Air Volume Fume Hood Control: A Case Study
Martin J. Wendel Jr.,
P.E., and Sarla M. Patel, P.E.,
We propose to present a case study of an innovative design of
a fume hood control system that we developed, as a low first cost
method of applying an energy savings technique to laboratory fume
hood control. This design innovation combines the best features
of traditional constant volume and variable volume fume hood controls,
while avoiding some of their perceived disadvantages.
Step-Variable Air Volume Laboratory Fume
Fume hoods are critical elements in the design and operation of research and
development laboratories. Fume hoods are essential in many applications to
protect workers from exposure to chemical fumes or other hazardous substances.
At the same time, fume hoods have a significant impact on laboratory construction
costs and operating costs because of the equipment and energy required to exhaust
air through the fume hoods, and to provide conditioned ventilation air to the
One of the many important laboratory design issues associated
with fume hoods is the selection of a fume hood control strategy,
which then leads to the control strategy for overall laboratory
airflow and pressurization. Constant volume fume hood control has
been used in many laboratories for years, and is generally considered
to be a solid, reliable approach to safeguard workers. For laboratories
with large numbers of fume hoods, however, constant volume fume
hood control results in enormous energy use and operating costs,
since the same amount of air must be conditioned and exhausted
through the fume hoods whether they are in use or not (that is,
whether the fume hood sashes are open or closed). More recently,
variable volume (VAV) fume hood controls have been developed and
installed to reduce energy consumption and operating costs in fume
hood-intensive laboratories by reducing air flow through a fume
hood when the sash is closed. Many of these systems, which typically
maintain a constant fume hood face velocity to capture fumes and
protect laboratory workers, are also generally considered to be
solid, reliable systems with good track records. VAV systems though
can carry a very high first cost and, in some cases, require high
degrees of maintenance and effort to set up properly due to their
multiple control points and complexity.
The many issues associated with fume hood control strategy selection
can be quantified and analyzed in terms of performance, installed
cost, operating and maintenance costs. However, it is essential
that this system selection (and most others!) include consideration
of owner acceptance, including the scientific research community
that will use the labs and the building engineers who will maintain
the systems. The building design must be responsive to the needs
of the people who will work in the building. Sometimes, as a result
of the consideration of both human and technical requirements,
the building design professional has to think outside the constraints
of pre-packaged solutions to achieve design excellence.
This presentation discusses one example of this type of innovation,
and the benefits of the resulting system design. Our intent is
to present a case study profiling the implementation of a Step-VAV
hood control design that provides only the required amount of air
to each hood, which minimizes the capital cost (through diversity
in equipment sizing) and operating costs. The control system is
simple, reliable and easy to maintain. It utilizes constant volume
bypass hoods. The only automatic sensing requires hood sash end
switch position monitoring by the BMS, using simple proven technology.
Exhaust flow for each hood is controlled in two steps: maximum
flow when any sash is open; and minimum flow when all hood sashes
are closed. We are, in essence, combining the best features of
two of the traditional methods of fume hood control in a non-traditional
manner to offer a low cost approach to energy savings.
Martin J. Wendel Jr., PE is an Engineering
Design Principal at Kling Lindquist, a Philadelphia based Architectural-Engineering
practice. He graduated from Drexel University with a Bachelor of
Science in Mechanical Engineering and is a registered Professional
Engineer in the state of Pennsylvania.
He has over 20 years of experience in the design of high technology
facilities. He has worked for Kling Lindquist for 10 years, with
a focus on the design of mechanical systems for laboratory, pharmaceutical,
animal and biotech facilities. He is responsible for the conception
and development of MEP systems for those projects.
Martin is a member of ASHRAE and ISPE (International Society of Pharmaceutical
Engineers) and has given several presentations on facility design.
Sarla M. Patel,
PE is Senior Instrumentation Engineer at Kling Lindquist, a Philadelphia
based Architectural-Engineering practice. She graduated from University
of Michigan with a Master of Science in Electrical Engineering
and is a registered Professional Engineer in the state of Pennsylvania.
She has over 30 years of experience in the Instrumentation and
control design for high technology facilities such as Pharmaceutical
facilities and Computer Data centers. She is responsible for the
I&C system design and its reliability evaluation.
Sarla is a member of ISA (Instrument Society of America) and has given several
presentations on Instrumentation and Control design.