Specifications

34
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 37
for a discussion of how the A 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=5and6) —
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 36.
Operating modes are under Operating Modes
→ MODE.
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 compensated start mode,
the occupied cooling set point (OCSP) is used. For all other
modes, the unoccupied cooling set point (UCSP)isused.For
further discussion and simplification this will be referred to as
the “cooling set point.” See Fig. 6.
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.
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)offsetdividedby2.
To enter into a LOW COOL mode, the controlling tempera-
ture must rise above [the cooling set point plus L.C.ON.]
To enter into a HIGH COOL mode, the controlling temper-
ature 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 temper-
ature 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 temper-
ature 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 con-
trol will hold off on the HIGH COOL mode. This is especially
true for the space sensor machine control types (C.TYP)=5
and 6, because they 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)operatesandmay
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 which
determine the trip points for bringing on and bringing off cool
modes there is a timeguard which enforces a time delay
between the transitioning from a low cool to a high cool mode.
This time delay is 8 minutes. 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 deter-
mined that a cooling mode is in effect, the cooling control
point (Run Status
→ VIEW → CL.C.P) is calculated and is
based upon either Setpoints
→ SA.HI or Setpoints → SA.LO,
depending on whether a high or a low cooling mode is in
effect, respectively. In addition, if supply air reset is config-
ured, it will also be added to the cooling control point.
Refer to the SumZ Cooling Algorithm section for a discus-
sion of how the A Series ComfortLink™ controls manage
supply-air temperature and the staging of compressors for these
control types.
Table 36 — Cool/Heat Set Point Offsets Configuration
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 CCN POINT
MODE MODES CONTROLLING UNIT
OCC Currently Occupied ON/OFF MODEOCCP
T.C.ST Temp.Compensated Start ON/OFF MODETCST
ITEM EXPANSION RANGE UNITS CCN POINT DEFAULT
D.LV.T COOL/HEAT SETPT. OFFSETS
L.H.ON Dmd Level Lo Heat On -1 - 2 ^FDMDLHON 1.5
H.H.ON Dmd Level(+)HiHeatOn 0.5-2.0 ^F DMDHHON 0.5
L.H.OF Dmd Level(-) Lo Heat Off 0.5 - 2 ^FDMDLHOFF 1
L.C.ON Dmd Level Lo Cool On -1 - 2 ^FDMDLCON 1.5
H.C.ON Dmd Level(+)HiCoolOn 0.5-2 ^F DMDHCON 0.5
L.C.OF Dmd Level(-) Lo Cool Off 0.5 - 2 ^FDMDLCOFF 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