Analysis of the microclimate of a greenhouse with two anti-insect screens of different thread density

Microclimatic studies were performed in a Meditterranean greenhouse (cropless multispan-type greenhouse, with three roof vents) divided in two independent sectors (25×24 and 20×24 m²). Screen number 1 (10×20 threads cm^-2; porosity φ = 35%) was installed in the 25×24 m² sector while screen number 2 (13×30 threads cm^-2; φ = 26.3%) was installed in the 20×24 m² sector. Tests were performed on 5^th and 6^th August, 2014, and the opening of the vents was managed with a climatic controller. Under similar radiation levels in both sectors, observed differences were +2.3°C between the average daily air temperature with screen 2 (φ = 26.3%) respect screen 1 (φ = 35%), 3.7°C for the average daytime temperature and +4.8°C for the average temperature between 12:00 and 16:00. An increase in the vertical gradient of the interior temperature with screen 2 was observed, with an average value between 12:00 and 16:00 of 1.6°C m^-1 with screen 1 (φ = 35%) and of 2.3°C m^-1 with screen 2 (φ = 26.3%). The difference in porosity between both screens also caused an important decrease in the interior air speed, with average values between 12:00 and 16:00 of 0.27 m s^-1 with screen 1 (φ = 35%) and of 0.16 m s^-1 with screen 2 (φ = 26.3%).