solar cover on/off for best heating?

[poolbee]

I searched, but 15 pages of threads! So point blank- will the pool water heat up faster with a blue solar cover on(and replacing at night) or off on sunny days? I don't care right now about evaporation etc., just heating.

thanks.

[JohnT]

No clear answer available, and you do care about evaporation because it is a major cause of cooler water. The cover blocks some of the sunlight without a doubt. I've never seen a good number for how much, but on a typical calm day you'd gain more heat with the cover off. On a windy day, evaporation might remove more heat than the extra sun would give you.

[Jeffski]

In my experience the pool warms faster with the cover on. For example, air temp here has been in the 60's and we keep the pool heated to 84 (with the heater). The last couple days the air temp has risen to low 70's and the pool has jumped to 86 during the day with the cover on. In my opinion if the pool water started at 84 it wouldn't rise like that due to 70 degree weather.

My two cents only, your results may vary.

[steveinaz]

I can give you a direct example: With my cover left on during day/night I get about 2.5 degrees a day (10,000 gal IG). With the cover on only at night and off during the day, I get about 1-1.5 degree increase. Keep in mind I'm in a very sunny, very dry climate. So, yes, leaving the cover on will get you higher temps--at least in my experience, at my location.

Lately, due to cool evenings, I can't seem to break the 82 degree barrier. Our daytime temps have been 88-92 degrees, with nights around 58-65 degrees. I usually loose about 1-1.5 degrees at night, even with the cover on, at the cooler temps. But the pool recovers quickly and by 1:00pm, it'll be back at where it was the day previous.

Like it or not, evaporation is everything; you loose 70% of your heat through evaporation. I think this is why even on a sunny/hot day you'll probably gain more heat with the cover on.

[tenax]

not sure it warms up faster for me with a cover on..more so, saving heat due to evaporation...and cools off a lot less definitely with a cover on.

[PhantomAndy]

My experience in Kentucky:

When the air temperature is going to be above the water temperature, and little to no wind, I get more heat gain without my solar cover on. The higher the air temp, the less of a problem the winds are, or so it seems for me.

When the air temperature is below the water temperature, it's usually better on.

Of course, if you are trying to maintain your water temp, you should always have it covered when not in use overnight.

Bottom line is that when the air temperature is below your water temperature you will experience much faster heat loss via evaporation than when it is at or above the water temperature. Wind and humidity obviously play parts as well (wind more so than humidity unless you have near 100% humidities).

I'm in the process of collecting some real numbers since our weather pattern for the past few days and into the coming week like a broken record. If I'm able to establish any solid numbers that indicate 'the truth' I'll be sure to submit my results here.

This particular topic is very hotly (no pun intended) debated in any pool forum. I'm wondering if Mythbusters would consider putting this one to the test in some scientifically controlled conditions? I think I'll send an e-mail to Adam and Jaime! They can use my pool as long as they send Kari to help out :D

[ePoolUser]

Our water was 78F at 12" when I opened the pool 2 weeks ago.

Over the past week, the weather has been generally calm with sunny warm days, 85-88F and cool nights, 55-65F. With the solar cover on 24/7*, the first 3-4" of water (at the surface) have hit a hot 95F repeatedly (pump off all day). At 12" the temp is 84, at 2' the temp is 80. *We remove the cover and swim for about an hour every evening and replace the cover.

I can't imagine the surface getting so hot without the cover. Would the water warm more evenly and deeper with direct sun rays? Idunno.

I am in the Nashville, TN area. If you are in this area without a solar cover, what are your temps?
27' AG

Steve

[ivyleager]

How about this test? It's not scientific, and has tons of flaws.

Lay on the ground on a sunny day.....how hot do you feel?

Lay on the ground on a sunny day with the solar cover over you....how hot do you feel? (heck, put a towel over you and you're still hotter).

My lawn burned last year from leaving the solar cover on the grass for 1.5 hours while I cleaned it off due to bugs, bird bombs, dirt, etc. My lawn doesn't burn from just the sun.

IMHO, the solar cover traps the heat and reduces heat loss.

BTW, yard totally recovered.

CaryB
Go Sens Go!

[CarlD]

With it on, period.

[poolbee]

Wow. I guess there is no definative answer. I am in Western NY-Buffalo area. My pool is in direct sun morning til night and we're in for a few cloudless days so I want to take advantage. I am just concerned about getting my water up to a comfortable temp. It was 70 yesterday. My youngest couldn't stand it any more and went in! Way to cold for me. We always have it on at night. Just wasn't sure if on/off during day was better. I have a heater, but would rather not pay to heat if I don't have to.

[Jeffski]

You could heat the water and then just use the cover to keep it hot.

[Poolsean]

Poolbee,

The solar cover is designed with the bubbles so that it actually reflects the sunlight to the water, acting as a solar collector directly on your pool. It also helps retain the heat that your heater has been generating.
Leaving your solar cover on at night is a definate "MUST DO" as this is the period of time of your greatest heat lost.
Leaving your solar cover on during the day, especially when it's sunny out is also a "MUST DO", and removing it when you actually go to use your pool.
It was pointed out by Phantom Andy that he's better with the cover off, when there is no wind and hotter ambient air temps than water temps.
This will change from morning to afternoon and unless you know when to do this from habit, and are around, you're going to even out the overall effects of the heating/cooling argument.

All in all, the solar cover is designed to help retain the heat in the pool. As Carl said, With it on, period! I agree. Take it off to go swimming.

Another good rule of thumb, point your return jets downward. Your pool is best heated from the bottom up. That way you're not dealing with only the top few inches of water being heated, but the rest being much cooler. Well pointed out information ePoolUser.

With kids, I don't think it really matters what temperature it is as long as their lips turn purplish/blue and it's shaking a million miles a minute! It's amazing what they can tolerate and what we REQUIRE!

[PhantomAndy]

Poolbee,

It was pointed out by Phantom Andy that he's better with the cover off, when there is no wind and hotter ambient air temps than water temps.
This will change from morning to afternoon and unless you know when to do this from habit, and are around, you're going to even out the overall effects of the heating/cooling argument.


You hit the nail on the head Poolbee: I usually remove the cover when I'm home for lunch if conditions are right. I've submitted this as a possible myth to bust at discovery.com/mythbusters

[steveinaz]

Another good rule of thumb, point your return jets downward. Your pool is best heated from the bottom up. That way you're not dealing with only the top few inches of water being heated, but the rest being much cooler.

True stuff, this is what I love about my in-floor system. The skimmer takes in the hot top-water, and it gets returned via the floor jets. I have no cold spots in my pool, it's uniformly warm.