Solar heater - could it also cool water a little?

Full disclosure: I've also posted this on another pool forum.

Here in the sunny south, near Atlanta, our swimming season is pretty long, but longer would be nice! I'd given some thought to installing the extruded plastic collectors on the south-facing roof of our pool house. The solar orientation is close to ideal, the collectors are relatively light, and the plumbing would be so simple, since the pump/filter is in the south-west corner of the building.

Then I had an idea, a dangerous event for me! I wonder if, in addition to collecting solar energy during the day in early spring and late fall to extend the swimming season, the same collectors could circulate pool water at night during the height of summer to dump excess heat. Our pool temperature seems to approach body temperature in late July and early August, hardly refreshing. I imagine that I'd need some idea of the average low night temperature during the height of summer, and the actual water temperature. I'm not an engineer, but I suspect that the greater the temperature difference (delta T?) between the pool water and the atmosphere the better this might work. Clear nights might be more effective in radiative cooling, while cloud cover might mean only conduction to cooler air would be effective.

A differential temperature control valve to bring the collector/radiator on or off line would be a nice though probably costly addition for either heating or cooling.

Any engineers out there? Any one have opinions? Any experience with the roll out collectors?

Several people here on the forum do run their water through their solar panels at night to try and cool the pool some.

My solar panels were installed with a Gold-Line GL-235 controller which controlls a valve that directs the water to the panels when the panels are warmer than the water and the water is cooler than the temperature setpoint. It will also send water to the panels when the water is warmer than the setpoint and the panels are cooler.

it won't cool nearly as good as it heats (btu-wise) but as long as the air temperature is cooler than the pool water temp the solar array will act somewhat like a car radiator. The greater the temperature difference the more effective the cooling will be.

Many thanks for the opinions.

I'd guess that, just as copper or aluminum collectors would be more efficient in gaining solar energy they'd also be more efficient in shedding heat. Of course if I had access to a large number of truck radiators and fans....

But metal collectors would be far, far more expensive, and there'd be a greater risk of freeze damage as opposed to the plastic sort. Do any of you users out there have drain-down provisions for frosty nights, or are the collectors pitched so that they drain themselves?

They should be installed to drain back. The GL-235 has a freeze protection option that will run water through the panels when temp gets near freezing to keep them from freezing and bursting.

Keep in mind, the glazing on the collector will work to prevent significant thermal losses at night.

If you have a large enough property with an area that is free from tree roots - you could use geo-cooling without too much of a problem. Ground temperature even a few feet below the surface are significantly cooler than air temperatures. You could use a thermostatically controlled valve to shunt water into a horizontal loop collector in order to cool the water before it goes back to the pool.

I am sure there is information around regarding the setup - and there isn't much difficult engineering in this particular application (nor extremely expensive materials). The biggest restriction would be the hole that you need. Horizontal loops are easy for DIY projects, you just need a large area to dig a 3 foot deep hole in. If that isn't an option - vertical loops work as well - though for those you usually need to hire a boring company to come in and drill your holes.