ACL Version 1.29

AirConditioning Library 1.29 is part of Modelon's 2025.1 release. New versions of Modelon's libraries are sold and distributed directly from Modelon, as well as approved resellers.

Version 1.29 contains the changes described below.

New features

  • Frost behaviors for simulating heat exchanger operation under frost accumulation/melting and retained water refreezing/melting are implemented. The frost feature is enabled by checking the flag enable_frost in heat exchanger models. Frost formation and melting behaviors are switched automatically depending on the heat exchanger operating conditions. Two examples including an evaporator-fan system R1234yfEvaporatorFrost and a complete reversible heat pump system (R1234yfDefrostCycle) are added to demonstrate frost/defrost features.

Enhancements

  • Robustness and performance improvements for zero-flow and phase boundary crossings have been implemented in two-phase fluid channels for pipes and heat exchangers. With this update, flow rate is taken into account when computing the fraction of each segment length that assumes two-phase properties for heat transfer and pressure loss computation. Pressure drop and heat transfer correlations for two-phase fluids have also been better smoothened at the saturated liquid and vapor lines for better performance and to avoid oscillating results in this region. With this update the "twoPhaseFraction stabilizer" feature has been removed, as well as the heat transfer coefficient "relaxation" feature. Parameters to enable these features have been removed and modifiers of them in user models will be removed by the included conversion script. Note: This update will affect results of existing models to some degree, as the heat transfer performance is now computed differently where there are two adjacent control volumes in different phases.
  • When running with the "pdh" states option, which can improve mass preservation by introducing the superfluous density dynamic state, there is an updated mechanism to keep the three states consistent over time. The new option is the default selection and works by dynamically correcting the mass. The time constant for this correction is configurable using the new parameter Tc_corr on the system_ACL component. The previous mechanism can be selected instead, by setting dynamicCorrection = false on the system_ACL component. The previous method could sometimes cause large peaks in the fluid pressure, as it adjusted pressure to correct the fluid mass.
  • In the TwoPhaseLiquid and LiquidAir packages, the initialization of wall temperature in heat exchangers has been improved. Previously, the wall temperature was calculated using the parameter dT_coolant. It is now determined as a weighted average between the refrigerant and air. This calculation is controlled by a parameter present in the initialization record for those heat exchangers, represented by the parameter wt_wall. Note: Legacy heat exchangers located in Heating_Deprecated.HeatExchangers are still initialized with dT_coolant.
  • Initialization parameters for coolant temperature within AirConditioning.ThermoFluidPro.InitConditions have been renamed to be consistent with other coolant parameters.
  • Robustness improvement for moisture condensation for TwoPhaseAir and LiquidAir Heat Exchangers. Now the condensation properties are calculated by default from downstream pressure (previously upstream), that change caused reduction in non-linear blocks size during simulation. Previous behavior can be resotred by deactivating flag useDownstreamPressure = false in HXAirFlowMoist. It may cause changes in the results.
  • The function to calculate receiver outflow quality by interpolation values from a table now uses smooth monotonicity-preserving interpolation that supports analytic derivatives and avoids external code.
  • Minor improvements for the description of media.