| Historical earthen sites,the historical remains with soil as the main construction material,are the important cultural relic treasure in China.Due to their large volume and unmovable features,it is an important measure to build in-situ museums to protect the sites.Inorganic cultural relics like stones and potteries are insensitive to natural light,so skylights are used for daylighting for most of the site museums.However,when the cultural relics are restored in the soil-air coupled environment,the heat from sunlight would promote water and salt migration in the environment.A variety of cultural relic deterioration would be brought in as well.Therefore,the deterioration of cultural relics restored in the soil-air coupled environment under the influence of daylighting through skylights should be further studied.This thesis concentrated on the influence of both indoor light environment and thermal environment caused by direct daylight through skylights.This thesis took the Chengdu Jiangnanguan Street Site Museum of Tang and Song Dynasty,hereafter abbreviated as the CJS Site,as a typical skylight site exhibition hall for a case study.Daylight and thermal environment problems caused by direct sunlight through the skylights of this museum were examined in detail,through field survey,parameter monitoring and numerical simulation.After that,an awning design was proposed to improve the situation.Field survey results showed that daylighting by skylights caused water leakage and the growth of mosses in the CJS Site.Too much natural light straightly shot on the cultural relics.Both cracking and salting out problems were found on the surface of the soil because of the increased soil temperature.All these problems could threaten the conservation of the cultural relics.Besides,glare problems outside the site museum caused by the glass reflection prevented tourists from viewing the relics.Parameter monitoring results in winter and summer showed that indoor air temperature,relative humidity,and surface temperature of soil in the CJS Site were more sensitive to outside weather changes because of the skylights.For this reason,the indoor thermal environment was improved under the skylights in winter,while the daylight and thermal environment was not suitable for relics conservation and display in summer.Daylight simulation results from Ecotect and Radiance indicated that the skylights brought in too much direct sunlight intensity,daylight exposure accumulation and radiation accumulation in the daylighted areas of the CJS Site.Moreover,the acute luminance contrast between the daylighted areas and shaded areas could result in serious glare,which might be harmful to the museum staff.The results of computational fluid dynamics(CFD)simulation in sunny conditions showed that the temperature distribution was affected both by direct sunlight intensity and the distribution of air conditions in the CJS Site.The indoor temperature requirements of relics conservation could be met in areas with shading or sufficient air supply,but the temperature would be higher in daylighting areas.In order to verify the effect of the proposed awning design,numerical simulation of indoor daylight and thermal environment under the shading circumstance was carried out.Results showed that the awning brought in more suitable environment for conservation and display of cultural relics in the CJS Site by significantly reducing direct natural light and improving heat distribution inside the museum.Taken the shading effect and construction cost into consideration,the recommended awnings could be those that had an extended length of 2 m when the height was 4 m or 6 m,or an extended length of 2 m or 3 m when the height was 8m.This thesis provided reasonable suggestions for cultural relics conservation and display in soilair coupled environment where the daylighting relies on skylights.It would also help to push forward the establishment of relevant natural light restrictions and standards for historical earthen sites. |
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