65
ECONOMIZER OPERATION CONFIGURATION
The configuration items in the E.CFG menu group affect how
the economizer modulates when attempting to follow an econ-
omizer cooling setpoint. Typically, they will not need adjust-
ment. In fact, it is strongly advised not to adjust these configu-
ration items from their default settings without first consulting
a service engineering representative.
In addition, the economizer cooling algorithm is designed to
automatically 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,
enthalpy and dew point temperature.
The following information can be found under the Local Dis-
play Mode Run Status
ECON. See Table 64.
Economizer Control Point Determination Logic
Once the economizer is allowed to provide free cooling, the
economizer must determine exactly what setpoint it should try
to maintain. The setpoint the economizer attempts to maintain
when “free cooling” is located at Run Status
VIEW
EC.C.P. This is the economizer control point.
The control selects setpoints differently, based on the control
type of the unit. This control type can be found at Configuration
UNIT
C.TYP. There are 6 types of control.
C.TYP = 1 VAV- RAT
C.TYP = 2 VAV- SPT
C.TYP = 3 TSTAT Multi-Staging
C.TYP = 4 TSTAT 2 Stage
C.TYP = 5 SPT Multi-Staging
C.TYP = 6 SPT 2 Stage
If the economizer is not allowed to do free cooling, then
EC.C.P = 0.
If the economizer is allowed to do free cooling and the Unoc-
cupied Free Cooling Mode is ON, then EC.C.P = Setpoints
SASP + Inputs
RSET
SA.S.R.
If the economizer is allowed to do free cooling and the Dehu-
midification mode is ON, then EC.C.P = the Cooling Control
Point (Run Status
VIEW
CL.C.P).
If the C.TYP is either 4 or 6, and the unit is in a cool mode, then
If Stage = 0 EC.C.P = the Cooling Control Point (Run Status
VIEW
CL.C.P)
If Stage = 1 53.0 + economizer suction pressure reset (see
below)
If Stage = 2 48.0 + economizer suction pressure reset (see
below)
NOTE: To check the current cooling stage go to Run Status
Cool
CUR.S.
If the C.TYP is either 1,2,3, or 5, and the unit is in a cool mode,
then EC.C.P = the Cooling Control Point (Run Status
VIEW
CL.C.P).
Economizer Suction Pressure Reset for Two-Stage Cooling
If the unit’s control type is set to either 2-stage thermostat or 2-
stage space temperature control, then there is no cooling con-
trol point. Stages 1 and 2 are brought on based on demand, irre-
spective of the evaporator discharge temperature. In this case,
the economizer monitors suction pressure and resets the econo-
mizer control point accordingly in order to protect the unit
from freezing. For those conditions when the economizer
opens up fully but is not able to make setpoint, and then a com-
pressor comes on, it is conceivable that the coil might freeze.
This can be indirectly monitored by checking suction pressure.
Rather than fail a circuit, the control will attempt to protect the
unit by resetting the economizer control point until the suction
pressure rises out of freezing conditions.
If either circuit’s suction pressure drops to within 5 psig of the
low suction pressure trip point, the control will start adding re-
set to the economizer control point if it is active. It will be pos-
sible to reset the control point upwards, 10 degrees (2 degrees
per psig), between the low suction pressure trip point of 93
psig. If this does not work, and if the suction pressure drops be-
low the trip point, then the control will further reset the control
point 1 degree every 15 seconds up to a maximum of 10 de-
grees. The resulting effect will be to warm up the mixed air en-
tering the evaporator, thereby raising the suction pressure.
Table 64 — Economizer Run Status Table
ITEM EXPANSION RANGE UNITS CCN POINT WRITE STATUS
ECN.P Economizer Act.Curr.Pos. 0 to 100 % ECONOPOS
ECN.C Economizer Act.Cmd.Pos. 0 to 100 % ECONOCMD forcible
ACTV Economizer Active ? YES/NO ECACTIVE
DISA ECON DISABLING CONDITIONS
UNAV Econ Act. Unavailable? YES/NO ECONUNAV
R.EC.D Remote Econ. Disabled? YES/NO ECONDISA
DBC DBC - OAT Lockout? YES/NO DBC_STAT
DEW DEW - OA Dewpt.Lockout? YES/NO DEW_STAT
DDBC DDBD- OAT > RAT Lockout? YES/NO DDBCSTAT
OAEC OAEC- OA Enth Lockout? YES/NO OAECSTAT
DEC DEC - Diff.Enth.Lockout? YES/NO DEC_STAT
EDT EDT Sensor Bad? YES/NO EDT_STAT
OAT OAT Sensor Bad ? YES/NO OAT_STAT
FORC Economizer Forced ? YES/NO ECONFORC
SFON Supply Fan Not On 30s ? YES/NO SFONSTAT
CLOF Cool Mode Not In Effect? YES/NO COOL_OFF
OAQL OAQ Lockout in Effect ? YES/NO OAQLOCKD
HELD Econ Recovery Hold Off? YES/NO ECONHELD
DH.DS Dehumid. Disabled Econ.? YES/NO DHDISABL
O.AIR OUTSIDE AIR INFORMATION
OAT Outside Air Temperature dF OAT forcible
OA.RH Outside Air Rel. Humidity % OARH forcible
OA.E Outside Air Enthalpy OAE
OA.D.T Outside Air Dewpoint Temp dF OADEWTMP
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