Sorption-based heat and mass exchangers for humidity control systems

In northern latitudes during the cold season, adding a dehumidification system can raise the total energy consumption of greenhouses by 80%. Developing an efficient dehumidification system for greenhouses is a necessity in order to reduce its energy consumption and emissions, e.g., greenhouse gas (GHG) emissions. One alternative solution to already existing systems are sorption-based systems. One of the main advantages of using a desiccant system is that the required heat for desorption could be supplied by low-grade energy sources and is a clean technology, which operates without the use of refrigerants. But, in the absence of such a heat source their performance will drop. In this thesis, a new isothermal sorption-based heat and mass exchanger (IsoHMX) as an alternative dehumidification system is proposed to increase water uptake (the amount of adsorbed water) and significantly reduce input energy. The novel concept is based on delivering the released heat of adsorption from the high humidity stream to the desorption part of the system where the drier air stream is being processed. This heat delivery results in an ideal isothermal condition during the adsorption/desorption process, which means cooler adsorption and warmer desorption processes. This will significantly improve the sorption kinetics in both the adsorption and desorption processes. As part of this research, a proof-of-concept test set up for the proposed IsoHMX is designed and built. The performance of the system was measured under different inlet conditions and substrate material. Furthermore, a numerical and a closed-form analytical model are developed and verified with the experimental data. Both models showed very good agreement with the experimental results. With the help of the closed-form analytical solution an optimized design of the IsoHMX was found using multi-objective genetic algorithm to maximize moisture removal capacity (MRC) and the dehumidification coefficient of performance (DCOP). This study showed that the optimized design is independent of the inlet temperature and relative humidity. In the end, the performance of the optimized IsoHMX is compared to a commercial desiccant wheel. The results showed that IsoHMX is more energy efficient, i.e., it has a higher DCOP and the desiccant wheel has higher MRC.