High-efficiency heat exchange: due to its unique design, the annular gap between the inner and outer tubes allows the cold and hot fluid to flow reversely, increasing the heat exchange area and improving the heat exchange efficiency. This structure is especially suitable for heat pump heating machine, because it can make full use of the heat of refrigerant to heat water, so as to achieve the purpose of high efficiency and energy conservation. Compact structure: coaxial design saves space, making the overall heat pump unit more compact and easy to install and maintain. This is particularly important for commercial or residential installation environments with limited space. Strong corrosion resistance and scale resistance: heat exchanger of heat pump heating machine needs to contact water for a long time, so corrosion resistance and scale resistance are the key. Coaxial heat exchangers are usually made of corrosion-resistant materials to reduce scale accumulation and ensure long-term operation stability and efficiency.