A heat recovery ventilation system for a building, wherein the system comprises: a primary heat exchanger arranged for heat recovery between an exhaust air flow from said building and an inlet air flow to said building, wherein the system comprises an exhaust air conduit for conveying the exhaust air flow in an exhaust air flow direction and an inlet air conduit for conveying the inlet air in an inlet air flow direction and a refrigerant circuit comprising a first heat exchanger and a second heat exchanger arranged for heat exchange between a refrigerant flowing in a refrigerant flow direction in said refrigerant circuit and the inlet air flow, wherein said first heat exchanger is arranged on the inlet air conduit upstream said primary heat exchanger and said second heat exchanger is arranged on the inlet air conduit downstream said primary heat exchanger in the inlet air flow direction, wherein the refrigerant circuit comprises an expansion valve, an evaporator and a compressor, wherein the expansion valve and the evaporator are arranged downstream said first heat exchanger and the compressor is arranged downstream said evaporator and upstream said second heat exchanger in the refrigerant flow direction, characterized in that the refrigerant circuit further comprises at least a third heat exchanger and a fourth heat exchanger arranged for transfer of heat between the refrigerant and a first heat carrier flowing through the third heat exchanger and a second heat carrier flowing through the fourth heat exchanger, wherein the third heat exchanger and the fourth heat exchanger are arranged downstream said compressor and upstream said second heat exchanger in the refrigerant flow direction. a primary heat exchanger arranged for heat recovery between an exhaust air flow from said building and an inlet air flow to said building, wherein the system comprises an exhaust air conduit for conveying the exhaust air flow in an exhaust air flow direction and an inlet air conduit for conveying the inlet air in an inlet air flow direction and a refrigerant circuit comprising a first heat exchanger and a second heat exchanger arranged for heat exchange between a refrigerant flowing in a refrigerant flow direction in said refrigerant circuit and the inlet air flow, wherein said first heat exchanger is arranged on the inlet air conduit upstream said primary heat exchanger and said second heat exchanger is arranged on the inlet air conduit downstream said primary heat exchanger in the inlet air flow direction, wherein the refrigerant circuit comprises an expansion valve, an evaporator and a compressor, wherein the expansion valve and the evaporator are arranged downstream said first heat exchanger and the compressor is arranged downstream said evaporator and upstream said second heat exchanger in the refrigerant flow direction, characterized in that the refrigerant circuit further comprises at least a third heat exchanger and a fourth heat exchanger arranged for transfer of heat between the refrigerant and a first heat carrier flowing through the third heat exchanger and a second heat carrier flowing through the fourth heat exchanger, wherein the third heat exchanger and the fourth heat exchanger are arranged downstream said compressor and upstream said second heat exchanger in the refrigerant flow direction.