TO-22-A003 - Numerical Assessment of Indoor Air Quality in Buildings Designed with Standard 62.1-2019 Natural Ventilation Procedure

The 2019 version of ASHRAE/ANSI Standard 62.1: Ventilation for Acceptable Indoor Air Quality includes updates to the Natural Ventilation Procedure (NVP) in order to "provide a more accurate calculation methodology and also define the process for designing an engineered system. Natural ventilation now requires considering the quality of the outdoor air and interaction of the outdoor air with mechanically cooled spaces." Opening sizes prescribed in the new prescriptive compliance path are specified in a much more detailed manner than in previous versions of the standard, and a new definition of engineered natural ventilation (NV) systems is given. An informative note states that "opening sizes have not been created to address thermal comfort", assumedly meaning their prescription is for indoor air quality (IAQ) purposes only. No further explanation or justification for the opening size prescriptions is given.

Since natural ventilation is a phenomenon that arises from naturally occurring and variable forces, rather than the predictable action of mechanical systems, resulting air quality in naturally ventilated buildings is less easily predicted than that in mechanically ventilated buildings (which itself is often quite challenging to predict). Furthermore, resulting IAQ in NV buildings is a function of variables not under a designer’s control, including weather and transient or mobile pollutant sources. However, methods exist for assessing the validity of the prescribed opening sizes and estimate their effect on resulting IAQ, which is the subject of the current work.