Economizer Operation Based On Reference Enthalpy; Economizer Operation Based On Comparative Enthalpy - Trane Voyager Commercial Installation & Operation Manual

Sequence of Operation
3. The modulating power exhaust actuator is a slave to the position of the economizer damper
4. When the Statitrac™ option is selected, the Exhaust Blade Actuator will modulate

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
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.
Figure 55. Humidity vs. Current Input

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
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one stop on each side of each damper. The practical range of blade position control is between
1.5" and 4.0" blade opening. The damper is wide-open at 4.0". The stops on each side of a
damper must be in the same position, such that the damper blade connecting member contacts
the stops at the same time.
actuator such that the power exhaust dampers proportionally follow or track the fresh air
damper position. The proportional 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.
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.
Table 22, p. 64 for the proper
RT-SVX34C-EN