Demand Limit; Demand Limit (2-Stage Switch Controlled); Externally Powered Demand Limit; Demand Limit (Ccn Loadshed Controlled) - Carrier AquaSnap 30RAP011-060 Controls, Start-Up, Operation, Service, And Troubleshooting

Design Rise
10
9
8
7
6
RT.F = 2
5
4
3
Reset Amount
2
1
0
0 1 2 3 4
Δ
T (°F), Entering Fluid Temperature - Leaving Fluid Temperature
LEGEND
EWT — Entering Water (Fluid) Temperature
LWT — Leaving Water (Fluid) Temperature
Fig. 36 — Standard Chilled Fluid
Temperature Control — No Reset
Under normal operation, the chiller will maintain a constant leav-
ing fluid temperature approximately equal to the chilled fluid set
point. As the cooler load varies, the entering cooler fluid will
change in proportion to the load as shown in Fig. 36. Usually the
chiller size and leaving-fluid temperature set point are selected
based on a full-load condition. At part load, the fluid temperature
set point may be colder than required. If the leaving fluid tempera-
ture was allowed to increase at part load, the efficiency of the ma-
chine would increase.
Return temperature reset allows for the leaving temperature set
point to be reset upward as a function of the return fluid tempera-
ture or, in effect, the building load (see Fig. 37).
Design Rise
10
9
8
7
6
RT.F = 2
5
4
3
Reset Amount
2
1
0
0 1 2 3 4
Δ
T (°F), Entering Fluid Temperature - Leaving Fluid Temperature
Fig. 37 — Reset Amount

Demand Limit

Demand limit is a feature that allows the unit capacity to be limit-
ed during periods of peak energy usage. There are 3 types of de-
mand limiting that can be configured. The first type is through 2-
stage switch control, which will reduce the maximum capacity to
2 user-configurable percentages. The second type is by 4 to 20 mA
signal input which will reduce the maximum capacity linearly be-
tween 100% at a 4 mA input signal (no reduction) down to the
user-configurable level at a 20 mA input signal. The third type
uses the CCN Loadshed module and has the ability to limit the
current operating capacity to maximum and further reduce the ca-
pacity if required.
NOTE: The 2-stage switch control and 4 to 20 mA input signal
types of demand limiting require the energy management module
(EMM).
RT.NO = 10
5 6 7 8 9 10
RT.DG = 5
RT.NO = 10
5 6 7 8 9 10
To use demand limit, select the type of demand limiting to use.
Then configure the demand limit set points based on the type
selected.

DEMAND LIMIT (2-STAGE SWITCH CONTROLLED)

To configure demand limit for 2-stage switch control set the De-
mand Limit Select (Configuration  RSET  DMDC) to 1.
Then configure the 2 Demand Limit Switch points (Configura-
tion  RSET  DLS1) and (Configuration  RSET  DLS2) to
the desired capacity limit. See Table 27. Capacity steps are con-
trolled by 2 relay switch inputs field wired to LVT as shown in
Fig. 6-19.
RT.DG = 5
For demand limit by 2-stage switch control, closing the first stage
demand limit contact will put the unit on the first demand limit
level. The unit will not exceed the percentage of capacity entered
as Demand Limit Switch 1 set point (DLS1). Closing contacts on
the second demand limit switch prevents the unit from exceeding
the capacity entered as Demand Limit Switch 2 set point. The de-
mand limit stage that is set to the lowest demand takes priority if
both demand limit inputs are closed. If the demand limit percent-
age does not match unit staging, the unit will limit capacity to the
closest capacity stage.
To disable demand limit configure DMDC to 0. See Table 27.
EXTERNALLY POWERED DEMAND LIMIT (4 TO 20 MA
CONTROLLED)
To configure demand limit for 4 to 20 mA control set the Demand
Limit Select (Configuration  RSET  DMDC) to 2. Then con-
figure the Demand Limit at 20 mA (Configuration 
RSET  DM20) to the maximum loadshed value desired. Con-
nect the output from an externally powered 4 to 20 mA signal to
terminal block LVT-7,8. Refer to the unit wiring diagram for these
connections to the optional/accessory energy management module
and terminal block. The control will reduce allowable capacity to
this level for the 20 mA signal. See Fig. 38 and Table 27.
Care should be taken when interfacing with other manufac-
turer's control systems, due to possible power supply differ-
ences, full wave bridge versus half wave rectification. The two
different power supplies cannot be mixed. ComfortLink con-
trols use half wave rectification. A signal isolation device
should be utilized if a full wave bridge signal generating
device is used.

DEMAND LIMIT (CCN LOADSHED CONTROLLED)

To configure Demand Limit for CCN Loadshed control set the
Demand Limit Select (Configuration  RSET  DMDC) to 3.
Then configure the Loadshed Group Number (Configura-
tion  RSET  SHNM), Loadshed Demand Delta (Configura-
tion  RSET  SHDL), and Maximum Loadshed Time (Config-
uration  RSET  SHTM). See Table 27.
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 Redline com-
mand is received, the current stage of capacity is set to the maxi-
mum stages available. Should the loadshed control send a Load-
shed command, the ComfortLink controls will reduce the current
stages by the value entered for Loadshed Demand delta. The Max-
imum Loadshed Time is the maximum length of time that a load-
shed condition is allowed to exist. The control will disable the
Redline/Loadshed command if no Cancel command has been re-
ceived within the configured maximum loadshed time limit.

Digital Scroll Option

The 30RAP010-090 units have a factory-installed option for a dig-
ital scroll compressor which provides additional stages of unload-
ing for the unit. The digital compressor is always installed in the
49
CAUTION