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G. PUMP SELECTION
When selecting a pump, there are two basic solar designs to consider: pressure glycol and closed loop
drain back.
In pressure glycol systems, two factors determine pipe size. These are:
•
Flow rate in gpm (gallons per minute)
•
Head loss
In drain back systems, an additional factor must be considered along with the previous two:
•
Lift
Each collector has a nominal flow rate of between .8 and 1.5 gpm.
When determining head loss, consider the following:
•
Head loss pumping through the collector(s)
•
Head loss pumping through piping and fittings
•
Head loss pumping through a heat exchanger
•
*Drain back only: Determine the vertical lift from the water level in the drain back tank to the top of
the solar panels (vertical lift is the same as head loss).
Refer to the chart below for pressure drop figures with a 40% glycol solution. When using distilled water
as HTF, there is a further 20% reduction in pressure drop.
NOTE:
To convert psi to head feet, multiply psi by 2.31 and divide total by specific gravity (1 for water,
1.02 for 30% propylene glycol, 1.04 for 50% propylene glycol).
Table 4 – Pressure drop. This chart applies from 1 to 8 collectors. Do not multiply for multiple collectors.
NOTE ON CHART (Table 3):
To figure feet of head, multiply pressure drop by 2.31.
For example:
1. FP-40SC at 3 gpm = 1.5 per panel and .071 psi = .071 for 2 panels at 3 gpm.
2. FP-40SC at 12 gpm = 1.5 per panel and .071 psi = .071 for 8 panels at 12 gpm.
Summary of Contents for FP-26SC
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