Smoke Flow in Chinese Kangs

Chinese kangs are widely used today, in nearly 85% of rural homes by 175 million people in Northern China. While Chinese kangs are a potentially energy sustainable solution for home heating, existing systems are characterized by their poor energy efficiency and significant concerns about the impact of indoor air pollution in homes caused by smoke backflow or smoke leakages. Existing kang designs are based on the intuition and historical accumulation of past craftsmanship experiences. As the first attempt, a macroscopic thermal-fluid approach is used to model the airflow and heat transfer process of an elevated kang with a focus on smoke flow. This model considers nonlinear interaction of thermal buoyancy force, wind force and heat transfer from kang plates and chimney walls. Five parameter groups are identified for characterizing the kang systems to guide the kang smoke flow design. Our work has explained the so-called smoke backflow phenomenon that can lead to serious indoor air quality problems in rural homes and based on the results, we have provided some design recommendations for avoiding smoke backflow, and for enhancing energy efficiency by increasing the heat utilization of the kang body.