53
Table 41 — Demand Limit Configuration
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 48/50Z series is managed directly by the ComfortLink™
controls. The controls are able to cycle two stages of outdoor
fans to maintain acceptable head pressure. Fan stages will react
to discharge pressure sensors with the pressure converted to the
corresponding saturated condensing temperature. Unit size is
used to determine if the second stage fans are configured to
respond to a particular circuit (independent control) or both
circuits (common control).
An option to allow fan cycling on the first stage is config-
ured by setting Configuration
→
COOL
→
M.M = Yes.
NOTE: The term Motormaster is used in the software to refer
to a fan cycling on the first stage. An actual Motormaster®
device is not used or required. Cycling is done by the
ComfortLink controls.
There are two configurations provided for head pressure
control that can be found at the local display:
Configuration
→
COOL
→
M.M. — Motormaster enable
Configuration
→
COOL
→
HPSP — Head Pressure Set point
There are three outputs provided to control head pressure:
Outputs
→
FAN S
→
CD.F.A — Condenser Fan A
Outputs
→
FAN S
→
CD.F.B — Condenser Fan B
Outputs
→
FAN S
→
CD.MM — “Motor master” or the fan
cycling output
Fan Stage 1 Operation — If Stage 1 Cycling (Motormaster)
is not selected, the stage 1 fan output will be ON whenever
mechanical cooling is ON (either circuit) and OFF when
mechanical cooling is OFF (both circuits).
If Stage 1 Cycling (Motormaster) is selected, the first stage
operates as follows:
The fan stage turns ON whenever either saturated condens-
ing temperature (SCT) is greater than 138 F.
The fan stage 1 turns OFF whenever both SCTs are less
than the HPSP – 37 F for 90 seconds and fan stage is 1.
Fan Stage 2 Operation (Sizes 030-050) — The control ener-
gizes fan CD.F.A when either of the SCTs exceeds HPSP and
the Stage 1 Fan (CD.MM) has been energized for 60 seconds.
Fan CD.F.A is turned OFF when both SCTs have been less
than the set point – 35 F for a period of 2 minutes. Fan stage 2
will turn OFF if both circuits are turned off.
Fan Stage 2 Operation (Sizes 055-105) — There are two
conditions that may request the second stage fan for indepen-
dent control:
• the control energizes fan stage 2 when the SCT for that
circuit exceeds HPSP and the Stage 1 fan has been ener-
gized for 60 seconds.
• the control energizes fan stage 2 if the SCT for the partic-
ular circuit exceeds 143 F during the first 60 seconds
after fan stage 1 has been turned on.
Fan stage 2 turns OFF when the SCT for the particular cir-
cuit has been less than HPSP – 35 F for a period of 2 minutes.
Head Pressure Control Exceptions — For size 105 units, cur-
rent sensor boards are able to diagnose a compressor stuck on
condition. If any of the current sensor boards for the four-
compressor unit detects a compressor stuck on, then the first
stage fan is turned on immediately (CD.MM). If compressors
A1 or A2 are diagnosed as stuck on, the second stage fan for
that circuit will be turned on (CD.F.A). If compressors B1 or
B2 are diagnosed as stuck on, the second stage fan for that
circuit will be turned on (CD.F.B).
If no compressors are stuck on, the next check will deter-
mine whether compressors are on or not. If any compressor has
not been commanded on, the first stage fan is not allowed on.
This is also true for the second stage fan and units configured
for unit sizes 030-050. For unit sizes 055-105, if no compres-
sors in a circuit are commanded on, the corresponding second
stage fan is not allowed on (CD.F.A, CD.F.B).
ECONOMIZER INTEGRATION WITH MECHANICAL
COOLING — When the economizer is able to provide free
cooling (Run Status
→
ECON
→
ACTV = YES), mechanical
cooling may be delayed or even held off indefinitely.
NOTE: Once mechanical cooling has started, this delay logic
is no longer relevant.
Multi-Stage Cooling Economizer Mechanical Cooling
Delay — This type of mechanical cooling delay is relevant to
the following machine control types:
C.TYP = 1 VAV-RAT
C.TYP = 2 VAV-SPT
C.TYP = 3 TSTAT-MULTI
C.TYP = 5 SPT-MULTI
ITEM EXPANSION RANGE UNITS CCN POINT DEFAULT
DMD.L DEMAND LIMIT CONFIG.
DM.L.S Demand Limit Select 0 - 3 DMD_CTRL 0
D.L.20 Demand Limit at 20 ma 0 - 100 % DMT20MA 100
SH.NM Loadshed Group Number 0 - 99 SHED_NUM 0
SH.DL Loadshed Demand Delta 0 - 60 % SHED_DEL 0
SH.TM Maximum Loadshed Time 0 - 120 min SHED_TIM 60
D.L.S1 Demand Limit Sw.1 Setpt. 0 - 100 % DLSWSP1 80
D.L.S2 Demand Limit Sw.2 Setpt. 0 - 100 % DLSWSP2 50