Measurements of Outdoor Air Distribution in an Office Building.
Measurements of Outdoor Air Distribution in an Office
Building.
(2838 K)
Dols, W. S.; Persily, A. K.
NISTIR 5320; 54 p. June 1994.
Sponsor:
Department of Energy, Portland, OR
Available from:
National Technical Information Service
Order number: PB95-210944
Keywords:
office buildings; age of air; air flow; building
performance; commercial buildings; measurement; tracer
gas; ventilation; ventilation effectiveness
Abstract:
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.
Building and Fire Research Laboratory
National Institute of Standards and Technology
Gaithersburg, MD 20899