Cooling Your Pool With Solar

In many climates pools gets too warm just from the direct sun heating them. A common joke we used to hear in the early decades of solar pool heating was that my pool is already solar heated. Its warm all summer just from the direct sun. Its true. The top surface area of the pool sees the same solar energy per square foot as the solar collectors up on the roof. The pool is also losing some of this energy at the same time same as the collectors. If the pool is in the shade it still has the same losses but 100% of pool top surface area in collector area is missing from the energy balance equation. That is why shading on the pool is almost a one to one relationship in terms of how we have to size solar. For every square foot of shading on the pool we need almost one sq ft of solar collector to get that pool back to the same temperature it would be at if it was in the sun. A shaded pool is a cold pool so we get a lot of demand for solar from these homeowners. When we factor in the shading AND size the system to extend the season as we normally would we're sometimes telling people to expect the pool to be 30 degrees F warmer than they are used to. Pools that are in the sun have the opposite problem. They get too hot on their own even with the cover off. Today I had an e-mail from someone in Slidell Louisiana asking about cooling a pool with solar and I thought I'd share my response.

Yes solar is very effective as a pool cooler. Many companies used to include the automatic cooling feature in their automatic controls but over time eliminated that feature because solar turning on automatically in the middle of the night woke everyone up. Air flushing through the pipes makes noise. We had one customer who left the system in cooling mode for 2 years without knowing it. For these reasons we don't automatically keep the pool temperature down. We just turn solar on manually at night on purpose.

Its hard to quantify it because its radiation heat loss as well as convection but it definitely does work as a pool cooler. Its very important in heating pools that we don't run solar when the sun isn't out because it will cool the pool. The more common use is as a house cooler. In this case the solar gain is taken off the house reducing or eliminating air conditioning loads. Now the pool gets too hot so you run solar at night to cool the pool. In other words you run solar all the time manually not automatically (you just switch the auto controller to test mode). Heating beats cooling because the sun is hotter than the night sky so you are still looking for ways to cool the pool but what isn't in question is the value of being able to pump water thru the black thing on the roof.


My best guess is that on a day you might gain 10 degrees from solar you might lose 3 degrees from running solar at night. Once we have these systems monitored we'll be able to look at this kind of thing quantitatively in the real world instead of trying to employ the Stefan-Boltzmann equation based on an equivalent night sky temperature that depends on cloud cover to calculate radiation heat loss and then add that to estimated convective losses. Real life is so much more real. Nobody has proven global warming mathematically. We need to see glaciers melting and extreme hurricanes before anyone pays attention. I use global warming as an example of how complex the heat balance on a swimming pool can be. The variables are too variable for anyone to be able to say with certainty what is happening but we have done a lot of work toward the goal of predicting what will happen to a pool after we solar heat it and a big part of that work is verification. Our charts under sizing have been verified hundreds of times on real situations. Whenever anyone asks us to quantify our claims we point right to the charts for an area close to them and we extrapolate up or down based on the variables. We try hard to not make unsubstantiated claims. You lose credibility really quick when you start playing salesman and telling people what you think they want to hear. Its a very tough habit for any professional salesman to break so if you're a salesman break the habit. Get technical. We have to be diligent about our technical approach to this industry.