Optimal Placement of Heat Exchangers in a Carbon Capture-Based Ventilation System

Abstract

Achieving acceptable air quality levels in indoor spaces by regulating the concentrations of H2O and CO2 is important for occupant health. Conventional techniques rely on supplying dehumidified outdoor air to dilute these species to within their healthy ranges. Typically, the outdoor air dehumidification is conducted using vapor compression cooling either as standalone systems or integrated with desiccant dehumidifiers. These methods are known to be energy intensive, especially in hot and humid climates. Ventilation systems using indoor air with adsorption-based CO2 capture are thus proposed. These systems use adsorbent packed beds to dehumidify and decarbonize the indoor air before it is sensibly cooled and supplied to the space. For energy efficient operation of these systems, heat recovery units are necessary. In this work, heat and mass balance models were developed and used to determine the optimal placement location of the heat recovery units. It was found that a heat exchanger preceding the decarbonization bed increased the MOFs capacity, resulting in 33 % lower mass requirements. This was accompanied by a reduction in the thermal and electrical energy consumption by 43.5 % and 25 %, respectively, with respect to the configuration where the heat exchanger was placed after both air treatment systems.