The earth tempering and heat recovery system with earth tubes and a heat recovery ventilator, for my office.
The earth tubes are buried in the ground and bring fresh air into the fan unit in the basement. I used two 4″ pipes not only because that is easier to obtain and install, but because two small tubes give more surface area to transfer heat from the earth, than say one 6″ or 8″ pipe, with the same ventilation rate.
I planted peppermint around the intakes, it probably does not do much to make air smell fresh but it cannot hurt…
The fan unit in the basement takes air out of the room and transfers it past the incoming air via a heat exchanger so they can exchange heating or cooling. there are four ducts which makes it a bit confusing. One of the ducts on the right is not insulated because that takes the exhausted air directly outside, no need to preserve its heat.
The system works better in the winter to temper the cold incoming air since the outgoing air is considerable warmer, and the earth pre-warms the outdoor air so that the final air that enters the space is nearly up to the indoor temperature.
In the hot summer weather the benefits work against each other to some extent. But it is still fresh air.