J. Cent. South Univ. (2016) 23: 479-483

DOI: 10.1007/s11771-016-3093-1

Improvement of thermal performance of envelopes for traditional wooden vernacular dwellings of Tujia Minority in Western Hunan, China

LI Zhe(李哲)^{1, 2}, SHI Lei(石磊)¹, YU Zhi-wu(余志武)²

1. School of Architecture and Art, Central South University, Changsha 410083, China;

2. Mobile Post-doctoral Stations of Civil Engineering at Central South University, Changsha 410083, China

 Central South University Press and Springer-Verlag Berlin Heidelberg 2016

Abstract: Thermal performance of envelopes and indoor thermal environment were technologically improved for traditional wooden vernacular dwellings of Tujia Minority in Western Hunan, China, on the premise of protecting their conventional styles. Thermal insulation boards and wooden boards were added to the interior side of external walls of vernacular dwellings to form two layers of air cavities, so as to gain excellent thermal performance. The indoor temperature of such dwellings after reconstruction was apparently improved compared with the data before reconstruction both in winter and summer, which verified the feasibility and the effectiveness of the reconstruction technologies proposed.

Key words: traditional wooden vernacular dwellings; thermal performance; reconstruction

1 Introduction

To avoid adverse impacts of climate upon traditional vernacular dwellings, passive design techniques are applied to obtain comfortable indoor environment. In Asia, OOKA [1] and LEE et al [2] respectively studied traditional Japanese and Korean vernacular dwellings, and summarized the corresponding sustainable design principles. Meanwhile, the reconstruction of traditional vernacular dwellings has been comprehensively researched in Japan [3–4]. In China, vernacular dwellings are mostly investigated by architects from the perspective of history, culture and design. In these studies, most conclusions are qualitative descriptions, which haven’t been confirmed by measured data and quantitative analysis [5–8]. Furthermore, vernacular dwellings have been tested and quantitatively analyzed in some studies [9–14], but the measurement and improvement for envelopes of traditional vernacular dwellings are often ignored, and relevant research is seldom reported as a research focus. For instance, ALEV et al [15] analyzed renovation alternatives to improve energy performance of historic rural houses in the Baltic Sea region, in which the envelopes were merely mentioned but not intensively studied. However, thermal performance of envelopes of urban houses and rural houses has been always a hot topic of research about energy-efficient buildings. For urban houses, dynamic characteristics of building envelope [16], and building envelope insulation [17–18], heat transfer of building envelope [19] and energy performance [20] are all hot topics in the area of building envelope. For rural houses, ZHOU [21] evaluated the appropriateness of energy- saving technologies for envelopes of rural houses in the Northeast China, SUN et al [22] investigated the current envelopes of rural houses in Shanghai, WANG et al [23] also investigated the building envelope of rural houses in Tianjin and proposed an energy-saving design scheme for the building envelope. Thermal performance of envelopes is crucial for rural houses, but these studies mainly focused on modern rural houses, and the importance of reconstructing envelopes of traditional vernacular houses for rural areas’ energy-efficient buildings has been somewhat neglected.

In this work, taking traditional wooden vernacular dwellings of Tujia Minority in Western Hunan, China, as an example, the technological improvement for heat transfer performance of envelopes and indoor thermal environment of traditional vernacular dwellings was studied on the premise of protecting their traditional styles.

2 Test plan

The traditional wooden vernacular dwellings of Tujia Minority in Western Hunan, China, are built with local materials available. Through 1000 years of development and evolution, such architectural styles have become highly adaptable to local climatic environment showing strong ecological consciousness. To correctly test the effects of technological improvement on indoor thermal environment, indoor temperature of a traditional vernacular dwelling was successively measured before and after improvement.

2.1 Test parameters and instruments

Test parameters and instruments are given in Table 1, while measurement points are presented in Fig. 1. A portable weather station was set up on a 10 m high roof without any barriers around. Placed at a height 2 m away from the floor, the automatic temperature and humidity recorder was wrapped with aluminium foil to prevent the impacts of light radiation upon the measured temperature. Before the test, all instruments were re-calibrated, and some of field instruments were readjusted to zero before each test to ensure accurate test data.

2.2 Tested building

Longxi Village in Qianling Town, Baojing County of Western Hunan, belonging to a typical climate zone with cold winter and hot summer, is located in a small basin encompassed by mountains, and the terrain is given priority with hills and downland. In this work, the most representative and complete preserved building in the village, WANG Fa-ming’s house (Table 2), was tested.

Figure 1 shows the floor plan, where the automatic temperature and humidity recorders were placed in Room A and C. The test was divided into two parts. In the first part, the indoor temperature of the traditional vernacular dwelling in summer before improvement was measured from August 1 to August 7, 2012, and corresponding temperature in winter was measured from January 17 to January 23, 2013; In the second part, the indoor temperature of the building after envelope reconstruction in summer was measured from August 1 to August 7, 2013 and corresponding temperature in winter was measured from January 17 to January 23, 2014.

Table 1 Test parameters and instrument

Fig. 1 Survey plan of Tujia Minority’s vernacular dwellings– Longxi Village, Qianling Town, Baojing County, Western Hunan, China

Table 2 Characteristics of WANG Fa-ming’s house in Longxi Village

2.3 Technological reconstruction scheme for envelopes and construction

The walls of WANG Fa-ming’s house were made from about 3 cm thick fir boards that were jointed with tongue and groove. Since there existed certain gaps, the walls were not completely sealed, resulting in the poor heat preservation and heat insulation effects.

