Critical wind speeds for maximum exhaust gas reentry from flush vents at roof level intakes
In considering the contamination of intake air by gases exhausted from nearby vents, it is usually impractical for a designer to make detailed estimates for all wind speeds and directions. The alternative is to determine the critical wind speed and direction at which the concentration of exhaust gases in the intake air will be highest, then locate the intakes and exhausts so that this highest concentration is less than an acceptable maximum value. Considerable information is available to estimate the minimum vent to intake dilution for the worst case critical wind direction. Here, the authors will attempt to predict the critical wind speed that would produce the absolute maximum concentration at this critical wind direction. Another important question that must occur to every designer is whether this ''worst case'' results in excessively conservative design. The analysis will show that the critical wind speed is typically 20% of the vent exit velocity, and that for variations in wind speed of a factor of six (from one-half to three times the critical value), the exhaust gas concentration at the air intake will only vary by a factor of about two. This leads to the conclusion that these worst case conditions will be a common occurrence, and that critical speeds are reasonable criteria to use for design purposes.
- Research Organization:
- Dept. of Mech. Eng., Univ. of Alberta
- OSTI ID:
- 6144292
- Report Number(s):
- CONF-820112-
- Journal Information:
- ASHRAE Trans.; (United States), Journal Name: ASHRAE Trans.; (United States) Vol. 88; ISSN ASHTA
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
320100* -- Energy Conservation
Consumption
& Utilization-- Buildings
AIR FLOW
AIR POLLUTION
AIR QUALITY
BUILDINGS
CALCULATION METHODS
ENVIRONMENTAL QUALITY
EXHAUST GASES
FLUID FLOW
FLUIDS
FORECASTING
GAS FLOW
GASEOUS WASTES
GASES
POLLUTION
ROOFS
VELOCITY
VENTS
WASTES
WIND