ASHP vs GSHP

[puntloos]

Apologies can't seem to find a topic that goes into this explicitly - maybe I am terrible at searching?

 

But - as the title indicates.. 

 

ASHP vs GSHP seems to be less clear than I thought.

 

ASHP:
+ Cheaper, roughly 16000 minus 10000 RHI funding - 6000

+ Easily creates hot water in summer

- Large outdoor unit

- Some noise

- Less efficient in winter when heating is needed most

 

GSHP

+ More efficient in winter

+ No ugly outside device

+/- medium indoor unit, standing fridge size.

- More expensive, roughly 44000 minus 30000 RHI funding = 14000 (includes 2x borehole of 10,000 each)

- Hard to install - either digging boreholes or digging up garden for slinky, so might be a dealbreaker

 

Of course the benefits of GSHP over ASHP are not dramatic, so one can certainly argue that for many cases it's perhaps not worth the 8000 quid. 

 

Am I missing any major pros/cons for either tech?

[pstunt]

Hi,

I am having the same questions for my new build but as I won’t be starting the build until later in the year, there is no way I would make the RHI cut off date. Which raises the question is either approach better financially ? 
 

[gc100]

I have too have room for ground source but went with air. The maths just don’t add up for ground source in the UK IMO. My house is so well insulated that the heating isn’t on much anyhow in the winter...

[Buzz]

19 minutes ago, pstunt said:

Which raises the question is either approach better financially ? 

How much will it cost to get gas connected to your site will be the deciding factor if just going pound for pound over say 10 yeas.  

[MikeSharp01]

Given that ASHP install can be done DIY with some electrical work that may bring in the professionals in a few days it is much the most cost effective way forward. GSHP needs professional help in a range of places so as you have shown the costs are around a third for ASHP. If that were all though the choice would be easy. If you are in close proximity to neighbors then ASHP might be a noise problem - there are other rules. https://www.planningportal.co.uk/info/200130/common_projects/27/heat_pumps/2

 

Just now, Buzz said:

How much will it cost to get gas connected to your site will be the deciding factor if just going pound for pound over say 10 yeas.  

We had gas connected to our build and run through the slab, but we will now disconnect it as we are going ASHP for heating and probably Sunamp for DHW.

[gc100]

Just to add , I think ground source is much better option if you can use it as a heat sink in the summer

[IanR]

I also looked at both, the small additional efficiency of the GSHP didn't outweigh the extra capital cost and extra maintenance cost.

 

Add into you comparison the maintenance cost (there's a lot of antifreeze in a GSHP that needs replacing). In the GSHP flavor is the option for "passive" cooling. 

[pdf27]

Financially it's a no-brainer to go for ASHP. I'm planning/hoping to go for GSHP, but I've got two particular circumstances which make it viable (TBC when we get quotes! )

1. It's going to be a very well insulated and not enormous house, a 3kW unit with a small ground array is viable as a result which brings the cost of the heat pump unit itself a lot closer.
2. We've got a very large back garden, and a lawn which could really do with re-laying and is more than big enough for the ground array. Couple this with the fact that it's cheaper to put some excess topsoil on top of the lawn than it would be to dispose of it and the groundworks costs should be very low.

That means we can justify the couple of thousand pounds higher install cost in exchange for not having an outside unit (which I find ugly) facing the garden. I don't think it would be viable if we had to pay much more of a premium than this however.

I'm not overly concerned about running/maintenance costs - Glycol should last a long time if kept cold and not exposed to UV, and a GSHP being indoors should probably last a bit longer than ASHPs so the higher unit cost should probably come out in the wash in the long term.

 

We have gas on site at present but are planning to disconnect it - this is primarily because cooling is a hard requirement for my wife which implies a heat pump, but also because for a very low energy house the standing charges make gas a surprisingly expensive way to heat.

Edited May 18, 2021 by pdf27

[nod]

We have looked at both for our second build 

We have gas on our first build But as above very well insulated so bills are low 

Three self builds near our plots have opted for oil So that’s another option 

 

[ProDave]

Another that looked at the 2 options.

