Humidi-Mizer - Carrier 50PG20-28 Controls, Start-Up, Operation, Service And Troubleshooting Instructions

SPACE S ENSOR CONTROL If theunitis in cooling,
operating under space t cnnperature control, theeconomizer is
available forcooling, and nocompressors areoperating, the
economizer willcontrol theSAT toeither
Setpoints--->LCgP or
Setpoints---_HCSP (see Table 40). If a compressor is ON, the
economizer will try to position itself at the economizer maxi-
mum cooling position (Configuration ---_EL_ON --_ECMX).
If the control senses low suction pressure for any active re-
fi-igerant circuit when the economizer is also providing cooling,
the maximmn allowable economizer position will be reduced.
Factory default confi_rations have been qualified over a lane
range of conditions and should only be changed with care. For
unit troubleshooting, factory default maximum economizer
limits for this condition are provided in Table 41.
Table 40 -- LCSP and HCSP Transitions for
Space Temperature Mode
CURRENT SAT
SET POINT
LCSP
HCSP
LCSP
LEGEND
HCSP -- High Coot Set Point
LCSP -- Low Cool Set Point
SAT -- Supply-Air Temperature
COOL DEMAND NEXT SAT
(AF) SET POINT
>05 HCSP
<0 LCSP
<-0.5 Exit Cooling
Table 41 -- Maximum Economizer Limits During
Low Suction Pressure
COOLING STAGE ] LIMIT (%)
Bottom ] 50
Middle 50
Top 0
ECONOMIZER ACTUATOR COMMUNICATIONS The
confi_ration Economizer Control Type determines the
colrnnunication method, either digital or analog, used to
colrnnunicate between the ECB and the economizer actuator.
Economizer Control Type is accessible via the Scrolling
Marquee at Configurations--_E(DN--_E.CTL. The power to
the unit must be cycled after E. CTL is changed.
E. CTL = 1 (Digital/Position) When E.(TL is set to 1, the
ECB will co_rnnunicate with the economizer actuator using the
digital protocol. The ECB 4 to 20 mA output will represent the
actuator's actual position. Because the wiring has a built-in
500-ohin resistor, the 4 to 20 mA signal is converted to a 2 to
10-v signal that is accessible via field connection terminal board
TB2-8 aald TB2-9. However, before this signal coal be read, the
violet wire that connects the actuator to field connection termi-
nal board TB2-J10-8 must be removed or cut.
E.CTL = 2 (Digital/Command) When E.(TL is set to 2,
the ECB will communicate with the economizer actuator using
the digital protocol. The ECB 4 to 20 mA output will represent
the actuator's colrnnanded position. Because the wiring has a
built-in 500-ohm resistor, the 4 to 20 mA signal is converted to
a 2 to 10-v signal that is accessible via field connection termi-
nal board TB2-8 and TB2-9. However, betbre this signal can
be read, the violet wire that connects the actuator to field con-
nection terminal board TB2-J10-8 must be removed or cut.
E. CTL = 3 (Analog Control) When E.(TL is set to 3, the
ECB wilt colrnnunicate with the economizer actuator using the
4 to 20 mA analog signal wired to TB2-8 and TB2-9 along
with the 500-ohin resistor producing a 2 to 10-v signal for the
actuator. While in this mode, the actuator's built-in 2 to 10-v
feedback signal is accessible via TB2-9 and TB2-10.
UNOCCUPIED FREE COOLING The unoccupied fiee
cooling algorithin attempts to maintain the building space at
the occupied cooling set point during unoccupied periods if the
coMitions in the building and the outdoors are suitable. Three
different confimlrations define this algorithm: Unoccupied
Free Cooling ((bnfiguration--+E_DN--+UEFC), Free Cool-
ing Preoccupancy Time (Configuration--_E(ON--_FC. TM)
and Free Cool Low Ternp Limit ((bnfiguration--_
ECON--_FC.LO).
(bnfiguration--_E_ON--_UEFC = 0 (Disabled) When
UEFC = 0, unoccupied fiee cooling is disabled.
(bnfigurafion-->ELON-->UEFC= 1 (Unoccupied) When
UEFC = 1, unoccupied fiee cooling can occur whenever the
building is unoccupied.
(bnfigurafion--_ECON_UEFC= 2 (Preoccupancy) When
UEFC = 2, unoccupied fi'ee cooling can only occux when the
time to the next occupied period is less than Configumtion--_
ECON--_FC. TMminutes.
Configumtion---_E_ ON---_F(: TM FC TM is the configura-
tion that determines how many minutes before occupancy that
fiee cooling can occur.
Configumtion--_ECON--_FCLO Unoccupied flee cooling
cannot occur if the Outdoor Air Temperature
(Tempera-
ture--_AIR. T_OA1) is less than FCLO.
POWER EXHAUST To enable power exhaust, Configu-
ration--+E_ON--_PE.EN must be set to ENBL. If power ex-
haust is enabled, Power Exhaust 1 will turn on when the econo-
mizer position is reeater than the value of Configuration--_
E_DN---_PE.1. If power exhaust is enabled, Power Exhaust 2
will turn on when the economizer position is re'eater than the
value of Configuration--_ELON--_PE.2. There are small time
delays to ensure that rapid cycling does not occur.
Optional Humidi-MiZer
TM
Dehumidification Sys-
tem--Units with the thctory-equipped Humidi-MiZer
option are capable of providing multiple modes of improved
dehumidification as a variation of the normal cooling cycle.
The Humidi-MiZer option includes additional valves in the
liquid line and discharge line of each refiigerant circuit, a small
reheat condenser coil downstream of the evaporator, and
Motonnaster, _R) v ariable-speed control of some or all outdoor
fans. Operation of the revised refiigerant circuit for each mode
is described belo,a:
NOTE: x refrigerant circuit A or B.
Normal Coolina Ret}igerant flows t}om the outdoor
condenser through the de-energized 3-way vane (RHI.x) to
the expansion device. Reheat2 Valve (RH2.x) is closed. See
Fig. 6.
Reheat 1 (Subcoolin_ Mode) This mode incaeases latent
cooling and decreases sensible cooling compared to normal
cooling. Refi-igerant flows fiom the outdoor condense1;
through the energized 3-way Valve (RH1 .x), and throu_l the
reheat condenser coil to the expansion device. Reheat2 _alve
(RH2.x) is closed. See Fig. 7.
Reheat 2 (Hot Gas Reheat Mode) This mode provides
maximum latent cooling with little to no sensible capacity.
This mode can operate to provide dehmnidification when there
is no cooling demand. Like Reheat 1 mode, refiigerant flows
fi'om the outdoor condenser, through the energized 3-way vane
(RH1 .x), and through the reheat condenser coil to the expan-
sion device. Reheat2 Valve (RH2.x) is open which provides
some compressor discharge gas to the reheat condenser to fur-
ther increase the reheat of the evaporator air stream. See Fig. 8.
Units with multiple circuits can operate with additional
staging of the cooling and dehumidification capacity. When
there is only cooling demand, based on a space temperature
sensor or thermostat, one or more circuits will operate in
normal cooling mode. When there is only dehumidification
demand, based on a space humidity sensor or switch, all
circuits will operate in reheat2 mode. When there is both
cooling demand and dehumidification demand, all circuits will
operate in either reheatl or reheat2 mode, with the portion of
reheat 1 circuits determined fiom the cooling demand.
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