Specifications
17
Ramp Loading
— Ramp loading (Configura-
tion
SLCT
CRMP) limits the rate of change of leaving
fluid temperature. If the unit is in a Cooling mode and config-
ured for Ramp Loading, the control makes 2 comparisons be-
fore deciding to change stages of capacity. The control calcu-
lates a temperature difference between the control point and
leaving fluid temperature. If the difference is greater than 4° F
(2.2° C) and the rate of change (°F or °C per minute) is more
than the configured Cooling Ramp Loading value (CRMP),
the control does not allow any changes to the current stage of
capacity.
Low Entering Fluid Temperature Unloading
— When the
entering fluid temperature is below the control point, the
control will attempt to remove 25% of the current stages being
used. If exactly 25% cannot be removed, the control removes
an amount greater than 25% but no more than necessary. The
lowest stage will not be removed.
Hot Gas Bypass
— If equipped, the hot gas bypass valve is
energized only when one compressor is running on the circuit
and capacity is decreasing.
Cooler Freeze Protection
— The control will try to prevent
shutting the chiller down on a Cooler Freeze Protection alarm
by removing stages of capacity. If the cooler fluid selected
is Water, the freeze point is 34 F (1.1 C). If the cooler fluid
selected is Brine, the freeze point is the Brine Freeze Point (Set
Points
FRZ
BR.FZ). This alarm condition (A207) only
references leaving fluid temperature and NOT Brine Freeze
point. If the cooler leaving fluid temperature is less than the
freeze point plus 2.0° F (1.1° C), the control will immediately
remove one stage of capacity. This can be repeated once every
30 seconds.
Low Saturated Suction Protection
— The control will try to
prevent shutting a circuit down due to low saturated suction
conditions by removing stages of capacity. The circuit alert
condition (T116) compares saturated suction temperature to the
configured Brine Freeze Point (Set Points
FRZ
BR.FZ).
The Brine Freeze point is a user-configurable value that must
be left at 34 F (1.1 C) for 100% water systems. A lower value
may be entered for systems with brine solutions, but this value
should be set according to the freeze protection level of the
brine mixture. Failure to properly set this brine freeze point val-
ue may permanently damage the brazed plate heat exchanger.
The control will initiate Mode 7 (Circuit A) to indicate a cir-
cuit’s capacity is limited and that eventually the circuit may
shut down.
Operation of Machine Based on Control
Method and Cooling Set Point Selection Set-
tings —
Machine On/Off control is determined by the
configuration of the Control Method (Configuration
OPT2
CTRL) and Cooling Set Point Select
(Configuration
SLCT
CLSP) variables. All units are fac-
tory configured with Cooling Set Point Select set to 0 (single
set point). With the control method set to 0, simply switching
the Enable/Off/Remote Contact switch to the Enable or
Remote Contact position (external contacts closed) will put the
chiller in an occupied state. The control mode (Run
Status
VIEW
STAT) will be 1 (OFF LOCAL) when the
switch is Off and will be 5 (ON LOCAL) when in the Enable
position or Remote Contact position with external contacts
closed.
Two other control methods are available for Machine On/
Off control:
OCCUPANCY SCHEDULE (Configuration
OPT2
CTRL = 1) — The main base board will use the operating
schedules as defined under the Time Clock mode in the scroll-
ing marquee display. These schedules are identical. The sched-
ule number must be set to 1 for local schedule.
The schedule number can be set anywhere from 65 to 99
for operation under a CCN global schedule. The Enable/Off/
Remote Contact must be in the Enable or Remote Contact posi-
tion. The control mode (Run Status
VIEW
STAT) will be
1 when the switch is Off. The control mode will be 3 when the
Enable/Off/Remote Contact switch input is On and the time of
day is during an unoccupied period. Similarly, the control
mode will be 7 when the time of day is during an occupied
period.
CCN SCHEDULE (Configuration
OPT2
CTRL =
3) — An external CCN device such as Chillervisor System
Manager controls the On/Off state of the machine. This CCN
device forces the variable ‘CHIL_S_S’ between Start/Stop to
control the chiller. The control mode (Run Status
VIEW
STAT) will be 1 when the switch is Off. The con-
trol mode will be 3 when the Enable/Off/Remote Contact
switch input is On and the CHIL_S_S variable is ‘Stop.’
Similarly, the control mode will be 6 when the CHIL_S_S vari-
able is ‘Start.’
Table 10 illustrates how the control method and cooling set
point select variables direct the operation of the chiller and the
set point to which it controls. The illustration also shows the
ON/OFF state of the machine for the given combinations.
Cooling Set Point Select
SINGLE — Unit operation is based on Cooling Set Point 1
(Set Points
COOL
CSP.1).
DUAL SWITCH — Unit operation is based on Cooling Set
Point 1 (Set Points
COOL
CSP.1) when the Dual Set
Point switch contacts are open and Cooling Set Point 2 (Set
Points
COOL
CSP.2) when they are closed.
DUAL CCN OCCUPIED — Unit operation is based on
Cooling Set Point 1 (Set Points
COOL
CSP.1) during the
Occupied mode and Cooling Set Point 2 (Set
Points
COOL
CSP.2) during the Unoccupied mode as
configured under the local occupancy schedule accessible only
from CCN. Schedule Number in Table SCHEDOVR (see Ap-
pendix B) must be configured to 1. If the Schedule Number is
set to 0, the unit will operate in a continuous 24-hr Occupied
mode. Control method must be configured to 0 (switch). See
Table 10.
4 TO 20 mA INPUT — Unit operation is based on an external
4 to 20 mA signal input to the Energy Management Module
(EMM).
Table 10 — Control Methods and Cooling Set Points
*Dual set point switch input used. CSP1 used when switch input is open. CSP2 used when switch input is closed.
†Cooling set point determined from 4 to 20 mA input to energy management module (EMM) to terminals TB6-3,5.
CONTROL
TYPE
(CTRL)
OCCUPANCY
STATE
COOLING SET POINT SELECT (CLSP)
0
(single)
1
(dual, switch)
2
(dual, occ)
3
(4 to 20 mA)
0 (switch)
Occupied ON,CSP.1 ON* ON,CSP.1 ON†
Unoccupied ON,CSP.1 ON* ON,CSP.2 ON
2 (Occupancy)
Occupied ON,CSP.1 ON* Illegal ON†
Unoccupied OFF OFF Illegal OFF
3 (CCN)
Occupied ON,CSP.1 ON* ON,CSP.1 ON†
Unoccupied ON,CSP.1 ON* ON,CSP.2 ON†