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Author Topic: Heat pump sytems  (Read 5087 times)
martin
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« on: June 22, 2006, 10:21:44 AM »

just had a chap on the 'phone who has been quoted by a rival firm for fitting a 28kw ground source heat pump system - seeing Ivan's only go up to 9kw, and bright suggestions? - if I have to go elsewhere for a biggie, who's good and affordable? Undecided
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Ian
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« Reply #1 on: June 22, 2006, 12:17:59 PM »

Martin, I know this is going to sound obvious.

28 kW ground source heat pumps are dammed expensive.† The economics of 3 times 9 kW systems from Navitron are probably the lowest cost option.† It may also be the best option for your potential customer.† I will try to give my reasoning:

If your customer has not used a ground source heat pump before then he is adding an awful lot of eggs into a single basket and taking a major leap of faith.† It may be that the type of heat that ground source heat pumps can provide will not suit your customer.† The best way in would be to run a pilot.

If the pilot is quite acceptable to your customer, whatever system is currently being used would not be decommissioned initially, but used in the normal way.† Suggest the installation of a single 9 kW system and use it to feed a "zone" which is installed at the same time as the ground source heat pump.† Run it like this for at least one season and find out if the customer is happy with the energy savings, the type and quality of heat provided, and generally to make sure the customer can live with such a system.

Assuming the customer is happy after a season or two then divide the rest of the current heating system up into two further zones and install an additional two ground source heat pumps to feed these new zones.† In this way the customer would end up with 3 x 9 kW ground source heat pumps and three individual zones within his household, which makes for much greater flexibility than can ever be achieved with a single large ground source heat pump.†

There may be other benefits from this route also.† A 28 kW system that will equate to something like 100,000 BTU real heat output, which is quite a large house.† The chances are that a large house also has a large amount of land.† There could be real advantages in being able to lay three individual ground loops instead of one big massive one.† But that could only be determined on a ground inspection and a real soil analysis.

As an aside, a few years ago I was working in Switzerland in an establishment that had a ground source heat pump.† Switzerland has really adopted ground source heat pumps big-time.† They are fairly commonplace now.† In this particular establishment, three boreholes each 300 m deep, were being used.† There was zero evidence of any pipework on the surface, it was totally invisible.† I can personally vouch for the effectiveness of the system.† The owner claimed that for every kilowatt of power input he was getting 3.6 kW output.

I hope this helps.

Regards,
Ian
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martin
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« Reply #2 on: June 22, 2006, 09:07:13 PM »

thanks very much for that - you obviously put a lot of thought into it, and it makes a great deal of sense. I've forwarded the gist of your post to my potential client, and hope he comes back to learn more! Cool
What sort of figures would you think we'd be looking at for a single loop?
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Ivan
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« Reply #3 on: June 23, 2006, 12:23:58 AM »

Just one point to add to this - check the power handling of the incoming mains.

 28kW would be 117Amps. Most household supplies are either 60A or 100A.....and that has to cover all electrical requirements, not just heating. Most heatpump suppliers (all?) will not supply single phase units above about 16kW. Instead they move up to 3phase. Navitron can supply anything up to 16kW in single phase and up to around 250kW in 3 phase - however, we only stock a very narrow range (not really a major product line for us), but we can get the larger units in as required, albeit with a time delay.

Ivan
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martin
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« Reply #4 on: June 23, 2006, 12:31:07 AM »

thanks for that - the prospective client was blanching at the thought of having 3-phase installed! Cool
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Ian
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« Reply #5 on: June 23, 2006, 08:27:12 AM »

Guys, Feel free to shoot me if I have my knickers in a twist here.

I have assumed that when we talk about a 28 kW system we are talking about the gross output from the unit. The actual electrical input would be 30% - 25% of that gross figure (i.e. 7 kW - 10 kW). Hence the Navitron 9 kW system actually draws about 2 - 2.2 kW (I think). Indeed, I DID get my knickers in a twist when I responded in my earlier post - part of my argument was that the pilot approach would allow the use of single phase and only when the customer was 100% sure would there be a need to install 3 phase. But just as I was reading through the preview just before posting, I THINK I realised my mistake and corrected it.

So, I am saying that the 28 kW system is actually the heat output (around 100, 000 BTUs which is substantial but in the right ball-park for a large house.

IF we are talking about 28 kW of ELECTRICAL power, then this is a different ball-park altogether. 28 kW of electrical input would equate to 90 - 120 kW of heat output (about 400,000 - 500,000 BTUs) and this is massive and more akin to industrial scale heating. And, yes, of course this would require 3 phase.

