65
Table 37 — Staged Heat Configuration
*Some configurations are model number dependent.
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 capacity 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 outside a delta temperature
band around set point and allows staging to react quicker.
Limit Switch Monitoring? (
LIM.M) — This configuration
allows the operation of the limit switch monitoring routine.
This is always enabled for 48N Series as a limit switch temper-
ature sensor is always present for 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 additional stages of heat
will be allowed.
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 48N units, the supply fan for staged heating is con-
trolled by the integrated gas control (IGC) boards and
unless the supply fan is on for a different reason, will be
controlled by the IFO. On 50N units, the fan is ON
whenever the heat is ON.
• Command all stages of heat ON
If the HVAC mode is LOW HEAT:
• On 48N units, the supply fan for modulating gas heating
is controlled by the integrated gas control (IGC) boards
and unless the supply fan is on for a different reason, will
be controlled by the IGC IFO input. On 50N 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
HT.C.P). The heating con-
trol point in a LOW HEAT HVAC mode for staged heat
is the heating supply air set point (Setpoints
SA.HT).
Staged Heating PID Logic
— The heat control loop is a PID
design with exceptions, overrides 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 capac-
ity. The basic factors that govern 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
algorithm 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 con-
trol 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.
Modulating Gas Heat Staging
— Different unit sizes will
control heat stages differently based on the amount of heating
capacity included. These staging patterns are selected based on
the unit model number. The selection of a set of staging pat-
terns is controlled via the heat stage type configuration parame-
ter Configuration→HEAT→SG.CF→HT.ST. Setting HT.ST
to 0, 1, 2, or 3 configures the unit for Modulating Gas Heat.
The selection of HT.ST = 0, 1, 2, or 3 is based on the unit size
and heat size. See Table 38.
As the heating capacity rises and falls based on demand, the
modulating gas control logic will stage the heat relay patterns
up and down respectively (Run Status→VIEW→HT.ST) and
set the capacity of the Modulating Gas section (Outputs
→HEAT→H1.CP). The Heat Stage Type configuration selects
one of the staging patterns that the modulating gas control will
use. In addition to the staging patterns, the capacity for each
stage is also determined by the modulating gas heating PID al-
gorithm. Therefore, choosing the heat relay outputs and setting
ITEM EXPANSION RANGE UNITS CCN POINT DEFAULT
SG.CF STAGED HEAT CONFIGS
HT.ST Staged Heat Type 0 - 3 HTSTGTYP 0*
CAP.M Max Cap Change per Cycle 5 - 45 HTCAPMAX 45*
M.R.DB St.Ht DB min.dF/PID Rate 0 - 5 HT_MR_DB 0.5
S.G.DB St.Heat Temp. Dead Band 0 - 5 ^F HT_SG_DB 2
RISE Heat Rise dF/sec Clamp 0.05 - 0.2 HTSGRISE 0.06
LAT.L LAT Limit Config 0 - 20 ^F HTLATLIM 10
LIM.M Limit Switch Monitoring? Yes/No HTLIMMON Yes
SW.H.T Limit Switch High Temp 80 - 210 dF HT_LIMHI 170*
SW.L.T Limit Switch Low Temp 80 - 210 dF HT_LIMLO 160*
HT.P Heat Control Prop. Gain 0 - 1.5 HT_PGAIN 1
HT.D Heat Control Derv. Gain 0 - 1.5 HT_DGAIN 1
HT.TM Heat PID Rate Config 30 - 300 sec HTSGPIDR 90*
IMPORTANT: When gas or electric heat is used in a VAV
application with third party terminals, the HIR relay output
must be connected to the VAV terminals in the system in
order to enforce a minimum heating cfm. The installer is
responsible to ensure the total minimum heating cfm is not
below limits set for the equipment. Failure to do so will
result in limit switch tripping and may void warranty.
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