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SPT Multi-Stage (C.TYP = 5) and SPT 2 Stage (C.TYP = 6)
— There is no difference in the selection of a heat mode
between the control types SPT 2-stage or SPT multi-stage.
These selections only refer to how cooling will be handled. So,
for a valid heating type selected (HT.CF not equal to zero) the
unit is free to select a heating mode based on space temperature
(SPT).
If the unit is allowed to select a heat mode, then the next
step is an evaluation of demand versus setpoint. At this point,
the logic is the same as for control types VAV-RAT and
VAV-SPT (C.TYP = 1,2), except for the actual temperature
compared against setpoint. See Temperature Driven Heat
Mode Evaluation section below.
TEMPERATURE DRIVEN HEAT MODE EVALUATION —
This section discusses the control method for selecting a heat-
ing mode based on temperature. Regardless of whether the unit
is configured for return air or space temperature, the logic is ex-
actly the same. For the rest of this discussion, the temperature
in question will be referred to as the "controlling temperature."
First, the occupied and unoccupied heating setpoints under
Setpoints must be configured.
ITEM
EXPANSION RANGE UNITS
Occupied Heat
OHSP
55-80
Setpoint
Unoccupied
UHSP
40-80
Heat Setpoint
Then, the heat/cool setpoint offsets under Configuration
D.LV.T should be set. See Table 51.
Related operating modes are under Operating Modes
MODE.
ITEM
EXPANSION
MODE
MODES CONTROLLING UNIT
OCC
Currently Occupied
T.C.ST
Temp.Compensated Start ON/OFF
The first thing the control determines is whether the unit
is in the occupied mode (OCC) or in the temperature compen-
sated start mode (T.C.ST). If the unit is occupied or in tempera-
ture compensated start mode, the occupied heating setpoint
(OHSP) is used. In all other cases, the unoccupied heating
setpoint (UHSP) is used.
The control will call out a low or high heat mode by
comparing the controlling temperature to the heating setpoint
and the heating setpoint offset. The setpoint offsets are used as
additional help in customizing and tweaking comfort into the
building space.
Demand Level Low Heat on Offset (L.H.ON) — This is the
heating setpoint offset below the heating setpoint at which
point Low Heat starts.
Demand Level High Heat on Offset (H.H.ON) — This is the
heating setpoint offset below the heating setpoint minus
L.H.ON at which point high heat starts.
ITEM
D.LV.T
COOL/HEAT SETPT. OFFSETS
L.H.ON
Dmd Level
H.H.ON
Dmd Level(+) Hi Heat On
L.H.OF
Dmd Level(-) Lo Heat Off
L.C.ON
Dmd Level
H.C.ON
Dmd Level(+) Hi Cool On
L.C.OF
Dmd Level(-) Lo Cool Off
C.T.LV
Cool Trend Demand Level
H.T.LV
Heat Trend Demand Level
C.T.TM
Cool Trend Time
H.T.TM
Heat Trend Time
CCN
DEFAULT
POINT
dF
OHSP
68
dF
UHSP
55
RANGE
CCN POINT
ON/OFF
MODEOCCP
MODETCST
Table 51 — Heat/Cool Setpoint Offsets
EXPANSION
Lo Heat On
Lo Cool On
Demand Level Low Heat Off Offset (L.H.OF) — This is the
heating setpoint offset above the heating setpoint minus
L.H.ON at which point the Low Heat mode ends.
See Fig. 10 for an example of offsets.
To enter into a LOW HEAT mode, if the controlling tem-
perature falls below the heating setpoint minus L.H.ON, then
HVAC mode = LOW HEAT.
To enter into a HIGH HEAT mode, if the controlling tem-
perature falls below the heating setpoint minus L.H.ON minus
H.H.ON, then HVAC mode = HIGH HEAT.
To get out of a LOW HEAT mode, the controlling tempera-
ture must rise above the heating setpoint minus L.H.ON plus
L.H.OF.
To get out of a HIGH HEAT mode, the controlling tempera-
ture must rise above the heating setpoint minus L.H.ON plus
L.H.OF/2.
The Run Status table in the local display allows the user to
see the exact trip points for both the heating and cooling modes
without doing the calculations.
L.H.ON
L.H.OF
H.H.ON
Fig. 10 — Heating Offsets
Heat Trend Demand Level (H.T.LV) — This is the change in
demand that must be seen within the time period specified by
H.T.TM in order to hold off a HIGH HEAT mode regardless of
demand. This is not applicable to VAV control types (C.TYP=1
and 2) in the occupied period. This method of operation has
been referred to as "Comfort Trending." As long as a LOW
HEAT mode is making progress in warming the space, the con-
trol will hold off on a HIGH HEAT mode. This is relevant for
the space sensor machine control types (C.TYP = 5 and 6) be-
cause they may transition into the occupied mode and see an
immediate and large heating demand when the setpoints
change.
Heat Trend Time (H.T.TM) — This is the time period upon
which the heat trend demand level (H.T.LV) operates and may
work to hold off staging or a HIGH HEAT mode. This is not
applicable to VAV control types (C.TYP=1 and 2) in the
occupied period. See Heat Trend Demand Level section for
more details.
HEAT MODE DIAGNOSTIC HELP — To quickly deter-
mine the current trip points for the low and high heat modes,
there is a menu in the local display which lets the user quickly
view the state of the system. This menu also contains the cool
trip points as well. See Table 52 at the local display under Run
Status
TRIP.
RANGE
UNITS
-1 - 2
^F
0.5 - 20.0
^F
0.5 - 2
^F
-1 - 2
^F
0.5 - 20.0
^F
0.5 - 2
^F
0.1 - 5
^F
0.1 - 5
^F
30 - 600
sec
30 - 600
sec
49
the "Heating Setpoint"
L.H.OF/2
CCN POINT
DEFAULT
DMDLHON
1.5
DMDHHON
0.5
DMDLHOFF
1
DMDLCON
1.5
DMDHCON
0.5
DMDLCOFF
1
CTRENDLV
0.1
HTRENDLV
0.1
CTRENDTM
120
HTRENDTM
120
A48-7702
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