Table 67 — Mode Trip Helper Table
ITEM | EXPANSION |
| UNITS |
| CCN POINT |
TRIP | MODE TRIP HELPER |
|
|
|
|
UN.C.S | Unoccup. Cool Mode Start |
| dF |
| UCCLSTRT |
|
| ||||
UN.C.E | Unoccup. Cool Mode End |
| dF |
| UCCL_END |
OC.C.S | Occupied Cool Mode Start |
| dF |
| OCCLSTRT |
OC.C.E | Occupied Cool Mode End |
| dF |
| OCCL_END |
TEMP | Ctl.Temp RAT,SPT or Zone |
| dF |
| CTRLTEMP |
OC.H.E | Occupied Heat Mode End |
| dF |
| OCHT_END |
OC.H.S | Occupied Heat Mode Start |
| dF |
| OCHTSTRT |
UN.H.E | Unoccup. Heat Mode End |
| dF |
| UCHT_END |
UN.H.S | Unoccup. Heat Mode Start |
| dF |
| UCHTSTRT |
HVAC | the current HVAC MODE |
|
|
| String |
If the HVAC mode is HIGH HEAT:
•If Electric Heat is configured, then the control will request the supply fan ON
•If Gas Heat is configured, then the IGC indoor fan input controls the supply fan request
•The control will turn on Heat Relay 1 (HS1)
•The control will turn on Heat Relay 2 (HS2)
*The logic for this “low heat” override is that one stage of heating will not be able to raise the temperature of the supply airstream sufficient to heat the space.
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 68.
Staged Gas Heat Type (HT.ST) — This configuration sets the number of stages and the order that 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 prevents the heat from staging up when the
LAT Limit Config (LAT.L) — This configuration senses when
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 removed.
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, it will be con- trolled by the IGC indoor fan 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, it will be con- trolled by the IGC indoor fan 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
•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
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
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.
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