.Buildings.Controls.OBC.ASHRAE.G36.AHUs.SingleZone.VAV.Economizers.Subsequences.Modulation

Information

This is a single zone VAV AHU economizer modulation block. It calculates the outdoor and return air damper positions based on the single zone VAV AHU supply air temperature control loop signal. Economizer dampers are modulated based on the calculated heating supply air temperature setpoint. The implementation is in line with Section 5.18.5.1 and 5.18.5.2 of ASHRAE Guidline 36, May 2020. Damper positions are linearly mapped to the supply air control loop signal. This is a final sequence in the composite single zone VAV AHU economizer control sequence. Damper position limits, which are the inputs to the sequence, are the outputs of Buildings.Controls.OBC.ASHRAE.G36.AHUs.SingleZone.VAV.Economizers.Subsequences.Limits and Buildings.Controls.OBC.ASHRAE.G36.AHUs.SingleZone.VAV.Economizers.Subsequences.Enable sequences.

When the economizer is enabled, the PI controller modulates the damper positions. Return and outdoor damper are not interlocked. When the economizer is disabled, the damper positions are set to the minimum outdoor air damper position limits.

The figures below show the input-output structure and an economizer damper modulation sequence assuming a well configured controller.

Control diagram:

Single zone AHU economizer modulation control chart:

Revisions

• July 29, 2019, by Kun Zhang:
  Reimplemented economizer modulation control sequence.
• October 31, 2018, by David Blum:
  Added heating coil output.
• October 19, 2017, by Jianjun Hu:
  Changed name of controller output limit from yMin and yMax to uMin and uMax.
• July 07, 2017, by Milica Grahovac:
  First implementation.