Bryant F appendix Heating With EconoMi$er, Demand Controlled Ventilation, Supplemental Controls

580J

When free cooling is available as determined by the appropriate changeover command (dry bulb, outdoor enthalpy, differential dry bulb or differential enthalpy), a call for cooling (Y1 closes at the thermostat) will cause the economizer control to modulate the dampers open and closed to maintain the unit supply air temperature at 50 to 55_F. Compressor will not run.

During free cooling operation, a supply air temperature (SAT) above 50_F will cause the dampers to modulate between Minimum Position setpoint and 100% open. With SAT from 50_F to 45_F, the dampers will maintain at the Minimum Position setting. With SAT below 45_F, the outside air dampers will be closed. When SAT rises to 48_F, the dampers will re-open to Minimum Position setting.

Should 100% outside air not be capable of satisfying the space temperature, space temperature will rise until Y2 is closed. The economizer control will call for compressor operation. Dampers will modulate to maintain SAT at 50 to 55_F concurrent with Compressor 1 operation. The Low Ambient Lockout Thermostat will block compressor operation with economizer operation below 42_F outside air temperature.

When space temperature demand is satisfied (thermostat Y1 opens), the dampers will return to Minimum Damper position if indoor fan is running or fully closed if fan is off.

If accessory power exhaust is installed, the power exhaust fan motors will be energized by the economizer control as the dampers open above the PE-On setpoint and will be de-energized as the dampers close below the PE-On setpoint.

Damper movement from full closed to full open (or vice versa) will take between 1-1/2 and 2-1/2 minutes.

Heating With EconoMi$er IV

During Occupied mode operation, indoor fan operation will be accompanied by economizer dampers moving to Minimum Position setpoint for ventilation. If indoor fan is off, dampers will close. During Unoccupied mode operation, dampers will remain closed unless a DCV demand is received.

When the room temperature calls for heat (W1 closes), the heating controls are energized as described in Heating, Unit Without Economizer above.

Demand Controlled Ventilation

If a field-installed CO2 sensor is connected to the Economize IV control, a Demand Controlled Ventilation strategy will operate automatically. As the CO2 level in the space increases above the setpoint (on the EconoMi$er IV controller), the minimum position of the dampers will be increased proportionally, until the Maximum Ventilation setting is reached. As the space CO2 level decreases because of the increase in fresh air, the outdoor-damper will follow the higher demand condition from the DCV mode or from the free-cooling mode.

DCV operation is available in Occupied and Unoccupied periods with EconoMi$er IV. However, a control modification will be required on the 580J unit to implement the Unoccupied period function.

Supplemental Controls

Compressor Lockout Relay (CLO) - The CLO is available as a factory-installed option or as a field-installed accessory. Each compressor has a CLO. The CLO compares the demand for compressor operation (via a 24-v input from Y at CLO terminal 2) to operation of the compressor (determined via compressor current signal input at the CLO’s current transformer loop); if the compressor current signal is lost while the demand input still exists, the CLO will trip open and prevent the compressor from restarting until the CLO has been manually reset. In the lockout condition, 24-v will be available at terminal X. Reset is accomplished by removing the input signal at terminal 2; open the thermostat briefly or cycle the main power to the unit.

Phase Monitor Relay (PMR) - The PMR protects the unit in the event of a loss of a phase or a reversal of power line phase in the three-phase unit power supply. In normal operation, the relay K1 is energized (contact set closed) and red LED indicator is on steady. If the PMR detects a loss of a phase or a phase sequence reversal, the relay K1 is energized, its contact set is opened and unit operation is stopped; red LED indicator will blink during lockout condition. Reset of the PMR is automatic when all phases are restored and phase sequence is correct. If no 24-v control power is available to the PMR, the red LED will be off. Smoke Detectors - Factory-installed smoke detectors are discussed in detail starting on page 17.

RTU-MP Sequence of Operation

The RTU-MP will control the compressor, economizer and heating outputs based on its own space temperature input and setpoints. An optional CO2 IAQ sensor mounted in the space can influence the economizer minimum position. The RTU-MP has its own hardware clock that is set automatically when the software is installed on the board. The RTU-MP’s default is to control to occupied setpoints all the time, until a type of occupancy control is set. Occupancy types are described in the scheduling section. The following sections describe the operation for the functions of the RTU-MP. All point objects that are referred to in this sequence will be in reference to the objects as viewed in BACview6 Handheld.

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