Returning and net escape probabilities of contaminant at a local point in indoor environment

The quantified recirculation of a contaminant in a local domain is an essential property of the ventilation efficiency in a room. The returning probability of a contaminant (α) generated in a local domain and its net escape probability (NEP) are essential information for understanding the structure of the contaminant concentration distribution in a room and for controlling the indoor air quality. Here, we propose the fundamental definitions of α and NEP and discuss their potential relation with the net escape velocity (NEV) concept. NEP is defined at a local point and/or local domain as the probability that a contaminant is exhausted directly through an exhaust outlet and does not re-circulate to the target local point/domain again. In a computational fluid dynamics (CFD) simulation, the minimum local domain in a room corresponds to the control volume (C.V.) of discretization; hence, NEP in a C.V. is assumed as the probability in a point without volume. In this study, the calculation results of α, NEP, and NEV distributions in a simple two-dimensional model room and a three-dimensional room with push-pull type ventilation system are demonstrated and discussed. •Net escape probability of a contaminant from a local point is defined.•Relation of net escape probability with net escape velocity addressed.•Net escape probability distributions in 2D and 3D model rooms are calculated.