DIAGNOSTIC TESTING USING ASHRAE 110. Gerhard Knutson, Ph.D., CIH Knutson Ventilation, Inc

Transcription

1 DIAGNOSTIC TESTING USING ASHRAE 110 Gerhard Knutson, Ph.D., CIH Knutson Ventilation, Inc

2 ASHARE 110 A Method of Testing Three components Face velocity measurements Smoke visualization Tracer gas testing Owner sets acceptance levels The problem What do you do when the results are unacceptable?

3 General Approach Operational Problems Tracer gas leakage Reentry Hood problems Aerodynamics Operations Room Conditions Other Considerations

4 Gas Delivery System Leakage Symptoms Steady increase No reduction when gas is turned off Analysis Use meter as a leak meter Solution Stop leak Place cylinder inside hood

5 Cylinder Inside the Hood

6 Reentry Tracer gas released inside the hood Characteristics Delayed onset Tracer gas in the room Often slow decay

7 Potential Reentry

8 Room Concentration

9 Repeat with Different Wind

10 Smoke Visualization ASHRAE 110 Failure Smoke spills out Diagnostic testing Lazy air Reverse air flow Interior roll

11 Reverse Flow Reverse flow

12 Lazy Flow Lazy Flow

13 Good sweeping flow Good Sweeping Action

14 Roll in top of hood Smoke Showing the Hood Roll

15 Summary Poor flow characteristic can pass but can contribute to poor performance Repeat somke tests with mannequin Vortex formed by mannequin interacts with the weak airflow in the hood Can show spillage where not seen without the mannequin

16 Equipment in the Hood

17 Other Issues Equipment in hood Sash Position Mandates other than left, right, center Difference between use and design Heat sources or disturbances in hood Work position Operator position

18 Room Air Supply The supply ventilation design is as important (or more important than) the exhaust ventilation design Rule 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

19 Room Air Currents Cross Draft Grid & Probe Orientation Top View Horizontal Draft Vertical Perpendicular Horizontal Left Center Right Vertical Draft Stand Perpendicular Draft High Midpoint Low Front View Side View

20 Minor Room Air Currents Hood 628, Position A, 52.5 inches 100 Velocity, fpm Vertical Perpendicular Horizontal Time, Seconds

21 Significant Room Air Currents Hood 628, Position AB, 52.5 inches 100 Velocity, fpm Vertical Perpendicular Horizontal Time, seconds

22 Case History New 12-foot bench top hoods Acceptance level AI 0.05 Preliminary tests not acceptable Diagnostic testing Reverse flow at work surface High Turbulence in laboratory High Cross drafts near hood Temperature variable in laboratory

23 Original Design

24 Approach Change diffusers to reduce room air turbulence Modify airfoil on laboratory hoods Modify room temperature control Recalibrate CV supply and exhaust boxes Rewire part of Building Management System Readout matched boxes

25 Diffuser Replacement

26 Original Diffuser and Hood Hood Rating 0.45

27 Change Diffuser Hood Rating 0.03

28 Changed Diffuser Modified Airfoil Hood Rating <0.01

29 Conclusions In many instances ASHRAE 110 can be used diagnostically to determine the probable cause of poor hood performance

30 Other Test Dynamic tests Human as a mannequin Artificial clutter Walk by tests Large apparatus (walk in hoods) Floor mounted fans

31 Philosophy Provides additional information relative to robustness Often no correlation to safety Interpretation is difficult

32 Caution Hoods are designed for specific strength Some hood manufacturers modifies the hood to provide strength in the top of the hood Reduce roll Airfoil that tends to lift the air up Some manufacturers provide a strong base Exceptional turning action by airfoil Piston flow in lower portion of the hood Many manufactures design for general flow

33 Manufacture Recommended Tests Higher release rate is better controlled by a hood strong at the top A lower diffuser is better controlled by a hood strong along the work surface Boxes and induced flow may work bit the geometry may be critical Some tests can be self serving

34 Conclusion Special tests are useful and provide additional information concerning the robustness of the hood Often suggested by user but have no comparative basis Hood manufactures recommend tests that favor their hoods