Solar Pool heater

[alchemysa]

I have no solar heater in my 24' above ground pool. I did have a solar cover for many years. However, it is a pain in the rear. On hot days, if we aren't home to roll back the cover, the pool water could get into the 90s. Much too warm for a comfortable swim.... it was like a hot bath. When the water gets that warm, the solar cover starts to break down and you get cute little dime-sized circles of plastic all over the place. However, with no solar cover, the water is always about air temps. 75 degree water feels cold on 75 degree days. There's no happy medium. That's why a thermostatically controlled solar heater not tied to the pool filter would be nice. You can't just run it on a timer like the pool filter, because on hot days, it will overheat and on cold days, it will actually cool off the pool as it will act like a radiator. So I take the suggestion of a separate pump for the solar heater seriously for good reason. It makes perfect sense.:thumbsup:

Blankets have lots of problems but I'm a fan of them nevertheless.

However, I have a theory that blankets do nothing to heat the water during the day and possibly have a negative effect because they 'shade' the water. All they do is heat the top few inches due to the physical contact between the blanket and surface water.

Their real advantage is stopping heat loss during the night. (i.e they are retaining the warmth that the pool would gain anyway during the day, with or without a blanket.)

My theory is that without the blanket the suns rays will penetrate deeper and warm more of the water overall. So, my theory goes, that for best heating, the blanket should be put on at night, but taken OFF during the day.

Arguments against my theory would be the cooling effect of the additional evaporation of an uncovered pool during the day and the cooling effect of the extra water required to top up the pool.

But if I'm right and the solar cover really could be left off during the day this would solve a number of the reasons people give for hating covers. (Not least that they get sun damaged and disintegrate after a few years).

I've tried to google an answer to this idea, and read numerous blurbs from solar blanket companies, but no-one specifically addresses it. The listed advantages of keeping the cover on during the day seem more concerned with evaporation, chemical use, reduced cleaning etc.

One small thing in support of my idea was a test I found regarding solar camping shower bags. They definately work better with the clear side up, rather than the black side up. In other words, letting the rays penetrate into the water is more efficient than trying to 'absorb' it into the plastic.

I'm 'sans pool' nowadays so I cant test this idea but I'm thinking of experimenting in summer with 3 tubs of water. One with a cover 24 hours a day. One with a cover at night only. And one with no cover at all.

Any comments?

 

[sodamo]

... If the same type systems, and everything is realative, is used to heat the OP's 39000gal pool, then it would take about 30,000 ft of pipe. Not exactly cost effective. I dont even know what the differences are between using copper pipe and using plastic tubing, but would guess the copper would be a lot more efficient. Dont think anybody would want to buy 30,000 ft of copper pipe to heat a pool with.

I' d hope for a more cost effective solution.

David Sent from my iPad Air using TractorByNet

 

[sodamo]

That is the reason I suggested using a check valve at the bottom of the collector, to stop the force of gravity from pulling the water back down the pipe. Using a solar collector to exchange water in a pool isnt exactly a closed system. In order for it to be a closed system, one would have to have loops of pipe or tube to act as a heat exchanger, and those loops of pipe would have to be submerged inside the pool under water. I dont know that this could be considered a open system either since both ends of any recirculting solar collector, using convection to move the heated water, would have to have the inlets and outlet below water level to prevent air from interrupting the continuouse flow of water. I think it could only be a fully open system if some sort of pump is used. Considering that a pool needs to fully exchange its entire water content every so many hrs anyways, its a safe bet that the pool already has a water pump. Why couldnt this pump be used to circulate the water thru the solar collector. I am pretty sure that you can purchase a solenoid valve you could just hook up to a thermostat that could switch from just recirculating water to exchangeing the water thru a solar collector.. I'm just speculating and guessing and dont know if anything I have suggested will work for what the OP is wanting to do.

I may not have made it clear that the current DC pump and existing pool plumbing are the basis for this project. The solar loop will get input after the sand filter. The heated water will return to the pool through the existing plumbing. There will be a check valve before solar loop. Most likely will also have a valve to isolate the loop if needed. I wondered about a thermostatic control but doubt I would achieve high enough temps. The pump will be changed from battery power to PV power through the controller.

