Buildings.Fluid.CHPs.BaseClasses

Package with base classes for CHP models

Information

This package contains base classes that are used to construct the models in Buildings.Fluid.CHPs.

Extends from Modelica.Icons.BasesPackage (Icon for packages containing base classes).

Package Content

Name	Description
AssertFuelFlow	Assert whether fuel flow is within boundary
AssertPower	Assert if electric power is outside boundaries
AssertWaterFlow	Assert if water flow is outside boundaries
AssertWaterTemperature	Assert if water outlet temperature is outside boundaries
Controller	Define current operation mode
EfficiencyCurve	Efficiency curve described by a fifth order polynomial, function of three input variables
EnergyConversion	Energy conversion control volume
EnergyConversionNormal	Energy conversion for typical CHP operation either in normal mode or warm-up mode based on time delay
EnergyConversionWarmUp	Energy conversion during warm-up mode based on engine temperature
EngineTemperature	Heat exchange within the engine control volume
FilterPower	Constraints for electric power
PowerConsumption	Power consumption during stand-by and cool-down modes
WarmUpLeaving	Model evaluating the condition for transitioning from warm-up to normal mode
WaterFlowControl	Internal controller for water flow rate
Functions
Types	Library of CHP operation modes
Validation	Validation of the baseclasses
Interfaces

Buildings.Fluid.CHPs.BaseClasses.AssertFuelFlow

Assert whether fuel flow is within boundary

Information

The model sends a warning message if the rate at which the fuel mass flow rate changes is outside the boundaries defined by the manufacturer.

Extends from Modelica.Blocks.Icons.Block (Basic graphical layout of input/output block).

Parameters

Connectors

Modelica definition

Buildings.Fluid.CHPs.BaseClasses.AssertPower

Assert if electric power is outside boundaries

Information

The model sends a warning message if the power demand is outside the boundaries defined by the manufacturer. Limits can be specified for the minimal and maximal electric power, and for the maximum rate at which the power can change.

Extends from Modelica.Blocks.Icons.Block (Basic graphical layout of input/output block).

Parameters

Connectors

Modelica definition

Buildings.Fluid.CHPs.BaseClasses.AssertWaterFlow

Assert if water flow is outside boundaries

Information

The model sends a warning message if the water mass flow rate is lower than the minimum defined by the manufacturer.

Extends from Modelica.Blocks.Icons.Block (Basic graphical layout of input/output block).

Parameters

Connectors

Modelica definition

Buildings.Fluid.CHPs.BaseClasses.AssertWaterTemperature

Assert if water outlet temperature is outside boundaries

Information

The model sends a warning message if the water outlet temperature is higher than the maximum defined by the manufacturer.

Extends from Modelica.Blocks.Icons.Block (Basic graphical layout of input/output block).

Parameters

Connectors

Modelica definition

Buildings.Fluid.CHPs.BaseClasses.Controller

Define current operation mode

Information

The CHP plant switches between six possible operating modes depending on the current mode, control signals and plant boundary conditions. The regular transition between them is as follows:

• off
• stand-by mode
• pump-on mode
• warm-up mode
• normal operation
• cool-down mode
• off or stand-by mode

Switching between operating modes

From the off mode:

• The transition from the off to the stand-by mode will occur when the plant availability signal avaSig becomes true.

From the stand-by mode:

• The transition from the stand-by to the pump-on mode will occur when the plant running signal runSig becomes true.
• If avaSig becomes false, the CHP will automatically change to the off mode.

From the pump-on mode:

• The transition from the pump-on to stand-by mode will occur after the specified time delay and if the water flow rate mWat_flow is greater than the minimum mWatMin_flow.
• If runSig becomes false, the CHP will automatically change to the off mode.

