In practice there is often a surprisingly high incidence of air spread and movement related problems This is often manifested as evaporation troubles and differences in mushroom development between the front/rear/ left/right lower/upper shelves and over the width of the bed All these factors lead to losses in quality and yield Regarding air spread many growers create extra openings in places where there is not enough air However this only makes matters worse as less static pressure is built up in the air duct As a guideline for good air spread the surface area of all the openings added together must never be more than half the surface area of the air duct Air movement in the growing room and over the beds is related to more complex influence factors The only guideline that can be given here is that outlets usually have a diameter of 55 centimetres with beds in 4 or 5 tiers and 5 centimetres or airliners with 6 or 7 tiers high Before making any adjustments the pattern of air movement in the growing room must be made visible using special smoke testers

Jan Gielen Specialist climate & energy C point jangielen@cpointnl