Fresh air handling unit system factory advantages and applications with limited space often use integrated exhaust heat pump heat recovery fresh air fans. Because the exhaust air volume is limited by the fresh air volume, the condensing temperature of this kind of fresh air blower is higher, the air supply temperature is higher, and the efficiency is lower. A new system of mixed air condensation and return air subcooling; under the premise of not changing the total heat exchange area of the exhaust coil, the supercooling section and the condensing section are arranged separately, so that the lower temperature indoor return air passes through the subcooling plate first The pipe is mixed with fresh air and then passes through the condensing exhaust coil. Simulation analysis shows that the new system effectively improves the problem of excessively high condensation temperature, and the system efficiency is significantly improved. The return air supercooling makes the supercooling degree greater and the unit refrigeration capacity increased, which can effectively reduce the supply air temperature, achieve equal enthalpy supply or even equal humidity supply, which can completely eliminate the heat and humidity load of the fresh air.