Groundloops for a heat pump

[knighty]

if 600m or 32mm pipe is only 4p/metre extra... thats only £24...

so I'd definitely go with the 32mm stuff..... ok 25mm pipe does have a better ratio of volume to surface area..... but that doesn't really matter here ?

you want to install enough pipe so that adding extra pipe won't make any difference... the pipes you have will bring the water in them up to ground tempriture... and you can't get any more heat than that anyway....

also, I'd think the extra volume of water in the ground would help too ?


I don't know how much the pipe costs, but if 32mm is only 4p/mete more than 25mm I guess it must be quite cheap... and I don't know how much it will cost to have the digger there - if you pay by the hour, by how much work he does, or by the day.... but I'd install as much pipe as possible.... relatively small cost now.... and you'll make it back over the lifetime of the system ?   - also helps make a more reliable robust system... and gives you the option to increase the size of the heat pump in the future ?

[Richard Owen]

..... but that doesn't really matter here ?

Might do, might not do.

This is a very inexact science. Nobody really knows how your site is going to behave.

Hopefully you'll be looking at a dT of about 3c which isn't very much really.

35mm pipe will probably be Ok, particularly if you have lots of pipe.

However, if you want to maximise the performance of your system, to give it the best possible chance of working optimally, narrow diameter pipe is best.

[welshboy]

..... but that doesn't really matter here ?

Might do, might not do.

This is a very inexact science. Nobody really knows how your site is going to behave.

Hopefully you'll be looking at a dT of about 3c which isn't very much really.

35mm pipe will probably be Ok, particularly if you have lots of pipe.

However, if you want to maximise the performance of your system, to give it the best possible chance of working optimally, narrow diameter pipe is best.

My thinking is the same as Richard for the reasons stated.
I have read that turbulence is important to mix the water in the pipe so that it all gets in contact with the walls at some stage.
I must confess I don't know how this is achieved in practice though.

[ecogeorge]

Remember , pushing 19 litres/ minute (isn't that what a wr09 needs ?) will be harder through small bore pipe!
Small bore pipe  is more likely to suffer from restrictions / kinking etc.
I would go 25mm or 32mm and run more liquid around the loop slower without strangling the pump. If in doubt add an extra 10m of pipe.
Just my 2p worth.
George.

Is anyone running pipe smaller than 25mm ?

[baker]

 Hi
 been getting ground loop temtature of -2 as the heatpump is been put to work the last two weeks
 with temp from 1 to -11   c0p 2.7

[welshboy]

What temps are you getting from your ground loops during this cold weather chaps?

im getting about7.6c and 8.4c from the loop in the well.

steve

I only monitor the return to the groundloop from the heatpump - currently 4c so I guess I am getting around 9c on the flow.

[knighty]

I've always read/thought that it all depends on surface area avalible...

you need a lot of flow and turbulence going through the heat pump to dump as much heat as possible, as fast as possible, over it's small surface area....

but even with 25mm vs 32mm hose.... you're going to have naff all turbulance.... or flow.... but have massive surface area... so might as well do as much as you can do take advantage of it ?

damn this is hard to describe.... - I'm dyslexic I know what I want to say, but just don't know how....

the point is... you want to have enough pipe/surface area in the ground that even if you added more flow/surface area/etc... it wouldn't make any difference because you're already extracting as much heat as your heat pump can take ?

[JMALW]

Hi
I did a lot of research prior to a new build I did some years ago and decided not to install a heat pump system even with an underfloor heating system I installed, I could not get the maths to add up in its favour. One of the things that alarmed me was the current draw from the pumps (especially on start up) and the fact that any advantage in the system revolved around the cost of energy.  Some of the disadvantage was born out by having to ask the utility company for permission to install since the high current draw may affect the neighbours supply.  Since the thread focuses on size of pipe in the ground loop would it not be prudent to examine load on the pump for various pipe sizes since this may affect the decision on any efficiency result?

[linesrg]

JMALW,
I was out buying a UBG car from somebody local to me who happened to be a builder and who lived in a steading conversion, the first things that struck was the temperature of the floor when we went inside. It occurred to me that whilst the UFH was probably a good idea it was clar that alot more money needed to have been spent on insulation.
We did discuss heat pumps and his comment was that his experience from other who had installed them was that the running costs had been quite high. This is of course subjective as I had no idea what their heating costs would have been with an alternative.
The point of this posting is that the heat in the floor of the place we were at served as a reminder that you need to improve insulation first to benefit from UFH and a heat pump. Our kitchen floor isn't that hot but we have a load of insulation installed and haven't made a feature of stone walls!!
My concern remains the potential running cost of the heat pump. Thus I still aim to go for an underpowered system and use the existing LPG system to take up the 'slack' as required.
All views still considered.
Regards
Richard 

[dhaslam]

The important thing is to have enough capacity to be able to do most of the heating at off peak rates. If you add up the total cost for  a 180 day heating period at the full off peak hours the cost won't be very great.    However if you have to add day time use and other systems to back up then it becomes less attractive.     

