A method of using a heat and power generation apparatus for heating at least one heat consumer in a heat distribution network by adopting the principle of a water source high temperature heat pump for waste heat source utilization, the method comprising: a fuel combustion process, wherein an engine cooling system of at least one internal combustion engine is used to provide a first heat releasing unit for heating at least one heat transfer medium in said heat distribution network and wherein at least one waste heat source arise when the internal combustion engine is turned on and operating by firing the fuel in the combustion process; a waste heat recovery process, wherein at least one waste heat recovery unit is used to collect at least a portion of the heat of at least one waste heat source from group of waste heat sources comprising a flue gas in exhaust system, charging air in charging air cooling system or lubrication oil in lubrication oil cooling system; a liquid-vapor phase change thermodynamic cycle utilization process, wherein at least one water source high temperature heat pump is used to provide a second heat releasing unit for heating at least one heat transfer medium in said heat distribution network when said heat pump is turned on and operating, the heat required for the liquid-vapor phase change cycle utilization is gained fully or in part by said waste heat recovery process, wherein at least a portion of the heat collected in the waste heat recovery process is used for liquid-vapor phase change thermodynamic cycle process utilization, and wherein at least a portion of the heat generated by at least one heat pump in the second heat releasing unit is used for heating the engine cooling system of at least one internal combustion engine in the first heat releasing unit; the heat in at least one closed loop circuit of said heat distribution network is preferably distributed by circulation of at least one heat transfer medium, wherein the lowest temperature of the heat distribution medium in the engine cooling system of at least one internal combustion engine in the first heat releasing unit is substantially higher than the lowest temperature of the heat distribution medium in at least one heat consumer in the the heat distribution network, characterized in that at least one heat transfer medium in at least one return line of said heat distribution network is reheated by the heat pump principle utilization, and wherein the temperature of the heat transfer medium in said engine cooling system of at least one internal combustion engine is substantially higher than 60°C, at least when a design temperature of the heat distribution network is reached and said internal combustion engine and heat pump are operating at full load. a fuel combustion process, wherein an engine cooling system of at least one internal combustion engine is used to provide a first heat releasing unit for heating at least one heat transfer medium in said heat distribution network and wherein at least one waste heat source arise when the internal combustion engine is turned on and operating by firing the fuel in the combustion process; a waste heat recovery process, wherein at least one waste heat recovery unit is used to collect at least a portion of the heat of at least one waste heat source from group of waste heat sources comprising a flue gas in exhaust system, charging air in charging air cooling system or lubrication oil in lubrication oil cooling system; a liquid-vapor phase change thermodynamic cycle utilization process, wherein at least one water source high temperature heat pump is used to provide a second heat releasing unit for heating at least one heat transfer medium in said heat distribution network when said heat pump is turned on and operating, the heat required for the liquid-vapor phase change cycle utilization is gained fully or in part by said waste heat recovery process, wherein at least a portion of the heat collected in the waste heat recovery process is used for liquid-vapor phase change thermodynamic cycle process utilization, and wherein at least a portion of the heat generated by at least one heat pump in the second heat releasing unit is used for heating the engine cooling system of at least one internal combustion engine in the first heat releasing unit; the heat in at least one closed loop circuit of said heat distribution network is preferably distributed by circulation of at least one heat transfer medium, wherein the lowest temperature of the heat distribution medium in the engine cooling system of at least one internal combustion engine in the first heat releasing unit is substantially higher than the lowest temperature of the heat distribution medium in at least one heat consumer in the the heat distribution network, characterized in that at least one heat transfer medium in at least one return line of said heat distribution network is reheated by the heat pump principle utilization, and wherein the temperature of the heat transfer medium in said engine cooling system of at least one internal combustion engine is substantially higher than 60°C, at least when a design temperature of the heat distribution network is reached and said internal combustion engine and heat pump are operating at full load.