blockStagingPlant
Information
This block implements the staging logic for the chillers and HRCs. The units are staged in part based on an efficiency condition using the operative part load ratio. The units are also staged based on failsafe conditions using the CHW and HW supply temperature and differential pressure.
For the sake of simplicity, equipment rotation (i.e. the possibility at a given stage that either one unit or another unit can be operating) is not taken into account.
Plant stages
At cooling (resp. heating) stage #i, a number i
of units are operating in cooling (resp. heating) mode.
The cooling (resp. heating) stage #0 (no unit operating in
that given mode) is active whenever the plant is disabled based on the cooling
and heating Enable condition (see below) or when the plant is enabled
and has been staged down due to the efficiency or failsafe conditions.
The plant stage is given by the couple (cooling stage, heating stage).
The minimum runtime of each plant stage is set to 15 min.
Direct heat recovery mode
All HRCs are allowed to operate in direct heat recovery mode, that is when their condenser is indexed to the HW loop and their evaporator is indexed to the CHW loop. Switching a HRC to operate in direct heat recovery mode is done on a load requirement basis. This means that HRCs are first switched over to cascading heating or cascading cooling mode. Only when all HRCs are operating and when a new stage up event is initiated, an additional HRC is then switched to operate in direct heat recovery mode. As described in Buildings.DHC.Plants.Combined.Controls.BaseClasses.ModeHeatRecoveryChiller the HRC with the highest index that is not operating operating in cascading cooling mode is the next to be switched into direct heat recovery mode.
For example, considering a plant with two chillers and three HRCs, the table below shows
the plant stages derived from this logic.
In this table, the chiller with index #i is denoted CHI#i,
the HRC with index #i is denoted HRC#i,
the units enumerated before (resp. after) the semicolon sign (:) operate
in cooling (resp. heating) mode, the units marked with a star (*) operate
in direct heat recovery mode.
| Heating stage ↓ Buildings.DHC.Plants.Cooling stage → | 0 | 1 | 2 | 3 | 4 | 5 |
|---|---|---|---|---|---|---|
| 0 | N/A: N/A |
CHI1: N/A |
CHI1 & CHI2: N/A |
CHI1 & CHI2 & HRC3: N/A |
CHI1 & CHI2 & HRC3 & HRC2: N/A |
CHI1 & CHI2 & HRC3 & HRC2 & HRC1: N/A |
| 1 | N/A: HRC1 |
CHI1: HRC1 |
CHI1 & CHI2: HRC1 |
CHI1 & CHI2 & HRC3: HRC1 |
CHI1 & CHI2 & HRC3 & HRC2: HRC1 |
CHI1 & CHI2 & HRC3 & HRC2: HRC1* |
| 2 | N/A: HRC1 & HRC2 |
CHI1: HRC1 & HRC2 |
CHI1 & CHI2: HRC1 & HRC2 |
CHI1 & CHI2 & HRC3: HRC1 & HRC2 |
CHI1 & CHI2 & HRC3: HRC1 & HRC2* |
CHI1 & CHI2 & HRC3: HRC1* & HRC2* |
| 3 | N/A: HRC1 & HRC2 & HRC3 |
CHI1: HRC1 & HRC2 & HRC3 |
CHI1 & CHI2: HRC1 & HRC2 & HRC3 |
CHI1 & CHI2: HRC1 & HRC2 & HRC3* |
CHI1 & CHI2: HRC1 & HRC2* & HRC3* |
CHI1 & CHI2: HRC1* & HRC2* & HRC3* |
Cooling and heating Enable condition
The cooling and heating Enable signals u1Coo and u1Hea
shall be computed outside of the plant model,
at least based on a time schedule and ideally in conjunction
with a signal representative of the demand such as the requests yielded by
the consumer control valves.
Based on those signals, the cooling (resp. heating) stage #1 is
activated whenever the cooling (resp. heating) Enable signal switches
to true and when cooling (resp. heating) has been disabled
for at least 15 min.
Operative part load ratio
The efficiency condition is based on the operative part load ratio which is computed as the ratio of the required capacity relative to design capacity of a given stage, which is the sum of the design capacity of each unit active in a given stage. The required capacity is calculated based on the primary mass flow rate and the temperature difference between supply and primary return, and averaged over a 5-minute moving window.
Cooling and heating staging
A stage up event is initiated if any of the following conditions is true.
- Efficiency condition: the operative part load ratio of the current stage exceeds the value of the parameter PLRStaTra for 15 min.
