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Use CSBs for HPS detect? (CS.HP)
On units with multiple compressors running on a circuit, the cur-
rent sensor boards (CSBs) are used to help detect a high pressure
switch trip. Setting this configuration to NO disables this addition-
al high pressure switch trip detection.
COOL MODE SELECTION PROCESS
The P Series ComfortLink controls offer three distinct methods by
which they may select a cooling mode.
1.
Thermostat (C.TYP=3): The thermostat does not depend
upon the state of occupancy or temperature and the modes
are called out directly by the discrete inputs (Inputs
STAT
Y1 and Y2).
2.
VAV cooling types (C.TYP=1 and 2) are called out in the
occupied period (Operating Modes
3.
VAV cooling types (C.TYP=1 and 2) are called out in the
unoccupied period (Operating Modes
OFF). They are also used for space sensor control types
(C.TYP=4) in both the occupied and unoccupied periods.
This section is devoted to the process of cooling mode determina-
tion for the three types outlined above.
VAV Cool Mode Selection during the Occupied Period
(C.TYP = 1,2 and Operating Modes
There is no difference in the selection of a cooling mode for either
VAV-RAT or VAV-SPT in the occupied period. The actual selec-
tion of a cool mode, for both control types, is based upon the con-
trolling return-air temperature (Temperatures
CTRL
R.TMP). Typically this is the same as the return air tem-
perature thermistor (Temperatures
under CCN Linkage.
Cool Mode Determination
If the machine control type (Configuration
1 (VAV-RAT) or 2 (VAV-SPT) and the control is occupied (Oper-
ating Modes
MODE
OCC=ON), then the unit will not follow
the occupied cooling set point (OCSP). Instead, the control will
follow two offsets in the determination of an occupied VAV cool-
ing mode (Setpoints
V.C.ON and Setpoints
ing them to the low-heat off trip point and comparing the resulting
temperature to the controlling return temperature (R.TMP).
The Setpoints
V.C.ON (VAV cool mode on offset) and Set-
points
V.C.OF (VAV cool mode off offset) offsets are used in
conjunction with the low heat mode off trip point to determine
when to bring cooling on and off and in enforcing a true "vent"
mode between heating and cooling. See Fig. 4. The occupied cool-
ing set point is not used in the determination of the cool mode. The
occupied cooling set point is used for supply air reset only.
OHSP
L.H.ON
DMDLHON
Fig. 4 — VAV Occupied Period Trip Logic
The advantage of this offset technique is that the control can safely
enforce a vent mode without worrying about crossing set points.
Even more importantly, under CCN linkage, the occupied heating
set point may drift up and down. As such, this technique of using
offsets ensures a guaranteed separation in degrees F between the
calling out of a heating or cooling mode at all times.
MODE
OCC=ON).
MODE
OCC=
MODE
OCC =ON)
AIR.T
AIR.T
RAT) except when
UNIT
C.TYP) =
V.C.OF), apply-
V.C. ON
V.C. OF
VAVOCON
VAVOCOFF
L.H.OF
DMDLHOFF
VAV Occupied Cool Mode Evaluation Configuration
There are VAV occupied cooling offsets under Setpoints.
ITEM
EXPANSION
VAV Occ.
V.C.ON
Cool On Delta
VAV Occ.
V.C.OF
Cool Off Delta
NOTE: There is a sub-menu at the local display (Run Status
TRIP) that allows the user to see the exact trip points for both the
heating and cooling modes without having to calculate them. Re-
fer to the Cool Mode Diagnostic Help section on page 55 for more
information.
To enter into a VAV Occupied Cool mode, the controlling tem-
perature must rise above [OHSP minus L.H.ON plus L.H.OF
plus V.C.ON].
To exit out of a VAV Occupied Cool Mode, the controlling tem-
perature must fall below [OHSP minus L.H.ON plus L.H.OF
plus V.C.ON minus V.C.OF].
NOTE: With vent mode, it is possible to exit out of a cooling
mode during the occupied period if the return-air temperature
drops low enough. When supply-air temperature reset is not con-
figured, this capability will work to prevent over-cooling the space
during the occupied period.
Supply Air Set Point Control and the Staging of Compressors
Once the control has determined that a cooling mode is in effect,
the cooling control point (Run Status
culated and is based upon the supply air set point (Setpoints
SASP) plus any supply air reset being applied (Inputs
RSET
SA.S.R).
Refer to the SumZ Cooling Algorithm section on page 55 for a
discussion of how the P Series ComfortLink controls manage the
staging of compressors to maintain supply-air temperature.
VAV Cool Mode Selection during the Unoccupied Period
(C.TYP = 1,2; Operating Modes
Space Sensor Cool Mode Selection (C.TYP=4)
The machine control types that utilize this technique of mode se-
lection are:
•
C.TYP = 1 (VAV-RAT) in the unoccupied period
•
C.TYP = 2 (VAV-SPT) in the unoccupied period
•
C.TYP = 4 (SPT-MULTI) in both the occupied and unoc-
cupied period
These particular control types operate differently than the VAV
types in the occupied mode in that there is both a LOW COOL
and a HIGH COOL mode. For both of these modes, the control of-
fers two independent set points, Setpoints
COOL mode) and Setpoints
The occupied and unoccupied cooling set points can be found un-
der Setpoints.
ITEM
EXPANSION
Occupied
OCSP
Cool Setpoint
Unoccupied
UCSP
Cool Setpoint
The heat/cool set point offsets are found under Configuration
D.LV.T. See Table 38.
53
RANGE
UNITS
CCN POINT
0 to 25
deltaF
VAVOCON
1 to 25
deltaF
VAVOCOFF
VIEW
CL.C.P) is cal-
MODE
OCC=OFF) and
SA.LO (for LOW
SA.HI (for HIGH COOL mode).
CCN
RANGE
UNITS
POINT
55 to 80
dF
OCSP
75 to 95
dF
UCSP
DEFAULT
3.5
2
DEFAULT
75
90
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Troubleshooting
