Non-invasive method of measuring the liquid level in refrigerant receivers
Natural refrigerants are becoming increasingly important as more attention is being paid to environmental protection in the use of refrigeration systems and heat pumps, and the associated regulations (e.g. the F-Gas Regulation and in the future the REACH Regulation). However, these refrigerants are typically flammable and/or toxic. This has led to strict regulations and increased demand for leak detection. A low-cost sensor that can measure the liquid level of refrigerant in receivers or accumulators would facilitate the development of refrigeration circuits and remove barriers to the use of natural refrigerants As part of the ‘CLEAR’ project, various non-invasive measurement methods for level measurement in refrigerant tanks were investigated in order to trigger a potential sensor development. With a non-invasive technique a potential sensor would not be exposed to the pressures and temperatures in the refrigeration circuit. This potentially enables a cost-effective sensor design. Furthermore, a sensor could also be retrofitted into existing refrigeration systems. The investigated methods can be used for a continuous determination of the liquid level and/or act as level switch in receivers of refrigeration systems and heat pumps during operation. The availability of such a sensor would enable condition-based diagnostics and open the door to further applications such as predictive maintenance. As part of the 'CLEAR' project, various measurement principles were evaluated and tested on different test benches. This article summarizes how the most promising measurement method works on the test rig and highlights some of their advantages and disadvantages.