Carrier WeatherExpert 48N2 Controls, Start-Up, Operation, Service, And Troubleshooting page 80

OUTDOOR AIR CFM CONTROL
If an outdoor air cfm flow station has been installed on an N Series
rooftop, the economizer is able to provide minimum ventilation
based on cfm, instead of damper position. The Outdoor Air Cfm
reading can be found in Inputs  CFM  O.CFM.
The following options are used to program outside air cfm control:
Outdoor Air CFM Sensor Enable (OCF.S)
This configuration enables the outdoor air cfm sensor and outside
air cfm control. This configuration has the following settings:
0 = NONE - OACFM sensor and control is disabled (default).
1 = STD AIR FLOW - OACFM sensor and control is enabled
using the factory standard airflow transducer having a range of
approximately 2,300 to 22,600 cfm (75-105 ton) or 2,700 to
26,200 (120-150 ton) (effective with Version 3.0 or later soft-
ware). Single actuator cfm, E.SAC, must be enabled (set to
YES) to reach the lowest cfms.
2 = EXT AIR FLOW - OACFM sensor and control is enabled
using extended airflow (field-installed upgraded range) trans-
ducer having a range of approximately 6,000 to 60,000 cfm
(75-150 ton) (standard with version 2.0 and earlier software;
optional effective with version 3.0).
Economizer Minimum Flow Rate (O.C.MX)
This "cfm" configuration option replaces Economizer Minimum
Position (EC.MN) when an outdoor air cfm sensor is enabled.
IAQ Demand Vent Minimum Flow Rate (O.C.MN)
This "cfm" configuration option replaces the IAQ Demand Ven-
tilation Minimum Position (Configuration  IAQ  DCV.C 
IAQ.M) when the outdoor air cfm sensor is enabled.
Economizer Minimum Flow Deadband (O.C.DB)
This "cfm" configuration option defines the deadband of the
cfm control logic.
Economizer Control Run Rate (OA.RR)
This rate will specify how often the economizer position is up-
dated based on ECMINCFM and OACFMAVG.
Economizer Control Minimum Position (OA.MP)
This is the minimum economizer position (% open) that will be
allowed during the OACFM control. This is to prevent the
economizer position from being calculated to 0% which results
in OACFM=0 or a very low value.
Enable DCFM/OACFM Clamp (EN.DO)
If EN_DOCFM = YES and OACFM<DCFM_MAX, DCFM
will be clamped at OACFM. If EN_DOCFM=NO, DCFM will
be clamped at DCFM_MAX. This configuration is to prevent a
very low OACFM value from causing the fan algorithm to lose
control of building pressure.
Enable Single Act CFM (E.SAC)
The configuration enables single actuator OACFM control and
has the following settings:
NO = Single actuator OACFM control is disabled (factory de-
fault). The control will use both outside air economizer damp-
ers to meet ECMINCFM. This is the recommended setting
when trying to control to greater than 7000 cfm outdoor air.
YES = Single actuator OACFM control is enabled. When EC-
MINCFM falls below S.MX.C (SAMAXCFM) one outside air
economizer damper shall be closed and the remaining damper
shall be modulated to meet ECMINCFM. This is the recom-
mended setting when trying to control to less than 7000 cfm
outdoor air.
Single Act. Max CFM (S.MX.C)
This configuration sets the single actuator maximum cfm. If
the OACFM sensor is enabled and E.SAC = YES, when EC-
MINCFM falls below this configuration one outside air econo-
mizer damper shall be closed and the remaining damper shall
be modulated to meet ECMINCFM. This configuration shall
default to 7500 cfm for the standard flow station and 17500 for
extended flow station.
Single Act Max CFM DB (S.M.DB)
This configuration sets the single actuator max cfm deadband.
When ECMINCFM is greater than S.MX.C + S.M.DB the con-
trol shall revert back to dual actuator OACFM control. This con-
figuration shall have a range of 0 to 5000 and a default of 2500.
During cfm control, the economizer must guarantee a certain
amount of cfm at any time for ventilation purposes. If the out-
door 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. Now, this configurable deadband helps
keep the economizer from attempting to close until the outdoor
air cfm rises to the current minimum cfm position PLUS the
deadband value. Increasing this deadband value may help to
slow down excessive economizer movement when attempting
to control to a minimum position at the expense of bringing in
more ventilation air than desired.
EC.MN is the set point the ComfortLink software is attempting
to meet for OACFM. It is determined using the following:
O.C.MX - Economizer Min.Flow [OACFMMAX]
O.C.MN - IAQ Demand Vent Min.Flow [OACFMMIN]
IQ.O.C - IAQ Override Flow [IAQOVCFM]
How single actuator control works:
• If E.SAC=NO, the ComfortLink software will attempt to
meet ECMINCFM using 2 actuators.
• If E.SAC=YES:
• If EC.MN < S.MX.C, the Comfortlink software will acti-
vate single actuator OACFM control and attempt to meet
EC.MN using a single actuator.
• If single actuator OACFM control is active and EC.MN >
S.MCX.C + S.M.DB, the ComfortLink software will revert
back to dual actuator cfm control.
• Control would also return to dual actuator when:
• Free cooling active and OACFM is greater than S.MX.C +
S.M.DB
• Fire/smoke emergency
• Special allowances for service test:
If Run Status  ECON  SACA =NO both outside actuators
shall be commanded from Service Test  FANS  E.POS and
Service Test  COOL  E.POS.
If Run Status  ECON  SACA=YES only a single outside ac-
tuator shall be commanded from Service Test  FANS 
E.POS and Service Test  COOL  E.POS.
This will allow verification that the OACFM measurement is
adjusted properly based on the number of dampers used. It also
allows easy comparison of OACFM for various fan speeds.
BACKWARDS COMPATIBILITY NOTE: Units with version
3.0 software or later and OACFM option will have OCF.S set
to "1," STD AIR FLOW. These units will have a control that
enables the single outside air actuator feature, allowing accu-
rate low OACFM measurement. When upgrading software on
units built prior to January 2015, it will be necessary to manu-
ally set OCF.S to "2" unless the OACFM transducer was previ-
ously changed to a range of 0 to 0.10 in. wg.
ECONOMIZER OPERATION CONFIGURATIONS (WHICH
AFFECT FREE COOLING ACTUATOR MODULATION)
There are configuration items in the E.CFG menu group that
affect how the economizer modulates when attempting to fol-
low an economizer cooling set point. Typically, they will not
need adjustment. In fact, it is strongly advised not to adjust
these configurations from their default settings without first
consulting a service engineering representative.
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