From the above it is clear that numerous variables affect the thermodynamic operation point. Some of these process variables, are chosen by the operator and, therefore, their influence is easily controlled. On the other hand, environmental or ambient variables are frequently not controlled by an air-conditioning system and can cause a ‘weather effect’. Consequently, when using fluidizing air of low temperature, climatic conditions can play a significant role in the fluid-bed process. In geographic locations where the specific humidity varies during the year, its effect on the relative humidity of the heated fluidizing air becomes pronounced [20]. Several approaches exist to counter this phenomenon.
The simplest approach is dehumidification to a predetermined maximum dew point. The lower this desired dew point, the more costly will be the equipment and operation. In the pharmaceutical industry, however, there is a trend towards expensive and more sophisticated air-handling systems with dehumidifying and humidifying elements to ensure that the specific humidity of the process air is constant [