.Buildings.Templates.Plants.Controls.StagingRotation.SortRuntime

Information

This block implements the rotation logic for identical parallel staged equipment that are lead/lag alternated.

Two runtime points are defined for each equipment. The Lifetime Runtime is the cumulative runtime of the equipment since equipment start-up. This point is not readily resettable by operators. Lifetime Runtime should be stored to a software point on the control system server so the recorded value is not lost due to controller reset, loss of power, programming file update, etc. The Staging Runtime is an operator resettable runtime point that stores cumulative runtime since the last operator reset.

In the case of available equipment, when more than one equipment is off or more than one is on, the equipment with the most operating hours as determined by Staging Runtime is made the last stage equipment and the one with the least number of hours is made the lead stage equipment.

In the case of unavailable equipment, the equipment that alarmed most recently is sent to the last position. The equipment in alarm automatically moves up in the staging order only if another equipment goes into alarm.

Staging runtime initialization

When the controller is initialized, the choice of the first equipment to run is random since all runtimes are equal to zero. So, before this first equipment reports status, all equipment will be considered off and only this first equipment will increase runtime and be queued in the staging order. At next stage change, another equipment will then be staged on instead, resulting in the first running equipment being "hot swapped". To avoid this behavior, the vector parameter runTim_start is used to initialize the staging runtime, which will be fixed at this parameter value until it becomes higher. The parameter runTim_start should be set to a vector of strictly increasing values, where the minimum value is greater than the time needed for the equipment to report status.

Details

The sorting logic is implemented using the following method.

• If a unit is on and available, its staging runtime is used as is.
• If a unit is off and available, its staging runtime is increased by a constant of 1E10 s.
• If a unit is unavailable, its staging runtime is replaced by the time that has elapsed since the unit became unavailable. This time is then increased by a constant of 1E20 s.
• A unique instance of the sorting block is then used to order the different units.

This is effectively the same as sorting the units within the three following subsets: units that are on and available, units that are off and available, units that are unavailable. In particular, the order index of a given unit remains unchanged if it is the only element of a given subset. Note that the staging runtime and the time elapsed since an equipment became unavailable are both computed from Boolean signals (u1Run and u1Ava). These are discrete-time, piecewise constant variables, which is why the caveat in the documentation of Buildings.Templates.Plants.Controls.Utilities.SortWithIndices for purely continuous time-varying variables does not apply here. Therefore, no sampling is performed before sorting the equipment runtimes.

To facilitate integration into the plant controller, the input vectors cover the full set of equipment, including equipment that may not be lead/lag alternate. The output vectors cover only the subset of lead/lag alternate equipment, and the vector of sorted equipment provides indices with respect to the input vectors (full set of equipment).

Revisions

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