Fast Calculation of Refrigerant Properties in Vapor Compression Cycles Using Spline-Base Table Look-Up Method (SBTL)

LIXIANG LI, JESSE GOHL, JOHN BATTEH, CHRISTOPHER GREINER, KAI WANG

APRIL 10, 2019

Presented at the 1st American Modelica Conference

Abstract

Refrigerant property calculation has a significant impact on the computational performance of vapor compression cycle simulations. This paper summarizes a Modelica implementation of Spline-Based Table Look-Up Method (SBTL) for fast calculation of refrigerant properties. External C functions are used for faster spline evaluation and inversion. Significant improvement in computation speed was observed without sacrificing accuracy. An SBTL property model of R134a is first validated against a highly accurate Helmholtz energy equation of state (EOS) model. Then the new model was tested rigorously from single function calls, to heat exchanger test bench, to system models of the vapor compression cycle in Modelon’s Air Conditioning Library. Finally, an SBTL property model of R1234yf was used in a drive cycle simulation and a shutdown-startup test of two complex air conditioning system models developed at the Ford Motor Company. These system models are running more than twice the speed of the ones using Helmholtz energy EOS.