4.2 Pipe-work
4.2.1 CPVC
CPVC is currently used for flow and return pipe-work between the solar panels and the tank
and the hot water flow to the shower. Its pressure rating is 100 PSI @ 180° F (82° C); it should
not be used for applications which exceed this temperature. In order to protect it from UV
degradation on a sunny roof it should be painted with exterior grade latex paint. Joins should
be sealed with CPVC solvent cement.
System installers in Guatemala report difficulty in connecting CPVC to fittings of other
materials even though they have the same nominal diameter. A length of CPVC, galvanized,
and PVC pipe which are all supplied as ½”, for example, will have different actual diameters
due to the allowance that is made for roughness. Make sure you leave the plumbing shop with
the right reducers/ adaptors for these connections.
4.2.2 Copper: Protection against high-temperatures
The author worries about the ability of CPVC to withstand maximum collector outlet
temperatures. See Design Manual: DIY Serpentine Solar Water Heating, Section 9.1 for
discussion on copper pipe.
4.2.3 Pipe-work installation for thermo-siphon.
Circulation between the collector and the tank requires an upwards gradient in the pipe, if
possible >45º. It is easier to achieve this gradient by keeping the pipe run as short as possible.
The only requirement for proper functioning is that relatively larger piping be used since the
pressure available to cause fluid to circulate is relatively small. 1/2” will do for typical
installations, but where there are long pipe runs or more than three collectors, larger diameters
may be necessary for good flow. Piping should have a minimum of tight elbows, and sweeping
bends are preferred to reduce pressure drops.
All Connections should slope upwards (B. Deus et al, 2004)
Connection from collector (bottom right) running up
to storage tank (top left). Because there is a dip in that
connection an air bubble will block the circulation
immediately and consequently the system stops functioning
This connection is sloping upwards and so there
are no problems with the hot water circulation.
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