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The spatial temperature distribution within greenhouses plays a crucial role in agricultural management, particularly in large glass greenhouses that provide optimal growing conditions for crops. The current study investigated the effects of solar radiation and external shading on the spatial distribution of air temperature inside a large glass greenhouse. Experiments were conducted during summer in Wuhan, China, with cherry tomatoes grown under removable black plastic external shading (50 % transmittance). The use of external shading reduced greenhouse temperatures by 6.80 % on sunny days with air conditioning and 4.62 % on cloudy/rainy days without air conditioning. It also decreased the correlation between solar radiation and indoor temperatures by 60.71 % on sunny days and 7.20 % on rainy days. The greenhouse exhibited uneven temperature distribution in all directions, with much greater vertical temperature gradients (0.67 °C/m on sunny days, 0.33 °C/m on rainy days) compared to east-west and north-south directions. While external shading reduced overall temperature unevenness, on rainy days the north-south temperature difference was only 0.28 %, but the middle position was 2.24 % warmer than boundaries. The findings provide insights into regulating external shading techniques for large greenhouses in humid subtropical climates to optimize temperature management and crop production efficiency.
Mao et al. (Mon,) studied this question.