Volume 12 Part 1 Article 53: Air Circulation in Mushroom Cropping Houses

Volume 12 Part 1 Article 53
Year 1989
Title: Air Circulation in Mushroom Cropping Houses
Author: G.E. Bowman

Abstract:

Air circulation systems in mushroom cropping houses often take the form of overhead, perforated polyethylene ducts which give substatially uniform discharge of air along the house, but commonly fail to secure sufficiently uniform lateral air movement over the cropping surfaces. Ideal aerial environmental conditions for are usually quoted as 16°C, 93 % relative humidity, 0.1 % carbon dioxide concentration and an air speed of 0.1 m/s. In practice it is possible to majntain adequate control of the first three parameters, but measurements over the cropping surfaces in a large commercial house revealed a wide range of variation in air speed.

Air speed alone is not the only factor of importance during cropping: whether a mushroom loses water too slowly (thus increasing the likelihood of attack by bacterial blotch) or too quickly (leading to scaling) is determined by the evaporating power of the air, or coefficient of evaporation. This is expressed as the product of air speed and water vapour pressure deficit, the latter being dependent on air temperature and moisture content. Edwards gives a table of values of air speed, temperature, relative humidity, water vapour pressure deficit and coefficient of evaporation, over which healthy mushrooms of good quality may be expected. Expressed as the product of millibars and metres/minute, acceptable values of evaporation coefficient range from 4 to 10. Thus even if precise control of air temperature and moisture content is attained, then the ratio between the highest and lowest air speeds should not be greater than 2.5:1.

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