Barriers to and Taking Advantage of Manifold Exhaust Systems
Industrial Design and Construction (IDC)
In my experience designing high performance laboratories, I have
encountered various obstacles, yet have recognized many opportunities
in the design of manifold laboratory exhaust systems. My objective
is to promote the design of manifold exhaust systems by highlighting
advantages and discrediting drawbacks associated with such systems.
I will identify apparent barriers to the design of manifold laboratory
exhaust systems such as code restrictions, cost implications, and
functional limitations and suggest means of overcoming these barriers.
I will also identify advantages of manifold systems including opportunity
for energy recovery, reduced maintenance, inherent redundancy, and
energy efficient control of exhaust stack discharge velocity.
I will give the engineer confidence in designing manifold exhaust
systems insofar as code compliance, functional reliability, and
innovative design strategies.
1. While the International Mechanical Code classifies laboratory
fume hood exhaust as a hazardous exhaust system, the exhaust fumes
are not necessarily classified as flammable as defined by the Code.
Exhaust fumes are considered flammable when they exceed 25% of their
Lower Flammability Limit (LFL). It can be proven that the most critical
chemical fumes exiting a fume hood, even in a minimum flow condition,
are diluted to a concentration well below that which qualifies them
2. By employing a manifold exhaust discharge arrangement with on/off
control dampers installed in multiple stacks, a minimum exhaust
stack discharge velocity can be maintained without imposing a false
load on the system, characteristic of Strobic fans, thus saving
3. A manifold exhaust system allows the convenient use of an energy
recovery system. A research laboratory uses a large amount of outside
air and therefore must exhaust air at nearly the same rate in order
to maintain desirable pressures within the building. By using a
manifold exhaust arrangement, the energy recovery system including
coils, piping, etc. can be simplified.
The design strategies addressed in this presentation offer credit
opportunities in the "Energy and Atmosphere" and "Innovation
in Design" categories of the LEEDTM certification process and
reflect many aspects of the Lab21 approach.
Adopt Energy and Environmental Performance
A manifold exhaust system typically employs two, three or four central
exhaust fans with N+1 redundancy. These fans would be part of a
variable air volume lab exhaust/supply system and would be controlled
with variable frequency drives (VFDs) offering energy savings at
low utilization. Since outside air conditioning and conveying represent
a large percentage of a laboratory's total energy consumption, this
strategy can have a significant impact on optimizing the energy
performance of a lab.
Assess Opportunities From a "Whole Buildings"
Integrating a manifold exhaust system into a high performance lab
design offers the opportunity for other energy saving strategies
such as energy recovery and a discharge damper control system as
Use Lifecycle Cost Decision-Making
A manifold exhaust system in itself may not provide an attractive
payback; however, by "bundling" upgrades such as described
above, the overall payback period can be significantly reduced.
This aspect of the Labs21 Approach exhibits synergy with the "Whole
Employ a Broad Range of Sustainable Energy
and Water Efficiency Strategies
A manifold exhaust system designed with a variable air volume lab
exhaust/supply system can optimize energy efficiency and provide
initial cost savings with the reduced number of exhaust fans and
VFDs. Also, as described above, a manifold exhaust system offers
a design opportunity for various methods of energy recovery.
Lee Chapman graduated
from Clemson University with a BS Degree in Mechanical Engineering.
I am a registered professional mechanical engineer employed by Industrial
Design and Construction (IDC) in Greenville, SC. I have 10 years
experience in mechanical design for commercial and industrial buildings
including churches, hospitals, libraries, universities, pharmaceutical
labs and manufacturing plants. The last three years of my career
have been primarily involved in cleanroom design for the microelectronics
industry. Most recently I performed lead design responsibilities
for the Clemson University Advanced Materials Research Laboratory,
a 110,000 square foot facility consisting of physical wet labs,
laser labs, instrument labs, electron microscope labs, and lab and
administrative offices. This building was designed in pursuit of
LEEDTM silver certification and is currently registered with the
USGBC. I am currently studying to take the exam to become a LEEDTM