Carrier 48/50PM C16-28 - Manual (Page 21)

21
Heating Operation
The 48/50PG and 48/50PM unit’s heating operation consists of:
demand, mode determination, staging request to satisfy the
demand, and handling a request with the unit’s resources. These
resources can be gas heat or electric heat. This section covers both
gas heat units and electric heat units. The Type of Heat Installed
(Configuration
→HEAT→HT.TY) configuration will be factory
set to 1 for gas units, 2 for electric heat units with heaters installed,
and 0 for electric heat units without heat installed. The unit enters
a heating mode based on a demand, decides how to satisfy the
demand, executes its plan, and then leaves the heating mode.
Heating Mode Control
The heating HVAC mode (Run Status →MODE→HVAC=4),
represents both types of heating (gas or electric) under all types of
control. For the unit to be allowed to enter the heat mode, heat
must be enabled (HT.TY = 1 or 2), and the Outdoor Air
Temperature (Temperatures
→AIR.T→OAT) must be less than the
Heating Lockout Temp (Configuration
→HEAT→HT.LO). Heat
OAT Lockout (Run Status
→MODE→H.LOC) displays when
heat is locked out on outdoor temperature and therefore can not
allow heat mode. The control will display if it is ok to select the
heating mode (Operating Modes
→HEAT →OK.HT= Yes).
Thermostat Control
For the unit to enter heating mode, three additional things must be
true: the indoor fan must be ok to use, the mode changeover time
guard must be expired, and there must be a heating demand (W1,
W2). The unit will remain in heating until the heating demand is
dropped or if any of the above conditions turn false. The heating
mode can not officially end until all heat stages are off and the IGC
fan request is dropped (on gas units without Humidi−MiZer
t).
Space Sensor Control
For the unit to enter heating mode, five additional things must be
true: the indoor fan must be ok to use, the mode changeover time
guard must be expired, the unit must have a valid space
temperature, the W1 jumper must be installed, and there must be a
heating demand. The unit will remain in heating for at least one
minute and until the heat demand drops below −0.5
_F or if any of
the above conditions turn false. The heating mode can not
officially end until all heat stages are off and the IGC fan request is
dropped (on gas units without Humidi−MiZer).
Supply−Air Temperature Sensor (SAT)
The SAT Heat Mode Sensing (Configuration
→HEAT→SAT→SAT.H) informs the unit if the supply air sensor
has been relocated downstream of the heat section. This
configuration affects the Supply Air Temperature (Temperatures
→AIR.T→SAT) value displayed as listed below.
When SAT.H = DSBL, the Supply Air Temperature (Temperatures
→AIR.T→SAT) value on the Scrolling Marquee and the CCN
tables will be forced to zero when heat outputs turn ON or OFF
and for 5 minutes after. The default Supply Air Temperature
location is at the fan inlet, upstream of the heat section.
When SAT.H = ENBL, the Supply Air Temperature (Temperatures
→AIR.T→SAT) sensor reading is displayed at the Scrolling
Marquee and the CCN tables during heating mode. This setting
should only be used if the original SAT sensor wires are removed
from the Main Base Board (MBB) and replaced by an accessory
SAT sensor located in the supply duct downstream of the
heat section.
There are two supply air temperature limits that affect heating
operation, the Maximum SAT Lower Level (Configuration
→HEAT→SAT→SAM.L) the Maximum SAT Upper Level
(Configuration
→HEAT→SAT→SAM.U). Any time the supply
air temperature rises above SAM.L the heat staging will be limited
to what is currently on and no additional stages can be added until
the supply air temperature falls back below SAM.L. If the supply
air temperature rises above SAM.U, then heating will be reduced
by removing a heat stage. That stage can not be added again until
the Supply Air Temperature falls below SAM.L. If the supply air
temperature stays above SAM.U, then another stage will be
removed after the Heat Stage Decrease Time (Configuration
→HEAT→H.DEC). If SAM.L and SAM.U are configured so that
they are close together, the last stage of heat might cycle rapidly,
slowed only by its minimum on and off−time requirements.
Staging Control
Once the unit is in a heating mode, it must decide what the demand
is and how to satisfy. Based on the unit control configuration,
requested heating stages (Run Status
→HEAT→REQ.H) will be
determined then passed to heat control to actually add the heating
stages.
Thermostat Control
There are two ways of requesting stages when thermostat control is
enabled: Traditional Thermostat control or Adaptive control.
Traditional Thermostat control is used if the Thermostat Control
Type (T.CTL) is set to 1, 2, or 3. Adaptive control is used if
Thermostat Control (T.CTL) is set for 0.
T.CTL = 0 (Adaptive Control)
Stage timers and supply air temperature limits apply when
determining the request for stages. The first request (REQ.C=1)
comes immediately when the W1 input is active. The Heat Stage
Increase Time (Configuration
→HEAT→H.INC) or the Heat
Stage Decrease Time (Configuration →HEAT→H.DEC) has to
expire before another stage can be added or a stage can be
subtracted. If at any time the Supply−Air Temperature (SAT) rises
above the Maximum Supply Air Temperature Lower Level
(Configuration
→HEAT→SAT→SAM.L), the requested stages
will not be allowed to increase. If at any time the SAT rises above
the Maximum Supply Air Temperature Upper Level
(Configuration
→HEAT→SAT→SAM.U), the requested stages
will be reduced by one without honoring H.DEC.
T.CTL = 1, 2 or 3 (Traditional thermostat control)
Stage timers and supply air temperature limits do not apply when
determining the request for stages. Request staging will follow the
thermostat inputs directly. W1 will request one stage. W2 will
request all stages.
48/50PG and PM