On the selection of shape and orientation of a greenhouse for composite climates

Abstract

Five most commonly used single-span shapes of greenhouses such as even-span, uneven-span, vinery, modified arch and quonset type have been selected for comparison in a composite type of climate. The length, width and height (at the centre) are kept the same for all the shapes. The comparison is based on total solar radiation input (beam, diffused and ground reflected) to each shape through each wall, inclined surfaces and roofs. Total solar radiation is theoretically computed for each shape in east–west and north–south orientations and compared for each month of the year. The computed values for each shape are then introduced in a transient thermal model developed to compute the hourly inside greenhouse air temperature for the selected day of the year in each month. It is observed that the variation in greenhouse shape can cause up to 3.5–5.5 °C change in the inside air temperature during different hours of the day. Experimental validation of the model is carried out using the measured inside air temperature data (for a typical summer day) for an even-span greenhouse (in which capsicum is grown) at Ludhiana (31°N and 77°E), Punjab, India. The predicted and measured values are in close agreement. The results show that even-span or quonset shape in east–west orientation is the most suitable shape for year-round agricultural operations.