Buildings.Fluid.Chillers.BaseClasses

Package with base classes for Buildings.Fluid.Chillers

Information

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

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

Package Content

Name	Description
Carnot
PartialCarnot_T	Partial model for chiller with performance curve adjusted based on Carnot efficiency
PartialCarnot_y	Partial chiller model with performance curve adjusted based on Carnot efficiency
PartialElectric	Partial model for electric chiller based on the model in DOE-2, CoolTools and EnergyPlus
warnIfPerformanceOutOfBounds	Function that checks the performance and writes a warning if it is outside of 0.9 to 1.1

Buildings.Fluid.Chillers.BaseClasses.Carnot

Information

This is the base class for the Carnot chiller and the Carnot heat pump whose coefficient of performance COP changes with temperatures in the same way as the Carnot efficiency changes.

The model allows to either specify the Carnot effectivness η_Carnot,0, or a COP₀ at the nominal conditions, together with the evaporator temperature T_eva,0 and the condenser temperature T_con,0, in which case the model computes the Carnot effectivness as

η_Carnot,0 = COP₀ ⁄ (T_use,0 ⁄ (T_con,0-T_eva,0)),

where T_use is the temperature of the the useful heat, e.g., the evaporator temperature for a chiller or the condenser temperature for a heat pump.

The COP is computed as the product

COP = η_Carnot,0 COP_Carnot η_PL,

where COP_Carnot is the Carnot efficiency and η_PL is the part load efficiency, expressed using a polynomial. This polynomial has the form

η_PL = a₁ + a₂ y + a₃ y² + ...

where y ∈ [0, 1] is either the part load for cooling in case of a chiller, or the part load of heating in case of a heat pump, and the coefficients a_i are declared by the parameter a.

Implementation

To make this base class applicable to chiller or heat pumps, it uses the boolean constant COP_is_for_cooling. Depending on its value, the equations for the coefficient of performance and the part load ratio are set up.

Extends from Buildings.Fluid.Interfaces.PartialFourPortInterface (Partial model transporting fluid between two ports without storing mass or energy).

Parameters

Connectors

Modelica definition

Buildings.Fluid.Chillers.BaseClasses.PartialCarnot_T

Partial model for chiller with performance curve adjusted based on Carnot efficiency

Information

This is a partial model of a chiller whose coefficient of performance (COP) changes with temperatures in the same way as the Carnot efficiency changes. This base class is used for the Carnot chiller and Carnot heat pump that uses the compressor part load ratio as the control signal.

Extends from Carnot.

Parameters

Connectors

Modelica definition

Buildings.Fluid.Chillers.BaseClasses.PartialCarnot_y

Partial chiller model with performance curve adjusted based on Carnot efficiency

Information

This is a partial model of a chiller whose coefficient of performance (COP) changes with temperatures in the same way as the Carnot efficiency changes. This base class is used for the Carnot chiller and Carnot heat pump that uses the leaving fluid temperature as the control signal.

Extends from Carnot.

Parameters

Connectors

Modelica definition

Buildings.Fluid.Chillers.BaseClasses.PartialElectric

Partial model for electric chiller based on the model in DOE-2, CoolTools and EnergyPlus

Information

Base class for model of an electric chiller, based on the DOE-2.1 chiller model and the CoolTools chiller model that are implemented in EnergyPlus as the models Chiller:Electric:EIR and Chiller:Electric:ReformulatedEIR.

The model takes as an input the set point for the leaving chilled water temperature, which is met if the chiller has sufficient capacity. Thus, the model has a built-in, ideal temperature control. The model has three tests on the part load ratio and the cycling ratio:

1. The test

     PLR1 =min(QEva_flow_set/QEva_flow_ava, PLRMax);
   

   ensures that the chiller capacity does not exceed the chiller capacity specified by the parameter PLRMax.
2. The test

     CR = min(PLR1/per.PRLMin, 1.0);
   

   computes a cycling ratio. This ratio expresses the fraction of time that a chiller would run if it were to cycle because its load is smaller than the minimal load at which it can operature. Notice that this model does continuously operature even if the part load ratio is below the minimum part load ratio. Its leaving evaporator and condenser temperature can therefore be considered as an average temperature between the modes where the compressor is off and on.
3. The test

     PLR2 = max(PLRMinUnl, PLR1);
   

   computes the part load ratio of the compressor. The assumption is that for a part load ratio below PLRMinUnl, the chiller uses hot gas bypass to reduce the capacity, while the compressor power draw does not change.

The electric power only contains the power for the compressor, but not any power for pumps or fans.

Implementation

Models that extend from this base class need to provide three functions to predict capacity and power consumption:

• A function to predict cooling capacity. The function value needs to be assigned to capFunT.
• A function to predict the power input as a function of temperature. The function value needs to be assigned to EIRFunT.
• A function to predict the power input as a function of the part load ratio. The function value needs to be assigned to EIRFunPLR.

Extends from Buildings.Fluid.Interfaces.FourPortHeatMassExchanger (Model transporting two fluid streams between four ports with storing mass or energy).

Parameters

Connectors

Modelica definition

Buildings.Fluid.Chillers.BaseClasses.warnIfPerformanceOutOfBounds

Function that checks the performance and writes a warning if it is outside of 0.9 to 1.1

Information

This function checks if the numeric argument is outside of the interval 0.9 to 1.1. If this is the case, the function writes a warning.

Inputs

Outputs

Modelica definition