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Geothermal Heating of Pool


Ozpete
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I am wanting to install geothermal heating pipe in an unsuccessful water borehole (80m) to possibly use as geothermal heating for my pool (75m3).

Does anyone know what length of HDPE pipe will be needed to heat this volume of water to 25 degrees say from May to October?

Thanks OzPete
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I agree with Théière and even then it would of course be subject to proper survey.

As a very very rough indication though as a concept it's reckoned that you will get 5kW from a 100m deep borehole but depending on location that could vary by factors of the order of  -75% to +500% or more !

One thing is for sure, you will need a great deal more than 5kw to heat your pool to your requirements [blink]

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Thanks for the advice - I have connected with a suggested geothermal outfit in the UK who calculated that with my borehole & connecting horizontals to a heat pump, we would get 4 tons or 14kW of heat. Not being a thermodynamics wiz I am wondering if this is enough heat to make a difference -ie what influence on a 75m3 pool will 14kW have under say conditions where daytime ambiant is 20 deg, (night-time ambient 10 deg) target temp is 25 deg but water temp is 15 deg and assuming a decent insulative floating cover?

I remember reading some posts a few years back where it was recommended that evacuated tube solar is a better bet than a heat pump - would this still be the case if the cost of the borehole is deducted ?

Thanks for any insights.

OzPete

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Ozpete

I guess the 'Oz' part of your avatar eludes to your origin. If that’s so then, as one Aussie to another I can tell you plane.

Geothermal no matter how you’re doing it is a very long investment for the cost of it. Most systems never reach break even if you equate current electrical prices. Biggest problem is not the finding of energy, as many will tell you there's plenty underground there for the asking. The big thing is the initial cost v. the life of the system - I've not seen to many Ground source, or geothermal installers give more and a few measly years warrantee on the system because (specially if its under powered and so you make it work hard) the life of the compressor and exchanger are by no means infinite. I normally encourage potential purchasers to factor renewing the heat pump after 10 years -most of the time that turns out to be true. All of that being true, then its very expensive energy indeed.

Solar thermal on the other hand is so simple (only one moving part) that its life could be construed as virtually indefinite. Couple that with a cost per watt of around 10% of Geo and heat pumps and it’s a no brainer to me. Many others disagree primarily because they cannot accept that the sun doesn't shine every day and therefore you cannot get heat out of a solar system every day. The people who can accept that in exchange for free heat are the ones who have already installed a few solar tubes and can be seen with the permanent smirk on their face.

It is now possible to link the pool heating to heat the house in winter as well. By this method its possible to get a return for your investment for 12 months of the year instead of just 3 months of the swimming season and much more such as lower TVA, credit impot and other benefits. Again.... no brainer.

Concomitantly, you can choose what you want for your own reasons, but renewable energy has come so far that for anyone to install fossil fuel based systems from new is sheer madness, verging on vandalism, in my view. So if to be renewables then ther are good, better, best as with everything. Even a single panel to get some hot water for a shower once in a while is a start. But for your Pool OZ me ol mate, go Solar thermal and you'll get a result you can see for yourself.

Andrew

 

 

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Andrew

Yes you are right - Wollongong boy but have lived in the UK for about 20yrs but about to shift to our place we have been renovating for 3 yrs in the Lot.

This started as a search for water for irrigation but a 80m dry hole started me thinking about what to do with it. I had been thinking about adding solar for the pool to extend the season but decided to leave it until I had finished the house and moved down (next year). The existing pool (10m x 5m) is lined and about 25 yrs old.

Just to heat the existing pool, what range of cost am I looking at ? I was thinking cheap & cheerful plastic tube arrays but I know you are a fan of high efficiency evacuated glass tubes? Is there a problem with dumping heat load in hot conditions with the latter?

Best Regards

OzPete
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Pete

If you want to contact me by email I can send you some proposals for solar systems for pools and show you a clever trick to heat the house as well during winter. Its a significnat investment and I think that it should be in use all year rather than just the swimming months. But your comment that your 'thinking cheap and cheerful' doesn't really sit well with geotherm/ground source heating - that game is researved for the well healed players, its spendy enough to make your eyes water. So consequently I'm not sure what your budget is so its difficult to advise you properly. Certianly I can tell you for definate that Solar thermal is the best bang for your buck by a country mile- I can easily prove that no other investment in renewables comes close (€/kw).

Drop me a line and we can chat - Oz style.

