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Unoccupied Economizer Free Cooling Time Configuration
(FC.TM)
This option is a configurable time period, prior to the next occu-
pied period, that the control will allow unoccupied economizer
free cooling to operate. This option is only applicable when
FC.CF = 2.
Unoccupied Economizer Free Cooling Outside Lockout Tem-
perature (FC.LO)
This configuration option allows the user to select an outside-air
temperature below which unoccupied free cooling is not allowed.
This is further explained in the logic section.
Unoccupied Economizer Free Cooling Logic
The following qualifications that must be true for unoccupied free
cooling to operate:
•
Unit configured for an economizer
•
Space temperature sensor enabled and sensor reading
within limits
•
Unit in the unoccupied mode
•
FC.CF set to 1 or FC.CF set to 2 and control is within
FC.TM minutes of the next occupied period
•
Not in the Temperature Compensated Start mode
•
Not in a cooling mode
•
Not in a heating mode
•
Not in a tempering mode
•
Outside-air temperature sensor reading within limits
•
Economizer would be allowed to cool if the fan were re-
quested and in a cool mode
•
OAT > FC.LO (1.0°F hysteresis applied)
•
Unit not in a fire smoke mode
•
No fan failure when configured for unit to shut down on a
fan failure
If all of the above conditions are satisfied, Unoccupied Economiz-
er Free Cooling will start when both of the following conditions
are true:
{SPT > (OCSP + 2)} AND {SPT > (OAT + 8)}
The Unoccupied Economizer Free Cooling Mode will stop when
either of the following conditions are true:
{SPT < OCSP} OR {SPT < (OAT + 3)} where SPT = Space
Temperature and OCSP = Occupied Cooling Set Point.
When the Unoccupied Economizer Free Cooling mode is active,
the supply fan is turned on and the economizer damper modulated
to control to the supply air set point (Setpoints
supply air reset that may be applied (Inputs
OUTDOOR AIR CFM CONTROL
If an outdoor air cfm flow station has been installed, the econo-
mizer is able to provide minimum ventilation based on cfm, in-
stead of damper position. The outdoor air cfm reading can be
found in Inputs
CFM
O.CFM. During cfm control, the econ-
omizer must guarantee a certain amount of cfm at any time for
ventilation purposes. If the outdoor air cfm measured is less than
the current calculated cfm minimum position, then the economizer
will attempt to open until the outdoor air cfm is greater than or
equal to this cfm minimum position. The following options are
used to program outside air cfm control.
Outdoor Air cfm Sensor Enable (OCF.S)
If this option is enabled, the outdoor air cfm sensor will be read
and outside air cfm control will be enabled.
Economizer Minimum Flow Rate (O.C.MX)
This option replaces the Economizer Minimum Position (Config-
uration
ECON
EC.MN) when the outdoor air cfm sensor is
enabled.
SASP) plus any
RSET
SA.S.R).
82
IAQ Demand Vent Minimum Flow Rate (O.C.MN)
This option replaces the IAQ Demand Ventilation Minimum Posi-
tion (Configuration
IAQ
air cfm sensor is enabled.
Economizer Minimum Flow Deadband (O.C.DB)
This option defines the deadband of the cfm control logic.
The configurable deadband is added to the economizer's
minimum cfm position and creates a range (ECMINCFM to
ECMINCFM ± OACFM_DB) where the economizer will
not attempt to adjust to maintain the minimum cfm position.
Increasing this deadband value may help to slow down ex-
cessive economizer movement when attempting to control
to a minimum position at the expense of bringing in more
ventilation air than desired.
ECONOMIZER OPERATION CONFIGURATION
The configuration items in the E.CFG menu group affect how the
economizer modulates when attempting to follow an economizer
cooling set point. Typically, they will not need adjustment. In fact,
it is strongly advised not to adjust these configuration items from
their default settings without first consulting a service engineering
representative.
In addition, the economizer cooling algorithm is designed to auto-
matically slow down the economizer actuator's rate of travel as
outside air temperature decreases.
ECONOMIZER DIAGNOSTIC HELP
Because there are so many conditions which might disable the
economizer from being able to provide free cooling, the control
has a display table to identify these potentially disabling sources.
The user can check ACTV, the "Economizer Active" flag. If this
flag is set to Yes, there is no reason to check DISA (Economizer
Disabling Conditions). If the flag is set to No, this means that at
least one or more of the flags under the group DISA are set to
Yes and the user can discover what is preventing the economizer
from performing free cooling by checking the table.
The economizer's reported and commanded positions are also
viewable, as well as outside air temperature, relative humidity, en-
thalpy and dew point temperature.
The following information can be found under the Local Display
Mode Run Status
ECON. See Table 67.
Economizer Control Point Determination Logic
Once the economizer is allowed to provide free cooling, the econ-
omizer must determine exactly what set point it should try to
maintain. The set point the economizer attempts to maintain when
"free cooling" is located at Run Status
the economizer control point.
The control selects set points differently, based on the control type
of the unit. This control type can be found at Configuration
UNIT
C.TYP. There are 4 types of control.
C.TYP = 1 VAV-RAT
C.TYP = 2 VAV-SPT
C.TYP = 3 TSTAT Multi-Staging
C.TYP = 4 SPT Multi-Staging
If economizer is not allowed to do free cooling, then EC.C.P = 0.
If the economizer is allowed to do free cooling and the Unoccu-
pied Free Cooling Mode is ON, then EC.C.P = Setpoints
+ Inputs
RSET
SA.S.R.
If the economizer is allowed to do free cooling and the Dehumidi-
fication mode is ON, then EC.C.P = the Cooling Control Point
(Run Status
VIEW
CL.C.P).
NOTE: To check the current cooling stage, go to Run Status
COOL
CUR.S.
If the C.TYP is either 1, 2, 3, or 4, and the unit is in a cool mode,
then EC.C.P = the Cooling Control Point (Run Status
VIEW
CL.C.P).
DCV.C
IAQ.M) when the outdoor
VIEW
EC.C.P. This is
SASP
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Troubleshooting
