Lab Hoods and Exhaust Fans

Lab Hoods and Exhaust Fans
Will Rea, Paul Pilutti, and James Breckenridge
March 19st, 2012
Motivation
Why use Lab Exhaust Systems
• Vent Space
• Dilute Lab Exhaust Air
• Remove the need for high stacks
• Keep people safe
• Allow work on roof
• Move diluted air high in the air
Contents
Fundamentals
• Exhaust fan terms
• Plume Generation
Lab Controls
• Fume Hoods
Technology
• Fan Types
• Components
Application
• Installation options
Case Study
• Induced Vs. Powered Nozzles
Fundamentals
Why use Lab Exhaust Fans
Photo Courtesy of CPP, Ft. Collins, CO
• Exhaust air spilled off the roof can fall into other building
• Need to ensure the air is directed up and away from people, inlets,
open windows
Plume Creation
• Need large mass to throw up into the sky
• Essentially a ‘powered’ stack
• Moves exhaust ‘elsewhere’
hr Plume Rise
hp Plume
Height
hf Fan Height
Terms
Dilution Ratio - Plume Outlet CFM/Lab System Exhaust Flow CFM
Entrainment Air– air which is drawn from the ambient through the
nozzle
Plume height – height at which the exhaust air levels off
Briggs Equation
hr = D (v/u) / 352 where
D = exhaust diameter, v windband exhaust, u is windspeed
Nozzle velocity – Plume face velocity leaving the nozzle
Bypass air – air used to make up if hoods are shut down, or door closed
AMCA Standard 260-07
AMCA is AHRI equivalent for sheet metal HVAC products
New standard started in 2007 – chaired by Cook
Allows for certification of
- Entrainment/dilution
- Total Fan Performance
- Discharge velocity
• Only use AMCA certified fans
• Loren Cook, MK Plastics, Twin City
Greenheck, – AMCA certified
• Plasticair, Strobic – On the AMCA committee, but fans not certified
AMCA Standard 260-07
Two tests to determine inlet and induced flow
Test #1
•SP can be changed
•Lab airflow is measured
•Fan curve is generated
Test #2
•Outlet airflow is tested
•Entrainment rate is calculated
•Nozzle curve generated
Fundamental Review
• Why
• Plume creation
• Terms
• AMCA Test
Laboratory Controls
Laboratory Air Control
Containment is the key
• Primary containment – the fume hood
• Fume hood design – constant & variable volume
• Secondary containment – the lab
Primary Containment – The Fume Hood
100
FPM
150
50 FPM
Fume Hood – Constant Volume
450 CFM
250 CFM
500 CFM
250 CFM
50 CFM
CONSTANT VOLUME
HOOD
Fume Hood – Variable Volume
250 CFM
500 CFM
50 CFM
VARIABLE VOLUME
HOOD
Fume Hood – Variable Volume
Measure: Face Velocity
Control: Simple Damper
Measure: Sash Area
Control: Venturi Valve
100 FPM
Venturi Valve
Secondary Containment – The Lab
-0.03”
200 CFM
400
20 Deg C
25
50 CFM
150 CFM
350
Lab With Fume Hood
50-500 CFM
0-500 CFM
-0.03”
50 CFM
200-450 CFM
Technology
Lab Exhaust Fan
• Combines lab effluent with ambient air
• Plume is diluted with ambient air
• Creates a large mass of air
• High velocity plume rises into the air
• Traditionally needed a constant airflow
through fan to generate plume/dilution
Lab Fan Styles
Airfoil - intake
M.K. Plastics
Powered Nozzle
Loren Cook
Airfoil – Motor
Access
Twin City
Inline – Motor out of
airstream
Greenheck
Entrainment Nozzle
• Nozzle causes ambient air (green) to be drawn into the main fan
exhaust air (red)
• Two types, high plume and high efficiency
Powered Nozzle
• Powered fan instead of entrainment nozzle
• Nozzle consumes 8.61 BHP
• Removes the need for bypass air
• Allows for true VAV turndown
• Can be mounted on existing fan,
stack, or AHU
Mixing Box
• When fume hood doors are open/close they quickly change the
system and the airflow through it
• Allows for bypass air to make up difference
• Typically at the inlet to the fan
• Bypass dampers allow the lab fan to keep a constant CFM through
Technology Review
• Lab Exhaust Fans
• Styles
• Nozzles – entrainment vs. powered
• Mixing box
Application
Min Fan Height
• Recommended to have 10ft height from roof
• Allows work to be done safely next to fan
Includes mixing
box and curb.
10 Feet above
roof line.
Motor Access/Service
• Need to understand
• Motor may be accessible – right height?
• Motor may be inline with airstream
Heat Recovery
• Exception to ASHRAE 90.1 - 50% effectiveness NOT required
• Need to have sufficient seperation between intake/exhaust
• Runaround Loop Coils
• Split Heat Pipes
Innovation – Power Plume
• Lab exhaust is typically 24/7 operation
• Used to allow sufficient airflow at all times
39,327 CFM
Outlet
• Removes bypass dampers
• Maintains 50ft plume at all times
• 200% dilution ratio at max exhaust rate
• Allows for easy expansion of existing system
27,327 CFM
Power Plume
• Can turn on system in phases
• Easy to combine multiple labs together
• Power Plume nozzle generates entrainment
regardless of lab exhaust rate
12,000 CFM
Lab
Sizing Bypass Damper
• Must be able to handle all scenarios
• Size for entire airflow?
− Big and can have control problems
• Size for fan flow–lowest possible turndown? − Can have rooms turned off, project built in stages
Exhaust with an AHU
• High quality construction
• Combines heat recovery,
bypass damper, and fan, in
one package
Biggest Application in Toronto
• Forensics Building – 40+ Fans
• Power Plumes would have saved $200,000 annually
Case Study
Normal Lab Fan vs. Power Plume
• Normal fans can’t turn down
• Entrainment is less efficient than fans
• The two fan option can have less total MHP/BHP than 1 fan option
• Requires two power feeds
• Can be louder since there are two fans
Normal Lab Fan vs. Power Plume ex 2
Normal Lab Fan vs. Power Plume ex 1
Wind/Exhaust Modeling Experts
Cermak Perterka Petersen (CPP) Inc
• Fort Collins, Colorado
• www.cppwind.com
Rowan Williams Davies and Irwin Inc
• Guelph, Ontario
• www.rwdi.com
Do NOT do
• Put the discharge band less than 10ft above roof height
• Select with outlet velocity below 3000 FPM
• Mix dampers and venturi valves on one fan system
Questions?
Questions?
Next Time – April 26th, 2011
Centrifugal Separators & Water Filtration
• Open Loop Problems
• Centrifugal Filters
• Application