Problems with evaporation form one of the main causes of bacterial blotch. The danger zone is reached in situations where mushrooms are developing while too much evaporative moisture is introduced from below and there is insufficient moisture extraction. Measurements show that in such a period a minimum of 25 grams of evaporation per square metre growing surface must be achieved per hour.
Using the new WVC (Water Moisture CO2) measuring system evaporation can be measured directly and immediate measures taken based on the read out. If a similar system is not on hand, use the fact that total moisture extraction is determined by the difference between the inlet moisture content compared to the growing room moisture content and also by the volume of air introduced - in other words the fan position.
Using more outside air (if its moisture content is low enough) or otherwise increasing dehumidifying (using cooling) creates a greater difference between inlet moisture content and the growing room moisture content resulting in more moisture being extracted. This can be achieved by lowering the RH (or raising the moisture deficit). In addition a higher fan position will always extract more moisture.
Jan Gielen, Specialist climate & energy, C point