Just read this discussion.
What I didn't read in this discussion, are these two things:
1. The heat transfer from water to the pipe is depending on water velocity.
As soon as waterflow is so low, that the flow isn't turbulent anymore but it becomes a laminar flow, the heat transfer from water to the inner pipe wall is reduced considerably.
So by dividing the flow over 18 parallel pipes (as in the first example), the water velocity is only 1/18 th of the original value, so there's a good chance velocity is too low to keep a turbulent flow.
So heat transfer might be much lower than expected.
2. It seems nobody was taking Bernouilli's law into account.
Let's assume the first lay out with the 18 parallel pipes.
Assume the input is at the bottom right of the drawing and the output is top left.
Since a radiant floor heating is in one horizontal surface, there's no difference in height between the pipes.
Then according to Bernouilli's law: 1/2*rho*(velocity)^2 + Pstatic = constant.
This leads to the fact that (contrary to what many people think), the flow is not evenly distributed over the 18 pipes. The highest flow will be in the most left pipe en the lowest flow in the most right pipe.
|