GSHP Sizing

[nudgerreturns]

Hi all, any thoughts on the following gratefully received. I'll bulletpoint to keep things short!

New build house, obviously well insulated Block and lime render. Completed 15 months ago.

6,100 square feet.

2X 7kw IVT GSHP's Installed.

Underfloor heating loops on ground floor, rads upstairs.

Usage is 30,500 units since 15 Nov 2011. Average of 114 units per day.

Rooms downstairs have stats set to 18 degrees and are a good temperature. Except one carpeted room that rarely reaches required temperature.

Rooms upstairs are generally always 17 or below. Too cold for my wife!

I'm told by the supplier that the Heatpumps are fine. Yet I'm not convinced..


I think the pumps are undersized?

Cheers

 

[D_Hailsham]

You can find out how much heat your house needs by using the Whole House Boiler Size Calculator. The fact that you have GSHP is irrelevant; you still need a certain amount of heat, irrespective of what type of heating you have.

6000sq ft is large! In modern measurements it's 558 sq metres, which is a two storey house approx 14m x 20m. This would require about 24kW.

That's for a 21C room temperature. For 18C you only need 21kW.

Whatever, it's still more than the 14kW you have.

Did your architect give you the heat loss calculations he had to do when applying for Building Regs approval?

 

[nudgerreturns]

Thank you very much. My relative has built a house of almost identical size and used 1x7kw and 1x14kw heat pumps. I think I should be at LEAST 21kw.

During the last few day's dip in temperature, 2 Bedrooms are reading around the 14 degree mark and we can't seem to get them above that.

I have asked the developer to come back to me on the Heat Loss.

Thanks again

 

[mickyg]

it sounds like a balancing or system design issue tbh. If your heat source is undersized then the whole house should suffer equally, not one some rooms better than others. It wouldn't hurt phoning the gshp manufacturer and running through some of the parameters on your HP to make sure its operating correctly, if they're happy to do that

 

[Norcon]

Well undersized. A house that big will need about 40kw easily imo. 14kw is a joke but the trade is full of cowboys unfortuanetly.
Their junk at the end off the day. Especially in the UK.

Worked in industrial refrigeration for several years and never met a single engineer who would install one in their own home.
Well apart from one maybe....

The consultant in the company I worked for designed and had one built to his own specifications.
Well lets just say thats the only one he ever made as it was a disaster.
Give him a supermarket or an industrial system however and it will be capable of out performing any system in the world.

 

[snb]

Well undersized. A house that big will need about 40kw easily imo. 14kw is a joke but the trade is full of cowboys unfortuanetly.
Their junk at the end off the day. Especially in the UK.

Worked in industrial refrigeration for several years and never met a single engineer who would install one in their own home.
Well apart from one maybe....

The consultant in the company I worked for designed and had one built to his own specifications.
Well lets just say thats the only one he ever made as it was a disaster.
Give him a supermarket or an industrial system however and it will be capable of out performing any system in the world.

40kw which planet are you on

have done a few ground source on large properties ranging from 4500 sq ft to 8000 sqft

if the build spec is 2010 regs then you would be looking at about 22kw.

but it could be as low as 18kw if the insulation is better.

should have read what you wrote more carefully.

was this system designed by ice energy??

how warm do the rads get up stairs?

if they hardly get any warmth then the problem is down to system design/balancing.

often they have the underfloor system with it's own pump on the manifolds.

these pumps will take 90 % of the flow volume from the heat pump.

they need to have either a flow restrictor fitted or an additional pump push the heat around the rads.

the underfloor system may also have the flow volumes for each loop set at too high a rate which will also not help.

 

[SimonH2]

Sounds like insufficient power - but you could check that it's lack of heat from the pumps rather than inadequate heat transfer inside the house.

If the rads are too small for the flow temperature, then you'll find that the flow water is up to temperature and the pumps have backed off. Similarly if there is thick carpet over the UFH areas.

If it's lack of pump power then you'll find the flow temperature is low.

