CFD modeling of the fire-induced pressure rise in passive houses

Nowadays, climate change is one of the greatest challenges worldwide; therefore, the intensified use of renewable resources has favoured the construction of airtight and energy-saving buildings, called passive houses. The main disadvantage of airtightness is the risk of pressure build-up in the event of a fire: several studies indicate that if the fire-induced overpressure exceeds 100 Pa, it will be impossible for occupants to open doors during evacuation. The pressure induced by a fire and the spread of smoke between compartments are the main causes of death, along with the inhalation of toxic substances. The objective of this Master's thesis is to examine the relationship between building airtightness and the pressure increase resulting from fire using Fire Dynamics Simulator (FDS) and Pyrosim software, which reproduce reality by predicting pressure trends and controlling them in order to build safe passive houses. The main topics covered are: the concept of a passive house, the origins of the term and the European directives; the types of fire that can identify higher risk situations; the procedure performed to validate the FDS software; and the connection with PyroSim is illustrated. PyroSim creates a correct format for the FDS input file and provides immediate feedback on the input. The main steps to validate the coupling of PyroSim with FDS are described; finally, the results of all simulations performed are shown, analysing the values of heat release measurements, pressures and flow rates. Thanks to the numerous simulations carried out, it was possible to compare different situations, in which the variations were related to: the volume of the room, the α parameter related to the HRR curve, the air tightness parameter or the ventilation system. The main solutions that can be adopted through the use of a natural ventilation system activated by a pressure gauge to mitigate a risk event were identified and designed.