Abstract
A pad and fan cooling system was introduced into China in the 1980s. Recently, this cooling system is noticed again accompanying large number of construction of the large-scale greenhouse in China. In this paper, the authors discuss the cooling effect of the pad and fan system on the greenhouse thermal environment under the climate conditions of Beijing, high temperature and dry humidity area, and Shanghai, high temperature and humid area, in China. Observed and analyzed data show the following results.
The average temperature decreases of inflow air through the pads are 6.1°C and 5.8°C, respectively, and the maximum ones are 12.6°C and 7.7°C, respectively, in Beijing and Shanghai. The average temperature decreases of inside air from outside temperature are 3.6°C and 2.7°C, respectively and the maximum ones are 10.0°C and 4.2°C, respectively, in Beijing and Shanghai. The temperature inside the greenhouses do not exceed 30-32°C which is the design criteria by ASAE. Thus, it is considered that the pad cooling method is applicable in both regions. The cooling efficiencies of the pads are 0.78 to 0.79, which are not affected by cooling water temperature, air-velocity across the pad and utilization period of the pads. There are temperature rises of 0.06 °C/m in Beijing greenhouse and 0.11°C/m in Shanghai greenhouse between inlet and outlet air. Higher temperature rise in Shanghai greenhouse are caused with higher inside solar radiation and the existence of the interior shading curtain.
