Research on the cooling effects of fan-pad evaporative cooling systems in regions such as North, Northeast, Southwest, and East China has been implemented based on theoretical models ( Fang et al., 2006 Li et al., 2002 Liao and Chiu, 2002 Shen et al., 2018 Tong et al., 2009 Yu et al., 2016 Zhou et al., 2014). Relevant research suggests that raising the installation position of the greenhouse fan and cooling pad directly influences the temperature field distribution of crops’ canopy flow fields ( Chen et al., 2017, 2018 Liu et al., 2012 Wang et al., 2011). Researchers have elucidated the mechanical properties of papery fan-pad evaporative cooling systems and proposed concepts such as compressive strength and peel strength ( Wang et al., 2011). Numerous scholars have performed in-depth research on fan-pad evaporative cooling systems as well as comparative analyses of the accuracy of measurement methods and the reasons for potential errors, targeting the difficulty in measuring the temperature of the air in the rear part of fan-pad evaporative cooling systems ( Bournet and Boulard, 2010 López et al., 2012 Zhang et al., 2008). As an effective cooling method in contemporary greenhouses, fan-pad evaporative cooling systems work by accelerating the vaporization of water mist in a cooling pad through mandatory ventilation, achieving cooling by absorbing the heat in the air ( Al-Ismaili et al., 2010 Franco et al., 2014 Malli et al., 2011 Xuan et al., 2012).
When low-energy consumption measures, such as natural ventilation and external sunshade, fail to reduce the indoor temperature in greenhouses, fan-pad evaporative cooling systems can be adopted ( Chai et al., 2008 Chen et al., 2012 Franco et al., 2011 Wang et al., 2011).
Keywords: energy-saving humidity temperature decrease variable air volume Our research results theoretically benefit cooling control and energy-saving design of greenhouses in the subtropics. The temperature of crops shared the same variation trend as temperatures inside the greenhouse. The VAV fan-pad evaporative cooling system increased the relative humidity in the greenhouse to satisfy crop production demands. When the warm-up time for a specific temperature zone (34 to 35 ☌) was 41 seconds, the indoor temperature could be reduced to the optimum temperature for crops only when the fan frequency was 50 Hz.
When the temperature increased for 71 seconds or 60 seconds in a specific temperature zone (34 to 35 ☌), the indoor temperature could be reduced to the optimum for crops with a fan frequency of 20 Hz, saving more than 87% of the energy output. The test results demonstrate that a higher fan frequency is typically accompanied by greater ventilation quantity, faster cooling speed, more pronounced effects of the fan-pad evaporative cooling system fan, and more intensive energy consumption during the cooling process compared with a low fan frequency. We discuss the effects of adjusting the VAV fan-pad evaporative cooling system on temperature and humidity, and we provide an estimate of the corresponding energy consumption under different highest stable temperature conditions. This research aims to optimize the energy consumption of a variable air volume (VAV) fan-pad evaporative cooling system via experimentation. Mechanical ventilation systems are applied in greenhouses for temperature adjustment, but they consume a large amount of energy.
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