Since measures of the global warming are becoming urgent issues, various technical innovations and social system reformations are being promoted. In the engineering fields of heating, refrigerating, and air-conditioning, the global warming caused by the refrigerants is a big problem that must be solved. At the present stage, however, there are no perfect solutions for next generation refrigerants and heat pump/refrigeration systems by which the global warming is successfully prevented. Therefore, we have to search possible ways to the next generation. In this paper, important four ways which are (1) natural refrigerants, (2) low GWP synthetic refrigerants, (3) refrigerant management, and (4) refrigerant mixtures are introduced. For the refrigerant mixture which are $CO_2$/DME and HFO-1234ze(E)/HFC-32, cycle simulations have been conducted under different operation modes. COP of the mixtures has a maximum at certain concentration and they are higher than those of conventional refrigerants. From a drop-in test of HFO-1234ze(E)/HFC-32, feasibility of the refrigerant mixture has been proved.