AIR CONDITIONING LIBRARY RELEASE INFORMATION

 

VERSION 1.9

2014-09-18

Improvements

  • Improved robustness for the refrigerant CO2 (R744) at the critical point.
  • A refrigerant flow source (Reservoirs.FlowSourceCharge) is introduced as an optional component in the liquid receiver model. This makes it more convenient to reach steady-state operating points in charge experiments, since the additional refrigerant is usually stored there and does not have to travel through the system.
  • Chens correlation for evaporative heat transfer is added. It is not dependent on the heat flux and therefore avoids this iterative loop in the non-linear equation systems. On the other hand it is known to be a little less accurate than other correlations
  • The parameter p_ambient, which is used in all air models is propagated to the top level of all heat exchangers. For numerical and efficiency reason this property is constant and not the time-varying downstream pressure. Making this parameter available at the component tops level makes it easier to simulate pressure levels different to the atmospheric pressure. The default behavior of the models is not influenced by this change.
  • Improved Modelica compliance 

Known fixed issues

  • A fix in the Dittus-Boelter function which is used in heat transfer correlations for evaporation. Deviations are expected, in case the air or incompressible liquid side is not limiting the heat transfer. For backward compatibility reasons, the conversion script converts the used correlation to the original bug-containing one with a new name. Calibrated existing components shall therefore not cause result deviations compared to previous library versions unless the default heat transfer correlation in the base class from the library has not been modified.
  • Wrong connector enthalpies in air components HeatExchangers.HXAirHandling.AirSplit1_2 and HeatExchangers.HXAirHandling.AirSplit1_2_n_segMtl were corrected.
  • Singularity for super-critical region in orifice tube model is removed.
  • Stability state as advanced feature included in refrigerant channel models. The variable twoPhaseFraction, which describes the fraction of a volume covered by two-phase fluid,is turned into an additional state with an artificial delay. This can in some cases avoid oscillations, which may occur for the hard-coupled dependency of the heat transfer coefficient on the amount of evaporated or condensed refrigerant in the volume. Note that activating this advanced feature may change the overall dynamic behavior of the component. The default behavior of the affected components is not influenced.

Conversion of user libraries

Automatic conversion from ACL 1.8.7 is supported using the included conversion script.

Base Library 

AirConditioning Library 1.9 is based on the Modelica Standard Library 3.2.1. 

It has been tested on:

  • Dymola 2015 FD01
  • Dymola 2015

 

Version 1.8.7

09-05-2014

Available for: Dymola 2015

DependenciesModelica Standard Library Version: 

Conversion: 

 

New components:

  •   Air split and junctions

Improvements:

  • Steady-state initialization of evaporators with homotopy method
  • Correct propagation of initial wall temperature in internal heat exchangers

Bug fixes:

  • Deviation in saturation properties of refrigerants R152a and R32 corrected
  • Temperature display unit in superheat sensor changed from degC to K

 

Version 1.8.6

 

Available for: Dymola 2014 FD01

DependenciesModelica Standard Library Version: 3.2.1

Conversion: None from 1.8.4 and 1.8.5

  • This release is based on MSL 3.2.1. Due to some structural modifications in the Modelica.Media base classes, small changes in ThermoFluidPro were necessary. Therefore, this version of AirConditioning is only compatible with MSL 3.2.1. Regression tests comfirmed unchanged simulation results for the models in this library, in some rare cases convergence of steady-state initialization was influenced. AirConditioning 1.8.5 is identical to version 1.8.6, but still based on MSL 3.2 and is recommended to be used instead in case MSL 3.2 is the chosen Modelica base library.


Version 1.8.5

 

Available for: Dymola 2014 FD01

DependenciesModelica Standard Library Version: 3.2

Conversion: None from 1.8.4

  • A new information section is included directly in the library, with guidelines on component testbench and cycle initialization.
  • Handling of refrigerant properties at the receiver outlet is improved for low or zero-flow simulations.
  • In- and outlet pressures, enthalpies and pressures in heat exchanger summary records properly take into account headers, in case those are activated. Previously, only the active heat exchanger part was considered for temperature and enthalpy variables. Enthalpy deviations from previous results are only expected, if heat transfer between headers is possible, temperature may be slighthly different in the two-phase region, due to the additional pressure drop in the headers. This concerns only summary variables, other model variables are unaffected.
  • The variability of correction factors for heat transfer and pressure drop in heat exchangers (CF_ ...) has been increased. They are now declared as input variables, which may change over time. As a feature request by many users, this increases the flexibility for user defined modifications. The default behavior of existing models is not expected to change. Manual steps may be required for the conversion of models for pressure drop and heat transfer correlations, which were copied and modified from previous versions of the library. Please, contact support, if you experience problems.
  • Display units in the four-value display visualizer are corrected to be consistent with the actual value.
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