14 June 2002
c. Transport Subsystem
(1) Heat transfer fluid. Propylene-glycol concentration (30 percent, 50
percent, or 0 percent).
(2) Heat exchanger (closed-loop system only). Single-isolation plate-type
or shell-in-tube heat exchanger? (plate heat exchangers are preferred).
Pipe sizes and design pressure drop.
(a) Pipe size to and from collector array. Upper limit is size of array
supply/return manifold; the lower limit is imposed by the 5 ft/s (1.5 m/s) velocity
restriction. To reduce life-cycle costs (pump power versus pipe cost), it is often
possible to size the piping to the array manifolds to be one size less than the manifold.
The designer must insure that fluid velocities with this reduced size are acceptable.
(b) Collector loop design pressure drop. The pressure drop around the
collector loop at the design flow rate (AFR) must be calculated and will be used to
determine pump capacity. The designer should note if the collector loop fluid is
propylene glycol and appropriate pressure drop allowances (x 1.2 for 30 percent or x
1.4 for 50 percent) will be made.
(c) Storage loop design pressure drop. The pressure drop around the
storage loop at the design flow rate (AFRx1.25) must be calculated and will be used to
determine pump capacity.
Expansion tank (closed-loop system only).
(a) Expansion tank acceptance volume. Calculate the total fluid
volume in collectors plus the volume of all piping located at the same level as or above
the bottom of the collectors.
(b) System fill pressure at the expansion tank. Determine the proper
system fill pressure by evaluating the system elevation head. This fill pressure should
allow for 10 to 15 psi (69 to 103 kPa) at the top of the collector loop.
(c) Expansion tank precharge pressure. The precharge pressure
should equal the fill pressure at the expansion tank location minus 5 to 10 psi (35 to 69
kPa) to provide an initial fluid volume in the tank.
(a) Collector pump minimum capacity. The circulation pump provides
the system flow rate determined above and should be sized according to standard
(b) Storage pump minimum capacity. The circulation pump provides
the storage flow rate determined above and should be sized according to standard