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1 Energy and Buildings 41 (2009) Contents lists available at ScienceDirect Energy and Buildings journal homepage: Chinese kang as a domestic heating system in rural northern China A review Zhi Zhuang a,b, *, Yuguo Li b, Bin Chen a, Jiye Guo c a Building Environment and New Energy Resource Laboratory, School of Civil and Hydraulic Engineering, Dalian University of Technology, Dalian, Liaoning , China b Department of Mechanical Engineering, The University of Hong Kong, Pokfulam Road, Hong Kong, China c Rural Energy Office, Liaoning Province, Shenyang, Liaoning , China ARTICLE INFO ABSTRACT Article history: Received 22 July 2008 Accepted 28 July 2008 Keywords: Chinese kang Elevated kang Thermal storage Northern China Home heating Rural indoor air quality The Chinese kang is an ancient integrated home system for cooking, sleeping, domestic heating and ventilation. It is still widely used today in nearly 85% of rural homes in northern China. In 2004, there were 67 million kangs used by 175 million people. Existing kang designs are mostly based on the intuition and accumulation of craftsman experience. There is a trend that Chinese kang is gradually replaced by bed and coal-burning radiators, domestic heating stoves, etc. using commercial energy. As rural building heating constitutes 25% of total building energy consumption in China, we consider that the transition and new technologies for rural home heating in northern China is crucial for managing future building energy consumption in China. This paper reviews the basic heat transfer and airflow principles of Chinese kang, as well as describing the traditional grounded kang and the relatively new elevated kang. The thermal performance of the kang is shown by data from literature and field surveys. The future of Chinese kang and research needs is also briefly discussed. There is also a need for scientific study in addition to experience accumulation, to form basis for engineering design. Crown Copyright ß 2008 Published by Elsevier B.V. All rights reserved. 1. Introduction As an ancient home technology, a typical Chinese kang consists of a stove, a kang body (similar to a bed) and a chimney. It allows at least four different home functions of cooking, bed, domestic heating and ventilation being integrated into one system. The kang was most probably first developed 2500 years ago during the Spring and Autumn period of the Zhou dynasty ( BC) [1]. Similar heating systems also existed in other cultures, such as the ondol (heated floor) in Korea [2] and hypocaust in ancient Rome [3,4]. Chinese kangs are still widely used today. A large scale field survey in 2006 showed that kangs were found in nearly 85% of rural homes in northern China where it is mostly cold and dry in winter with 6 9 months of heating season, and as well as in Shandong and Henan provinces [5]. According to the Ministry of Agriculture, in 2004 there were million kangs used by million rural families (or million people, assuming a family * Corresponding author at: Building Environment and New Energy Resource Laboratory, School of Civil and Hydraulic Engineering, Dalian University of Technology, Linggong Road 2, Gan Jingzi District, Dalian, Liaoning , China. Tel.: ; fax: address: zhgzhi@gmail.com (Z. Zhuang). size of four). Some homes may have more than one kang in different rooms to accommodate family members privacy. The kang has undergone different phases of development, from the earliest baked floor to the latest elevated kang [6]. The kang design also varies slightly between regions, for example the wei kang is often found in northwest China, which utilizes a smoldering process for heating without a chimney. Today, the traditional grounded kang and the new elevated kang are mostly used. There were million elevated kangs in 2004, accounting for nearly 30% of the total number of kangs. With the improving living conditions and continuing urbanization of rural China, there is an increasing urgency in improving rural building energy efficiency. The annual commercial energy consumption in rural China increases from 398 Mtce (million tons of coal equivalent) in 1995, to 446 Mtce in 2000 and 563 Mtce in 2005 [7], while the annual rural income per capita increases from 1578 RMB in 1995 to 2253 RMB in 2000 and 3255 RMB in 2005 [8]. In 2005, accounting for 39% of the total national energy consumed, the total rural energy consumption of China was 870 Mtce, of which 34% was non-commercial energy, i.e. biomass materials such as straw and stalk, and firewood, mostly used for cooking and domestic heating [7]. Rural building heating constitutes 25% of total building energy consumption in China [9]. Hence, transition and new technologies for rural home heating in northern China has been considered the /$ see front matter. Crown Copyright ß 2008 Published by Elsevier B.V. All rights reserved. doi: /j.enbuild

