39
Demand Limit —
Demand limit is a feature that allows
the unit capacity to be limited during periods of peak energy
usage. This allows the owner to keep energy costs down. There
are three types of demand limiting that can be configured. The
first type is through 2-step 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 between 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 capaci-
ty to maximum and further reduce the capacity if required. De-
mand limit control can be based on a calculated capacity level
or by compressor current level.
NOTE: If using the compressor current level for demand limit,
take into account the other power draws such as the condenser-
fan motors when determining the limit value desired.
SWITCH CONTROLLED DEMAND LIMIT — The con-
trol system is capable of demand limit based on a field-sup-
plied switch for 1-step demand limit or 2 switches for 2-step
demand limit. One-step demand limit is standard. The 2-step
switch control of demand limiting requires the Energy Man-
agement Module (EMM). Demand limit steps are controlled
by two relay switch inputs field wired to TB5-5 and TB5-14
for Switch 1 and TB6-14 and TB6-15 for Switch 2.
For demand limit by switch control, closing the first de-
mand limit contact will put the unit on the first demand limit
level, either by capacity or compressor current. The unit will
not exceed the percentage of capacity or compressor current
entered as Demand Limit Switch 1 set point. Closing contacts
on the second demand limit switch prevents the unit from ex-
ceeding the demand limit entered as Demand Limit Switch 2
set point. The demand limit percent capacity or compressor
current that is set to the lowest demand takes priority if both de-
mand limit inputs are closed. If the demand limit percentage
does not match unit operation, the unit will limit capacity or
current to the closest step without exceeding the value.
To use demand limit, select the type of demand limiting to
use by configuring the Demand Limit Select variable (
De-
mand Limit Type Select
, DMDC
) to Switch. Configure the
Demand Limit set points based on the type selected.
Switch Controlled (Capacity Based) — If using 2-step de-
mand limit control, an energy management module must be in-
stalled. One-step demand limit control does not require the en-
ergy management module. To configure Demand Limit for
switch control, three parameters for 1-step switch control must
be configured. For 2-step control, four parameters must be
configured. The parameters are: the type of Demand Limit
Selection (
Demand Limit Type Select
, DMDC
), the setting
for Switch Limit Set Point 1 (
Switch Limit Setpoint 1
, DLS1
),
The setting for Switch Limit Set Point 2 (
Switch Limit Set-
point 2,
DLS2
), and Current Limit Select (
Current Limit Se-
lect
, CUR.S
). Current Limit Select must be set to NO.
To configure this option with the Touch Pilot™ display:
To configure this option with the Navigator™ display:
DISPLAY NAME
PATH
LINE NO.
VALUE
Demand Limit
Type Select
Config
USER
24
1 (Switch Control)
Default = 0 (None)
Switch Limit
Setpoint 1
Setpoints
SETPOINT
33
Default = 100%
Switch Limit
Setpoint 2
Setpoints
SETPOINT
34
(Not required
for 1-Step)
Default = 100%
Current Limit
Select
Config
USER
30
No
Default = No
ITEM
ITEM EXPANSION
PATH
VALUE
DMDC
Demand Limit
Select
Configuration
RSET
SWITCH
Default = NONE
DLS1
Switch Limit
Setpoint 1
Setpoints
MISC
Default = 100%
DLS2
Switch Limit
Setpoint 2
Setpoints
MISC
(Not required
for 1-Step)
Default = 100%
CUR.S
Current Limit
Select
Configuration
OPTN
NO
Default: NO
Fig. 23 — 4 to 20 mA Temperature Reset
0
1
2
3
4
5
6
0
10
14
20
mA
S
i
g
nal
De
g
ree
s
Re
s
et (de
g
F)
2
Cooling Re
s
et
Deg. V
a
l
u
e,
DGRC
C
u
rrent No Re
s
et V
a
l
u
e,
CRV1
C
u
rrent F
u
ll Re
s
et V
a
l
u
e,
CRV2
4
6
8
12
16
1
8
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