The effectiveness method to predict the behaviour of a desiccant wheel: an attempt of experimental validation

Abstract

The desiccant wheel is a key component in solid-desiccant systems. At present, the analysis of the behaviour of air handling units based on desiccant wheels is a complex task. It is difficult to access a simple model that can represent the behaviour of commercialized desiccant wheels with sufficient accuracy.

Experimental data measured in an air handling unit equipped with a desiccant wheel are considered in the present work. The air handling unit belongs to a test facility with a microcogeneration system located at Università degli Studi del Sannio (in Benevento, Southern Italy). Thermal energy from the microcogenerator is used to heat up the regeneration airflow. An attempt of investigating the validity of the simplified effectiveness method in predicting the global behaviour of a desiccant wheel is performed. Two approaches are used with different pair of effectiveness parameters.

Only one sensor of temperature and one sensor of relative humidity were used in each measuring section of the air handling unit. This constraint is most crucial at both outlet sections of the desiccant wheel due to the strong dependence of the air state on the angular position.

An empirical correction of the measured state of the process air at the outlet of the desiccant wheel is used. The corrected data are used in the investigation of the validity of the effectiveness method by using constant values in a large set of cases where the rotation speed of the desiccant wheels and the fans are kept constant. Important deviations between the predicted and the experimental results were found in a significant number of cases, therefore there is the need of improving the method by taking into account the effect on the effectiveness parameters of varying the inlet states of both airflows.