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 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.
PremierLink Control
THERMOSTAT MODE — If the PremierLink controller is configured for Thermostat mode (TSTAT), it will control only to the thermostat inputs on J4. These inputs can be overridden through CCN communication via the CV_TSTAT points display table. When in this mode, the fire safety shutdown (FSD) input cannot be used, so any fire/life safety shutdown must be physically wired to disable the 24 vac control circuit to the unit.
Indoor Fan — The indoor fan output will be energized whenever there is 24 vac present on the G input. The indoor fan will be turned on without any delay and the economizer damper will open to its minimum position if the unit has a damper connected to the controller. This will also occur if the PremierLink controller has been configured for electric heat or heat pump operation.
Cooling — For cooling operation, there must be 24 vac present on G. When G is active, the PremierLink controller will then determine if outdoor conditions are
suitable for economizer cooling when an economizer damper is available. A valid OAT, SPT (CCN space temperature) and SAT (supply air temperature) sensor MUST be installed for proper economizer operation. It recommended that an outdoor or differential enthalpy sensor also be installed. If one is not present, then a jumper is needed on the ENTH input on J4, which will indicate that the enthalpy will always be low. Economizer operation will be based only on outdoor air dry bulb temperature. The conditions are suitable when: enthalpy is low, OAT is less than OATL High Lockout for TSTAT, and OAT is less than OATMAX, the high setpoint for free cooling. The default for OATL is 65_F. The default for OATMAX is 75_F.
When all of the above conditions are satisfied and all the required sensors are installed, the PremierLink controller will use the economizer for cooling. One of three different control routines will be used depending on the temperature of the outside air. The routines use a PID loop to control the SAT to a supply air setpoint (SASP) based on the error from setpoint (SASPSAT). The SASP is determined by the routine.
If an economizer is not available or the conditions are not met for the following economizer routines below, the compressors 1 and 2 will be cycled based on Y1 and Y2 inputs respectively.
Any time the compressors are running, the PremierLink controller will lock out the compressors if the SAT becomes too low. These user configurable settings are found in the SERVICE configuration table:
Compressor 1 Lockout at SAT < SATLO1 (50 to 65_F) (default is 55_F)
Compressor 2 Lockout at SAT < SATLO2 (45 to 55_F) (default is 50_F)
After a compressor is locked out, it may be started again after a normal time-guard period and the supply-air temperature has increased at least 8_F above the lockout setpoint.
Routine No. 1: If the OAT ≤ DXLOCK (OAT DX lockout temperature) and DX Cooling Lockout is enabled when Y1 input is energized, the economizer will be modulated to maintain SAT at the Supply Air Setpoint (SASP) = SATLO1 + 3_F (Supply Air Low Temp lockout for compressor 1). When Y2 is energized, the economizer will be modulated to control to a lower SASP = SATLO2
+3_F (Supply Air Low Temp lockout for compressor no.
2). Mechanical cooling is locked out and will not be energized.
Routine No. 2: If DXLOCK (or DX Cooling Lockout is disabled) < OAT ≤ 68_F when Y1 input is energized, the economizer will be modulated to maintain SAT at SASP = SATLO1 + 3_F. If the SAT > SASP + 5_F and the economizer position > 85% then the economizer will close the to minimum position for three minutes or until the SAT > 68_F. The economizer integrator will then be reset and begin modulating to maintain the SASP after stage one has been energized for 90 seconds.
