Adventitious ventilation: a new definition for an old mode?

Abstract

Adventitious ventilation: A new definition for an old mode? Does your home have a mechanical ventilation system? If not, does this mean that your home is naturally ventilated? Probably not. Several studies have compared the effects of naturally versus mechanically ventilated buildings on indoor air quality. However, these comparisons may be unfair to some naturally ventilated buildings. Let’s discover why. Ventilation is the process of supplying air to and/or removing air from a space for the purpose of controlling air contaminant concentrations, humidity, or temperature within the space (ASHRAE, 2013a). Buildings are usually classified according to their ventilation system as mechanically, naturally or mixed (hybrid) ventilated. In a mechanically ventilated building, ventilation is provided by powered equipment, such as motor-driven fans and blowers. In a naturally ventilated building, ventilation is provided by natural forces such as wind-induced pressure differences or temperature-induced differences in air density. In natural ventilation, air is introduced to the ventilated space through intentional openings in the building envelope. In the third mode, mixed or hybrid ventilation (Heiselberg, 2002) the two strategies are alternated spatially or temporally. ASHRAE Standard 62.1-2013 (ASHRAE, 2013a) specifies that a natural ventilation system should be “designed.” This specification implies that there should be a professional who takes responsibility for designing openings and methods for their control according to standards or best practices, e.g. CIBSE AM 10 (CIBSE, 2010). The designer may take into consideration parameters that affect the performance of the natural ventilation system, like wind speed and direction, indoor and outdoor temperatures, and location and size of the designed and controlled openings. So, here is a key question to consider. Should buildings without a mechanical ventilation system automatically be classified as naturally ventilated? In my view, the proper answer is “no.” It is reasonable to assume that — for a significant part of the world’s building stock — no one designed a ventilation system according to pertinent best practices. In the absence of appropriate design, it seems wrong for the default building classification to be “naturally ventilated.” If buildings without designed ventilation should not be classified as “naturally ventilated,” then how should we classify them? How should we refer to this case? One option would be “noncompliant ventilation.” However, this name may be too ambiguous. The ventilation system may not comply with a specific standard or a version of a standard but it may comply with other guidelines or standards. This name does not shed light on the fact that the no one deliberately designed the system. Another name might be “unknown ventilation” or, to draw on a classical Greek root, we might refer to such circumstances as possessing “agnostic ventilation” (from “agnōstos” in classical Greek: “άγνωστος , “not –(to be) known”). This nomenclature, too, presents problems. One could argue that even for designed mechanical or natural ventilation systems, the actual or Indoor Air, December 2014 www.escholarship.org/uc/item/8hm7w0bk