Keeping a clean and steady flow of air is
extremely important in any enclosed environment.
This is particularly true in a laboratory
environment, where isolation and
control of all elements and potential containments
is essential. The animal caging systems discussed here were designed with
those requirements in mind.
The Air Flow Technology (AFT) department
of Allentown Caging Equipment
(Allentown, NJ) is responsible for designing
and developing a range of airflow-related
products. For over 35 years, the
company has been providing the biomedical
research community with the most
technologically advanced animal housing
systems. Recently, the AFT department
designed two products that offer improved
ventilation of the company’s P/NC
Positive/Negative Control Systems.
The P/NC system is an individually ventilated
caging system with 60–160 cages
designed to hold up to 800 mice, rats,
guinea pigs, or other rodents. These safe and
flexible environments are HEPA filtered,
and can switch from positive to negative
pressure at the press of a button, providing a
safe environment for both the animals and
laboratory personnel. These caging systems
use microprocessor-controlled supply and
exhaust blowers to provide the required
number of controlled air changes per hour.
To help ensure that the systems maintain a
stable airflow, and to measure airflow both
into and out of the cages, the AFT team
used differential pressure transducers from
Setra Systems Inc. (Boxborough, MA).
Handling the pressure
Figure 1 - The model 265 series of pressure transducers, a primary ingredient in the
SE6000 Smart Exhaust Pak. The Pak extracts dirty air from the animal cages and HEPA
filters the air before it returns to the cage.
Setra Systems offers more than 35 years of
experience in the design and manufacture
of pressure measurement systems for HVAC
control. The model 265 differential pressure
transducer (Figure 1) was a perfect fit for the AFT
team’s airflow monitoring and control needs. The
team selected the model 265, which is offered with
±0.25% accuracy (±0.4% optional and ±1% standard)
in pressure ranges from ±0.1 to 100 in. of water
column (WC). The model 265 provided the stability
and high-level output that is required for high-efficiency
air control systems.
The team considered less expensive options, but it
was determined that the model 265 offered the high
level of quality and accuracy Allentown Caging
Equipment was looking for, specifically, accuracy in
low-range applications. The instrument is a key
component in the SE6100 Smart Exhaust Pak
(Allentown Caging Equipment), the unit that is
responsible for extracting air from the P/NC system’s
animal cages. Custom-made for the P/NC system,
the Smart Exhaust Pak features a microprocessor
control board and feedback control technology to
automatically adjust the blower speed and maintain
the desired 15–50 cfm airflow as the HEPA filters
begin to load. The model 265 pressure transducer
allows the SE6100 to constantly monitor the flow of
evacuating air—air that is replete with airborne particulates
such as dander, bedding, and dust, as well as
potential pathogens.
Allentown Caging Equipment uses mass flow sensor
technology with a hot tip anemometer on its supply
blower to control the fan motor and adjust for HEPA
filter loading. The problem with using this method
for an exhaust system is that the delicate sensor
would be exposed to airborne particles. This mass
flow technology would require constant cleaning.
The particles would block the hot tip and cause the
unit to go out of calibration and greatly
detract from accuracy. The model 265
allows the company to measure and monitor
the pressure, permitting the Smart Exhaust
Pak to precisely measure and control the
P/NC system’s airflow accurately, without
the added costs of recalibration and additional
maintenance.
Easy detection
Figure 2 - The Range Finder Rack Flow and Cage Flow Detectors provide simple, fast
verification regarding acceptable airflow and air quality into animal cages. The model 265
pressure transducer provides the positive and negative pressure sensing that is required in such
a system to ensure a high-efficiency air control system.
The model 265 is also central to the company’s
Range Finder Rack Flow and Cage
Flow Detectors (Figure 2), which are also
used with the P/NC cage rack. The Range
Finder Rack Flow Detector provides supply
or exhaust air confirmation for an entire
ventilated rack, while the Cage Flow
Detector provides cage-level airflow confirmation
as low as 0.15 cfm from cage to cage.
The Range Finder products can be used
while the ventilated rack is in service and
fully populated, with no disruption to its
inhabitants. Both of these detectors utilize
Setra’s transducer technology to provide
simple, easy-to-read analogue output and
accurate pressure measurement. The model
265 transducers used in Range Finders measure
low differential pressures from 0 to ±0.25
in. WC with a high-level output accurate to
±0.4% of full scale.
Allentown Caging Equipment’s customers
need to know how much fresh air their animals
are getting in real time. The Range
Finder products with the Setra technology
provide the simple and fast verification the
company’s customers require. Verification is
easy: a green light for airflow that is within
the selected range (typically ±10%) and a
red light signifying unacceptable airflow
falling outside that range. Within seconds,
the Range Finder solutions allow users to
spot check every rack and every duct connection
in the cage system.
By taking advantage of the model 265’s precise pressure
measurement and tight tolerances, the
Allentown Caging AFT team was able to produce
easy-to-operate air measurement and control solutions
that do not require an abundance of extra parts.
As a result, the P/NC system’s environmentally
sound cage equipment ensures that the system’s residents
are not the only ones who can breathe easier.
Mr. Troyer is HVAC Product Marketing Manager, Setra Systems
Inc., 159 Swanson Rd., Boxborough, MA, U.S.A.; tel.: 978-266-3607; fax: 978-264-0292; e-mail: [email protected].