diagnostic testing using ashrae 110 · diagnostic testing using ashrae 110 gerhard knutson, ph.d.,...
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DIAGNOSTIC TESTING USING ASHRAE 110
Gerhard Knutson, Ph.D., CIHKnutson Ventilation, Inc.
952-928-0195
ASHARE 110A Method of TestingThree components
Face velocity measurementsSmoke visualizationTracer gas testing
“Owner” sets acceptance levelsThe problem
What do you do when the results are unacceptable?
General Approach
Operational ProblemsTracer gas leakageReentry
Hood problemsAerodynamicsOperations
Room Conditions Other Considerations
Gas Delivery System Leakage
SymptomsSteady increaseNo reduction when gas is turned off
AnalysisUse meter as a leak meter
SolutionStop leakPlace cylinder inside hood
Reentry
Tracer gas released inside the hoodCharacteristics
Delayed onsetTracer gas in the roomOften slow decay
Smoke Visualization
ASHRAE 110 Failure – Smoke spills outDiagnostic testing
Lazy airReverse air flowInterior roll
Summary
Poor flow characteristic can “pass” but can contribute to poor performanceRepeat somke tests with mannequin
Vortex formed by mannequin interacts with the weak airflow in the hoodCan show spillage where not seen without the mannequin
Other Issues
Equipment in hoodSash Position
Mandates other than left, right, centerDifference between use and design
Heat sources or disturbances in hoodWork positionOperator position
Room Air Supply
The supply ventilation design is as important (or more important than) the exhaust ventilation designRule of thumb:
Room air currents in the laboratory near the hood should be less than half, preferably less than one third, of the face velocity
Room Air Currents
Side ViewFront View
Top View
Left Center Right
High
Midpoint
Low
VerticalDraft
PerpendicularDraft
HorizontalDraft
Cross Draft Grid & Probe Orientation
Vertical
Horizontal
Perpendicular
Stand
Minor Room Air Currents
Hood 628, Position A, 52.5 inches
0
20
40
60
80
100
1 3 5 7 9 11 13 15 17 19 21 23 25 27 29
Time, Seconds
Velo
city
, fpm Vertical
Perpendicular
Horizontal
Significant Room Air Currents
Hood 628, Position AB, 52.5 inches
0
20
40
60
80
100
1 3 5 7 9 11 13 15 17 19 21 23 25 27 29
Time, seconds
Velo
city
, fpm Vertical
Perpendicular
Horizontal
Case History
New 12-foot bench top hoodsAcceptance level AI 0.05Preliminary tests not acceptableDiagnostic testing
Reverse flow at work surfaceHigh Turbulence in laboratoryHigh Cross drafts near hoodTemperature variable in laboratory
Approach
Change diffusers to reduce room air turbulenceModify airfoil on laboratory hoodsModify room temperature controlRecalibrate CV supply and exhaust boxesRewire part of Building Management System – Readout matched boxes
Conclusions
In many instances ASHRAE 110 can be used diagnostically to determine the probable cause of poor hood performance
Other Test
Dynamic testsHuman as a mannequinArtificial clutterWalk by testsLarge apparatus (walk in hoods)Floor mounted fans
Philosophy
Provides additional information relative to robustnessOften no correlation to safetyInterpretation is difficult
Caution
Hoods are designed for specific strengthSome hood manufacturers modifies the hood to provide strength in the top of the hood
Reduce rollAirfoil that tends to “lift” the air up
Some manufacturers provide a strong baseExceptional turning action by airfoilPiston flow in lower portion of the hood
Many manufactures design for general flow
Manufacture Recommended Tests
Higher release rate is better controlled by a hood strong at the topA lower diffuser is better controlled by a hood strong along the work surfaceBoxes and induced flow may work bit the geometry may be criticalSome tests can be self serving