UFC 3-440-01
14 June 2002
length by an appropriate factor (usually between 1.2 and 2, depending on the
complexity of the plumbing circuit). Manufacturers should supply the pressure drops
associated with the heat exchanger, solar collectors (or collector array), and other
components at the respective loop flow rates. The pressure drops listed for these
components will most likely assume water as the working fluid. The designer should be
slightly conservative to account for the difference between pure water and the
propylene glycol solution in these components. The correct values for the system
piping should be available, since Table 4-1 provides corrections for pressure losses
with propylene glycol solutions.
4.4.1.6.3
Pump Sizing and Specification. Pump performance is usually plotted as
pressure rise versus flow rate. The pressure drop in the loop at a given flow rate is
represented by a point on this plot (or a line if the pressure drops for a variety of flow
rates are known). Figure 4-10 shows an example of these curves. If this operating
point is inside, or to the left of a given pump curve, that pump can be used. In Figure
4-10, pump "B" can be used. It should be noted that the pump could only operate at
points along its curve. For this reason, the designer should try to find a pump curve
lying as near the recommended system operating point as possible (unless this point
lies on the pump curve, the pump will be slightly oversized). After the selected pump is
installed and the system is started, the flow at the pump outlet must be throttled slightly
to increase the pressure drop (or resistance) of the loop (refer to the system
performance curve "D"). This procedure is normally done using a ball valve at the
pump outlet (cavitation is possible if the throttling is done on the suction side). Many
pump manufacturers supply pumps with built-in throttling valves (refer to Figure 4-10).
4-4.2
Transport Sub-System Checklist
4-4.2.1
Schematic. Based on the topics discussed thus far, the complete closed-
loop system schematic can be completed. Except for the collector array and piping
layout, the system schematic is not specific to any given building. For this reason, the
system schematic need not be to scale and thermal expansion loops need not be
shown. Information should be provided on the drawings wherever possible to ensure
that construction is completed according to design. A design checklist is provided in
APPENDIX D and a drawings checklist is provided in APPENDIX E, for additional
guidance.
4-4.2.2
Construction Details. This section provides information on various system
details that commonly cause problems. These details are not necessarily solar-specific
issues, but are important to ensure a quality solar energy system.
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