Brochure

3
Rooftop units are a popular application and can be seen
on the top of buildings.
Rooftop Unit issues that directly relate to the damper
actuators are seen in the Economizer or Outside Air Damper
space. An economizer is a style of damper for when the
outdoor conditions present themselves and allow for free
cooling to the unit. An example could be when there is a
current ambient temperature of 55 degrees Fahrenheit
outside, but it is still warm within the indoor space, and some
cool air is required to reach a current set-point. Instead of
running compressors to create cool air within the RTU and
have it pumped into the zone with the fan, the controller will
command the damper actuator to fully open the Economizer
or Outside Air Damper and will use the outside ambient air
instead. This is “free cooling” since there isn’t a need to have
the actual compressors working to create the cool air you
require.
The number one issue for economizer dampers is when
they aren’t functioning properly, and in most cases AT ALL.
Roughly 70% of all economizers in the field are not
functioning properly, and this is typically due to either not
being fitted with an actuator in the first place or using an
improperly sized actuator. An example of this occurred
when visiting a customer site and assisting with some
troubleshooting on a handful of rooftop units. Within a
minute of being on the roof, the technician noticed the
economizer dampers weren’t functioning on the 7.5 ton and
12 ton units that were installed at this location. It was a
brisk morning and the units could have of easily been taking
advantage of the cool ambient air. The technician found that
the actuators were improperly sized and had the incorrect
control signal for this application. An assessment of the
damper was made by estimating the torque requirement and
the technician picked a proper actuator to fit. The technician
chose a GPC actuator on the 7.5 ton unit and a GMA on the
12 ton unit, both of which are spring return style actuators
that have 24V power, modulating 2-10 control signal and
built-in positional feedback, as these are the most common
types for economizer damper control.
Properly setting up the economizer damper on the Rooftop
Unit is crucial for a building to be energy efficient since it
utilizes the cool ambient air when it is available and gives
the RTU components and equipment a much-needed rest.
Rooftop Units
(RTU)
Rooftop Units (RTU):
Contains all air conditioning components, including:
• Evaporator Coil • Fan • Compressor • Condenser
Issues found typically on RTU’s are inoperable Outside Air Dampers or Economizer Dampers:
• 70% of economizer dampers in the field are not working properly
• Typically not correctly fitted with an electric damper actuator
This can easily be solved by properly fitting the Economizer Damper with a modulating actuator (typically 2-10 Vdc)
that provides a feedback signal to the unit to notify position.
Main benefit of this would be energy savings of the RTU, by having the unit open the Economizer Damper which then
allows the fan to pull in cool, fresh air when available; instead of running the unit at full load to cool the air.