Space Pressurization: Concept and Practice - ASHRAE

1 Handout 1 Space pressurization : Concept and Practice ASHRAE Distinguished Lecture SeriesJim CooganSiemens Building TechnologiesYEA Conference Specialty Environmental DesignMarch 25, 2014 Page 2 Copyright 2014. All rights ( Concept , purpose, uses, scope)Physics: Infiltration and ContainmentPressurization MethodsDesign StepsContaminant Control PerspectiveSummaryHandout 2 Page 3 Copyright 2014. All rights PressurizationA ventilation technology that controls migration of air contaminants by inducing drafts between 4 Copyright 2014. All rights PressurizationExhaust system removes airSupply system delivers lessRoom pressureis negativeInfiltration makes up the differenceInward air flow contains pollutantsHandout 3 Page 5 Copyright 2014.

2 All rights : Who uses it? Why?Biological and Chemical Laboratories prevent spread of airborne hazardsHospital Isolation Rooms protect patients and staff from germsHospital Pharmacies facilitate sterile compoundingClean Manufacturing maintain product qualityPage 6 Copyright 2014. All rights : Who else uses it?Office towers control smoke in a fire; maintain exit pathAny Building separate rest rooms from other spacesRestaurants keep kitchen smells out of the dining roomAny Building keep unconditioned OA out of occupied spacesThese uses are out of today s scopeHandout 4 Page 7 Copyright 2014. All rights is success defined?Success is control of contaminants, not flows and pressure valuesPage 8 Copyright 2014.

3 All rights and ContainmentInfiltration: mechanical processVelocity, Area, PressureInfiltration CurvesImportance of the EnvelopeSelect pressurization LevelSpecifying the EnvelopeHandout 5 Page 9 Copyright 2014. All rights Process:Pressure, Velocity, Area, FlowInfiltration is a physical processPressurization is an engineered resultASHRAE Handbook and Ventilation Manual from ACGIH model the processPage 10 Copyright 2014. All rights vs. VelocitySimple approach is to model the velocity with a discharge coefficientACGIH Industrial Ventilation: 7-3 ASHRAE Fundamentals Handbook presents more complex model, but the result is nearly the samePv' )4000( 6 Page 11 Copyright 2014. All rights Model for PressurizationAir velocity through gaps in envelope controls contaminantsVelocity related to pressure by orifice flowTransfer flow and HVAC flow difference is leak area times velocityPage 12 Copyright 2014.

4 All rights of Room Air MotionPhotograph of flow field (2D) in cross section of a room Particle Image Velocimetry Zhao L., ASHRAE Transactions, DA-07-044 Handout 7 Page 13 Copyright 2014. All rights and Leakage AreaFlow is velocity times area2011 ASHRAE Handbook HVAC Applications, puts it together: 53-9 Q = infiltration flow, cfm A = leakage area, sqft P = pressure across envelope, inwcPAQ' 2610 Page 14 Copyright 2014. All rights Curve Pressure Difference vs. Air FlowPressure DifferenceHandout 8 Page 15 Copyright 2014. All rights Curves for Several Values of Leakage Air FlowPressure DifferencePage 16 Copyright 2014. All rights of the EnvelopeLeakage area is the main mechanical parameter in the pressurization systemLike knowing the hx characteristics to apply a heating coilLike knowing the pipe diameter in a hydronic systemHandout 9 Page 17 Copyright 2014.

5 All rights pressurization LevelChoose the flow offsetLet it determine the Air FlowPressure DifferencePage 18 Copyright 2014. All rights pressurization LevelChoose the pressureLet it determine the flow Air FlowPressure DifferenceHandout 10 Page 19 Copyright 2014. All rights pressurization LevelDifferent ways to express the level of pressurization in terms of the pressure difference in terms of the infiltration flow Specify either the pressure or the flow offset, not both. Unless you are trying to specify the envelopePage 20 Copyright 2014. All rights and MigrationPositive room pressure drives air and contaminants outNegative room pressure draws air and contaminants inNeutral room pressure exchanges air and contaminants in both directionsHandout 11 Page 21 Copyright 2014.

