Hi,
I have a 20'x'40' In-ground vinyl liner pool (36,000 gallons). I'm located in Pittsburgh, PA. So, our weather/climate is not too different from Toronto I think.
I have either 12 or 16 mil blue clear cover. I read the post you linked earlier, and I think he has some good points. I will say, April is probably the soonest that solar gain from the sun through a solar cover will be significant, and late Sept is the latest, in my experience. I think that is the biggest factor, and then air temp is the second.
You mention pool being 15C (59F for me), and air being 27C (80F).
If it's a fully sunny day, and no/low wind, leaving the cover off is probably the best solution. If you have wind above say 5mph all day, then you are probably better off keeping your solar cover on. With that scenario, you are going to be gaining heat from the sun, but losing from evaporation effects, and possibly getting lots of debris in your pool.
For me, it's almost always a 5mph or more wind here in Pittsburgh, and so I leave my solar cover on all the time. On a fully sunny day in April, and air temp is at least 15C (60F), the top foot of water will reach 80 to 90F (27C or above). So, I have set my pool pump to run automatically between 11am and 4pm to mix/distribute the warm water in the pool. Otherwise, it just sits at the top, and doesn't really warm the lower depths very well, but instead loses it's heat to the air.
I took my winter solid cover off on April 11th, and put on my solar cover to take advantage of the warm weather (we missed a week of it, as we were on Easter break). The water temp was a chilly 53F (11C). Today, the water temp is 60F (15C). I haven't run my 140K BTU HP yet. And the temps were in the 80's by day for a while, but have been in the 50 and 60's the past last week.. So, you have a combined air temp and solar heat gain happening, which is helped by my pump circulation.
When it starts getting into the mid 70's or 80's in May for a period, I will then run the HP during the day (8 hours minimum) with the solar cover on. I find that I can go from approx 60F (15C) to 80F (27C) pool temp in about 2 days of HP running with warm/sunny days. The HP gives approx 5 to 7 F temp rise a day, with the rest from solar gain.
Once we reach June, HP isn't even necessary with the solar cover. I easily maintain 82F to 86F pool temps with it on. And as July approaches, we start to hit 86F to 90F (which honestly is getting too warm for me). The only time I turn on the HP from Mid-June to end of August is to simulate a hot tub by the return jet (a poor mans hot tub perhaps, but it's probably 100F water coming out then).
We bought our current house in June 2020, so the pool was reasonably warm by that month, but it had no heater, and an opaque bubble cover. When we put on a clear blue solar cover the next year, the difference in solar heating was easily felt with the pool being warmer and just more comfortable). And of course adding the heat pump later the next year, helped even more.
Now the topic of if a solar cover is effective, when it should be on, etc has been exhausted with the general consensus being to leave a solar cover on as often as possible.
However, I am curious about the effects of a solar cover when there is a drastic difference between the temperature of the water and ambient.
Let me explain my situation:
Here in Toronto, we just came out of winter and have unseasonal highs. This means that it's 27C outside, but my pool temperature is less than 15C.
At such a drastic temperature difference, would the solar cover act as an insulator, keeping the pool cold for longer?
It seems that this
question has been asked before here, with a single user providing an anecdotal response
Does the TFP community have any thoughts on this?
