GSHP vs ASHP magic spreadsheet?

[CADjockey]

So we went to the build show at the NEC earlier in the year and had a chat with one of the guys on the Kensa stand.

Anyway I got them to do me a kit quote for our plans at the time and it came in at £17k for GSHP & Accessories.

 

So add local installation to that and it's a chunk of budget. I gather GSHP is supposed to be more expensive initially,

and cheaper over the long term, but having read about disposal of antifreeze etc on the forum I am questioning costs.

 

Does anyone have a magic formula or spreadsheet that you can feed in the numbers and get a cost based answer out of?

 

The other thing the guy on the Kensa stand said, was that ASHP systems work at their best at the time of the year when

you don't need them and whilst I can see a salesman coming, it's not such a stupid comment, is it?

 

So I could go either way, but If I go ASHP I need to plan in a site for the external kit from the outset. comments?

[jack]

4 minutes ago, CADjockey said:

The other thing the guy on the Kensa stand said, was that ASHP systems work at their best at the time of the year when you don't need them and whilst I can see a salesman coming, it's not such a stupid comment, is it?

 

Yes, they do work better in summer, but they're still useful for hot water during that time (assuming you aren't using PV and diverter - our ASHP basically turns off for several months a year during summer).

 

And while it's true they work better at a time when you need them less, that it a misleading way of putting it. The question is, do they still work, in a cost-effective way, when you need them most. Assuming a well-insulated house and a properly designed and scaled ASHP heating system, the answer is an emphatic "yes".

 

As others have said, the much higher capital and maintenance costs for GSHPs make them generally uncompetitive against ASHPs, assuming you're not prevented from using an ASHP due to, eg, planning restrictions.

[Jeremy Harris]

12 minutes ago, CADjockey said:

So we went to the build show at the NEC earlier in the year and had a chat with one of the guys on the Kensa stand.

Anyway I got them to do me a kit quote for our plans at the time and it came in at £17k for GSHP & Accessories.

 

So add local installation to that and it's a chunk of budget. I gather GSHP is supposed to be more expensive initially,

and cheaper over the long term, but having read about disposal of antifreeze etc on the forum I am questioning costs.

 

Does anyone have a magic formula or spreadsheet that you can feed in the numbers and get a cost based answer out of?

 

The other thing the guy on the Kensa stand said, was that ASHP systems work at their best at the time of the year when

you don't need them and whilst I can see a salesman coming, it's not such a stupid comment, is it?

 

So I could go either way, but If I go ASHP I need to plan in a site for the external kit from the outset. comments?

 

I doubt that you will never get the money back for such an expensive GSHP installation.  At best a GSHP may cost a few percent a year less in electricity cost over an ASHP, if you ignore the ongoing maintenance cost, like replacing the (expensive) brine every few years.  You need to work out the energy saving over the 10 to 15 year likely life of the system, and then see if it makes economic sense.

 

I costed up installing a Kensa GSHP (and, FWIW, I though the Kensa was about the best option) and it came to around £8k, for a largely DIY install.  I ended up fitting an ASHP that cost around £2k installed (again a DIY install).  I get a real-world COP of around 3.5 on average and a GSHP might possibly have given an average COP of up to perhaps 4.  Our ASHP uses around 2000 kWh per year, so if we had a GSHP that would reduce to about 1700 kWh, or an annual saving, at current electricity prices, of around 300 kWh, or £45 p.a. at most.  Over the estimated life of the kit, of perhaps 15 years, then the GSHP would save around £675. 

 

So, had we opted to fit the GSHP, then we'd have saved £645 in energy cost through life, for an increased capital cost initially of around £6,000.  In addition, the GSHP would need two or three brine replacements, at a few hundred pounds a time, through life.

 

The efficiency difference for an ASHP with air temperature changes is tiny.  Air at 10 deg C only has about five or so percent more heat energy than air at -5 deg C, not enough to make a significant difference.

[CADjockey]

3 minutes ago, JSHarris said:

I doubt that you will never get the money back for such an expensive GSHP installation.

 

Ok, so it was probably a bit circumstantially true on the salesman's side. But it sounds like ASHP is the source of choice.

I had figured that some of the big builders really only fitted them because of the lower cost.

 

Question... How noisy are ASHP in reality?

[AliG]

There have been numerous discussion of this in the past.

 

Generally if mains gas is available then it is the cheapest way to heat hot water. ASHP are more competitive versus oil heating or electric heating.

