Help! I need to Replace my GSHP

[Nially]

13 hours ago, Iceverge said:

@Nially what model of GSHP do you have installed at the moment, it may be useful to get an idea of your alternatives? 

 

Is it an option to mend,isolate, or bypass the broken ground loop and carry on as is? 

 

An ASHP is the obvious solution. A split unit can have an external unit quite a distance away  out of sight if you have an viable option to install the interlinking pipework. 

 

 

It is a 12kw Mastertherm Aquamaster inverter combi heat pump.

Option to mend is not an option for me as i believe it has failed in several places where the pipe bends at the end of trenches and will continue to do so. We have at least 2 more leaks after repairing one as explained above.

I have a patio outside my back door which I could consider lifting to route pipes and move the unit away form the house. Thanks for the suggestion

 

[Dillsue]

I have no idea if such a thing exists but have you looked to see if a Radwell type of sealant is available that may keep you running till the spring? A dose in the ground loops may seal things up temporarily??

[Nially]

13 hours ago, sharpener said:

 

If the bends are too tight then the new pipes might well fail in the same way in due course. But you could re-work it with bigger radius bends by looping to the next-but-two or next-but-three etc instead (like the tops of hooped iron railings), this would require digging up both ends of the array though.

 

Hence (assuming my understanding that the GSHP itself is OK) my suggestion of a vertical loop which would have a much smaller footprint.

 

 

YES correct, this is they way it should be looped, so please note everyone. The outside of the pipe has stress from being in a bent state over 8 years and eventually will crack. So the larger the radius the less chance of failure.

 

[Nially]

Just an update for everyone. So the consensus seems to be Air to water or repair what I have. I wanted to see if there were any other options as I have not explored this area since I built my home in 2015.

 

I am based in Ireland and have been getting quotes of around 12,000 euro for an air to water system which seems ridiculous to me as all the pipework is in place and the unit costs about 6,000.

I have had one quote for some boreholes for 13,000 euro. I plan to get a few more quotes before i decide what to do.

 

Thanks for the help.

 

[Redbeard]

Removed

 

Edited December 16, 2023 by Redbeard
Whimsy

[JohnMo]

12 minutes ago, Nially said:

based in Ireland and have been getting quotes of around 12,000 euro for an air to water system which seems ridiculous to me as all the pipework is in place and the unit costs about 6,000.

Installers just see ASHP as a good reason to overcharge you, not sure it makes much difference what country you are in.

 

Replace your combi unit with a heat pump cylinder, Ideal sell ones that are good and generally a low price. You only really need a 6kW ASHP. They can be picked for £2k or less. You need a 3 way diverter valve. A plumber for a day or two.

 

Or you may be able tap the ASHP into the water circuit of your combi, so can utilise the cylinder and buffer, but control the 3 way valve by the ASHP.

[Beelbeebub]

Just to be clear, do you have a gas combi boiler at the moment? Or is the "combi" in the Heatpump name just refering to the fact it does hot water and heating as well?

 

Are you able to get an idea if the 12kw unit you had was correctly sized?  Part of the higher cost might be that 12kw units are expensive.

 

If you could confirm by data or accurate heatloss assement the actual size you might be able to get away with a 9kw unit or similar.

 

If you already have a water tank and all the emitters correctly sized then it should be  near stright swap. All you need to do is locate the new site, put in a slab, run some pipes and cables to it.  

 

Locating the pump away from the back door will add cost for the longer runs of pipe (and in particular the trench and patio work) plus the slab etc.  you need to be happy with the trade off between cost and location.

[JohnMo]

6 minutes ago, Beelbeebub said:

ust to be clear, do you have a gas combi boiler at the moment

It's GSHP and cylinder in a single container, not a gas combi.

[JohnMo]

Think the heat capacity is nearer 7 than 12, looks like it can do 12kW if the brine is close to 20 degs, which is unlikely without geothermal.

[Iceverge]

We have a 185m2 passive house in Cork with 2adults and 3kids. 

 

Operating on direct electric only we use about 3300kWh for DHW and the same for space heating. Higher than PHPP predicted but still only 18kWh/m²/year per year or 37kWh/m²/yr total. 

