55
remove a cooling stage and open up the economizer further to
make up the difference.
Mechanical Cooling Lockout (
Configuration
COOL
MC.LO) — This configuration allows a configurable outside-
air temperature set point below which mechanical cooling will
be completely locked out.
DEMAND LIMIT CONTROL — Demand Limit Control
may override the cooling algorithm and clamp or shed
cooling capacity during run time. The term Demand Limit
Control refers to the restriction of the machine capacity
to control the amount of power that a machine will use.
Demand limit control is intended to interface with an external
Loadshed Device either through CCN communications, exter-
nal switches, or 4 to 20 mA input.
The control has the capability of loadshedding and limiting
in 3 ways:
• Two discrete inputs tied to configurable demand limit set
point percentages.
• An external 4 to 20 mA input that can reset capacity back
linearly to a set point percentage.
• CCN loadshed functionality.
NOTE: It is also possible to force the demand limit variable
(Run Status
COOL
DEM.L).
To use Demand Limiting, select the type of demand limiting
to use. This is done with the Demand Limit Select configura-
tion (Configuration
BP
DMD.L
DM.L.S).
To view the current demand limiting currently in effect,
look at Run Status
COOL
DEM.L.
The configurations associated with demand limiting can be
viewed at the local display at Configuration
BP
DMD.L.
See Table 33.
Demand Limit Select (
DM.L.S) — This configuration deter-
mines the type of demand limiting.
• 0 = NONE — Demand Limiting not configured.
• 1 = 2 SWITCHES — This will enable switch input
demand limiting using the switch inputs connected to the
CEM board. Connections should be made to TB202
terminals 1,2,3, and 4.
• 2 = 4 to 20 mA — This will enable the use of a remote 4
to 20 mA demand limit signal. The CEM module must
be used. The 4 to 20 mA signal must come from an exter-
nally sourced controller and should be connected to
TB202 terminals 10 and 11.
• 3 = CCN LOADSHED — This will allow for loadshed
and red lining through CCN communications.
Two-Switch Demand Limiting (DM.L.S = 1) — This type of
demand limiting utilizes two discrete inputs:
• Demand Limit Switch 1 Setpoint (D.L.S1) — Dmd Limit
Switch Setpoint 1 (0 to 100% total capacity)
• Demand Limit 2 Setpoint (D.L.S2) — Dmd Limit Switch
Setpoint 2 (0 to 100% total capacity)
The state of the discrete switch inputs can be found at the lo-
cal display:
Inputs
GEN.I
DL.S1
Inputs
GEN.I
DL.S2
The following table illustrates the demand limiting (Run
Status
COOL
DEM.L) that will be in effect based on the
logic of the applied switches:
4-20 mA Demand Limiting (DM.L.S = 2) — If the unit has
been configured for 4 to 20 mA demand limiting, then the
Inputs
4-20
DML.M value is used to determine the
amount of demand limiting in effect (Run Sta-
tus
COOL
DEM.L). The Demand Limit at 20 mA
(D.L.20) configuration must be set. This is the configured
demand limit corresponding to a 20 mA input (0 to 100%).
The value of percentage reset is determined by a linear
interpolation from 0% to “D.L.20”% based on the Inputs
4-20
DML.M input value.
The following examples illustrate the demand limiting
(Run Status
COOL
DEM.L) that will be in effect based on
amount of current seen at the 4 to 20 mA input, DML.M.
CCN Loadshed Demand Limiting (DM.L.S = 3) — If the unit
has been configured for CCN Loadshed Demand Limiting,
then the demand limiting variable (Run Status
COOL
DEM.L) is controlled via CCN commands.
The relevant configurations for this type of demand limiting
are:
Loadshed Group Number (SH.NM) — CCN Loadshed Group
number
Loadshed Demand Delta (SH.DL) — CCN Loadshed
Demand Delta
Maximum Loadshed Time (SH.TM) — CCN Maximum
Loadshed time
The Loadshed Group Number (SH.NM) corresponds to
the loadshed supervisory device that resides elsewhere on the
CCN network and broadcasts loadshed and redline com-
mands to its associated equipment parts. The SH.NM variable
will default to zero which is an invalid group number. This
allows the loadshed function to be disabled until configured.
Upon reception of a redline command, the machine will be
prevented from starting if it is not running. If it is running,
then DEM.L is set equal to the current running cooling capac-
ity (Run Status
COOL
C.CAP).
Upon reception of a loadshed command, the DEM.L vari-
able is set to the current running cooling capacity (Run Status
COOL
C.CAP) minus the configured Loadshed Demand
Delta (SH.DL).
A redline command or loadshed command will stay in
effect until a Cancel redline or Cancel loadshed command is
received, or until the configurable Maximum Loadshed time
(SH.TM) has elapsed.
HEAD PRESSURE CONTROL — Condenser head pressure
for the 48/50N Series is managed directly by the ComfortLink
controls. The controls are able to cycle up to 9 stages of outdoor
fans to maintain acceptable head pressure. Fan stages will be
turned on or off in reaction to discharge pressure sensors with
the pressure converted to the corresponding saturated condens-
ing temperature.
An option to allow fan speed control (Motormaster
®
) on the
first stage is configured by setting Configura-
tion
COOL
M.M = Yes.
There are five configurations provided for head pressure
control that can be found at the local display:
Configuration
COOL
M.M (MotorMaster enable)
Configuration
M.PID
SCT.H (Maximum Condensing
Temp)
Configuration
M.PID
SCT.L (Minimum Condensing
Temp)
Switch Status Run Status
COOL
DEM.L = 1
Inputs
GEN.I
DL.S1 = OFF
Inputs
GEN.I
DL.S2 = OFF
100%
Inputs
GEN.I
DL.S1= ON
Inputs
GEN.I
DL.S2 = OFF
Configuration
DMD.L
D.L.S1
Inputs
GEN.I
DL.S1= ON
Inputs
GEN.I
DL.S2 = ON
Configuration
DMD.L
D.L.S2
Inputs
GEN.I
DL.S1= OFF
Inputs
GEN.I
DL.S2 = ON
Configuration
DMD.L
D.L.S2
D.L.20 = 80% D.L.20 = 80% D.L.20 = 80%
DML.M = 4mA DML.M = 12 mA DML.M = 20mA
DEM.L = 100% DEM.L = 90% DEM.L = 80%
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