From the warm-up mode:

• The transition from the warm-up mode to the normal operation will occur after the specified time delay (if warmUpByTimeDelay is true) or when the engine temperature TEng becomes higher than the nominal temperature TEngNom (if warmUpByTimeDelay is false).
• If runSig becomes false or if the water flow rate mWat_flow becomes less than the minimum mWatMin_flow, the CHP will automatically change to the cool-down mode.

From the normal mode:

• The transition from the normal operation to the cool-down mode will occur when runSig becomes false or if the water flow rate mWat_flow becomes less than the minimum mWatMin_flow.

From the cool-down mode:

• The transition from the cool-down mode will occur after the specified time delay. If avaSig is true, the CHP will change to the stand-by mode; else, it will change to the off mode.
• If the CHP has the mandatory cool-down configuration (if coolDownOptional is false), the plant has to complete the cool-down period before it can be reactivated. If the CHP has the optional cool-down configuration (if coolDownOptional is true), the plant may imediatelly change to the warm-up mode if it gets reactivated (runSig= true).

Extends from Modelica.Blocks.Icons.Block (Basic graphical layout of input/output block).

Parameters

Connectors

Modelica definition

Buildings.Fluid.CHPs.BaseClasses.EfficiencyCurve

Efficiency curve described by a fifth order polynomial, function of three input variables

Information

The block computes the efficiency as a polynomial function of three input variables. The polynomial has the form

y = a₁ + a₂ x₁² + a₃ x₁ + a₄ x₂² + a₅ x₂ + a₆ x₃² + a₇ x₃ + a₈ x₁² x₂² + a₉ x₁ x₂
+ a₁₀ x₁ x₂² + a₁₁ x₁² x₂ + a₁₂ x₁² x₃² + a₁₃ x₁ x₃ + a₁₄ x₁ x₃² + a₁₅ x₁² x₃ + a₁₆ x₂² x₃² + a₁₇ x₂ x₃ + a₁₈ x₂ x₃²
+ a₁₉ x₂² x₃ + a₂₀ x₁² x₂² x₃² + a₂₁ x₁² x₂² x₃ + a₂₂ x₁² x₂ x₃² + a₂₃ x₁ x₂² x₃² + a₂₄ x₁² x₂ x₃ + a₂₅ x₁ x₂² x₃ + a₂₆ x₁ x₂ x₃² + a₂₇ x₁ x₂ x₃

where x₁ is the net power output, x₂ is the water mass flow rate, x₃ is the water inlet temperature.

Extends from Modelica.Blocks.Icons.Block (Basic graphical layout of input/output block).

Parameters

Connectors

Modelica definition

Buildings.Fluid.CHPs.BaseClasses.EnergyConversion

Energy conversion control volume

Information

The model defines energy conversion that occurs during the normal mode and warm-up mode. The model Buildings.Fluid.CHPs.BaseClasses.EnergyConversionWarmUp is used only for the warm-up mode dependent on the engine temperature (case of Stirling engines). The model Buildings.Fluid.CHPs.BaseClasses.EnergyConversionNormal is used for all other cases, i.e. the normal mode, and the warm-up mode based on a time delay (case of internal combustion engines).

Extends from Modelica.Blocks.Icons.Block (Basic graphical layout of input/output block).

Parameters

Connectors

Modelica definition

Buildings.Fluid.CHPs.BaseClasses.EnergyConversionNormal

Energy conversion for typical CHP operation either in normal mode or warm-up mode based on time delay

Information

The model defines energy conversion for a typical CHP operation that includes the normal mode and warm-up mode based on the time delay (CHPs with internal combustion engines). Energy conversion from fuel to the electric power and heat is modeled using system's part-load electrical and thermal efficiencies, based on the empirical data from the manufacturer. The curves are described by a fifth order polynomial, a function of the electric power, water flow rate and water inlet temperature. The air flow rate is modeled using a second order polynomial, a function of the fuel flow rate.

Extends from Modelica.Blocks.Icons.Block (Basic graphical layout of input/output block).