Andrew

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The biggest difference between evacuated glass collectors and poly tube EPDM rubber is that the glass tubes require light to activate the system (plentiful in spring and autumn) whereas the rubber mats require heat from the sum (not so plentiful at those times) Also with a bit of clever plumbing you can provide plenty of hot water to the house too using the glass tube system.
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As I understand it, both glass evacuated tube and Poly Tube colectors use IR not UV A or B,However you can always use the Poly Tube or Solar thermal as the energy source for a small heat pump or just use a small air to water heat pump and

>> with a bit of clever plumbing you can provide plenty of hot water to the house too using the glass tube system. << as you say.

regards

Roy G
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Roy

You've got the wrong end of the stick I think. Modern Evacuated Tube solar collectors use Ultra Violet light as well as Infra red spectrum to gather energy which is why they are so revolutionary. It means that they (Evac Tubes)can still work on dull days unlike the EPDM matting which is pury ornamental in these conditions.

Also as almost anyone who has owned EPDM mats will tell you that they eventually leak at one or all of the vast number of little connections and also have to be drained down in winter, which makes them a bit  of a pain in my view. Its a difference between low tech (take lots of space) or high tech (takes less than half the space for the same Kw)


Andrew

 

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Good Evening Andrew,

Solar Thermal use IR radiation not UV A or B and evac tubes are more expensive and have more service problems as oposed to flat plate collectors if you have a problem with one tube you might lose all the fluid from the system also the tubes can  be difficult to replace/repair.

Solar PV uses UV A or and B to cause the reaction in the receptor.

Yes you can have problems with EPDM matting but always use an anti-freeze mix as you should with Solar thermal so that you do not need to drain down the system. They are simple and cheap to repair. Again you can use Solar Thermal and /or EPDM matting as an energy source for a small heat pump, extending the use of the pool. to later in the year.

regards

Roy G

www.theheheatpumppeople.co.uk

 

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Roy, you seem to be as is Andrew concentrating on only the ends of the light spectrum I.R. or U.V My understanding is that evacuated tubes work on solar radiation accross a very broad spectrum of light mainly the visible spectrum but also for obvious reason the I.R. end as well. The first demonstration I witnessed many years ago used a 40 watt light bulb to demonstrate the heat at the collector.

As I said earlier EPDM mat's left out in spring or autumn will do precious little unless the sun is hot enough to heat the water. The same cannot be said of evacuated tubes which with visible daylight and an ambient outdoor temperature of zero will still produce hot water which is why they can be used at the south pole. 

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Good morning Théière,

To cut to the chase, I would never personally use EV tubes, I sell them but do not recommend them for all sort of reasons, I personally use and sell Flat plate Solar Thermal, I also sell and install PV, We also are heat pump specialists. All I am trying to say is a simple cost effective way to heat a pool / DHW is using EPDM mats installed correctly connected to a heat pump will work 365 days a year 24 hours a a day. There is a care home using EPDM mats on the roof which produce 4000lts hot water (yes 4000) daily providing ALL the hot water needs for the home all year. You can all argue all day about Uv a and B if you want. only trying to help.

regards

Roy G
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Point taken Roy, just confused my poor overworked brain as EV tubes are the most efficient in terms of collecting energy but as you say EPDM mats and a heat pump together may well be a more cost effective way.

Please do post some more information on the performance of the mats + Pump.

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[quote user="Bino"]Good morning Théière,

To cut to the chase, I would never personally use EV tubes, I sell them but do not recommend them for all sort of reasons, I personally use and sell Flat plate Solar Thermal, I also sell and install PV, We also are heat pump specialists. All I am trying to say is a simple cost effective way to heat a pool / DHW is using EPDM mats installed correctly connected to a heat pump will work 365 days a year 24 hours a a day. There is a care home using EPDM mats on the roof which produce 4000lts hot water (yes 4000) daily providing ALL the hot water needs for the home all year. You can all argue all day about Uv a and B if you want. only trying to help.

regards

Roy G[/quote]

Roy - I have sent you a PM

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[quote user="Bino"] Solar Thermal use IR radiation not UV A or B and evac tubes are more expensive and have more service problems as oposed to flat plate collectors if you have a problem with one tube you might lose all the fluid from the system also the tubes can  be difficult to replace/repair. [/quote]

Now there's a thing. You claim to be an installer of ET systems, but make a statement like that. I also install them, but have never come across one that has the tubes in direct contact with the heat transfer fluid. How so? A significant benefit of ET systems is that the loss of 1 tube has little effect on the system as a whole.... All the ET systems I have seen have a UV transmissive (IR block) coating on the inside. How can they work on IR?

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I claim quite a lot of ignorance of all this (and would like to know more), but I did have a useful graph in an old book (courtesy of Messrs Pilkingtons) showing how much energy arrives at the earth's surface from difference frequencies of sunlight. It's not much in the UV end of the total spectrum, a very substantial peak indeed in the visible spectrum, and substantially declining amounts even before you get to the IR end, with three small peaks in the IR end.

