180 tubes heating a swimming pool.

[betwixt]

We have 200 Navitron tubes in total, 20 providing our domestic hot water and 180 helping to heat the swimming pool.

In the photograph, the top panel is 120 runs of neoprene pipe between manifolds carrying the pool water directly. The Navitron manifolds and pipework can't handle chlorinated water so an in-line heat exchanger is used to keep the fresh and pool water apart. At the moment the pool water is at about 30C but it has been above 25C for several weeks now. The pool holds 150,000 litres of rain water collected from gutters below the top panel.

Brian.
(Aberdyfi, West Wales)

[room101]

That looks so nice.......

[kristen]

"150,000 litres"

Your pool doesn't look that big in the picture - either that or I've grossly mis-calculated the size of my pool! (Which might be why its green at the moment and not responding to the measured quantities of chemical I have put in  )

We had a system similar to the pipework in your top panel on the pool at a previous house, and we found the contraction in the winter cold caused all sorts of problems with the joints; also that it was good at getting the pool up to about 20C, but above that needed some very good weather (can't quite see in your diagram whether your top panels are enclosed, or if the pipe is open to the atmosphere?)

25C seems to be the cutoff whether our children will go in the pool, or not!, and 30C is definitely the preferred temperature so that they stay in all day long!

Kristen

[betwixt]

The pool is 58' long by 21' wide. At the shallow end it is 3' deep and it slopes to 7' 6" at the deep (far end). The angle the picture was taken from doesn't do it justice.

The top panel is adapted from two Solarmatt kits and assembled on a home-made frame of salvaged timber from a demolition site. It is not enclosed but under the pipes a mineral felt skin allows me to collect rainwater which is then filtered and put in the pool. All the water is straight from the sky - proof of how much it rains in Wales!

Together the panels work very well. Each has it's strengths and weaknesses, the Solarmatt is more efficient in strong sunlight than the Navitron system but works just as efficiently as a radiator when insolation drops. A graphs of inlet vs. outlet temperatire differential looks like a profile of the Alps and even a few seconds of shade, such a as cloud passing over, can cause a cooling rather than heating effect.

The biggest problem with the Solarmatt has been squirrells chewing the pipes and it only took them two days to munch through the vacuum release valves! I fixed that by adding a tee (in the far top corner of the picture) and running a pipe up one of the trees so it ended above the pump head height. No water can get out but air can get in to stop the pipes collapsing if it gets drained.

Navitron's pipes work very well, even in gloomy conditions and the vertical mounting should ensure good output even when the sun is low in winter time. Controlling which system to use for optimum output is complicated and for technical reasons, I can't use both at once. It will be automated very shortly but for the time being, I have to manually switch panels every 15 minutes when its sunny or they overheat. I've already managed to melt the 2" ABS water pipes (with water in them) at the heat exchanger twice this year through not watching the time!

When finished, a controller in the house will talk to the pump room via a radio link to allow the whole pool system to be managed remotely. It will monitor all the temperatures and allow control of the pumps, pool lights (LEDs!) and other equipment completely automatically. Keeping the 'brain' of the system indoors will make it much easier to debug and optimise the software. A PV panel and backup battery will keep the control system and  pumps running in case of power failure. I hope to keep controller consumption below 5W although the pumps of necessity take considrably more.

There is the start of an article on the smaller but similar control system on www.atv-projects.com but although it is in daily use, I think I can improve its performance yet more before releasing the full design plans.

Brian.

[kristen]

"The pool is 58' long by 21' wide"

That's a relief, its quite a lot bigger than it looks in the pics 

Kristen

[Paulh_Boats]

Betwixt,

200 tubes!  Wow its great to see a large scale investment in solar heating. It would be interesting to see how well it works through the year. 
Maybe in the winter you could divert 40 tubes or more to hot water heating? Then you might be able to get free hot water all year.

-Paul

[kristen]

Any reason not to divert all 200 tubes to Central Heating supplement during the non-swimming season?

Kristen

[betwixt]

non-swimming season.....?

I thought this was supposed to keep it open all year !

We already have 20 tubes for domestic hot water (currently at 50C) and with thick timber walls we generally have problems keeping the house cool in winter rather than heating it.  The plan is, subject to finding some money and getting planning permission, to fit an arch type cover over the pool to keep the heat in and leaves out so it can be used all the time. Those trees in the picture make a lovely backdrop but very shortly they will be dumping tons of leaves into the pool. I hope a cover will let the light and heat in but keep the leaves outside.

The view the other way is on http://www.dyfi.com/Dyficam.html if anyone is interested.

Brian.

[kristen]

"non-swimming season"

I thought this was an outdoor pool in Wales ... but you are probably more hardy than we are!

