.Buildings.Controls.OBC.ASHRAE.G36.AHUs.SingleZone.VAV.SetPoints.Supply

Information

Block that outputs the set points for the supply air temperature for cooling, heating and economizer control, and the fan speed for a single zone VAV system. The implementation is according to the Section 5.18.4 of ASHRAE Guideline 36, May 2020.

Fan speed setpoint

The supply fan shall run whenever the unit is in any mode other than unoccupied mode. Also, a ramp function should be applied to prevent changes in fan speed of more than 10% per minute.

Minimum, medium, and maximum fan speeds shall be as follows:

1. Minimum speed minSpe, maximum cooling speed maxCooSpe, and maximum heatng speed maxHeaSpe shall be given per Section 3.2.2.1 of ASHRAE Guideline 36.
2. Medium fan speed shall be reset linearly based on outdoor air temperature TOut from minSpe when outdoor air temperature is greater than or equal to Endpoint 1 to maxCooSpe when TOut is less than or equal to Endpoint 2.
   • Endpoint 1: the lesser of zone temperature TZon plus 0.5 °C (1 °F) and maximum supply air dew point TSupDew_max.
   • Endpoint 2: the lesser of zone temperature TZon minus 6 °C (10 °F) and maximum supply air dew point TSupDew_max minus 1 °C (2 °F).

Control mapping

1. For a heating-loop signal uHea of 100% to spePoiOne (default 50%), fan speed is reset from maxHeaSpe to minSpe.
2. For a heating-loop signal uHea of spePoiOne to 0%, fan speed set point is minSpe.
3. In deadband (uHea=0, uCoo=0), fan speed set point is minSpe.
4. For a cooling-loop signal uCoo of 0% to spePoiTwo (default 25%), fan speed is minSpe.
5. For a cooling-loop signal uCoo of spePoiTwo to spePoiThr (default 50%), fan speed is reset from minSpe to medium fan speed.
6. For a cooling-loop signal uCoo of spePoiThr to spePoiFou (default 75%), fan speed is medium.
7. For a cooling-loop signal of uCoo spePoiFou to 100%, fan speed is reset from medium to maxCooSpe.

The figure below shows the sequence.

Supply temperature setpoints

The output TSupCooSet is to be used to control the cooling coil, and the output TSupHeaEcoSet is to be used to control the heating coil and the economizer dampers.

When it is in deadband state, the output TSupCooSet and TSupHeaEcoSet shall be average of the zone heating setpoint THeaSet and the zone cooling setpoint TCooSet but shall be no lower than TSupDea_min, 21 °C (70 °F), and no higher than TSupDea_max, 24 °C (75 °F),

Control mapping

1. For a heating-loop signal uHea of 100% to temPoiOne (default 50%), TSupHeaEcoSet should be TSup_max.
2. For a heating-loop signal uHea of temPoiOne to 0%, TSupHeaEcoSet is reset from TSup_max to the deadband value.
3. In deadband (uHea=0, uCoo=0), TSupHeaEcoSet is the deadband value.
4. For a cooling-loop signal uCoo of 0% to temPoiTwo (default 25%), TSupHeaEcoSet is reset from deadband value to TSup_min minus 1 °C (2 °F), while TSupCooSet is the deadband value.
5. For a cooling-loop signal uCoo of temPoiTwo to temPoiThr (default 50%), TSupHeaEcoSet and TSupCooSet are unchanged.
6. For a cooling-loop signal uCoo of temPoiThr to temPoiFou (default 75%), TSupHeaEcoSet remains at TSup_min minus 1 °C (2 °F), while TSupCooSet is reset from the deadband value to TSup_min.
7. For a cooling-loop signal uCoo of temPoiFou to 100%, TSupHeaEcoSet and TSupCooSet are unchanged.

The figure below shows the sequence.

Note that the inputs uHea and uCoo must be computed based on the same temperature sensors and control loops.

Revisions

• August 1, 2020, by Jianjun Hu:
  First implementation.