Help! I need to Replace my GSHP

[Nially]

Hi all.

I built my home back in 2015 and thankfully I was interested enough at the time to go the passive route. Although not certified It has preformed very well.

I have been reading numerous posts over the past few days with great interest.

 

Performance wise over 8 years the GSHP has used 24,000 kwh for space heating (wet UFH) and daily hot water so about 3,000kwh per year. The temperature in the house  was set at a constant 22 degrees, upstairs never called for heat as the heat rises from downstairs.

I do have an open loop to bathrooms so once any room calls for heat the bathrooms will heat.

 

The house is 290sq mt, 250mm pumped wide cavity with block on flat on interior walls, 0.37 ach air tightness, 400mm of pumped cellulose in the vaulted ceilings and 400mm of rockwoll in the flat ceiling to attic space.

 

So I am now on here as i need a bit of help/advice as our ground loop to run our Geothermal  pump has failed. The 32mm pipe has developed stress cracks where is was looped at the end of a trench (1000mm wide trench). We found and dug up one leak and I believe our installer looped the pipe too tightly and over time it has simply developed a crack on the apex of the curve. The leak we found was exactly on the apex of the curve. We had discussions and he is not willing to take responsibility. Digging up my mature 8 year old lawn and garden is now not an option.

 

So I am probably left chasing him through the legal route if I am willing to take on that stress.

 

Luckily enough I have a stove so that is keeping the house somewhat warm.

 

I am now left looking for an alternative heating source. Air to water is the obvious answer but maybe now that I have 8 years of data that might be overkill for my house? I am also turned off by the unit which will have to be retro fitted right outside my back door which is not ideal. Maybe someone might have suggestions how to heat my existing buffer tank? 30 degrees in my buffer would easily heat the house. I would of course also need an option for my daily hot water.

 

Any advice or opinions are appreciated, thanks.

 

 

 

 

 

[IanR]

Hi and welcome,

 

Assuming you are not considering fossil fuels or Biomass(?), then your energy usage does suggest ASHP is the best option. Say your SCOP is around 4, then a direct electric solution is going to require 12,000kWh a year, so your heating and DHW will be around £3,600/yr on a standard tariff.

 

Can you move the ASHP a little further away from your back door? 

[Beelbeebub]

That heat requirement is very low, and probably mostly hot water.

 

Presumably there is a bigish unit inside for the GSHP? Probably near the back door (boot room?).  Maybe the hot water cylinder next to it?

 

This might be a bit out there, but what about one of those integrated heatpump water cylinders?

 

It's an unvented water cylinder heated by a little air source heatpump sat on top fed by two ducts, usually about 180mm.

 

That could replace your water cylinder or GSHP as long as there was relatively easy access route the two ducts outside.

So that would take care of hot water

 

The slightly funky bit would be rigging up some way of powering your UFH from that setup. If the cylinder had a secondary loop you could power your UFH from that via a heat exchanger?

 

A bit out there, but it would remove the need for an external unit

 

 

Edit: Just reread the OP, I misinterpreted 3,000kwh/year as the output no the consumption.   So maybe too much for my suggestion

Edited December 15, 2023 by Beelbeebub

[ReedRichards]

The issue with an ASHP, I think, is that you will need a low power output to heat your house and, I think, a higher power output to heat your hot water in a reasonable amount of time.  So you would need an ASHP with a good dynamic range of power inputs.  Also, some ASHPs seem to start up on full or high power and then work their way down whilst others start at low power and work their way up.  I think the latter type would be more appropriate to a low heat requirement.  I might be wrong about this, my ASHP starts low.  But I have seen data from another ASHP user indicating that theirs starts high.  I'm sure others her could comment about this.        

[Nially]

2 hours ago, IanR said:

Hi and welcome,

 

Assuming you are not considering fossil fuels or Biomass(?), then your energy usage does suggest ASHP is the best option. Say your SCOP is around 4, then a direct electric solution is going to require 12,000kWh a year, so your heating and DHW will be around £3,600/yr on a standard tariff.

 

Can you move the ASHP a little further away from your back door? 

Hi and thanks,

Yes correct on your COP and figures

I am limited where I can place it so near the back door it will have to be if I go for it

[IanR]

4 minutes ago, ReedRichards said:

The issue with an ASHP, I think, is that you will need a low power output to heat your house and, I think, a higher power output to heat your hot water in a reasonable amount of time.  

That's exactly my situation. A 6kW ASHP would easily cover my heating requirement, but I have a 12kW HP for faster DHW reheat times (500l UVC). I therefore have a 200l 4 port Buffer in my install.

[Nially]

2 hours ago, Beelbeebub said:

That heat requirement is very low, and probably mostly hot water.

 

 

Thanks for the suggestion, yes I had read up on them units and it would be an option for the DHW. I have the buffer tank and GSHP unit near the back.

