ACL Version 3.0

AirConditioning Library 3.0 is part of Modelon's 2026.1 release.

New versions of Modelon's libraries are sold and distributed directly from Modelon, as well as approved resellers.

Version 3.0 is updated to be compliant with Modelon Base Library 7.0

New features

  • Significant improvements and bug fixes have been applied to refrigerant Valves to support reverse flow conditions. Previously, refrigerant valves always assumed positive flow (positiveFlow = true), and fluid properties were calculated based on that assumption. This was a limitation in certain scenarios. With this update, fluid properties are now determined automatically according to the actual flow direction, which significantly increases model accuracy. By default, all Valves, Junction, Split, and bend components now use positiveFlow = false. This change may cause variations in model results.

    Note: If users wish to restore the previous behavior, they can either:

    • Set the boolean parameter positiveFlow = true in the Advanced tab for individual components, or
    • Enable positiveFlow_ref in the System_ACL settings to apply the change globally across all components.

  • SimpleTXV has been enhanced to provide greater control over the initialization of the integrator output of the internal LimPI controller, improving start-up behavior and physical consistency.
  • LimPI has been enhanced with extended options for integrator initialization, enabling explicit control of initial state, steady-state behavior, or output-based initialization.
  • All Air Handling related components, including sources, volumes, and sensors, now support trace component flow within the model. This feature allows users to monitor the movement of trace components in the air medium.

Improvements

  • Changes for improved simulation performance and robustness of two-phase fluids:
    • The wall sub-component in heat exchangers now has two temperature states per segment, reducing or removing the need for iterative solving of convection models. The previously used, single temperature state per segment can be brought back if needed by setting the "surfaceState" parameter on the wall sub-component to false.
    • All heat transfer correlations for two-phase fluids now have the option to filter or "relax" the heat transfer coefficients, which can improve simulation performance for transient scenarios. This option can be enabled either for single components by setting the useRelaxation parameter on the "Advanced" tab of correlation parameters, or for all components in a system by including the System_ACL component and enabling the useRelaxation parameter there. When enabled, the time constant of heat transfer coefficients can be determined by the parameter "tau". Values in the range of 1 to 10 seconds are recommended.
    • Minor changes to equations in the two-phase flow channel component that reduce risk of simulation slow-down. These changes only affect the transient behavior, not steady-state results.
  • Several minor corrections to improve Modelica compliance and reduce warnings.
  • This Junction model summary record name has been modified from flowJoinSummary to summary. In addition, pressure, temperature, and enthalpy variables have been added to the records FlowSplitSummary and FlowJoinSummary.

Bug fixes

  • The UserSelectable_TwoModels model from the heat transfer correlations has been enhanced to support two separate ConstantHTCoefficient models. Now, the alpha0/alpha values can be explicitly defined for each selected correlation (Previously, both correlations shared a common alpha0 value).
  • The Nusselt number can by definition not be smaller than 1.0, but some empirical correlations might return smaller values. The values calculated by correlations are now smoothly limited to return values equal to or greater than 1.0.
  • Bug fix on coolant side header parameterization for PlateRefLCLCoolantHX and AirLCLCoolantHXGrid models. Additionally, coolant header hydraulic diameter parameter names have been renamed for better understanding. This change applies to heat exchanger models in TwoPhaseLiquid and LiquidAir. Note: Conversion script will handle these changes automatically.
  • Changed the split diameter value in the Co2CycleWithVICompressor model model to maintain realistic consistency with the pipe diameter..

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