 

Scaling it up to match your house size it would be 10700kWh/yr for DHW and space heating. 

 

That's a COP of 3.5. Your numbers look about right.

 

 

 

 

[Beelbeebub]

1 hour ago, JohnMo said:

Think the heat capacity is nearer 7 than 12, looks like it can do 12kW if the brine is close to 20 degs, which is unlikely without geothermal.

So replace the GSHP/Cylinder combo with either a manufacturer specific unit (eg Vaillant Unitower) or a large coil area cylinder then fit a something like a 7 or 10kw single fan monoblock either by the door or across the patio?

[Nially]

2 hours ago, Beelbeebub said:

Just to be clear, do you have a gas combi boiler at the moment? Or is the "combi" in the Heatpump name just refering to the fact it does hot water and heating as well?

 

Are you able to get an idea if the 12kw unit you had was correctly sized?  Part of the higher cost might be that 12kw units are expensive.

 

If you could confirm by data or accurate heatloss assement the actual size you might be able to get away with a 9kw unit or similar.

 

If you already have a water tank and all the emitters correctly sized then it should be  near stright swap. All you need to do is locate the new site, put in a slab, run some pipes and cables to it.  

 

Locating the pump away from the back door will add cost for the longer runs of pipe (and in particular the trench and patio work) plus the slab etc.  you need to be happy with the trade off between cost and location.

Thanks, The combi is in the heatpump so the heat pump does the dhw and ufh.

I am thinking the 12kw unit was oversized but at a loss how to calculate if it was.

Can anyone help with that? The 290 sq mt house used 3000KWH every year to run the geothermal pump for hot water and space heating, Id imagine them figures could be used to size the heat pump?

[Nially]

1 hour ago, JohnMo said:

Think the heat capacity is nearer 7 than 12, looks like it can do 12kW if the brine is close to 20 degs, which is unlikely without geothermal.

I am thinking the 12kw unit was oversized but at a loss how to calculate if it was.

Can anyone help with that? The 290 sq mt house used 3000KWH every year to run the geothermal pump for hot water and space heating, Id imagine them figures could be used to size the heat pump?

[Iceverge]

1 minute ago, Nially said:

Thanks, The combi is in the heatpump so the heat pump does the dhw and ufh.

I am thinking the 12kw unit was oversized but at a loss how to calculate if it was.

Can anyone help with that? The 290 sq mt house used 3000KWH every year to run the geothermal pump for hot water and space heating, Id imagine them figures could be used to size the heat pump?

 

Do you have your PHPP from the passivhaus designer? How many occupants for DHW ? 

 

 

[Nially]

24 minutes ago, Iceverge said:

We have a 185m2 passive house in Cork with 2adults and 3kids. 

 

Operating on direct electric only we use about 3300kWh for DHW and the same for space heating. Higher than PHPP predicted but still only 18kWh/m²/year per year or 37kWh/m²/yr total. 

 

Scaling it up to match your house size it would be 10700kWh/yr for DHW and space heating. 

 

That's a COP of 3.5. Your numbers look about right.

 

 

 

 

Hi There, Yes it looks like very similar performance for both houses. Any reason you didn't go for a heat pump? Based on them figures can a new pump be sized accordingly?

[Nially]

Just now, Iceverge said:

 

Do you have your PHPP from the passivhaus designer? How many occupants for DHW ? 

 

 

There are 2 adults and 3 kids.  I have no data from the designer as the construction started in late 2013 when passive houses were not that common. I had the house designed by an architect and researched all the construction details myself to get it to passive standard. An engineer then completed drawings based on the spec i provided so PHPP was never used. I competed all the airtighness myself and a lot of the trickier details like closing the 10" wide cavities etc..

[Nially]

19 minutes ago, Beelbeebub said:

So replace the GSHP/Cylinder combo with either a manufacturer specific unit (eg Vaillant Unitower) or a large coil area cylinder then fit a something like a 7 or 10kw single fan monoblock either by the door or across the patio?

Yes thanks I am also thinking of a mono block unit  and to mount it 9ft up on the outside wall as I can run pipes across the ceiling to my heating cupboard. I will need new dhw cylinder as you rightly suggested.

