随着ASI/ASHRAE/IESNA标准90.1、除低层住宅建筑外的建筑能源标准、andANSI/ASHRAE标准90.2、低层住宅建筑节能设计的每次建筑规范更新和修订，建筑围护结构热性能标准变得更加严格，以减少建筑能耗。众所周知，在确定某些建筑围护结构组件的U系数时，必须考虑二维热传递（例如，带batt隔热层的钢柱框架墙）。然而，目前的能源法规计算方法缺乏关于整墙U系数和净墙U系数（Kosny和Desjarlais 1994）的指导和/或要求，包括内外角、门窗周围的附加框架，以及框架墙的顶部和底部轨道，包括两个- 以及组件之间的三维热传递效应（例如，悬臂混凝土板对墙体的影响U系数、钢架角度）安装时门窗产品的U系数，而非NFRC标准100，用于确定门窗产品U系数的程序，标准尺寸产品的值，用于门窗产品的并排比较，并且通常不能代表大多数项目中实际使用的方法。这种简化可能会导致高估建筑物的热性能。分析和论证现实节能的最终目标，而不是由过于简化的模型所预测的保护，设计者必须考虑整个墙的R值、组件的二维和三维（2D和3D）交互以及实际的玻璃装配U。 因素。本文通过实例讨论和展示了当前的U系数计算方法的不足之处，并提出了更详细的U系数计算方法，包括对建筑实践的认可，以考虑能源规范和ASHRAE标准的未来修订。以前，由于缺乏软件和计算能力，进行更详细的计算（包括2维和三维热分析）是不现实的。然而，如今，必要的软件和计算能力已经存在，因此要求进行更详细的计算是可行的。引文:2010年国际会议热性能

With each building code update and revision ofANSI/ASHRAE/IESNA Standard 90.1, Energy Standard for Buildings Except Low-Rise Residential Buildings, andANSI/ASHRAE Standard 90.2, Energy-Efficient Design of Low-Rise Residential Buildings, building enclosure thermal performance criteria are becoming more stringent to reduce building energy consumption. It is well understood that two-dimensional heat transfer must be considered in determining the U-factor of certain building enclosure assemblies (e.g., steel-stud-framed walls with batt insulation). However, the current approach to energy code calculations lacks guidance and/or requirements forWhole-wall U-factors versus clear-wall U-factors (Kosny and Desjarlais 1994), including inside and outside corners, additional framing around windows and doors, and top and bottom track for framed wallsIncluding two- and three-dimensional heat transfer effects between assemblies (e.g., the effect of a cantilevered concrete slab on the wall U-factor, steel shelf angles)U-factors of fenestration products as installed, rather than NFRC Standard 100, Procedure for Determining Fenestration Product U-Factor, values for standard-sized products, which is intended for side-by-side comparison of fenestration product, and are not typically representative of those actually used on most projectsSuch simplifications can result in overestimating building thermal performance. With the ultimate goal of analyzing and demonstrating realistic energy conservation, rather than conservation predicted by oversimplified models, it is imperative that designers consider whole-wall R-values, two- and three-dimensional (2D and 3D) interaction of assemblies, and actual glazing assembly U-factors. This paper discusses and presents how current methods for U-factor calculations are insufficient through the use of examples, and proposes more detailed methods for calculating U-factors that include recognition of construction practices to be considered future revisions of energy codes and ASHRAE standards. Previously, the lack of software and computing power made conducting more detailed calculations including 2- and 3D thermal analysis unrealistic. However, today the necessary software and computing power exists, making it feasible to require more detailed calculations.