.Buildings.Templates.Plants.Controls.Utilities.StageIndex

Information

This block is used to compute the stage index for a group of multiple equipment such as CHW pumps or chillers.

• At initial time, stage 0 is active – all units are disabled.
• From stage 0, the transition to the next higher available stage is triggered when the lead unit is enabled (u1Lea = true) and if at least one stage is available.
• From any stage i (1 ≤ i ≤ nSta), the transition to the next higher or lower available stage j (1 ≤ j ≤ nSta, j ≠ i) is triggered when stage i has been active for the minimum runtime and there is a stage up command u1Up or stage down command u1Dow, respectively.
• From any stage i (1 ≤ i ≤ nSta), the transition to stage 0 is triggered when stage i has been active for the minimum runtime and the lead unit is disabled (u1Lea = false).

Unavailable stages are handled by the following requirements.

• Any unavailable stage (u1Ava[i] = false) is skipped during staging events.
• If all higher (resp. lower) stages are unavailable, then the transition to a higher (resp. lower) stage is blocked.
• If the current stage is unavailable, the transition to the next higher available stage is triggered.
• Stage transitions due to availability conditions are not subject to the minimum stage runtime requirement.

Caveats

The only way to transition to stage 0 is by disabling the lead unit (u1Lea = false). The stage down command u1Dow cannot be used to transition below stage 1.

When the current stage becomes unavailable, the transition to the next higher available stage is triggered. However, it can happen that equipment that is enabled at the current stage is no longer available while the current stage is not deemed unavailable – for example if a lead/lag alternate equipment remains available. In this case, the equipment rotation logic must stage on the lead/lag alternate equipment to replace the faulty equipment.

Revisions

• March 29, 2024, by Antoine Gautier:
  First implementation.