If a 7kw unit will do the job it will look a lot neater on the wall outside

[Iceverge]

18 minutes ago, Nially said:

Any reason you didn't go for a heat pump?

 

The electricity savings would have taken 25 years to pay for the capital cost of €7k+VAT at the time (2019). The ASHP would have broken long before that.  

 

That case has changed since with electricity prices since. Hence the A2A HP being installed at the moment. At a total installed costs of <€2k it should have itself paid for in 3-4 years. I want to put some PV for DHW at some stage. A heat pump for DHW is a much harder payback case as it's COP suffers a lot once you get above UFH temperatures. 

 

 

 

  

14 minutes ago, Nially said:

There are 2 adults and 3 kids.  I have no data from the designer as the construction started in late 2013 when passive houses were not that common. I had the house designed by an architect and researched all the construction details myself to get it to passive standard. An engineer then completed drawings based on the spec i provided so PHPP was never used. I competed all the airtighness myself and a lot of the trickier details like closing the 10" wide cavities etc..

 

Sounds similar to my route but I did PHPP for myself. The lack of knowledge among "professionals" is nearing negligence. It might be fair to say you probably use 3300kWh like us in DHW in that case too. That at a COP of 2.5 for the GSHP would be 1320kWh of energy @COP of 4 used per annum for DHW. That leaves your space heating at 1680kWh/yr at a COP of 4 is 6720kWh of primary energy demand for the Space heating. It's about 23kWh/m2/yr vs 15 for a passivhaus but as you're running at 22deg that'll increase the figure quite a bit. 

 

 

 

TLDR: Use 6720kWh/year for heating and 3300kWh/year for DHW. 

 

That gives something a bit more solid to work on. 

 

 

 

Edited December 16, 2023 by Iceverge

[JohnMo]

Sizing for heat pump cylinders, the number in model number is size in litres

 

Edited December 16, 2023 by JohnMo
Wrong file added

[Iceverge]

Here's some running costs. ( Electricity prices from switcher.ie, standing charge and other elec usage excluded, 65% usage on night rate tariff, rural user)

 

€2299/yr direct electric on a 80% usage night rate tariff. Capital cost €400 for Willis heater/immersion. 

€935/year on cheaper monoblock ASHP( COP for SH/DHW of 3/2). Capital cost of €7000

€ 728/year on an expensive split ASHP(COP for SH/DHW of 4/2.5) . Capital cost for AHSP+ cylinder inc install is €12,000. 

€728/year for GSHP with same COP's. Cost of borehole and pipes €6000. 

€1169/yr on Oil. Capital cost say €4000 for new boiler/tank and external store

 

Here's a quick table of total costs based on my above guesses. 

 

 

As you can see direct electricity wins for years 1-3.

 

Then oil for year 4. 

 

Then a GSHP repair for years 5- onwards although the cheap ASHP is a not far off.  The expensive ASHP never catches up. 

 

 

Although it's rough and ready you can probably discount oil, and an expensive ASHP and direct electric. 

 

 

 

You're back to 2 options. A cheap ASHP and fixing the GSHP. I would get some accurate quotes,revert and I can redo the sums. 

 

 

 

PS. What was the spec you were quoted for the ASHP for €12k?

 

 

 

 

 

 

 

 

 

 

 

 

Edited December 16, 2023 by Iceverge

[Alan Ambrose]

I’m still very surprised by the mdpe - I have not found specs or guarantees yet (I’ve spent all of 10 mins looking) - but see ‘50-100 year life, 16 bar’ touted around. Apart from uv impact, I’ve never even considered lifetime - the same way that I think of copper pipe, bricks, blocks etc. Do you have any of the pipe that was taken out that could be tested? Maybe it was sub-standard? You may indeed need to sue the installer - at least that would offset the costs of whatever fix is required.

[Iceverge]

43 minutes ago, Alan Ambrose said:

I’m still very surprised by the mdpe - I have not found specs or guarantees yet (I’ve spent all of 10 mins looking) - but see ‘50-100 year life, 16 bar’ touted around. Apart from uv impact, I’ve never even considered lifetime - the same way that I think of copper pipe, bricks, blocks etc. Do you have any of the pipe that was taken out that could be tested? Maybe it was sub-standard? You may indeed need to sue the installer - at least that would offset the costs of whatever fix is required.

