Vol. 10, Special Issue 12 (2021)

Author(s):
D Mahender Reddy, R Lalitha, A Raviraj, S Vallal Kannan, M Baskar and M Nagarajan

Abstract:
Protected cultivation is a technology for off-season crop cultivation based on market requirements. Temperature and relative humidity are always higher inside the polyhouses than outside climate and maintenance of favorable microclimate under the polyhouse is a tedious job. Fan-pad operated evaporative cooling system is a better method for maintaining suitable temperature and relative humidity under the polyhouses. But the main drawback of this cooling system is the thermal gradient development along the direction of the airflow from the cooling pad to exhaust fans. High-temperature gradients of this cooling system can affect plant growth. Different ventilation rates were experimented in this study to reduce the temperature gradients and to maintain favourable climate inside the greenhouse. A climate model was used to predict the temperature gradients along the greenhouse which incorporates the effect of ventilation rate, roof shading, and crop transpiration. The model was calibrated and validated with the experimental data and used to study air temperature profiles along the length of the polyhouse with the influence of the outside air temperature and humidity. The temperature gradients up to 8 ˚C were observed from pads to fans at hot times (during 13:00-15:00) and with the experiment of high ventilation rates thermal gradients were lowered to 2 ˚C in all the times. Experimental data showed that the cooling system was able to keep the polyhouse air temperature at low levels. Despite its simplicity, the climate model is sufficiently accurate to improve the design and the management of the cooling system.