ENERGY SAVING


carrying refrigerant and the associated loss of refrigerant. In the evaporator, the coolant withdraws heat from the interior. Depending on its size, a refrigerator contains between 35 and 100 grams of refrigerant, usually R600a. Too little refrigerant in the system leads to a low-pressure fault and, as a result, the refrigerator has to use more electricity for the same capacity: meaning it takes longer to reach the desired temperature or requires more energy to maintain the temperature. In the worst case scenario, the available coolant is no longer even sufficient to reach the desired temperature. If a refrigerator loses 15% of its refrigerant through leaks, its cooling capacity will be reduced by 50% or its energy consumption doubled. Leaks are therefore harmful in many ways: They allow environmentally and climate-damaging refrigerants to escape into the environment if the refrigerant R600a is not used. If there is too little refrigerant in the cooling circuit, the electricity demand increases, which has a negative impact on the energy and environmental balance and also increases costs. That is why it is important to detect leaks during the production process so that these faulty refrigerators are never even delivered in the first place. This is also the case with all other appliances containing closed circuits with refrigerants, such as air conditioning systems, heat pumps or ORC systems. The Organic Rankine Cycle (ORC) is a drive method for steam turbines that are operated with an organic refrigerant instead of steam because


a lower evaporation temperature is required – for example in energy generation using geothermal energy. They can, for example, be the fluorinated greenhouse gases R134a and R245fa. These ORC system are then also subject to the F-Gas regulation.


Automated leak testing Using robot-assisted leak testing, leak tests can be efficiently integrated into the production processes in system construction. This also has the advantage that it no longer depends on the form on the day, experience or skill of the human tester, but instead provides consistently reliable test results. However, leak testing using robots in the refrigerator industry is posed with special challenges: Potential leakage points are only structurally accessible to a limited extent. What's more, there are high production tolerances when assembling and soldering the refrigerant components and pipes and a very low leak rate allowed by DIN EN 8964. The weaknesses of a refrigerator with regard to refrigerant tightness are well known: The soldering points on the inside of the rear wall, where the freely accessible copper or aluminium pipes of the refrigerant circuit run, are problematic. Ideally, the sniffing tip would bypass each soldering point so that it can suck up all the refrigerant escaping from the leak. However, the inside of the rear wall is not always accessible for the robot arm due to structural restrictions. It is therefore only able to attach the sniffing tip to the solder joint from one side.


Only part of the gas cloud can be sucked into the sniffer tip – and the smaller this part is, the greater the risk that relevant leaks will not be detected at all. It is therefore absolutely essential that the robot arm approaches the solder joint as accurately as possible and that the gas cloud on the rear side is detected reliably using adapted sniffer tips. This is achieved by combining the control of the sniffer leak detector with a robot and 3D image recognition system: A 3D image recognition system determines the exact position of the solder joint. Static image recognition is used here, i.e. individual points on the metal surface are visually detected. The image recognition system must be accurate to one millimetre. This can be achieved, for example, by real-time comparison of a 3D point cloud generated with strip light. Dynamic robot sniffer leak detection in the refrigeration and air conditioning sector Refrigerator producers are taking a pioneering role by pushing ahead with robot-assisted leak testing. It is foreseeable that the air conditioning industry will follow suit and also integrate fully automated leak tests into their production processes. A special feature will be the dynamic leak test:


In contrast to a purely static measurement at individual points such as in the refrigerator area, air conditioners or heat pumps tested for leak tightness are moved along a predefined path, for example along a heat exchanger and at individual points such as pipe connections. The distance to the component and the scanning speed of the sniffing tip are crucial for reliable leak detection – so that no leak is overlooked. The requirements for specialised sniffing tips are significantly higher than those of refrigerator production due to components and structural conditions. Due to the production tolerances, a 3D image recognition process must also be used here to enable robot-assisted leak testing. Even the smallest leaks of 10-5 mbar∙l/s lead to a loss of refrigerant, thus resulting in the power consumption of a refrigerator increasing significantly. The same consequences can be expected for air-conditioning systems and heat pumps. In terms of the energy balance too, it is therefore urgently recommended to check the devices for leaks during production.


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January 2021 21


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