Evaluation of Cooling Performance and Characteristics of Air-Distribution in a Pad and Fan Cooling Greenhouse

Abstract

Many studies have confirmed the cooling efficiency of the pad and fan cooling system, however, few have systematically studied cooling performance at the point of characteristics and air-distribution efficiency. In this study, the field measurement of a large-scale commercial pad and fan greenhouse was carried out. The pad and fan cooling greenhouse was kept in a relative favorable state in such a hot summer, that is, the average inside air temperature at noon was under 28 ℃ and the average evaporative cooling efficiency of pad was 75 %. The distribution of airflow velocity combined with operations of fans was monitored. It can be easily observed that the air velocity was relatively low and the maximal airflow velocity was about 1 m/s. It also can be found the airflow was in an uneven distribution due to the function of cooling system and plant canopy. The distribution of air temperature with the process of time in greenhouse was monitored. The non-uniform characteristic of air temperature distribution was clarified not only in horizontal direction but also in horizontal direction. The temperature rises in horizontal and vertical directions of the greenhouse were 2 to 5 ℃ and 0.8 to 5 ℃, respectively. The latent heat and sensible heat was affected by weather conditions. The total value of latent heat and sensible heat in sunny days approached to 5 MJ/m2 and was greater than that in cloudy day. In addition, in sunny days the latent to sensible heat ratio was over 0.6 and was greater than that in cloudy days.