THE THEORY OF FAN VENTILATION

L.G. Morris
When comparing the forced ventilation of greenhouses by means of extractor fans with the more conventional natural ventilation through hinged ventilators it is necessary to consider the capital and running costs of the fans, any saving in structural cost of the greenhouse and any differences in crop value which result from the use of fans. Most of this information must be derived from practical experience or from experiment, but a theoretical treatment can be useful in studying the effectiveness of fans in reducing the temperatures of air and plants in the greenhouse and can give some guidance in the choice of ventilation rate. Even through the theory may lack accuracy at the present time it can give a useful indication of the effect of ventilation rate on these temperatures and also of the effects of different greenhouse coverings and of various devices to give additional cooling.

The purpose of ventilation is to carry away surplus solar heat admitted into the greenhouse after it has been converted into sensible heat and latent heat of vaporization in the greenhouse air, but other heat losses occur through the greenhouse covering. It is therefore necessary to express all the transfers of energy which take place in mathematical terms and solve the equations to find the change in condition of the air as it passes through the greenhouse and also the effect on the temperature of

Morris, L.G. (1971). THE THEORY OF FAN VENTILATION. Acta Hortic. 22, 74-85
DOI: 10.17660/ActaHortic.1971.22.12
https://doi.org/10.17660/ActaHortic.1971.22.12

Acta Horticulturae