There are a variety of ways to use heat energy of municipal sewage, the most effective of which is to use sewage. That is, release the excess heat in the building into the city sewage through the unit in summer and extract and release it into the building in winter.
The resource potential of municipal sewage heat energy depends mainly on the temperature of the sewage.
The temperature of the treated municipal sewage varies within a certain range, such as after secondary treatment in a sewage treatment plant, the water temperature in winter ranging in 13-16 ℃ and that in summer ranging in 22-26 ℃.
In general, in the northern winter the sewage water temperature is above the ambient temperature by 20 ℃ in average while in summer it is below ambient temperature by over 10℃. Using the temperature difference between the sewage and the environment for generating thermal energy resource has huge prospects. However, sometimes even the heat exchanger does not work. Thus, the water quality of sewage has a great impact on the system characteristics.
In addition, there is no available data regarding on corrosive effects of the harmful ingredients in sewage on the heat exchanger material as a reference. These cause great difficulties in the research on the sewage heat exchanger.
For different wastewater quality, what system form we take and what materials and type of the heat exchanger we use to get a good heat transfer performance in sewage is the difficulty of system design.
The sewage system used in the building cooling or heating can make full use of the waste heat of municipal sewage and reduce the consumption of high energy. It can not only save energy but also reduce environmental pollution and water consumption.
Besides, high efficiency and less space demand of the sewage units greatly reduce operating costs and initial investment costs.
Therefore the sewage as a renewable energy used in air conditioning systems for buildings has been recognized by everyone and the domestic application is gradually expanding.
Despite many advantages the sewage source heat pump system has, the particularity of sewage easily leads to poor working conditions for the pump, especially worse for the heat exchanger. When the sewage flows through the heat exchanger, its complex wastewater composition causes scaling, blocking and even the erosion phenomenon in the heat exchanger.
These reduce the heat transfer efficiency, increase the flow resistance of the fluid and reduce the service life of the heat exchanger.
Due to the complex composition and impurity content of the raw sewage, taking into account the corrosion, scaling and other factors of the heat exchanger, it is recommended to adopt sewage plastic heat exchanger which is corrosion-resistant, long life and easy to clean. For sewage source heat pump system using secondary or reclaimed water of the sewage treatment plant, reclaimed water can be used as water quality standard for cooling water.
If the reclaimed water meet the corresponding water quality standards, the metal heat exchanger can be used, otherwise the non-metallic water heat exchanger.
From the aspects of price, heat transfer performance and service life, recommend PE-x and HDPE pipe as the non-metallic heat exchanger pipe.