Simulation of passive ventilation strategies towards indoor CO2 concentration reduction for passive houses

Population awareness and economic growth are responsible for the increasing requirements of indoor thermal comfort in buildings. However, the use of active systems to ensure indoor thermal comfort, contributes for the building sector to be responsible for high levels of energy consumption and consequently greenhouse gas emissions. Passive Houses are one step forward towards low energy demand and indoor environmental quality in buildings. Airtightness of the building's envelope is one of the major PH requirements, that in association with the mechanical ventilation system are responsible to assure adequate ventilation levels. These parameters result in additional challenges towards PH applications in Mediterranean and warm subtropical climates due to the overheating risk, providing new opportunities to explore potential night ventilation strategies. This study is focused on the analysis of different passive ventilation strategies towards indoor CO2 concentration reduction preventing overheating risk, thus assuring high levels of indoor environmental quality. The adopted methodology relied on collected data acquired from interviews performed to Passive Houses residents as the starting point, to identify their major expectations as well as complaints and concerns regarding indoor environmental quality. Following the interviews analysis, whole building dynamic simulation was performed using as a case study a PH building constructed in Cyprus (Tseri Passive House). Three different ventilation scenarios were evaluated: original settings (scenario 1); mechanical ventilation active during the day and turned off during the night (scenario 2); natural night ventilation (scenario 3). An ideal scenario, considering night ventilation through window openings, in which indoor CO2 concentration never exceeded the normative limit of 1000 ppm during a summer design week was achieved.