Carrier Weathermaster 48P2030-100 Controls, Start-Up, Operation, Service, And Troubleshooting page 64

SCR ELECTRIC HEAT CONTROL (HT.CF = 5 AND HT.ST
= 6, 7, OR 8)
As an option, the units with electric heat can be equipped with
modulating SCR electric heater controls that will provide in-
finite stages of heat capacity. This is intended for tempering
mode and tempering economizer air when in a cooling mode
and the dampers are at minimum vent position. Tempering can
also be used during a pre-occupancy purge to prevent low tem-
perature air from being delivered to the space. Tempering for
staged gas, modulating gas, hydronic and SCR electric heat
will be discussed in its own section. This section will focus on
heat mode control, which ultimately is relevant to tempering,
minus the consideration of the supply air heating control point.
Staged Heat Type (HT.ST)
This configuration instructs the control as to how many stages
and in what order they are staged. Setting HT.ST = 0, 1, or 2
configures the unit for Staged Gas Heat. See Table 45. Setting
HT.ST = 3, 4, or 5 configures the unit for Modulating Gas
Heat. See Table 46. Setting HT.ST = 6, 7, or 8 configures the
unit for SCR Electric Heat.
Table 45 — Staged Gas Heat
NUMBER OF HT.ST
STAGES CONFIGURATION
2 0
5 1
9 2
Table 46 — Modulating Gas Heat
NUMBER OF HT.ST
STAGES CONFIGURATION
1 3
3 4
6 5
Max Cap Change per Cycle (CAP.M)
This configuration limits the maximum change in capacity per
PID run time cycle.
St.Ht DB Min.dF/PID Rate (M.R.DB)
This configuration is a deadband minimum temperature per
second rate. See capacity calculation logic on this page for
more details.
St.Heat Temp.Dead Band (S.G.DB)
This configuration is a deadband delta temperature. See capac-
ity calculation logic on this page for more details.
Heat Rise in dF/Sec Clamp (RISE)
This configuration clamps heat staging up when the leaving-air
temperature is rising too fast.
LAT Limit Config (LAT.L)
This configuration senses when leaving air temperature is out-
side a delta temperature band around set point and allows stag-
ing to react quicker.
Limit Switch Monitoring? (LIM.M)
This configuration allows the operation of the limit switch
monitoring routine. This is always enabled for 48P Series as a
limit switch temperature sensor is always present for staged
and modulating gas operation. It is not used on SCR electric
heat units.
Limit Switch High Temp (SW.H.T)
This configuration is the temperature limit above which stages
of heat will be shed.
Limit Switch Low Temp (SW.L.T)
This configuration is the temperature limit above which no ad-
ditional stages of heat will be allowed.
UNIT SIZE
HEAT SIZE
48P
030-050 Low
030-050 High
055-100 Low
055-100 High
UNIT SIZE
HEAT SIZE
48P
030-050 Low
030-050 High
055-100 Low
055-100 High
64
Heat Control Prop. Gain (HT.P)
This configuration is the proportional term for the PID which
runs in the HVAC mode LOW HEAT.
Heat Control Derv. Gain (HT.D)
This configuration is the derivative term for the PID which
runs in the HVAC mode LOW HEAT.
Heat PID Rate Config (HT.TM)
This configuration is the PID run time rate.
Staged Heating Logic
If the HVAC mode is HIGH HEAT:
• On 48P units, the supply fan for staged heating is con-
trolled by the integrated gas control (IGC) boards and, un-
less the supply fan is on for a different reason, will be con-
trolled by the IFO. On 50P units, the fan is ON whenever
the heat is ON.
• Command all stages of heat ON.
If the HVAC mode is LOW HEAT:
• On 48P units, the supply fan for staged and modulating gas
heating is controlled by the integrated gas control (IGC)
boards and, unless the supply fan is on for a different rea-
son, will be controlled by the IGC IFO input. On 50P
units, the fan is ON whenever the heat is ON.
• The unit will control stages of heat to the heating control

point (Run Status VIEW
point in a LOW HEAT HVAC mode for staged heat is the
heating supply air set point (Setpoints
Staged Heating PID Logic
The heat control loop is a PID design with exceptions, over-
rides, and clamps. Capacity rises and falls based on set point
and supply-air temperature. When the ComfortLink control is
in Low Heat or Tempering Mode (HVAC mode), the algorithm
calculates the desired heat capacity. The basic factors that gov-
ern the controlling technique are:
• how frequently the algorithm is run.
• the amount of proportional and derivative gain applied.
• the maximum allowed capacity change each time this al-
gorithm is run.
• deadband hold-off range when rate is low.
This routine is run once every "HT.TM" seconds. Every time the
routine is run, the calculated sum is added to the control output
value. In this manner, integral effect is achieved. Every time this
algorithm is run, the following calculation is performed:
Error = HT.C.P – LAT
Error_last = error calculated previous time
P = HT.P*(Error)
D = HT.D*(Error – Error_last)
The P and D terms are overridden to zero if:
Error < S.G.DB AND Error > – S.G.DB AND D < M.R.DB
AND D > – M.R.DB.
"P + D" are then clamped based on CAP.M. This sum can be
no larger or no smaller than +CAP.M or –CAP.M.
Finally, the desired capacity is calculated:
Staged Heat Capacity Calculation = "P + D" + old Staged Heat
Capacity Calculation.
NOTE: The PID values should not be modified without approval
from Carrier.

HT.C.P). The heating control

SA.HT).