Thermal Performance Of Heating System Of Hot-wall Kang In Northern Rural Areas

Chinese kang, which is one of the most important heating facilities in the rural areas of china, has been more than thousands of years in China. It can fulfill the needs of heating when the weather is very cold, and is also an essential facility for farmers to go through winter. Although this unique heating system is inherited and have been using on time, it has little improvement because of the neglecting farmers' quality of life. The heating-effect of existing kang is very bad, the temperature of kang-surface is not even and the fuel utilization is very low, which results in a gradual replacement of kangs with the heating technologies using commercial energy. This will add a heavy burden to the rural energy supply. So how to evaluate and improve the thermal performance of kangs, the improvements or innovations of the traditional kangs are crucial for the future transition and new heating technologies for rural residences in northern China.This text based on theoretic analysis, the knowledge of the kang is systemic presented. The thermal performance of kang is analyzed from the aspect of hydrodynamics, heat transfer theory and physiology. New evaluation indicator and testing methods are put forward, such as the temperature standard deviation on upper plate of kang, heat storage capacity of kang, systemic synthesis resistance coefficient etc. Then a whole systemic thermal performance evaluation indicator of kang is generalized.The prototype experiment is carried out to certificate the feasibility of the thermal performance indicator, on the other side the thermal indicator of kang is scientifically analyzed and recognized, heat receiving, storage and dissipation is systemically analyzed. It is provided for the basis of the structure improvement and design of kang. The experiment results show that:①main thermal performance: Changing the structure of kang can promote the leveling of thermal comfort and the heating rapid of kang, strengthen the heat capacity with a rate of 33.3kWh. The radiation heat takes a big role in the total heat release, recovered with almost 65% of the total heat. Hot-wall style kang can keep the indoor temperature above 15℃, 13℃warmer than house without heating, about 20℃warmer than outdoor. Hot-wall style kang improves the indoor building thermal environment, realizing to satisfy the indoor heating without using consuming commercial energy. ②Heat Transfer and Smoke Flow Performance: The smoke temperature is about 250-400℃, when using corn cob as fuels. The smoke temperature at the Chimney Export is higher. When burning hot-wall to heat kang,The smoke velocity is Larger than burning stoves to heat. There are two layers in kang when heating it, and the layer of soil in kang can prevent heat loss, it plays some part in heat preservation.Experimental results show that: Exhaust temperature is too high, when burning; the temperature of the front plate is too low when hot-wall is run while kang faceplate temperature is not uniform when only stove is run.. According to the existed problems of hot-wall kang, several efficient measures have been adopted to improve the structure of hot-wall. Ash stamp was removed inside the hot-wall and a broad was also installed at the end of kang internal to stop smoke. Besides, two pillars were used to displace the one pillar which is located nearby kang inlet. The results of structure improvement show that, improving the structure can low the fuel temperature nearly 30℃, rise the wall temperature 10-15℃.The exhaust smoke heat losses is less than before, the efficiency of energy utilization and heating capacity of kang are improved.The thermal performance and the test method of kang are introduced in this paper. It firstly systematicly analyzes the thermal performance; heat transfer and internal smoke flow of the hot-wall kang, takes steps to improve structure according to its defects to reduce exhaust gas losses and short individual difference of the heating capacity between front and back and so on, thus providing some guidance in the structure design and optimization of kang.