The Effect of Transient Characteristics on Optimization of Fixed-Bed Regenerators

Fixed-bed regenerators (FBRs) have high sensible effectiveness, making them an energy-efficient air-to-air energy recovery exchanger (AAEE) to reduce energy consumption for ventilation in buildings. FBRs operate by alternately storing and releasing heat in fixed exchangers, which result in outlet temperature that varies with time during both heating and cooling periods. This variation in FBR's outlet temperature adds a new optimization variable that needs to be considered when designing FBRs. For example, in heating, ventilating, and air conditioning (HVAC) systems, careful design is required to prevent large variations in FBR’s outlet temperature (temperature swing (TS)), which might deteriorate occupant thermal comfort and introduce a variable load on the HVAC system. In this paper, a correlation for TS is developed as a function of FBR design parameters. FBRs optimization is performed considering TS as an additional objective to the traditional parameters of exchanger effectiveness, pressure drop, payback period (PBP), and mass. A selection procedure (decision-making procedure) is also integrated into the optimization process to select the optimized FBRs from Pareto fronts. The results show that when TS is included as an additional objective to the optimization and selection process, the selected optimized FBRs have higher mass and effectiveness.