Section 15941 - Sequence of Operation - Supply Air Handling System

Chrysler LLC Construction Standards

12/17/04

SECTION 15941 - SEQUENCE OF OPERATION - SUPPLY AIR HANDLING SYSTEM

PART 1 - GENERAL

1.1  GENERAL

1. Refer to drawing for schematic flow and control component locations. This operating sequence is divided under headings: Normal Operation, Manual Operation, Normal Alarms, Safeties and Abnormal Alarms, and Interlocks.

1.2  NORMAL OPERATION

1. Air Handling units operate normally through the Energy Management System (EMS). This is initiated by selecting the REMOTE AUTO position on the OPERATION selector switch on the control panel on the air handling unit.

1.3  STARTUP

1. With an air handling unit operating in REMOTE AUTO, the unit is started and stopped by starting and stopping the fan at the EMS terminal. When the fan is started, the outdoor air damper automatically positions itself to the setpoint percentage of outdoor air. The return air damper in turn automatically adjusts in reverse proportion to that of the outdoor air damper.
2. Outdoor Air Damper Setting Adjustment:
3. The percentage of outdoor air may be set at the EMS terminal for each air handling unit through the local position controller by scrolling to the desired value on the OUTDOOR AIR DAMPER OPENING SELECTOR and entering it. The percentage of outdoor air may also be set locally at air handling unit panel. Initial setting shall be 100% outdoor air.

1.4  TEMPERATURE CONTROL

1. With the unit operating in REMOTE AUTO and the fan on, the temperature controls operate automatically to satisfy room temperature setpoint as sensed by room sensor TE2. Sensor TE2 is shared among 6 air handling units and is linked into the control loop through the EMS.
2. Summer Cooling:
3. When room temperature rises above the summer setpoint of TE2, the refrigerant condenser system operates to satisfy discharge air temperature control loop as sensed by sensor TE1. TE2 initial summer setpoint shall be 22.2 degC (75 degF). The TE1 control loop resets its setpoint in straight-line reverse proportion to the room temperature deviation from TE2 setpoint as follows:

1. Discharge air temperature deviation above the setpoint of TE1 shall provide input to the condensing unit controls furnished with the condensing unit. On a call for cooling and when air flow is sensed by pressure switch DPS 2, condensing unit controls shall:

1)  Operate solenoid valves in their circuits to allow refrigerant flow when needed for cooling

2)  Operate compressors in their stages to provide the required cooling

3)  Operate condenser fans to maintain proper refrigerant pressure, and

4)  Operate hot gas bypass when outdoor temperatures are too low to maintain sufficient refrigerant pressure.

1. As cooling loads drops below the condensing unit minimum load, the condensing unit shall cycle off when discharge temperature drops to 3 degF below TE1 setpoint.
2. Winter Heating:
3. When room temperature drops below the winter setpoint of TE2, the gas fired heater operates to satisfy discharge air temperature control loop as sensed by sensor TE1. TE2 initial winter setpoint shall be 72 degF. The TE1 control loop resets its setpoint in straight-line reverse proportion to the room temperature deviation from TE2 setpoint as follows:

1. Discharge air temperature deviation below the setpoint of TE1 shall provide input to the local heater controls in the air handling unit. On a call for heating and when air flow is sensed by pressure switch DPS 2, heating controls shall:

1)  Start burner fan M2 on a call for heat

2)  After sensing combustion air flow with FL1, enable burner

3)  Start burner sequencing through purge cycle, pilot light, flame verification, burner light, and burner modulation control to satisfy setpoint of TE1.

1. As heating loads drops below the heater minimum, the heater shall cycle off when discharge temperature rises to 3 degF above TE1 setpoint.
2. Dead Band:
3. When room temperature is between the summer and winter setpoints of TE2, and after cooling and heating systems have cycled off, the air handling unit shall neither cool nor heat the air. The control system shall change system operation from heating to ventilating to cooling and back again automatically through the dead band temperature range without permitting the simultaneous operation of heating and cooling systems. Initial dead band shall be set for 3 degF.
4. Room Temperature Setpoint and Dead Band Adjustment:
5. The summer room temperature setpoint for TE2 and dead band may be set at the EMS terminal by scrolling to the desired values and entering them for SUMMER ROOM TEMPERATURE SETPOINT and DEAD BAND TEMPERATURE. The winter room temperature setpiont will equal the summer setpoint minus the dead band value. The dead band value must be a positive number and no less than 3 degF. The summer room temperature setpoint may also be set at the air handling unit control panel.

