Performance evaluation of a ventilated roof desiccant bed by direct use of solar energy for zero-energy buildings

Abstract

Indoor dehumidification is usually achieved by mechanical cooling resulting in significant consumption of high-grade energy resources such as electricity. Conventional rotary dehumidification systems also require the use of high-grade energy to heat the desiccant and regenerate it. Utilization of renewable energy for indoor dehumidification is highly of concern. Ventilated roof desiccant bed system is a novel dehumidification method which can regenerate itself automatically with low-grade energy usage by taking advantage of solar energy and natural ventilation directly. Using renewable energy as an alternative, it can reduce the building energy consumption, which is beneficial to achieve nearly zero energy building (nZEB) target. This study establishes the heat and moisture transfer model of the ventilated roof desiccant bed while the moisture transfer model is validated by using the reference data. The flow-field characteristics in the airflow channels are numerically analyzed, and the regeneration process of the desiccant bed in a typical day is also simulated. Results show that both the temperature and air velocity in the channel are increasing from the inlet to the outlet. The air velocity increment can reach 0.5 m/s, and the temperature can rise about 6 °C under the same boundaries. On a typical day, the regeneration process of the ventilated roof desiccant bed lasts for approximately 3 h, and 80 g of water is desorped per unit. It means that about 18 units are sufficient to remove the moisture produced in 8 h by a man. The research results can provide data reference for the design of the system, and thus facilitates the realization of engineering application.