# Presentation: 280174

***Taming the Hoods***

**Dale Sartor, P.E.**
**LBNL Applications Team**
**Energy Efficiency Working Group**
**Energy 2006**
**August 2006**

## Labs21 Five BIG HITS

**Tame the hoods**
**Scrutinize the air changes**
**Drop the pressure drop**
**Get real with plug loads**
**Just say no to re-heat**

## Fume Hoods—Critical But Costly

**High Operating Cost**
*Large exhaust flows*
*High energy cost for make-up and exhaust air*
*...**Filtration*
*...**Circulation*
*...**Heating/cooling*
*...**Scrubbing*

**Fume Hoods****—****Critical But Costly**

## Standard Fume Hood Designs

**Exhaust system induces airflow through hood.**
**Airflow through hood’s open sash is ~100 FPM**
**Supply air must “make up” combined hood exhaust**
**Consequently, large air volumes are conditioned and expelled from laboratories 24/7**

## High Air Flow Impacts Other Systems 

**Typical labs**
- 4–5 times more energy intensive than typical commercial space

**Larger equipment **...chillers...boilers...fans

**Hoods “drive” lab airflow**

**Fume hoods typically operate 24 hours/day**
**Many laboratories have numerous hoods**

## =

**Fume Hood Energy Consumption**

## Higher air flow   better containment

**Note two zones of re-circulation...  **

**Idealized flow shown; user standing in front of hood increases turbulence. **
**Higher air flow  ******** ****better containment**

**Two-dimensional airflow visualization with Computational Fluid Dynamic (CFD) models.**

**Standard Hood Airflow Modeling **

## Fume hood efficiency technologies

- Reduce number and size of hoods
- Restrict sash opening
- Auxiliary air hoods
- Two “speed” occupied and un-occupied
- Variable air volume (VAV)
- High performance hoods

## 1.  Reduce the number and size of hoods

**Size distribution for ample capacity**
**Install only hoods needed immediately**
**Provide tees, valves, and pressure controls for easy additions/subtractions**
**Encourage removal of underutilized hoods**
**Consider hoods as a shared resource**

- Is this hood intensity necessary?

**Notes:**
New labs often standardize on a single hood size (increasingly larger) and install more than needed to allow for growth and flexibility (for example two per lab module).  Existing labs often have rooms needing hoods (one of the reasons new labs get so many), while many other rooms have underutilized hoods.  It is best to:

## 2.  Restrict sash openings

**Sash stops****	****	****Horizontal sashes****	****     Combination**

**Notes:**
Combination horizontal/vertical sliding sashes

## 2.  Restrict sash openings

**Vertical Sash Opening**
**Most common sash**
**Good horizontal access**
**Energy use reduced with sash stop**

**Vertical Sash Stop**

**Notes:**
In an effort to maintain 100 fpm face velocity, fume hood designs have been developed to simply reduce/restrict the sash opening and thus save air/energy.  The two most popular techniques are horizontal sash stops and sliding sashes.
Sash stops prevent the sash from opening all the way.  Usually the stops are placed at 18” thus blocking the top two fifths of the opening.  In most cases the stops are designed for easy override to lift the sash out of the way during setup.  Systems designed for the 18” opening violate Cal/OSHA standards when the sash stops are bypassed.  A corporate culture that assures bypass only when hazards are not present is needed.  Sash stops “encourage” diversity in VAV hoods (at least the hood is partially closed – 2/5ths – most of the time). 

## 2.  Restrict sash openings

**Sash Panels**

**  ****Horizontal Sash**
**Can be more energy efficient due to reduce airflow volume**
**May increase worker safety**
**Caution – sash panels can be removed; defeats safety**

**Notes:**
Horizontal sliding sashes are used to restrict the fume hood opening and protect the user.  In theory these sliding sashes cannot be opened all the way but two (or more) can overlap, creating an opening.  Users often feel the sashes get in the way and remove them (not a safe or efficient option).  Further the sashes’ sharp edges can cause turbulence.  Some companies, with strong sash management cultures, have successfully used this technique.

