Dehumidification in a Chinese Solar Greenhouse Using Dry Outdoor Air Heated by an Active Heat Storage-Release System

Abstract

At nights during winter, Chinese solar greenhouses are heavily insulated with little ventilation and therefore suffer from high humidity. In this study we presented a 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 provided 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 incoming outside dry air through a water-air heat exchanger. The outdoor dry air was drawn in by a ventilator (blower) and distributed evenly across the greenhouse through a plastic duct. Electric heaters served as auxiliary heating when the AHS system could not meet the heat demand. Experiments were conducted in two Chinese solar greenhouses in Beijing. One of the greenhouses was equipped with the dehumidification system and the other was not. This study showed that 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 can remove vapor at the level of 15g m-2 h-1 at an air exchange rate of 1 h-1. The power requirement to drive the dehumidification system was 4.2 W m-2. For commercial application, the capacity of the AHS system needs to be increased to eliminate the use of electric heaters.