| Because the building sector is responsible for 30%-40%of the primary energy used by the society as a whole,developing energy-efficient buildings is an urgent requirement for a sustainable and environmentally friendly society.More than one-third of the operation energy of a building is consumed to neutralize the effect of the oscillating outdoor environment on the indoor environment and maintain a comfortable indoor environment.This part of energy consumption can be reduced by improving the performance of building envelopes because it is the building envelope that separates the indoor and outdoor environments.As a result,several types of advanced materials have been applied to the building envelope.For example,phase change materials(PCMs)are perceived as an effective way to increase the heat capacity of walls,and thermochromic materials receive continuous attention due to their potential application as a regulator for the solar radiation through the windows.A lot of efforts have been made to improve the properties of those materials,such as enhancing the conductivity of PCMs,decreasing the transition temperature of thermochromic materials.However,few study focuses on how the properties affect the performance,and whether the improvement is efficient.In this dissertation,performances of some advanced materials or components were demonstrated,and the effects of material properties on energy performance were discussed,aiming to provide suggestions on how to construct a high-performance building envelope.Performances of heat storage materials,e.g.,PCMs,and thermal insulation materials applied to the opaque part of building envelopes were demonstrated in an outdoor testing platform,which contains two 2.9 m ×1.8 m ×1.8 m testing rooms,and through building energy analysis programs.The effects of installation locations,seasons,and climate on performance were also discussed.It was found that the fluctuation of the indoor air temperature could be reduced by applying PCMs to the envelope,leading to an increase in the indoor thermal comfort.Such increase was more obvious in lightweight rooms than in heavy buildings.The thermal insulation materials were found effective in winter but ineffective in summer.Based on these case studies,the effects of heat storage capacity and thermal insulation property on application performance were analyzed,aiming to reveal the properties of the ideal materials for the walls.Performance improvement for the transparent part of envelopes,i.e.,windows,was also discussed.The application demonstrations of vanadium dioxide(VO2)thermochromic windows showed that the performance of current VO2 windows was acceptable only in summer due to the limited ability to adjust solar transmittance.The relation between the adjustment ability of thermochromic windows and their energy performance was then analyzed.A type of advanced window which can simultaneously regulate both the long-wave thermal radiation and solar radiation was introduced,showing a better performance than the conventional thermochromic window.The influence of double-glazed windows on energy consumption was also discussed.On the basis of discussions on these advanced materials or components,properties of ideal envelopes were elucidated in this dissertation.For example,for summer applications in passive buildings,the south wall should consist of materials with high thermal conductivity and large heat capacity;the roof should consist of materials with low thermal conductivity.The properties of the ideal walls for an active building were location-dependent:materials with excellent insulation performance were required for external walls,and those with great heat capacity were preferred for internal walls.An ideal thermochromic window should transfer its state at a transition temperature around 20?,and the difference in solar transmittance between the two states should be larger than 30%.These conclusions provided a route along which a high-performance building envelope can be constructed. |
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