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33
CCN CONTROL — An external CCN device such as Chill-
ervisor 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 Status Unit Control Type (
Run Status
VIEW
STAT
) will be
0
(Local Off) when the Enable/Off/
Remote Contact switch is Off. The Status Unit Control Type
will be
2
(CCN) when the Enable/Off/Remote Contact switch
is in the enable or remote contact position with external con-
tacts closed and the CHIL_S_S variable is Stop or Start.
UNIT RUN STATUS (
Run Status
VIEW
STAT
) — As the
unit transitions from off to on and back to off, the Unit Run
Status will change based on the unit’s operational status. The
variables are:
0
(Off),
1
(Running),
2
(Stopping), and
3
(Delay).
• 0 indicates the unit is Off due to the Enable/Off/Remote
Contact Switch, a time schedule or CCN command.
• 1 indicates the unit is operational.
• 2 indicates the unit is shutting down due to the command
to shut down from the Enable/Off/Remote Contact
Switch, a time schedule or CCN command.
• 3 indicates the unit has received a command to start from
Enable/Off/Remote Contact Switch, a time schedule or
CCN command, and is waiting for the start-up timer
(
Configuration
OPTN
DELY
) to expire.
Cooling Set Point Selection (
Operating Modes
SLCT
SP.SE
) —
Several options for controlling the
Leaving Chilled Water Set Point are offered and are configured
by the Cooling Set Point Select variables. In addition to the
Cooling Set Point Select, Ice Mode Enable (
Configura-
tion
OPTN
ICE.M
), and Heat Cool Select (
Operating
Modes
SLCT
HC.SE
) variables also have a role in deter-
mining the set point of the machine. All units are shipped from
the factory with the Heat Cool Select variable set to
HC.SE
=
0
(Cooling). All set points are based on Leaving Water Control,
(
Configuration
SERV
EWTO
=
NO
).
In all cases, there are limits on what values are allowed for
each set point. These values depend on the Cooler Fluid Type
(
Configuration
SERV
FLUD
) and the Brine Freeze Set
point (
Configuration
SERV
LOSP
). See Table 26.
Table 26 — Configuration Set Point Limits
*The minimum set point for Medium Temperature Brine applications
is related to the Brine Freeze Point. The set point is limited to be no
less than the Brine Freeze Point +5° F (2.8° C).
SET POINT 1 (
Operating Modes
SLCT
SP.SE
=
1
) —
When Set Point Select is configured to 1, the unit’s active set
point is based on Cooling Set Point 1 (
Set
Point
COOL
CSP.1
).
SET POINT 2 (
Operating Modes
SLCT
SP.SE
=
2
) —
When Set Point Select is configured to 2, the unit’s active set
point is based on Cooling Set Point 2 (
Set
Point
COOL
CSP.2
).
4 TO 20 mA INPUT (
Operating Modes
SLCT
SP.SE
=
3
) — When Set Point Select is configured to 3, the
unit’s active set point is based on an external 4 to 20 mA signal
input to the Energy Management Module (EMM).
See Table 25 for Control Methods and Cooling Set Points.
The following equation is used to control the set point. See
Fig. 18.
Set Point = 10 + 70(mA – 4)/16 (deg F)
Set Point = –12.2 + 38.9(mA – 4)/16 (deg C)
DUAL SWITCH (
Operating Modes
SLCT
SP.SE
=
4
) —
When Set Point Select is configured to 4, the unit’s active set
point is based on Cooling Set Point 1 (
Set Point
COOL
CSP.1
) when the Dual Set Point switch contacts are open and
Cooling Set Point 2 (
Set Point
COOL
CSP.2
) when they
are closed.
Ice Mode — Operation of the machine to make and store ice
can be accomplished many ways. The Energy Management
Module and an Ice Done Switch is required for operation in the
Ice Mode. In this configuration, the machine can operate with
up to three cooling set points: Cooling Set Point 1 (Occupied)
(
Set Point
COOL
CSP.1
), Cooling Set Point 2 (Unoccu-
pied)
(
S
et Point
COOL
CSP.2
), and Ice Set Point
(
Set Point
COOL
CSP.3
).