David Sent from my iPad Air using TractorByNet

 

[sodamo]

If both ends of the system are under water then its a closed system regardless of any check valves or pumps being in the line. So the pipe will collapse if it cant drain when the pump is turned off. This is why most plastic systems have a vacuum breaker at the top. I dont think the OP has yet described the outlet end of the solar system. Is it above or below the water surface? I think I was also told once that a solar system should be allowed to drain when its not running anyway, to minimise bacteria buildup in the pipe. And the trouble with simply diverting the pool pump to run through solar pipe is the problem of trying to balance the flow. Pool pumps are usually high capacity. If you try to push loads of water through small diameter pipe you create a heap of problems. The last pool I had built was plumbed to have two completely separate lots of pipework and two separate pumps. The solar system was 'closed' so i was able to use a relatively small pump and I was able to run it when it was most effective. And there were no valves to worry about and no excessive load on the filter pump. And the filter could be run separately at off peak rates. Its possibly a myth to think you are saving money by running a solar system through an existing pool filter pump. (Let alone all the plumbing problems it creates). My guess is that it just encourages people to run a big expensive filter pump far more that they would otherwise. A pool filter pump is probably the biggest electricity guzzler that you can own.

Some things for me to consider here. I actually have both a DC pump and 240AC pump plumbed into the system, both feed the filter. I could tee from the DC pump if necessary, but wasn't my first choice. With the revised PV run pump I was also hoping to get more filtering without drawing from my house power (we are off grid) batteries. Thanks for your input. I need it.

David Sent from my iPad Air using TractorByNet

 

[sodamo]

In this case I simply meant whether air can get into either end of the system or not. If both ends are under water then its effectively closed in this case. Antifreeze? The OP is on Hawaii, and we are talking about pools. "The black poly pipe will only collapse if it has sufficient vacuum and sufficient temperature to cause it to collapse" Believe me it will collapse. Thats why even rigid plastic pool solar systems have vacuum breakers.

Sounds like I need to learn about these vacuum breaker things

David Sent from my iPad Air using TractorByNet

 

[sodamo]

If you use a manifold with the same diameter pipe as the existing outlet of the sand filter you can use the pool pump to circulate water through a solar collector. However, as mentioned, pool pumps use a lot of power. However, you can get two speed pumps to reduce power consumption. Example: 2" out of the filter goes into 2" manifold. Parallel runs of smaller pipe between the inlet manifold and outlet manifold. The diameters of the parallel runs have to add up to be at least the same cross sectional area as the 2" maifold pipes or pressure will build too high. The more parallel runs you put in, the longer the water will spend in the heater at lower pressure. Then a 2" outlet manifold and return to the pool.

Looking at 2 parallel runs of 1", so just need to finesse the manifold aspect (I think)

David Sent from my iPad Air using TractorByNet

 

[sodamo]

You guys are great, thanks.
This could end up being one of those projects that evolves with lessons learned.

A bit more background. This is my first pool, never had one as a kid or anyplace else I've lived. Bought this pool as a kit. Basically everything except the piping and wiring. We just had to follow the plan. Unfortunately, I've thought of a number of things I'd have done differently based on what I've learned. Too late!!!! Because of being off grid, I did add the DC pump w/ controller. The pool is an in ground unit concrete floor, polymer walls, vinyl liner. The high point of the roof I'm using is about 7ft higher than the pool surface. All water inlets are below the surface normally.

While my original plan with the PV powered pump was to achieve filtering whenever the sun shined, I would not be opposed to making the solar loop controlled separately if I can do so reasonably.

I share concerns about the daytime effectiveness of the blanket. I have other issues that dissuade me as well, pool is L shaped, ladder handles in the deep end, stair rail in the shallow end. We also get 140+ inches of rain per year. Pool actually has 2 adjustable overflows.

I've seen poly collapse before, so definitely a concern.

David Sent from my iPad Air using TractorByNet

 

[alchemysa]

You guys are great, thanks.
This could end up being one of those projects that evolves with lessons learned.

You'll probably have plenty of frustrations but you'll enjoy it anyway. Solar heating a pool is not as simple or as cheap as it may appear at first. Ideally you need a lot of heating area and a lot of running time for it to be really effective. If you have a small heating array then you have to run it for a long time, so then electricity usage and costs play a big part. Its a balancing act.

I'd still consider a blanket if I were you, or every night you are going to lose a lot of heat that you have put into the water. The blanket doesn't have to cover every inch of the pool. Even if it just covers most of the main rectangle of the pool it will make a big difference.

 

[alchemysa]

Finally found a reasonable explanation about pool covers, and whether they should be left on during the day.
Swimming Pool Covers | Department of Energy

Basically a cover certainly reduces solar penetration, from about 10 to 40%, but the reduction MIGHT be offset by reduced heat loss due to evaporation. Bottom line seems to be... If you live in a humid area take it off, if your air is very dry then leave it on.

 

[alchemysa]

A lot of good DIY stuff here too...
Solar Pool Heating