To improve thermal performance of envelopes of traditional vernacular dwellings and maintain their traditional styles indoors and outdoors, a convenient and practical construction measure was developed by the research group. Namely, a layer of board was added inside original external walls with single-layer board and heat preservation board at certain thickness was sandwiched, fixed with wooden grids and bamboo nails (see Fig. 2 and Fig. 3 for construction details). Meanwhile, the people living in ethnic minority areas in Western Hunan cannot afford excessively high costs for reconstructing vernacular dwellings. Therefore, heat preservation boards were selected from rigid polyurethane foam boards, rock mineral wool boards, polystyrene foam boards and polyethylene foam boards through simulative tests. The heat insulation and preservation performance of walls made from heat preservation boards with a variety of thickness was simulated with ACS, so as to analyze the thermal shielding efficiency (Figs. 4 and 5). Considering the prices of various heat insulation boards, 3 cm thick polystyrene foam boards showed the highest performance-to-price ratio. Thus, we concluded that the heat insulation and preservation boards in reconstructed walls should be placed from outside to inside in the following order: 3 cm thick fir board, 1 cm thick air layer, 3 cm thick polystyrene foam board, 1 cm thick air layer and 2 cm thick fir board.

Fig. 2 Section of reconstructed walls (Unit: mm)

Fig. 3 Floor plan of reconstructed walls (Unit: mm)

Fig. 4 Indoor temperature of WANG Fa-ming’s house in summer before reconstruction (1st–7th August, 2012)

Fig. 5 Indoor temperature of WANG Fa-ming’s house in winter before reconstruction (17th–23rd January, 2013)

3 Test results and analysis

The indoor temperature of Room A and C of WANG Fa-ming’s house was between 29 °C and 34 °C when outdoor temperature was as high as 37 °C in summer before reconstruction (Fig. 4). The indoor and outdoor temperature difference was less than 3 °C, the delay time of maximum temperature between outdoor and indoor was about 3 h, while the delay was almost not observed in the lowest value, suggesting that the heat insulation performance of the wooden envelopes of vernacular dwellings was moderate and the heat conduction showed a certain delay effect. From the perspective of human comfort, the most comfortable indoor temperature would range from 23 °C to 28 °C in summer. The existing room temperature cannot meet the needs of residents living in comfort. In winter, the indoor temperature of Room A and C was between 0 °C and 6 °C as the outdoor temperature was as low as –1 °C (Fig. 5). At the same time, there existed small differences in outdoor temperature curve and indoor temperature curve, indicating that the heat preservation performance of the wooden envelopes of vernacular dwellings was moderate. Since the most comfortable indoor temperature for human would range from 18 °C to 25 °C in winter, the traditional wooden envelopes cannot meet the demand of residents comfortable living either. Therefore, the traditional vernacular dwellings had relatively poor indoor air quality in winter and summer regardless of indoor and outdoor temperature difference or human comfort, with great defects in thermal performance of envelopes. Relative to the winter, the envelopes showed some insulation effect in summer, indicating that the influence of hot summer on residents dwelling was greater than that of the thermal insulation in winter.

The outdoor air temperature was basically identical to that of the last year (Fig. 6 and Fig. 7). In summer, the maximum outdoor temperature was even up to 37 °C, whereas the indoor temperature of Room A and C was between 23 °C and 29 °C, a range of indoor temperature most comfortable for human in summer (Fig. 6). In winter, the lowest outdoor temperature was –3 °C, while the indoor temperature of Room A and C was up to 14 °C–21 °C, a range of indoor temperature generally comfortable for human in winter (Fig. 7). Hence, indoor thermal environment of improved vernacular dwellings was relatively favorable no matter based on indoor and outdoor temperature differences or human comfort.

Fig. 6 Indoor temperature of WANG Fa-ming’s house in summer after reconstruction (1st–7th August, 2013)

Fig. 7 Indoor temperature of WANG Fa-ming’s house in winter after reconstruction (17th–23rd January, 2014)

As the test proved, indoor temperature of Tujia Minority’s traditional vernacular dwellings in Western Hunan, China, was declined by 5 °C on average in summer once their anti-radiation and thermal performances were improved. In addition, their indoor temperature was increased by 10 °C on average in winter after reconstruction. The dual requirements of heat insulation in summer and heat preservation in winter were satisfied to some degree and indoor thermal comfort was apparently improved. The thermal performance of envelopes of vernacular dwellings was significantly improved, directly affecting indoor thermal environment. These results implied that the technology proposed in this work was feasible and effective for reconstructing envelopes.

4 Conclusions

Technological improvement of thermal performance of envelopes for traditional wooden vernacular dwellings of Tujia Minority in Western Hunan, China, on the premise of protecting their traditional styles was examined, so as to improve the indoor thermal comfort of these buildings. Thermal resistance of walls were greatly increased while preserving original styles of vernacular buildings by adding a layer of board inside original exterior walls, sandwiching 3 cm thick polystyrene foam boards and fixing them with wooden grids together with bamboo nails. By reconstructing WANG Fa-ming’s house in Longxi Village, Qianling Town of Baojing County and comparing measured indoor temperature before and after reconstruction, the thermal performance of envelopes was strongly improved, thereby confirming feasibility and effectiveness of the technology put forward for improving envelopes.

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(Edited by YANG Bing)

Foundation item: Project(51308548) supported by the National Natural Science Foundation of China; Project(2014M552155) supported by China Postdoctoral Science Foundation; Project(2013RS4054) supported by the Science and Technology Fund of Hunan Province, China

Received date: 2014-12-15; Accepted date: 2015-04-20

Corresponding author: LI Zhe, PhD; Tel: +86–13507318013; E-mail: 382888561@qq.com