1.5  HUMIDITY CONTROL

1. With the unit operating in REMOTE AUTO and the fan on, the temperature controls operate automatically to satisfy room relative humidity setpoint as sensed by sensor HE2.
2. When room relative humidity rises above the setpoint of HE2, the humidifier operates to satisfy discharge relative humidity control loop as sensed by sensor HE1. HE2 initial setpoint shall be 30 percent relative humidity. The HE1 control loop resets its setpoint in straight-line reverse proportion to the room relative humidity deviation from HE2 setpoint as follows:

1.6  MANUAL OPERATION

1. An Air Handling unit may be switched from operation through the Energy Management System (EMS) to local manual operation. This is initiated by selecting the LOCAL MANUAL position on the OPERATION selector switch on the control panel on the air handling unit.

1.7  STARTUP

1. With an air handling unit operating in LOCAL MANUAL, the unit is started and stopped by starting and stopping the fan at the air handling unit control panel. When the fan is started, the outdoor air damper automatically positions itself to the setpoint percentage of outdoor air. The return air damper in turn automatically adjusts in reverse proportion to that of the outdoor air damper.
2. Outdoor Air Damper Setting Adjustment:
3. The percentage of outdoor air may be set at the air handling unit control panel by scrolling to the desired value for the outdoor air percentage. The percentage of outdoor air may also be set remotely at the EMS terminal. The outside air damper shall open on unit startup and close on unit shutdown with the return air damper working in reverse mode.

1.8  TEMPERATURE CONTROL

1. With the unit operating in LOCAL MANUAL, the system operates without the common room sensor TE1. Therefore the unit will operate to cool and heat to satisfy a discharge air control loop through sensor TE2. When discharge air temperature rises above 75degF (23.9 degC), the refrigerant condenser system starts and operates to satisfy discharge air temperature of 72 degF (22.2 degC). When discharge air temperature drops below 70 degF (21.1 degC) the condensing unit stops. When discharge air temperature drops below 60 degF (15.6 degC), the heater starts and operates to satisfy discharge air temperature of 65 degF (18.3 degC). When discharge air temperature rises above 68 degF (20 degC) the heater stops.

1.9  HUMIDITY CONTROL

1. With the unit operating in LOCAL MANUAL, the humidification system does not operate.

1.10  NORMAL ALARMS

1. When differential pressure sensed by DPS1 rises above 1 inch (2.54 cm) w.g., the CHANGE FILTER alarm shall occur on the EMS. A change in system operating status, that is, from Normal to Manual or Manual to Normal, shall alarm on the EMS.

1.11  SAFETIES AND ABNORMAL ALARMS

1. High Supply Temperature:
2. If supply air temperature rises above the setpoint of TSH1, the burner shall shut down and initiate a HIGH SUPPLY TEMPERATURE alarm on the EMS.
3. Low Supply Temperatures:
4. After 2 minutes of burner operation at high fire, TE1 shall sense more than 45degF (7.22degC) or the burner shall shut down and initiate a BURNER MALFUNCTION alarm on the EMS.
5. After TE1 senses supply air temperature below 40 degF (4.44 degC) for 3 minutes, supply fan shall shut down, outdoor air damper shall close, and the system shall initiate a FREEZE alarm on the EMS.
6. Smoke:
7. Smoke detectors shall be provided in the supply system of each ASU. Additional smoke detectors shall be provided and located in the return air ductwork and at each floor serviced by the ASU, if return air ducts are used. Smoke detectors shall be fully accessible. Each smoke detector shall have 2 sets of contacts. One set of contacts shall be wired to the ASU control panel. If smoke is present, the smoke detector shall trip the supply air fan, closing the outdoor air damper and shutting down heating and cooling systems. The secondary set of contacts shall be available for the Fire Alarm System Contractor to connect to the FA System (24/7 location).

1.12  INTERLOCKS

1. Supply fan motor must be running to permit the condensing unit to operate.
2. Supply fan motor must be running to permit the burner to operate.
3. Supply fan motor must be running to permit the humidifier to operate.
4. Burner fan motor must be running to permit the burner to operate.
5. Burner fan motor must be running to permit the humidifier to operate.
6. The return air damper moves in reverse proportion to that of the outdoor air damper.
7. Fan access doors must be closed to permit the supply fan to operate.

PART 2 - PRODUCTS (Not Used)

PART 3 - EXECUTION (Not Used)

END OF SECTION

SEQUENCE OF OPERATION - SUPPLY AIR HANDLING SYSTEM 15941 - 1 of 4