- Failsafe conditions: the CHW (resp. HW) supply temperature is 1 K higher (resp. lower) than setpoint for 15 min, or the CHW (resp. HW) differential pressure is 1.5E4 Pa lower than setpoint for 15 min.
A stage down event is initiated if both of the following conditions are true.
- Efficiency condition: the operative part load ratio of the next lower stage falls below the value of the parameter PLRStaTra for 15 min.
- Failsafe conditions: the failsafe stage up conditions are not true.
Parameters
| Type | Name | Default | Description |
|---|---|---|---|
| Real | PLRStaTra | 0.85 | Part load ratio triggering stage transition |
| Real | cp_default | Buildings.Utilities.Psychrometrics.Constants.cpWatLiq | Specific heat capacity of the fluid |
| CHW loop and cooling-only chillers | |||
| Integer | nChi | Number of units operating at design conditions | |
| Real | QChiWatChi_flow_nominal | Cooling design heat flow rate of cooling-only chillers (all units) | |
| HW loop and heat recovery chillers | |||
| Integer | nChiHea | Number of units operating at design conditions | |
| Real | QChiWatCasCoo_flow_nominal | Cooling design heat flow rate of HRC in cascading cooling mode (all units) | |
| Real | QChiWatCasCoo_flow_nominal_approx | Cooling design heat flow rate of HRC in cascading cooling mode (all units), approximate for scaling | |
| Real | QHeaWat_flow_nominal | Heating design heat flow rate (all units) | |
Connectors
Components
| Type | Name | Default | Description |
|---|---|---|---|
| Buildings.Controls.OBC.CDL.Reals.MovingAverage | movAve | Moving average | |
| Buildings.Controls.OBC.CDL.Reals.Multiply | loaChiWat | Compute total chiller load (>0) | |
| Buildings.Controls.OBC.CDL.Reals.Subtract | dTChiWatPos | Compute deltaT (>0) | |
| Buildings.Controls.OBC.CDL.Reals.Multiply | loaHeaWat | Compute total chiller load | |
| Buildings.Controls.OBC.CDL.Reals.Subtract | dTHeaWat | Compute deltaT | |
| Buildings.Controls.OBC.CDL.Routing.IntegerScalarReplicator | rep | Replicate | |
| Buildings.Controls.OBC.CDL.Integers.GreaterEqualThreshold[nChi] | cmdChi | Compute chiller On/Off command from number of units to be commanded On | |
| Buildings.Controls.OBC.CDL.Reals.MultiplyByParameter | timCp | Scale | |
| Buildings.Controls.OBC.CDL.Reals.MultiplyByParameter | timCp1 | Scale | |
| Buildings.Controls.OBC.CDL.Reals.MovingAverage | movAve1 | Moving average | |
| Buildings.Controls.OBC.CDL.Routing.IntegerScalarReplicator | rep5 | Replicate | |
| Buildings.Controls.OBC.CDL.Integers.GreaterEqualThreshold[nChiHea] | cmdChiHea | Compute chiller On/Off command from number of units to be commanded On | |
| Buildings.Controls.OBC.CDL.Integers.Subtract | numChiHeaCoo | Number of HRC required in direct HR mode | |
| Buildings.Controls.OBC.CDL.Integers.Sources.Constant | numChiHea | Number of HRC | |
| Buildings.Controls.OBC.CDL.Integers.Add | nChiHeaAndCooUnb | Number of HRC required to meet heating and cooling load - Unbounded | |
| Buildings.Controls.OBC.CDL.Integers.Subtract | numChiCasCoo | Number of HRC required in cascading cooling | |
| Buildings.DHC.Plants.Combined.Controls.BaseClasses.ModeHeatRecoveryChiller | modHeaCoo | Compute the cascading cooling and direct HR switchover signals | |
| Buildings.Controls.OBC.CDL.Integers.Min | nChiHeaHeaAndCoo | Number of HRC required to meet heating and cooling load - Bounded by number of HRC | |
| Buildings.Controls.OBC.CDL.Reals.Subtract | errTChiWatSup | Compute tracking error | |
| Buildings.Controls.OBC.CDL.Reals.Subtract | errDpChiWat | Compute tracking error | |
| Buildings.Controls.OBC.CDL.Reals.LessThreshold | cmpErrLim | Check tracking error limit | |
| Buildings.Controls.OBC.CDL.Reals.GreaterThreshold | cmpErrLim1 | Check tracking error limit | |
