Assessing the Impacts of Natural Ventilation on Building Energy Use: A Case Study of a Mid-Rise Residential Building in Chicago, IL

Natural ventilation as a passive strategy in buildings has been increasingly studied in recent years for its potential advantages to reduce building energy use and improve indoor environmental quality (IEQ), especially during shoulder seasons (i.e., transition months or colder summer days). This study investigates the energy impacts of natural ventilation in a mid-rise multifamily building in Chicago, IL, using computational fluid dynamics (CFD) simulations and building energy modeling. Considering weather conditions in Chicago, natural ventilation is assumed to be applied only for the shoulder seasons (i.e., spring and fall). To this end, this study used (1) a coupled modeling method to simulate the exterior environment to investigate the overall behavior of outdoor airflow around the building, (2) a decoupled modeling method to simulate the detailed interior environment with various opening scenarios to demonstrate natural ventilation effectiveness, (3) applied building energy models to evaluate the impact of natural ventilation on energy use compared to mechanical ventilation, and (4) performed a parametric analysis to explorevarious natural ventilation scenarios with different environmental control set points, including minimum and maximum outdoor temperatures and wind speeds. The CFD simulations showed that the rates of wind-driven natural ventilation were estimated to be about 8430 L/s (25.4 ACH) in the gym space and 1270 to 2050 L/s (4.8 to 7.8 ACH) in the residential space at average shoulder season climate conditions, depending on different ventilation scenarios, which satisfied the required ASHRAE Standard 62.1-2019 minimum ventilation rates. The parametric study of building energy simulations indicated that natural ventilation can reduce seasonal building energy consumption by up to 30% (21,610 kWh) and save about $1550 during the shoulder seasons compared to the mechanical ventilation system.