Air change rates and carbon dioxide concentrations in a high-rise office building

The feasibility of controlling ventilation rates using occupant-generated carbon dioxide (CO{sub 2}) as the control index has been examined in a large high-rise office building with a constant-volume heating, ventilating, and air-conditioning (HVAC) system. Daily CO{sub 2} concentration profiles throughout the building and air change rates, using sulfur hexafluoride (SF6) as a tracer gas, were measured for several outdoor air supply rates. Of particular interest was how well the CO{sub 2} concentrations measured in the central ventilation system`s return air plenum represented the average CO{sub 2} concentration behavior in the building as a whole. CO{sub 2} concentration profiles were also measured on individual floorspaces in the building to determine the range of variability in the concentration behavior in occupied zones. The influence of fresh air supply rates on the speed of mixing of the tracer gas (surrogate contaminant) was also examined. The practicability of using CO{sub 2} as an active tracer gas to measure air change rates was also investigated. The results are discussed in the paper.