Design fabrication and testing of a low cost greenhouse

Abstract

Controlled environment agriculture in the form of greenhouses, low tunnels and cloches are being practiced at commercial levels in many countries. Among these the greenhouses are the best for active environmental control. The major hurdle for adopting greenhouse cultivation is its high initial investment. Considering the importance of developing greenhouses of simple design with low initial investment, the thesis entitled ‘Design, Fabrication and Testing of a Low Cost Greehouse’ was undertaken. A greenhouse of size 12 m x 3 m was constructed at the Instructional Farm, KCAET, Tavanur. The structure was gable shaped. The main structural members were hoops, ridge line mechanism, foundation material and the structure for pad gripping and fan replacement. Ultraviolet stabilized polyethylene film was used as the glazing material. The fan and pad system of cooling in which the air is cooled by the moist air drawn through the wetted pads was adopted. The system was designed based on the rate of air to be removed from the greenhouse. A fan of maximum air flow rate of 10450 m3 /hr and a pad of size 3000 mm x 1200 mm was found necessary to satisfy the cooling requirements. The climatological parameters namely dry bulb temperature, wet bulb temperature and intensity of solar radiation were measured both inside and outside the greenhouse. The cooling system was operated for various time intervals and the observations were taken under cooled and uncooled conditions of the greenhouse. The temperature inside the greenhouse was higher than that outside. The maximum temperature recorded inside the greenhouse was 47.60C without cooling and 38.50C with cooling. Longitudinal temperature gradient of 50C existed between the fan end and pad end of the greenhouse. Cooling increased the relative humidity inside the greenhouse. Variation in humidity existed between the pad end and the fan end. A desired temperature and relative humidity can be maintained inside a greenhouse by operating the cooling system for various time intervals. The variation of solar intensity inside the greenhouse was similar to that outside. The polyethylene cover transmitted 60 per cent of the solar radiation incident on it. The average efficiency of the pad was 65 per cent. The cost of construction was Rs. 375.58 per square metre.