Best method of running a solar pool heater

[melvin2345]

Given the following:


Water Volume: 15,000 gallons
Water Starting Temperature: 75 F
Heating System: 420 GPH
Active Heating Hours Per Day: 8


Which of the following methods would raise the temperature of the water the most in 8 hours?

A) Heating system running constantly: In 8 hours, this method would introduce 3,360 gallons at a 4 degree increase.

B) 15 minute interval: Heating system on for 15 minutes, off for 15 minutes. The water coming out of the heating system after 15 minutes is about 120 degrees. It takes 1 minute to move 7 gallons of water at 120 degrees, followed by 14 minutes of water at 4 degrees warmer than it entered the system at. Then the system would turn off for 15 minutes. In 8 hours, this method would introduce 112 gallons at 120 degrees, and 1,568 gallons at a 4 degree increase.

 

[JohnT]

Running all the time without question.

3360 gallons at a 4 degree increase is 112,000 BTU total. 1568 gallons at a 4 degree increase is 52,000 BTU. 112 gallons at 45 degree rise is 42,000BTU.

Assuming perfect heat transfer from the panel to the pool, the first method would deliver 18,000 more BTU. But it won't be perfect and the second method will be far worse in terms of both gain in the panels and loss to the air because heat transfer works better going from very hot panels or plumbing to cooler air or soil (this is bad for heating your pool) and going from hot panels to cool water inside them.