If we are talking about 28 kW of heat output, then I am happy with 7 - 10 kW of electrical input which equates to a cuirrent draw of 35 - 50 amps (and an initial surge probably 50 - 100% higher than this as the compressor kicks in - but it is momentary and well within the capability of any circuit breakers or the supply fuse). I am happy this would be OK on a typical 80 - 100 amp single phase supply.

I hope this helps.

Regards,
Ian
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Ian
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« Reply #6 on: June 23, 2006, 08:33:40 AM »

Damn ! - I forgot to add in my above post that if we are talking about a 28 kW electrical input (100 kW heat output), then† I hope your customer has a couple of fottball pitches that he can dig up and sink a 10 mile ground loop !! Seriously, it would be a hell of a ground loop or a good number of deep boreholes.

I hope this helps.

Regards,
Ian
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martin
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« Reply #7 on: June 23, 2006, 09:57:30 AM »

some cheering news! Your excellent input has resulted in us receiving a request to visit the property, and to do them a survey to look further into the matter! - many, many thanks indeed! Grin Grin Grin
I have a feeling that it is pretty massive, he was talking of putting a ground loop "in the paddock" Roll Eyes
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Ian
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« Reply #8 on: June 23, 2006, 12:02:40 PM »

At the risk of teaching you to suck eggs again - keep a look-out for water during your survey.

As is mentioned in a few posts on this forum (I think Ivan mentions it a fair amount) water is a MUCH better conductor of heat energy than the average soil / rock that a ground loop is sunk into. Flowing water is best - as, if you can guarantee security of supply, you can do away with the ground loop altogether. Even a big pond is good if you decide not to pump water (or you could even pump this as long as you returned the water to the pond); again, my guess is that only about one third of the "ground" loop will be required if sunk into a pond and it is less critical how it is laid as long as the depth of water is over about 3- 4 feet.

I think technically you may need an extraction permit from the Environment Agency to move water around but they are, I am told, quite easy to deal with.

If your customer is in a big old house (say, more than 150 years old) it is very likely that there will be water nearby. However, if he really is in a big old house, with stone floors, etc. it could be quite tricky to get the right kind of "house side" heat exchangers in. My guess is that they would be on something like an oil-fired boiler feeding readiators. Does your customer know that radiators really aren't very good for GSH pumps ?

Another point about the ground loop (no matter if it is laid in the ground or a pond) - make sure that you use a biocide. All sorts of things can grow in a closed loop water system and they have a habit of building up on the heat exchanger surfaces - reducing efficiency. Once they are built up, it is a difficulty task to eradicate. Brine is a better heat exchanger than water and a reasonable biocide in its own right - but it is also corrosive so make sure that only stainless materials are used in valves, couplings, pumps, and heat exchangers.

I hope this helps.

Regards,
Ian
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Ivan
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« Reply #9 on: June 24, 2006, 01:06:10 AM »

All good advice. You should not need an extraction licence if you are putting water back where it came from without losing any (new regulations to encourage renewable energy in particular) - unless you are generating 5MW of usable power.

The Navitron single phase turbines are available up to 16kW only. Above this, the factory can only produce 3phase compressors. I think they offer up to 200kW!!

Ivan
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neilbridget
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« Reply #10 on: July 12, 2006, 10:23:30 PM »

I am re-submitting my planning applciation for a proposed extension and would like to incorporate your 9kw heat pump using an open loop system connected to a well.  I need however to find out details of what type of flooring to use with the underfloor heating connected to the system.  I would appreciate talking to someone to get more details and also to find out a recommedned installer inthe north bristol area
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mtimm
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« Reply #11 on: July 13, 2006, 01:26:21 PM »

Getting a bit off topic but
Most types of flooring can and have been used with underfloor heating
(Tiles, wood (solid, semi-solid and laminate), carpet and lino)

Tiles work well but you should use flexible adhesive and grout, be careful with natural stone the changing temps can cause cracks.

Wood: ash and beech generally arenít recommended
Solid can move a lot, it is generally is around 20mm thick which is the max wood thickness for use with UFH and needs to be fixed to the floor.

Semi-solid works well, some are guaranteed for use with UFH, choose the underlay carefully.

Laminates work very well.

Carpet is used but avoid heavy carpets and/or heavy underlay.

In general the covering should be of minimum thickness (insulation) to allow the heat travel from the floor into the room

Hope this is of some help





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