blockSupplyTemperature
Information
Block that outputs the supply air temperature setpoint and the coil valve control inputs for VAV system with multiple zones, implemented according to the ASHRAE Guideline G36, PART 5.N.2 (Supply air temperature control).
The control loop is enabled when the supply air fan uSupFan is proven on,
and disabled and the output set to Deadband otherwise.
The supply air temperature setpoint is computed as follows.
Setpoints for TSupSetMin, TSupSetMax,
TSupSetDes, TOutMin, TOutMax
The default range of outdoor air temperature (TOutMin=16°C,
TOutMax=21°C) used to reset the occupied mode TSupSet
was chosen to maximize economizer hours. It may be preferable to use a lower
range of outdoor air temperature (e.g. TOutMin=13°C,
TOutMax=18°C) to minimize fan energy.
The TSupSetMin variable is used during warm weather when little reheat
is expected to minimize fan energy. It should not be set too low or it may cause
excessive chilled water temperature reset requests which will reduce chiller
plant efficiency. It should be set no lower than the design coil leaving air
temperature.
The TSupSetMax variable is typically 18 °C in mild and dry climate,
16 °C or lower in humid climates. It should not typically be greater than
18 °C since this may lead to excessive fan energy that can offset the mechanical
cooling savings from economizer operation.
During occupied mode (uOpeMod=1)
The TSupSet shall be reset from TSupSetMin when the outdoor
air temperature is TOutMax and above, proportionally up to
maximum supply temperature when the outdoor air temperature is TOutMin and
below. The maximum supply temperature shall be reset using trim and respond logic between
TSupSetDes and TSupSetMax. Parameters suggested for the
trim and respond logic are shown in the table below. They require adjustment
during the commissioning and tuning phase.
| Variable | Value | Definition |
|---|---|---|
| Device | AHU Supply Fan | Associated device |
| SP0 | iniSet | Initial setpoint |
| SPmin | TSupSetDes | Minimum setpoint |
| SPmax | TSupSetMax | Maximum setpoint |
| Td | delTim | Delay timer |
| T | samplePeriod | Time step |
| I | numIgnReq | Number of ignored requests |
| R | uZonTemResReq | Number of requests |
| SPtrim | triAmo | Trim amount |
| SPres | resAmo | Respond amount |
| SPres_max | maxRes | Maximum response per time interval |
During Setup and Cool-down modes (uOpeMod=2, uOpeMod=3)
Supply air temperature setpoint TSupSet shall be TSupSetMin.
During Setback and Warmup modes (uOpeMod=4, uOpeMod=5)
Supply air temperature setpoint TSupSet shall be TSupWarUpSetBac.
Valves control
Supply air temperature shall be controlled to setpoint using a control loop whose output is mapped to sequence the hot water valve or modulating electric heating coil (if applicable) or chilled water valves.
Parameters
| Type | Name | Default | Description |
|---|---|---|---|
| Temperatures | |||
| Real | TSupSetDes | 285.15 | Design coil leaving air temperature |
| Real | TSupSetMin | 285.15 | Lowest cooling supply air temperature setpoint when the outdoor air temperature is at the higher value of the reset range and above. This should not be lower than the design coil leaving air temperature |
| Real | TSupSetMax | 291.15 | Highest cooling supply air temperature setpoint. It is typically 18 degC (65 degF) in mild and dry climates, 16 degC (60 degF) or lower in humid climates |
| Real | TOutMin | 289.15 | Lower value of the outdoor air temperature reset range. Typically value is 16 degC (60 degF) |
| Real | TOutMax | 294.15 | Higher value of the outdoor air temperature reset range. Typically value is 21 degC (70 degF) |
| Real | TSupWarUpSetBac | 308.15 | Supply temperature in warm up and set back mode |
| Trim and respond logic | |||
| Real | delTim | 600 | Delay timer |
| Real | samplePeriod | 120 | Sample period of component |
| Integer | numIgnReq | 2 | Number of ignorable requests for TrimResponse logic |
| Real | triAmo | 0.1 | Trim amount |
| Real | resAmo | -0.2 | Response amount |
| Real | maxRes | -0.6 | Maximum response per time interval |
Connectors
| Type | Name | Default | Description |
|---|---|---|---|
| Buildings.Controls.OBC.CDL.Interfaces.RealInput | TOut | Outdoor air temperature | |
| Buildings.Controls.OBC.CDL.Interfaces.RealInput | TZonSetAve | Average of heating and cooling setpoint | |
| Buildings.Controls.OBC.CDL.Interfaces.BooleanInput | uSupFan | Supply fan status | |
| Buildings.Controls.OBC.CDL.Interfaces.IntegerInput | uOpeMod | System operation mode | |
| Buildings.Controls.OBC.CDL.Interfaces.IntegerInput | uZonTemResReq | Zone cooling supply air temperature reset request | |
| Buildings.Controls.OBC.CDL.Interfaces.RealOutput | TSupSet | Setpoint for supply air temperature |
Components
| Type | Name | Default | Description |
|---|---|---|---|
| Buildings.Obsolete.Controls.OBC.ASHRAE.G36_PR1.Generic.SetPoints.TrimAndRespond | maxSupTemRes | Maximum cooling supply temperature reset |
Revisions
-
December 21, 2021, by Jianjun Hu:
Improved comments of the setpoint limits and made the limit parameters of trim and respond logic to be protected. This is for #2828. -
March 12, 2020, by Jianjun Hu:
Propagated supply temperature setpoint of warmup and setback mode.
This is for #1829. -
July 11, 2017, by Jianjun Hu:
First implementation.