Ventilation efficiency in an occupied office with displacement ventilation — A laboratory study

Abstract

A number of room-ventilation design principles are in use. Common practice in offices is to use mixing ventilation. Increasingly, however, displacement ventilation is being applied; ideally, this involves fresh air displacing contaminated air without mixing. There is very little quantitative documentation of actual improvements in air quality resulting from the installation of such ventilation systems. By means of a chamber study (an occupied office), the performance of displacement vs. mixing ventilation was evaluated in terms of exposure to a simulated (tracer gas) body odor. Flow patterns of air and body odor were evaluated using a signal-response tracer gas technique. The mean age of air was split into two parts: a transit and a present time, respectively. In case of a “smelling” occupant walking around in the office displacement ventilation improved air quality by a factor of 2 as compared to mixing ventilation at an air change rate of 4.3 h −1. At a higher air change rate (7.5 h −1), the improvement came to a factor of 2.7. Displacement ventilation is always at least as good as mixing ventilation or better; however, it performs better with higher air exchange rates which may exceed those specified in accepted ventilation standards.