2 112 Z. Zhuang et al. / Energy and Buildings 41 (2009) top priority for managing future building energy consumption in China. Chinese kang has rarely been mentioned in open scientific literature. Chinese kang techniques have been largely based on accumulation of experience by craftsman. In this paper, we review the technical aspects of two typical kangs, the grounded and elevated. The thermal performance of a typical kang heating system was discussed based on the data from literature and our own field surveys. We also discuss the future of Chinese kang as well as related research needs. 2. Kang heat transfer and airflow Chinese kang utilizes the residual heat of smoke from an adjacent cooking stove which burns biomaterials or coal, and uses the kang plate to release both radiative and convective heat to the bedroom. It can be a potentially effective heating system if properly designed. The most recent elevated kang system is illustrated in Fig. 1. There are two important heat transfer and airflow processes. The first is the circulating smoke flow driven by buoyancy force and wind. Hot smoke generated in the stove first enters the kang flue and heats up the kang body which acts as a heat exchanger, and raises its surface. The smoke then leaves the kang, being exhausted through the chimney. The buoyancy force is produced by the difference between the hot smoke and ambient air. The wind pressure depends on wind speed and direction. The smoke flow is enhanced with the assisting wind. On the contrary the flow is weakened under opposing wind, with the possibility of smoke backflow resulting in poor indoor air quality if the kang is not well designed. The smoke flow is also affected by the system resistance. The second is the thermal storage of kang plates. The kang plates (often made of high thermal mass material such as concrete and stone) heated by the flow-through hot smoke store heat during cooking time, maintaining a heating period of several hours or more, and creating a local warm climate under the blanket/quilt. A kang mainly releases its heat to room air by convection, but also heats up the room surfaces, as well as people in the room by thermal radiation. 3. Grounded and elevated kangs 3.1. The grounded kang basics The commonly used kangs today include the traditional grounded kang and new elevated kang. In the first, the kang body is grounded on the floor in a bedroom, having adobe or brick laid to Fig. 1. (A) An illustration of the elevated kang system including the chimney, the kang body and the stove. (B) Photos of a complete elevated kang system, the chimney (left), the kang body (middle), and the stove (right).

3 Z. Zhuang et al. / Energy and Buildings 41 (2009) form the base of the kang. Several poles with regular intervals are stood on the base, and used to raise the upper plate laid on them. This creates void space or channels allowing the flow of smoke from the stove to heat the kang plates. A typical family kang is about m wide (e.g. the typical height of an adult), m high, and 3 4 m long (i.e. the full bedroom length). Fig. 2A illustrates a typical grounded kang. The kang body consists of a solid earth platform, upon which is an adobe flue, with an upward slope of 3% to draw air from the stove to the chimney. The flue consists of several channels, each of cm high and cm wide. Fig. 2B shows photos of some grounded kangs. The kang body is mostly used for leisure activities at daytime and sleeping at night. Thus the upper surface of the faceplate should have a moderate level and a uniform distribution at all times for the purpose of thermal comfort. According to experience of craftsmen, the surface should be maintained in the range of C [10], but there has not yet been a systematic study on the comfortable surface for kangs. The surface of the faceplate is greatly affected by the kang flue. The flue layout determines the residence time of smoke (or flow resistance) and heat transfer between smoke and kang plates. In general, the greater flow resistance (or the more residence time) a flue has, the better heat utilization a kang has, but at the same time, a large flow resistance does not benefit kang ventilation and may lead to smoke backflow. The flue has