Modeling a run-around heat and moisture recovery system

Run-around energy recovery systems are one of the several ways for transferring energy between two air streams. Compared with other air-to-air energy recovery systems, run-around systems are very reliable and flexible, especially in retro-fit applications. Previous research in this area has mainly dealt with sensible run-around heat recovery system. However, an ideal air-to-air energy recovery device should be able to recover moisture as well as sensible heat. It is the objective of this research project to simulate a run-around system that exchanges both moisture and sensible heat, and to do a performance analysis to find the design characteristics of such a system.The first step in the study was to develop a numerical model for a run-around system with two sensible heat exchangers and validate the model using data from the published literature. Following this, a mathematical/numerical model of a heat and moisture exchanger and the run-around heat and moisture recovery system was developed using only basic physical and chemical principles, component properties and operating conditions. With this model, the position dependent temperature and moisture content properties of both a single exchanger and a run-around system were simulated for steady state operating conditions. This simulation enables the study of the performance of the exchanger and the run-around system. In the investigation, the method was employed to characterize the performance of a single exchanger and a run-around system and two new independent parameters, the number of mass transfer units and mass flow rate ratio, were introduced.The results show that, for the sensible run-around heat recovery system with a specified NTU, the maximum effectiveness occurs approximately at a heat capacity ratio, but for the run-around system with both heat and moisture exchange, the maximum effectiveness occurs approximately at heat capacity ratio for ARI summer and winter test conditions and the maximum effectiveness varies with . The analysis of the run-around system with both heat and moisture exchange with and as independent parameters shows that the maximum effectiveness occurs approximately when . As well, the value of maximum effectiveness was found to be different when different coupling salt solutions were used