Research On Indoor Thermal Environment Improvement And Energy-saving Of Tibetan Dwellings In Northwest Sichuan Based On Optimization Of External Building Envelope

The Tibetan area in Northwest Sichuan belongs to the severe cold and cold area in the building thermal design zoning.The climate in this area is complex,and the cold season is long,with an average annual temperature of less than 6℃ and an extreme minimum temperature of less than-20℃.As the second-largest Tibetan area in China,Northwest Sichuan has distinct regional cultural features,including traditional Tibetan dwellings such as stone bunker houses and rammed earth dwellings.The unique external envelope structure of Tibetan dwellings,such as thick stone walls and single-layer wooden windows,reflects the architectural experience accumulated by local residents in resisting the harsh natural environment of the outside world.However,the thermal performance of the external envelope is insufficient,resulting in a poor indoor thermal environment.In the background of traditional village protection,rural revitalization and double carbon goals,it is essential to improve the thermal performance of the external envelope of Tibetan dwellings so that to improve the indoor thermal environment and reduce building energy consumption.In this paper,the on-site questionnaire survey of a Tibetan case village in Northwest Sichuan and the field measurement of a Tibetan case dwelling are adopted to obtain the primary information of dwellings,indoor thermal sensation,indoor thermal comfort,indoor and outdoor air temperature and relative air humidity,thermal performance of the external envelope.Based on the energy consumption simulation by Energy Plus,the hourly thermal environment parameters and the annual cooling and heating load of the residential dwellings are numerically simulated and calculated.PMV-PPD and APMV indexes are used to evaluate the indoor thermal environment of Tibetan dwellings.On this basis,the optimization schemes of the external envelope are also simulated and analyzed.The effects of different optimization schemes on the increase of indoor temperature and the reduction of the total building load are discussed.Furthermore,the optimization schemes’ economic analysis is carried out.Finally,a comprehensive optimization scheme of the external envelope considering the indoor thermal environment,building cooling and heating load and transformation economy is put forward.Through the study of the current situation of the indoor thermal environment,it can be seen that the average PMV of the mainly rooms of the case dwellings in winter are between-4 and-3,and the PPD of each room tends to be 100%.The APMV of each room is between-1 and 0 in most time periods,and the heat and humidity environment assessment in winter is about grade III.The study on the optimization strategy of the external envelope can be concluded as follows:(1)The best external wall optimization strategy is to use 60 mm thick EPS insulation board for external wall insulation,with an annual average temperature increase of 0.54℃,an energy-saving rate of 25.58%,and an investment payback period of6.65 years.(2)The best external window optimization strategy is to use the 6+12A+6transparent hollow glass wooden window,with an annual average temperature increase of1.75℃,an energy-saving rate of 13.87%,and an investment payback period of 3.77 years.(3)The optimization effect of roof insulation is not obvious,so the optimization of roof insulation can be ignored when considering economy.(4)The optimization effect of the attached sunspace is pronounced,with an annual average temperature increases of 7.4℃,an energy-saving rate of 34%,and an investment payback period of 4.42 years.(5)Applying all the optimal strategies for the external envelope into a comprehensive optimization for the case dwelling,the annual average temperature of the room is increased by about 10℃,the hourly APMV of each room is between-1 and 1,the energy-saving rate is 67%,and the investment payback period is 6.52 years.This study can provide a reference for the improvement of indoor thermal environment and building energy conservation of Tibetan dwellings and similar rural buildings,and promote the protection and inheritance of traditional dwellings and the development of building energy conservation in China.