two basic layouts in plan, i.e. the linear and grid. A kang can be categorized by its flue layout. As for the grounded kang, some examples are shown in Fig. 3 [11,12]. Grid-flue kang: The grid-flue kang uses several small stones as pillars to bear the faceplate. The irregular flue helps to increases the flow resistance and smoke turbulence. The distribution of the faceplate is relatively uniform. The grid-flue kang is now only used by Chinese Koreans. Fig. 3A1 and A2 illustrates two types of gird-flue kangs. Perpendicular flue kang: In a perpendicular flue kang, the brick or adobe pillars are perpendicular to the smoke inflow direction. There are two types, one with a smoke divider (Fig. 3B1), and one with a smoke-leading flue (Fig. 3B2). The narrow voids between two pillars mostly result in a large flow resistance in the first type. The faceplate at the smoke inlet of kang body (kang head) may be overheated, while at the smoke outlet (kang tail) can be relatively cold. The smoke backflow often occurs in this kang. By adding a leading flue of about half the kang s length in the second type, the inlet smoke is led directly into the middle of the flue. This kang improves the uniformity of surface, but still has a large flow resistance. Parallel flue kang: In this kang, the brick or adobe pillars are parallel to the smoke inflow direction. Again, two types can be found, shown in Fig. 3C. In the first type, the pillars are placed in rows allowing inlet smoke to flow through the flue with a short Fig. 2. (A) Illustration of a grounded kang heating system in northern China with a plan view (top-left), and the cross-sectional view (Section A-A) (bottom) and the crosssectional view (Section B-B) (top-right), adapted from Ref. [11]. The symbol i indicates the slope gradient. The relative location of the kang, stove and chimney can also be seen in the top-left figure. (B) Two photos of the grounded kangs; one occupies half of the room and the other a corner of the room.

4 114 Z. Zhuang et al. / Energy and Buildings 41 (2009) Fig. 3. (A) Illustration of two types of grid-flue kangs: (A1) grid-flue kang with a single zone and (A2) grid-flue kang with multiple zones. (B) Two types of perpendicular flue kangs: with a smoke divider (B1) and with a smoke-leading flue (B2). (C) Two types of parallel flue kangs: without (C1) and with (C2) a leading flue. (D) A mixed-mode flue kang (D1) and a turn-around flue kang (D2). residence time. That is not desirable for the purpose of heat exchange and also causes uneven surface. In the second type, the kang has interrupted flues to diffuse inlet smoke and a leading flue also used to increase the smoke residence time. Mixed flue kang: The mixed flue kang integrates the merits of both the perpendicular and parallel flue types (Fig. 3D1), having the perpendicular flue placed in the front part and the parallel one in the back part. The inlet hot smoke can be quickly taken to the center and then fully diffused to heat up the kang plates. Turn-around flue kang: The stove and chimney in a turn-around flue kang has a partition (Fig. 3D2). The stove has two fire throats, one to the kang body and the other directly to the chimney. Both of them are controlled by a damper. In heating seasons, the damper at the kang inlet is open and the other is closed so that hot smoke can flow into the turn-around flue and then is exhausted through the chimney. In other seasons, the smoke from stove is directly exhausted through the chimney without passing through the kang body. As the flow path has a turn, both the flow resistance and the smoke residence time in the flue are increased Design issues of the grounded kang At least two drawbacks can be identified in practice with the grounded kang. Firstly, the conventional grounded kang has low-efficiency burning of biomass, and causes significant fuel waste. The heating efficiency of kang body is about 14 18%, and that of the stove is only 8 10% in a grounded kang [13]. As tested by the Chinese Rural Energy Office, a family with a grounded kang consumes 4 tons of firewood per year [14]. Secondly, the grounded kangs often lead to poor indoor air pollution. This is mainly caused by the combustion of biomass or coal in poorly ventilated stoves (see Fig. 4A), especially when the stove and the kang body are put together in the same room. Li [15] found that in Inner Mongolia 42.7% of stoves were in bedroom, and 67.2% of households never opened windows and doors during cooking, and indoor air pollution from burning is a serious issue for local people. Besides, a grounded kang with bad ventilation design often easily results in smoke backflow, smoke blocking up or flue