SET POINT OCCUPANCY (
Operating Modes
SLCT
SP.SE
=
0
) — When Set point Select is configured to
0, the unit’s active set point is based on Cooling Set Point 1
(
Set Point
COOL
CSP.1
) during the occupied period while
operating under
Time Clock
SCH1
. If the
Time Clock
SCH2
is in use, the unit’s active set point is based on
Cooling Set Point 1 (
Set Point
COOL
CSP.1
) during
the occupied period and Cooling Set Point 2 (
Set Point
COOL
CSP.2
) during the unoccupied period.
Temperature Reset —
Temperature reset is a value
added to the basic leaving fluid temperature set point. The sum
of these values is the control point. When a non-zero tempera-
ture reset is applied, the chiller controls to the control point,
not the set point. The control system is capable of handling
leaving-fluid temperature reset based on cooler fluid tempera-
ture difference. Because the change in temperature through the
cooler is a measure of the building load, the temperature differ-
ence reset is in effect an average building load reset method.
The control system is also capable of temperature reset based
on outdoor-air temperature (OAT), space temperature (SPT), or
from an externally powered 4 to 20 mA signal. An accessory
sensor must be used for SPT reset (33ZCT55SPT). The energy
management module (EMM) is required for temperature reset
using space temperature or a 4 to 20 mA signal.
Under normal operation, the chiller will maintain a constant
leaving fluid temperature approximately equal to the chilled
fluid set point. As the cooler load varies, the cooler fluid
temperature difference will change in proportion to the load as
shown in Fig. 19. Usually the chiller size and leaving-fluid
temperature set point are selected based on a full-load condi-
tion. At part load, the fluid temperature set point may be lower
than required. If the leaving fluid temperature were allowed to
increase at part load, the efficiency of the machine would
increase.
Temperature difference reset allows for the leaving temper-
ature set point to be reset upward as a function of the fluid
temperature difference or, in effect, the building load.
To use Water Temperature Difference Reset, four vari-
ables must be configured. They are: Cooling Reset Type
(
Configuration
RSET
CRST
), Delta T No Reset Temp
(
Setpoints
COOL
CRT1
), Delta T Full Reset Temp
(
Setpoints
COOL
CRT2
) and Degrees Cool Reset
(
Setpoints
COOL
DGRC
). In the following example us-
ing Water Temperature Difference Reset, the chilled water
temperature will be reset by 5.0° F (2.8° C) when the
T is
2° F (1.1° C) and 0° F (0° C) reset when the
T is 10° F.
The variable
CRT1
should be set to the cooler temperature
difference (
T) where no chilled water temperature reset
should occur. The variable
CRT2
should be set to the cooler
temperature difference where the maximum chilled water
temperature reset should occur. The variable
DGRC
should
be set to the maximum amount of reset desired. To verify that
reset is functioning correctly proceed to
Run
Status
VIEW
,
and subtract the active set point (
SETP
) from the control
point (
CTPT
) to determine the degrees reset. See Fig. 19 and
Table 27.
SET POINT LIMIT
COOLER FLUID TYPE, FLUD
1 = Water
2 = Medium Brine
Minimum*
38 F (3.3 C)
14 F (–10.0 C)
Maximum
60 F (15.5 C)
Summary of Contents for AQUASNAP 30RBA315
Page 77: ...77 Fig 37 Control Schematic 30RB060 080 a30 4619...
Page 78: ...78 Fig 38 Control Schematic 30RB090 150 a30 4620...
Page 79: ...79 Fig 39 Control Schematic 30RB160 190 a30 4622...
Page 80: ...80 Fig 40 Control Schematic 30RB210 300 a30 4622...
Page 81: ...81 Fig 41 Heat Reclaim Control Schematic a30 4622...