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intothezone.Thesupplyairwillmaintainthespacetempera-
turebetweentheheatingandcoolingsetpointsasindicatedin
Fig.47.
ThePremierLinkTM will integrate the compressol_ 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 space
temperature and space set point.
When outdoor-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-tOT temperature
from &'opping 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
c:dculated 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 initkd cooling then the
PremierLink controller will modulate the economizer using an
enor reduction calculation to hold the space temperature
between the heating and cooling set points. See Fig. 47.
The controller uses the following conditions to determine
economizer cooling:
• Enthalpyis 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 me not met, the economizer
submaster reference (ECSR) is set to maximum limit and the
dmnper moves to minimum position. The operating sequence
is complete. The ECSR is recalculated every 30 seconds.
If an optional power exhaust is inst:dled, as the outdoor-air
dmnper opens and closes, the power exhaust fans will be
energized and deenergized.
If field-installed accessory CO2 sensors are connected to
the PlemierLink control, a PID-controlled demand ventilation
strategy will begin to operate. As the CO2 level in the zone
increases above the CO2 set point, the minimum position of the
dmnper will be increased proportionally. As the CO2 level
decreases because of the increase in fresh all: the outdoor-air
dalnper will be proportionally closed.
HEATING. UNIT WITH ECONOMI$ER2, PREMIERLINK
CONTROL AND A ROOM SENSOR -- Every 40 seconds
the controller will calculate the required heat stages (maximum
of 3) to maintain supply air temperature (SAT) if the following
qualifying conditions are met:
• Indoor fan has been on for at least 30 seconds.
• COOL mode is not active.
• OCCUPIED, TEMRCOMPENSATED START or HEAT
mode is active.
• SAT reading is available.
• Fire shutdown mode is not active.
If all of the above conditions m'e met, the number of heat
stages is c_dculated; otherwise the required number of heat
stages will be set to 0.
If the PremierLink controller detemfines that heat stages are
required, the economizer dalnper will be moved to minimum
position if occupied and closed if unoccupied.
Staging should be as follows:
If Heating PID STAGES=2
• HEAT STAGES=I (75% capacity) will energize HSI
• HEAT STAGES=2 (100% capacity) will energize HS2
In order to prevent short cycling, the unit is locked into the
Heating mode forat least 10 minutes when HSI is deenergized.
When HSI is energized the induced-di'aft motor is then
energized and the burner ignition sequence begins. On units
equipped for two stages of heat, when additional heat is need-
ed, HS2 is energized and the high-fire solenoid on the main gas
valve (MGV) is energized. When the space condition is satis-
fied and HSI is deenergized the IFM stops after a 45-second
time-off delay unless in the occupied mode. The fan will run
continuously in the occupied mode as lequired by nafiomd
energy and fiesh air standards.
TEMPERATURE CONTROL
w 75,
•_ 73
w 72 ............................................... """ SET POINT
2: 71 -- TEMPERATURE
_- 70
W
o
694
cO 68J
TIME
NOTE: PremierLink control performs smart staging of 2 stages of DX
cooling and up to 3 stages of heat.
Fig. 46 -- DX Cooling Temperature
Control Example
W
QZ
QZ
W
Q_
W
W
09
TEMPERATURE CONTROL
75
741_ "
73
72 ......... _ .................................... ------COOL SETPOINT
71 t _ /j X_"_H%_,_-_'- -- TEMPERATURE
704 ........ _ .......................... -- - HEAT SETPOINT
J
69
68
TIME
Fig. 47 -- Economizer Temperature
Control Example
38