A naturally ventilated greenhouse has been designed and developed for efficient use in a composite climate. The major feature of this greenhouse is that it has continuous side vents on the north and south walls for the entry of outside cool air and continuous roof vents for the removal of inside hot air. Roof vents are formed by designing asymmetric overlap roof for more effective natural ventilation. Experimental performance (in terms of inside air temperature rise) of the asymmetric overlap roof ventilator (AORV) greenhouse was compared with previously designed window type roof ventilator (WTRV) greenhouse and fully closed (FC) greenhouse from January to June 2007. Complete experiment was conducted in three stages viz. (1) keeping the side and top vents fully closed in January and February, (2) opening the top vents but keeping the side vents fully closed in March and up to mid April and (3) opening the side and top vents from mid April to mid June. It was observed that the daily average inside air temperature (daytime) of the AORV greenhouse during stage (1) was 6.96°C above the ambient air temperature as compared to 7.47°C in WTRV greenhouse and 8.14°C in FC greenhouse; during stage (2) it was 3.87°C above the ambient air temperature as compared to 5.46°C in WTRV greenhouse and 8.87°C in FC greenhouse; and during stage (3) it was just 0.64°C above ambient air temperature as compared to 2.28°C above ambient air in WTRV greenhouse and 11.34°C in FC greenhouse. Various parameters of ornamental plants (marigold and calendula) such as, plant spread, days to bud opening, days to flowering, duration of flowering and number of flowers per plant etc., were observed better in AORV greenhouse as compared to WTRV greenhouse, FC greenhouse and in open field condition during the summer months.
Greenhouse, Nethouse, Polyhouse, Solar energy, Thermal control
