solar heater

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

I agree with Poconos. If you want to get the most heat, it really is a matter of temp rise x flow rate.

But, this thread has me thinking I might add a diverter valve to my system so that once the pool reaches the temp we like, I can set it up to "trickle" water through my panels to get that LEGAL, non-biological return line rush.

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