Abstract :
In this study, five most commonly used single span shapes of greenhouses viz. even-span, uneven-span, vinery, modified arch and
quonset type have been selected for comparison. The length, width and height (at the center) are kept same for all the selected shapes.
A mathematical model for computing transmitted total solar radiation (beam, diffused and ground reflected) at each hour, for each
month and at any latitude for the selected geometry greenhouses (through each wall, inclined surfaces and roofs) is developed for both
east-west and north-south orientation. Computed transmitted solar radiation is then introduced in a transient thermal model developed
to compute hourly inside air temperature for each shape and orientation. Experimental validation of both the models is carried out for
the measured total solar radiation and inside air temperature for an east-west orientation, even-span greenhouse (for a typical day in
summer) at Ludhiana (31 N and 77 E) Punjab, India. During the experimentation, capsicum crop is grown inside the greenhouse.
The predicted and measured values are in close agreement. Results show that uneven-span shape greenhouse receives the maximum
and quonset shape receives the minimum solar radiation during each month of the year at all latitudes. East-west orientation is the best
suited for year round greenhouse applications at all latitudes as this orientation receives greater total radiation in winter and less in summer
except near the equator. Results also show that inside air temperature rise depends upon the shape of the greenhouse and this variation
from uneven-span shape to quonset shape is 4.6 C (maximum) and 3.5 C (daily average) at 31 N latitude.
2008 Elsevier Ltd. All rights reserved.
