The standard DEC systems currently used for air-conditioning are mostly based on solid sorbent, and show a process path similar to the one shown in Figure 1. These systems present thermodynamic limits, which affect the process performance. In particular:

— Limited dehumidification efficiency: the dehumidification process is nearly adiabatic. The heat of condensation and the heat of bonding released during the sorption process causes an increase in temperature of the air and the sorption material; the latter results in a lower sorption potential.

— Cooling potential not completely exploited: the return stream is saturated before entering the heat exchanger wheel (7) but it leaves with a state far distant from saturation. If it could be humidified during the heat exchange process, the potential uptake of heat and thus the potential cooling would be far higher.

— Low efficient processes sequence: during the standard DEC process the supply air is heated, i. e., during the dehumidification (1)-(2) and then cooled by means of the heat recovery wheel (2)-(3). The sequence is not efficient since one of the aims of the process is the air temperature reduction. Moreover the sequence of the two processes (i. e., dehumidification and heat transfer) sets thermodynamic limits of the cycle and restricts the applicability of the cycle in severe conditions, i. e., conditions at high ambient air temperature and humidity.

Furthermore conventional DEC technology, following the scheme of Figure 2, is not used for small size systems (typically below 3000 m3/h). The main reason is that they result economically not convenient in comparison to other technologies. Furthermore on small capacity plants technical problems such as leakages between return and supply air are more difficult to tackle with success [2].