Experimental study on startup characteristics of R290 air conditioner with low lubricant charge|Étude expérimentale des caractéristiques de démarrage d'un climatiseur fonctionnant au R-290 avec une faible charge en lubrifiant

As an A3 refrigerant, the charge of the natural refrigerant R290 in the refrigeration system is limited. The use of partially miscible lubricants and a reduction of the lubricant charge can effectively decrease the refrigerant charge. These two measures affect the startup dynamic characteristics of the compressor and the air conditioner. In this paper, variations in system temperature, pressure, and oil sump parameters during the cold startup process of a 1.5P R290 split inverter room air conditioner with different charges of PAG VG40 were experimentally measured under the rated cooling and low-temperature heating condition. The experimental results showed that the viscosity of the refrigerant/lubricant mixture of low lubricant charge (LLC) was lower than that of the normal lubricant charge (NLC), and the duration of low viscosity with LLC was longer. The low viscosity during startup is mainly due to the insufficient amount of lubricant in the oil sump. Three measures were proposed to alleviate the problem of low startup viscosity. Among them, the modification of the bearing cover effectively improved the viscosity of the LLC mixture, and the minimum viscosity of the bearing cover with LLC was even higher than that of the prototype with NLC. Furthermore, the bearing cover modification allows using a lower viscosity grade of lubricant for R290 rotary compressors.