Solar heating for salt water pool

I've often wondered why anyone with a decent size pool would be bothered about saving a few bob a year on running costs. They are expensive toys & I'd have thought that anybody who can afford to install one can't be exactly skint. The same people presumably buy cars & are happy ? to take the hit that comes with ownership, maintenance & running costs of another toy so why the big deal on a pool? I'm not talking about anyone trying to 'save the planet' by the way, just interested in the psyche of the thing.

Some friends have a German system made by Lorentz. It is driven by a DC brushless motor that is apparently extremely efficient and reliable. They have it connected to the solar generator through a controller that monitors monitors the system, controls pump speed and volume and temperature of the water circulaing based on power available. They have clear light, that is to say no house or trees shadows, that obscure their PV panels thus restrict power generation, and can bathe all year round. Both are sports teachers so feel that is a justifiable essential. The downside is that it is quite expensive, their pool being a bit bigger than your 10m x 5m may have some bearing on installation needs and price of course, however they are also entirely power independent using ground sources, PV, conventional solar water heating and wood so have the entire set up in place. They are neither affected by power cuts nor have mounting bills is one of their main arguments, certainly the pool is constantly available.

Thanks again John. So what are the turnover rates you are achieving? Do you have any specific figures? I'm not trying to nick your ideas as my contracting days are well past. I'm purely interested as someone who has designed the filtration & circulating systems for a few commercial pools in his time.

Yes that's a subject all of it's own. Who and why are the turnover rates we have set as they are? Are they actually any good? What is the point of a high turnover rate if it fails to achieve an excellent level of filtration? Is it more important to remove more from the water by filtration or to have an unrealistic turnover rate that simply re circulates the fine particles straight back through the pool, isn't that just a waste of electricity?

If a Chef wants a clear consomme, they don't push the liquid through the sieve, the same principle applies with filtration. Unfortunately the industry only has itself to blame as the filter manufacturers try to out do each other with ridiculous stated turnover rates for their filters which would result if they were actually achievable in terrible water quality but of course someone somewhere would be able to tick a box on their civil servant form.

Because of the DDASS or ARS regs, I must be able to hit the given target turnover and do, in the case of the 12m x 6m it takes 464 watts to reach the target turnover, still a long way from the 2,200 watts used previously which by the way couldn't hit the regulation turnover as measured in pipe flow Not pump stated rate of flow. The really stupid part of the regulations is although they state turnover, they don't state the maximum flow per m2 of the filter, thus meaningless as the quality will hit the floor and dirt, bacteria will just be pushed through the sand and out into the pool.

Thanks. I'd be interested to know what turnover rates you achieve.

Hi Vic, The €2500-€3000 is a figure based on the 10 year saving in electricity of a small pool setup (10 year whole of life?). I have a pool running in the Dordogne which is a 12m x 6m with a deep end and we replaced the 2,200 watt pump and setup with my Eco version and although I wanted to run the pump with a bit more through put the customer wanted to experiment and has just completed the second season with it running at 124 watts which is a massive saving so at 10 years I think it was over €5500 compared to the previous setup.

Pool pumps are the most expensive domestic appliance to run as they run for such a long time compared to a hot water tank etc and the reason they became the focus of my attention. Also the reason why it should take priority over any other money saving idea as it would produce the biggest saving.

Hi John
Thanks for your response. The discussion is already beyond my technical ability!

Our pool is 10m x 5m and has a depth between 1.1 and 1.8m. In summer we run the filtration system during the day for about 7 hours. In the winter we filter overnight for about 4 hours (early morning) to take advantage of the heures creuses. Our garden lies SE / NW and the pool end gets sun from sunrise until around sunset. We presumed that photovoltaic cells / solar panels would provide enough power to raise the temperature of the water to allow us to use the pool from April until November at around 25 degrees.

As far as insulation is concerned I have no idea about the pool itself, we do have a roller shutter type cover.

You're quite correct in your assumptions of course John & hopefully you recognised my Solar panel thing as a joke! My system was controlled by a thermistor stuck on a panel which sensed if there was any worthwhile 'heat' in the panels & switched on/off the pump so it couldn't run at night. The panels were fitted on a ground floor extention roof with a dedicated circuit to & from 'em. The return to the pool was throttled so that the dropping pipe was always full thus affecting a sort of syphonic action which greatly reduced the pump head & hence energy required. I think the pump was about 200w so I was more than happy to get what I did out of the panels at this energy input. I wasn't interested in 'running Eco' & was simply trying (& succeeding) to cobble together a cheapo solar heating system for my pool. It worked for me & might work for others with a bit of DIY skill. That's all. Notice I'm not arguing ;-) Where do you get your 2,500 -3.000 figures from ? That's an awfull lot of leccy!

