61
HEAT MODE SELECTION PROCESS
There are two possible heat modes that the control will call out
for heating control: HVAC Mode = LOW HEAT and HVAC
Mode = HIGH HEAT. These modes will be called out based on
control type (
C.TYP
).
VAV-RAT (C.TYP = 1) and VAV-SPT (C.TYP = 2)
There is no difference in the selection of a heating mode for ei-
ther VAV-RAT or VAV-SPT, except that for VAV-SPT, space
temperature is used in the unoccupied period to turn on the
supply fan for 10 minutes before checking return-air tempera-
ture. The actual selection of a heat mode, LOW or HIGH for
both control types, will be based upon the controlling return-air
temperature.
With sufficient heating demand, there are still conditions that
will prevent the unit from selecting a heat mode. First, the unit
must be configured for a heat type (
Configuration
HEAT
HT.CF
not equal to “NONE”). Second, the unit must have a
configuration which can enable or disable heating in the occu-
pied period except for a standard morning warmup cycle (
Con-
figuration
HEAT
OC.EN
). See descriptions in the Setting
Up the System section on page 60 for more information.
Tstat-Multi-Stage (C.TYP = 3)
With thermostat control the W1 and W2 inputs determine
whether the HVAC Mode is LOW or HIGH HEAT.
W1 = ON, W2 = OFF: HVAC MODE = LOW HEAT*
W2 = ON, W2 = ON: HVAC MODE = HIGH HEAT
* If the heating type is either 2-stage electric or 2-stage gas,
the unit may promote a low heat mode to a high heat mode.
NOTE: If W2 = ON and W1 is OFF, a “HIGH HEAT” HVAC
Mode will be called out but an alert (T422) will be generated. See
Alarms and Alerts section on page 118.
SPT Multi-Stage (C.TYP = 4)
The unit is free to select a heating mode based on space tem-
perature (SPT).
If the unit is allowed to select a heat mode, then the next step is
an evaluation of demand versus set point. At this point, the log-
ic is the same as for control types VAV-RAT and VAV-SPT,
(
C.TYP
= 1,2) except for the actual temperature compared
against set point. See Temperature Driven Heat Mode Evalua-
tion
section below.
TEMPERATURE DRIVEN HEAT MODE EVALUATION
This section discusses the technique for selecting a heating mode
based on temperature. Regardless of whether the unit is config-
ured for return air or space temperature, the logic is exactly 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 set points under
Setpoints
must be configured.
Then, the heat/cool set point offsets under
Configuration
D.LV.T
should be set. See Table 41.
Related operating modes are under
Operating Modes
MODE.
.
The first thing the control determines is whether the unit is in
the occupied mode (
OCC
) or in the temperature compensated
start mode (
T.C.ST
). If the unit is occupied or in temperature
compensated start mode, the occupied heating set point
(
OHSP
) is used. In all other cases, the unoccupied heating set
point (
UHSP
) is used.
The control will call out a low or high heat mode by comparing
the controlling temperature to the heating set point and the
heating set point offset. The set point offsets are used as addi-
tional help in customizing and tweaking comfort into the build-
ing space. See Fig. 8 for an example of offsets.
Demand Level Low Heat on Offset (L.H.ON)
This is the heating set point offset below the heating set point
at which point Low Heat starts.
Demand Level High Heat on Offset (H.H.ON)
This is the heating set point offset below [the heating set point
minus
L.H.ON
] at which point high heat starts.
Table 41 — Heat/Cool Set Point Offsets
Fig. 8 — Heating Offsets
ITEM
EXPANSION
RANGE UNITS
CCN
POINT
DEFAULT
OHSP
Occupied Heat
Setpoint
55-80
dF
OHSP
68
UHSP
Unoccupied
Heat Setpoint
40-80
dF
UHSP
55
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 to 2
^F
DMDLHON
1.5
H.H.ON
Dmd Level(+) Hi Heat On
0.5 to 20.0
^F
DMDHHON
0.5
L.H.OF
Dmd Level(-) Lo Heat Off
0.5 to 2
^F
DMDLHOFF
1
L.C.ON
Dmd Level Lo Cool On
–1 to 2
^F
DMDLCON
1.5
H.C.ON
Dmd Level(+) Hi Cool On
0.5 to 20.0
^F
DMDHCON
0.5
L.C.OF
Dmd Level(-) Lo Cool Off
0.5 to 2
^F
DMDLCOFF
1
C.T.LV
Cool Trend Demand Level
0.1 to 5
^F
CTRENDLV
0.1
H.T.LV
Heat Trend Demand Level
0.1 to 5
^F
HTRENDLV
0.1
C.T.TM
Cool Trend Time
30 to 600
sec
CTRENDTM
120
H.T.TM
Heat Trend Time
30 to 600
sec
HTRENDTM
120
H.H.ON
L.H.OF
L.H.OF/2
L.H.ON
HEATING
S
ET POINT
66.5 F
67.5 F
66.0 F
6
8
.0 F
Summary of Contents for Weathermaster 48P2030-100
Page 130: ...130 Fig 19 Typical Power Schematic Sizes 040 075 Shown ...
Page 131: ...131 Fig 20 Main Base Board Input Output Connections ...
Page 132: ...132 Fig 21 RXB EXB CEM SCB Input Output Connections ...
Page 133: ...133 Fig 22 Typical Gas Heat Unit Control Wiring 48P030 100 Units Shown ...
Page 134: ...134 Fig 23 Typical Electric Heat Wiring 50P030 100 Units Shown ...
Page 135: ...135 Fig 24 Typical Power Wiring 115 V ...
Page 136: ...136 Fig 25 Typical Gas Heat Section Size 030 050 Units Shown ...
Page 138: ...138 Fig 27 Component Arrangement Size 030 035 Units ...
Page 139: ...139 Fig 28 Component Arrangement Size 040 075 Units ...
Page 140: ...140 Fig 29 Component Arrangement Size 090 100 Units ...
