Criteria for heat recovery and dehumidification.

Two factors - CO2 emissions fiom heating and cooling systems and restrictions on the use of CFC refrigerants - have accelerated the development and introduction of new and more environmentally friendly cooling systems. These new cooling systems also include the so-called "Desiccant Cooling Systems (DCS)" [1]. The desiccant cooling systems consist of a rotating dehumidifier, a rotating heat exchanger and evaporative coolers. For design, control and operation of desiccant cooling systems new criteria have to be considered because of the specific properties of these new technologies. Therefore consulting engineers as well as installers of air conditioning systems are hesitating to trust the efficiency and performance of these new components. Dehumdification of moist air is one of the least known and understood thermodynamic processes. On the other hand the same rotating desiccant wheels and the same rotating heat exchangers are used for many years in a similar joint combination in thousands of installations in the field of air dehumidification for industrial processes for heat recovery and cooling. In general the dehumidification rotor is devided into two sectors (Fig. 1). One is the process zone where humidity is accumulated. The other zone is the regeneration zone where humidity is removed by the counterflow of heated air. The typical operation is unbalanced with a ratio of 1:3 for regeneration to process zone area or air flow. For a balanced ra$o the regeneration temperatures can be below 80°C. To reach high efficiency for the dehumidification process the rotor is divided in three sectors to have in a multistep operation an intermediate cooling in the so-called purge sector. In the following a standard design of an industrial air dehumidification system is described in order to show that design criteria as well as experience can be derived and transferred to the desiccant cooling systems in the comfort field application.