Survey of ventilation rates in office buildings

Building ventilation is a primary determinant of indoor air quality in buildings as it impacts indoor contaminant concentrations and occupant comfort. However, relatively few measurements of office building ventilation performance have been conducted, and those data that exist generally have not employed consistent measurement methods and have not involved representative collections of buildings. The US Environmental Protection Agency (EPA) Building Assessment Survey and Evaluation (BASE) study involved indoor environmental measurements, including ventilation, in 100 US office buildings using a standardized protocol. This paper presents an analysis of the measured outdoor air ventilation rates, including comparisons with the requirements in the American Society of Heating, Refrigerating, and Air-Conditioning Engineers (ASHRAE) Standard 62-2001 (2001). The outdoor ventilation rates measured using duct traverses at the air handler intakes are higher than might be expected, with a mean value of about 55 litres/second (1/s) per person. However, these elevated values are not so unexpected given the low occupant density (mean of about four persons per 100 m(2)) and the high outdoor air fractions (mean of about 35%). Air change rates based on peak carbon dioxide concentrations in the space are lower than the volumetric values with a mean of about 20 1/s per person. Questions exist regarding these peak carbon dioxide values based on the assumptions on which the determinations are based.