Heat-pump system on natural refrigerant CO2 Kudrat Karimov, Asatilla Karabayev, Taxir Nurmatov, Abdullakhuja Norkhujayev and Mirolim Abdullayev E3S Web Conf., 461 (2023) 01078 Published online: 12 December 2023 DOI: 10.1051/e3sconf/202346101078