 

[nudgerreturns]

Ive been through parameters many times with the supplier - they always insist the HP's are doing their job and that there is a balancing issue. However, the plumber's opinion is that the Rads offer not nearly enough heat fo the rooms.

(would the rads only ever run at the same temps as the underfloor loops?)

Any other views on whether the balancing must be the cause as the house would be poor in every room if it was the HP's? That interesting - although I can't help thinking that 14kw seems light.

Thanks again...

 

[nudgerreturns]

Sounds like insufficient power - but you could check that it's lack of heat from the pumps rather than inadequate heat transfer inside the house.

Is this done by accessing the HP's? I'm not technical enough to mess with them, all I know is that the heat slope is set to 6, which according to the supplier is as high as should be necessary for rads. But the rooms are too cold so something's not right!

If the rads are too small for the flow temperature, then you'll find that the flow water is up to temperature and the pumps have backed off. Similarly if there is thick carpet over the UFH areas.

If it's lack of pump power then you'll find the flow temperature is low.

U/F areas are toasty - never had a problem except one carpeted room which is questionable. Wood and stone floors are all good. The problem is upstairs rooms with rads that are tepid at best and I'm not sure are actually doing anything of much use, and any heat is actually coming from downstairs... However, we spent a fair fee on having the rads calculated and specced correctly, so I think the sizes are right.

 

[SimonH2]

You need a means of measuring the temperature of a pipe. See what temperature the pipe is going into the rads. If that's too low then you won't get enough heat out of the rads.

The UFH will normally have it's own pump and mixing valve. Ie, on the manifold, it will have it's own pump that circulates water round the UFH loops, with a TMV that pulls in hot water from the main system as required.
So typically the UFH loops run at a lower temperature than the rads - unless you have very large rads !

 

[mickyg]

start from the basics. Its new build so you should have heat loss calcs available. Work out what each room has, then see what each room has got. Remember radiator quoted outputs are based on a flow/return of 75/65 so they will need to be oversized to run at whatever your gshp output is, usually around 40-45.

 

[nudgerreturns]

SNB, thanks very much, I will look into sorting all those points, in the meantime I've found the spec list (I have noticed the incorrect floor size for a start!): I have also seen one to an identically sized property, and that has been specced by the same supplier with a IVT Greenline HC+ 33kW Ground Source Heat Pump (Three Phase) Thanks again guys for looking. This could end up getting messy.


SPEC:
Ground Source Heating System comprising design, supply, commissioning and warranty. Project Type is defined as RETRO (Domestic)
Floor Area to be heated is 511m2 using Measurements (no plans seen) provided by client. Maximum heating demand is assumed at 20.2 kW
Heat Pump
IVT Greenline HT+ E7 Ground Source Heat Pump (Single Phase)
Rego 600 Computer Controller and Weather-Indoor temperature compensation sensors
Please refer to Unit Specifications to ensure electrical & space requirements can be met.
Water Storage Cylinder
IVT DVB300 300 litre (mains pressure) hot water cylinder
Ground Loop (per Heat Pump)
2 trenches 50m long, 1m wide by 1m deep are required.
Total of 400m of pipe work to be supplied as 2 x 200m coils, with connectors. Each trench to recieve 200m of pipework in 200mm sand bed. Trenches must have a minimum separation of 2m.
Ground works and sand works to be sub-contracted by customer.

 

[nudgerreturns]

Thanks everyone, I think I really need to bring in an independent engineer to go through this in detail and submit a report. If anyone can recommend a way to find anyone in the Wilts region, that would be brillant.

Cheers once again.

 

[Norcon]

Maximum heating demand is assumed at 20.2 kW

 

[snb]

those trenches for the ground loops are too small.

design spec is 50m trench for every 3 to 4 kw of heat pump output.

so that causes concern

you do have a 300lt sling tank

it is still possible for these pumps to heat your house. unless we have long sustained periods of cold below 3 degrees.

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.