All4 inc awma re-entrainment

2 Your environmental compliance is clearly our business.

Agenda

Introduction

Methodology

Case Study

AIR QUALITY MODELING


What is entrainment?

An atmospheric event that occurs when suspended particles or compounds that are exhausted in a plume are carried back into a plume of air

Introduction


Re-Entrainment

Emissions source(ex: Emergency Generator, Hot Water Boiler, Combined Heat and Power Unit)

Exhaust from emissions source containing CO, NOX, SO2, VOC, etc.

Rooftop mounted air handling unit or fresh air intake

Potential location for exhaust plume

to be entrained into the building

through an intake

Pollutants in plume can become re-entrained due to effects of buildings


Not traditionally required under Federal or state air quality regulation

• American Society of Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE) or Indoor Air Quality (IAQ) guidelines

Prompted by either a consideration during the designphase of a capital project or in response to comments about odor in an existing facility

Who Cares?

• Especially for healthcare facilities, where the same people may occupy them 24-hours per day and for extended periods of time.

• Sensitive populations in a concentrated area (ex. patients, students)


Utilize air quality modeling to predict the concentration of pollutants of concern at air intakes around a facility

Compare the predicted concentrations with published health guidelines

• National Ambient Air Quality Standards (NAAQS)

• Occupational Safety and Health Administration (OSHA)

• American Conference of Governmental Industrial Hygienists (ACGIH)

• National Institute for Occupational Safety and Health (NIOSH)

The How


Methodology

U.S. EPA’s AERMOD

• Allows the user to input building dimensions and tiers to account for building downwash

• Receptors can be set at flagpole heights to represent air intake locations

• Model single sources and the combination of multiple sources

• Meteorological data is readily available through the National Weather Service (NWS) online to process


Emissions sources – point sources, stack parameters

Buildings – dimensions, height, tiers

Receptors – air intake locations

Develop emissions rates – either manufacture guarantees or utilize published emissions factors

Model Inputs


1-hour and 8-hour maximum modeled concentrations at receptors (intakes)

Apply screening factor to 1-hour concentrations to evaluate 15-minute averaging periods

Compare results with published health guidelines

Refine model

• Apply NOX refinements (ARM, ARM2)

• Raise stack heights or change stack locations

Model Outputs


New hospital

Central utility plant

▪ 2 emergency generators (ULSD)

▪ 2 domestic hot water heaters (natural gas)

▪ 1 steam boiler (natural gas)

▪ 3 hot water boilers (natural gas with propane back-up)

7 air intake locations

Case Study


Modeled sources at full capacity, operating simultaneously at worst-case conditions

Modeled concentrations of CO resulted in no exceedances of health guidelines or NAAQS

Modeled concentrations of NOX resulted in exceedances

• Design phase, change configuration:

• (1) with the stacks closest to the building [problem]

• (2) with the stacks farther from the building (i.e., turning the equipment to face away from the building) [no problem]

The Strategy – Part 1


Engineering company did not want to change configuration, so….

NOX refinements – utilize Ambient Ratio Method (ARM)

• Refine amount of NOX emitted that is converted to NO2

Modeling iterations:

• 2 EGENs @ 100% load

• 1 EGEN @ 100% load



The Strategy – Part 2


Other Considerations

Debug options in AERMOD to evaluate how plume is being affected by building downwash

Evaluate travel time of plume to receptor (intake) locations for understand NOX conversion rate

Wind tunnel modeling – comprehensive but expensive


Other Considerations

All4 inc awma re-entrainment

Environment

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