Investigating the impact of different natural ventilation modes on indoor air quality and overheating

The introduction of fresh air by means of natural ventilation is a technique that can improve indoor environmental quality in an energy-efficient manner. Nevertheless, recent studies revealed that the window opening during the summer months, even though it reduces overheating and the energy consumption for cooling, it can increase the exposure of building occupants to outdoor air pollution. But existing literature is limited to office buildings, and they do not include all the major outdoor air pollutants. To address these gaps, data regarding the buildings' envelope (wall, roof, floors, and windows' materials, thicknesses, and U values) and operation (occupancy schedule, ventilation, and infiltrations rate) were collected in order to build typical building cell simulation models, which represented the European apartment buildings archetypes. These building cells had a geometry, which is defined in ISO 15265 and ISO 13790. The buildings' envelope and operation data were acquired from the TABULA-EPISCOPE database. The building energy simulations ran with the typical climatic data of the years 2015-2019. For the same time period, a database for ambient air quality data was used to represent the typical pollution levels. For each archetype, four different ventilation scenarios were used: 1) windows always closed and continuous mechanical ventilation, 2) windows open based on schedule and on indoor temperature during summer, 3) windows open based on a control algorithm that takes into account indoor and outdoor temperature, relative humidity, and indoor CO2 concentration, 4) windows open based on a more advanced control algorithm that also takes into account the ambient air pollution. The simulations gave information about indoor thermal comfort and the ventilation rates according to the different ventilation scenarios. A mass balance model was used to calculate the penetration of the ambient air pollution indoors for the different ventilation scenarios, using the ventilation rates calculated from the building energy simulations. The results revealed that the demand control ventilation models reduced the penetration of outdoor pollution as they had reduced air change rates. In addition, the window opening was capable of eliminating or reducing significantly the overheating phenomena according to the climate. The window control algorithm that did not permit the window opening for cooling when the outdoor air pollution levels reduced the pollution penetration, but it increased the overheating hours significantly. In addition, the airtight models presented higher overheating and higher pollution penetration when natural ventilation was applied. Moreover, the indoor concentrations of traffic-related pollutants were significantly higher in the traffic locations. The results can be used to better understand the tradeoffs between natural ventilation use, overheating and summer comfort and the penetration of outdoor air pollution.