Economizer Operation Based On Reference Enthalpy; Economizer Operation Based On Comparative Enthalpy; Economizers With Traq - Trane Voyager Commercial Installation, Operation And Maintenance Manual

• The modulating power exhaust actuator is a slave
to the position of the economizer damper actuator
such that the power exhaust dampers
proportionally follow or track the fresh air damper
position. The proportional offset between the
dampers is adjustable. With barometric dampers
the offset between the dampers is adjusted under
the rain hood by hole position selection of the
power exhaust actuator jack shaft on the damper
linkage arm. With direct-drive ultra-low-leak
exhaust options, the actuator stroke can be
adjusted as described in
Dampers," p. 84. The stroke limit can be set
between 33% and 100% of full stroke.
• When the Statitrac™ option is selected, the Exhaust
Blade Actuator will modulate independently to the
economizer in order the relieve positive building
pressure. If the space pressure transducer fails, the
unit will revert back to fresh air tracking control.
Economizer Operation Based on
Reference Enthalpy
Reference enthalpy is accomplished by using an
Outdoor Humidity Sensor (OHS). The reference
enthalpy is field selectable to one of five standard
enthalpies. Refer to Table 34, p. 59
potentiometer setting for each enthalpy selection.
If the outdoor air enthalpy is greater than the selected
reference enthalpy, the economizer will not operate
and the damper will not open past the minimum
position setting.
If the outdoor air enthalpy is less than the reference
enthalpy, the dampers will modulate to maintain a 45°
to 55°F minimum supply air temperature (constant
volume or variable air volume applications). The ECA
modulates the economizer dampers from minimum
position to fully open based on a 1.5°F control point
below either the space temperature setpoint for
constant volume applications or 1.5° F below the
discharge air temperature setpoint for variable air
volume applications. With reference enthalpy control,
reference enthalpy is not allowed if the outdoor
temperature is below 32°F. Below 32°F, dry bulb
economizer control is enabled.
If communications between the Outdoor Humidity
Sensor (OHS) and the Economizer Actuator Control
(ECA) were to fail, the economizer will operate using
the dry bulb parameters.
RT-SVX34R-EN
"Economizer (O/A)
for the proper
Figure 98. Humidity vs. current input
Humidity in %RH
Economizer Operation Based on
Comparative Enthalpy
Comparative enthalpy is accomplished by using an
outdoor humidity sensor (OHS), return humidity sensor
(RHS), and the return air sensor (RAS).
If the outdoor air enthalpy is greater than the return air
enthalpy, the economizer will not operate and the
damper will not open past the minimum position
setting. The economizer will not operate at outdoor air
temperatures above 75°F.
If the outdoor air enthalpy is less than the return air
enthalpy, the dampers will modulate to maintain a 45°
to 55°F supply air temperature (constant volume or
variable air volume applications). The ECA modulates
the economizer dampers from minimum position to
fully open based on a 1.5°F control point below either
the space temperature setpoint for constant volume
applications or 1.5°F around the supply air temperature
setpoint for variable air volume applications. Refer to
Figure 98, p. 109 for the Humidity versus Voltage Input
Values.
If either or both the return air humidity sensor (RHS) or
the return air sensor (RAS) fails, the economizer will
operate using the reference enthalpy setpoint
perimeters.

Economizers with Traq

OA Damper Min Position Arbitration
The Economizer Minimum Position will be controlled to
maintain outdoor air CFM at a CFM control setpoint. Air
Velocity will be measured across the Traq assembly
utilizing a pressure transducer and will be calibrated
(zeroed) against ambient pressure to correct for
changing environmental conditions.
The local Minimum OA CFM Setpoint input (or a
calculated Min OA Flow Target Setpoint from the DCV
description below) is used unless a valid BAS/Network
Minimum OA CFM Setpoint has been selected and
received in which case the BAS/Network value is used.
The BAS/Network Minimum OA CFM Setpoint, if valid,
S S e e q q u u e e n n c c e e o o f f O O p p e e r r a a t t i i o o n n
109