 

This is due to he fact that gas costs around 3p per kWh and electricity costs around 13p. Thus an ASHP with a COP of 4 would provide no saving over gas and in winter when the COP might fall in cold weather gas would be cheaper again to run.

 

If you have a very large amount of PV and use it to run an ASHP then the calculations could start to turn in its favour, I believe this is what @JSHarris has. But it would be tough to make such a system to work well in the winter.

[jack]

Ours is on the far side of our (attached) garage and I've literally never heard it. When it's ticking away at low speed providing UFH heating during winter, you can feel the cold breeze from the fan as you walk by, but that's about it.

Admittedly, it only does water heating between 4 and 6 am, so I suppose it could be making a huge racket at that time. We certainly can't hear anything in our bedroom, and its the closest room to the ASHP.

 

1 minute ago, AliG said:

If you have a very large amount of PV and use it to run an ASHP then the calculations could start to turn in its favour, I believe this is what @JSHarris has. But it would be tough to make such a system to work well in the winter.

 

We have 8.5kW of PV, but during winter, there are many days when it hardly generates any energy at all. It's much better in the shoulder months - spring can provide some useable energy at a time when the ASHP might sometimes be on.

[MrMagic]

Not sure on a A2W ASHP, but I've got a couple of A2A HPs and they are pretty darn quiet.

 

One thing which I hadn't considered is background noise - where I live the daytime noise is high but after 8pm it's basically silent - when the background noise drops you can certainly hear the compressor running... but even then it's pretty much whisper quiet. The only time that the noise is noticeable for me is at the end of a heating/cooling cycle - the outside unit kicks the fan in to full pelt for 60 seconds and theres some noticeable 'wooshing' then.

[Jeremy Harris]

14 minutes ago, CADjockey said:

 

Ok, so it was probably a bit circumstantially true on the salesman's side. But it sounds like ASHP is the source of choice.

I had figured that some of the big builders really only fitted them because of the lower cost.

 

Question... How noisy are ASHP in reality?

 

Ours is about four feet from our back door.  Standing at the back door I can't tell whether it's running or not, and invariably have to go and look at it to see if the fan is turning.  One or two from here have been over and seen it, including @SteamyTea, and they may be able to give their own view on the noise level.

[SteamyTea]

15 minutes ago, JSHarris said:

including @SteamyTea, and they may be able to give their own view on the noise level.

I did not realise it was running at the time and we were standing right next to it looking at your PV inverter.

 

I think part of the problem is that many people see and air-conditioning unit that has been hanging from a wall for years, if not decades, and think that it must be the same.

I also suspect that if an ASHP was undersized too much that it was running at full pelt all the time, and it was neglected i.e. used at a bike rack, then it could rattle a bit.

[MikeSharp01]

5 minutes ago, SteamyTea said:

I also suspect that if an ASHP was undersized too much that it was running at full pelt all the time

So - taking the hint, it looks like it makes best sense to oversize the ASHP unit to keep the noise down? Ours will be right beside the public footpath and I don't want comments about the noise.

[Jeremy Harris]

4 minutes ago, MikeSharp01 said:

So - taking the hint, it looks like it makes best sense to oversize the ASHP unit to keep the noise down? Ours will be right beside the public footpath and I don't want comments about the noise.

 

The experience and experiments that I've done with ours suggests that over sizing an inverter drive (and that's important) ASHP has two benefits.  It makes the unit less likely to defrost, because the external heat exchanger is larger than needed for the heat output, and so the COP will generally be better, and the fan and compressor only need to run relatively slowly in order to deliver the required output.  This makes the unit run very quietly, but having said that, when ours is running flat out it really doesn't make much noise, either.  When it turns on it takes around 30 seconds to ramp up to full speed, and this tends to make it far less noticeable ( there's no big "whoosh" as it turns on).  It then runs at full power for around a minute, whilst it reaches the set flow temperature, and then it ramps back down to whatever power it needs to maintain the set flow temperature.

[SteamyTea]

They need to be oversized anyway.

If you look at the installation spec for the RHI, then they say it must supply all the heat load for the house 99% of the time.

Most gas installations don't do that, and I suspect that most ASHP installed don't either.

 

The physics of heat pumps is well understood, so sizing should never be an issue.

 

[MikeSharp01]

@SteamyTeaThat graph is for Ammonia refrigerant, do they use that in domestic systems,? / does it matter much what the refrigerant is anyway I wonder.

