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PUBLICATIONS

Reverse Airflow Through the Exhaust Air Damper of Variable-Air-Volume Air-Handling Units: Part 1 - Problem Description

Published

Author(s)

J House, J E. Seem, George E. Kelly

Abstract

A common method of controlling building pressurization with variable-air-volume air-handling units is to control the return fan to provide a constant differential airflow rate between the supply and return air ducts. Simulation and experimental results for air-handling units controlled in this manner demonstrate that outdoor air can enter the air-handling unit through the exhaust air damper. The purpose of this study is to draw attention to the reverse airflow problem and to demonstrate the conditions that can lead to this phenomenon. Simulation results were obtained using a model based on conservation of mass and energy principles. Experimental results were obtained from a laboratory scale air-handling unit. Both sets of results reveal that reverse airflow through the exhaust air damper occurs as the outdoor and exhaust air damper are closed, and that the phenomenon becomes more pronounced as the volume matching differential becomes a larger percentage of the supply airflow rate. Reverse airflow through the exhaust air damper of the laboratory air-handling unit was verified using smoke tests.
Citation
Hvac&R Research
Pub Type
Journals

Keywords

air flow, air handling, air quality, dampers, variable volume
Fire and Buildings and Construction

Citation

House, J. , Seem, J. and Kelly, G. (2021), Reverse Airflow Through the Exhaust Air Damper of Variable-Air-Volume Air-Handling Units: Part 1 - Problem Description, Hvac&R Research (Accessed October 27, 2025)

Issues

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Created October 12, 2021
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