An original heat driven air-conditioning concept: advanced desiccant and evaporative cooling cycle numerical analysis

The use of thermal energy for air conditioning in buildings has gained interest in the past years. For humid-warm climates, systems based on thermodynamic open cycles and employing a solid desiccant material result convenient, from an energetic point of view. Their application has been studied in the past decades, for large size air conditioning plants with compulsory ventilation. The disadvantage of such systems is the thermodynamic limit of the cycle employed which reduces the possibility to exploit the technology in any condition. Moreover desiccant cooling air conditioning systems are not economically suitable for small size applications. In this paper, a new desiccant-cooling concept is presented. It is based on a combination of cooled sorption and continuous indirect evaporative cooling processes. The cycle offers theoretically the chance to overcome the disadvantages of sorption open cycles employing solid sorbents. The thermodynamic analysis of the cycle reveals that the range of application can be extended so that more severe climate conditions, i.e., conditions at high ambient air humidity, can be covered. The component where the cycle takes place is derived from a conventional cross flow air-to-air heat exchanger, and additionally aims to make desiccant air conditioning economically feasible for small size applications. A theoretical study aiming on the process potential assessment has been worked out. An accurate mathematical modelling of the physical processes has been carried out. In particular the heat and mass transfer processes have been modelled in order to study the optimum configuration and system’s design parameters. The performance of the sorptive coole heat exchanger for typical air-conditioning applications has been investigated. The new system offers the possibility to use low temperature heat such as heat from cogeneration systems or solar collectors for air conditioning, i.e. air treatment in an air handling unit for supply of cold, dry air during summer, without refrigeration even under climatic conditions with high humidity values of the ambient air.