Abstract
Passive houses are becoming more and more popular due to energy efficiency requirements. An important aspect is their airtightness, i.e., they have a very low leakage. The present paper describes a preliminary numerical study on fire-induced pressure variations in a structure that resembles a passive house compartment. The configuration without ventilation system is considered in this paper. The fire source used in the experiment consists of wood cribs that have been simulated in the Fire Dynamics Simulator (FDS), version 6.5.2, as a cube with a prescribed heat release rate (HRR) curve (based on experimental measurements). The grid sensitivity study is conducted by using different mesh cell size and comparing the results of pressure variation. A cell size of 0.1 m is considered sufficient in this preliminary study. The maximum over-pressure obtained without ventilation reached up to 870 Pa in the experiment. Such high over-pressure will definitely hinder the escape of occupants. The structural integrity may also be affected by the over-pressure. Using a constant leakage area, which is the default option, the pressure difference without ventilation rises up to 2027 Pa in the simulation. A good agreement with the experimental data can only be achieved if the simulated leakage area is not kept constant when the room pressure rises. Tuning the leakage pressure exponent in FDS significantly reduces the deviation between the simulation and experimental results. The default setting of reference pressure difference in FDS is used to examine the influence of this parameter on the pressure prediction. When applying the default reference pressure difference, a smaller leakage pressure exponent is needed to reproduce experimental results. Therefore, the reference pressure difference has a certain influence on leakage area and should be set according to the pressure used in determining the reference leakage area during experiments. The overall pressure evolutions are qualitatively well captured in the FDS simulations, as these strongly depend on the fire heat release rate evolution, which was prescribed to match the experimental profile. However, in order to improve the current level of accuracy and address the general validity of the observations made in the present study, more experimental and numerical work need to be carried out.
Highlights
With the increase of energy-saving and environmental awareness, the development of low-energy buildings continues to grow [1]
Finer cell size leads to more accurate simulation results but will take more computational cost and storage space
The mesh grid sensitivity was studied based on the case in this paper, focusing on the pressure variation in the fire room of the compartment
Summary
With the increase of energy-saving and environmental awareness, the development of low-energy buildings continues to grow [1]. From a fire safety standpoint, the construction requirements of passive houses, in particular the very low leakage, may result in a substantial pressure increase in the event of a fire, due to the release of hot combustion products in a well-confined enclosure. In the framework of the OECD PRISME project [5,6], a series of experiments have been conducted in confined and mechanically ventilated compartments and over-pressures of more than 2500 Pa have been reported. These experimental results confirm that pressure variation is an important issue to be considered in a confined compartment fire [5,6]. The objective of the present paper is to study the fire-induced high-pressure level due to the airtightness, by comparing novel experimental and numerical results
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