Heating the buffer tank then for the UFH would need a solution

[JohnMo]

Realistically you need a 6kW heat pump, not sure a 4 kW would be big enough. With that size (6kW) heat pump and a 210L cylinder we are basically heating it once per day and it takes 45 minutes. There is plenty of capacity to do heating as required. A bigger cylinder a couple of heats a day would make the heating times short enough. We are using a 6kW on a smaller heat load (smaller house) and it just stops and start as required, generally runs for about 10 mins on and 10 to 15 off on a mild day, may run a few hours when cold.

 

Our ASHP ramps up and then down, no issues.

 

Just plumb exactly the same as your gshp was.

[Alan Ambrose]

>>> We found and dug up one leak and I believe our installer looped the pipe too tightly and over time it has simply developed a crack on the apex of the curve.

 

Are you assuming that there are equivalent problems all the way down the pipe now? Is it possible the problems are localised and they could simply get a patch fix?

 

p.s. what kind of pipe, MDPE? Also, any idea what pressure it's running at?

Edited December 15, 2023 by Alan Ambrose

[sharpener]

4 hours ago, Nially said:

Digging up my mature 8 year old lawn and garden is now not an option.

 

But maybe drilling a hole for a vertical loop would avoid this, and although expensive would still be cheaper and less disruptive than replacing the whole shebang.

[Gus Potter]

7 hours ago, Nially said:

Any advice or opinions are appreciated, thanks.

Hi there.

 

As a stop gap can you fit an Essex Cylinder Flange - 2.1/4" BSP F Brass to your buffer tank near the bottom?  see link below:

 

https://www.stevensonplumbing.co.uk/immersion-heater-mechanical-flange.html

 

Then into that fit and electric immersion say 3.0 kW like below with a timer etc.

 

https://www.screwfix.com/p/tesla-titanium-immersion-heater-14-/74662#product_additional_details_container

 

Mind you that all sounds easy on paper but.. you need to know about the tank and in particular where the coil is located inside. Before cutting a hole in the tank I would phone the manufacturer, explain the problem and find out where they install a factory fitted electric immersion.. which they probably do from time to time.

 

Now with a bit of care you can do this yourself.. if you take your time and use the right tools then you can get them to work.. @Nickfromwales could maybe provide some tips.

 

I take it that the buffer tank is unvented thus it is a "pressure vessel" and as such the unvented cylinder regs apply. Anyway I'll let you mull that over, no need to say any more.

 

If you make a good job of it then at least you'll have a backup next time your system breaks down.. merry Xmas ba humbug etc.. just kidding. On the upside if you later fit pv panels you'll have a ready made destination for the electricity you generate.. have a great xmas and remember that every cloud has potentially a silver lining! If you crack on it could alll be up and running ok ish for Santa.

 

 

 

 

 

 

[ProDave]

3 hours ago, Alan Ambrose said:

>>> We found and dug up one leak and I believe our installer looped the pipe too tightly and over time it has simply developed a crack on the apex of the curve.

 

Are you assuming that there are equivalent problems all the way down the pipe now? Is it possible the problems are localised and they could simply get a patch fix?

 

p.s. what kind of pipe, MDPE? Also, any idea what pressure it's running at?

I was going to suggest that.  If it is just the bends at the end, then can you not fix it by digging up just a strip of the lawn and repairing / replacing the damaged sections?

[JohnMo]

42 minutes ago, Gus Potter said:

As a stop gap can you fit an Essex Cylinder Flange - 2.1/4" BSP F Brass to your buffer tank near the bottom?  see link below:

Or a simple Willis heater if easier to hook up.

[Jilly]

But the problem is that the heat pump has failed AND the loops in the ground are suspect. Patching the loops would be a good idea if the GSHP was working properly, but to buy another and find the loops are leaking would be stressful to say the least.
I have a friend who has just replaced their GSHP, at approx £9k, I don’t know the details but think it was about 10 years old. It’s a worry if they are not repairable. 

[Redbeard]

21 minutes ago, Jilly said:

But the problem is that the heat pump has failed AND the loops in the ground are suspect.

 

@Jilly, this was not my understanding. The OP said, in the OP, "our ground loop to run our Geothermal  pump has failed". Have I missed something?

[Gus Potter]

57 minutes ago, Redbeard said:

Have I missed something?

Etiquette.

 

[Iceverge]

@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. 

 

 

[sharpener]

4 hours ago, ProDave said:

I was going to suggest that.  If it is just the bends at the end, then can you not fix it by digging up just a strip of the lawn and repairing / replacing the damaged sections?

 

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.

[Nickfromwales]

3 minutes 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.

Agreed, in principal.... but the price of a borehole is high. Would need estimating by the OP before we could vote / offer feedback on that.