"... an arch type cover over the pool ..."

This sort of thing perhaps?

http://www.pool-enclosures.co.uk/telescopic-pool-enclosures.html

we have friends in France with something like this and it works well.

We have a telescopic cover rather like this

http://www.pool-enclosures.co.uk/oxford-swimming-pool-enclosure.html

but we don't attempt to use the pool between 1/2 term in the Winter term (mid October I suppose) and the start of the Easter school holiday.  The air temperature is too low to make swimming enjoyable.  But then we are soft-Southerners so YMMV! (East Anglia)

Personally I think year round swimming needs a brick + etc. building.

Kristen

[betwixt]

We breed them hardy here!

That's pretty much the kind of enclosure we have in mind but it has to span 7.5m so even the Abrisud is a tad to small. We are restricted in available width by being on a steep hillside. The pool and house are built on a 'shelf' cut into the hill and if we make the enclosure too high, it shadows the Navitron tubes yet it has to be wide enough to span the pool and skimmer pot covers. Something like the 'Oxford' but not as tall and with double layered glass or polycarbonate would be ideal but there isn't anything around that meets that spec.

Being inside a national park might also cause planning problems although as it can't be seen from anywhere outside our own land boundary we might be able to twist the Park Authority into letting us get away with more than usual.

I melted the ABS pipes again this morning. The heat exchanger got up to almost 150C due to me getting involved in something else and forgetting to dump the heat. I've just ordered new plumbing bits to repair whats there and hopefully provide a different route for water returning from the top (Solarmatt) panel so it also goes through the heat exchanger. It isn't quite as efficient that way but it buys me peace of mind and save a lot of leg work.

Brian.

[dhaslam]

A building with insulated walls to the North and a lot of polycarbonate on the south side  would be nice but you have to deal with very heavy condensation when water is heated.   You need to have a system which turns water vapour into dry air and heat.      All said  there is a lot to be said for keeping the pool as an open pool  and spend a little extra on heating facility.    Isn't it normal  to use lower cost flat panels for pool heating?

[kristen]

"Isn't it normal  to use lower cost flat panels for pool heating?"

I imagine they need a large area, relative to the pool size.

Benefit, IMHO, of higher efficiency tubes would be to use them for the house when the pool was closed during the Winter (either DHW or CH).

Nov-Mar inclusive would provide 272kWh per (20 tube) panel, and I reckon that 6-8 panels is about the norm for a pool, so that would be 1,632 - 2,176kWh total.

Kristen

[dhaslam]

That makes good sense.   Mid winter  needs ten times the collection area compared to mid summer. 

[betwixt]

dhaslam, you are quite right about flat panels being more economical than tubes for heating a pool, but the plastic pipe system already there is even better. We got quotes from several companies for flat panels but the figures were unrealistic. One company, who shall remain nameless, quoted £48,500 and when asked to reconsider, came back with £39,000 if we installed it ourselves. The quote was given the respect it deserved and we did our own version using exposed black pipes. The cost was a little under £3,000 ! The surface area is 24.5m x 3m = 73.5sq metres.

Looking at what it replaced, an oil burning furnace, £3K was very economical, between May and September the old system drank 4,600 litres of oil which cost £1,400. Oil was not only highly eco-unfriendly but of course an ongoing expense. So the top panel in the photograph paid for itself in a little over two years.

The Navitron tubes are essentially for extending the swimming season and we calculate (too soon for real life figures yet) the payback time will be about 3 years. They are working extremely well and because of being mounted vertically, their efficiency should rise as the peak angle of the Sun drops toward mid-winter. They face slightly east of South and are unobstructed view almost to the horizon. We run a holiday chalet and with luck the pool will still be open for our guests well into October. A private pool is a big selling point!

Controlling the heat flow is proving to be the most difficult task. Electronics is my forte so over the coming winter I'll be working on a system that not only controls the solar heating but entry to the pool area with electronic keys, pool and outside lighting and of course, will itself be solar powered. The prototype is pretty much working, it has been in use for several months but at the moment it does everything except controlling the heat dump.

Brian

[betwixt]

Just an update :

We got a specially made Abrisud arched roof about two months ago and the pool became warm enough for daily use almost immediately. It looks like our biggest problem wasn't the heating - it was the cooling! Now it's insulated from evaporation and the moisture under the roof is channelled back to the pool the temperature is much higher and water loss is virtually zero.

The highest water temperature reached so far is 37.5C which is too warm but buys us several days of use before it cools too much again. Even after torrential rain over the past few days has raised the water level by 2cm and with no sunshine, the water is still at 33C. It looks like we should be able to keep it open through October, possibly later depending on the weather.

Brian.