System Description: Kang bed-stove(炕) is one of the oldest primary floor heating system that commonly used for residential heating in North Eastern Asia. It has been implemented for at least 2500 years, and still widely installed in rural region today. Till 2004, there were around 67 million kangs which served 175 million people in Northern China. Similar systems include Korean ondol and hypocaust in ancient Rome.
The illustration on the left demonstrates essential structure of a kang. Smoke is generated from the stove in the kitchen, and conveyed in flues that constituted by brick or adobe pillars and plate. Fire throat is the operating switch of the system, while chimney is the exhaust system. Adjacent to the chimney is a smoke stopper (typical dimension: 42cmx16cmx6cm) which controls the flow rate of smoke. As shown in the figure below, there are generally two types of kang: Grounded kang, which is the traditional form that soleplate is grounded. The other one is the elevated kang in which soleplate is suspended in order to promote energy efficiency and controllability of the system. The common dimension for faceplate is 100cmx60cmx5cm, and it requires two or three plates to constitute the bed plate. For elevated kang, soleplate is supported by several columns that 20~30 cm in height. |
Typical Uses: Despite Numerous modifications have been made during 2500 year history of kang, the fundamental structure did not changed substantially. Kang was the most commonly used system prior industrial revolution. And to some extent, it is still an effective solution today in term of providing heat during 6~9 month winter season in North Eastern Asia. It is the best approach in most rural region with unstable electrical supply. In urbanized region, kang is a great alternative due to its high cost effectiveness. Sustainability is another reason which encourages people to use kang since the system use biomaterials as the primary fuel instead of coal or other fossil fuels.
The chart below shows the comparative results of grounded and elevated kang in terms of temperature controallabilty. According to a research in 2000, the typical outdoor temperature is -20°C (-4°F) in winter, and average indoor temperature is 24.8°C(76.6°F). |
System Limitations: There are several constrains fro the system. The major challenge is that kang is only available for extensive residential building. For commercial building or modern intensive residential building such as condominium, kang is not the best choice.
Another limitation is that kang is not designed for providing constant heating supply. Despite the stove can be operated 24 hours per day, it losses the primary advantage, which is the cost-effectiveness. The third issue the safety. Surface temperature controllability is the most important design criteria for a kang. Generally, elevated kang is more controllable in terms of temperature than traditional form. |
Typical Materials: Common materials are shown in the table on the right. Adobe or adobe bricks is the most oldest construction material of kang, which is used for pillar and plates. clay mixed sand brick is another old and cost effective choice. Concrete as well as reinforced concrete slab have better performance in term of smoke insulation and thermal storage capability, while there are most costly than traditional materials.
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Construction Issues: The construction of kang is relatively easy since the system is very small in scale than other HVAC system. One design challenge is the spatial arrangement of flues and chimney. The figure on the left shows four common layouts of grid flues in elevated kang. The arrangement of flues is flexible, which depends on the location of chimney and stove in the kitchen.
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Reference:
"Chinese kang as a domestic heating system in rural northern China—A review",by Zhi Zhuang, Yuguo Li, Bin Chen, Jiye Guo, Energy and Building, Vol.41 Issue.1, Jan. 2009
"Chinese kang as a domestic heating system in rural northern China—A review",by Zhi Zhuang, Yuguo Li, Bin Chen, Jiye Guo, Energy and Building, Vol.41 Issue.1, Jan. 2009