Air Source Heat Pumps…

[Gasguru]

What's your COP at 80 degrees?

 

[Munroast]

If i may chip in with some uneducated comment.

The issue isn't heat, or lack of it.

The issue is what happens to the heat.

ASHP's need an efficient, low loss building. This means that air flow through the building needs to be strictly managed.
Old buildings and methods of construction often require unrestricted airflows.
You cannot reduce the airflow without having significant impact on the building and its inhabitants.
The forum is full of posts from people complaining about mold, condensation, etc. from the reduced airflow rates of modern buildings.

IMHO, a ASHP needs the building to be designed for it and old housing stock isn't really suitable.
I have friends who have ASHP's in new-builds and they have no issues with them because they are an integral part of the building design.

As for ripping out a perfectly good Gas system, i think if you do a cost/benefit analysis, you may be surprised at the results.

And here lies the nonsense - If your house is well insulated enough that an ASHP would work, then you are probably using so little gas there is little point changing.

 

[Bodgedbuild]

If i may chip in with some uneducated comment.

The issue isn't heat, or lack of it.

The issue is what happens to the heat.

ASHP's need an efficient, low loss building. This means that air flow through the building needs to be strictly managed.
Old buildings and methods of construction often require unrestricted airflows.
You cannot reduce the airflow without having significant impact on the building and its inhabitants.
The forum is full of posts from people complaining about mold, condensation, etc. from the reduced airflow rates of modern buildings.

IMHO, a ASHP needs the building to be designed for it and old housing stock isn't really suitable.
I have friends who have ASHP's in new-builds and they have no issues with them because they are an integral part of the building design.

As for ripping out a perfectly good Gas system, i think if you do a cost/benefit analysis, you may be surprised at the results.

I would agree that I would not rip out a gas system to replace with an Air Source one, however I don't think you know quite how good the newer units are, I live in a village that has no mains gas and oil or Calor Gas are either no convenient for many or there is no space in some of the cottages for such tanks.
The ASHP systems that have been fitted in the last 3 or 4 years can EASILY heat non cavity wall homes with the only provision that that are sized correctly.

 

[BlueLoo]

I would agree that I would not rip out a gas system to replace with an Air Source one, however I don't think you know quite how good the newer units are, I live in a village that has no mains gas and oil or Calor Gas are either no convenient for many or there is no space in some of the cottages for such tanks.
The ASHP systems that have been fitted in the last 3 or 4 years can EASILY heat non cavity wall homes with the only provision that that are sized correctly.

Fair enough.

I suppose the key point is how, or rather, is that just using the recovered heat from the air, or is it with electric heating assistance?

I think the latter is the crux because if you look at the energy balance over a full year, any extended periods spent where electricity is used to boost the heat output will reduce the annual efficiency to a point where its not viable.

If it were a few bob to install, you could say "so what" but ashp's are not cheap


Lifecycle costs are not always obvious.

 

[Bodgedbuild]

What's your COP at 80 degrees?

That's rather a variable answer because the initial heating stage is either COP 5.00 at 7 degrees external (or 2.74 at -7 degrees) but then reduces to 3.32 once the water is at 55 degrees with 7 degrees external (2.30 at - 7 degrees) and then at over 65 degrees it drops to 2.90 (7 degrees external (2.10 at -7).
In practice, I can see a noticeable reduction in cost if I keep the temperature below 65 degrees. It is still slightly cheaper than I was used to paying for oil though.
I'm not sure what oil prices are currently as my ASHP has been installed for over 2 years now.......

 

[Bodgedbuild]

Fair enough.

I suppose the key point is how, or rather, is that just using the recovered heat from the air, or is it with electric heating assistance?

I think the latter is the crux because if you look at the energy balance over a full year, any extended periods spent where electricity is used to boost the heat output will reduce the annual efficiency to a point where its not viable.

If it were a few bob to install, you could say "so what" but ashp's are not cheap


Lifecycle costs are not always obvious.

If I had gas, I would not change, it is undoubtedly more expensive to replace a gas boiler with an ASHP but the grant does take some of the pain away!

 

[Nintendofan]

And here lies the nonsense - If your house is well insulated enough that an ASHP would work, then you are probably using so little gas there is little point changing.

I live in a newbuild and within 30 minutes of switching the heating on the house is toastie warm. It will then stay warm all evening with very little boiler activity. I don't have any trickle filters that lets the heat escape either as the house has a positive pressure system installed instead.

 

[winston1]

How do ground source heatpumps compare? Yes I know you need land to bury the pipes, would a suburban semi with a 50 foot garden be enough?
I imagine the temperature of the ground is much more constant through the seasons. What sort of cop would you get?

 

[Bodgedbuild]

How do ground source heatpumps compare? Yes I know you need land to bury the pipes, would a suburban semi with a 50 foot garden be enough?
I imagine the temperature of the ground is much more constant through the seasons. What sort of cop would you get?

