Trane RT-PRC010-EN manual Controls, CV Units, Gas Heating Modulating Gas, Electric Heating

Controls (CV Units)

Gas Heating: Modulating Gas

Upon a call for heating, the UCM closes the heating contacts, beginning the firing sequence. First, the heat exchanger combustion blower begins operation. Upon positive proving of combustion airflow, a pre-purge cycle is executed. Then the ignition sequence takes place.

If ignition is not proven, the ignition transformer is de-energized. After a time delay, another pre-purge cycle takes place, followed by another attempt to ignite. If ignition fails a second time, the heating section will be shut down and locked out until manually reset at the unit mounted Human Interface Panel.

As additional heat is required, the air damper opens, increasing the firing rate.

During heating operation, an electronic flame safety control provides continuous flame supervision. If combustion should become unstable for any reason, heating will automatically shut down. After one minute, another 60 second pre-purge and ignition cycle begins.

As the heating requirement is satisfied, the UCM will reduce the combustion air, and the firing rate will lower to maintain the desired outlet temperature. When the requirement is fully satisfied, the heating contacts are opened, de- energizing the heat.The specific sequence of operation of the gas heat will depend on the size of the heat exchanger.

Electric Heating

The three stages of electric heat will be sequenced on the zone demand signal from the zone sensor.The signal is sent to the UCM and the stages are sequenced based on load demand.

HotWater or Steam Heating

Upon a call for heat, the UCM will send a varying voltage signal to the valve actuator.The valve will modulate to meet building demand as indicated by the voltage signal. When heating is satisfied, the valve will modulate closed.

A temperature sensor is located on the coldest section of the coil. When it senses an impending freeze condition, a signal is sent to the hydronic valve to

drive it full open. If the supply fan is on, or if the outside air damper is open when this freezing condition is sensed, the supply fan is turned off and the outside air damper is closed.

B

Supply AirTempering

For gas and electric heat units in the Heat mode but not actively heating, if the supply air temperature drops to 10 F below the Occupied zone heating temperature setpoint, one stage of heat will be brought on to maintain a minimum supply air temperature.The heat stage is dropped if the supply air temperature rises to 10 F above the Occupied zone heating temperature setpoint.

C

Auto Changeover

When the System Mode is “Auto,” the mode will change to cooling or heating as necessary to satisfy the zone cooling and heating setpoints.The zone cooling and heating setpoints can be as close as 2 F apart.

2

Unoccupied ZoneTemperature Control

Cooling and Heating

Both cooling or heating modes can be selected to maintain Unoccupied zone temperature deadbands. For Unoccupied periods, heating, economizer operation or compressor operation can be selectively locked out at the Human Interface Panels.

78 RT-PRC010-EN