Impact of optimized residential ventilation with energy recovery on health and well-being

With rising insulation standards and air tightness in buildings, the use of mechanical ventilation becomes more relevant. In this context, energy recovery offers a significant contribution to the decarbonisation of building operations. Heat recovery systems are widely spread in residential ventilation. Moreover, enthalpy exchangers recovering sensible and latent heat have an increasing share of use in residential ventilation, especially in cold climates, as they not only reduce the energy demand but also increase the indoor air humidity in winter seasons. In moderate climates, the outdoor air provides sufficient moisture content in transitional periods. Hence, enthalpy exchangers have to be bypassed to avoid too high indoor air humidity. Since heat and moisture transfer are conjugated in membrane-based enthalpy exchangers, this leads to a decrease of recovered sensible heat as well. Consequently, the research question arises regarding how efficient moisture transfer in an enthalpy exchanger has to be in order to provide a healthy and comfortable indoor air environment with minimum energy demand.
In this study, we optimize a membrane-based enthalpy exchanger regarding membrane thickness and permeability to improve the overall performance of a residential ventilation unit. Therefore, we develop a simulation setup consisting of a thermal zone model, residential ventilation unit with the enthalpy exchanger model, and the control logic for the system. This simulation setup is combined with a genetic algorithm for optimization. We define a multi-objective optimization problem in order to optimize energy demand and indoor air humidity level.
The study shows that the system’s energetic optimum in moderate climates (Cuxhaven) lies at a membrane thickness of 120 μm. Regarding humidity level, thin membranes with 65 μm lead to overall more comfortable humidities. In consequence, enthalpy exchanger with lower latent efficiency lead to not only better overall energetic performance in moderate climates but also more comfortable indoor air conditions. With slightly higher energy demand compared to the energetic optimum, a significant increase regarding comfortable indoor air humidities is achievable.