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20171
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Subject: Agricultural Engineering × Author: Amanpreet Singh × Start date: 1978 × Type: Thesis ×
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    ThesisItemOpen Access
    Thermal modeling of asymmetric overlap roof greenhouse for year round microclimate control
    (Punjab Agricultural University, Ludhiana, 2017) Amanpreet Singh; Sethi, V. P.
    In this study global solar radiation availability and thermal model for newly developed asymmetric overlap roof shape of greenhouse was developed. A mathematical model for global solar radiation availability was utilized to compute monthly average daily solar radiation, hourly solar radiation and instantaneous solar radiation; the computed values of solar radiation were utilized in dynamic thermal model to ascertain hourly plant and inside air temperature. Newly developed shape was also compared with previously developed two best shapes of greenhouse viz. even-span and modified arch in terms of solar radiation capture and for inside plant and air temperature buildup. Experimental validation of both the models is carried out for the measured instantaneous solar radiation, plant and inside air temperature for an east-west orientation, asymmetric overlap roof greenhouse (for a typical day in summer) at Ludhiana (310N and 770E) Punjab, India. The per cent difference between predicted inside air temperature and the average of measured values ranged from 0.49 to 24.58 with root mean square error of 5.69. The difference between the measured and predicted values of plant temperature varies from 3.96 to 26.99 per cent with root mean square error of 3.7. During the experimentation, tomato crop is grown inside the greenhouse and modified fan-fogger evaporative cooling system was installed and operated in sequence with different combinations of back side screen net (40×40 mesh size) and assorted sequential timings of on/off operations of fan-fogger. In this study, three different combinations of back side screen net with operational timings of fan-foggers combinations were employed and in order to optimize the operation time of fans and foggers, different combinations of operational time at fixed back side screen opening were also tested. By using modified fan-fogger evaporative cooling system, inside air temperature (Tai) drop was 120 C in twelve minutes during peak hours of solar load. During summer months of May and June, modified fan-fogger evaporative cooling system extracts heat at the rate of 9-10 kW to maintain inside air temperature lower by 8-90 C as compared to ambient air. Optimum value of cooling efficiency of modified fan-fogger evaporative cooling system comes out to be at 6 feet back side screen net slot and at 25 seconds of total operational time of MFFECS.