| Buildings.Controls.OBC.CDL.Logical.Timer | timErrExcLim | Timer for error exceeding error limit | |
| Buildings.Controls.OBC.CDL.Logical.Timer | timErrExcLim1 | Timer for error exceeding error limit | |
| Buildings.Controls.OBC.CDL.Logical.Or | or2 | Failsafe condition to stage up | |
| Buildings.Controls.OBC.CDL.Logical.And | and2 | Apply failsafe condition only in stage >= 1 | |
| Buildings.Controls.OBC.CDL.Logical.And | and3 | Apply failsafe condition only in stage >= 1 | |
| Buildings.DHC.Plants.Combined.Controls.BaseClasses.StageIndex | staCoo | Compute cooling stage | |
| Buildings.Controls.OBC.CDL.Reals.Greater | cmpOPLRLimUp | Check OPLR limit | |
| Buildings.Controls.OBC.CDL.Logical.Timer | timOPLRExcLim | Timer for OPLR exceeding limit | |
| Buildings.Controls.OBC.CDL.Logical.Or | or1 | Failsafe condition or efficiency condition to stage up | |
| Buildings.Controls.OBC.CDL.Integers.Min | numOpeChi | Number of operating chillers | |
| Buildings.Controls.OBC.CDL.Integers.Sources.Constant | numChi | Number of chillers | |
| Buildings.Controls.OBC.CDL.Integers.Subtract | numOpeCooChiHea | Number of HRC required for cooling | |
| Buildings.Controls.OBC.CDL.Reals.Greater | cmpOPLRLimUp1 | Check OPLR limit | |
| Buildings.Controls.OBC.CDL.Logical.Timer | timOPLRExcLim1 | Timer for OPLR exceeding limit | |
| Buildings.DHC.Plants.Combined.Controls.BaseClasses.StageIndex | staHea | Compute heating stage | |
| Buildings.Controls.OBC.CDL.Reals.Less | cmpOPLRLimDow | Check OPLR limit | |
| Buildings.Controls.OBC.CDL.Logical.Timer | timOPLRExcLim2 | Timer for OPLR exceeding limit | |
| Buildings.Controls.OBC.CDL.Reals.Less | cmpOPLRLimDow1 | Check OPLR limit | |
| Buildings.Controls.OBC.CDL.Logical.Timer | timOPLRExcLim3 | Timer for OPLR exceeding limit | |
| Buildings.Controls.OBC.CDL.Logical.Not | notFail | Failsafe conditions are not true | |
| Buildings.Controls.OBC.CDL.Logical.And | dowAndNotFail | No stage up failsafe condition and efficiency condition to stage down | |
| Buildings.Controls.OBC.CDL.Reals.Subtract | errTChiWatSup1 | Compute tracking error | |
| Buildings.Controls.OBC.CDL.Reals.Subtract | errDpHeaWat | Compute tracking error | |
| Buildings.Controls.OBC.CDL.Reals.GreaterThreshold | cmpErrLim2 | Check tracking error limit | |
| Buildings.Controls.OBC.CDL.Reals.GreaterThreshold | cmpErrLim3 | Check tracking error limit | |
| Buildings.Controls.OBC.CDL.Logical.Timer | timErrExcLim2 | Timer for error exceeding error limit | |
| Buildings.Controls.OBC.CDL.Logical.Timer | timErrExcLim3 | Timer for error exceeding error limit | |
| Buildings.Controls.OBC.CDL.Logical.Or | or3 | Failsafe condition to stage up | |
| Buildings.Controls.OBC.CDL.Logical.And | and1 | Apply failsafe condition only in stage >= 1 | |
| Buildings.Controls.OBC.CDL.Logical.And | and4 | Apply failsafe condition only in stage >= 1 | |
| Buildings.Controls.OBC.CDL.Logical.Not | notFail1 | Failsafe conditions are not true | |
| Buildings.Controls.OBC.CDL.Logical.Or | or4 | Failsafe condition or efficiency condition to stage up | |
| Buildings.Controls.OBC.CDL.Logical.And | dowAndNotFail1 | No stage up failsafe condition and efficiency condition to stage down | |
| Buildings.DHC.Plants.Combined.Controls.BaseClasses.IntegerArrayHold | hol | Minimum plant stage runtime (needed because cooling and heating stage runtimes are handled separately) | |
| Buildings.DHC.Plants.Combined.Controls.BaseClasses.StagingCapacity | staCap | Total capacity at current stages times stage-up PLR limit |
Revisions
-
February 25, 2025, by Jianjun Hu:
Reimplemented it to comply with CDL specification. This is for #4110. -
February 24, 2023, by Antoine Gautier:
First implementation.