Maintaining correct RH levels is no guarantee for sufficient evaporation. With more active cycles the difference in compost-air temperature contributes to the growth process generating increased evaporation and CO2 production. This means that more fresh air is required for RH and CO2 Cycles that are less active accordingly have less evaporation and CO2 production. This results in a lower demand for fresh air and the air inlet can close to its minimum position. The measured RH and CO2 values are correct at that moment but there is no evaporation and activity will continue to decrease. Air is being circulated without extracting any moisture from the compost.
In order to create enough evaporation in this situation the minimum air inlet position should be set higher so there is enough fresh air In this case the CO2 will drop further but the advantage of increased evaporation is greater. In this kind of situation the fan will be running on its minimum position. By taking these steps activity can start again.
Jan Gielen, C point