XVIII. OPERATING SEQUENCE
A. Cooling, Units Without EconoMi$er+
When thermostat calls for cooling, terminals G and Y1 and the compressor contactor (C) are energized. The indoor (evap- orator) fan motor (IFM), compressor, and outdoor (condenser) fan motor (OFM) start. The OFM runs continuously while the unit is in cooling. When the thermostat is satisfied, C is deen- ergized and the compressor and OFM shut off. After a
B. Heating, Units Without EconoMi$er+
When the thermostat calls for heating, terminal W1 is ener- gized. The
C. Cooling, Units With EconoMi$er+
For EconoMi$er+ operation, there must be a thermostat call for the fan (G). This will move the damper to its minimum position.
When the EconoMi$er+ control is the occupied mode and a call for cooling exists (Y1 on the thermostat), the control will first check for indoor fan operation. If the fan is not on, then cooling will not be activated. If the fan is on, then the control will open the EconoMi$er+ damper to the minimum position.
On the initial power to the EconoMi$er+ board, it will take the damper up to 21/2 minutes before it begins to position itself. With subsequent fan signal (G) to the board, the change in damper position will take up to 30 seconds to ini- tiate. Damper movement from full closed to full open (or vice versa) will take 21/2 minutes.
If the damper is in the process of a change (for example going to 100% open) and the signal (G) is turned off, the damper will continue to open to 100% before it closes (due to no fan signal [G]).
If free cooling can be used as determined from the appropri- ate changeover command (switch, dry bulb, enthalpy curve, differential dry bulb, or differential enthalpy), then the con- trol will modulate the dampers open to main the supply air temperature set point plus 2° F.
If there is a further demand for cooling (cooling second stage
—Y2 is energized), then the control set point for the leaving air will be set at the supply air set point to increase the cool- ing capacity. If this cannot satisfy the load then the control will bring on compressor stages as needed to maintain the supply air temperature set point. The EconoMi$er+ damper will be locked open at 100% or the maximum damper posi- tion set point.
To ensure that there is oil return, the compressors will oper- ate for at least 3 minutes. If, during this period, the leaving temperature drops below the set point by 5° F, then the EconoMi$er+ dampers will be closed to 60% until the com- pressor is turned off to avoid cold leaving air temperatures.
If the conditions are not suitable for free cooling then the EconoMi$er+ dampers will be closed to the minimum venti- lation position.
Compressor stages will be used to cool the air. If the control is configured for direct control by Y1 and Y2, then the stages will sequence based on the demand of Y1 and Y2. If the control is configured for leaving air temperature control, then Y1 will maintain the leaving air temperature at the supply air set point plus 2° F. If Y1 and Y2 are closed, then the leaving air will be controlled to the supply air set point. If Y2 is closed and Y1 is open, then control will shut down and indicate an error due to a thermostat failure or improper wiring of the thermostat.
If the unit is in the unoccupied mode, then the control of the temperature will depend on the unoccupied free cooling con- figuration: no unoccupied cooling, unoccupied free cooling with any mechanical cooling, or unoccupied free and mechanical cooling. If free cooling is enabled, then the con- trol will check if free cooling can be used. The EconoMi$er+ will then control to the leaving air temperature set point plus 2° F for a Y1 command, or the leaving air temperature set point for a Y1 and Y2 command. If mechanical cooling is allowed to be used, then the control will then bring on addi- tional stages of mechanical cooling if free cooling cannot sat- isfy the load.
If the EconoMi$er+ control:
•is in the occupied mode
•is configured to use demand ventilation
•cannot use free cooling
•has return air or space CO2 levels below the DAQLO limit,
then the EconoMi$er+ damper position will be set to the IAQMIN_SP set point. If the CO2 level rises above the DAQLO limit, then the dampers will modulate open in a lin- ear relationship until the return air or space CO2 levels are at or above the DAQHI limit. The damper position will be at the ECONOMIN_SP set point.
When the EconoMi$er+ is being used for free cooling and the position exceeds the power exhaust set point, then the con- trol will turn on the appropriate power exhaust fans. Refer to Fig. 23 for barometric relief capacity, Fig. 24 for outdoor air leakage, and Fig. 25 for pressure drop.
Unoccupied and Occupied Minimum Position Control
There is an unoccupied minimum damper position and an occupied minimum damper position on the EconoMi$er+ controller. When the HVAC fan is off the outdoor air damper will always be closed. When the fan is on and in the unoccu- pied mode, the outdoor air damper will be at the unoccupied minimum position. When the fan is on (G call) and in the occupied mode, the outdoor air damper will be at the occu- pied minimum position.
A jumper wire is
The 2 minimum position settings are also used in the IAQ sequence of operation. See Indoor Air Quality Sensor on page 21.
NOTE: The minimum position signal takes priority over the maximum position signal. If the maximum damper position is set below the minimum damper position, the EconoMi$er+ controller will maintain the actuator at minimum position.