5 Z. Zhuang et al. / Energy and Buildings 41 (2009) Fig. 4. Two photos show (A) a grounded kang with a built-in combustion chamber to provide heating and (B) a housewife adding fuel to the stove in kitchen. Deposition of smoke particles on various surfaces is seen by the black pigmentation. choking (see Fig. 4B). In rural China, exposure to home air pollution due to the biomass combustion has been implicated with a series of diseases such as acute respiratory infections, chronic obstructive pulmonary disease, lung cancer and asthma [16 18]. Indoor air pollution caused an estimated 425,000 annual deaths in China in 2000 [19]. Thus, the traditional grounded kang needs to be improved for both better energy efficiency and home air quality. In 1990s, the Chinese Government promoted the elevated kang. In the new elevated kang system, both the stove and kang body are improved. The heating efficiency of a new stove is 25 35%, and the total kangstove heating efficiency is claimed to be over 70% as compared to 45% for a grounded kang [20]. A family with an elevated kang consumes 2.8 tons of firewood per year [14]. The increasing heating efficiency of stove leads to less fuel consumption and shorter firing time (also exposure time of occupiers) for cooking and heating. Wei et al. [21] compared the effects of four types of stove (i.e. open stove, traditional stove, old style stove and high impact stove) on rural indoor air pollution. The heating efficiencies of stoves were found to be negatively correlated with indoor CO concentration. But for a given biomass fuel type, increasing overall stove heat efficiency tends to increase emissions of products of incomplete combustion [22]. Thus ventilation design of the kang is very important to avoid the smoke backflow to pollute indoor air. Li et al. measured hourly concentrations of carbon dioxide (CO 2 ), carbon monoxide (CO) and PM 10 in six rural homes, two each in Liaoning, Heilongjiang and Gansu provinces [23]. The average CO concentration in a Gansu home was 25 ppm between midnight and 6 am. The 24-h average PM 10 concentration in a Heilongjiang home was 10 mg/m 3. The test results identified the improvement of the elevated kang and there was still a serious indoor air quality problem in rural homes with kangs, in particular in homes with the so-called Wei kang in Gansu province The elevated kang basics The elevated kang is the latest development of Chinese kangs. The major difference between a grounded kang (Fig. 5A) and an elevated kang (Fig. 5B) is that an elevated kang is suspended from the floor, while a grounded kang is directly built into the floor. In an elevated kang, nine slabs (each 100 cm 60 cm 5 cm) in one piece (soleplate) are built on several columns to about cm in height, on which short pillars stand at regular intervals, rising to a height of 20 cm; a flat surface (faceplate, 100 cm 60 cm 5 cm), as a bed plate, is then paved on the top of the pillars [24]. The faceplate is coated and leveled with plaster. Plate materials include slate, concrete, adobe or clay, with concrete being the most commonly used. The thermal characteristics of these materials are summarized in Table 1. In an elevated kang the complicated flue arrangements are removed and the grid flue and turn-around flue are commonly used, as shown in Fig. 6. There is a smoke stopper built close to the kang exit to the chimney, which can be used to restrain the flow rate of smoke. Generally, the dimensions of a smoke stopper are 420 mm in length, 160 mm in height and 60 mm in width [24]. The stove used in a kang is often different from a stand-alone stove, since kang stoves are used for both cooking and heating. The chamber volume of the stove for elevated kangs is about m 3, and the area of the fire grate is about m 2 [12] The major improvements of the new elevated kang Several improvements have been adopted in the elevated kangs to resolve the problems experienced with the grounded kang. Fig. 5. Illustration of the basic differences between two types of representative kangs (chimney is not shown): (A) the grounded kang and (B) the elevated kang Increased heat utilization of smoke by kang body The grounded kang only uses the upper faceplate for heat transfer, and heat is lost via heat conduction to the ground. The elevated kang raises the platform so that the heat transfer area increases about % between the kang surface and indoor air comparing to that of the grounded kang with the same dimension.