 

4 hours ago, Gus Potter said:

Now with a bit of care you can do this yourself.. if you take your time and use the right tools then you can get them to work.. @Nickfromwales could maybe provide some tips.

Yes, an immersion can work here. I'd probably swap the buffer out for a unit with the capacity to take 2x 3kW immersions, it would be a lot for 1 to take on and then you'd be stuck with a single point of failure (for the sake of bit more capital investment).

 

I've installed several immersion based heating systems (temporary and permanent) and they work brilliantly, for cheap as chips money in installation costs, but you are then tied to a 1:1 running cost. Not really a huge issue when you look at bank-rolling this endeavour, and at how much electricity you can buy with the change!!

 

More ammunition for changing the buffer would be to fit a much bigger one (500L) to utilise load shifting off a cheap rate tariff like E10.

[Gus Potter]

20 minutes ago, Nickfromwales said:

Yes, an immersion can work here.

You're brand new Nick. I was wondering if you could retro fit a two and quarter inch Surrey flange to an unvented buffer tank, but was worried about the immersion fowling a modern coil/ plates

 

My intention was to see what you could do as a stop gap to get @Nially over the Christmas holidays without having to burst the bank, use the existing cylinder and not do something that you can't reverse later.. or may be of use later. I'm still thinking.. you need to know where the coils / plates are inside so you can get the electric element in. Maybe if thing go wrong it would be advisable to order a 2" 1/2"  blank plug and pretend it never happened.

 

Fitting a flange of that diameter and getting a good seal I found is tricky. I used to do them when I was young but one mistake on cutting the hole and the cylinder is finished. Also the link I posted has a cork seal..I think.  I'm not sure that would work with an unvented cylinder say potentially working up to 3 bar before the relief valve kicks in. Mind you in the old days I used Boss White and horsehair, still do at times (and is in my plumbing box) when working traditionaly on DIY but most now I use a non setting jointing compound for any threaded fittings.

 

Yes I know an electric immersion is not probably cost effective in the long term but in the short.. it (the leccy) is about the cost of a crappy bottle of port in Surrey.. or in Newcastle 6 good sized bottle of Newcastle Brown.. or two bottles of Buckfast tonic wine in Scotland.  Now ask do you know how much a stamp costs to send a Christmas card?

[Gus Potter]

4 hours ago, Gus Potter said:

Etiquette.

@Nickfromwales

 

Jilly has forgotten more than we both know!

[Nially]

21 hours ago, Alan Ambrose said:

>>> We found and dug up one leak and I believe our installer looped the pipe too tightly and over time it has simply developed a crack on the apex of the curve.

 

Are you assuming that there are equivalent problems all the way down the pipe now? Is it possible the problems are localised and they could simply get a patch fix?

 

p.s. what kind of pipe, MDPE? Also, any idea what pressure it's running at?

Hi Alan, Yes my fear is the pipe will eventually fail at every tight turn. We repaired one leak but have at  least 2 more (two ground  loops so they can be isolated and tested and no pressure in either which means 2 more leaks).

I suspect pressurising the loop to 3 bar to find the leaks normally ran at .5 bar exposed the pipes weakness and has split in several places. It s just not worth ripping up lawns and patios and most likely have problems again. Yes it is an MDPE gethermal pipe with an MJS logo on it. Any idea who MJS are? I googled the manufacturer but nothing turns up.

 

Edited December 16, 2023 by Nially

[Nially]

17 hours ago, Gus Potter said:

Hi there.

 

As a stop gap can you fit an Essex Cylinder Flange - 2.1/4" BSP F Brass to your buffer tank near the bottom?  see link below:

 

https://www.stevensonplumbing.co.uk/immersion-heater-mechanical-flange.html

 

Thanks for the detailed reply Gus.

So the heat pump has an auxiliary immersion heater that heats a coil that heats the buffer tank. I have this set to come on at night to top the tank up to 35 degrees. This is keeping the main hallway at 18 degrees and bearable. I also have a stove in the living are so things could be a lot worse. Bedrooms are at about 16/17 so not too bad

 

 

 

 

 

 

 

 

 

 

[Nially]

15 hours ago, Jilly said:

But the problem is that the heat pump has failed AND the loops in the ground are suspect. Patching the loops would be a good idea if the GSHP was working properly, but to buy another and find the loops are leaking would be stressful to say the least.
I have a friend who has just replaced their GSHP, at approx £9k, I don’t know the details but think it was about 10 years old. It’s a worry if they are not repairable. 

The heat pump unit its self is perfect Jilly, just the loop has failed

[Nially]

15 hours ago, Redbeard said:

 

@Jilly, this was not my understanding. The OP said, in the OP, "our ground loop to run our Geothermal  pump has failed". Have I missed something?

correct, just the ground loop has failed