## 2.  Restrict sash openings

**Telescoping sash arrangement by:**

## 3.  Auxiliary air hoods

**Auxiliary Air Hood**
**Wastes energy**
**Reduces containment performance**
**Decreases worker comfort**
**Disrupts lab temperature and humidity**
**Not Recommended**

**Notes:**
Auxiliary air hoods bring tempered make-up air directly to the hoods and introduce it above the sash (above the users head).  These hoods were introduced in the 1970’s for energy efficiency.  They are still shown in manufacturers’ catalogs, however their popularity has waned due to comfort and safety issues.  Energy savings has been less than anticipated as the “tempered” air is conditioned to provide comfort.  Auxiliary air hoods are not recommended.

## 4.  Two “speed” occupied/un-occupied

**Zone Occupancy Sensor**

**Sash Sensor/Monitor**

**Notes:**
In theory, a hood that is unoccupied doesn’t need the same airflow than one with a person at or near its face.  Control companies offer an occupancy sensor based two-position control that reduces the face velocity from 100 fpm to around 60 fpm unoccupied.  These systems are often marketed as a “substitute” for VAV but they could be combined with VAV and other technologies.  There benefit is lower cost (than VAV) and they assure some savings even when the fume hood sash is left open.  Therefore, in an environment of poor sash management, they can save more energy than VAV.  Cal/OSHA is close to approving this technology, which is already in use in California  

## 5.  Variable air volume (VAV)

**...****Combination of sophisticated monitoring sensors and controls**
**How Do They Operate?**
**...****Communicate between hood and supply/exhaust systems ****...Modulate supply/exhaust systems**
**...****Maintain constant face velocity and room pressure relationships**

**5.  Variable air volume (VAV)**

**Notes:**
VAV fume hood systems control the airflow to maintain a constant face velocity.  As the sash is closed, the exhaust air volume is automatically decreased.  In a VAV system, energy savings occur when a hood’s sash is less than fully open, which reduces exhaust flow while maintaining a constant face velocity.  Each hood user must operate the sash properly to ensure that the system achieves full energy savings potential.  The VAV exhaust must be coupled with a VAV supply system to maintain required air pressure relationships in labs.  “Rightsizing” the HVAC system requires an assumption regarding the diversity of the sashes.  The most conservative designers assume all the hoods are open when sizing their equipment.  Other designers assume up to a 50% (closed) diversity depending on the number of hoods (greater the diversity is assumed with larger numbers).  

## 5.  Variable air volume (VAV)

**VAV System**

## VAV Drawbacks

**Notes:**
 The biggest problem with VAV is no energy is saved if the fume hood sashes are left wide open.  Therefore, the savings depends on the users.  Energy and safety goals are synergistic with VAV hoods – a closed hood is much safer than an open hood.

## 5.  VAV sash management

**Training and education**
**The stick**
**The carrot**
**Demand responsive sash management**
**Automated sash management**
**occupied and unoccupied set points (reset velocity set point)**
**Auto sash closure system**

**Notes:**
Any effort to encourage sashes being closed is called sash management.  This can include:  signs, pamphlets, training, incentives (e.g. monetary awards when spot checks find sashes closed), and penalties (e.g. monitoring systems that can provide information to back-charge users for individual fume hood use).  A study at Duke University showed user training improved sash management by over 30% (from 5% of the time closed to 39% of the time closed)

Demand responsive sash management (unutilized technique)
Using a variety of notification systems (PA, e-mail, and telephone) this sash management technique would alert users to peak conditions and request closure of fume hood sashes.  Users would be provided feedback via a graphical web site that shows reduction in energy, demand, and cost resulting from their action.  A large potential savings in peak cooling will occur as reductions in outside air will occur at peak outside air temperature conditions.  Also supply and exhaust fan savings are almost a cubed function (small reduction in flow yields large reduction in energy).  This technique is ripe for demonstration.
Occupied and unoccupied set points
The two “speed” technology described above can be applied to VAV such that the velocity set point can be reset when the hood is “unoccupied.”  Savings would accrue as a result of both the hood being unoccupied as well as the sash being closed or partially closed.  This concept is not widely used, but soon will be legal in California  

