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New tracer gas techniques for measuring airflow rates in HVAC ducts and buildings airflow systems are described. These pulse tracer techniques are based upon the application of integral mass balance equations to the tracer gas concentration response of an airflow system to pulse injections of tracer. For building airflow systems, or portions of them, the airflow system is first idealized by an appropriate multi-zone model, pulse injections of tracer are applied to each zone independently, and the concentration response of each of the zones is measured. The multi-zone integral mass balance equations are formed and solved to determine the airflow rates between the zones. The airflows that are determined and the accuracy of these determinations are dependent not only upon the air exchange characteristics of the building, but also on the appropriateness of the system idealization employed.
This paper presents the theoretical basis of the pulse techniques for measuring airflows in ducts, and for studying single-zone and multi-zone building airflow systems. Procedures for formulating appropriate multi-zone idealizations of building airflow systems are described and practical details of pulse testing outlined. A series of field studies are reviewed, providing examples of procedures used to formulate system idealizations, experimental techniques employed to conduct the tests, and airflow rate measurement results.
air exchange, airflow, infiltration, measurement, multi-zone, tracer gas, ventilation
Mechanical engineer, National Institute of Standards and Technology, Gaithersburg, MD
Massachusetts Institute of Technology, Cambridge, MA