A Desiccant Thermal and Humidity Control System

Environmental control and life support (ECLS) within closed environments must remove humidity from the air both to maintain crew comfort and to recycle potable water. The current state-of-the-art technology recovers water vapor by cooling air to below its dew point in a condensing heat exchanger. This requires chilled water at about 5 C as the cooling sink. However, desiccants can be used to recover water vapor without cooling the air to below its dew point. This allows 1) independent control of environment temperature and humidity, 2) the delivery of very low dewpoint air for special purposes, and 3) a higher design temperature for the coolant loop, with concomitant savings in weight for the thermal bus and radiator. Furthermore, desiccants can recover water vapor without creating water-wetted surfaces or producing saturated air. These characteristics, combined with the fact that many common liquid desiccant are biocidal, offers the possibility of a lighter weight water recovery system that is immune to bio-fouling and cannot inadvertently spread disease. Two novel desiccant Thermal and Humidity Control (THC) systems are evaluated in the proposed work. Their size, weight, power and resupply requirements will be compared to those of a THC system that uses a conventional condensing heat exchanger.