Carrier WeatherExpert 48N2 Controls, Start-Up, Operation, Service, And Troubleshooting page 61

Heating Control Type (HT.CF)
The heating control types available are selected/configured
with this variable.
0 = No Heat
1 = 2 Stage Electric Heat
2 = 2 Stage Gas Heat
3 = Staged Gas Heat or Modulating Gas Heat
4 = Hydronic Heat (Hot Water or Steam)
5 = SCR Electric Heat
Heating Supply Air Set Point (HT.SP)
In a low heat mode for either modulating gas, SCR electric, or
hydronic heat, this is the supply air set point for heating.
Occupied Heating Enable (OC.EN)
This configuration only applies when the unit's control type
(Configuration  UNIT  C.TYP) is configured for 1 (VAV-
RAT) or 2 (VAV-SPT). If the user wants to have the capability
of performing heating throughout the entire occupied period,
then this configuration needs to be set to "YES." Most installa-
tions do not require this capability, and if heating is installed, it
is used to heat the building up in the morning. In this case, set
OC.EN to "NO."
NOTE: This unit does not support simultaneous heating and
cooling. If significant simultaneous heating and cooling de-
mand is expected, it may be necessary to provide additional
heating or cooling equipment and a control system to provide
occupants with proper comfort.
MBB Sensor Heat Relocate (LAT.M)
This option allows the user additional performance benefit when
under CCN Linkage for the 2-stage electric and gas heating types.
As 2-stage heating types do not "modulate" to a supply air set
point, no leaving air thermistor is required and none is provided.
The evaporator discharge thermistor, which is initially installed
upstream of the heater, can be repositioned downstream and the
control can expect to sense this heat. While the control does not
need this to energize stages of heat, the control can wait for a suffi-
cient temperature rise before announcing a heating mode to a
CCN Linkage system (ComfortID™).
If the sensor is relocated, the user will now have the capability
to view the leaving-air temperature at all times at Tempera-
tures  AIR.T  CTRL  LAT.
NOTE: If the user does not relocate this sensor for the 2-stage
electric or gas heating types and is under CCN Linkage, then
the control will send a heating mode (if present) unconditional-
ly to the linkage coordinator in the CCN zoning system regard-
less of the leaving-air temperature.
HEAT MODE SELECTION PROCESS
There are 2 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 has a
configuration which can enable or disable heating in the occu-
pied period except for a standard morning warm-up cycle
(Configuration  HEAT  OC.EN). See descriptions above in
the Setting Up the System section for more information.
Morning Warm-up
The morning warm-up is a VAV RTU Linkage/ComfortLink
mode. This is initiated in the air system (VAV zone controllers)
and communicated through Linkage, when a set of conditions
occur. Those conditions are below:
• The RTU's schedule is initially in the unoccupied time pe-
riod and transitions to an occupied time period
• A call for heating initiated by the zone controllers and/or
their system.
The unoccupied set points are changed to the occupied set
points. This morning warm-up mode remains through to the
scheduled occupied time period and continues as long as a call
for heating is still valid. Morning warm-up will terminate when
a call for cooling is initiated.
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
NOTE: 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 121.
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
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 set points under
Setpoints must be configured.
ITEM EXPANSION
OHSP Occupied Heat
Setpoint
UHSP Unoccupied
Heat Setpoint
Then, the heat/cool set point offsets under Configuration
 BP  D.LV.T should be set. See Table 35.
Related operating modes are under Operating Modes  MODE.
.
ITEM EXPANSION
MODE MODES CONTROLLING UNIT
OCC Currently Occupied
T.C.ST Temp.Compensated Start
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.
61
CCN
RANGE UNITS DEFAULT
POINT
55 to 80 dF OHSP
40 to 80 dF UHSP
RANGE CCN POINT
Off/On MODEOCCP
Off/On MODETCST
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