Improvement of greenhouse microclimate distribution by means of air mixing fans

Abstract

The objective of this work was to experimentally investigate the influence of air mixing fans on air temperature and humidity distribution in an arched roof greenhouse. The greenhouse was occupied by a tomato crop and equipped with two side roll-up openings for ventilation, a PVC pipe heating system and a fan coil heater. Furthermore, for air mixing purposes, an air mixing fan was used. Air temperature and relative humidity was simultaneously recorded in 17 positions equally distributed inside the greenhouse. Concerning the effects of air mixing fan on microclimate distribution, it was found that the mixing fan increased microclimate homogeneity. On the other hand, the use of fan-coil heater was found to increase microclimate heterogeneity. The maximum absolute air temperature and relative humidity difference (observed above the crop) between the centre of the greenhouse and the different measuring positions at the same level, was about 1°C and 4% respectively when the air mixing fan was not used and about 0.4°C and 1% respectively, when the air mixing fan was used. The use of a fan-coil heater increased the above mentioned differences to the level of about 1.7°C and 6% respectively when the air mixing fan was not used and about 1°C and 3% respectively, when the air mixing fan was used. Finally, it was observed that the use of an air mixing fan and/or a fan-coil heater reduced the greenhouse air relative humidity.