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T24 Test Maximum Position (ET.MX)
Maximum position above which tests for a mechanically discon-
nected actuator will not be performed. For example, if the actuator
moves entirely within the range ET.MX to 100, a determination of
whether the actuator is mechanically disconnected will not be
made. This is due to the fact that at the extreme ends of the actua-
tor movement, a change in position may not result in a detectable
change in temperature. When the actuator stops in the range 98 to
100% (the actuator is considered to be open), a test will be per-
formed where SAT is expected to be approximately equal to OAT.
If SAT is not determined to be approximately equal to OAT, a
"damper not modulating" alert will be logged. Range is 50 to 100;
default is 85.
Economizer Deadband Temp (AC.EC)
The allowed deadband between measured SAT and calculated
SAT when performing economizer self-test. Range is 0 to 10; de-
fault is 4.
Econ Fault Detect Gap (E.GAP)
The discrepancy between actuator command and reported position
in percentage. Used to detect actuator stuck/jammed. Range is 2 to
100; default is 5.
Econ Fault Detect Timer (E.TMR)
The timer for actuator fault detection in seconds. Used to detect
actuator stuck/jammed. Range is 10 to 240; default is 20.
Excess Air CFM (X.CFM)
The max allowed excess air in CFM. Used to detect excess outside
air. Range is 400 to 4000; default is 800.
Excess Air Detect Timer (X.TMR)
The timer for excess air detection with a range of 30 to 240. De-
fault is 150.
Econ Auto-Test Day (EC.DY)
The day on which to perform automatic economizer test.
Range=NEVER, MON, TUE, WED, THR, FRI, SAT, SUN. De-
fault is SAT.
Econ Auto-Test Time (EC.TM)
The time at which to perform automatic economizer test. The
range is 0 to 23; default is 2.
T24 AutoTest SF Run Time (AC.MR)
Amount of time to run supply fan before sampling torque or mak-
ing torque comparison. Range is 1 to 10; default is 2.
T24 Auto-Test VFD Speed (AC.SP)
Speed to run VFD during economizer auto-component test. Range
is 10 to 50; default is 20.
T24 Auto-Test Econ% Opn (AC.OP)
Amount to open each economizer during auto-component test.
Range is 1 to 100. Default is 50.
T24 Auto-Test VFD% Chng (VF.PC)
Expected change in torque when damper opens from 0 to AC.OP
and then from AC.OP to 0. Range is 1 to 20; default is 10.
SETTING UP THE SYSTEM
The economizer configuration options are under the Local Display
Mode Configuration
ECON. See Table 66.
Economizer Installed? (EC.EN)
If an economizer is not installed or is to be completely disabled,
the configuration option EC.EN may be set to No. Otherwise, in
the case of an installed economizer, this option must be set to Yes.
Economizer Actuator 2 Installed? (EC2.E)
For 48/50P055-100 units, a second economizer actuator is re-
quired. For sizes 055-100, set this configuration to Yes.
Economizer Minimum Position (EC.MN)
The configuration option EC.MN is the economizer minimum po-
sition. See the section on indoor air quality for further information
on how to reset the economizer further to gain energy savings and
to more carefully monitor IAQ problems.
Economizer Position at Minimum VFD Speed (EP.MS)
The configuration option EP.MS is the economizer command-
ed position at SP.MN (STATPMIN), which is the minimum
speed for the supply fan VFD. Typically the value is chosen to
maintain a minimum level of ventilation. See the section on
indoor air quality for further information on how to reset the
economizer further to gain energy savings and to more careful-
ly monitor IAQ problems.
Economizer Position at Maximum VFD Speed (EP.XS)
The configuration option EP.XS is the economizer command-
ed position at SP.MX (STATPMAX), which is the maximum
speed for the supply fan VFD. This is usually set to 100% See
the section on indoor air quality for further information on how
to reset the economizer further to gain energy savings and to
more carefully monitor IAQ problems.
NOTE: This minimum position calculation based on VFD
speed is only applied for units configured for SP.CF and en-
abled for Duct static pressure control.
SAV and CV fan control use EC.MN unless offset by IAQ or
the unit is controlling OACFM.
Economizer Maximum Position (EC.MX)
The upper limit of the economizer may be limited by setting
EC.MX. It defaults to 98% to avoid problems associated with
slight changes in the economizer damper's end stop over time.
Typically, this will not need to be adjusted.
Economizer Trim for Sum Z? (E.TRM)
Sum Z is the adaptive cooling control algorithm used for multiple
stages of mechanical cooling capacity. The configuration option
E.TRM is typically set to Yes, and allows the economizer to mod-
ulate to the same control point (Sum Z) that is used to control ca-
pacity staging. The advantage is lower compressor cycling cou-
pled with tighter temperature control. Setting this option to No
will cause the economizer, if it is able to provide free cooling, to
open to the Economizer Max. Position (EC.MX) during mechani-
cal cooling.
ECONOMIZER OPERATION
There are four potential elements which are considered concur-
rently which determine whether the economizer is able to provide
free cooling:
1.
Dry bulb changeover (outside-air temperature qualification)
2.
Enthalpy switch (discrete control input monitoring)
3.
Economizer changeover select (E.SEL economizer
changeover select configuration option)
4.
Outdoor dewpoint limit check (requires an installed out-
door relative humidity sensor installed)
Dry Bulb Changeover
Outside-air temperature may be viewed under Tempera-
tures
AIR.T
OAT. The control constantly compares its out-
side-air temperature reading against the high temperature OAT
lockout (OAT.L). If the temperature reads above OAT.L, the econ-
omizer will not be allowed to perform free cooling.
NOTE: If the user wishes to disable the enthalpy switch from run-
ning concurrently, a field-supplied jumper must be installed
between TB201 terminals 3 and 4.
78
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Troubleshooting
