trends in lab design - airflow requirements

8/10/2019 Trends in Lab Design - Airflow Requirements

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Trends in Laboratory Design

J. Patrick Carpenter, PE

Convergence

Airflow RequirementsAirflows:

Evolution of Impactsof Designing for

Historical PerspectiveHistorical Perspective

VERY early Hoods and Less than safe practices

What Are Laboratory Facilities ?What Are Laboratory Facilities ?

Places of Risk

Sources of Contamination

Places of Uncertainty

How does the degree of each element vary among lab types?

How does or should the variation impact the design criteria?


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SafetySafety

Risks / Hazard Assessments Materials, Activities

Codes and Standards Technologies

Need a Comprehensive Hazard Assessment

Codes, Regulations and StandardsCodes, Regulations and Standards

OSHA 29 CFR 1910.1450 Occupational Exposure to Hazardous

(1990-1996) Chemicals in LabsANSI Z 9.2 (2001) Local Exhaust Ventilation Systems

Z 9.5 (2003) Laboratory Ventilation

NFPA 45 (2004) Fire Protection for Labs Using Chemicals

ICC/IMC 510 (2003) Hazardous Exhaust Systems

ASHRAE 62.1/.2 (2004) Ventilation for Acceptable Indoor Air Quality90.1 (2004) Energy Standards for Buildings110 (2007?) MOT Performance of Lab Fume Hoods

NSF 49 (2004) Class II (Laminar Flow) Biosafety Cabinetry

SEFA 1 (2006) Lab Fume Hoods Recommended PracticesASHRAE (2002) Laboratory Design Guide

LBNL Design Guide for Energy-Efficient Research Laboratories

Building and Operating Codes and RegulationsBuilding and Operating Codes and Regulations

American

National

Standard

For

Laboratory

Ventilation

A

IH

A

2003

ASHRAE Ventilation, Energy, Fume Hood PerformanceASHRAE Ventilation, Energy, Fume Hood Performance

2001


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How Can Material Storage Practices be used to Minimize RisksHow Can Material Storage Practices be used to Minimize RisksHow can they help Reduce Resulting Airflows?How can they help Reduce Resulting Airflows?

Primary Issues in Laboratory EnvironmentsPrimary Issues in Laboratory Environments

People Issues

Comfort Personal! Safety Health & Welfare Specific NOT generic

Security Natural, Accidental and Intentional Events

Process Issues

Environmental Control

Contamination Control

Product Integrity

Qualitative Issues Reliability

Flexibility

Efficiency

Basic Parameters that Dictate RiskBasic Parameters that Dictate Risk

Materials Used

Type / Form (solid, liquid, gas pressures?)

Quantity

Dispensing / Handling

Activities

Demonstration

Teaching

Research

Unknown

Occupants Building Code Occupancy Class plus

Density

Knowledgeable

Independent or Supervised

Schedule (Intermittent or Continuous occupancy?)

Basic Design Considerations for OccupantsBasic Design Considerations for Occupants

Safety / Health

Exposure (to Hazardous Materials)

Local Containment Fume Hoods, BSCs, snorkels, etc.

Room Containment and/or Isolation

Dilution and mixing effectiveness

Transport Dispersion

Security

Fire


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Contamination Control Achieved byContamination Control Achieved by

Elimination

Intake & Exhaust Locations Materials

Maintenance Accessibility

Removal

Air Flows in Rooms

Methods of Capture

Methods of Treatment Maintenance

Dilution

Air Volumes

Source of Make-up

Room Air Distribution Mixing

Isolation

Physical vs. Airflow

Types Direct / Reverse / Mutual

Relative Pressures Differentials Control

Closed / Sealed Systems

CONTAMINATION

Basic Design Considerations for OccupantsBasic Design Considerations for Occupants

Comfort

Temperature Relative Humidity

Air Motion

Trends in Laboratory Design Convergence in Airflows

Balancing the Key Drivers to Airflows in LabBalancing the Key Drivers to Airflows in Lab

Contamination Control through Dilution

Contamination Removal through Exhaust

Environmental Control through Cooling (and Heating)

CONVERGENCE = approaching a LIMIT!

Coming Together!


