Indoor air quality (IAQ) is a high priority for Purdue
University, so much so that an IAQ team comprised of
supervisors, industrial hygienists, mechanical engineers,
and other interested staff hold monthly meetings to
discuss IAQ issues. To further this dedication to healthy
environments, Purdue recently installed Telaire carbon
dioxide (CO2) sensors to monitor and control the ventilation
in six of its largest lecture halls. Demand Controlled
Ventilation (DCV) was seen as the way to provide both
the desired air quality and to keep a rein on energy
“It is a win-win technology,” according to Luci Keazer,
Controls Systems Engineer at Purdue. “I applied for
a Venture Grant (from the physical facilities budget)
to provide a technology that would deliver the right
amount of air for the space usage”.
A coeducational, state-assisted system in Indiana, Purdue
University is one of the nation’s leading research institutions
with a reputation for excellent and affordable education.
This dual goal of excellence and affordability pervades
the institution, right down to its facilities management.
University sought a way to provide the American Society
of Heating, Refrigerating, and Air-Conditioning Engineers
(ASHRAE)-recommended ventilation rate in an economical
way. Maintaining the ASHRAE recommended ventilation
rate can be difficult and expensive with the variable
occupancy of a classroom. Using a CO2 sensor allows
ventilation to be controlled based on the actual number
of people in a classroom. The sensor is wired to the
ventilation system and automatically provides the right
amount of fresh air so students will not experience
drowsiness and headaches, which can impair productivity
as well as be uncomfortable.
According to Keazer, “The best applications are lecture
halls and classrooms. While use is pretty solid from
9 a.m. to 4 p.m., it falls off in the evening. But the
air handlers are still in the ‘occupied mode’ until
10 p.m.” This change in occupancy resulted in using
an unnecessary amount of energy to heat and humidify
air in the winter, and to cool and dehumidify air in
the summer. The university had, in fact, suffered a
shortage of chilled water provided to the cooling coils
on especially hot days.
Scope of Work
Purdue has over 100 buildings on campus with several
types of existing automation systems. The university
was looking for a CO2 sensor that did not need much
maintenance or calibration, and would work with all
the existing automation systems. After researching the
different sensors available, Purdue purchased six Telaire®
Ventostat® 8002W CO2 sensors.
The Venture Grant covered the cost of the equipment
and the associated installation costs for each of the
six locations. The installation was done by university
maintenance technicians and involved installing wiring
and power from the control panel to the equipment.
A CO2 sensor is duct-mounted in the return air duct
for each room that is being controlled. The 4-20 milliamp
(mA) output signal from the CO2 sensor is wired to the
control panel. The control panel reacts to the different
mA signals by increasing or decreasing the amount of
outside air that is brought into the room. A 4 mA signal
from the sensor tells the control panel that CO2 levels
and occupancy are low, so the control panel calls for
the minimum amount of outside air. A 20 mA signal tells
the control panel that CO2 levels and occupancy are
high. When this happens the control panel calls for
the maximum amount of fresh air. If the outside air
temperature allows for free cooling, the CO2 signal
is ignored and the maximum amount of outside air is
brought into the room.
Telaire® Ventostat® 8002W CO2 Ventilation Controller
features a five year calibration guarantee, multiple
output options, on-board programming, and is specified
for accuracy of ±50 parts per million (PPM) at 1000
PPM. The five year calibration guarantee was an important
factor in Purdue’s decision making. “We wanted to be
able to trust the equipment and not have to check it
very often,” according to Keazer.
Employees can monitor CO2 levels and students are ensured
that CO2 concentration levels remain at or below 700
PPM above the outdoor air level of 375 PPM. This reading
indicates that ventilation rates of 15 cubic feet per
minute (CFM) per person are maintained at all times,
as recommended by ASHRAE.
Benefits to owner
used energy analysis software to determine the estimated
energy savings from using the Telaire® Ventostat® 8002W.
They provided input including occupancy, room size,
and expected occupancy levels, and projected that there
would be a 50% reduction in ventilation with a cost
savings of $0.14 to $0.23 per square foot in the lecture
Keazer stated that the university doesn’t measure energy
on a room or building level, but is convinced that the
reduced need for conditioning ventilation air has provided
a 1 to 2 year payback on the equipment. “We are ventilating
adequately by demand, not by a schedule.”
Another unexpected result was noted. One sensor indicated
that there was an under-ventilated space of which the
facility management was unaware. “We added another outside
air damper as a result of the troubleshooting we were
able to do with the CO2 sensor.”
The Ventostat® 8002W sensors were installed and were
operational in the spring session of 1999. The calibration
was checked, and found to be in line with expectations.
Purdue University is completely satisfied with the sensors
that have been operational for over a year. They have
identified 10 more locations in which they plan to use
Educational institutions are finding the many reasons
for using CO2 sensors to provide both improved air quality
for employees and students and to reduce energy costs.
Most classrooms are partially empty some of the time,
full for a period of time, and empty for more than half
of the day. Sensors fit into most existing automation
systems with the addition of simple wiring.
Purdue University, like many other schools and academic
institutions, found a sensor that would reliably provide
the right amount of fresh air needed, based on the sensing
of occupancy in a room. “It was easy to install, easy
to maintain, and saved energy by not conditioning more
outside air than was necessary” is how Keazer summed
up the project. The Telaire® CO2 sensors make sense
for schools and classrooms.