 

What i found was GSHP the price doubled when you added the collector pipes and fittings and the brine to fill them with.  And the brine has a finite life so an ongoing maintenance / replace schedule.

 

And GSHP puts the noisy compressor inside your house vs an ASHP which puts the noisy bit outside.

 

I was doing a DIY install so no RHI and materials as cheap as I could source them so that probably made more difference to the overall cost than a paid for install perhaps?

 

My ASHP carries on working all winter including the one night this year it got down to -17, so stop worrying they won't work in cold weather.

[joe90]

1 hour ago, ProDave said:

Another that looked at the 2 options.

 

What i found was GSHP the price doubled when you added the collector pipes and fittings and the brine to fill them with.  And the brine has a finite life so an ongoing maintenance / replace schedule.

 

And GSHP puts the noisy compressor inside your house vs an ASHP which puts the noisy bit outside.

 

I was doing a DIY install so no RHI and materials as cheap as I could source them so that probably made more difference to the overall cost than a paid for install perhaps?

 

My ASHP carries on working all winter including the one night this year it got down to -17, so stop worrying they won't work in cold weather.

@ProDave beat me to it....+1 the above . And I do have the room and my own digger!

[SteamyTea]

It is worth asking the question "What are you trying to achieve?"

 

Are you after the cheapest system to buy, run, claim subsidies, lowest energy use, reliability, comfort levels, etc.

 

I often see a price comparison, never an overall energy usage.

 

If heating was purely down to price, then open fires, burning rubbish, with a large kettle to boil water in, would be the easy option.

[BotusBuild]

I often see on this forum the "connect to the gas network" comments. Recently there has been a lot of talk about the ban on gas boilers, including just today this article - https://www.bbc.co.uk/news/science-environment-57149059

 

I do wonder why people make the "connect to the gas network" for new builds in light of this probable move to no new gas boilers. Just my 2p worth

[Onoff]

Didn't @Barney12 put a gshp coil in, very deep trenches from memory...did he ever connect it?

[pstunt]

I dont want to hijack puntloos original question but in answer to SteamyTea's question, for me it's about initial cost vs longer term expenditure ( Rising fuel costs / maintenance ) along with reliability and comfort levels.

 

My initial quotes for a 360 sqm single story stable conversion ( No gas mains ) are coming in similar to puntloos and whilst I would morally prefer to go down the renewable route. It seems to me it would make financial sense to go LPG but ensure the infrastructure is there ready for when costs come down for ASHP/GSHP. 

 

I need to look into more as to how effective ASHP would be along with how much electricity it would use compared to an LPG boiler. 

[SteamyTea]

14 minutes ago, BotusBuild said:

I often see on this forum the "connect to the gas network" comments. Recently there has been a lot of talk about the ban on gas boilers, including just today this article - https://www.bbc.co.uk/news/science-environment-57149059

 

I do wonder why people make the "connect to the gas network" for new builds in light of this probable move to no new gas boilers. Just my 2p worth

 

There was almost certainly going to be mission creep when it was announced that no new had boilers could be fitted. Same will happen with cars, pure ICEs will be banned, and like CDs, the hybrid will be a short lived format. The CEO of Stellantis had already said that it is legislation that is forcing the EV route.

There really is no need to continue developing combustion technologies now, our the resources into HPs and better building testing.

[SteamyTea]

8 minutes ago, pstunt said:

need to look into more as to how effective ASHP would be along with how much electricity it would use compared to an LPG boile

Do you mean compare the kWh used, a gas system will not use much electricity.

 

What puts most people off then comparing is the "known unknowns". Or the weather and build quality. Weather can be calculated pretty well within small errors, build quality can't. Why it amazes me that people don't get an interim air test done while it is still possible to easily fix things.

£250 for a test, people spend more on a tap.

