Carrier 48TJ016-028 - Manual (Page 38)

into the zone. The supply air will maintiiin the space tempera­
ture between the heating and cooling set points as indicated in
Fig. 47.
Tlie PremierLink''''* will integrate the compressors stages
with the economizer based on similar logic as the three routines
listed in the previous section. Tlie SASP will float up and down
based on the eiror reduction calculations that compare space
temperatuie 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-tiir temperature
from di'opping too quickly and creating a freeze condition that
would make tlie compressor turn off prematurely.
Tlie high space set point is used for DX (direct expansion)
cooling control, while the economizer space set point is a
ciiiculated value between the heating and cooling set points.
Tlie 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.
Tlie compressors may be used for initial cooling then the
PremierLink controller will modulate tlie economizer using an
error reduction calculation to hold the space temperature
between the heating and cooling set points. See Fig. 47.
Tlie 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
diunper moves to minimum position. The operating sequence
is complete. The ECSR is recalculated eveiy 30 seconds.
If an optional power exhaust is installed, as the outdoor-air
diunper opens and closes, tlie power exhaust fans will be
energized and deenergized.
if field-installed accessoiy 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, UNIT WITH ECONOMI$ER2. PREMIERLINK
CONTROL AND A ROOM SENSOR ^ Eveiy 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, TEMP.COMPENSATED START or HEAT
mode is active.
• SAT reading is available.
• Fire shutdown mode is not active.
If all of the above conditions lu'e met, tlie number of heat
stages is calculated; otheiwise the required number of heat
stages will be set to 0.
If tlie PremierLink controller detennines that heat stages are
required, the economizer damper 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 HS1
• HEAT STAGES=2 (100% capacity) will energize HS2
In order to prevent short cycling, the unit is locked into the
Heating mode for at least 10 minutes when HS I is deenergized.
When HSl is energized tlie induced-draft motor is then
energized and tlie 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 tlie space condition is satis­
fied and HSl is deenergized the IFM stops after a 45-second
time-off delay unless in the occupied mode. The fan will mn
continuously in the occupied mode as required by nationtil
energy and fresh air standards.
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
38