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Measurements of Outdoor Air Distribution in an Office Building.

pdf icon Measurements of Outdoor Air Distribution in an Office Building. (2838 K)
Dols, W. S.; Persily, A. K.

NISTIR 5320; 54 p. June 1994.


Department of Energy, Portland, OR

Available from:

National Technical Information Service
Order number: PB95-210944


office buildings; age of air; air flow; building performance; commercial buildings; measurement; tracer gas; ventilation; ventilation effectiveness


The National Institute of Standards and Technology (NIST) has performed a study of outdoor air distribution in an office building. This study, performed in the Portland East Federal Office Building in Portland, Oregon, is a follow-up to a study in which outdoor airflow rates to the whole building were measured. This report focuses on the delivery of outdoor air to smaller sections of the building. The technique used to measure these "local" outdoor airflow rates is referred to as the multiplicative method. It consists of measuring the supply airflow rate and the percentage of outdoor air in the supply air, and then multiplying them together to obtain the outdoor airflow rate. Outdoor airflow rates were measured to various zones of the building ranging in size from an individual workstation or office cubicle to the entire space served by an air handler. In addition, both automated and manual sampling techniques were demonstrated for measuring local age of air to determine air change effectiveness and to provide information on the distribution and mixing of ventilation air. Some of the major findings of this study are as follows. When performing supply airflow rate measurements, the selection of the measurement location and the use of recommended guidelines were important for obtaining reliable results. Measurements of the same supply airflow rate made at different locations in the system were generally within 20% of each other. Also, while appropriate levels of outdoor air were brought in by the main air handling system, this outdoor air did not always reach the individual diffusers in the occupied space. In this study, the measured outdoor airflow rates per person, when considered on the scale of an air handler, were consistent with the recommendations of 10 L/s per person given in ASHRAE Standard 62-1989. However, measured outdoor airflow rates per person on smaller scales, i.e., in spaces served by individual terminal units and at individual workstations, were sometimes below the recommended levels of the current ASHRAE Standard 62-1989 and ASHRAE Standard 62-1981 to which the building was designed to conform. Several instances were observed when terminal units were completely shut off, thus eliminating the flow of outdoor air to as many as fifteen diffusers at a time. Measured values of air change effectiveness based on tracer gas decay measurements of local age of air were consistent with good mixing of the ventilation air in the occupied space.