Fill level measurement in compressors or receivers has been a key element in ensuring reliable operation for decades: oil shortage can be detected in time, and upper or lower fill limits in the receiver can be reliably maintained. The requirements of new refrigerants and the demand for simplified installation have led to a new development at KRIWAN.

1. Introduction

For decades, optical-based fill level measurement has been the proven method in refrigeration and air conditioning technology. An infrared emitting diode (LED) transmits light through a glass cone. This glass cone is screwed into the compressor or receiver so that its tip protrudes into the interior of the refrigeration system. If gas, rather than liquid, is present, the two media—glass and gas—have very different optical refractive indices. This causes the infrared light to be completely reflected back to the infrared receiving diode.

If the glass cone is instead immersed in liquid, part of the light is not reflected but propagates into the liquid. This weakens the signal at the receiving diode, and the difference between gas and liquid can be electronically detected.

An alarm can be triggered in the sensor, depending on the type, if the liquid level is exceeded or falls below a threshold. Thanks to the two-part design—glass cone and attached electronics—the electronics can be replaced without having to open the refrigeration circuit.

2. New Requirements from New Refrigerants

Due to the F-Gas Regulation, natural refrigerants such as CO₂, propane, or ammonia have been increasingly used in recent years. These refrigerants often lead to higher discharge temperatures. Likewise, applications such as high-temperature heat pumps pose a challenge for the electronics. The level sensors use LEDs as light sources and light sensors. LEDs—now standard in lighting technology—are semiconductors. They offer a high efficiency and generate relatively little heat compared to traditional light sources, but they must be protected against excessive temperatures to avoid premature aging.

While LED self-heating is the primary challenge in lighting applications, in level sensors used in refrigeration/air-conditioning and heat pumps, it is the medium temperature of the refrigerants that becomes critical. Another key factor is that many of the new refrigerants are flammable. A2L and A3 refrigerants introduce new safety requirements for the components used. Therefore, level sensors for these new refrigerants must be structurally adapted to meet these challenges. KRIWAN has responded by expanding its level sensor family: