Table of Contents
Advertisement
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 method 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 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 Gas Capacity Calculation = "P + D" + old Staged Gas
Capacity Calculation
NOTE: The PID values should not be modified without
approval from Carrier.
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.
Staged 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 mod-
el number. The selection of a set of staging patterns is con-
trolled via the heat stage type configuration parameter (HT.ST).
As the heating capacity rises and falls based on demand, the
staged gas control logic will stage the heat relay patterns up and
down, respectively. The Heat Stage Type configuration selects
one of 4 staging patterns that the stage gas control will use. In
addition to the staging patterns, the capacity for each stage
is also determined by the staged gas heating PID control. There-
fore, choosing the heat relay outputs is a function of the capaci-
ty desired, the heat staging patterns based on the heat stage type
(HT.ST) and the capacity presented by each staging pattern. As
UNIT SIZE
HEAT CAPACITY
020-030
035-050
060
Table 54 — Staged Gas Heat — 48A2,A3,A4,A5 Units
UNIT MODEL NO.
POSITION NO. 5
Low
High
Low
High
Low
High
the staged gas control desired capacity rises, it is continually
checked against the capacity of the next staging pattern.
When the desired capacity is greater than or equal to the
capacity of the next staging pattern, the next heat stage is select-
ed (Run Status
VIEW
HT.ST + 1). Similarly, as the capacity of the control drops, the
desired capacity is continually checked against the next lower
stage. When the desired capacity is less than or equal to the next
lower staging pattern, the next lower heat stage pattern is select-
ed (Run Status
VIEW
HT.ST - 1). The first two staged gas heat outputs are located on
the MBB board and outputs 3, 4, 5, and 6 are located on
the SCB board. These outputs are used to produce 5 to 11 stages
as shown in Table 54. The heat stage selected (Run Sta-
tus
VIEW
HT.ST) is clamped between 0 and the maximum
number of stages possible (Run Status
the chosen set of staging patterns. See Tables 54-58.
INTEGRATED GAS CONTROL BOARD LOGIC — All gas
heat units are equipped with one or more integrated gas control
(IGC) boards. This board provides control for the ignition sys-
tem for the gas heat sections. On size 020-050 low heat units
there will be one IGC board. On size 020-050 high heat units
and 060 low heat units there are two IGC boards. On size 060
high heat units there are three IGC boards. When a call for gas
heat is initiated, power is sent to W on the IGC boards. For
standard 2-stage heat, all boards are wired in parallel. For
staged gas heat, each board is controlled separately. When en-
ergized, an LED on the IGC board will be turned on. See
Table 59 for LED explanations. Each board will ensure that the
rollout switch and limit switch are closed. The induced-draft
motor is then energized. When the speed of the motor is proven
with the Hall Effect sensor on the motor, the ignition activation
period begins. The burners ignite within 5 seconds. If the burn-
ers do not light, there is a 22-second delay before another
5-second attempt is made. If the burners still do not light, this
sequence is repeated for 15 minutes. After 15 minutes have
elapsed and the burners have not ignited then heating is locked
out. The control will reset when the request for W (heat) is tem-
porarily removed. When ignition occurs, the IGC board will
continue to monitor the condition of the rollout switch, limit
switches, Hall Effect sensor, and the flame sensor. Forty-five
seconds after ignition has occurred, the IGC will request that
the indoor fan be turned on. The IGC fan output (IFO) is con-
nected to the indoor fan input on the MBB which will indicate
to the controls that the indoor fan should be turned on (if not al-
ready on). If for some reason the overtemperature limit switch
trips prior to the start of the indoor fan blower, on the next at-
tempt the 45-second delay will be shortened by 5 seconds. Gas
will not be interrupted to the burners and heating will continue.
Once modified, the fan delay will not change back to 45 sec-
onds unless power is reset to the control. The IGC boards only
control the first stage of gas heat on each gas valve. The second
stages are controlled directly from the MBB board. The IGC
board has a minimum on-time of 1 minute. In modes such as
Service Test where long minimum on times are not enforced,
the 1-minute timer on the IGC will still be followed and the gas
will remain on for a minimum of 1 minute.
Configuration
S
T
S
T
S
T
51
HT.ST = Run Status
VIEW
HT.ST = Run Status
VIEW
VIEW
H.MAX) for
HEAT
SG.CF
HT.ST
ENTRY VALUE
1 = 5 STAGE
2 = 7 STAGE
1 = 5 STAGE
1 = 5 STAGE
4 = 11 STAGE
3 = 9 STAGE
Advertisement
Table of Contents
