Carrier WEATHERMASTER 48/50Z030-105 - Manual (Page 48)

48
VAV Cool Mode Selection during the Occupied Period
(C.TYP = 1,2 and Operating Modes → MODE → OCC =ON)
— There is no difference in the selection of a cooling mode for
either VAV-RAT or VAV-SPT in the occupied period. The actual
selection of a cool mode, for both control types, is based upon
the controlling return-air temperature (Temperatures →
AIR.T → CTRL → R.TMP). Typically this is the same as the re-
turn air temperature thermistor (Temperatures → AIR.T → RAT)
except when under CCN Linkage.
VAV Occupied Cool Mode Evaluation Configuration — There
are VAV occupied cooling offsets under Setpoints.
Cool Mode Determination — If the machine control type
(Configuration → UNIT → C.TYP) = 1 (VAV-RAT) or 2 (VAV-
SPT) and the control is occupied (Operating Modes →
MODE → OCC=ON), then the unit will not follow the occu-
pied cooling set point (OCSP). Instead, the control will follow
two offsets in the determination of an occupied VAV cooling
mode (Setpoints → V.C.ON and Setpoints → V.C.OF), applying
them to the low-heat off trip point and comparing the resulting
temperature to the return-air temperature.
The Setpoints → V.C.ON (VAV cool mode on offset) and
Setpoints → 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. 5. The
occupied cooling set point is not used in the determination of
the cool mode. The occupied cooling set point is used for sup-
ply air reset only.
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 and 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.
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 calcu-
late them. Refer to the Cool Mode Diagnostic Help section on
page 50 for more information.
To enter into a VAV Occupied Cool mode, the controlling
temperature 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
temperature 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
configured, 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 → VIEW
→ CL.C.P) is calculated 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 50
for a discussion of how the Z 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 → MODE → OCC=OFF)
and Space Sensor Cool Mode Selection (C.TYP=5 & 6) —
The machine control types that utilize this technique of mode
selection are:
• C.TYP = 1 (VAV-RAT) in the unoccupied period
• C.TYP = 2 (VAV-SPT) in the unoccupied period
• C.TYP = 5 (SPT-MULTI) in both the occupied and
unoccupied period
• C.TYP = 6 (SPT- 2 STG) in both the occupied and
unoccupied 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 offers two independent set points, Setpoints → SA.LO
(for LOW COOL mode) and Setpoints → SA.HI (for HIGH
COOL mode). The occupied and unoccupied cooling set points
can be found under Setpoints.
The heat/cool set point offsets are found under Configura-
tion → D.LV.T. See Table 38.
Table 38 — Cool/Heat Set Point Offsets Configuration
ITEM EXPANSION RANGE UNITS
CCN
POINT
DEFAULT
V.C.ON VAV Occ.
Cool On Delta 0-25 deltaF VAVOCON 3.5
V.C.OF VAV Occ.
Cool Off Delta 1-25 deltaF VAVOCOFF 2
ITEM EXPANSION RANGE UNITS
CCN
POINT
DEFAULT
OCSP Occupied
Cool Setpoint 55-80 dF OCSP 75
UCSP Unoccupied
Cool Setpoint 75-95 dF UCSP 90
ITEM EXPANSION RANGE UNITS
CCN
POINT
DEFAULT
D.LV.T COOL/HEAT SETPT. OFFSETS
L.H.ON Dmd Level Lo Heat On -1 - 2 ^F DMDLHON 1.5
H.H.ON Dmd Level(+) Hi Heat On 0.5 - 20.0 ^F DMDHHON 0.5
L.H.OF Dmd Level(-) Lo Heat Off 0.5 - 2.0 ^F DMDLHOFF 1
L.C.ON Dmd Level Lo Cool On -1 - 2 ^F DMDLCON 1.5
H.C.ON Dmd Level(+) Hi Cool On 0.5 - 20.0 ^F DMDHCON 0.5
L.C.OF Dmd Level(-) Lo Cool Off 0.5 - 2 ^F DMDLCOFF 1
C.T.LV Cool Trend Demand Level 0.1 - 5 ^F CTRENDLV 0.1
H.T.LV Heat Trend Demand Level 0.1 - 5 ^F HTRENDLV 0.1
C.T.TM Cool Trend Time 30 - 600 sec CTRENDTM 120
H.T.TM Heat Trend Time 30 - 600 sec HTRENDTM 120
L.H.OF
DMDLHOFF
L.H.ON
DMDLHON
V.C. ON
VAVOCON
V.C. OF
VAVOCOFF
OHSP
Fig. 5 — VAV Occupied Period Trip Logic
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