ACL Version 1.24
AirConditioning Library 1.24 is part of Modelon's 2022.2 release. New versions of Modelon's libraries are sold and distributed directly from Modelon, as well as approved resellers.
Version 1.24 contains the changes described below.
- Robustness improvement when using pressure, density & specific enthalpy (p, d, h) as dynamic states in refrigerant control volumes.
Especially in the low pressure liquid region, it has been observed that due to the density function, the state change from volume mass & internal energy to pressure and specific enthalpy is numerically sensitive and can result in mass loss or increase during simulation. The option to introduce density as additional state mitigated this by integrating the density as a independant state, ensuring that solver error control is applied to it. However, using this option has shown other issues in this region, such as inaccurate pressure fluctuations & negative density appearing in results. The root caue of this has been identified as inconsistency appearing between the independent states, p, d & h.
With this release, a consistency check is implemented in all control volumes (both in pipes & heat exchanger channels, as well as other components like junctions, valves, receivers, etc) using p, d & h as states, so that if an inconsistent state occur, the pressure is corrected so that when computing density from p, h, the result is consistent with the density state. Multiple tests has shown that this mitigate inaccurate pressure behavior and precense of negative density values.
The feature is controlled via the "System_ACL" component parameters and affect all volumes in the model. On the "Refrigeration side" tab, pdh states is enabled by setting the parameter stateChoice. When pdh is selected, the parameter d_tol_rel on the same tab determine the maximum allowed relative error between the density state and the density from pressure and enthalpy states in each volume. Tolerances in the range of 1e-3 to 1e-4 has appeared giveing good trade-off between accuracy and simulation speed.
- A method has been implemented to automatically compute the total refrigerant volume & mass in a system. Include the component "AirConditioning.AggregateTwoPhase" at the top level of a system model, and its internal variables M & V will be the total mass & volume of all refrigerant volumes in that system.
- Corrected issues with ph-visualizers. The visualizer for r1234yf with log pressure scale had an error that would show pressure levels incorrectly. Further many examples in ACL had instances with non-default aspect ratio of the ph-visualizer. That cause mis-alignment between the ph diagram bitmap and the plotted simulation results. To allow easier detection of any error, the visualizer component will render a rectangle overlaying the bitmap grid axes. If they do not align, the plotted results will also be incorrectly plotted. The solution is to resize the visualizer on the diagram to correct aspect ratio. Tools should only allow correct aspect ratio due to annotations in the visualizer components.
Build 2 (2022-09-26)
- Improved robustess when exactly 0 degree C occur as inlet or outlet air temperature in heat exchangers. At this temperature the moist air model return very high heat capacity, and the abrupt change made the solving difficult. The updated air channel model uses the actual enthalpy difference between inlet and outlet temperature instead. Minimal result deviations can occur due to this change, being largest in when condensation occur. Typical observed result deviations have been < 1% for the air heat capacity and < 0.1% for the total transferred heat. Affected components are heat exchangers where AirModel options "Analytic solution air flow model (moist)" or "Analytic solution air flow model (dry)" are used.
Build 1 (2022-06-17)
- Density as additional state has been ported from ThermalModel_ph to ThermalModelLumped_ph
- Improved compliance with the Modelica Language Specification: clean up duplicate variable declarations; corrected derivative annotation syntax, improved conversion scripts.