Summary
The Thermosys Toolbox for Matlab® is a software package for simulating and analyzing the behavior of air conditioning and refrigeration systems. The toolbox contains dynamic models of the basic components used in subcritical and transcritical vapor compression cycles, with nonlinear, linearized, and reduced order models.
Key Benefits
Simple models for simulating the complex multi-phase fluid dynamics associated with air-conditioning and refrigeration systems.
GUIs for entering the necessary component parameters
Built-in refrigerant properties for R22, R134a, R404a, R410a, and R744 (CO2)
Nonlinear models suitable for simulation and linear models suitable for control design
Sample system models, including: subcritical, transcritical, and multi-evaporator systems
Open architecture code suitable for customizing
The heat exchangers are modeled using lumped-parameter, moving boundary assumptions. For example, the evaporator is modeled as shown in the figure, with two assumed regions of fluid. An average wall temperature is assumed for each of the two regions, and the effective dry-out point is allowed to be a dynamic boundary between the two regions.
The mass flow devices, such as compressor and expansion valve, are assumed to have dynamics significantly faster than the heat exchangers, and are modeled with static, nonlinear maps. Although the model derivation is not trivial, the resulting models are of relatively low-order. These models are then programmed as Simulink blocks to be used in a "drag-and-drop" manner.
For more detail regarding model derivations, please see Recent Publications.
Graphical User Interfaces (GUIs)
Graphical User Interfaces (GUIs) simplify the task of entering component parameters for simulation. The GUIs allow the user to save or load previous parameter sets, enabling the user to switch quickly and easily from simulating different systems or operating conditions. The GUI can calculates heat-transfer coefficients based on user supplied correlations or from supplied data. The GUI also calculates refrigerant charge inventory, and allows the user to specify which simulated outputs to record for later use.
Refrigerant Properties
The Thermosys Toolbox currently contains refrigerant property look-up tables for R22, R134a, R404a, and R744 (CO2). The thermodynamic property tables were generated using Engineering Equation Solver (EES) which uses the most accurate Equations of State available.
These look-up tables can be used from the Matlab prompt (using the "interp1" or "interp2" command) or using Simulink blocks included in the Thermosys Toolbox.
Model Validation
The modeling methodology has been validated using several experimental facilities, and the work of model refinement is ongoing. In general, the model exhibits a few discrepancies when compared with the data, but captures a majority of the dynamic behavior. Because the changes necessary to improve the model match would result in models that are significantly more complex, the models presented are viewed to be an acceptable compromise between model accuracy and model simplicity.
The models have been validated for:
For detail regarding the model validation results, please see Recent Publications.
Control Design
Several control studies were part of this research. These studies included typical SISO control strategies as well as demonstrating the benefits of MIMO control strategies. The Thermosys Toolbox greatly facilitates the control design process by supplying the user with linearized models for each component. The user can enter proprietary component parameters, and then use the resulting linear models to develop an appropriate control strategy.
As part of this research, several control design strategies have been investigated using the Thermosys Toolbox. These include:
For detail regarding the control implementation results, please see Recent Publications.