49
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) is used. 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) offset divided by 2.
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) operates and may
hold off staging or a HIGH COOL mode. This is not applica-
ble 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 Z Series ComfortLink™ controls manage
supply-air temperature and the staging of compressors for these
control types.
C.TYP = 3 and 4 (Thermostat Cool Mode Selection) —
When a thermostat type is selected, the decision making pro-
cess involved in determining the mode is straightforward.
Upon energizing the Y1 input only, the unit HVAC mode will
be LOW COOL. Upon the energizing of both Y1 and Y2 in-
puts, the unit HVAC mode will be HIGH COOL. If just input
G is energized the unit HVAC mode will be VENT and the
supply fan will run.
Selecting the C.TYP = 3 (TSTAT – MULTI) control type
will cause the control to do the following:
• The control will read both the Configuration
→
UNIT
→
SIZE and Configuration
→
UNIT
→
50.HZ configura-
tion parameters to determine the number of cooling
stages and the pattern for each stage.
• An HVAC mode equal to LOW COOL will cause the
unit to select the Setpoints
→
SA.LO set point to control
to. An HVAC mode equal to HIGH COOL will cause the
unit to select the Setpoints
→
SA.HI set point to control
to. Supply air reset (if configured) will be added to either
the low or high cool set point.
• The control will utilize the SumZ cooling algorithm and
control cooling to a supply air set point. See the section
for the SumZ Cooling Algorithm section for information
on controlling to a supply air set point and compressor
staging.
Selecting the C.TYP = 4 (TSTAT – 2 STG) control type
means that only two stages of cooling will be used. An HVAC
mode of LOW COOL will energize one circuit and an HVAC
mode of HIGH COOL will energize both circuits provided the
economizer is not able to provide adequate free cooling. Refer
to the section on Economizer Integration with Mechanical
Cooling for more information.
ITEM EXPANSION RANGE CCN POINT
MODE MODES CONTROLLING UNIT
OCC Currently Occupied ON/OFF MODEOCCP
T.C.ST Temp.Compensated Start ON/OFF MODETCST
H.C.ON
L.C. OF/2
L.C.ON
Cooling Setpoint (OCSP,UCSP)
L.C. OF
Lo Cool End
Hi Cool End
Lo Cool Start
Hi Cool Start
Fig. 6 — Cool Mode Evaluation