I've just changed this as I actually wrote "symphonic". Ooops!

Yeah yeah a predictable answer (solar panels) ;-) point being at shoulder season there isn't always enough heat to make much of a difference and if you forget to switch off the pump at night or by thermal siphon you could cool the pool as the panels are black they also make good radiators. With standard pumps the water arrives at the other end no matter what the tiny hole size is even if there are many in the panel but when you run Eco these things are far more important. Not much point in buying cheap solar if it cost €2500-€3000 more to run the system. if it doesn't effect the flow like heat pumps or evacuated tubes then it maybe a go er but pool equipment has never been made to be efficient. I am having to design and manufacture bespoke parts in some cases, not always though.

John, of course they only work when the sun is out. That's why they're called ' Solar Panels'. :-) They do indeed have small galleries but to compensate have lots of 'em so the resistance is very small. Mine was a home made job with a small plastic pump Stuart Turner job. Don't ask how many watts but it wasn't a lot. I had 4 biggish panels & seem to remember getting about 7 kw on a good day. (M Cp delta t) It was a cheapo solution but worked for me as I didn't want to swim outdoors in freezing weather. We did run the pool up to about 30 deg for our new year parties but that was by a heat exchanger coupled to the house heating system. Now they used to be fun :-)

sounds like the pool installer is very wealthy then. There are considerations, what size is his pool, does he have a good thermal cover, what size is his heat pump and is there any insulation on the pool construction. 2.2kw input power x 12hours per day = 26.4KW x €0.135 (1 kw) = €3.564 per day x 30 days = €106.92 for a month or if by some weird way it's actually running for 24 hours €213.84 Maybe he is including his pool filtration in the €300 per month?

I think you may have hoped for my figures but mis understood slightly. by saving 85-90% on the filtration pump electricity say and 800 watt .75hp pump down to 60watts. Creates 740 watts of available energy for the heat pump at no additional electricity charge. A 2kw heat pump would therefore only require an additional 1-1.3 kw to run a 10kw output heat pump. Of course when the heating is not required the saving on the filtration is still being made but also results in better water quality and less maintenance.

Heat pumps are already very efficient, have a low dynamic head loss so no savings can really be made unless a voltage optimisation unit is used and whether that would actually recoup it's outlay is questionable.

Yes, the great debate, they have their plus points too but really only work when the sun is out. They also have only small 6mm I believe tubes passing the water so increase the strain on the pump (= more electricity + shorter lifespan in a lot of cases ) and seriously decrease the water turnover rate through increased dynamic headloss.

Whereas usable heating can be gained via evacuated solar tubes system even in the middle of winter as daylight is required to produce the heat, hence why the British Antarctic team use them for hot water near the south pole.

So do you want all year round use, that can also preheat the house hot water/underfloor heating when not heating the pool? or heating when it's already warm?

It's also very important that measurements of the temperature of the water are taken at depth not just on the surface. I spoke to a Lady in the UK the other week who has an Abri on their pool and at the deepest end measured the temperature for me at an astounding 26 degrees, that's pretty good.

Likewise with heat pumps, some are produced for use in warmer climates and therefore the efficiency drops like a stone as it gets colder, Scandinavian units produced for cooler climates can still produce useable heat close to 0 degrees so you may have a warm pool but it will still feel like an autumn at Camber sands when you get out!

I fitted this sort of solar panels to my pool in England. They were cheap & worked extremely well for the intended purpose of producing lots of low temperature energy. Being Polypropylene they should be OK for salt water.

Elaine, you say you would like to be as "environmentally friendly as possible" I don't know the details of your pool but your current pool pump and filter setup, if standard, will be at the opposite end of that spectrum. Re engineering that will reduce the electricity used by 85-90%. That would mean on an average pool the electrical cost of running a heat pump would be met 50% by reducing the electricity used to filter the water. (assuming a 10kw heat pump)

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And of course, you could install solar [photovoltaic] electricity and use that to run the heat pump!

We would like to be as environmentally friendly as possible, we get all day sunshine to the rear of our garden adjacent to the pool, and would like to keep our electric bills to a minimum as we are retired.