Research On Design Strategy Of Building Envelope For Nearly Zero Energy Oriented Lightweight Prefabricated Building

In recent years,the construction and operation of buildings account for about 16% and 20% of the total energy consumption in China.As a result,changing the construction way and reducing the operating energy become extremely vital for energy conservation in building sector,which also promotes the growth of prefabricated buildings and nearly Zero Energy Buildings.In China,however,both of them are just in their infancy,and the researches or practices integrating these two are still in the blank.Therefore,this paper selects the lightweight prefabricated building(LPB)and the nearly Zero Energy Building(n ZEB)as research objects,and adopts the building envelope as the carrier and platform to investigate the design strategy of LPBs oriented to nearly zero-energy goal.Firstly,this paper systematically investigates the development of LPB and n ZEB,and extracts the former’s three envelope tectonic features with the latter’s three envelope design targets.On this basis,the core contradictions between LPB and n ZEB are consequently established at a “tectonics-energy” level,leading to three pillars of envelope design strategies,including the thermal leakproof design,the thermal stability design,and the climate responsive design.For the thermal leakproof design,this paper starts with the thermal bridge and airtightness of the opaque building envelope.By using the THERM and Airpak software,multi-series of simulation of envelope constructions in thermal leakage area,including thermal bridge position and panel joints,are carried out.Based on quite a lot of quantitative comparisons,the thermal bridge-free design for three typical LPB systems and the airtight design for two major panel joint systems of LPB are further proposed,which latter provides a decentered tongue-and-groove panel joint prototype with better airtight performance.For the thermal stability design,this paper mainly focused on the main body and double-skin systems of the opaque envelope.Trough the Design Builder simulating and the field measuring on a dual-capsule experimental platform in the Cold Zone,different envelope constructions for the main body and the double-skin systems are investigated and compared.Consequently,on one hand,the “light and heavy materials composite” and “phase change material composite” strategies are proposed,which can balance the prefabricated demand with the thermal stability improvement.On the other hand,the optimal structures for double-skin systems in summer and winter are respectively obtained,even their “general prototype” is further proposed,which can effectively adapt the distinct seasonal thermal stability demands through a same double-layered structure.For the climate responsive design,this paper reveals the key point to adapt LPBs to the diverse climates is improving the changeability of transparent building envelope.On this basis,a series of experiments for the double transparent envelope is successfully conducted following an “extraction-application-iteration” prototype path.Base on the typological research,the Prototype 1.0 of double transparent envelope is proposed and applied on two detached experimental platforms in the Moderate Zone and the Cold Zone.Through multi-season field measurements,the Prototype 1.0’s suitable design and operating strategies are obtained and examined,laying the foundation of the optimized Prototype 2.0 with higher changeability.The Prototype 2.0 is applied on a dual-capsule experimental platform in the Cold Zone with multi-series field measurements carried out in both summer and winter,leading to its optimal design and operating strategies.Summing up the results of the former two prototypes,a Climate Responsive Prototype is finally proposed,which can effectively adapt LPBs to the diverse climates in China based on a standard transparent envelope system.Finally,from the view of both tectonics and energy,this paper reveals the deep correlation among the thermal leakproof design,the thermal stability design and the climate responsive design.On this basis,the envelope design strategies for nearly zero energy LPBs of residential type and office type are further integrated respectively.