Building Pressure Control - Carrier WEATHERMASTER 48/50Z030-105 Operation And Service Manual

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
→
Display Mode Run Status
Economizer Control Point Determination Logic — Once the
economizer is allowed to provide free cooling, the economizer
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 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
Unoccupied Free Cooling Mode is ON, then EC.C.P =
→ →
Setpoints SASP + Inputs
If the economizer is allowed to do free cooling and the
Dehumidification mode is ON, then EC.C.P = the Cooling
→
Control Point (Run Status
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
If Stage = 1 53.0 + economizer suction pressure reset
If Stage = 2 48.0 + economizer suction pressure reset
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).
ITEM
ECN.P Economizer Act.Curr.Pos.
EC2.P Economzr 2 Act.Curr.Pos.
ECN.C Economizer Act.Cmd.Pos.
ACTV Economizer Active ?
DISA ECON DISABLING CONDITIONS
UNV.1 Econ Act. Unavailable?
UNV.2 Econ2 Act. Unavailable?
ENTH Enth. Switch Read High ?
DBC DBC - OAT Lockout?
DEW DEW - OA Dewpt.Lockout?
DDBC DDBD- OAT > RAT Lockout?
OAEC OAEC- OA Enth Lockout?
DEC DEC - Diff.Enth.Lockout?
EDT EDT Sensor Bad?
OAT OAT Sensor Bad ?
FORC Economizer Forced ?
SFON Supply Fan Not On 30s ?
CLOF Cool Mode Not In Effect?
OAQL OAQ Lockout in Effect ?
HELD Econ Recovery Hold Off?
DH.DS Dehumid. Disabled Econ.?
O.AIR OUTSIDE AIR INFORMATION
OAT Outside Air Temperature
OA.RH Outside Air Rel. Humidity
OA.E Outside Air Enthalpy
OA.D.T Outside Air Dewpoint Temp
ECON. See Table 57.
→ →
VIEW EC.C.P. This is
→
RSET SA.S.R.
→
VIEW CL.C.P).
→
CL.C.P)
Table 57 — Economizer Run Status Table
EXPANSION
Economizer Suction Pressure Reset for Two-Stage
Cooling — If the unit's control type is set to either 2-stage ther-
mostat or 2-stage space temperature control, then there is no
cooling control point. Stages 1 and 2 are brought on based on
demand, irrespective of the evaporator discharge temperature.
In this case, the economizer monitors suction pressure and
resets the economizer 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 set point, and
then a compressor comes on, it is conceivable that the coil
might freeze. This can be indirectly monitored by checking suc-
tion 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 reset to the economizer control point if it is active. It
will be possible to reset the control point upwards, 10 degrees
(2 degrees per psig), between the low suction pressure trip
point of 48 psig and 5 psig above it. If this does not work, and if
the suction pressure drops below the trip point, then the control
will further reset the control point 1 degree every 15 seconds
up to a maximum of 10 degrees. The resulting effect will be to
warm up the mixed air entering the evaporator, thereby raising
the suction pressure.
Building Pressure Control —
provides control of the building pressure through the modulat-
ing flow rate functions of one of the modulating power exhaust
options or through management of the return fan option. This
function also provides control of the constant volume 2-stage
power exhaust option. See below for available power exhaust
options for each unit model.
CONSTANT
UNIT VOLUME
2-STAGE
48ZG, 50ZG,Z2
48ZN, 50ZN,Z3
48ZT,ZW
50ZT,ZW,ZX,ZZ
48Z6,Z8
50Z6,Z7,Z8,Z9
→
LEGEND
X — Available as Factory Option
S.O. — Available as Special Order
NA — Not Available on this Unit
STD — Standard Feature on this Unit
RANGE UNITS
0-100 %
0-100 %
0-100 %
YES/NO
YES/NO
YES/NO
YES/NO
YES/NO
YES/NO
YES/NO
YES/NO
YES/NO
YES/NO
YES/NO
YES/NO
YES/NO
YES/NO
YES/NO
YES/NO
YES/NO
dF
%
dF
69
This control sequence
HIGH
MODULATING
S.O. CAPACITY
POWER
VFD* POWER
EXHAUST
EXHAUST†
X X S.O. NA
NA X S.O. NA
NA NA NA STD
NA NA NA NA
*Single VFD controlling both fan
motors.
†Single VFD controlling one fan
motor and staging of the second
fan motor.
CCN POINT WRITE STATUS
ECONOPOS
ECON2POS
ECONOCMD forcible
ECACTIVE
ECONUNAV
ECN2UNAV
ENTH
DBC_STAT
DEW_STAT
DDBCSTAT
OAECSTAT
DEC_STAT
EDT_STAT
OAT_STAT
ECONFORC
SFONSTAT
COOL_OFF
OAQLOCKD
ECONHELD
DHDISABL
OAT forcible
OARH forcible
OAE
OADEWTMP
RETURN/
EXHAUST†
NA
NA
NA
STD