6 All rights via HVACC ontrol Methods Explained and Compared Differential Flow Control Pressure Feedback Cascade ControlSelecting a pressurization Control Method How Tight is Tight? Required Pressure RelationshipsPage 22 Copyright 2014. All rights Methods ComparedThree widely published methods Space pressure feedback Differential flow control Cascade controlReferences: 2011 ASHRAE Handbook, HVAC 16 Laboratory Systems Siemens Building Technologies: Doc #125-2412. Room pressurization ControlHandout 12 Page 23 Copyright 2014. All rights Methods ComparedSome other ways Adaptive leakage model Trim valveReferences: W Sun, ASHRAE Transactions, NA-04-7-2. Quantitative Multistage Pressurizations in Controlled and Critical Environments L.

7 Gartner and C. Kiley, Anthology of Biosafety Room Design Issues in High ContainmentPage 24 Copyright 2014. All rights FeedbackHandout 13 Page 25 Copyright 2014. All rights FeedbackMeasure pressure differenceacross room boundaryCompare to selected setpointAdjust supply flow or exhaustto maintain pressure differencePage 26 Copyright 2014. All rights Flow ControlHandout 14 Page 27 Copyright 2014. All rights Flow ControlCarefully control air supply to roomCarefully control all exhaust from roomEnforce a difference between themSelect the size of differenceto reliably contain pollutantsPage 28 Copyright 2014. All rights ControlHandout 15 Page 29 Copyright 2014. All rights ControlHas other names: adaptive offset DP reset Measure pressure differenceacross room boundaryCompare to selected setpointControl supply and exhaust flowEnforce a difference between themDynamically adjust flow differenceto maintain the pressure setpointPage 30 Copyright 2014.

8 All rights a Control MethodFactors affecting selection Tightness of envelope Number of pressure levels needed Speed of disturbances and response Duct conditions for flow measurementReference: 2011 ASHRAE Handbook HVAC Applications, Chapter 16 - Laboratory Systems, page 16 Page 31 Copyright 2014. All rights of Envelopeoxxxxo00. Air FlowPressure DifferencePage 32 Copyright 2014. All rights of Pressure LevelsRelatively simple requirement2-levels, OK for Differential Flow TrackingHandout 17 Page 33 Copyright 2014. All rights of Pressure LevelsIndicate intended relative pressure levels+++------------------Page 34 Copyright 2014. All rights of Air Flow Errors, In and OutNominal valueErrorExhaust flow1000+/- 100 Supply flow850+/- 85 Transfer flow150+/- 185 Numerical illustrationHandout 18 Page 35 Copyright 2014.

9 All rights pressurization Air FlowPressure DifferenceOBased on leakage areaExample: 150 cfm for square footPage 36 Copyright 2014. All rights Accuracy Air FlowPressure DifferencexxOBased on need to control contaminantsNot product spec sHandout 19 Page 37 Copyright 2014. All rights Flow Control AccuracyNominal valueErrorExhaust flow1000+/- 30 Supply flow850+/- 30 Transfer flow150+/- 45 Numerical illustrationBase flow control accuracy on desired infiltrationANSI , Laboratory VentilationPage 38 Copyright 2014. All rights Flow Control AccuracyNominal valueErrorExhaust flow1000200+/- 30+/- 30 Supply flow85050+/- 30+/- 30 Transfer flow150+/- 45 Numerical illustrationConsider accuracy across range of flow valuesPressurization specs easier to meet at low flowHandout 20 Page 39 Copyright 2014.

10 All rights ( Concept , purpose, uses)9 Physics: Infiltration and Containment9 pressurization Methods9 Design StepsContaminant Control PerspectiveSummaryPage 40 Copyright 2014. All rights and Contaminant ControlTheory: net inward flow blocks contaminantsRecent research relates pressurization to contaminant control ASHRAE research relates pressure to clean room contamination: RP 1344 and RP 1399 Bio lab experiments: Bennet, Applied Biosafety, 2005 Isolation room research, Tang, et is control of contaminants, not flows and pressure valuesFact: contaminants cross boundaries for many reasonsHandout 21 Page 41 Copyright 2014. All rights s like baseballEven if the wind s blowing in, sometimes stuff gets 42 Copyright 2014.