Dehumidification In A Chinese Solar Greenhouse On The Base Of An Active Heat Storage-release System

Humidity is one of the important environmental factors that affect the vegetable production in greenhouse. At nights during winter Chinese solar greenhouses are heavily insulated and therefore suffer from high humidity. That increases the risks of fungal diseases. Temperature changes and energy losses while dehumidifying. Traditional Chinese solar greenhouse is lack of dehumidification system in case of saving energy.In this study we presented an energy-saving dehumidification system that suits Chinese solar greenhouses. Dehumidification is achieved by introducing outside dry air into greenhouses after being heated. An active heat storage-release(AHS) system will provide part of the heating energy. During daytime the AHS system stores the surplus solar energy in water and releases this energy at night to the outside dry air through a water-air heat exchanger. The outdoor dry air was drawn in by a ventilator and distributed evenly across the greenhouse through a plastic duct. Electric heaters served as auxiliary heating when the AHS system cannot meet the heat demand. Dehumidification system was tested in a simply assembled Chinese solar greenhouse. A way to improve the dehumidification system was suggested based on the experiment results.The study showed that:1. The relative humidity in the greenhouse with the dehumidification system was maintained below 85% while air temperature was not significantly lower than the greenhouse without the dehumidification system. The dehumidification system removed vapor at the level of 15 g m-2 h-1 and improved the vapor pressure deficit(VPD) by 106 Pa on average at an air exchange rate of 1 h-1.2. The power requirement to drive the dehumidification system was 4.2 W m-2. The value seems reasonable compared to the latent heat removal of 9.5 W m-2. The energy supplied by AHS system and electric heaters were almost the same. Dehumidification combined with AHS system saved 49.8% of heating energy.3. Dehumidification system applied to simply assembled Chinese solar greenhouse, which has higher insulation of the wall material. Temperature in a simply assembled Chinese solar greenhouse with AHS system is 4.5℃ higher than that in a traditional solar greenhouse at night on sunny days, and 1.1℃ higher on cloudy days. The wall of simply assembled Chinese solar greenhouse saved 72% of land resources.4. The RH gradients in the ridge direction of greenhouse can be limited by optimizing the size and space of the holes on the duct. Total hole area should be 1.75 times of duct area. Dehumidification system combine with heat recovery can reduce the sensible heat losses. For commercial application, the capacity of the AHS system needs to be increased to eliminate the use of electric heaters.