16
ROUTINE 2 (DXCTLO < OAT < 68°F)
• If only Y1 energized, the economizer maintains a
SASP = ( 3)
• If SAT > SASP + 5 and economizer position > 80%
economizer will go to minimum position for 3 minutes or
until SAT > 68° F.
• First stage of mechanical cooling will be energized.
• Integrator resets.
• Economizer opens again and controls to current SASP
after stage one on for 90 seconds.
• With Y1 and Y2 energized, economizer maintains a
SASP = 3
• If SAT > SASP + 5 and economizer position > 80%
economizer will go to minimum position for 3 minutes or
unit SAT > 68° F.
• If compressor one is on then second stage of mechanical
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° F)
• Economizer is opened 100%
• Compressors 1 and 2 are cycled based on Y1 and Y2 using
minimum on and off times and watching the supply air
temperature as compared to SATLO1 and SATLO2 set
points.
Heating, Units with EconoMi$er 2, PremierLink
™
Control and a Thermostat
When the thermostat calls for heating, terminal W1 is energized.
The PremierLink control will move the economizer damper to the
minimum position if there is a call for G and closed if there is a
call for W1 without G. In order to prevent thermostat from short
cycling, the unit is locked into the heating mode for at least 10
minutes when W1 is energized. The induced draft motor is then
energized and the burner ignition sequence begins.
On units equipped for two stages of heat, when additional heat is
needed, W2 is energized and the high fire solenoid on the main
gas valve (MGV) is energized. When the thermostat is satisfied
and W1 is de-energized, the IFM stops after 45 second time-off
delay, unless G is still maintained.
Cooling, Units with EconoMi$er2,
PremierLink Control and a Room Sensor
When free cooling is not available, the compressors will be
controlled by the PremierLink controller using a Proportional
Integral Derivative Loop (PID) Error reduction calculation as
indicated by Fig. 31.
Fig. 31 — DX Cooling Temperature Control Example
NOTE: PremierLink control performs smart staging of 2 stages of
DX cooling and up to 3 stages of heat.
The PremierLink controller will use the following information 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 an 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 Derivative
Loop (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. 32.
Fig. 32 — Economizer Temperature Control Example
The PremierLink
controller
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 space
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 point (See
Fig. 32).
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 the maximum limit and the
damper moves to minimum position. The operating sequence is
complete. The ECSR is recalculated every 30 seconds.
TEMPERATURE CONTROL
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SP
ACE TEMPERA
T
URE
SETPOINT
TEMPERATURE
TIME
TEMPERATURE CONTROL
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SP
ACE TEMPERA
T
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COOL SETPOINT
TEMPERATURE
HEAT SETPOINT
TIME
