In the field of air conditioning and refrigeration (AC&R), there is an urgent need to reduce atmospheric emissions of greenhouse gas by energy saving and switch to lower global warming potential (GWP) refrigerant. To achieve energy savings in AC&R system, it is essential to reduce the power input of the compressor, which accounts for approximately 80% of the power consumption of the whole system. Various efforts are being made to develop compressor that is more efficient and compatible with new refrigerants. This paper describes some of the technological trends in development of compressors for AC&R.

Recently, refrigerants with low global warming potential (GWP) have been required for refrigerating machines to protect the environment. Refrigeration oils are applied in the refrigeration cycle together with refrigerant to lubricate the compressor. Thus,inside the compressor, both the refrigerant and refrigeration oil have a major impact on the lubrication performance. In this paper, we explain the history of refrigerants and the tribological characteristics of refrigerants and refrigeration oil. According to previous reports, hydrofluoroolefin (HFO) refrigerants with lower GWP showed higher anti-wear performance than hydrofluorocarbon (HFC) refrigerants. In addition, the adsorption behavior of each refrigerant on nascent ferrous surfaces was studied. We focus on polyol ester (POE), which is widely used for refrigeration oil, and introduce previous research.

It is very important to improve a compressor efficiency in low capacity region for compressors used in refrigerant cycle. In low speed operation, a compressor efficiency is influenced by characteristics of an oil pump which supplies the lubricant oil to frictional faces because supplied lubricating oil amount is reduced and the thickness of the oil film decreases. For this reason,developing oil pump with good characteristics in low speed operation is important. In this paper, technologies of oil pumps used in the refrigerant compressors are introduced. Especially, centrifugal oil pump and viscosity oil pump used in compressors for refrigerators are explained.

Refrigerating and air conditioning technology is one of essential technologies in modern society, and its demand will continue to increase in the future. Therefore, further energy saving in refrigeration cycle is strongly required. Since a refrigerant compressor consumes about 80 % of total energy in refrigeration cycle, improvement of the performance of refrigerant compressor is required for reducing the energy consumption. To improve the performance of refrigerant compressor, it is important to reduce both friction and leakage of refrigerant in the compressor. At the same time, the technique to evaluate these values precisely is necessary to develop new technologies. In this commentary, the test equipment for evaluation of both friction and leakage at the sliding surface simulating the inside of a scroll compressor and typical evaluation results are reported. Moreover, some technologies for reducing friction in compressor such as texturing, nano-oil and magnetic nano-oil are introduced.

In refrigerant compressors, both journal and thrust bearings are used. In a scroll compressor or a rotary compressor, the radial load fluctuates greatly during the refrigerant compression process. Therefore, the design of oil film of the journal bearing is important for ensuring reliability and reducing machine loss. Sintering resistance, abrasion resistance and low friction are required for the thrust bearings. Recently, lubricating conditions have become severe in refrigerant compressors requiring large capacity and high speed. Therefore, it is necessary to design the oil film considering the change of temperature and dissolution viscosity in the oil film. And the dissolution viscosity affects the seizure. In this paper, the lubrication analysis method which the change of the dissolution viscosity by temperature and pressure of the oil film inside the journal bearing. And the bearing characteristics (Oil film pressure, oil film thickness, friction coefficient) test under the refrigerant atmosphere which evaluated the validity are introduced. Then the seizure resistance test in refrigerator oil diluted with liquid refrigerant is described in detail.

This article introduces the lubrication analysis of the sliding surfaces in rotary compressors used in air conditioners and refrigerators. Lubrication analysis, taking into consideration elastic deformation and solid contact, has been developed to investigate the lubricating characteristics of the main sliding surface, such as the vane top, bearings, and vane sliding surface. Additionally, to investigate the behavior of key mechanical components such as the shaft and rolling piston, dynamic analysis has been developed by coupling the equations of motion with the Reynolds equation.

The effect of hydrogen on the rolling contact fatigue life of steel was investigated using a four-ball rolling tester under a controlled atmosphere of hydrogen, deuterium and air. The isotope effect of deuterium on the fatigue life was observed, and thus the kinetic processes, such as the dissociation of deuterium molecule and the diffusion of deuterium atoms affect the fatigue life. Time-of-flight secondary ion mass spectrometry (TOF-SIMS) revealed that deuterium was absorbed and diffused into the steel during lubrication tests, and dissolved deuterium was concentrated underneath the friction track and around microcracks. The role of hydrogen in subsurface initiated fracture was considered based on the deuterium behavior observed by TOF-SIMS.