Evolution of Dilution RequirementsEvolution of Dilution Requirements

Early approaches influenced by lack of Fume Hoods ortheir poor performance

Before advent of A/C, lab had no supply concept onlya source of make-up air through doors or windows

As FHs became standard, ways to ascertain theireffectiveness established exhaust airflow benchmarks

Performance of FHs shown to be influenced by supplyconcepts indirectly drove distribution concepts but withoutscientific basis to optimize approaches

Room ventilation without scientific basis standards andguidelines gave no directed guidance only generalizations

Evolution of dilution concepts, mixing effectiveness andCFD modeling improved understanding of airflow conceptsin rooms. Move towards effectiveness concepts.


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Evolution of Room Airflows for CoolingEvolution of Room Airflows for Cooling

EquipmentLoadDensityWatt/sf

TotalCoolingDensityWatt/sf

ResultingCoolingAirflowsCFM/sf

ResultingExhaustAirflowsCFM/sf

10 14 3+ 3.5+

15 19 4+ 4.5+

20 24 5+ 5.5+

4-8 6-10 1.3-2.2 1.7-2.6


Evolution of Airflows for Exhaust Make-upEvolution of Airflows for Exhaust Make-up

Initially driven by Fume Hood Design concepts

Baffling options Impact of exhaust connection configuration

Bypass concepts to stabilize velocities

Airfoil inlet improvements

Exploding research increases fume hood & Exhaust Air

Densities

Sizes

Sash openings

Fume Hood performance research and testing standardsstabilize and focus design directions on concepts

Excess face velocities loose favor

Impacts of room conditions increase focus on supply airconcepts in space



Energy Issues drive alternatives

Auxiliary air concepts later shown as wrong move

Combination Sash concepts lower effective sash areasand resulting airflows

Consideration of alternate criteria for set-up modes

VAV/diversity concepts improve options for right-sizing

Improved inlet conditions and Reduced sash areas

Sash closing concepts to reduce opening and flows

Industry Guidelines (esp. Z-9.5) shift focus to verifiedperformance based concept for hoods instead of just FV

Expanding use of Fume Hood Performance Testing createsbetter understanding of external influences on Hood



Maturity & increasing acceptance of VAV concepts leads to:

Improved methods to detect fume hood face velocity on areal time basis aid in user feedback

Concerns about response times of control systems

User presence or in use detection allows reset of fumehood airflows for changing face velocities

Evolution of testing protocols to address dynamics

Other refinements in Fume Hood design evolve from moresophisticated performance testing:

Impacts of Vortex concepts in Hoods

Importance of Hood depth on overall containment

Sensitivity to Cross currents and Turbulence

Evolution of High Performance hoods lower Face Velocity


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Mainstream acceptance of VAV concepts reinforces value

in manifolded systems because of Opportunity to take advantage of diversity

Ability to improve reliability with partial redundancy

Ability to improve reliability with emergency power

Ability to improve overall dilution and dispersion

EH&S develop better appreciation for advantages

Codes, esp. fire, create conflicting perspectives forcing

compromise definition of lab scale use of materials Duct, shaft and dampering concepts still somewhat in flux

because of differing opinions and interpretations by AHJs

Uncertainty limits some applications of manifolding


Evolution of Room Airflows for Exhaust (6 FT hoods)Evolution of Room Airflows for Exhaust (6 FT hoods)

Sash DimensionsWidth x Height

Sash

AreaSF

Face

VelocityFPM

Exhaust

AirflowsCFM

62 x 30 12.9 100 1300

62 x 18 7.7 100 775

62 x 30 12.9 60 775

2 @ 16 x 30 6.7 100 670

62 x 18 7.7 80 620

62 x 18 7.7 60 465



Impacts of Hood Exhaust Airflows at current minimums

6 Ft hood w/ lower face velocity & sash area < 500 CFM!

Assuming one FH per (2) 250 SF modules = < 1.0 CFM / sf

Actual Exhaust flow of 0.9 CFM/SF ~ 6 ACPH (9 ceiling)

Well below most occupied standards for ACPH

Provides about 0.7 CFM/SF for supply with balance fromtransfer into room (negatively pressurized lab!)

Results in less than 3. 5 watts/SF cooling!

Dilution and Cooling now dominate airflows!

With unoccupied ACPH at 4.0, Hood has little turn-down!

Even at twice the density (1 hood / module), 12 ACPHexhaust => 10.5 ACPH supply = 7 watts cooling capacity!


Other ConsiderationsOther Considerations

Current FH Exhaust minimums for LEL control requireabout 250-300 CFM for 6 Ft hood depending on depth

This only allows FH turndown of about 50%!

Are there options to monitor this and allow furtherreductions under most normal conditions?


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trends in lab design - airflow requirements

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