GSHP Sizing

[Norcon]

I wouldn't put any less than a 40kw boiler in an underfloor heated property (which is what I read it as btw) that size regardless of the heat loss.
And it would have a quality controller and modulating valve/s.

This is where you cowboys fall flat on yer faces. The extra power is there for intermittent use where the client uses the ufh system similar to a radiator system.

Big engine means fast ufh heat up (less than 1 hour) and the controller takes care of any boiler oversizing inefficiencies.

When your dealing with clients like that they don't care where the heat comes from as long it comes fast and shortly after the button is pressed.

 

[nudgerreturns]

those trenches for the ground loops are too small.

I was worried - my relative in question has 1000m vs my 400m!

it sounds like the main problem is lack of flow around rad circuit. have had to alter one install by fitting another pump just on rad circuit to assist. This solved the problem.

We have already added another two pumps to try and solve the rad heat problem!

I've attached a few pics for interest

//www.diynot.com/network/nudgerreturns/albums/14916

 

[SimonH2]

Hmm ...
First pic, there's the UFH manifold with a pump and no TMV. So unless there is a TMV somewhere else in that loop, it means you cannot run the supply to the rads any higher than the UFH - probably something like 30-35˚C max ?

At that sort of temp, you need really big rads. Output drops by (IIRC) 50% just going from 50˚ to 30˚ delta-T - that would be something like 50˚C in. You may need rads an order of magnitude bigger by the time you get down to 30-40˚ flow temp.

Second pic is hard to make out what goes where, but it's interesting to see what looks like a combination safety valve with a port blanked off - the blank cap just underneath the red pump. What's that valve doing ? If it's part of the safety system for the unvented cylinder then it looks like it's not installed correctly.

 

[mickyg]

Hmm ...
First pic, there's the UFH manifold with a pump and no TMV. So unless there is a TMV somewhere else in that loop, it means you cannot run the supply to the rads any higher than the UFH - probably something like 30-35˚C max ?

Thats pretty standard, you dont want your heat pump trying to get up to 50-60c even if it could it would be horrendously inefficient.

At that sort of temp, you need really big rads

precisely, hence my previous post.

Personally wouldn't have mixed rads and ufh on gshp. should go ufh only, left on 23hrs a day, with set back temp 2-3c lower than normal temp. Anyway, controlling is a bit irrelevent here as its not getting to temp. Something seriously amiss, I think a combination of problems.
If this has never performed properly if left on 24hr for say a few weeks through what until now has been a pretty mild winter, then there is a fault, not udnersizing. If it were undersized it would only be a problem when its very cold. When its 10c outside you might only need 10-12kw for example so there is a fault with either the GSHP install or the system, I suspect both. Whats the flow and return temp of the ground loop? can you get that info?
Also the flow rate on the ufh loops, you have timoleon ufh and you should see the flow rate on the return loop manifold.

 

[nudgerreturns]

The issue is definitely climate related in the sense that we a re comfortable as long as it is mild. As soon as we get a cold snap, the rooms in question become very cold. (My son's room is 12 degrees, from 16 degrees last week)

How can I find the flow return temps to the ground loops?
Whats a TMV and what should I look for?

Thanks again for your help, I am awaiting quotes now for an independent supplier to come and assess the entire property.

I understand as our system was commissioned August sept 2011 that the regs have changed? I'm also seeing what course I have for complaint/legal action.

Cheers

 

[Agile]

Is this a one off house or part of a development of several? If the latter how do the others get on?

Its best to measure the flow and returns with a contact thermometer ( IR ones are pretty useless for this purpose.

Do you have a single 14 kW GSHP ? How does that meet the assumption of 21 kW being needed?

Tony

 

[nudgerreturns]

We're a single detached house, and we have 2 7kw IVT heat pumps. (single phase as we couldn't get 3 phase here) One serving DHW and the other CH & DHW if I recall correctly.

Opinion thus far is that the loops are insufficient and so are the pumps.

 

[Agile]

We're a single detached house, and we have 2 7kw IVT heat pumps. (single phase as we couldn't get 3 phase here) One serving DHW and the other CH & DHW if I recall correctly.

If what you say is correct then you only have 7 kW trying to heat a house needing an assumed 21 kW ! Thats a bit underpowered !

Tony

 

[doitall]

The Hp maybe undersize but if you try and take any more out of the collectors you'll end up with a permafrost and a solid block of ice that'll take years to recover.

As said you need to double the loops in the ground and ideally sink them a foot lower.

 

[Agile]

Nothing he has said implies to me that he is freezing the ground.

Why not pop round John and have a look?

As you are now retired you dont need to raise an invoice!

Tony

 

[nudgerreturns]

If there was anyone with the expertise to offer their services, then please let me know as that may prove invaluable. I am Nr Marlborough SN8, perhaps someone would be happy to do it? Obviously there would be a cost involved.

Anyway do shout if so, I need to press on gathering data with a sense of emergency!

Cheers

 

[doitall]

Not as simply as that Tony.

Its whats in the ground that matters more than anything.

We would probably have used somewhere around 8-10 x 100m loops of 32mm mdpe without working it out. 600mm centers and at least 1200-1400mm in depth. 20Kw approximately.

Obviously they have used slinkies which give you the best chance to permanently turn the ground into a block of ice.

All our systems where designed for 50c, 30c is ridiculous.

Probably the best plan now would be a small boiler to top up when needed.

 

[nudgerreturns]

Not as simply as that Tony.

Its whats in the ground that matters more than anything.

We would probably have used somewhere around 8-10 x 100m loops of 32mm mdpe without working it out. 600mm centers and at least 1200-1400mm in depth. 20Kw approximately.

Obviously they have used slinkies which give you the best chance to permanently turn the ground into a block of ice.

All our systems where designed for 50c, 30c is ridiculous.

Probably the best plan now would be a small boiler to top up when needed.

Ground loops are straight runs, not coiled. 400m.

Getting any other supplementary heating is a no no - this system has cost a fortune to install and now a fortune to run, I'll go to court first!

 

[doitall]

Supplementary heating is essential in my opinion. The cylinder should have a monthly purge cycle, (immersion would do that)

The collectors should be spaced 600mm centers, so 4 x 100m loops requires 4 x 700mm wide trenches the recommended depth is 1200-1400m where the temperature will be fairly constant at 12c depending on the terrain.

If the numbers add up to 20Kw, you would need to at least double that to 8 x 100m loops.

As a rule of thumb you need an area of unshaded open ground twice the footprint of the property.

What size pipe have they used.

 

[nudgerreturns]

Supplementary heating is essential in my opinion. The cylinder should have a monthly purge cycle, (immersion would do that)

The collectors should be spaced 600mm centers, so 4 x 100m loops requires 4 x 700mm wide trenches the recommended depth is 1200-1400m where the temperature will be fairly constant at 12c depending on the terrain.

If the numbers add up to 20Kw, you would need to at least double that to 8 x 100m loops.

As a rule of thumb you need an area of unshaded open ground twice the footprint of the property.

What size pipe have they used.

Do you mean supplementary heating is essential in any GSHP installation? On in this case? If it's the latter, I will have the whole system removed and replaced before adding more expense, if they've got it wrong then they are liable in my opinion!

we have an area of flat, south facing garden approx 2 acres in size. The 400m of loops take up about a third of this area. There's always been plenty of space. I know they are at 1m deep with about 1m between trenches. I think they used 32mm pipe.