The collector is made from standing seam aluminum roofing material, and is glazed with twin wall polycarbonate glazing. The back of the collector is insulated with a sheet of rigid polyisocyanurate insulation. A manifold across the top distributes water across the width of the absorber. The water runs down the surface of the absorber removing heat from it and then is collected by a manifold across the bottom.
The standing seam aluminium roofing collector absorber.
The system uses two small PV panels in series to power a 24 volt DC diaphragm pump. When the pump is off, the fluid in the collector and plumbing drain back to the tank for freeze protection. Since the PV panels only generate power when they are in sunlight, they act as the controller for the system.
The tank is wood framed with a waterproof liner. The liner is unique in that it uses a heavy cotton material that is then waterproofed with silicone. Lu can let us know how this liner holds up over time. If it works, it would have some advantages over the usual EPDM liner.
Lu used a length of copper tubing for the heat exchanger that transfers heat from the tank to the domestic hot water line. While copper is common (and good) heat exchanger, Lu has coiled the copper tubing into a unique shape that should be more efficient at transferring heat than the usually cylindrical coil. Preliminary testing indicates that the heat exchanger performance is good.
Lu's detailed description provides more construction detail and some good performance graphs. The efficiency of the system looks good to me.
I'll offer a caution on the twinwall polycarbonate glazing. I agree with Lu that the twinwall is great stuff to work with and the double glazing is a particular benefit on the Thomason style collectors. But, General Electric (one of the makers of twinwall polycarbonate) advises against using it when it will be in contact with hot water vapor. The tests they ran with this condition showed a significant drop in material properties over a not very long period. It may be that they were using hotter water vapor than will be present in this collector, and that the life of the twinwall on this collector will be OK. Lu can let us know in a while whether he is seeing any degradation.
Some additional information on trying to get water to run down sheet metal without diverting off to one side or the other... Another possibility would be to use corrugated galvanized or aluminum roofing sheets that have closely spaced channels.
The standing seam aluminium roofing collector absorber.