Wednesday, 16 November 2011

Spot the deliberate mistake.

Here is our heat exchange ventilation system. Can you spot the deliberate mistake? Just to help you work out what's going on, the four ducts coming out of the top are, from the right, clean air supply from outside, return air from the house, clean air supply to the house, exhaust air going outside. Can you see what's strange?

The supply air splits straight after leaving the heat exchanger, then goes through two soundproofers. This should make the house a bit quieter. The clean air supply duct is insulated. That's why it's thicker.

The exhaust air duct is not insulated. That is the problem.

I know it makes some kind of sense to insulate the pipe coming in, because that's bringing in cold air from outside, but as it's a heat exchanger, the heat from the return air is largely transferred to the supply air, so by the time it goes out through the exhaust air duct, it's going to be close to the temperature of clean air supply from outside, and close to the actual outside temperature. So it needs insulation every bit as much as the insulated duct does. Perhaps there is some rational reason why there is no insulation there.