[buffalobillpatrick]

This type of heat transfer mechanism is governed by the basic equation:

Q = (k A/x) (T1 – T2)
where:
Q = Heat transfer, BTU/hr,
k = Thermal conductivity, BTU/in/ft 2/hr/°F
A = Heat transfer area, ft 2
x = Wall thickness, inches
T1 = Outside temperature, °F
T2 = Inside pipe temperature, °F

"Note: The above equation only addresses the question of heat transfer through the PE pipe. Depending on the application (ground source heat exchange systems, snow melting, radiant heating, etc.) there are other factors that may have a significant influence on the accuracy of the heat transfer calculation including the thermal conductivity of the surrounding embedment material, the inside and outside film coefficients of the pipe and perhaps others. Therefore it is recommended that such calculations should be referred to engineers who are expert in this field."

"Badges? we ain't got no stinking badges"

I have read that inducing a slow rotation of water in the solar tank by setting the ends of all pipes to have a 90* elbow cordinated (inputs all set one direction parallel with a tangent to circumference & outputs the opposite direction)
This is suppose to not effect stratification of water vertically.

Some flow should greatly enhance thermal transfer through HDPE tank walls.

BBP