Closing the air inlet to the maximum CO2-limit can result in a situation with an oxygen shortage. The fact that this maximum CO2-limit differs in the winter and in the summer indicates that more than one factor is influential here: It is generally well known that a too high CO2 concentration can cause a lack of oxygen.
However, that excessively high moisture contents (except with evaporation problems) can also lead to a lack of oxygen is not such a commonly known fact. Maintaining a fixed maximum CO2-limit in situations with a high moisture content in the growing room air creates a risk of too low oxygen concentrations which has a negative effect on the decomposition process in the compost. Current climate controls do not (yet) automatically correct this. But growers can adjust the maximum CO2 limit themselves to suit the moisture content in the growing room air. Calculations show that the maximum CO2-limit must be lowered by on average 326 ppm per gram of too high moisture content and the reverse.
So a maximum CO2 limit of eg 2000 ppm with a moisture content of eg 105 g/kg will give the same oxygen concentration as a maximum CO2 limit of 1674 ppm with a moisture content of 115 g/kg etc.
Jan Gielen Specialist climate & energy, Cpoint
