OK. Here's a bit of brain exercise.
I plan to add a solar pool heater ( this weekend ), in the form of a 4 poly pipe coils on my carport roof - strong, flat, protected, full sun.
I have done a load of research and have the assembly all planned out, except for 1 small detail : the pipe diameter.
What are the pros / cons of using 12mm compared to 20mm poly pipe ?
I want to add 4 coils, each 100m of pipe.
My feed from the pump / filter is a 50mm pipe ( and so is the return pipe back to the pool ), and I plan to add 4 T-pieces to that line ( 1 T for each coil ). So the water from the pump will be split to the 4 coils.
I just can't figure out which diameter pipe to use.
My logic tells me that :
1. using a set outer diameter for the total coil (say 1.3m diameter), will result in the same area of pipe in the coil being exposed to sunlight.
2. the larger diameter pipe will put less back pressure on the pump.
3. the larger diameter pipe ( x 4 coils ) will have a better flow rate than the thinner pipe, thereby giving better thermal transfer to the water - research shows that the best thermal transfer to the water occurs when you can not feel the heat on the outside of the black pipe. If the pipe gets hot, then it means the solar energy, collected by the pipe, is dissipating to the surrounding air, instead of into the water.