Solar Pool heater

[muddstopper]

I don't think a pumpless closed system will work with poly pipe. Gravity acting on the water at both ends will suck the pipe flat. And even with a pump thats something you have to consider when the pump is turned off.

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.

 

[alchemysa]

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.

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.

 

[Raspy]

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. 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.

Couple things:

The semantics of closed vs open loop don't really matter in this case. Usually closed loop means a closed circle of pipe not open to the atmosphere or other liquids. This means any fluid can be used and it will not mix with any other in the system. It also means no new oxygen can get into the closed loop so iron pumps and fittings can be used with plain water. I would call the solar system in this discussion an OPEN loop, because it is open to a pool that it draws water from and drains back into. It has an infinite supply of oxygen available and a much larger supply of water available than the loop holds. Any contaminants introduced are shared by the stored water and the loop water.

It's not true that ALL solar systems should be drained when not collecting. For instance closed loop systems with antifreeze don't get drained when shut off.

The black poly pipe will only collapse if it has sufficient vacuum and sufficient temperature to cause it to collapse. There is not enough info here to predict that it will collapse. And putting a check valve on one side only, will not prevent it. The vacuum would be because the center of the pipe loop was higher than the pool and both ends were under water. Either open end will cause a suction on the loop.

Only a percentage of the pumped water would go through the solar if it was very restrictive by design. A simple diverter setup would be put in to balance how much went through the solar and how much went straight back to the pool. It's not all or nothing.

 

[alchemysa]

Couple things:

The semantics of closed vs open loop don't really matter in this case. Usually closed loop means a closed circle of pipe not open to the atmosphere or other liquids.

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.

 

[MossRoad]

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.

 

[Raspy]

Alchemy,

Antifreeze was mentioned only to demonstrate that not ALL systems are drained. That's why I used the term "for instance". Only ones that must have freeze protection for plain water are drained.

Please tell us how much vacuum is in the lines, their temperature and the pipe specs, so you can demonstrate that pipes will collapse. Since those values are not known or haven't been posted, you are just guessing.

This is why it's so interesting to discuss solar and radiant and water physics. So many misconceptions or blanket statements that just confuse the issue.

 

[Raspy]

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.

Good points. This is the successful theory that most low temp, fair weather solar pool systems use. If the weather is more windy, glazed copper panels can be used with lower flow rates and then some diverting can be done to mix the return water with the bypassed filter water. Or if it's a spa and only a small number of collectors are used, you might have to divert some water to keep the pressure reasonable on the collection side. The two speed pump works well too and reduces the cost of collecting solar.

 

[MossRoad]

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:

 

[alchemysa]

Please tell us how much vacuum is in the lines, their temperature and the pipe specs, so you can demonstrate that pipes will collapse. Since those values are not known or haven't been posted, you are just guessing.

Of course I cant put a figure on the vacuum but the OPs picture looks like its at least 10 feet above the pool so I'm pretty confident with my guess. Like I said, professionally installed system have a vacuum breaker. For good reason.

It won't collapse instantly of course but over the course of a day or week in hot sun it surely will (its only poly pipe remember) and then when the pump goes on again you'll have restricted flow, higher pressures, less efficiency etc.

If the system is not closed, if the end is loosely hanging near the edge of the pool, or if there are any leaks in the solar piping then this is all moot. (But there are advantages in the 'return to pool' being a couple of feet below the surface).

Will the 'return to pool' be a separate pipe or will it be routed back into the filter piping?

One more thing for the OP to consider. Poly pipe expands and contracts in length A LOT, so he needs to factor that into his considerations. Dont stretch it and fit saddles to those end fittings.

 

[Raspy]

Moss,

A differential solar controller is always a good idea for the reasons you've said. Only runs when needed or when solar is available and shuts off when the pool gets to the temp you like. You'll always average more energy delivered with a solar controller than with a timer.