Feasibility study of a desiccant packed bed system for air humidification

In winter conditions air humidifiers are particularly important because low indoor relative humidity can lead to occupants' discomfort, such as dry throat, skin and eyes and, in addition, it can facilitate virus and bacteria transmission among persons. In this work, a study of a novel humidification system based on silica gel packed beds is carried out. In the proposed device, vapour is adsorbed from the exhaust airflow leaving the building and it is released to the fresh air stream supplied to the indoor environment. The analysis is carried out through both experimental and numerical approach: a specific test rig has been implemented to evaluate performance of the packed bed apparatus and obtained data have been used to validate a phenomenological model. The adsorption isotherm and the heat of adsorption of the adopted silica gel have been evaluated though a gravimetric approach. Numerical results highlight the proposed system can provide satisfactory air humidification even when it is driven by low temperature heat sources. Depending on bed thickness, airflows arrangement and air velocity, the humidity ratio of airflow supplied to the building can be increased from 1.5 g kg-1 to 4.8-5.8 g kg-1 when the indoor humidity ratio is 5.8 g kg-1 and the regeneration temperature is around 50 °C.