CoP can increase.

 

4 minutes ago, ASHP newbie said:

Yes I do use the woodburner every evening in the winter

Have you read the stuff on here, and over at the other place, about views on woodburning?

Not a good thing.

[joe90]

@ASHP newbie SSHHHHH don’t mention wood burning here, not the done ting ? (but I do occasionally) ?

[ASHP newbie]

4 minutes ago, SteamyTea said:

Probably only need to go up to 45°C, so should be a little higher.

There is also a quirk when the external air temperature is between 0° and 7°C, the CoP can reduce.  This is to do with frosting.  On a really cold, but dry, day, the CoP can increase.

 

Have you read the stuff on here, and over at the other place, about views on woodburning?

Not a good thing.

No I haven't read up on woodburners on this site but when the wood is free from the garden and very well seasoned ie several years, I think its env impact is acceptable. After all, it would just rot down otherwise (or go on a bonfire). 

Considering SCoP values I was looking at worst case scenario as I only have normal rads and am likely to need them reasonably hot. And I like my bath water pretty hot!

[joe90]

Just now, ASHP newbie said:

And I like my bath water pretty hot!

@ProDave and I heat via an ASHP to 48’ and that’s more than adequate, however our DHW tanks are a bit larger as we don’t blend hot water down as much as others. Also having a DHW tank at that temp means the losses are a lot less. With cooler heating water you may need to oversize your radiators.

[ProDave]

Wood burners are a marmite subject.

 

The man complaints are pollution to near neighbours.  Some, in sheltered valleys, experience foul air from nearby wood burning stoves on a still night.

 

Here in the Highlands with such a low population density and almost always some wind it does not seem to be a problem.

 

 

[ASHP newbie]

1 minute ago, joe90 said:

@ProDave and I heat via an ASHP to 48’ and that’s more than adequate, however our DHW tanks are a bit larger as we don’t blend hot water down as much as others. Also having a DHW tank at that temp means the losses are a lot less. With cooler heating water you may need to oversize your radiators.

I've just asked for a bigger DHW tank to cope with my baths. And don't intend to change my rads unless I need to later on, tho was told one in my open plan living/kitchen area will need to be a triple. That's why I was looking at 50-55 degC for the rad water.

[ASHP newbie]

1 minute ago, ProDave said:

Wood burners are a marmite subject.

 

The man complaints are pollution to near neighbours.  Some, in sheltered valleys, experience foul air from nearby wood burning stoves on a still night.

 

Here in the Highlands with such a low population density and almost always some wind it does not seem to be a problem.

 

 

My nearest neighbours are 1/4 mile away. And we are on a hill.

[joe90]

1 minute ago, ProDave said:

Here in the Highlands with such a low population density and almost always some wind it does not seem to be a problem.

Ditto Cornish Devon border, middle of nowhere near Atlantic Ocean.

[Nickfromwales]

On 10/08/2020 at 16:40, dpmiller said:

Since when was a PV diverter £500?

Installed, with gubbings and consumables, that's about right, if not cheap!! Companies do actually need to make some money to stay in existence  

https://www.google.com/search?q=eddi+pv+diverter&rlz=1C1CHBF_en-GBGB910GB910&source=lnms&tbm=shop&sa=X&ved=2ahUKEwjUz-i0vZjrAhXLTsAKHfCBB2AQ_AUoAXoECA0QAw&biw=1280&bih=610#spd=988388954505620188

[scottishjohn]

52 minutes ago, ASHP newbie said:

my LPG savings is that they get wiped out by increased electricity consumption

no way lpg is at least 3 times as expensive -my lpg bill was £1600 a year  and i saved £1000 overall -eg my electric bill went up by £600 and no lpg --you do the maths

 If you got so much wood why you not using that and nothing else?

Edited August 13, 2020 by scottishjohn