[stevehull]

Just re did calculations for Reynolds number (predictor of turbulent conditions) in each of the loop fields Len spoke of above. Here 0.75 inch internal diameter at 3 gallons per minute of water flow.

The velocity of a flowing fluid in such a diameter pipe (0.75 inch; 0.0195 M) is 0.66 m/sec.

Using Rn = [Velocity (m/sec) x pipe diameter (m) x density (kg/m3)]/dynamic viscosity (kg/m.s)

Rn = (0.66 x .0195 x 1000)/1.004

Rn = 12.82

This is also way below the critical Reynolds number for turbulence (typically must be 2000 - 4000).

To get turbulence (Rn = 2,000) the flow rate of 3 GPM would have to be 156 times higher - or about 468 GPM - clearly impossible in a pipe of this diameter.

The important bottom line here is that straight pipes lead to laminar flow conditions with the exception of inlet, abrupt turn and exit conditions.

I have toyed with running HDPE pipe through a machine that creates dimples inside the pipe. That would minimize the laminar boundary flow conditions and should increase heat flow markedly.

BTW, I guess I may be wrong on turbulence in the supply and return pipes! As a proper engineering disclosure report would have it, the calculations suggest a distinct laminar flow situation, but physical measurements in the pipe field would confirm. However, the mechanical energy to supply this exchange bed with water flow also suggests laminar conditions.

Steve