I have only just caught up with this thread so I may be a bit out of date.
However, for what it is worth, I do the 'ventilation' thing by means of an 'attached' greenhouse.
Because the house is well designed thermally, it doesn't need summer ventilation but I use the attached greenhouse to supply warm air for back up heating in winter.
(The house doesn't have an inbuilt heater).
The greenhouse grows a good proportion of my vegetable needs so the air fed into the house is 'oxygenated'.
The size of the greenhouse is on a base of 4m x 2.5m and is 2.5m high. I was able to build it myself for several hundred dollars - fairly cheap - especially in the light of the benefits it provides. I sometimes think of it as a 'walk-in' Solarmate.
It is big enough to produce food and seedlings for the re-vegetation of the land.
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