Energy saving potential of thermoelectric modules integrated into liquid desiccant system for solution heating and cooling

Abstract

The main objective of this research was to investigate the impact thermoelectric modules (TEMs) integrated into a liquid desiccant (LD) system have on the heating and cooling of the desiccant solution, and to evaluate the energy saving potential of the proposed system. Two TEM-integrated LD systems were considered; in the first case (i.e., Case A), the TEMs accommodated the solution heating load at the regenerator and a portion of the solution cooling load at the absorber. The remaining solution cooling load was met by an auxiliary chiller. In the second case (i.e., Case B), the TEMs accommodated both the solution cooling and heating loads before the absorber and the regenerator, while extra heat released from the hot side of the TEMs was reclaimed and used to heat the scavenger air entering the regenerator. The conventional LD system, with a boiler and a chiller for heating and cooling the desiccant solution, was also considered as a reference case, to evaluate the energy saving potential of both TEM-integrated LD systems. Hourly energy consumption and temperature variation in the desiccant solution in each system case were predicted via detailed energy simulation with existing mathematical and empirical models for each system component, such as the absorber, regenerator of LD, and TEMs. An approach for determining the required number of TEMs and the optimum temperature difference between the hot side and the cold side of the TEMs is also suggested, based on the coefficient of performance (COP) of the TEMs. It was found that a primary energy saving of about 2% could be expected in Case A compared with the reference case, whereas 55% more primary energy was consumed in Case B. Consequently, based on detailed energy simulations for the TEM-integrated LD system, it was found that the TEMs should be sized to accommodate the regeneration heating load of the desiccant solution before the solution enters the regenerator. In this case, the cooling capacity of the TEMs would be insufficient for cooling the strong solution before the solution enters the absorber, and an auxiliary cooling device would be required.