[joe90]

With building regs getting better and us buildhubbers building much better than that the need fir heating will diminish (although DHW will still be required). With the UFH and infrastructure within the house already in place the “means” of providing heat can change as prices and policy change. When my ASHP finally gives up the gost there well may be some newly developed gadget to replace it running of my waste plastic ?‍♂️

[joe90]

6 minutes ago, SteamyTea said:

build quality can't.

I believe it can, us buildhubbers certainly make sure of that (insulation and airtightness)

 

6 minutes ago, SteamyTea said:

£250 for a test, people spend more on a tap.

Some may, I don’t ?, spent it all on insulation ?
 

it amazes me that buyers don’t take much notice of the EPC when buying a house, (I.e the potential running cost of a house). As heating a house gets more expensive hopefully it will focus minds on insulation and build quality.

Edited May 18, 2021 by joe90

[nod]

34 minutes ago, BotusBuild said:

I often see on this forum the "connect to the gas network" comments. Recently there has been a lot of talk about the ban on gas boilers, including just today this article - https://www.bbc.co.uk/news/science-environment-57149059

 

I do wonder why people make the "connect to the gas network" for new builds in light of this probable move to no new gas boilers. Just my 2p worth

While I think a ban on gas boilers fitted to new builds is achieved 

Getting rid of the rest won’t happen for decades 

It’s unenforceable 

[joe90]

7 minutes ago, nod said:

While I think a ban on gas boilers fitted to new builds is achieved 

Getting rid of the rest won’t happen for decades 

It’s unenforceable 

It will be a bit like cars, the old ones will be scrapped at the end of their life. The ban is not on gas boilers purely fir new builds but a ban on all new gas boilers.

 

https://www.bbc.co.uk/news/business-55948531

Edited May 18, 2021 by joe90

[pstunt]

1 minute ago, SteamyTea said:

Do you mean compare the kWh used, a gas system will not use much electricity.

Sorry, I should have been clearer but in simple terms I really mean an overall running costs comparison.

 

I was reasoning on not having MVHR because I am only going with standard insulation. I guess my question should be whether to increase the insulation thus reducing heating costs whichever technology I choose. By having better insulation does it follow the question of MVHR needs to be revisited for ventilation ? 

 

[Onoff]

Didn't @Barney12 put a gshp coil in, very deep trenches from memory...did he ever connect it?

[SteamyTea]

26 minutes ago, pstunt said:

Sorry, I should have been clearer but in simple terms I really mean an overall running costs comparison.

 

I was reasoning on not having MVHR because I am only going with standard insulation. I guess my question should be whether to increase the insulation thus reducing heating costs whichever technology I choose. By having better insulation does it follow the question of MVHR needs to be revisited for ventilation ? 

 

 "Standard" insulation levels are pretty good in reality, that isn't really the problem. Though increasing the level in the largest surface areas, or the coldest side of a building can pay dividends.

Air tightness is more than just stopping drafts, you don't want cold, outside air, to be able to bypass the insulation and get behind any interior surfaces. This is why building a are wrapped in Tyvek, or similar. They let moisture out the insulation, but don't let the wind or rain in.

But because it is harder for water vapour to escape, we reduce the amount by fitting a vapour control layer, which is anything that is basically gas tight. This is not to stop drafts. I shall repeat, this is not to stop drafts (I hope I have spelt draught right). It is purely there to reduce the air mass in the house, which will be at higher absolute humidity and higher temperature than the outside, escaping.

This is why MVHR is fitted. Basic fans can be used to just expel the moist air, but why throws the energy out with it.

You can still open windows if you want to.

 

So basically, it is not a trade-off with one thing or another, it is a combination of all things.

Like a car, I can get away with budget tyres on my low powered C-Max as it is driven steady, but if I had someone else's Porche, or C-Max for that matter, I would expect decent tyres as I know I would drive it like a (expletive deleted) at their expense.

 

Edited May 18, 2021 by SteamyTea

[pstunt]

@SteamyTea Thanks for such an informative response. There just seems so much to consider and it's a challenge, for a novice like myself, to know how to apportion the limited budget.