solar heater

[ScottEvil]

I made my own solar heater and use a booster pump set on a timer for optimal heating. You should see a 10-15 degree difference between pool temp and heater return line.

[Poconos]

The 10-15 deg rise is too much and the efficiency could be better. Maximum solar efficiency occurs with the lowest temperature differential between inlet and outlet. There is a happy tradeoff between temperature rise and flow. Every system is different and anything is better than nothing especially when it's free. I get about a 4 degree rise on a 4x20' mat heater at around a 15 GPM flow rate (very rough numbers from memory). I don't try and control the flow exactly but shoot for about 1/3 to the field heater, 1/3 to the mat, 1/3 to the returns.
Al

[CarlD]

Al is right.

But there is a paradox. The more water you can flow through the panels, the less of a temperature differential you'll see. This leads people to believe that a lower flow is better.

WRONG!!!!!!!!

The ONLY reason to limit flow is that some part of the plumbing (the pump, the valves, the hoses or the panel itself) is likely to fail from too high or too low pressure. The more water you can flow, the more efficient your system will be and the more heat you'll transfer. Your panels, at peak efficiency, on a blistering hot sunny day, will be no warmer than your pool. While you never achieve this, it is quite common for panels to be cool to the touch when you expect them to burn you.

That's because to warm your pool you are working on transferring HEAT, not temperature. BTUs are what count, gang, not degrees.

[rmeden]

As I mentioned before, I try to keep my rise close to (but not over 10). The reason? I like feeling warm water dropping into the pool! (I have a vacuum hose leaving the panels on the deck and dropping into the pool.. I pull it out when I want to feel. )

I agree I lose some efficiency, but nothing beats feeling the warm water going into the pool. I bet the efficency loss is negligable.

Robert

[JohnT]

I agree I lose some efficiency, but nothing beats feeling the warm water going into the pool. I bet the efficency loss is negligable.

Robert

I would guess the efficiency loss to be in excess of 50%

[rmeden]

I would guess the efficiency loss to be in excess of 50%

*WOW* that much? I was thinking less than 10%... we're talking about a 77->87 degree rise... you're saying a 77->80 degree would put twice as many BTUs in the water?

Granted, I never had thermo in college, but that seems a bit much...

Robert

[Poconos]

Been a long time since I had Thermo (40 years?) but what you have to know is that the temperature differential is what governs heat transfer. You are trying to get maximum heat transfer from the surface that is heated by the sun to the flowing water. In the case of a solar heater the differential would be the temp of the heater surface with 'normal' water flow compared to the temp without water flow. Pretty close, not exact. Without flow probably pretty hot...120F+. In tphaggertys post, a couple above, you can think of a term like 'GPM x degree rise'. What it means is you have some constant heat input to a panel therefore higher flow yields less temp difference input to output of the heater and visa versa. 'GPM x degree rise' is a constant...almost. If you are trying to squeak every last BTU (British Thermal Unit...a measure of heat) from the system then you want max flow. Do what is best for the equipment, circulating, and sanitizing and enjoy the warm water flow. Whatever that implies.
Al

[harryk]

Flow rates intrigue me. I'm about to spring for a mat, and I'll be putting it on my roof the OTHER side of the pool from my pump. This means I can't easily use my pump system. I'm planning on using a submersible pump (kind of like a cover pump) on a timer to run it during the day. These aren't good for terribly good flow, but then again, they are cheaper than the pool pump (I don't use the pool much, and it's mostly covered, so I get by very nicely running the pump and filter about 90 minutes in the morning and 90 minutes in the evening).

So, the question is, will I be killing my efficiency with this lower flow? And, I am a degreed and licensed mechanical engineer, so I fully understand and agree with the statements that the lower the temperature rise, the higher the effectiveness.

Thanks,

Harry

[tphaggerty]

CarlD is right on for this one. The most efficient panel setup may see less than a 2 degree rise from the panels, but if you're turning over 40gpm vs 10 degrees at 5gpm, that's almost twice as much HEAT going into the pool. Thats why many permanent installations push for as many panels as possible, not only do you get a larger surface area, but you can put through a lot more water. I just saw JohnT's post, I would have to agree that it is probably that or more.

But, if your pool is at or close to where you want it to be, I like the idea of slowing it down and getting a warm rush from the returns!

[CarlD]

But, if your pool is at or close to where you want it to be, I like the idea of slowing it down and getting a warm rush from the returns!

There's ANOTHER way to get that