Solar Pool Blankets don’t have to cover the entire pool!
Recently we wrote about an idea of partial solar pool blankets and their many advantages. This was brought to my attention by a pool remodel client in an email which we have included for you to read.
Customer Email – Solar Pool Blankets Theory
John,
I don’t know the physics of it, but from observation, deduction and just plain guessing, I have a theory.
First, let’s start with something we’re familiar with – the car. Park your car outside on a mild, but fully sunny day. Say its noon and about 65 degrees. If you leave your windows open, your car will be relatively cool when you return in an hour. A few surfaces in the direct sun may be quite hot depending on their color, but the general air temperature will be cool. However, if your windows are closed, the air temperature in the car upon your return will be considerably hotter than 65. If you leave a window cracked a bit, it will still be hotter than the ambient temperature, but not as much.
Observation/deduction/guess: Infrared radiation passes through the glass once, but apparently loses enough energy doing so that it doesn’t pass back out. This causes the inside to heat up above the ambient air temperature.
Application to Pool: Full cover – infrared goes in, but it can’t get out (like a roach motel). OK, but with a partial cover, shouldn’t the infrared escape like it does when your car windows are down?
- Perhaps pool water plus the darker bottom is enough to stop some of the infrared from bouncing back out. In that case, perhaps the partial covers merely insulate the pool from losing its heat to the ambient air temperature.
However, the pool temperature with the partial pool covers often exceeds the ambient air temperature. Also, if we get lazy and leave the covers off, the pool does not warm up as fast or much during the day. Therefore, number 1 can’t be the whole story.
- Perhaps only some of the infrared escapes through the uncovered portions, as with a car that has the windows only cracked and not down all the way. This would explain the record temperature of 97 degrees with the full cover and the mid to high 80’s achieved with partial covers.
- I think it’s a combination of several factors – reduction of heat loss, trapping of infrared at a higher rate than with just water and plaster color alone and reduction of evaporation.
JZ’s Approach
I felt inclined to flush out the idea. I carefully read and thought through the information. Then I purchased solar pool blankets of my own. I purchased 3 for the pool and 1 for the spa. I started logging water and air temperatures 3 times per day. To follow is observations, data and conclusions from the experiment. Please enjoy the information.
JZ’s Observation
After several weeks of careful monitoring the partial solar pool blankets on my pool I came to very similar conclusions! A small problem was I started the test in late April and now concluded in early June. As we all know this is not always the sunniest time of the year but there were obvious trends. I started with the cover on for a week and a half, then took the covers off for a week. Finally, back on the final week plus. I did take a vacation so there is a gap in the data. (Full Data Set)
JZ’s Conclusion
There is definitely an effect that traps heat in the water. The increase is often 5 to 7 degrees higher than the ambient air temperature.This is very impressive to me with a max temp I got of 89 degrees on a day with air temp high of 82 degrees.- Insulation factor exists as well to have less loss of heat over night. The morning water temps all started out higher with the covers on.
- There was definitely less evaporation with the covers on. I calculated that my 3 covers on the pool covered 75% of the water surface area and the spa is completely covered. I have an electronic auto fill that typically adds about a one-minute blast of water every other day. With the covers on it cut that back by 75% to a one-minute blast every week.
- The time to remove and put back the covers has shortened with each time I do the process. It’s to the point that I feel the benefit well out weighs any unsightliness and inconvenience.
Save Water, Save Gas and Save Time with Partial Solar Pool Blankets!!!
Thanks for the tip Tim!!!