.Buildings.Obsolete.Controls.OBC.ASHRAE.G36_PR1.AHUs.MultiZone.VAV.SetPoints.SupplyTemperature

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.

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.

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.