6 116 Z. Zhuang et al. / Energy and Buildings 41 (2009) Table 1 Thermal characteristics of commonly used materials for the elevated kang [12] Material Density (kg m 3 ) Specific heat (kj kg 1 8C 1 ) Coefficient of thermal storage a (kj m 2 8C 1 ) Thermal diffusivity b (10 3 m 2 h 1 ) Concrete Adobe Clay mixed sand Slab a Coefficient of thermal storage is defined as heat release rate or heat storage flux per square meter as surface decreased or increased by 1 8C under a periodical heat source. b Thermal diffusivity is defined as the ratio of thermal conductivity to the product of specific heat capacity and density. At the same time, the void space for smoke flow in the elevated kangs is much greater. Based on field measurements, the smoke velocity is reduced to 0.1 m/s inside the kang flue, which increases the residence time of the smoke [25] Improved uniformity of surface for faceplate The of the smoke gradually decreases along the flue, so that the surface at the front part of the faceplate is generally higher than that at the back in the grounded kang. Two measures are used to achieve a better uniformity in distribution of the kang faceplate in an elevated kang. One is to regulate the thickness of the leveling coat. The leveling coat is thicker (about 50 mm) close to the stove and thinner (about 30 mm) close to the chimney, so as to help even out the surface. A mixture of clay and straw is commonly used for the layer of coat with an oiled paper outside. Second, a smoke stopper is installed at the end of flue to hold up the smoke flow for increasing the residence time and enhances the flow turbulence, to allow better heat transfer Improved control and insulation level The elevated kang should be airtight to avoid smoke leakage and fully use the buoyancy-induced force for smoke circulation. Also, the bottom level of chimney is lower than that of the flue, so that cold air from outside is trapped within it and so as to prevent backflow to the kang. The smoke circulation is moderated by installing a smoke damper at the smoke exit of the kang. Both the damper and the stove gate can be closed to shut off the flow during non-cooking time. An insulation layer is added between the kang body and the external wall to reduce the heat loss to outside. 4. Thermal performance of Chinese kangs The thermal performance of Chinese kangs may be evaluated by the Chinese Standard GB , which specifies the testing method for the kang when used with firewood or straw stoves. According to this standard, the thermal performance evaluation includes two aspects: the thermal performance of stove and the kang body Thermal performance indexes for stove and kang body Thermal performance of a stove may be measured by the following indexes: the heating efficiency, the water rise per unit time for heating a certain amount of water, and the amount of water evaporation per unit time after boiling. The water rise rate measures the initial heat intensity of the stove, while the water evaporation rate measures the sustained heat intensity of the stove. The heating efficiency of a stove measures the utilization of fuel, which is the ratio of heat absorbed by boiling water in a wok to the total heat generated by the wood per unit, dry weight. For kang body, three aspects of thermal performance are of interest here: the kang surface distribution, the kang insulation level, and the total heating efficiency. For kang surface, the average rise is used to measure the average change during a test period (from6:00amto9:00pmin1day),andthenon-uniformityof surface is adopted to measure the difference between the maximum and minimum average of all sampling points. In addition, the extreme difference ratio of Fig. 6. Four types of elevated kang heating system [24] (unit: mm): (A) illustration of grid-flue elevated kang with two different positions for the chimney and (B) turn-around flue elevated kang with two different positions of the chimney.

