Buildings.Templates.Plants.Controls.StagingRotation

Package of sequences for equipment staging and rotation

Information

This package contains equipment staging and rotation sequences.

Package Content

Name	Description
EquipmentAvailability	Equipment availability for heating and cooling applications
EquipmentEnable	Return array of equipment to be enabled at given stage
EventSequencing	Staging event sequencing
SortRuntime	Sort equipment by increasing staging runtime
StageAvailability	Compute stage availability
StageChangeCommand	Generate stage change command
StageCompletion	Checks successful completion of stage change
Validation	Collection of validation models

Buildings.Templates.Plants.Controls.StagingRotation.EquipmentAvailability

Equipment availability for heating and cooling applications

Information

If a heat pump is commanded enabled in either heating or cooling mode, it is removed from the staging order of the opposite mode until it has been off for dtOff.

Parameters

Connectors

Modelica definition

Buildings.Templates.Plants.Controls.StagingRotation.EquipmentEnable

Return array of equipment to be enabled at given stage

Information

This block generates the equipment enable commands based on the active stage index uSta, the equipment available signal u1Ava and the indices of lead/lag alternate equipment, sorted by increasing staging runtime.

A staging matrix staEqu is required as a parameter.

• Each row of this matrix corresponds to a given stage.
• Each column of this matrix corresponds to a given equipment.
• A coefficient staEqu[i, j] equal to 0 means that equipment j shall not be enabled at stage i.
• A coefficient staEqu[i, j] equal to 1 means that equipment j is required at stage i. If equipment j is unavailable, stage i is deemed unavailable.
• A coefficient staEqu[i, j] strictly lower than 1 and strictly greater than 0 means that equipment j may be enabled at stage i as a lead/lag alternate equipment. If equipment j is unavailable but another lead/lag alternate equipment is available, then the latter equipment is enabled. Stage i is only deemed unavailable if all lead/lag alternate equipment specified for stage i are unavailable.
• The sum of the coefficients in a given row ∑_j staEqu[i, j] gives the number of equipment required at stage i. If this number cannot be achieved with the available equipment, stage i is deemed unavailable.
• The condition ∑_j staEqu[i+1, j] ≥ ∑_j staEqu[i, j] is required for all i < size(staEqu, 1).

The state of the enable signals is only updated at stage change, or if the number of previously enabled equipment that is available is strictly less than the number of equipment required to run. This avoids hot swapping equipment, e.g., an equipment would not be started and another stopped during operation just to fulfill the priority order. However, when a lead/lag alternate equipment becomes unavailable and another lead/lag alternate equipment can be enabled to meet the number of required equipment, then the state of the enable signals is updated.

Parameters

Connectors

Modelica definition

Buildings.Templates.Plants.Controls.StagingRotation.EventSequencing

Staging event sequencing

Information

If a heat pump is commanded on in a desired heating or cooling mode:

• The isolation valves for desired heating or cooling mode are commanded open.
• Plants with dedicated primary pumps: The dedicated primary pumps are commanded on when the associated isolation valves are commanded open.
• Plants with headered primary pumps: The headered primary pumps are commanded on as described in Buildings.Templates.Plants.Controls.Pumps.Generic.StagingHeadered.
• Once the isolation valves are fully open (based on nominal valve timing dtVal) and the lead pumps are proven on, the heat pump is enabled in heating or cooling mode.

If a heat pump is commanded off:

• The heat pump is disabled.
• After the time required for the internal shutdown cycle to time out (dtOff to be determined empirically, defaulting to 3 min), all isolation valves are commanded closed.
• Plants with dedicated primary pumps: The dedicated primary pumps are commanded off when the associated isolation valves are commanded closed.
• Plants with headered primary pumps: The headered primary pumps are commanded off as described in Buildings.Templates.Plants.Controls.Pumps.Generic.StagingHeadered.

Parameters

Connectors

Modelica definition

Buildings.Templates.Plants.Controls.StagingRotation.SortRuntime

Sort equipment by increasing staging runtime

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).

Parameters

Connectors

Modelica definition

Buildings.Templates.Plants.Controls.StagingRotation.StageAvailability

Compute stage availability

Information

A stage is deemed available if both the following are true:

• Each equipment required to run at that stage without lead/lag alternate is available.
• The number of equipment required to run at that stage – with or without lead/lag alternate – and available is greater or equal to the number of equipment required to run at that stage.

Otherwise, the stage is deemed unavailable.

Parameters

Connectors

Modelica definition

Buildings.Templates.Plants.Controls.StagingRotation.StageChangeCommand

Generate stage change command

Information

The plant equipment is staged in part based on required capacity, Qrequired, relative to nominal capacity of a given stage, Qstage. This ratio is the operative part load ratio, OPLR.

OPLR = Qrequired / Qstage

If both primary and secondary hot water temperatures and flow rates are available, the sensors in the primary loop are used for calculating Qrequired. If a heat recovery chiller is piped into the secondary return, the sensors in the primary loop are used. (These conditions are implemented in Buildings.Templates.Plants.Controls.HeatPumps.AirToWater.)

The required capacity is calculated based on return temperature, active supply temperature setpoint and measured flow through the associated circuit flow meter.

The required capacity used in logic is a rolling average over a period of dtMea of instantaneous values sampled at minimum once every 30 s.

When a stage up or stage down transition is initiated, Qrequired is held fixed at its last value until the longer of the successful completion of the stage change and the duration dtRun.

The nominal capacity of a given stage, Qstage, is calculated as the sum of the design capacities of all units enabled in a given stage.

Staging is executed per the conditions below subject to the following requirements.

• Each stage has a minimum runtime of dtRun. (This condition is implemented in Buildings.Templates.Plants.Controls.Utilities.StageIndex.)
• Timers are reset to zero at the completion of every stage change.
• Any unavailable stage is skipped during staging events, but staging conditionals in the current stage are evaluated as per usual.

A stage up command is triggered if any of the following is true:

• Availability Condition: The equipment necessary to operate the current stage is unavailable. The availability condition is not subject to the minimum stage runtime requirement. (This condition is implemented in Buildings.Templates.Plants.Controls.Utilities.StageIndex.)
• Efficiency Condition: Current stage OPLR > plrSta for a duration of dtRun.

A stage down command is triggered if the following is true:

• Next available lower stage OPLR < plrSta for a duration of dtRun.

Details

A staging matrix staEqu is required as a parameter. See the documentation of Buildings.Templates.Plants.Controls.StagingRotation.EquipmentEnable for the associated definition and requirements.

An "if" condition is used to generate the stage up and down command as opposed to a "when" condition. This means that the command remains true as long as the condition is verified. This is necessary, for example, if no higher stage is available when a stage up command is triggered. Using a "when" condition – which is only valid at the point in time at which the condition becomes true – would prevent the plant from staging when a higher stage becomes available again. To avoid multiple consecutive stage changes, the block that receives the stage up and down command and computes the stage index must enforce a minimum stage runtime of dtRun.

Parameters

Connectors

Modelica definition

Buildings.Templates.Plants.Controls.StagingRotation.StageCompletion

Checks successful completion of stage change

Information

Block that detects a stage change and evaluates whether the stage transition is completed.

The completion of a stage change is considered successful when both of the following conditions have been verified.

• Following a stage transition event, or exactly at the same time, there is a change in the enable command of at least one equipment.
• The equipment status matches the enable command for all units, after any change in the enable command has been detected.

The output signal y1End is true exactly at the time when the successful completion of the stage change is confirmed. The output signal y1 is true during the entire time in which the stage change is in progress.

Connectors

Modelica definition