Conference Year

2016

Keywords

internal heat exchanger, suction line heat exchanger, effectiveness, test standard, customized test facility

Abstract

The Internal Heat Exchanger (IHX) is widely known for its potential to improve the performance of air conditioning systems.  The adoption of alternative, more environmentally friendly, refrigerants such as R744 has brought elevated attention to IHX development due to relatively large performance increases from IHX usage compared to conventional refrigerants. In addition, the increasing need for even small incremental improvements in systems using conventional refrigerants has driven the expanded development and implementation of IHXs. The focus of this study is the quantification and comparison of the performance of internal heat exchangers and the effects of location of measurements and oil in circulation rates on the measurement accuracy and actual IHX performance. Typical IHX performance measurements yield the heat exchanger capacity, effectiveness, and the refrigerant pressure drop across each side of the heat exchanger. Existing test standards vary widely on the required test conditions, allowable oil in circulation rates, and instrument locations. The goal of comparison testing is of course to accurately quantify performance while also achieving repeatable results which allow for a fair and useful comparison between IHXs. Test conditions and temperature measurement location can have a large effect on both the accuracy and repeatability of measurements. Conditions close to the saturation dome, i.e. low subcooling or superheat, can make it difficult to accurately determine and control the state point. Thermal stratification across the cross section of the IHX tubes can also lead to measurement difficulty depending on the temperature probe placement. Oil in circulation rates directly factor into the heat exchanger capacity calculations but also can affect the actual heat exchanged as well as the measurements themselves. This paper will discuss these effects and their implications on standard development and test facility design.

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