The first bend is 20cm along the steel pipe, leaving a vertical threaded inlet: a 107.5° bend to
commence the upwards gradient of the serpentine.
!! Note: ensure this vertical run is at right-angles with the horizontal bisection of each bend, so
that the inlet hole to the frame can be made accurately.
The serpentine will run upwards, 17.5° from horizontal. This will require seven 215° bends
(inner diameter 10cm.) The first 215° turn comes approximately 20 cm from the end of the
tube. There-after there is approximately 56cm between bends. One last 107.5° bend is made
20cm from the end of the pipe to leave a threaded vertical outlet. Again, care is necessary to
ensure it is vertical to enable the frame to be accurately cut and drilled.
2.1.2 Joining the serpentine to the absorber plate with wire
Instructions in Deus et al. (2004) are given for joining the pipe to the absorber plate with rivets
or by welding. These methods would improve heat transfer, although attachment with wire is
the easiest.
Tin snips are effective to cut the plate to size: 915mm x 1225mm. Cutting with an angle grinder
should not be necessary and accuracy is difficult for sheet metal. The serpentine is placed on
top of the sheet to mark its fixing positions: the mid-point of each 17.5° run, and of each bend.
These points in the sheet are drilled with a 1mm hole either side of the pipes. Gal or stainless
steel wire (to prevent rust) is threaded through from above, holding the serpentine in place
(join by twisting on the underside.)
Absorber pipe fixed to backing plate with gal. wire
The absorber is painted with black anti corrosive matte paint. Painting before assembly may
allow better access to tight crannies, but wastes spray paint. See Design Manual: DIY
Serpentine Solar Water Heating, Section 9.1 on Selective Absorber coating. Painting the
underside of the absorber plate will help protect against rust but is not essential. Ensure
paintwork is not scratched by subsequent rough treatment.
10