An air supply unit for transferring heat energy between exhaust air and supply air, the air supply unit comprising - a casing, - in the casing an exhaust air channel for leading exhaust air through the casing of the air supply unit, the exhaust air channel having a first inlet for leading exhaust air into the exhaust air channel and a first outlet for leading exhaust air out of the exhaust air channel, - in the casing a supply air channel for leading supply air through the casing of the air supply unit, the supply air channel having a second inlet for leading supply air into the supply air channel and a first outlet for leading supply air out of the supply air channel, - in the casing a heat pump having a first heat interchanger having a first interior for refrigerant, and a second heat interchanger having a second interior for refrigerant, a first fluid tube for leading refrigerant between the first interior of the first heat interchanger and the second interior of the second heat interchanger., a second fluid tube for leading refrigerant between the second interior of the second heat interchanger and the first interior of the first heat interchanger, an expansion device for effecting a pressure difference between the first and the second interior, and a compressor for circulating the refrigerant from the first heat interchanger to the second heat interchanger and from the second interchanger to the first interchanger, and - that the second heat interchanger of the heat pump is adapted into the supply air channel leading through the casing, characterized in that - the air supply unit comprises in the casing a heat exchanger comprising a rotating heat transfer element for transferring heat energy from exhaust air flowing in the exhaust air channel through the casing at least partially to supply air that flows through the casing in the supply air channel, and - that the first heat interchanger of the heat pump is adapted between the first inlet and heat exchanger in the exhaust air channel leading through the casing. - a casing, - in the casing an exhaust air channel for leading exhaust air through the casing of the air supply unit, the exhaust air channel having a first inlet for leading exhaust air into the exhaust air channel and a first outlet for leading exhaust air out of the exhaust air channel, - in the casing a supply air channel for leading supply air through the casing of the air supply unit, the supply air channel having a second inlet for leading supply air into the supply air channel and a first outlet for leading supply air out of the supply air channel, - in the casing a heat pump having a first heat interchanger having a first interior for refrigerant, and a second heat interchanger having a second interior for refrigerant, a first fluid tube for leading refrigerant between the first interior of the first heat interchanger and the second interior of the second heat interchanger., a second fluid tube for leading refrigerant between the second interior of the second heat interchanger and the first interior of the first heat interchanger, an expansion device for effecting a pressure difference between the first and the second interior, and a compressor for circulating the refrigerant from the first heat interchanger to the second heat interchanger and from the second interchanger to the first interchanger, and - that the second heat interchanger of the heat pump is adapted into the supply air channel leading through the casing, characterized in that - the air supply unit comprises in the casing a heat exchanger comprising a rotating heat transfer element for transferring heat energy from exhaust air flowing in the exhaust air channel through the casing at least partially to supply air that flows through the casing in the supply air channel, and - that the first heat interchanger of the heat pump is adapted between the first inlet and heat exchanger in the exhaust air channel leading through the casing.