## 5.  VAV sash management

**New-Tech Automatic Sash Positioning System**

**Notes:**
In response to poor sash management, several companies have introduced automated sash closure systems.  Market penetration has been slow.  Reports of problems in early installations (there are no known installations in California) have reinforced general concerns about the technology (e.g. what if it closes or opens when you don’t want it to).  A product, recently displayed at Labs21 and now represented on the west coast, seems to overcome the barriers and concerns.  This product is ripe for demonstration and third party evaluation.  An auto sash closure system coupled with a VAV fume hood control system will come very close to meeting the end state goals since most hoods are “occupied” only a few hours a week.  Much higher diversity assumptions could be made with such a system, potentially reducing first cost. 

## 6.  High Performance Hoods

**Different Approaches to Maximizing Effective Containment **
**Does the Low Flow / Low Velocity Hood provide:**
**Energy-efficient operation?**
**Equivalent or Better Containment at Reduced Face Velocities and Flow Volumes?**
**Improved performance for all users, even under misuse conditions?**
**More Robust and Less Susceptible to External Factors? **
**Better Monitoring and Flow Control?**
**	****	****If so... =  High Performance Hood**

## 6.  High Performance Hoods

**Improved Performance Through Better Design...**
**Aerodynamic Entry**
**Directed Air Supply**
**Perforated or Slotted Rear Baffle **
**Airfoil Sill and Sash Handle**
**Integrated Monitors **
**Interior Dimensions **
**First Generation:  20 to 40% savings**
**Second Generation:  40 to 75% savings**

**Notes:**
First generation (20 to 40% savings)
High performance fume hoods by Air Sentry and Labconco (representative)Several high performance hoods (safe and low flow) are on the market (outside of California).  They offer advantage (over VAV) of simplicity (generally constant volume), lower peak requirements, safety, and the ability to downsize the mechanical/electrical systems (no diversity assumptions required).  There is a major institutional barrier to high performance hoods in California where Cal/OSHA requires hoods to have 100 ft/min face velocity. 

## 6.  High Performance Hoods

**Current fabricators...**
**Lab Crafters**
**Labconco**
**Fisher Hamilton**
**Kewaunee Scientific**
**Laboratory Equipment Manufacturers**
**Esco Global**
**Others**

## 6.  High Performance Hoods

**Lab Crafters Air Sentry HPFH**
**Upper chamber Turning Vane **
**Aerodynamic Sash Frame**
**Side Post Airfoils**
**Multi-Slot Front Airfoil**

**Notes:**
The first low flow product was introduced to the market by Lab Crafters, Inc.  They named it the Air Sentry fume hood.   
The design is one for which the engineers choose to control the naturally forming vortex (the roll) of air which establishes itself in the upper region of all vertical rising sash fume hoods.   The speed of this roll, which the manufacturer refers to as the “bi-stable vortex,” is monitored using a proprietary sensing system called the VFV Control System.   As the sash is raised or lowered the speed or strength of the roll varies.  The premise of this design is that allowing the vortex to diminish (slow down) will cause the hood to loose containment.  To prevent this from occurring a set of modulating dampers in the rear of the hood continuously open or close at the demand of the VFV Control System.  Another feature of this hood, which probably aids in performance, is the increased depth.  It is about 9” deeper than previous standard models.  This hood is a constant volume bypass hood but not intended for use in conjunction with VAV applications.  To the contrary, a big selling point since the fume hoods cost more that standard hoods, is making VAV controls unnecessary by returning to CAV design.

