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S If SAT > SASP + 5 and economizer position >80%,
economizer will go to minimum position for 3 minutes
or until SAT > 68_F.
S If compressor one is on then second stage of
mechanical cooling will be energized; otherwise the
first stage will be energized.
S Integrator resets.
S Economizer opens again and controls to SASP after
stage one on for 90 seconds.
Routine 3 (OAT > 68)
S Economizer is opened 100%.
S Compressors1and2arecycledbasedonY1andY2
using minimum on and off times and watching the
supply 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 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.
HEATING -- UNITS WITH ECONOMI$ER2,
PREMIER-
LINK CONTROL AND A THERMOSTA
T
When the thermostat calls for heating, terminal W 1 is ener gized.
The PremierLink control will move the economizer damper to the
minimum position if there is a call for G and closed if there is a
call for W1 without G. In order to prevent thermostat from short
cycling, the unit is locked into the heating mode for at least 10
minutes when W1 is energized. The induced--draft motor is then
energized and the burner ignition sequence begins.
On units equipped for two stages of heat, when additional heat is
needed, W2 is energized and the high--fire solenoid on the main
gas valve (MGV) is energized. When the thermostat is satisfied
and W1 is deenergized, the IFM stops after a 45--second time--off
delay unless G is still maintained.
COOLING -- UNITS WITH ECONOMI$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 Error
reduction calculation as indicated by Fig 51.
The PremierLink controller will use the following information to
determine if free cooling is available:
S Indoor fan has been on for at least 30 seconds.
S The SPT, SAT, and OAT inputs must have valid
readings.
S OAT must be less than 75_F.
S OAT must be less than SPT.
S Enthalpy must be LOW (may be jumpered if an
enthalpy sensor is not available).
S Economizer position is NOT forced.
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.
C06042
Fig. 51 --- DX Cooling Temperature
Control Example
68
69
70
71
72
73
74
75
SPACE TEMPERATURE
TIME
TEMPERATURE CONTROL
COOL SETPOINT
TEMPERATURE
HEAT SETPOINT
C06043
Fig. 52 --- Economizer Temperature
Control Example
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 temperature
between the heating and cooling set points as indicated in Fig. 52.
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 compare s pace
temperature and space set point.
When outside-air temperature conditions require the economizer
to close for a compressor stage-up sequence, the economizer
control integrator is reset to zero after the stage-up sequence 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. 52.)
The controller uses the following conditions to determine
economizer cooling:
S Enthalpy is Low
S SAT reading is a vailable
S OAT reading is available
48HE,HJ