Indoor Environmental Quality—Ventilation

Abstract

The primary goal of ventilation is to provide dilution capacity for diluting contaminants generated within a room. The properties of the dilution curve are discussed first; this is the concentration as a function of the ventilation flow rate and the varying efficiency of dilution at different levels of concentration. The purging flow rate is the flow rate at which ventilates are introduced. In situations where the air supply is laden with the contaminant that is going to be removed it is important to distinguish between the purging flow rate and the flow rate supplied by the ventilation system. The trade-off between control of contaminant levels by ventilation and source control is addressed. Factors that may diminish the dilution capacity, such as short circuiting and direct loss of air, are discussed. A sensation of draft may be counteracted by the occupants’ manipulation of the ventilation system, which may lead to reduced dilution capacity. Situations where there is a risk of draft occurs are identified and design parameters are introduced whose use in design can help in avoiding systems that cause draft. Communication about how ventilation works is important for avoiding mistakes and having the wrong expectations about what can be achieved with ventilation.