Economizing - Trane Tracer AH540 Setup And Operation

Chapter 4 Sequence of operation
58
If ventilation is not a concern, the Tracer AH540/541 controller can be
configured for mixed-air temperature control when preheat capacity is
available. Mixed-air preheat control is the best choice for preheat air-han-
dling units with ventilation requirements.
Mixed-air temperature sensor location
It is important to mount the mixed-air temperature sensor in the proper
location according to the mixed-air temperature control configuration (see
Table 22).
Table 22. Mixed-air temperature sensor location
Mixed-air temperature control
configuration selected
Mixed-air temperature control
Mixed-air preheat control

Economizing

This sequence applies to both space temperature control and discharge
air temperature control.
Economizing is a mode in which outdoor air is used as a source of cooling
capacity before hydronic cooling. With a valid outdoor air temperature
(either hard-wired or communicated) or a communicated Enable com-
mand from the Tracer Summit system, the Tracer AH540/541 controller
uses the modulating economizer damper as the highest priority source of
free cooling.
Economizing is possible during the occupied, occupied standby, unoccu-
pied, and occupied bypass modes. It requires a mixed-air temperature
sensor and an air-handling unit equipped with a mixing box. The mixed-
air temperature sensor is used as a low-temperature limit, to keep mixed-
air temperatures above freezing. It also requires an outdoor air tempera-
ture value to be present. If an outdoor temperature is not available, a
communicated request can enable economizing.
The controller initiates the economizer function if the outdoor air temper-
ature is cold enough to be used as free cooling capacity. If the outdoor air
temperature is less than the economizer enable setpoint (absolute dry
bulb), the controller modulates the outdoor air damper (between the
active minimum damper position and 100%) to control the amount of out-
door air cooling capacity. When the outdoor air temperature rises 5°F
above the economizer enable point, the controller disables economizing
and moves the outdoor air damper back to its predetermined minimum
position based on the current occupancy mode or communicated mini-
mum damper position (see Table 23 on page 59).
Mixed-air temperature sensor
location
Entering air side of the first coil
Leaving air side of the first coil
CNT-SVX05B-EN