SEQUENCE OF OPERATION 3-50 TON RTU SYSTEM

FACE AND BYPASS HOT GAS REHEAT SYSTEM

SPACE TEMPERATURE/ SPACE HUMIDITY CONFIGURATION

A.SPACE TEMP OCCUPIED CONTROL:

Control of the Trane Hot Gas Reheat DX rooftop unit is accomplished through a dedicated standalone control module (MP581, UC400, UC600). One controller will be installed on each rooftop unit (RTU). The function of this controller is to maintain a programmed space air temperature.

A temperature sensor is mounted after the DX evaporator coil. This temperature sensor will be used by the controller to control the compressors to cycle on on and offbased on the DX supply setpoint with PID logic.A humidity sensor is field mounted in the space and will be used by the controller to reset the DX supply setpoint down toward the DX low limit (44 degrees, adjustable) if the space humidity rises above the adjustable humidity setpoint. The DX supply setpoint will stay lowered until the humidity setpoint in the space is satisfied, at which time it will be reset back toward the DX high limit (58 degrees, adjustable).

The spacetemperature sensor with a thumbwheel setpoint dialis field mounted in the space and will be used by the controller to enable the cooling or heating mode and control reheat and heat. In the cooling mode the DX sensor is active and staging compressors as per the above paragraph. Once temperature setpoint is reached an analog signal is sent to the hot gas reheat coil face and bypass damper actuatorto modulate free condenser heat into the airstream to maintain the space temperature setpoint. The space temperature is adjustable based on the sensor setpoint dial input. After a 3 degree deadband (adjustable) heating is enabled.

One strap-on temperature sensor will be located on the suction line of circuit #1. This temperature sensor will disable both cooling circuits when the temperature goes below 28 degrees and enable them above 38.One strap-on temperature sensor will be located on the liquid line of circuit #1. This temperature sensor will control the condenser fan. On larger, multiple fan units the fan will enable above 90 degrees, and disable below 85 degrees. On smaller single fan units, the fan will enable above 72, and disable below 67.

A temperature sensor is mounted in the outside air stream and monitors the outdoor air temperature.

When heating is called for,the controller will go into heating mode and the heat will be controlled as required to maintain the space heating setpoint (adjustable). The actual output signal for the heat control will operate based on the type of heat the unit has.

If the unit has electric or gas staged heat then the following will occur:

The 1st stage will come on when the zone temperature is below heating setpoint with a 1 degree deadband. The 2nd stage will be on 1 degree below heating setpoint with a 1 degree deadband.

If the unit has modulating electric heat then the following will occur:

The modulating heat is controlled by an analog signal from the controller based on the heating setpoint. On a multiple stage heater the analog signal controls the first stage. Once the analog signal reaches 100% a binary output closes to energize the next stage of heat and the analog signal modulates the 1st stage beginning at 0%.Once the analog signal reaches 100% again a binary output closes to energize the next stage of heat at 100% and the analog signal modulates the 1st stage beginning at 0% again.

If the unit has modulating hot water or steam heat then the following will occur:

An analog output from the controller will modulate the heating valve with a 0-10VDC signal.

B. FAN PROVING DEVICE:

A contact closure into the controllerwill indicate proof of airflow from a differential pressure switch that will allow either cooling or heating to operate.

C.OCCUPIED/UNOCCUPIED CONTROL:

A contact closure into the controller will indicate to the occupied mode of operation (the system will operate in the unoccupied mode while the contacts are open). The dry contact input will be wired from either a time clock or the building energy management system. If the system receives a timed override request from the zone sensor, the system will be overridden for a period of two hours. If the scheduling function of the controller is enabled, the system will recognize and follow the occupied state of the controller. If the system is controlled using an MP581 and is connected to a LonWorks network, and Lon control is established, the nviOccManCmd variable will control occupancy. If the system is controlled by a UC400 or UC600, and is connected to a BacNet network, the BacNet system can override the system occupancy.

D.UNOCCUPIED MODE:

When the controller is in the unoccupied mode, the system will be off. An unoccupied setpoint can be programmed in the controller to bring on the supply fan and cooling and/or heating to a setback temperature.

E.SETPOINT SELECTION:

The setpoints for unit operation will be selected based on a priority level that will seek communications with various devices to determine the correct set of setpoints to be used. An MP581 will search 1st for a LonTalk device. If no such network server is found or if the communication to that device has been lost, then the MP581 will try to control to setpoints that are being sent from a Tracer Summit BCU (Building Control Unit). If a Tracer Summit system is not located or has lost its communication to the MP581, then the MP581 will default to its own “Local” setpoints. These setpoints are embedded in the software that is loaded at the factory and can only be accessed from Trane “ROVER” software/hardware or if the MP581 has a display connected to the controller. A UC400 will operate based on local setpoints unless setpoints are overridden by a BacNet control system.