that shown to ensure flow balance.

4-2.2.5

4.2.2.5.1

on the relative pressure drop associated with the different piping branches of the array.

The change in pressure along any flow path is a measure of the resistance to flow. Of

interest to the solar system designer are the pressure losses across the collector risers,

along a manifold, and along linear uninterrupted pipe. As the ratio of a manifold's

pressure drop to its riser pressure drop becomes smaller, the flow becomes more

uniform. To ensure uniform flow through the collector bank, this ratio should be around

10 percent, and under no circumstances should it exceed 30 percent (for a pressure

drop ratio of 30 percent, the flow in any riser does not deviate from the average riser

flow rate by more than plus or minus 5 percent). It is thus an advantage to choose a

collector with a relatively large pressure drop and to ensure that the pipe diameters

throughout the system are sized correctly to maintain adequate riser to manifold

pressure drop while allowing enough cross-sectional area for the calculated flow rate

and keeping the flow velocity below the 5 ft/s (1.5 m/s) limit for copper pipe.

4-7

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