Carrier WeatherExpert 48N2 Controls, Start-Up, Operation, Service, And Troubleshooting page 50

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=4)
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 = 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
offers 2 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.
ITEM EXPANSION
Occupied
OCSP
Cool Setpoint
Unoccupied
UCSP
Cool Setpoint
The heat/cool set point offsets are found under Configura-
tion  BP  D.LV.T. See Table 30.
Operating modes are under Operating Modes  MODE.
ITEM EXPANSION
MODE
MODES CONTROLLING UNIT
OCC Currently Occupied
T.C.ST Temp.Compensated Start
Cool Mode Evaluation Logic
The first thing the control determines is whether the unit is in the
occupied mode (OCC) or is in the temperature compensated start
mode (T.C.ST). If the unit is occupied or in temperature compen-
sated start mode, the occupied cooling set point (OCSP) is used.
For all other modes, the unoccupied cooling set point (UCSP) is
used. For further discussion and simplification, this will be re-
ferred to as the "cooling set point." See Fig. 5.
H.C.ON
L.C. OF L.C. OF/2
L.C.ON
Lo Cool End
Cooling Setpoint (OCSP,UCSP)
Fig. 5 — Cool Mode Evaluation
Demand Level Low Cool On Offset (L.C.ON)
This is the cooling set point offset added to the cooling set
point at which point a Low Cool mode starts.
Demand Level High Cool On Offset (H.C.ON)
This is the cooling set point offset added to the "cooling set
point plus L.C.ON" at which point a High Cool mode begins.
CCN
RANGE UNITS POINT DEFAULT
55-80 dF OCSP 75
75-95 dF UCSP 90
RANGE CCN POINT
Off/On MODEOCCP
Off/On MODETCST
Hi Cool Start
Lo Cool Start
Hi Cool End
Demand Level Low Cool Off Offset (L.C.OF)
This is the cooling set point offset subtracted from "cooling set
point plus L.C.ON" at which point a Low Cool mode ends.
NOTE: The "high cool end" trip point uses the "low cool off"
(L.C.OF) offset divided by 2.
To enter into a LOW COOL mode, the controlling temperature
must rise above [the cooling set point plus L.C.ON.]
To enter into a HIGH COOL mode, the controlling temperature
must rise above [the cooling set point plus L.C.ON plus
H.C.ON.]
To exit out of a LOW COOL mode, the controlling temperature
must fall below [the cooling set point plus L.C.ON minus
L.C.OF.]
To exit out of a HIGH COOL mode, the controlling tempera-
ture must fall below [the cooling set point plus L.C.ON minus
L.C.OF/2.]
Comfort Trending
In addition to the set points and offsets which determine the
trip points for bringing on and bringing off cool modes, there
are 2 configurations which work to hold off the transitioning
from a low cool to a high cool mode if the space is cooling
down quickly enough. This technique is referred to as comfort
trending, and the configurations of interest are C.T.LV and
C.T.TM.
Cool Trend Demand Level (C.T.LV)
This is the change in demand that must occur within the time
period specified by C.T.TM in order to hold off a HIGH COOL
mode, regardless of demand. This is not applicable to VAV
control types (C.TYP=1 and 2) in the occupied period. As long
as a LOW COOL mode is making progress in cooling the
space, the control will hold off on the HIGH COOL mode. This
is especially true for the space sensor machine control type
(C.TYP) = 4 because the unit may transition into the occupied
mode and see an immediate large cooling demand when the set
points change.
Cool Trend Time (C.T.TM)
This is the time period upon which the cool trend demand level
(C.T.LV) operates and may hold off staging or a HIGH COOL
mode. This is not applicable to VAV control types (C.TYP=1
and 2) in the occupied period. See the Cool Trend Demand
Level section for more details.
Timeguards
In addition to the set points and offsets that determine the trip
points for bringing on and bringing off cool modes, there is a
timeguard that enforces a time delay between the transitioning
from a low cool to a high cool mode. This time delay is 8 min-
utes. There is a timeguard which enforces a time delay between
the transitioning from a heat mode to a cool mode. This time
delay is 5 minutes.
Supply Air Set Point Control
Once the control has determined that a cooling mode is in effect,
the cooling control point (Run Status  VIEW  CL.C.P) is cal-
culated and is based upon either Setpoints  SA.HI or Set-
points  SA.LO, depending on whether a high or a low cooling
mode is in effect, respectively. In addition, if supply air reset is
configured, it will also be added to the cooling control point.
Refer to the SumZ Cooling Algorithm section for a discussion of
how the N Series ComfortLink controls manage supply-air tem-
perature and the staging of compressors for these control types.
50