## 6.  High Performance Hoods

**Labconco XStream Hood**

**Modified Aerodynamic Sash Pull**

**Modified Baffle ****and Slots**

**Aerodynamic** **Airfoil**

## 6.  High Performance Hoods

**	****Fisher Hamilton PIONEER**
**Automatic sash closer**
**Directed supply flow @ full open sash **
**Flush Airfoil Sill**

**Notes:**
A uniquely different approach to reducing face velocity was that pursued by the engineers at Fisher Hamilton.  The resulting product was named the Pioneer. 
Once again a small supply air fan slightly pressurizes a plenum above the sash.  The subtle difference when comparing this design to the design of the LBNL team is where the air is introduced for capture by the exhaust.  In the LBNL hood the air is introduced at the plane of the sash.  In the Fisher Hamilton design the air is introduced exterior to the fume hood in a plane slightly in front of the sash.  A small downward laminar flow of air purges the lab technicians breathing zone; similar to the old auxiliary air hood. 
Of significant importance; two facts, the air supply is conditioned lab air and the flow is imperceptible to the hood user.  Thus, eliminating the unacceptable effects of unconditioned outside air on the operator and the science.  Another important point to make is the flow of air is activated only when the sash is raised above the 18” operating position.  It makes good sense since this is the critical time when contaminants could escape.  When the Pioneer sash is raised the airflow and the sash position alarms indicate an unsafe condition. The sash can be locked in setup position but automatically returns to the recommended maximum operation height when the lock is released during use.  This is a very nice feature in facilities where sash management disciplines are difficult to enforce; like student teaching applications. 

## 6.  High Performance Hoods

**	****Berkeley Hood by LBNL**
**Push/Pull Air Divider Technique**
**Perimeter Air Supply**
**Perforated Rear Baffle**
**Slot Exhaust & Optimized Upper Chamber**
**Designed to minimize escape by reducing reverse flow**
**Reduces air flow 50-75%**

**Notes:**
The people at Lawrence Berkeley National Labs in California have produced another fume hood using a push-pull approach. Low volume air fans deliver conditioned lab air, supplying inside and outside plenums above the sash and supplying a perforated air foil below.  That is the push.  The pull is supplied by the standard exhaust fan sized to draw the appropriate amount of air. Both smoke and containment testing indicate superior performance and containment in compliance with the ASHRAE-110 procedures.  LBNL has entered into a licensing agreement with a manufacturer to produce this hood and expect to have it available in 2007.  This design represented the second generation approach to low-flow.

## What Makes These Fume Hoods Superior to the Manufacturer’s Standard Product Offerings? 

- CONTAINMENT & EFFICIENCY !

**6.  High Performance Hoods**

**Notes:**
At the same face velocity, these hoods exhibit superior air flow characteristics and improved containment..  At lower face velocities, they are able to pass ASHRAE-110-1995 down to 60FPM and lower.

## A Revolutionary New Technology

**The Berkeley High-Performance Fume Hood**

**A Revolutionary New Technology**

## Context of the Berkeley Hood

***Industry Issues/Planning****...Roadmaps for Labs, Cleanrooms, and Datacenters of the Future*
***Technology****...Fume Hood Containment*
***Design Tools****...Design Guides, Airflow Design, Design Intent Tool*
***Information Technologies****... Energy-Performance Benchmarking*

**Context of the Berkeley Hood**

## Objective

**	****Reduce fume hood air flow requirements at least 50% while improving user safety**

## Supporters

**U.S. Department of Energy**

**California Institute for Energy Efficiency**

**California Energy Commission**

**Supporters**

**Montana** **State University**

**San Diego Gas and Electric**

## Partners

**Labconco**

**Siemens Controls**

**University of California, San Francisco**

**Tek-Air**

**Partners**

**Fisher-Hamilton**

**San Diego State University**

## “Push-Pull” Design

**“****Push-Pull” Design**
**Small fans at top and bottom**
**Low-turbulence intensity**
**Displacement ventilation**
**Creates an air divider separating hood interior from exterior**
**Push-pull improves containment**
**U.S. Patents # 6,089,970, # 6,428,408**

