Where are you, as a matter of interest?
The black finish is probably PIB (polyisobutylene, I think) sheet, which is used to waterproof insulation. The black PIB will absorb solar radiation, but since it will be separated from the duct by the insulation, the heat gains into the supply airstream...
I’ve got an old run-around-coil heat-recovery system, which is handling about 12 cu m/sec of air. Heat is extracted from the exhaust air streams with 4-row coils and the water is pumped to 6-row coils to heat the supply air. The system seems to recover about 50% of the available heat, when it...