[Jeremy Harris]

The curves change for different refrigerants, but remain much the same sort of shape, so the general principle still applies I think.

[CADjockey]

So I currently have both an oil boiler for heating and an old 1952 Aga converted to oil at some point which we cook on and delivers hot water in the winter. For the other 5-6 months we use Emerson rarely as shower is electric and we just do without & without noticing too much. So  pretty much any switch to gas/GSHP/ASHP will be cheaper to run probably. Is gas really better if available? It seems too reliant on market forces tbh.

[PeterW]

Mains gas is the cheapest for supply and install in a standard build and scores best in SAP for some reason. If it’s available then it’s worth it but remember the cost of servicing etc needs to be factored in and you can’t self install.*

 

ASHP can be self installed and they are simple bits of kit that don’t need much in the way of servicing and if sized correctly they have an equivalent lifespan to a decent gas boiler. UVC and other bits are pretty similar to what is required for a gas or oil boiler, just remember that the CoP reduces dramatically as you go higher than 45c with DHW so you may need a secondary heat source to boost either the flow temperature or the the store temperature to provide a decent hot water supply. 

 

Daikin make a dual heat source ASHP that has a small gas boiler indoors and is very efficient as the boiler only has to take the water from 40-55c so this can be a compromise if you have PV and ASHP and also gas. 

 

* you can potentially install gas appliances yourself in your own house if you are deemed “competent” and in a new build you would need to get BCO sign off however it is not something I would ever advise on doing. Ever. 

[AliG]

The actual cost of wholesale gas is a relatively small part of the bill thus gas and indeed electricity costs do not vary anywhere near as much as you would think.

 

The price of gas has varied over time especially with the large commodity price inflation we had a few years ago, but even then the price of electricity is pretty well correlated with the price of gas so the relative economics are unlikely to change much.

 

OFGEM

 

Dept for Business, Energy and Industrial Strategy

[Declan52]

I looked into a gshp at the time and even with free access to a drilling rig I still couldn't make the sums work. 

It's important to note that not every borehole will be successful as nobody knows what's down there. You need a good few water strikes on the way down for the pipe to draw enough heat from the ground.

You can do the slinky type installation but that requires a lot of ground to pay the pipe.

[vivienz]

Our neighbour at the new place has a couple of LG ASHPs for his cottage. When we there on a cool day a few weeks ago, we could distinctly hear it running from about 20 feet away. It is really quiet out at the new place, but I only seem to encounter noisy ones and this has really put me off them.

 

[Jeremy Harris]

10 minutes ago, vivienz said:

Our neighbour at the new place has a couple of LG ASHPs for his cottage. When we there on a cool day a few weeks ago, we could distinctly hear it running from about 20 feet away. It is really quiet out at the new place, but I only seem to encounter noisy ones and this has really put me off them.

 

 

Where we are it's very quiet, yet the gentle noise from the air intake for our MVHR is louder than the ASHP below.  I think it very much depends on the type of ASHP and how heavily it's being loaded.  For a new build, even one that's just built to the bare minimum required by building regs, the heating requirement isn't going to be massive, so there shouldn't really be an issue with ASHP noise.

[Gone West]

17 hours ago, CADjockey said:

Question... How noisy are ASHP in reality?

Our neighbour has a Nibe ASHP which is about 2m from our fence and on a still day with no other sounds you can just about hear a gentle whirring sound when standing next to the fence.

[ProDave]

It is funny that some people get bothered by a gently low level noise from a heat pump outside, yet the same people are happy to have a pressure jet oil burner roaring away inside the house creating very much more noise.

[vivienz]

8 minutes ago, ProDave said:

It is funny that some people get bothered by a gently low level noise from a heat pump outside, yet the same people are happy to have a pressure jet oil burner roaring away inside the house creating very much more noise.

 

? I don't plan to burn oil or anything else, so I'm a bit puzzled by your comment.

[ProDave]

1 minute ago, vivienz said:

 

? I don't plan to burn oil or anything else, so I'm a bit puzzled by your comment.

I was just commenting that people in general have a fear of noise from a heat pump, but you never hear anyone saying "I don't want an oil boiler in my house because they are so noisy"

[SteamyTea]

I think it is to do with the unmeasurable effects of different noises.

Quite often they seem irrational.

There are certain noises I really hate, barking dogs, crying children and dot matrix printers spring to mind.

But then I hate dogs, small children and really hated the women in accounts who ran the DMP.

So probably nothing to do with the noise, just pure, healthy prejudice.