Parameters

Connectors

Modelica definition

Buildings.Fluid.CHPs.BaseClasses.EnergyConversionWarmUp

Energy conversion during warm-up mode based on engine temperature

Information

The model defines energy conversion for the warm-up mode that is dependent on the engine temperature (e.g. CHPs with Stirling engines). The engine fuel flow rate is a function of the fuel flow rate at the maximum power output, as well as the difference between the nominal engine temperature and the actual engine temperature. Energy conversion from fuel to the electric power and heat is modeled using system's part-load electrical and thermal efficiencies, based on the empirical data from the manufacturer. The curves are described by a fifth order polynomial, a function of the electric power, water flow rate and water inlet temperature. The air flow rate is modeled using a second order polynomial, a function of the fuel flow rate.

Extends from Modelica.Blocks.Icons.Block (Basic graphical layout of input/output block).

Parameters

Connectors

Modelica definition

Buildings.Fluid.CHPs.BaseClasses.EngineTemperature

Heat exchange within the engine control volume

Information

The model defines the dynamic behavior of the CHP thermal mass (i.e. engine block, encapsulated working fluid, and internal heat exchange equipment) using a single, engine control volume. The thermal energy stored within this volume is quantified using an aggregate thermal capacitance capEng and an equivalent average engine temperature TEng. The heat transfer between the engine and the cooling water control volume is quantified using the overall thermal conductance UAHex, while the heat loss to the surroundings is quantified using the overall thermal conductance UALos.

Extends from Modelica.Blocks.Icons.Block (Basic graphical layout of input/output block).

Parameters

Connectors

Modelica definition

Buildings.Fluid.CHPs.BaseClasses.FilterPower

Constraints for electric power

Information

The model checks if the electric power and power rate are within the boundaries specified by the manufacturer. The constraints are applied and a warning message is sent if the electric power is outside the boundaries.

Extends from Modelica.Blocks.Icons.Block (Basic graphical layout of input/output block).

Parameters

Connectors

Modelica definition

Buildings.Fluid.CHPs.BaseClasses.PowerConsumption

Power consumption during stand-by and cool-down modes

Information

The model calculates the power consumption during the stand-by and cool-down modes of operation.

Extends from Modelica.Blocks.Icons.Block (Basic graphical layout of input/output block).

Parameters

Connectors

Modelica definition

Buildings.Fluid.CHPs.BaseClasses.WarmUpLeaving

Model evaluating the condition for transitioning from warm-up to normal mode

Information

The model computes a boolean variable which is true when warm-up is over. CHP will transition from the warm-up mode to the normal mode

• after the specified time delay if warmUpByTimeDelay is true, or
• when the engine temperature exceeds the nominal value or the net power produced exceeds that requested by the controller if warmUpByTimeDelay is false.

Extends from Modelica.Blocks.Icons.Block (Basic graphical layout of input/output block).

Parameters

Connectors

Modelica definition

Buildings.Fluid.CHPs.BaseClasses.WaterFlowControl

Internal controller for water flow rate

Information

The model calculates the water mass flow rate that is determined by the internal controller. In CHPs that use this type of internal control the cooling water mass flow rate is controlled to optimize engine performance and heat recovery. In the main model of the CHP unit Buildings.Fluid.CHPs.ThermalElectricalFollowing, this optimum water mass flow rate is specified as the set point signal for the external pump controller.

Implementation

The mass flow rate is computed as a biquadratic function of the net power output of the system and the water inlet temperature. Note that this implementation is a truncated version of the empirical correlation proposed in Beausoleil-Morrison (2007) which includes terms of higher order (up to four).

References

Beausoleil-Morrison, Ian and Kelly, Nick, 2007. Specifications for modelling fuel cell and combustion-based residential cogeneration device within whole-building simulation programs, Section III. [Report]

Extends from Modelica.Blocks.Icons.Block (Basic graphical layout of input/output block).

Parameters

Connectors

Modelica definition