7 Z. Zhuang et al. / Energy and Buildings 41 (2009) Table 2 Thermal performance of grounded kangs (adapted from Ref. [11]) Flue layout (material) Surface of faceplate, average (minimum maximum) Indoor air, average (minimum maximum) Smoke at kang inlet Smoke at kang outlet Heat efficiency (kang/total) (%) Heat release rate of faceplate (kj/hm 2 ) Grid-flue mixed with ( ) 15.4 ( ) / turn-around flue (brick) Grid-flue mixed with ( ) 16.3 ( ) / backward flue (adobe) Grid-flue (brick) ( ) 12.9 ( ) / surface s measures the ratio between the maximum and minimum surface differences of the kang plate and the average surface of the kang plate during the entire test period. The insulation level of a kang is measured indirectly by the relative drop rate between two firings. The total heating efficiency of a kang can be obtained by considering the heat loss such as the flue gas loss, the incomplete combustion loss and the heat transfer loss through conduction to the walls or ground Previous studies on thermal performance of kang Only a few field studies exist on the thermal performance of Chinese kangs. Early in 1959, Yang [11] measured three rural houses with traditional kangs in Harbin, the capital city of Heilongjiang province. Three types of traditional kangs were investigated, and the measured results are reproduced in Table 2. The average outdoor air was 20 8C during the measurement period, and the average indoor air was between 12.9 and C. This showed that the kang can help improve the indoor thermal environment during the winter. Possibly due to a poor insulation level of the building envelope, the indoor air fluctuated highly in different homes, ranging from 2 to4.6 8C. In 2000, Deguchi and Sanda [26] also investigated the thermal environments of some houses with grounded kangs in the Heilongjiang province. According to their data, the indoor air could reach up to C withan average ambient of 0.5 8C, and the Predicted Mean Vote (PMV) value was In 1991 Xu et al. [25] tested and compared both an elevated kang and a grounded kang. Some of the tested data is reproduced in Table 3. This study showed that the total heat efficiency of an elevated kang is much higher than that of a grounded kang. The study also concluded that the elevated kangs were more energy efficient as well, resulting in fuel savings and environmental benefits A recent field survey and investigation A field survey was conducted between 11 November and 30 December 2004 to investigate thermal performance of rural residences under a coupled Chinese kang and passive solar wall heating [27]. During this study, we also measured two other rural homes, located in Dalian, Liaoning province. This is an extremely cold part of China, and the outdoor air can be as low as 22 8C during the test period. One home was heated by a grounded kang and the other by a half-elevated kang. In the half-elevated kang, only half of its soleplate is suspended and the other half remains on the floor. The field survey included the building structure, the indoor and outdoor air s, and the surface s of the kang plates. All the s and relative humidity levels were automatically recorded every 10 min by a Thermo Recorder TR-72S (T&D Corporation, Sasaga Matsumoto, Japan). There was no other heating system in the two measured homes. Fig. 7 shows the frequency distribution of indoor air s and average of the kang plate surface in the two homes during the measuring period. In the home with a grounded kang, the indoor air was between 8 and 10 8C for more than 50% of the time, less than 8 8C for nearly 20% of the time, and sometimes exceeded 22 8C. In the home with a half-elevated kang, the indoor air ranged from 16 to 18 8C for 65% of the time, while remaining continually higher than 14 8C. Accordingly, the range of kang plate surface with elevated kang was between 20 and 35 8C for 95% of the time, while the surface s of the plate in grounded kang ranged from 10 to 35 8C. Hourly variations of the indoor air and relative humidity for the traditional and elevated kangs, as compared to outdoor air and relative humidity, are shown in Fig. 8. The indoor air with a half-elevated kang was C, even while the ambient reached below 10 8C. Table 3 Thermal performance comparison between a grounded kang and an elevated kang (adapted from Ref. [25]) Kang type Indexes of stove Indexes of kang body Other indexes Heat efficiency (%) Temperature rise rate (8C/min) Evaporation rate (kg/min) Surface of kang Average rise Temperature drop rate (8C/h) Outlet smoke Inlet smoke Flue gas loss (%) Incomplete combustion loss (%) Total heat efficiency (%) Elevated kangs Average Grounded kang

