Navitron Renewable Energy and Sustainability Forum

HEAT PUMPS & Geothermal Energy => Heat Pumps => Topic started by: stumpy on August 29, 2006, 04:55:21 PM

Title: PIPE
Post by: stumpy on August 29, 2006, 04:55:21 PM
Hi all

I've been investigating GSHPs and have had a couple of quotes from 'reputable companies'.  For my house (220m2) their quaotes are between 6500-8000 for the pump and c1000 for the pipe (400m - 2 x 200m lengths).

They are also quoting c700 installation of pump and commissioning.  The groundworks for the pipe's installation is additional, and I'd probably do that myself.  Fortunately I have a reasonably sized rear garden to accommodate this pipe.  This would be c750 for a machine for a couple of days + sand.

One of the systems will supposedly give me a CoP of 4.83, as it requires 5000kWh/a, and will deliver 24,000kWh/a which I understand is pretty good?

If I chose to DIY, and purchase Navitron's 9kW pump, does anyone know of a supplier of the appropriate pipe, and approx cost?  I'm sure I saw a thread on here somewhere but can't find it now!  Also, does anyone know an installer?  Not something I could manage myself... Location = Kent.

Any responses from individuals who have installed their own GSHP's and how well they work with wet UFH systems would be greatly appreciated.  I'm having a few problems convincing the missus it would be better going this route than using a traditional gas boiler!

Many thanks

Title: Re: PIPE
Post by: ecogeorge on August 29, 2006, 10:26:35 PM
Use 32mm MDPE "normal" waterpipe. Usually rated at 12 bar. Choose black colour -donates non-potable water. Available in 100m or larger rolls (remember you have to handle them). Use heavy duty cable ties to hold slinkies in place. Fusion joining of pipes is best - use good quality Philmac or Plasson water fittings if fusion not an option.Minimise no. of joints.
I bought pipe 12 mths ago for less than 50p / m (incl vat) but that was cost price (I work for a large Agricultural co.). I can check price tomorrow if you require.
rgds George.

ps Keep pipe lengths on multiple runs exactly the same length - stops the pump favoring one section .

Title: Re: PIPE
Post by: stumpy on August 30, 2006, 09:02:46 AM
Thanks for that George

Yes please do get a quote for me.

Thanks again

Title: Re: PIPE
Post by: madandy on August 31, 2006, 03:36:02 PM
Ref the above - 32mm pipe. I'm am putting in navitron's 5 Kw GSHP and plan to use 200m of 25mm slinkies (is that how you spell it?). After reading your comments I am now worried that this will not be up to the job - please advise if you can :-\ Thanks


Title: Re: PIPE
Post by: stumpy on September 01, 2006, 02:58:08 PM
I've heard that slinkies are generally used where there may be insufficient space to run long single lengths of pipe in the garden.  Slinkies being closer-packed therefore can be placed in a smaller hole.

I also understand, it's the length of pipe that is important as I guess this is what gets heated up - the longer the pipe the more heat that is generated...?

Certainly do not profess to know very much...!


Title: Re: PIPE
Post by: Bargeman on September 01, 2006, 11:07:38 PM
Hello madandy,

My understanding is that the 'rule of thumb' for slinkies is 10m of trench for every kW power installed, so 200m for a 5 kW pump seems more than adequate. One thought occurred to me - my understanding (please check with Ivan) is that the navitron 5kW model is ground source to air, meaning that your internal domestic heating system probably needs to be air blown ? Sorry if this sounds patronising, but I thought it might be worth checking. The 9 kW model is ground source to water which would link to most wet domestic heating systems.

Hello Carl,

I'm also based in Kent (Faversham). I did quite a lot of research, obtained Clear Skies funding and took part in the installation of a large (24 kW)system, supplied by Kensa, at my daughter's local primary school. I'm also considering the navitron 9 kW. Depending upon how close we are, I'd be happy to help you out just to get some hands on experience with the navitron system. If you're interested please send me a message offline.


Title: Re: PIPE
Post by: Ian on September 02, 2006, 09:31:23 AM
Just when you thought all was clear, along comes another guy and tells you the exact opposite!

There is no way that I would factor 100 watts per metre in any installation that I would undertake -even sunk in a lake!

Guys that try to sell the kit tell you that you can get somewhere between 30 - 50 watts per linear metre. Personally,I work to 20 watts per linear metre and I have never had a poblem. Am I OVERspecifing ? maybe - and there is no real way of finding out without trying something different.

In my opinion, 200m for a 5 kW GSHP should be fine (25 watts per linear metre) unless you live on a very dry sand dune.

If I install a slinky (helix) rather than linear pipes, then I allow a greater de-rating and I would never use more than 20 watts per metre of pipe.

I would also try to use a thin bore pipe. 32mm is OK but is on the large side. 20 - 25mm is what I normally propse. It is all a game of compromises. Too small a diameter means that the pump has to work harder and airlocks are more likely; too large a diameter and the surface area to volume is lower so more water has to pass through the heat exchanger in order to extract the same energy.

I hope this helps.


Title: Re: PIPE
Post by: Bargeman on September 02, 2006, 01:59:01 PM
Hello Ian,

You're right that the 10m:1kW 'rule of thumb' cited is sourced from a heat pump manufacturer, in this case Kensa Engineering in Cornwall. They apply it to slinkies laid in 1.8 m deep trenches in favourable soil conditiions. To be clear it refers to the trench length, not the pipe length.

If you can find the time, take a look at some of the case studies (for slinky installations) available on the Kensa ( web site, e.g. Auldyn School, Sevenoaks barn conversion, Aberdeen, Cucklington, Honiton. Those which give data for the closed ground loop collectors with slinkies are consistent with the 10m:1kW rule. Having followed up references for a number of their installations, I found that their customers were in general satisfied with outcome. At our local school we have proceeded on this basis, with 5 x 50 m x 1.8m trenches laid out across the school playing fields to supply a 24 kW pump.


Title: Re: PIPE
Post by: madandy on September 04, 2006, 03:27:12 PM
Ian & Bargeman

Thanks for the info above, I now feel happy with my choice of pipe. Am I correct in thinking that a straight run of pipe is more efficient than a slinky? I am lucky enough to have the space to do this if required but had been led to believe that a slinky is more efficient ???

Thanks for the reminder about the 5Kw pump being water to air - yes this is what I am after as I plan to link this into my HRV system.

Title: Re: PIPE
Post by: Ian on September 05, 2006, 09:09:04 AM
Madandy - it depends how you define efficiency!

Slinky (coiled) is more efficient if you measure :
Time and labour taken to dig the trench
Amount of space required to bury the same linear length of pipe

Uncoiled linear is more efficient if you measure :
Absolute ability to extract as much energy as possible from the ground loop
Minimum physical linear length of pipe
Reduced depth of trench
Cost of pipe.

I would agree that in a normal conversation that a single run of pipe would be regarded as more efficient. If space were not an issue, and all other things were equal, I would install a single (uncoiled) run of pipe (but there is not a lot in it really).

I hope this helps.