**The Invention**

## Benefits

**Enhances worker safety**
**Simpler design than VAV systems****...Easier and less-expensive installations**
**Constant volume operation****...Energy savings not dependant on operator**
**Clean air flows into operator’s breathing zone****...Reduces potential hazards**
**Airflow patterns reduce eddies and vortices****...Improving containment**

**Benefits**

## Extensive Testing

**ASHRAE 110-1995 tracer gas containment**
**Large and small volume smoke**
**Sash-movement effect tests**
**Dry Ice tests**
**Different SF6 flow rates**
**Various mannequin heights**
**Cluttered hood interior**
**Helium Bubbles**
**Schlieren flow studies**
**Envelope testing**
**Expert evaluations**
**New SF6 ejector designs**
**Cross drafts**

## Laboratory Fume Hood Testing for Safety

**Ejector: **
**	****8L/min.**

**Exhaust: **
**	****40% “normal” flow**

**Breathing Zone: **
**	****18 inches**

**Laboratory Fume Hood Testing for Safety**

## Smoke containment...

**Smoke visualization test at 30% “normal” flow**

**Laboratory Fume Hood Testing for Safety**

## Montana State University

**Adapted standard Fisher-Hamilton hood**
**Installed Berkeley hood September 2000**
**Passed standard ASHRAE 110 tests per ANSI Z9.5 recommendations**

***Fisher-Hamilton alpha prototype Berkeley Hood.***

## University of California, San Francisco

**Adapted standard Labconco hood**
**Installed Berkeley hood November 2000**
**Passed standard ASHRAE 110 tests per ANSI Z9.5 recommendations**

***Researcher working at Berkeley hood.***

## San Diego State University

**Adapted standard Labconco hood**
**Passed standard ASHRAE 110 tests per ANSI Z9.5 recommendations**
**Performed advanced challenges including cross drafts**
** ****Evaluated experimental tracer gas devices**
**Three experts and inventor contributed**

***Berkeley hood in testing and ready for shipping.***

## Prototype Work

## High Performance Fume Hood Status

**Patents issued**
**Field tests completed**
**Scaled up to six foot**
**Licensed to Esco Global**

**Next Steps**

**Refine production models**
**Overcome institutional  barriers**

**High Performance Fume Hood Status**

## Installation Options/Opportunities

**New Construction**
**Specify in place of standard hood**
**Cost premium expected, but can be offset with**...smaller fans and central plants...simpler controls

**Installation Options/Opportunities**

**Retrofit**
**Replace existing hoods**
**Labs “starved for air” can: **...Regain air flow capacity...Add new hoods...Improve exhaust performance

## Good Fume Hood Design Practice

**Choose an efficient device...**
**VAV and high performance hoods provide additional benefits**
**Consider location and air management...**
**Locate hood away from traffic flow**
**Flow clean air to dirty **
**Supply air temperature and air change rate can impact hood performance**
**Diffuser type and air “throw” impact hood performance**
**Require full ANSI/ASHRAE 110 testing as installed...**
**Tracer gas containment****  **
**Fully commission fume hood systems and room pressure controls...**

## Resource...

- _[http://fumehoodcalculator.lbl.gov/](http://fumehoodcalculator.lbl.gov/)__ _

**Fume Hood Energy Calculator****:**** **

**Resource...**

**The calculator can be used to test the energy and cost impacts of improving component efficiencies (e.g. fans or space conditioning equipment), modifying face velocities, and varying energy prices.  Supply air set points can be varied, as can the type of reheat energy.  Several hundred weather locations around the world are available.  The calculator allows for an instantaneous comparison of two scenarios.**

## Design Considerations

**Anticipate user interface...!**

## Design Considerations

**Know the operating limitations!**

## Dale Sartor, P.E.

- Lawrence Berkeley National Laboratory
- Applications Team
- MS 90-3011
- University of California
- Berkeley, CA 94720
- _[DASartor@LBL.gov](mailto:DASartor@LBL.gov)_
- (510) 486-5988
- http://Ateam.LBL.gov

**Contact Information:**