I have a 50 foot garden and I was told it was too small for me to consider ground source and I needed over 3 times the area of my house. It was also extremely expensive. Given the modest efficiency over Air Source, I chose not to go that route.
Edit:- TBH I can't see many situations in the UK when it would be worth the extra cost and upheaval, in Canada or Scandinavia, definitely but the UK rarely even gets much into the minuses let alone stays there for long

 

[mattylad]

I'm sure I saw on FBook that there is a new type of ASHP that's been developed that is as hot as gas in the development/trial stage.

 

[Munroast]

I'm sure I saw on FBook that there is a new type of ASHP that's been developed that is as hot as gas in the development/trial stage.

but how much electric is it using, the big question is how efficient not how hot. ?

at the moment gas (80% efficient boiler) is 5p per kwh of heat (4p per unit) electricity is 20p. 4X more expensive. So an ASHP needs to be 400% efficient gust to break even with gas.

The big question is where are prices going to go in the future. Gas is certainly going to go up a hell of a lot. But with the massive demand for electric from Heat Pumps and Electric cars and the fact 40% of or eleccy comes from Gas, I can imagine the cost of electric going up proportionally with gas.

 

[Bodgedbuild]

I'm sure I saw on FBook that there is a new type of ASHP that's been developed that is as hot as gas in the development/trial stage.

My system at 80 degree C ain't far off! it's a two stage unit that uses two types of refrigerant with R134 in the second stage. The first stage pre-heats it's refrigerant and if further heat is required, it is heated further using the second stage.

 

[Harry Bloomfield]

My system at 80 degree C ain't far off! it's a two stage unit that uses two types of refrigerant with R134 in the second stage. The first stage pre-heats it's refrigerant and if further heat is required, it is heated further using the second stage.

The first stage offers reasonable efficiency, the second stage is much less efficient - so the second stage will only be fired up when it is essential.

 

[Bodgedbuild]

The first stage offers reasonable efficiency, the second stage is much less efficient - so the second stage will only be fired up when it is essential.

The second stage also sounds like a distant lorry driving in a tunnel, it's the only time the indoor unit makes any noise, fortunately its quite well damped...

 

[ScottishGasMan]

With ASHP its all about the system design. 55°c is the highest heating temperature most want to be designed to, however that's not the gold standard by any stretch, you want the system designed to be able to produce the required heat output at the lowest possible temperature (bigger radiators/UFH) if you can hit 45°c that system will run a better COP than at 55°c, if you can design it to 35°c that will be significantly more efficient again.

The units use different refrigerant gasses and as such have different outputs at different outside temperatures, ie: R410a units are an older type that can generally only scrape just over 60°c and will require an immersion heater to boost the cylinder temperature during legionella cycles or in winter when the ASHP may struggle to reach required output. R290 units (newer types) can typically hit 75°c so do not need immersion backup, they work to lower outdoor temperatures although there will still be a drop off when very cold, ie it may only reach 65°c when its -10°c outside.

With regards to only being suitable to heat newbuilds, well that's just nonsense. If your house requires X kilowatts of heat, and you provide x kilowatts of heat, you will have successfully heated it. The difference is in the economy of cost, electricity is much more expensive than gas (at the moment) So even on efficient systems its difficult to have the ASHP running cheaper than a gas boiler. This may well change with energy pricing going nuts, and the likelihood that the government will probably shift the green levies off of electricity and load them onto gas in the near future.

Compared to oil/LPG, many people with good installs find them cheaper to run, with mains gas and a good setup you can reasonably break even and have it not cost any more. Insulation is certainly something that should be looked at first, regardless of your heat source, just because we can heat a building "easier" with gas, doesn't mean its not an unforgivable amount of wastage and CO2 emissions. Getting basic insulation and draught proofing done first should be the priority of any house hold, not just those going to ASHP.

Heat pumps are being pushed to help the environment, not to save you money. But there are factors that can help. Solar panels if you already have them lend themselves nicely to heat pumps, as you dont have a heat pump "off" during the day, it has a "set-back" temperature ideally only a few degrees lower than your "comfort" temperature, so the solar often covers this there for making significant contribution to your heating which otherwise may be wasted during the day or fed back to grid for pittance. Time of use tarrifs, such as those that gave 5p/kwh overnight for electric vehicle charging means the HP would run overnight for very very little cost maintaining the background heat when the outside temperature is lowest and therefore least efficient. Also the cheap tarrfis can be used to preheat the hot water cylinder or heating buffer to store heat when the electricity cost is at its lowest.

I know people who take advantage of the above points and have significantly reduced running costs compared to gas. Plus once gas meter is removed they instantly save from the standing charges applied to a gas supply.