ISHS Acta Horticulturae 710: International Symposium on Greenhouses, Environmental Controls and In-house Mechanization for Crop Production in the Tropics and Sub-Tropics
EFFECT OF VENTILATION RATE BY FLOOR AREAS ON NATURALLY VENTILATED TROPICAL CROP PROTECTION STRUCTURES |
| Authors: | K. Rezuwan, Mohd, A. Mohd Soom, J. Jamaluddin |
| Keywords: | crop protection structure, multiple-bays, natural ventilation, micro-climate |
| Abstract:
Natural ventilation rate inside a crop protection structure is defined as the rate of air exchanges in volume per unit floor area per hour. Basically, a crop protection structure is made of a simple galvanized steel tube portal frame, covered with a transparent polyethylene sheet roofing and an insect-screen sidewall. The structure provides cultivation area and a conducive microclimate for optimum crop growing, producing high yield and premium quality. The driving forces of air exchanges are the pressures induced by stack effect, wind effect or a combination of both effects. The main functions of natural ventilation are to reduce air temperature and humidity, and maintain carbon dioxide inside the structure. Four naturally ventilated crop protection structures were designed and constructed in the tropical lowlands. The structures were fixed to 50 m long and 4 m high, while the floor areas varied: 10 m (single bay), 20 m (double bay), 30 m (triple bay) and 40 m (quadruple bay). Microclimate inside the structures was measured to quantify the natural ventilation rates. The regressions of stack effect ventilation rates against temperature differences between inside and outside structures were ΦSINGLE = 0.032 ΔT0.439, ΦDOUBLE = 0.021ΔT0.48, ΦTRIPLE = 0.017ΔT0.474 and ΦQUADRUPLE = 0.0153ΔT0.467 for single, double, triple and quadruple bays respectively. In addition, the coefficients of determinations showed strong relationships with R2=0.984, R2=0.987, R2=0.981 and R2=0.989 respectively. All equations follow the theory of power curve with exponent 0.5. Generally, the means of in-house air temperature, wind speed, relative humidity, light intensity and carbon dioxide for all structures in the afternoon were found to be in the range of 30-40°C, 0.5-3.0 m s-1, 53-83%, 170-1400 x 103 Lux and 300-400 ppm respectively. | |
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