 

I've long been suspect of GSHPs. They're effectively an interseasonal solar store, harvesting sunlight during the summer and releasing it in winter.

 

However given the variability if water levels, thermal conductivity of soil, moisture content of the soil, vegetation on the above ground, direct sunlight on the ground above it's a massive mess of variables. To call it an accurately engineered solution would be a stretch. More lightly to just oversize it a bit and hope for the best.

 

Localised freezing can occur, moving the soil and mechanically stressing the pipes  which are already embrittled due to prolonged low flow temperatures. I'm not surprised they sometimes crack. 

 

An improved COP is their selling point but once you're above about 3 the maths start to look poor. 

 

For example going from a COP of 3 to 4 looks good on paper but it only saves you a further 9% of your original bill. Going from 4 to COP 5 Is worse, it only save 5% of the bill. 

 

Heat pumps only make sense if you can keep the initial purchase cost sensible, GSHPs almost never are. 

 

 

 

 

 

Edited December 16, 2023 by Iceverge

[saveasteading]

31 minutes ago, Iceverge said:

I've long been suspect of GSHPs. They're effectively an interseasonal solar store, harvesting sunlight during the summer and releasing it in winter

Suspect is generous.

I was involved in proving the failure of an inappropriate gshp situation, and getting them replaced by ashp, so i studied it in detail and spoke to many.

that was perhaps 10 years ago, and there were many companies giving the industry a bad name, through inappropriately promoting the principle in the wrong situation, as well as poor installation.

I also spoke to many of these contractors and it was shocking how little they knew. I teased them by asking for quotes for sites with deep, heavy clay, and getting their recommendations.

Meanwhile the good companies were suffering from the overall loss of confidence in their industry.  One at the very top of the industry was openly proposing that the summer recharge of the ground was insufficient , and that the earth had to be heated by reversing the flow, or adding solar heating and 'storing' it in the ground. That was to apply to boreholes and also 'slinky' systems.

 

So I'm thinking about the original question.  Was it ever a good and efficient installation? is it worth repairing? It sounds like a simple case of repairing the pipe locally.  But how good would it ever be?

 

 

[Nially]

18 hours ago, Alan Ambrose said:

I’m still very surprised by the mdpe - I have not found specs or guarantees yet (I’ve spent all of 10 mins looking) - but see ‘50-100 year life, 16 bar’ touted around. Apart from uv impact, I’ve never even considered lifetime - the same way that I think of copper pipe, bricks, blocks etc. Do you have any of the pipe that was taken out that could be tested? Maybe it was sub-standard? You may indeed need to sue the installer - at least that would offset the costs of whatever fix is required.

Yes I have the pipe, going the legal road is something to consider but I don’t know would the stress be worth it

[Nially]

16 hours ago, saveasteading said:

Suspect is generous.

I was involved in proving the failure of an inappropriate gshp situation, and getting them replaced by ashp, so i studied it in detail and spoke to many.

that was perhaps 10 years ago, and there were many companies giving the industry a bad name, through inappropriately promoting the principle in the wrong situation, as well as poor installation.

I also spoke to many of these contractors and it was shocking how little they knew. I teased them by asking for quotes for sites with deep, heavy clay, and getting their recommendations.

Meanwhile the good companies were suffering from the overall loss of confidence in their industry.  One at the very top of the industry was openly proposing that the summer recharge of the ground was insufficient , and that the earth had to be heated by reversing the flow, or adding solar heating and 'storing' it in the ground. That was to apply to boreholes and also 'slinky' systems.

 

So I'm thinking about the original question.  Was it ever a good and efficient installation? is it worth repairing? It sounds like a simple case of repairing the pipe locally.  But how good would it ever be?

 

 

Thanks for your input. It certainly was an efficient system and never gave trouble in 9 years. We had all our heating and hot water for 3000kwh per year which is very satisfying for a large house. Repair isn’t a solution/option here so it’ll be a replace ground loop or drill bore holed if I continue with the GSHP