Applications Guide Tracer Graphical Programming - Trane
Applications Guide Tracer Graphical Programming - Trane Applications Guide Tracer Graphical Programming - Trane
® Chapter 8 Constant-volume AHU with warm-up, pre-cool, and communications Figure 164: Constant-volume air handler Reviewing the sequence of operation In this scenario a constant-volume air handler provides comfort heating and cooling to a space. The air handler contains a fan, both cooling and heating coils, and an outdoor air damper (Figure 164). Modes, setpoints, and communications The following parameters for the sequence of operation are presented according to the occupancy mode, the heat/cool mode, or the setpoint. Occupied mode (including occupied bypass) When the air handler is in occupied mode, operate the supply fan continuously and modulate the cooling valve, heating valve, and outside air damper to maintain space comfort conditions. During unoccupied periods, when the local timed override button (the ON button on the space temperature sensor) is pressed, transition the air handler to occupied bypass mode for the configured occupied bypass time period. When the local CANCEL button is pressed, terminate the timed override request and revert the air handler to the scheduled mode. Occupied standby mode When the air handler is in occupied standby mode, operate the supply fan continuously and modulate the cooling valve, heating valve, and outside air damper to maintain space comfort conditions. Use occupied standby mode to save energy by using lower heating and higher cooling temperature setpoints and reduced ventilation requirements during intermittent unoccupied periods. An occupancy sensor determines the presence of people in the space served by the air-handling unit. When the space is occupied, operate the air handler in occupied mode. When the space is unoccupied during a scheduled occupancy period, control the space temperature to follow the 190 CNT-APG001-EN
® Reviewing the sequence of operation occupied standby setpoints and maintain the outdoor air damper to its minimum position. Unoccupied mode (including night heat/cool) When the air handler is in unoccupied mode, turn the supply fan off, close the outside air damper fully, and close the cooling and heating valves fully. Open the heating valve completely if the outdoor air temperature falls below the freeze avoidance setpoint, 35°F (adjustable). If the space temperature falls below the unoccupied heating setpoint, start the supply fan and transition the air handler to heating and keep the outdoor air damper closed to maintain the unoccupied heating setpoint. When the space temperature rises above the unoccupied heating setpoint, shut down the air handler. If the space temperature rises above the unoccupied cooling setpoint, start the supply fan and transition the air handler to cooling to maintain the unoccupied cooling setpoint. Modulate the outside air damper if the outside air temperature is less than the economizer changeover setpoint. When the space temperature falls below the unoccupied cooling setpoint, shut down the air handler. Warm-up and pre-cool modes During occupied and occupied standby modes, when there is a call for heating and the space temperature is 3°F or more below the effective occupied heating setpoint, initiate a warm-up sequence. During warm-up, operate the supply fan continuously, close the outdoor air damper, and opentheheatingvalveto100%.Whenthespacetemperaturecomes within 2°F of the heating setpoint, open the outside air damper to the occupied minimum position and transition the air handler to occupied mode. During occupied and occupied standby modes, when there is a call for cooling and the space temperature is 3°F or more above the effective occupied cooling setpoint, initiate a morning cool-down sequence. Operate the supply fan continuously and the air handler in the economizing mode, if possible. If economizing is not possible, open the cooling valve to 100% and keep the outside air damper closed. When the space temperature reaches the cooling setpoint, open the outside air damper to the occupied minimum position and transition the air handler to occupied mode. Setpoints For occupied, occupied standby, and occupied bypass modes, calculate effective cooling and heating setpoints based on a single space temperature setpoint and the configured default occupied and occupied standby setpoints. The space temperature setpoint source may be the building automation system, the operator display, or a wired thumbwheel setpoint CNT-APG001-EN 191
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®<br />
Chapter 8 Constant-volume AHU with warm-up, pre-cool, and communications<br />
Figure 164: Constant-volume air handler<br />
Reviewing the sequence of operation<br />
In this scenario a constant-volume air handler provides comfort heating<br />
and cooling to a space. The air handler contains a fan, both cooling and<br />
heating coils, and an outdoor air damper (Figure 164).<br />
Modes, setpoints, and communications<br />
The following parameters for the sequence of operation are presented<br />
according to the occupancy mode, the heat/cool mode, or the setpoint.<br />
Occupied mode (including occupied bypass)<br />
When the air handler is in occupied mode, operate the supply fan continuously<br />
and modulate the cooling valve, heating valve, and outside air<br />
damper to maintain space comfort conditions. During unoccupied periods,<br />
when the local timed override button (the ON button on the space temperature<br />
sensor) is pressed, transition the air handler to occupied bypass<br />
mode for the configured occupied bypass time period. When the local<br />
CANCEL button is pressed, terminate the timed override request and<br />
revert the air handler to the scheduled mode.<br />
Occupied standby mode<br />
When the air handler is in occupied standby mode, operate the supply fan<br />
continuously and modulate the cooling valve, heating valve, and outside<br />
air damper to maintain space comfort conditions. Use occupied standby<br />
mode to save energy by using lower heating and higher cooling temperature<br />
setpoints and reduced ventilation requirements during intermittent<br />
unoccupied periods.<br />
An occupancy sensor determines the presence of people in the space<br />
served by the air-handling unit. When the space is occupied, operate the<br />
air handler in occupied mode. When the space is unoccupied during a<br />
scheduled occupancy period, control the space temperature to follow the<br />
190 CNT-APG001-EN