Installation for supplying a respiratory gas to a user, comprising: - a gas source for supplying an oxygen-containing respiratory gas, - a respiratory interface for administering the respiratory gas to the user, during each inspiratory phase of said user, - a main gas conveying line fluidically connecting the gas source to the respiratory interface in order to convey the respiratory gas from the gas source to the respiratory interface, - a gas recovery line in fluidic communication with the respiratory interface in order to recover and convey at least some of the exhaled CO 2 /O 2 gas mixture found in the respiratory interface, during each expiratory phase of the user, - a gas purification system supplied with exhaled CO 2 /O 2 gas mixture via the gas recovery line, and configured to: ▪ eliminate at least some of the CO 2 contained in the exhaled CO 2 /O 2 gas mixture and ▪ obtain a purified gas containing mainly O 2, - and a gas recycling line fluidically connecting the gas purification system to the main gas conveying line in order to convey at least some of the purified gas coming from the gas purification system and to reinject it into the main gas conveying line, and in which the gas purification system comprises at least three adsorbers arranged in parallel and each containing at least one adsorbent, each adsorber being configured to operate according to adsorption/ desorption cycles comprising: ▪ an adsorption phase during which at least some of the CO 2 contained in the exhaled CO 2 /O 2 gas mixture is adsorbed by the adsorbent, and ▪ a regeneration phase during which at least some of the CO 2 adsorbed by the adsorbent is desorbed and evacuated to the atmosphere, characterized in that the installation further comprises a turbine controlled by microprocessor-based control means (150, 151), said turbine being arranged on an air duct fluidically connected to the atmosphere and making it possible to generate a flow of unheated ambient air in said air duct, said flow of unheated ambient air being used during each regeneration phase to regenerate at least one adsorbent contained in at least one of the adsorbers by desorption of at least some of the CO 2 adsorbed by said adsorbent. - a gas source for supplying an oxygen-containing respiratory gas, - a respiratory interface for administering the respiratory gas to the user, during each inspiratory phase of said user, - a main gas conveying line fluidically connecting the gas source to the respiratory interface in order to convey the respiratory gas from the gas source to the respiratory interface, - a gas recovery line in fluidic communication with the respiratory interface in order to recover and convey at least some of the exhaled CO 2 /O 2 gas mixture found in the respiratory interface, during each expiratory phase of the user, - a gas purification system supplied with exhaled CO 2 /O 2 gas mixture via the gas recovery line, and configured to: ▪ eliminate at least some of the CO 2 contained in the exhaled CO 2 /O 2 gas mixture and ▪ obtain a purified gas containing mainly O 2, ▪ eliminate at least some of the CO 2 contained in the exhaled CO 2 /O 2 gas mixture and ▪ obtain a purified gas containing mainly O 2, - and a gas recycling line fluidically connecting the gas purification system to the main gas conveying line in order to convey at least some of the purified gas coming from the gas purification system and to reinject it into the main gas conveying line, and in which the gas purification system comprises at least three adsorbers arranged in parallel and each containing at least one adsorbent, each adsorber being configured to operate according to adsorption/ desorption cycles comprising: ▪ an adsorption phase during which at least some of the CO 2 contained in the exhaled CO 2 /O 2 gas mixture is adsorbed by the adsorbent, and ▪ a regeneration phase during which at least some of the CO 2 adsorbed by the adsorbent is desorbed and evacuated to the atmosphere, ▪ an adsorption phase during which at least some of the CO 2 contained in the exhaled CO 2 /O 2 gas mixture is adsorbed by the adsorbent, and ▪ a regeneration phase during which at least some of the CO 2 adsorbed by the adsorbent is desorbed and evacuated to the atmosphere, characterized in that the installation further comprises a turbine controlled by microprocessor-based control means (150, 151), said turbine being arranged on an air duct fluidically connected to the atmosphere and making it possible to generate a flow of unheated ambient air in said air duct, said flow of unheated ambient air being used during each regeneration phase to regenerate at least one adsorbent contained in at least one of the adsorbers by desorption of at least some of the CO 2 adsorbed by said adsorbent.