Did you know you could cool your swimming pool with a solar pool heater? You can! It’s called nocturnal cooling, and this feature can be activated on many solar controllers and existing pool automation systems.

The Pentair SolarTouch Solar Pool Heating Controller and many other controllers have a nocturnal cooling function included.

In Southwest Florida, pools can get unpleasantly warm in the heart of summer, and people that swim for exercise or competitive purposes often prefer to have water cooler. Cooling a pool with an electric heater is also possible, but consider how much energy it takes to cool your home in summer and then consider that an average pool has over 50 tons of water in it. Water requires far more energy to heat or cool than an equal volume of air. Cooling your pool with solar panels requires only the energy to run your pool pump.

Nocturnal cooling works to cool your pool by running water through your solar panels at night or any time that the roof is cooler than your pool water temperature. The same sensors that turn your heater on will also work in reverse and provide a cooling effect. The process is automatic when you have a an automated solar controller.

Because solar panels have what’s called high emissivity, they expel heat very well to the black night sky. They are excellent at heat transfer (both ways), allowing them to emit heat trapped in your pool to the ambient air. The same qualities that allow solar panels to absorb heat efficiently also allow them to expel heat. This can work especially well when the ambient temperature is relatively cool at night and during windy conditions that carry heat away efficiently.

You can also achieve some cooling during the day during rainy conditions.

For this to work properly, the solar controller needs to be able to sense your pool temperature using the water sensor, which is usually in a pipe near your pool pump. That means you will need to run your pump at night to keep the water flowing. If you have a single speed pump, it can get expensive to run your pump 24/7, so we advise people who want to cool their pool to switch their pump run schedule to run during the late night and early morning hours.

If you have a variable speed pump, you can run it 24 hours a day at a very efficient low speed that costs pennies a day. When nocturnal cooling is needed and available the pump will automatically change speed to improve cooling performance. If you do this we advise that you schedule a few hours a day to run your pump at a higher speed to achieve adequate turnover and sanitation.

For most pools we recommend the Pentair SolarTouch controller with the Pentair Intelliflo pump for the best nocturnal cooling performance with a solar pool heater. This controller is easy to program and the pump works in tandem to change speed as necessary.

For additional cooling effect we also advise homeowners to turn on pool features like fountains, waterfalls, bubbles, and negative edges at night. Exposing more pool surface area to the relatively cool ambient air at night will have some cooling effect.

Don’t expect to drop your pool temperature too much with a solar pool heater. It is heavily reliant on the ambient night temperature being significantly cooler than the pool. For example, unheated pools in late May are typically around 82 degrees and nighttime temperatures drop to around 70 degrees. You won’t be able to get your pool down to 70, but you can expect a few degrees drop. This is usually enough to make nocturnal cooling worth it for people that don’t like warm pools. In the dead of summer, the nighttime temperature may not even drop below the pool temperature around here!

We consider nocturnal cooling to be an ancillary feature to a solar pool heater. It isn’t a primary function of solar collectors and controllers, but it is an added benefit to those that want to heat their pool at times and cool it at others.