A transient numerical model for desiccant-coated fixed-bed regenerators and compensation for transient sensor errors

Desiccant-coated fixed-bed regenerators (FBRs) can achieve high effectiveness due to high ratio of energy transfer area to volume, and therefore, they are favorable air-to-air energy recovery exchangers for HVAC systems. However, unlike other types of energy recovery exchangers, the air properties (i.e., temperature and humidity) at the outlet of FBRs vary with time. The variations in outlet airflow properties can cause errors in measurements because the measurements include the FBR and sensors transient responses. In this paper, a numerical model is developed to evaluate the performance of desiccant-coated FBRs and their transient operation. The model consists of an exchanger model (FBR model) and sensor (temperature and humidity) models to distinguish the actual performance of the FBR alone from the measured performance, which includes both the FBR and the sensor's response. The model is validated with experimental measurements and available results in the literature. The model can decouple the measured response of the FBR and sensors to predict the FBR performance. This paper's main contribution is an insight into the complex heat and mass transfer processes in desiccant-coated FBRs and measurement sensors. The results of this paper could be used to provide practical recommendations for humidity measurements of different types of desiccant-coated FBRs developed for HVAC applications. Furthermore, the measurement requirements in the current testing standards (ASHRAE 84 and CSA C439-18 standards) for FBRs are examined. Recommendations from this paper could be implemented in future versions of these standards.