Specifications
44
HT.CF
=3(Staged Gas Heating Control) — As an option,
the units with gas heat can be equipped with staged gas
heat controls that will provide from 5 to 11 stages of heat
capacity. This is intended for tempering mode and tempering
economizer air when in a cooling mode and the dampers
are fully closed. Tempering can also be used during a pre-
occupancy purge to prevent low temperature air from being
delivered to the space. Tempering for staged gas will be dis-
cussed 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.
The staged gas configurations are located at the local
display under Configuration
→
HEAT
→
SG.CF. See Table 50.
Staged Gas Heat Type (
HT.ST) — This configuration instructs
the control how many stages and in what order are they staged.
Max Cap Change per Cycle (
CAP.M) — This configuration
limits the maximum change in capacity per PID run time cycle.
S.Gas DB Min.dF/PID Rate (
M.R.DB) — This configuration
is a deadband minimum temperature per second rate. See
Staged Gas Heating logic below for more details.
St.Gas Temp.Dead Band (
S.G.DB) — This configuration is a
deadband delta temperature. See Staged Gas Heating logic
below for more details.
Heat Rise in dF/Sec Clamp (
RISE) — This configuration
clamps heat staging up when the leaving-air temperature is ris-
ing 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 should be set to NO as a limit switch temperature sensor is
not used with A series 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 Gas Heating Logic
If the HVAC mode is HIGH HEAT:
• The supply fan for staged 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.
• Command all stages of heat ON
If the HVAC mode is LOW HEAT:
• The supply fan for staged 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.
• 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 gas is
the heating supply air set point (Setpoints
→
SA.HT).
Staged Gas Heating PID Logic
— The heat control loop is a
PID (proportional/integral/derivative) design with exceptions,
overrides and clamps. Capacity rises and falls based on set
point and supply-air temperature. When the staged gas control
is in Low Heat or Tempering Mode (HVAC mode), the algo-
rithm calculates the desired heat capacity. The basic factors that
govern the controlling technique are:
• how fast 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 Gas Capacity Calculation = “P + D” + old Staged Gas
Capacity Calculation
NOTE: The PID values should not be modified without
approval from Carrier.
Table 50 — Staged Gas Configuration
*Some configurations are model number dependent.
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 airflow rate. 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.
ITEM EXPANSION RANGE UNITS CCN POINT DEFAULTS
SG.CF
STAGED GAS CONFIGS
HT.ST
Staged Gas Heat Type 0 - 4 HTSTGTYP 0*
CAP.M
Max Cap Change per Cycle 5 - 45 HTCAPMAX 45*
M.R.DB
S.Gas DB min.dF/PID Rate 0 - 5 HT_MR_DB 0.5
S.G.DB
St.Gas Temp. Dead Band 0 - 5 ^FHT_SG_DB 2
RISE
Heat Rise dF/sec Clamp 0.05 - 0.2 HTSGRISE 0.06
LAT.L
LAT Limit Config 0 - 20 ^FHTLATLIM 10
LIM.M
Limit Switch Monitoring? Yes/No HTLIMMON Yes
SW.H.T
Limit Switch High Temp 110 - 180 dF HT_LIMHI 170*
SW.L.T
Limit Switch Low Temp 100 - 170 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 60 - 300 sec HTSGPIDR 90