近零能耗导向的轻质装配式建筑热桥优化设计——以K型活动板房为例#br#

在“双碳”发展愿景下，重“建构”而轻“能量”已然成为轻质装配式建筑的制约瓶颈，并以伴随装配建造而来的热桥问题最为典型。研究选取K型活动板房为例，通过实测与调研提取其4类关键热桥节点：平壁墙柱、转角墙柱、屋面檐口、地面基础节点。融合近零能耗体系要求，建立轻质装配式建筑的围护热桥评价体系，提出其核心指标的新计算方法。依托有限元传热模拟，对关键热桥节点开展以性能为导向的正向构造优化，并同步对其建构效率影响进行逆向评估检验，据此建立兼顾“建构-能量”平衡的轻质装配式建筑热桥优化设计策略及其技术体系。

Optimisation Design of Thermal Bridge for Lightweight Prefabricated Building Oriented to Nearly Zero-energy Consumption: A Case Study of the K-type Prefab House

Contemporary lightweight prefabricated buildings (LPBs) generally emphasise 'construction efficiency' rather than 'energy performance'. Under the current development vision of 'double carbon', how to significantly improve energy efficiency and environmental performance of buildings while maintaining high construction efficiency is an opportunity for the development of LPBs and the development bottleneck. For example, many connection nodes in envelope assemblies often are the thermal bridges that destroy heat in the insulation structure of the envelope, forming ‘fabrication-thermal resistance leakage’. For this reason, the K-type prefab house used extensively in China was chosen as a typical research object. Further, the index of nearly zero-energy buildings (nZEBs) was introduced as the evaluation standard to explore optimisation design strategies and technical routes for the thermal bridge of LPBs.　　Based on the analysis of the prefab house construction system, thermomechanical measurements in cold regions in winter and comprehensive literature reviews, the limitations of currently associated studies were pointed out. Moreover, four types of typical thermal bridge nodes of the K-type prefab house were extracted, including the flat wall-column joint, corner wall-column, roof cornice joint, and ground foundation joint. Concerning the research method, a comprehensive thermal bridge evaluation system for the LPBs was established based on the requirements of nZEBs, where the average heat transfer coefficient and the linear heat transfer coefficient were used as the core indexes, and the lowest internal surface temperature of the envelope served as an auxiliary index. Combined with the finite element heat transfer simulation software of THERM, a fast calculation method that could adapt to complex constructions and is easy to be mastered was further proposed. This method could provide transverse comparisons and systematic evaluations of the optimisation designs of structures of different typical thermal bridge joints.　　For the flat wall-column joint, a new type of external insulating envelope structure was introduced to could achieve thermal bridge-free by separating the structure and the insulation without influencing the basic construction principles and efficiency of the K-type prefab house. For the corner wall-column and roof cornice joint, it was necessary to introduce the ‘appropriate customisation’ strategies beyond the continuous external insulation, such as panel end bevelling or partial skin removal. For the ground foundation joint, external insulation should continuously cover the ground floor and the base walls to meet the requirement of nZEBs. Furthermore, the simulation proved that when the thickness of the external sandwich panel reached 160 mm, both primary and secondary evaluation indexes could meet the requirements of the nZEBs system.　　After the thermal performance-oriented ‘forward’ optimisation for the key thermal bridge joints of the K-type prefab houses, it was essential to conduct a ‘reversed’ test to apply the optimised joints to the real construction process. This could validate the true effects of these key thermal bridge joints on the construction efficiency of the LPBs. From the four perspectives of systematic construction logic, component prefabrication, space adaptation efficiency and economic cost of materials, some construction indexes such as the absolute mass of a single plate, unit area mass, labour cost per plate and increased material cost were introduced to examine the feasibility and effectiveness of the optimisation construction of different thermal bridge joints.　　In general, three principles of the thermal bridge-free optimisation design for the LPBs were summarised: the 'insulation-structure'integration principle, 'forward-reverse' coordination principle, and 'customisation-standardisation' balance principle. This study is expected to improve the application potentials and market prospects of LPBs through the 'construction-energy' integral design with a low-carbon, high-performance system and facilitate the sustainable transformation of the architectural industry in China.