8 118 Z. Zhuang et al. / Energy and Buildings 41 (2009) Fig. 7. Frequency distribution of indoor air in two different homes in Dalian, China, measured during November and December Fig. 8. Hourly profiles of the indoor and outdoor air and relative humidity during the measurement period (from 13th December to 20th December 2004). It is also noticed that the relative humidity remained between 45 and 65%. The preliminary data shows the promising potential of the elevated kang to provide a comfortable indoor environment in cold climates during the winter. 5. The future of Chinese kang Presently many different alternative heating methods emerged in rural areas of northern China, such as coal-burning radiators, domestic heating stoves, coal-burning low-emission stoves, as well as domestic biomass gasifier and semi-gasifier stoves. Some of these techniques rely completely on commercial energy resources such as coal, electricity, and gas. It may be argued that heating technologies relying on fossil fuels, coal and electricity are not sustainable for such a large rural population. If these heating techniques using commercial energy resources replace those using non-commercial energy resource such as biomass in rural areas, that would double the building energy consumption in China [9]. As for domestic biomass gasifiers, it may also take a long time before they could be widely installed in all villages in China without mentioning their own technical problems such as tar. The future of kangs is related to a more general question on how can the traditional sustainable approach of using biomass by Chinese rural homes be developed to meet the energy needs of a modern living standard, while minimizing the increasing use of commercial energy. A rough estimate suggested that by using the elevated kang, the existing biomass resources would be sufficient to meet the energy use in rural northern China [7]. Furthermore, from a sociological point of view, Chinese kang plays an important role as the social centre of a family or extended families, and is the place where many domestic activities take place. This cultural aspect must not be overlooked when considering a change in energy supply technology [28]. Guo[29] explored the origin and history of the kang, and traced the development of forms and its application from the archaeological aspect. Li et al. [30] discussed its connotation, form type and developments and claimed to takes improvement and application into the kang in inheriting the excellent traditional foundation and further improving the living quality of rural people. Considering both the culture and technique aspects of Chinese kangs, it is very unlikely (and it should not be the case) that the kang will disappear soon from rural homes in northern China in the near future. Thus the improved kangs may serve as an alternative of sustainable and energy-efficient heating systems for rural homes in northern China considering the huge usage, sustainable energy utilization concept, long history and great culture accumulation. There is also a need for scientific study in addition to experience accumulation, to form basis for engineering design. The basic principles of kangs in terms of thermal storage, radiative heating and local heating design may also benefit and inspire other building heating system design for other regions. The research topics for the kang will include: (1) Analyse the smoke distribution in the kang body for optimizing the flue design using computational fluid dynamics and other thermo-fluid dynamics tools. (2) Study the optimum kang surface as well as preferred surface distribution for both thermal comfort and individual sleeping habits. (3) Modern materials techniques such as phase change materials may help in identifying the optimum thermal storage materials for the kang body. Integration with a modern bed may lead to development of a modern, movable, light bed-type structural kang system for rural homes. (4) Integration of the kang into building as a whole energy-efficient system should be studied. The improved kang can perform well together with a high level of building thermal performance such as good envelope insulation and airtightness. Acknowledgements This work was supported by a grant from the Research Grants Council of the Hong Kong Special Administrative Region, China (Project No. HKU 7154/05E) and NSFC Young Researcher Award (Project No ) on investigating energy consumption and indoor air quality in rural homes in Northern China. The work is a part of the International Energy Agency Annex 44 project on Integrating Environmentally Responsive Elements in Buildings. References [1] R. Men, Origin of Everything, China Economy Press, 2004 (in Chinese). [2] M.S. Yeo, I.H. Yang, K.W. Kim, Historical changes and recent energy saving potential of residential heating in Korea, Energy and Buildings 35 (7) (2003)

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