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46
• If SAT > SASP + 5 and economizer position >80%,
economizer will go to minimum position for 3 minutes or
until SAT > 68 F.
• If compressor no. 1 is on then second stage of mechani-
cal cooling will be energized. Otherwise the first stage
will be energized.
• Integrator resets.
• Economizer opens again and controls to SASP after
stage one on for 90 seconds.
Routine 3
— (OAT > 68)
• Economizer is opened 100%.
• Compressors 1 and 2 are cycled based on Y1 and Y2
using minimum on and off times and watching the sup-
ply air temperature as compared to SATLO1 and
SATLO2 set points.
If optional power exhaust is installed, as the outdoor-air
damper opens and closes, the power exhaust fans will be ener-
gized and deenergized.
If field-installed accessory CO
2
sensors are connected to the
PremierLink™ control, a PID-controlled demand ventilation
strategy will begin to operate. As the CO
2
level in the zone
increases above the CO
2
set point, the minimum position of the
damper will be increased proportionally. As the CO
2
level
decreases because of the increase in fresh air, the outdoor-air
damper will be proportionally closed.
HEATING, UNITS WITH ECONOMI$ER2, PREMIER-
LINK CONTROL AND A THERMOSTAT — When the
thermostat calls for heating, terminal W1 is energized. The
PremierLink control will move the economizer damper to the
minimum position if there is a call for G and closed if there is a
call for W1 without G. In order to prevent thermostat from short
cycling, the unit is locked into the heating mode for at least
10 minutes when W1 is energized.
COOLING, UNITS WITH ECONOMI$ER2, PREMIER-
LINK CONTROL AND A ROOM SENSOR — When free
cooling is not available, the compressors will be controlled by
the PremierLink controller using a PID (proportional integral)
Error reduction calculation as indicated by Fig. 41.
The PremierLink controller will use the following informa-
tion to determine if free cooling is available:
• Indoor fan has been on for at least 30 seconds.
• The SPT, SAT, and OAT inputs must have valid readings.
• OAT must be less than 75 F.
• OAT must be less than SPT.
• Enthalpy must be LOW (may be jumpered if and
enthalpy sensor is not available).
• Economizer position is NOT forced.
When free cooling is available, the outdoor-air damper is
positioned through the use of a Proportional Integral (PID)
control process to provide a calculated supply-air temperature
into the zone. The supply air will maintain the space tempera-
ture between the heating and cooling set points as indicated in
Fig. 42.
The PremierLink control will integrate the compressor
stages with the economizer based on similar logic as the three
routines listed in the previous section. The SASP will float up
and down based on the error reduction calculations that com-
pare space temperature and space set point.
When outside-air temperature conditions require the econo-
mizer to close for a compressor stage-up sequence, the econo-
mizer control integrator is reset to zero after the stage-up se-
quence is completed. This prevents the supply-air temperature
from dropping too quickly and creating a freeze condition that
would make the compressor turn off prematurely.
The high space set point is used for DX (direct expansion)
cooling control, while the economizer space set point is a
calculated value between the heating and cooling set points.
The economizer set point will always be at least one degree
below the cooling set point, allowing for a smooth transition
from mechanical cooling with economizer assist, back to
economizer cooling as the cooling set point is achieved.
The compressors may be used for initial cooling then the
PremierLink controller will modulate the economizer using an
error reduction calculation to hold the space temperature
between the heating and cooling set points. See Fig. 42.
The controller uses the following conditions to determine
economizer cooling:
• Enthalpy is Low
• SAT reading is available
• OAT reading is available
• SPT reading is available
•OAT≤SPT
• Economizer Position is NOT forced
If any of the above conditions are not met, the economizer
submaster reference (ECSR) is set to maximum limit and the
damper moves to minimum position. The operating sequence
is complete. The ECSR is recalculated every 30 seconds.
If an optional power exhaust is installed, as the outdoor-air
damper opens and closes, the power exhaust fans will be
energized and deenergized.
If field-installed accessory CO
2
sensors are connected to
the PremierLink control, a PID-controlled demand ventilation
strategy will begin to operate. As the CO
2
level in the zone
increases above the CO
2
set point, the minimum position of the
damper will be increased proportionally. As the CO
2
level
decreases because of the increase in fresh air, the outdoor-air
damper will be proportionally closed.
68
69
70
71
72
73
74
75
SPACE TEMPERATURE
TIME
TEMPERATURE CONTROL
SET POINT
TEMPERATURE
NOTE: PremierLink control performs smart staging of 2 stages of DX
cooling and up to 3 stages of heat.
Fig. 41 — DX Cooling Temperature
Control Example
68
69
70
71
72
73
74
75
SPACE TEMPERATURE
TIME
TEMPERATURE CONTROL
COOL SETPOINT
TEMPERATURE
HEAT SETPOINT
Fig. 42 — Economizer Temperature
Control Example