Studies on the Environmental Control of Farm Building (1)

Evaporative fan-and-pad system for green house cooling in summer

Abstract

The influence of the performance of an evaporative fan-and-pad system on climatic conditions in a glasshouse was studied in this paper. Measurments of air temperature, air humidity and wind velocity in and out the glasshouse (east-west orientation) with the scale of 11.2m long and 5.2m wide were made respectively during the summer seasons of 1964 and 1965.
The evaporative pad was set on the north side wall of the glasshouse and four exhaust fans (0.4KW) with the diameter of 50cm were also set on the south side wall. The ventilation rate of this glasshouse was expected to be 180 times per hour. In the summer of 1964, no more than 40 per sent of the ventiration was found to be drawn through the evaporative pad because the house was not very air tight. In the summer of 1965, the house was repaird in order to prevent the draft. Results obtained in the experiments can be summarized as follows;
1. Air temperature was lowered considerably by passing through the evaporative pad as can be seen in Fig. 1. The cooling effect of the fan-and-pad system was much larger in 1965 than that in 1964, because the air ventilation in 1965 was almost made through the pad and fan system. In experiments of 1965, air flow in the house was relatively uniform just behind the pad, the wind speed somewhat decreased in the central section of the house and increased again before the each exhausting fan (see Fig. 2).
2. The pad temperature was found to be in accordance with the temperature of a wet bulb treasured out doors (see Fig. 3 and Table 1). However, the air temperature just behind the pad was slightly higher than the temperature of the wet bulb. No significant change of the cooling effect of incoming air with the water volume flowing down through the pad was observed in our experiments (see Fig. 4).