Digital Compressor Required Configurations; Ccn Loadshed Demand Limit; Ccn Controlled Demand Limit; Digital Scroll Operation - Carrier 38APS025 Manual

CCN Loadshed Demand Limit — To configure Demand
Limit for CCN Loadshed control, set the Demand Limit Select
(Configuration RSET DMDC) to 3. Then configure the
Loadshed Group Number (Configuration RSET SHNM),
Loadshed Demand Delta (Configuration RSET SHDL),
and Maximum Loadshed Time (Configuration RSET
SHTM).
The Loadshed Group number is established by the CCN
system designer. The ComfortLink controls will respond to a
Redline command from the Loadshed control. When the Red-
line command is received, the current stage of capacity is set to
the maximum stages available. Should the loadshed control
send a Loadshed command, the ComfortLink controls will re-
duce the current stages by the value entered for Loadshed De-
mand delta. The maximum loadshed time is the maximum
length of time that a loadshed condition is allowed to exist. The
control will disable the Redline/Loadshed command if no Can-
cel command has been received within the configured maxi-
mum loadshed time limit. Refer to the Loadshed Overview
and Configuration Manual for additional information.
CCN Controlled Demand Limit — With the control method
set to CCN Control (Configuration OPT2 CTRL=3
[CCN]), an external CCN device controls the On/Off state of
the machine. While in this control mode, the demand limit can
be written to the CCN Point, DEM_LIM. No other configura-
tion is required. Any value less than 100% written to this point
will limit the capacity to this value.
Units controlled via communications by a separate third-
party building automation system through a translator or UPC
Open Controller must be set to CCN Control (CTRL=3). If the
unit is to be monitored only via communications, CTRL=3
(CCN) is not required.
DIGITAL COMPRESSOR — The 38AP units have a fac-
tory-installed option for a digital scroll compressor which pro-
vides additional capacity control for the unit. If equipped, the
digital compressor is always installed in the A1 compressor
location. When a digital compressor is installed, a digital
unloader solenoid (DUS) is used on the digital compressor.
Digital Scroll Operation — A digital scroll operates in two
states: the "loaded state" when the digital unloader solenoid
valve (DUS) is normally closed, and the "unloaded state"
when the DUS is open. During the loaded state, the compres-
sor operates like a standard scroll and delivers full capacity and
mass flow. However, during the unloaded state, there is no
capacity and no mass flow through the compressor. The capac-
ity of the system is varied by varying the time the compressor
operates in an unloaded and loaded state during a 15-second
period. If the DUS is energized for 7.5 seconds, the compres-
sor will be operating at 50% capacity. If the DUS is energized
ITEM DISPLAY
A1.TY NO/YES
MAX.T XX Sec
Table 43 — Digital Compressor Required Configurations
CONFIGURATION UNIT
EXPANSION
A1 Compressor Digital?
Maximum A1 Unload Time
for 11 seconds, the compressor will be operating at approxi-
mately 25% of its capacity. Capacity is the time-averaged sum-
mation of loaded and unloaded states, and its range is
continuous from 10% to 100%. Regardless of capacity, the
compressor always rotates with constant speed. As the com-
pressor transitions from a loaded to unloaded state, the dis-
charge and suction pressures will fluctuate and the compressor
sound will change.
When a digital compressor is started, it will run at full load
for 90 seconds prior to beginning the digital operation. This is
for oil return.
The ComfortLink controller controls and integrates the op-
eration of the DUS into the compressor staging routine to
maintain temperature control. When a digital compressor is in-
stalled, an additional discharge gas thermistor (DTT) is in-
stalled along with the AUX board for control of the DUS.
Digital Compressor Configuration —
compressor is installed,
Configuration UNIT A1.TY is configured to YES. There
is also a maximum
Configuration UNIT MAX.T, that is set based on unit
size, which indicates the maximum unloading for the digital
compressor. The factory default for MAX.T is 10
(38APD,APS025-030) or 8 (38APD,APS040-130). These
numbers can be lowered, but cannot be increased more than
the factory default. The upper limit for the maximum unload
time is preset based on the unit and is set for oil return. See
Table 43 for required configurations.
HEAD PRESSURE CONTROL — The main base board
(MBB) controls the condenser fans to maintain the lowest con-
densing temperature possible, and thus the highest unit effi-
ciency. The MBB uses the saturated condensing temperature
input from the discharge pressure transducer and outside air
temperature (OAT) sensor to control the fans. If OAT is greater
than 70 F (21.1 C) before a circuit is starting, then all con-
denser fan stages will be energized. A fan stage is changed
based on SCT (saturated condensing temperature).
Fan staging is controlled by four parameters: Head Setpoint
On (Setpoints HEAD H.SP), Head Setpoint Off (Set-
points HEAD H.SP.F), Fan Stage Delta (Setpoints
HEAD F.DLT), and Fan Delta Active Time (Setpoints
HEAD F.TME). From these parameters, two control points
are calculated, Fan On Set Point (Setpoints HEAD F.ON)
and Fan Off Set Point (Setpoints HEAD F.OFF).
See Table 44 for head pressure control settings. Tables 45-
52 show the number of fan stages, contactors energized and the
fans that are on during the fan stage.
YES = Factory Equipped (Default)
NO = Not Equipped
Range: 0 to 10 (38AP025-030)
0 to 8 (38AP040-130)
Default: 10 (38AP025-030)
117
When a digital
the configuration
unload time configuration,
COMMENTS
8 38AP040-130)
parameter