26
than the configured Econo Cool Lo Temp Limit (Configura-
tion
ECON
EL.LO). Econo Diff DBulb Lockout (Operating
Modes
ECON
D.LOC) occurs when Diff Dry Bulb Control
is enabled (Configuration
ECON
DF.DB = Enable) and the
accessory return air temperature (RAT) is lower then the outdoor
air temperature (OAT). Econo Cool Enth Lockout (Operating
Modes
ECON
EN.LO) occurs when an enthalpy sensor is
installed and the Outdoor Enthalpy is HIGH. OAQ Lockout
Mode (Operating Modes
ECON
AQ.LO) occurs when the
outdoor air quality sensor is configured for lockout and the value
is greater then the OAQ Lockout Limit (Configura-
tion
AIR.Q
OAQ.L). Any one of these lockouts will disable
economizer free cooling.
THERMOSTAT CONTROL
If the unit is in cooling, operating under thermostat control, Y1
= ON, and the economizer is available for cooling, the econo-
mizer will control the supply-air temperature to the low cool
set point (Setpoints
LCSP). When Y2 = ON, the economizer
will control the supply-air temperature to high cool set point
(Setpoints
HCSP). If a compressor is also being used during
Free Cooling, the damper will be locked at the economizer
maximum position (Configuration
ECON
EC.MX).
SPACE SENSOR CONTROL
If the unit is in cooling, operating under space temperature
control, the economizer is available for cooling, and no com-
pressors are operating, the economizer will control the SAT to
either Setpoints
LCSP or Setpoints
HCSP (See Table 8.) If
a compressor is ON, the economizer will be at the economizer
maximum cooling position (Configuration
ECON
EC.MX).
If the control senses low suction pressure for any active refrig-
erant circuit when the economizer is also providing cooling,
the maximum allowable economizer position will be reduced.
Factory default configurations have been qualified over a large
range of conditions and should only be changed with care. For
unit troubleshooting, factory default maximum economizer
limits for this condition are provided in Table 9.
Table 8 — LCSP and HCSP Transitions for Space
Temperature Mode
Table 9 — Maximum Economizer Limits During Low
Suction Pressure
Air-Side Economizer High Limit Switches Con-
trol
DIFFERENTIAL DRY BULB CUTOFF CONTROL
Econo Diff DBulb Lockout (Operating
Modes
ECON
D.LOC) occurs when Diff Dry Bulb Control
is enabled (Configuration
ECON
DF.DB = DISABLE).
The accessory return air temperature (RAT) will then be com-
pared to the outdoor air temperature (OAT) based on the
DF.DB setting to determine whether lockout should occur as
shown in the following table:
The OAT/RAT comparison must maintain the same result for
60 consecutive seconds before D.LOC will be changed.
UNOCCUPIED FREE COOLING
The unoccupied free cooling algorithm attempts to maintain
the building space half way between the Occupied Cool Set
Point (Setpoints
OCSP) and Occupied Heat Set Point (Set-
points
OHSP) using only the economizer when the condi-
tions in the building and the outdoors are suitable, during unoc-
cupied periods. Three different configurations define this algo-
rithm: Unoccupied Free Cooling (Configuration
ECON
UEFC), Free Cooling Preoccupancy Time (Configura-
tion
ECON
FC.TM), and FreeCoolLowTemp Limit (Con-
figuration
ECON
FC.LO).
UEFC = 0 (Disabled)
When UEFC = 0, unoccupied free cooling is disabled. Cooling
will only occur if the space exceeds the unoccupied setpoints.
UEFC = 1 (Unoccupied)
When UEFC is set to 1, unoccupied free cooling can occur
throughout the entire unoccupied period. The space tempera-
ture must be higher than the mid-point between the occupied
cooling and heating setpoints.
UEFC = 2 (Preoccupancy)
When UEFC is set to 2, unoccupied free cooling can only oc-
cur when the time until the next occupied period is less than the
Free Cool PreOcc Time (FC.TM) in minutes.
Free Cool PreOcc Time (FC.TM)
FC.TM is the configuration that determines how many minutes
before occupancy that free cooling can occur when set for Pre-
occupancy (UEFC = 2).
Free Cool Low Temp Limit (FC.LO)
Unoccupied free cooling cannot occur if the Outdoor Air Tem-
perature (Temperature
AIR.T
OAT) is less than FC.LO.
POWER EXHAUST (CV UNITS)
To enable power exhaust, Configuration
ECON
PE.EN
must be set to ENBL. If power exhaust is enabled, Power Ex-
haust 1 will turn on when the economizer position is greater
than the value of Configuration
ECON
PE.1. Power Ex-
haust 2 will turn on when the economizer position is greater
than the value of Configuration
ECON
PE.2. There are
small time delays to ensure that rapid cycling does not occur.
POWER EXHAUST (SAV UNITS)
To enable power exhaust, set Power Exhaust Installed (Config-
uration
ECON
PE.EN) to YES. Both power exhaust fans
are wired together and are controlled by the configuration
Power Exhaust Stage1 CFM (Configura-
tion
ECON
PE1.C). When the Indoor Fan Max Speed
CFM (Configuration
ECON
IDF.C) is set to the correct
supply duct CFM (either by fan tables or air balance report) the
control will calculate the outside air CFM based on outside air
damper position and Commanded Fan Speed (Out-
puts
FANS
F. S P D ) to turn on the power exhaust when the
calculated outside air CFM reaches Power Exhaust Stage1
CFM (PE1.C). The power exhaust will then turn off when the
CURRENT SAT SET
POINT
COOL DEMAND
(delta F)
NEXT SAT SET
POINT
LCSP >0.5 HCSP
HCSP <0 LCSP
LCSP <–0.5 Exit Cooling
LEGEND
HCSP — High Cool Set Point
LCSP — Low Cool Set Point
SAT — Supply-Air Temperature
COOLING STAGE SIZES 04-14 SIZES 17-28
Bottom 50 50
Top 25 0
DF.DB (DIFFBULB)
OAT/RAT
Comparison
D.LOC (DFDBLOCK)
DISABLE N/A NO
RAT- 0
OAT>RAT YES
OAT<=RAT NO
RAT- 2
OAT>RAT- 2 YES
OAT<=RAT-2 NO
RAT- 4
OAT>RAT- 4 YES
OAT<=RAT-4 NO
RAT- 6
OAT>RAT- 6 YES
OAT<=RAT-6 NO
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