12/6/101Case Study: Design of a Calibration Reference Device for ANSI/ASHRAE Standard 52.2 2007ME 4054WNovember 16, 2010T. H. KuehnDEFINE THE PROBLEMIDENTOPPDEFINE PROBLEMGEN CONCEPTSGATHER INFOIMPLEMENTSCREEN CONCEPTSHANDOFFBackgroundUNIVERSITY OF MINNESOTA12/6/102Objective as defined by the members of ASHRAE TC 2.4Develop a calibration reference device for use in ANSI/ASHRAE Standard 52.2 filter test facilities that can be replicated to serve as a check on a facility’s capability to provide the proper performance values for filters being tested.• Receive filters from each location.• Remove filter samples.• Elute filter samples in PBS by hand shaking and vortex mixing.• Use resulting eluate in molecular and culturable identification methods.Typical Ventilation System for Typical Ventilation System for a Commercial Buildinga Commercial Building12/6/103Primary performance values determined by the ASHRAE 52.2 standard method of testPressure Drop: measured in inches of water at 2000 cfm of air flowParticle Size Removal Efficiency: measured as fraction of airborne particles removed versus particle size in 12 size bins ranging from 0.3 to 10 microns (using KCl)Example Filter Test Results(ASHRAE Standard 52.2-2007 Figure D-1)12/6/104Primary Test OutputMinimum Efficiency Reporting Value (MERV)Based on average particle removal efficiency in three particle size bins: 0.3 to 1, 1 to 3, and 3 to 10 micronsRanges from 1 (low efficiency) to 16 (high efficiency)ASHRAE 52.2 Test Facility at U of MN8Schematic Diagram of ASHRAE Standard 52.2 Test Facility at the University of Minnesota Department of Mechanical Engineering12/6/105ASHRAE 52.2 Test Facility at U of MN9Photographs of ASHRAE Standard 52.2 Test Facility at the University of Minnesota Department of Mechanical EngineeringWhy this project?Filter manufacturers were receiving different MERV values for the same filters sent to different test facilities.A Calibration Reference Device was desired so that test facilities could compare their measurements to accepted values using the same device12/6/106DETERMINING CUSTOMERSProject Monitoring SubcommitteeASHRAE Technical Committee 2.4 (TC 2.4)ASHRAE Standards Committee for 52.2Operators of Filter Test Facilities that Comply with Standard 52.2Filter ManufacturersPurchasers and users of particulate air filters in buildingsIDENTOPPDEFINE PROBLEMGEN CONCEPTSGATHER INFOIMPLEMENTSCREEN CONCEPTSHANDOFFUNIVERSITY OF MINNESOTAInitial Product Design SpecificationsNumber Description Metric Desired Value1 Air flow rate cfm 450-20002 Pressure drop in. water <1.53 Particle size range µm 0.3 - 104 Particle collection efficiency MERV 105 Cost $ <10,0006 Weight lbs <507 Dimensions inches 24x24x28 Material stainless steel12/6/107CONCEPT GENERATIONOPTION 1: INERTIAL IMPACTOR 14Advantages:• Impactor theory well known, therefore easy to design• Repeatable and accurate results• Foolproof design• RobustDisadvantages:• Small nozzle sizes for low pressure drop requirement might increase manufacturing costs• Potential for solid particle bounce12/6/108Impactor Example-Respirable Cut Impactor (Marple and McCormack, 1983)1516Filters B and C Curves with Three Parallel-Flow Slit Impactor Efficiency Curves01020304050607080901000.1 1 10Minimum Efficiency CurvesFilter BFilter CImpactor TheoryParticle Size Removal Efficiency, %Particle Diameter, µm12/6/109OPTION 2: ELECTROSTATIC PRECIPITATOR (ESP) 17Advantages:• Low pressure drop• Robust• Ease of cleaningDisadvantages:• Would need to alter commercial unit design to meet requirements• Charged particles upstream of ESP may alter collection efficiency characteristics• Humidity effects may alter collection efficiency characteristicsESP Calibration Using KCl at 1,750 CFM(provided by Air Quality Engineering)Efficiency vs. Particle Diameter0204060801000 1 10Particle Diameter (µm)% Fractional Efficiency18∆P=.261” H2012/6/1010Two Reference Device Alternatives Selected Based Upon Literature Review, Further Analysis and Discussions with Committee Members1. MULTIPLE ROUND NOZZLES, PARALLEL-FLOW IMPACTOR.2. STAINLESS STEEL WIRE MESH.Impactor Design Considerations-Nozzle vs. Sharp-Edged Orifice20Flow StreamlineNumerical Model:Re = 62,000S/W = 1.0T/W = 1.0NozzleImpaction Plate Tapered Inlet12/6/1011Impactor Design Considerations-Nozzle vs. Sharp-Edged Orifice21Flow StreamlineNumerical Model:Re = 62,000S/W = 1.0T/W = 0.03OrificeImpaction Plate Change to PDSThe impactor with orifices requires 3 in. water to operate so the ASHRAE monitoring subcommittee allowed us to increase the allowable pressure drop from 1.5 to 3 in. water after consulting with a sample of test facility operators to make sure their fans could handle this increase in pressure drop.12/6/1012Impactor Design Considerations-Cross-flow Parameter23DnN/4Dc < 1.2Where: Dn is the nozzle diameterN is the number of nozzlesDc is the nozzle cluster diameter24Collection efficiency curve for five parallel-flow nozzle impactor design showing sampling points of OPC01020304050607080901000.1 1 10Parallel-FLow Impactor with Five Nozzle SizesImpactor Collection EfficiencyOPC Mean of Particle Size RangeParticle Size Removal Efficiency, %Particle Diameter, µm1.66 um Cutsize3.0 um Cutsize5.45 um Cutsize1.0 um Cutsize0.71 um Cutsize12/6/1013Scaled-Down Impactor Design-Nozzle Plate 0.030 in. ThickFabricating Holes in Nozzle Plate0.030 in. Stainless• 1. Drilling: too time consuming and expensive for over 60,000 holes for full scale unit• 2. Punching: we tried this and the material deformed, we also broke the smallest punch• 3. Chemical etching: this worked the best, different sized holes can be fabricated from a single sheet of material, hole diameter standard deviation very low12/6/1014Scaled-Down Impactor Design-Impaction PlateWire Mesh Specifications28• Start with 0.04 mm/0.07 mm stainless steel wire mesh.• Specifications based upon previous work by Palas from their presentation “Influence on Measurement of Fractional Efficiency on Test Systems in Accordance with DIN 71460-1” (provided by Bruce McDonald).• Sample obtained from G. Bopp USA, Inc. for testing.12/6/1015Wire Mesh Specifications29Wire Mesh Calibration by Palas3012/6/1016Two Small-Scale Reference Device Candidates Ready for TestingPARALLEL-FLOW IMPACTOR-ETCHEDReference Devices: SelectionSTAINLESS STEEL WIRE MESH• Generate monodisperse fluorescent particles using VOAG in the size range from