ABSTRACT This paper reports environmentally friendly technologies for compressors and refrigerators. For household refrigerators@ HC-600a isobutane refrigerant is used worldwide. First@ we compare its characteristics to HFC-134a refrigerant and discuss the technologies regarding the higher volumetric efficiency of compressors. Second@ we discuss technologies for improving the volumetric efficiency at the piston and the cylinder bore portions. The piston groove outperforms oil seals. We also report the optimum groove design and fluid analysis using CFD at the groove portion.