[edit] In fact,something rather like this graphic, from NASA:

[IMG]http://i585.photobucket.com/albums/ss293/Vanman15/em_radiation_atmosph_depth_stsci.jpg[/IMG]

which I found on this useful website: http://www.windows2universe.org/earth/Atmosphere/earth_atmosph_radiation_budget.html

where they also say by way of explanation of the graphic:

A relatively narrow "window" of EM wavelengths around visible light

reaches the ground. It includes some of the longer wavelength UV

frequencies, some of the shorter wavelength IR frequencies, and all of

the visble light region of the spectrum.

Most of the longer wavelength IR waves, and many of the shorter

radio waves, are absorbed by the stratosphere before reaching the

ground. There is a sizeable "radio window" of radio wave frequencies

that also reach terra firma.

To me this suggests that although evacuated tubes can be more efficient at collecting solar energy in the IR and UV ends of the spectrum, they won't add such a very large amount to the energy that can be collected just from the visible spectrum, because that's where most of the energy is (and presumably it's why most animals, including us, evolved eyes which see in what we call the visible spectrum). And I'd be very surprised if the flat plate collectors didn't harvest any of the energy from the IR and UV ends of the spectrum.

But I'm sure someone can post a link to say what the facts are as they relate to actual solar collectors of both types.

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Again, I can't give any specifics either but evacuated tubes do collect from the visible spectrum, the early post skewed the info. The first demo I saw used a standard 40 watt light bulb, most definitely in the visible spectrum and you could not touch the collector at the top of the evacuated tube.
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[quote user="Nick Trollope"]

[quote user="Bino"] Solar Thermal use IR radiation not UV A or B and evac tubes are more expensive and have more service problems as oposed to flat plate collectors if you have a problem with one tube you might lose all the fluid from the system also the tubes can  be difficult to replace/repair. [/quote]

Now there's a thing. You claim to be an installer of ET systems, but make a statement like that. I also install them, but have never come across one that has the tubes in direct contact with the heat transfer fluid. How so? A significant benefit of ET systems is that the loss of 1 tube has little effect on the system as a whole.... All the ET systems I have seen have a UV transmissive (IR block) coating on the inside. How can they work on IR?

[/quote]

I am not an installer, just a bloke who wants more time out of the swimming season and I installed my EV system. I pressure checked the complete hot side of that system before I installed any of the tubes.

The system that I have is the Navitron one and the collector manifold is a 28mm tube with smaller, about 15mm, tubes braised across it to take the hot bulbs on the top end of the tubes. As Nick said, the hot bulbs at the top of those tubes are not in any kind of contact with the water. Another advantage of the tubes over any kind of flat plate is that there is a lot less water in the presurised hot side of the system. This is because the only water in the collector is the water in the 28mm manifold that runs along the top that the tubes are plugged into. With the flat plate the complete plate is full of water. This means that there is a lot less water to be heated and the response times are quicker. For water please read anti-freeze or any other liquid.

My system is filled with water only. It doesn't get drained in the winter because I have the controller set up to run the circulating pump for 5 mins in the hour when the temp goes down to 5 deg C and for continuous running if it goes neg. It is only a 40 wat pump, so it is not a problem. We have had temps here down to -7.5 with no problems.

The reference to the South Pole earlier is to do with the fact that scientific expeditions down there use EV tubes for their hot water and through the summer they get that from said tubes in temps of -40 deg. Not sure if that's Farengrade or centiheight? [8-)][8-)][;-)]

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[quote user="Jonzjob"]

The system that I have is the Navitron one and the collector manifold is a 28mm tube with smaller, about 15mm, tubes braised across it to take the hot bulbs on the top end of the tubes. As Nick said, the hot bulbs at the top of those tubes are not in any kind of contact with the water. Another advantage of the tubes over any kind of flat plate is that there is a lot less water in the presurised hot side of the system. This is because the only water in the collector is the water in the 28mm manifold that runs along the top that the tubes are plugged into. With the flat plate the complete plate is full of water. This means that there is a lot less water to be heated and the response times are quicker. For water please read anti-freeze or any other liquid.

[/quote]

Jonzjob

It's very hard to get sensible comparisons of the two types of systems, but the manufacturers of the flat plate collectors I am in the process of buying say they contain 0.6 litres of fluid for each square metre of aperture area. There is a Swiss solar testing outfit called SPF (www.spf.ch) who have tested a couple of Navitron EV systems - the SFB20 and the SFC10 - and the SPF report lets you work out that the fluid content of these two is 0.64 litres and 0.79 litres per square metre of aperture area. They give aperture area and fluid content and it's a fairly easy sum.

I should add that I have no doubt at all that EV systems are generally more efficient than flat plate ones, but I don't think it's because of the different fluid contents.

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