A family of new working materials for solid sorption air conditioning systems

In this communication a family of new working materials, so called selective water sorbents, is presented for sorption air conditioning. These materials are composites “hygroscopic salt inside porous matrix with open pores” and possess intermediate behaviour between solid adsorbents, salt hydrates and liquid absorbents, so that their water sorption properties can be controllably modified by varying (a) porous structure of the host matrix, (b) chemical nature of the impregnated salt and (c) the amount of the salt inside the pores. For these materials the water sorption equilibrium and specific heat have been measured in a wide temperature and uptake range. This study shows that composites based on CaCl2 and LiBr as impregnated salts and different micro- and mesoporous silica gels as host matrices are able to absorb up to 0.75 g H2O per 1 g of the dry sorbent. After presentation of sorption equilibrium curves, the thermodynamic performance for their utilisation in heat pump and refrigeration systems, is calculated. The results show that these new materials can be operated with cycles whose maximum temperature is about 95 °C (for cooling) and 140 °C (for heating) that are lower than those for other pairs known so far. The values of coefficient of performance are considerably higher than those reported for silica gel/water system at the same temperature of the heat source.