Algorithm for steady contaminant distribution in ventilation systems with air recirculation: Contaminant release in ventilation ducts

When contaminants are released naturally or deliberately in ventilation ducts, they can contaminate the supply air and rooms through the return air recirculation of the ventilation and air conditioning system. Few studies have considered the impact of contaminant transport through air recirculation on the non-uniform indoor contaminant distribution. In this study, a method for calculating the steady-state contaminant distribution in a ventilation system with air recirculation when there is a contaminant release from the ventilation duct is presented. The ventilation ducts are considered as a virtual room and modelled separately from the rooms, both using linear superposition expressions based on accessibility indicators to obtain a relationship between contaminant concentrations at the outlet and inlet. A total of four sub-methods are proposed considering different treatments for the return and supply air ducts connected to each air handling unit (AHU). The proposed methods (Methods 1–3) considering the non-uniform characteristics of the ducts are shown to have an accuracy comparable to that of CFD (computational fluid dynamics) simulations, with an average prediction deviation of less than 5%, whereas the use of well-mixed assumption in the ducts (Method 4) results in an average prediction deviation of up to 45% in one of the rooms when the contaminant source is close to the diversion position of the supply air duct. The proposed method avoids the need for holistic modelling and iterative simulation of complex ventilation and air-conditioning system and multiple rooms, and allows for rapid prediction of contaminant distribution