Carrier WeatherExpert 48N2 Controls, Start-Up, Operation, Service, And Troubleshooting page 65

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.
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, un-
less the supply fan is on for a different reason, will be con-
trolled 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 control
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, 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 per-
formed:
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 ap-
proval from Carrier service personnel.
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 or-
der to enforce a minimum heating cfm. The installer is re-
sponsible to ensure the total minimum heating cfm is not be-
low limits set for the equipment. Failure to do so will result
in limit switch tripping and may impair or negatively affect
the Carrier product warranty.
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 patterns is controlled via the heat stage type configura-
tion parameter Configuration→HEAT→SG.CF→HT.ST. Set-
ting 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.
Table 38 — Modulating Gas Heat
NUMBER
HT.ST
OF
CONFIG.
STAGES
3
0
4 1
5 2
7
3
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
the modulating gas section capacity is a function of the capaci-
ty desired, the available heat staging patterns configured with
heat stage type (HT.ST), and the capacity range presented by
each staging pattern.
As the modulating gas control desired capacity rises, it is con-
tinually checked against the capacity ranges of the next higher
staging patterns. Since each stage has a range of capacities, and
the capacities of some stages overlap, the control selects the
highest stage with sufficient minimum capacity.
Similarly, as the modulating gas control desired capacity drops,
it is continually checked against the capacity ranges of the next
lower stages. The control selects the lowest stage with suffi-
cient maximum capacity.
The first 2 modulating gas heat outputs are located on the
MBB. Outputs 3, 4, 5, 6, and the analog output that sets the
modulating gas section capacity are located on the SCB out-
puts 7 and 8 are located on the CXB. The heat stage selected
(Run Status→VIEW→HT.ST) is clamped between 0 and the
maximum number
→VIEW→H.MAX). See Tables 39-42.
SCR Electric Heat Staging
For all SCR electric heat units there is only 1 heat stage. When-
ever the heat is energized, all heaters are active and modulated
through the SCR control.
65
NO. OF HEAT
UNIT SIZE
EXCHANGER
48N
SECTIONS
2 75, 90, 105
75
3 90, 105
120,130,150
90-105
4
120,130,150
5 120,130,150
of stages possible (Run
HEAT
SIZE
Low
High
Med
Low
High
Med
High
Status