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Design and realization of a primary and secondary leak standards for the measurement of leak flow rates of refrigerants

The European regulation n°842/2006 on May 17th 2006 relating to the refrigerant greenhouse gases defines the duties of the owners of these equipment. Thus, the owner of equipment confining more than 3 kg of refrigerant fluids must control periodically the tightness of their equipment. In France, the French order established on May 7th 2007 specifies that the leak tightness of the equipment containing refrigerant must be controlled by refrigerant leak detectors and room controllers whose sensibilities are respectively 5 g/yr and 10 µmol/mol. These sensibilities must be measured according to the European standard EN 14624. According to this standard, calibrated leaks between 1 and 50 g/yr are needed. Therefore, it is then necessary to get standard leaks in order to verify the leak flow rate measurements. As there is a measurement chain of helium leak flow rates, an inventory and an analysis of the main existing methods to measure gas leaks flow rates have been carried out. This study underlines that a new method to calibrate refrigerant leaks is required. Therefore, the Center for Energy and Processes (CEP) has developed an infrared method. It consists in measuring the accumulation of a tracer gas emitted by the refrigerant leak and diluted in an enclosed volume. Using this method, a primary standard to measure refrigerant leak flow rates : between 1and 50 g/yr - has been designed by the LNE and the CEP, with the support of ADEME. The design phases are presented. Particularly, as the method is mainly based on the concentration change measurement in a well-known accumulation volume, the choices of the concentration measurement and of the volume measurement methods have been identified as the key point of the design and they are explained. Once the design study is done, the primary standard has been realized and qualified. The leak flow rate is calculated from several quantities: concentration, pressure, temperature and the accumulation volume. The measurement chain of each quantity has been analyzed in order to determine the operating process to estimate the quantity value and its uncertainty. The combined uncertainty of a refrigerant leak flow rate has then been established. As the calibrated leak traceability is now ensured, the refrigerant detector sensitivity threshold can be measured according to the existing standards: the European standard EN 14624, the SAE standard and the ASHRAE standard project. Theoretical, phenomenological and experimental studies have been carried out in order to identified the influence parameter of the sensitivity threshold measurement. They conclude by defining the precautions to take during the measurements. Finally, the study has been extended to identify the precautions to take during a real detection in the industry.