It is important also not to have floors too hot.   It the floor is too hot it can lead to a lot of rising dust and also when the sun comes out some rooms can overheat.   Obviously  badly insulated houses won't work too well.    The maximum floor temperature I normally get is about 23C and this corresponds to a room temperature of 20C or so.

[JMALW]

Hi Richard
There were more than one issue that persuded me, amongst them was the high cost of the system and possible payback. The underfloor supplier designed my system very well and it is the best investment I ever made. The fact that it is said to be compatible with a heat pump was very misleading. They said it was so since the operating temperature was lower but that proved not to be the case and if I had have installed a heat pump it would not have worked based on the heat requirements we need and do have since installing a condensing gas boiler and the gas is way cheaper than electricity at current prices.
I spent a bundle on the best high density foam insulation and that has paid for itself in the last 4 years.

[linesrg]

JMALW,
I agree with you entirely re the insulation issue. We have spent a lot of money on improving insulation in this here stone built farmhouse with each room being effectively ripped out as we can afford to improve. As I have said elsewhere we went 'overboard' with the kitchen 14-15 months ago because 'her indoors' wanted UFH as she didn't want a radiator compromising the kitchen design. After lots of Googling and some conflicting advice we eventually did our own thing in conjunction with a local plumber who we have used for a number of years even though he clearly wasn't entirely 'au fait' with all the finer points he was able to readily source the bits required. The kitchen is approx 5.5 x 5mtrs and so we ended up with two loops off a 6 way manifold (room for expansion downstairs) and basically filled the whole floor with the exception of under the fitted units.
The walls were battened out with 75 x 50mm battening infilled with 50mm Celotex and then further overlaid with another 25mm, the floor was underlaid with 90mm Celotex and the ceiling has another 50mm with fibreglass over that. It is not sealed from all external air so the rear of the walls are 'open' to the outside via the roof.
Our kitchen floor sits at about 23 degrees as mentioned by dhaslam.
We are still using a fair amount of gas and still have to do the bathroom, hall-stairs-landing and both living and dining room. I am occasionally intrigued as to the gas usage (down 14% year on year currently) as none of the radiators are ever 'hot' given the water goes out at 55degrees.
Given the extreme weather we're currently enjoying up here in Aberdeenshire I do wonder how an ASHP would cope?
Regards
Richard

[JMALW]

Hi Richard

Although I'm a seasoned veteran with conventional central heating and had confidence in the maths for the designs I did not feel confident with the same for my UFH so I let a pro do the maths and installed it myself - radiator sizing is pretty much well established but coils in floors left me clueless on emission rates.  Seriously though this property system loses 1 degree C of room temperature in two days with outside temps of -7 and no heat input so I'm well chuffed. I believe you use LPG so I'm not sure what cost differential there is between Natural which is what we have.  Problem is I just heard that UK don't have more than 5 days storage at any one time so we may have some problems if that is not redressed.  We got stocked up with long johns and body warmers just in case.  Oh and there is an anomaly on temperatures that I have never figured out - in summer we are happy with 20 degrees or less room temps but in winter the other half says she feels cold if it drops below 24 deg C. Take a look at my digestor efforts on another thread.
Regards
John

[EccentricAnomaly]

Oh and there is an anomoly on temperatures that I have never figured out - in summer we are happy with 20 degrees or less room temps but in winter the other half says she feels cold if it drops below 24 deg C.

How dare you misspell my name? 

As well as the air temperature there are two other factors which go into the perceived temperature.  One is the temperature of the walls and other materials.  As I understand it, that's about as important as the air temperature.

The other is the humidity though I'm not sure what difference that makes.  It often seems that damp air feels colder and all the comments about "but it's a dry cold" when comparing cold wet England and even colder but dry ski slopes backs that up but that rather contradicts your summer/winter observation when you'd expect the relative humidity inside a heated house to be slightly lower (given the absolute humidity of any incoming air will be a lot lower).

It's also the case that people adapt to ambient temperatures over a number of days though, again, that confounds your observation.

Another consideration is the accuracy of thermometers.  Are you sure you're comparing like with like?  I have a number of different thermometers and their temperatures seem to be spread over about 4°C at room temperatures.

[JMALW]

How dare you misspell my name?
I agree with your points entirely - all our rooms are monitored for humidity and temperature and other devices seem to agree with the readings. The humidty as you would expect from a UFH is actually too low for good health (32%) and less in summer we have to induce a little to get the optimum of 45/50%.  Also with the floor being charged all around the area the walls are much warmer than any conventionally heated room we ever had, but then they are stuffed with all this insulation (100mm) too. Actually I'm always a tadd too warm but she wins every time.  Sorry to digress - the point being that if enough insulation is thrown at a property then even a heat pump should be enough.  Fact is they do struggle with 300sq mtr property with a margin over and I think Richard agrees, but the cost does not add up to a renewable energy system.

John