Comments on this opinion pls...

[Mr Sandman]

Hi all,

i am asking this question because i know there are some intelligent chaps on here that will be able to advise me on the following situation.

Basically, i am having a swimming pool built and i intend to heat it with solar panels. It seems important to me to insulate the pool as much as possible, so to this end i have researched products that could be used to insulate a swimming pool. One solution is the use of Kingspan Styrozone H350R, which was the product recommended by Kingspan themselves as suitable to withstand the weight and moisture etc. I have put to my installer my thoughts, wants etc and he has commented as below. This installer is clearly pushing me not to insulate the pool at all as he is adamant that the earth will heat the pool. Please read his response and let me know your thoughts.

"With regards to the Kingspan I have done my own research and calcs and it follows. My digger driver was doing a dig the other day so I went along to help him set out and took my tarmac temperature guage. Despite there being a heavy frost on the day, and also the snow and freeze we`ve just had ,the dig started to steam at 0.75m depth and at 1.5m deep the temperature read 11 degrees. In contrast a sheet of extruded polystyrene in my van measured -2 degrees which was the ambient temperature. I placed the sheet on the grass near the work and later in the day I measured the dig at 7 degrees (4 above ambient) ,the top of the insulation at 3 degrees which was the ambient temperature and whereby the frost on the grass had melted and the ground had softened when I lifted the sheet of polystyrene the grass was still in frost and the ground still frozen. All this maintains that insulation DOES NOT CREATE HEAT but will retain it to the same efficiency as it will retain cold. I took Kingspans U value of 0.39 Wm2/degrees K and based on a an average soil density of 14oo kg/m2 and a thermal conductivity of 0.51 W/m2 based on a depth equivilent of your pool I arrived at a figure of 0.34 Wm2/degrees K,0.05 superior to Kingspan and the advantage also that the ground,in fact,DOES CREATE HEAT. Kingspan can justify no failure in their product with movement but make no statement about structural failure of the adjacent structure due to movement caused by its application. In addition Kingspan will need to supply schedules for is resistance to crushing for UD loads and dynamic loads,will the pool have to be overloaded primarily to take the flexibilty of the product beyond the yield point and its elastic limit to prevent settling below your patio on filling or trying to spring up if the pool is emptied ? Though I am confident that my pool can rise up and down by

10mm( 20mm overall) I cannot see the patio wanting to do the same. To apply this product to obviate the above a primary concrete sub base will have to be constructed so that the Kingspan can be laid flat with no voids under, the pool base would then be constructed on top of that only if I could be satisfied that its resistance to crushing is 0mm.My feelings are that given a slab of Kingspan,a slab of src 11cm thick on top and a column of water 1.5m high the same diamension as the slab a before and after measurement will show a significant change in thickness. My conclusions are that its application will need a more expensive 2 part foundation construction with crushing ratios still in question and a thicker 1 part foundation will only augment the loads increasing the crushing potential. The product will not improve the insulation value to the underside of the foundation and will serve to isolate it from ground heat and my recommendation is at most to insulate the exterior walls of your pool with a cheaper polystyrene product. Pipe insulation is the same and I would only consider that at depths less that 50cm and if I was paying for my heat. My advise is free with no catches these guys want to sell you something you do not need."

Thanks for all your comments in advance!

Greeny

[pcb1962]

Assuming that you will heat the pool to about 25 degrees, and also assuming that the surrounding earth will rarely if ever achieve this temperature itself, I would think it obvious that there will always be a temperature gradient and therefore the pool will always lose heat to the surrounding ground.

[Ed Sirett]

I'm no expert but a pool at 11C is somewhat chilly. In summer you may well be able to capture a fair bit of heat using passive solar heating and retaining the heat with a cover. The principle heat loss mechanisms being evaporative cooling.

It strikes me that in winter no insulation will keep the pool warmer, when it is unlikely to be used (?). Whilst in summer the reverse will be true where the pool will lose heat to the surrounding ground.

The structural arguments however need to be weighed. And given that the reply is numerate and coherent I take it quite seriously. I suspect that control of heat loss by evaporation is probably the most crucial factor and the bigger the pool, the more so.

I will love to hear how this pans out.

[The Natural Philosopher]

Yes, BUT the insulation propertiess of 50m of kingspan are far less than the 24000 miles of earth all round the pool ;-)

And that represents a loverly heatbank also, that will keep the pool warm at night.

If the pool aint inside, its pointless insulating it. ALL the heatloss is from the water surface.

Hint. You never see a pond frozen down the SIDES do you?

[Newshound]

Well, it's current wisdom that you should insulate a solid floor to prevent heat loss if using underfloor heating (and if not?). It's quite true that heat comes up out of the earth. If you put an area of perfect insulation on the ground, the ground immediately under it will warm up to the point where heat loss sideways balances heat input upwards, if you see what I mean. The equilibrium temperature will depend on the area covered and the conductivity of the local ground. If that temperature is hotter than your pool, you might win with no insulation. You would gain heat in the middle, but probably lose some towards the edges. But if that temperature is lower than the pool, you will definitely be better off with insulation from a thermal efficiency viewpoint. Of course thermal insulation brings a lot of extra structural issues.

The other thing you might consider is thermal capacity. In the days of "home made" concrete shower trays, builders used to "insulate" them with old wine bottles, actually so that the surface would warm up more quickly and not feel so cold. I was interested to see them using the same technique on a pigsty in the Victorian Farm program a few days ago.

[dennis]

*If* you have enough solar panels the ground will warm during the summer and will help to maintain the heat for a while after the summer has finished. It will also delay the temp rise in spring as you will be heating the ground too. Adding insulation reduces this effect as it removes the heat capacity of the ground from the equation.

[PCPaul]

No, because there is a lot more heat loss from the water surface. But that doesn't mean there is none from the rest of the edges.

If the pool water is warmer than the earth, then it will lose temperature. Adding even 50mm of a good insulator will slow that loss down.

Adding an insulated cover will help more, obviously, but again that doesn't mean insulating the sides is worthless.

As for the Earth acting as a heatbank, that only works if (a) you go deep enough and (b) you want to keep the pool at the same temperature as the earth.

Otherwise it's just a constant temperature heatsink.

[Rod]

So unless we know the temperature of the earth at the site, and at the depth being talked about, the question cannot really be answered. Perhaps it is right over a hot spring?

[The Natural Philosopher]

BUT it will, in the process warm the earth around it. You alreadu have, with a pool, a MASSIVE heatbank, anddinga few hundred tons f soil to it, is no big deal.

But the earth immediately surrounding the pool WILL be at the same temperature.

No, because its not infinitely conductive.