LaboratoryDesign|MAY|JUNE 2018 21
which cannot be matched by valves
requiring flow measurement (e.g., VAV
boxes and other alternatives) due to
inherent signal latency between the flow
sensor, controller and actuator.
• Mechanical pressure independence,
which instantly maintains flow—even with
constant changes in static pressure—so
that a stable, reliable amount of directional
airflow is not compromised. No movement
of the actuator is needed, thereby extending the life of the entire assembly.
• Factory characterized flow metering
technology that provides higher turndowns to achieve a number of stable, accurate room pressure states. The cone assembly quickly moves into position to achieve
the flow set point vs. having to measure and
find its position.
• Volumetric offset guarantees directional airflow. Zone balance controls
for some venturi valves track each other,
maintaining a design offset between
supply and total exhaust to ensure directional pressure in the space.
Higher turndown ratios mean the
device has a wider range over which it can
accurately provide the correct airflow.
With this improved accuracy, labs can
better manage ventilation and maintain
air pressure relationships for worker safety
and research/testing/production integrity,
regardless of room state (occupied,
unoccupied or purge condition).
WHAT ABOUT ENERGY COSTS?
While lab managers and designers
usually prioritize safety as job one in their
facilities, they also care about reducing
energy consumption where possible.
To reduce energy consumption in the
HVAC system, it is important to consider airflow. For example, to flow 1,000
cubic feet per minute (CFM) of air into
a lab space, the facility designers could
specify a 10-inch VAV terminal box or a
10-inch venturi valve. Based on the physics
underlying the two valve types, a venturi
valve can accurately exhaust as little as
50 CFM, compared to a minimum 250
CFM required from a VAV terminal box.
Because a lab typically requires dozens of
air control devices or more (depending on
its size), and it costs a handful of dollars to
vent each CFM, the energy cost difference
between venturi valves and VAV boxes is
substantial. Thus, to save energy while still
also ensuring worker safety, venturi valves,
are an excellent alternative to VAV boxes
and other traditional airflow controls.
BE SURE TO WATCH OUT FOR THE
“LOW PRESSURE MYTH”
In light of the above benefits of venturi valves, some manufacturers of traditional valves attempt to promote their
products’ energy saving potential using
a dubious premise. Such manufacturers
tell customers their valves can control
air at ultra-low pressure (0.1 inches of
water column—wc). They contend this
allows lab operators to turn down the
building’s HVAC fans to save energy.
But falling for this “low pressure myth”
won’t get you any energy savings and can
compromise safety in labs.
If you look closely at these manufacturer’s product data sheets, you’ll see
the reported operating values are for
situations virtually never seen in the
real world. It appears they test their air
terminal devices in the wide-open position at low pressure, and claim sufficient
airflow control. Yet, by definition controlling airflow requires some level of
impediment to the airstream, and typically differential pressure of 0.5 inches
wc, not 0.1 inches wc. As a result, operating a lab’s ventilation system at ultra-low
pressure could lead to inadequate ven-tilation/build-up of airborne hazards—
and injury or death for lab workers.
In addition to higher-than-necessary
energy consumption costs, a traditional
airflow control system using VAV boxes
incurs high maintenance costs. If not
properly maintained, VAV boxes can accu-
mulate lint on their sensors, which can
result in poor airflow control that reduces
lab worker safety. In a facility with 500
traditional VAV terminal boxes, annual
cleaning costs are on the order of $50,000
to $100,000. The design of venturi valves
eliminates this problem and the cost and
hassle of regular cleaning.
While thousands of labs around the
world continue to operate fine using traditional airflow controls, for enhanced safety and energy savings—as well as reduced
valve maintenance—venturi valves offer
a higher-performance alternative. Many
HVAC system engineers throughout
North America can discuss in detail ways
to optimize airflow control using these
valves and sophisticated building automation systems (BAS).
Dave Rausch is the market manager
for Phoenix Controls. He has more than
20 years of experience in the building
industry, including engineering and
product management roles in airflow
controls and fire suppression systems.
VAV terminal box sensors can become fouled due to build-up of lint. Image: Phoenix Controls