Heat transfer in composite walls: a practical two-dimensional thermal circuit method

Because of the potential significance of two-dimensional effects associated with heat transfer in series/parallel composite walls, it is important that evaluation/design decisions not be based solely on either of the one-dimensional methods featured in most heat transfer textbooks. To complement the more pragmatic ASHRAE approach that features the use of both upper-bound and lower-bound approximations and a qualitative criterion for selecting between R_U and R_L, this paper presents a practical two-dimensional thermal circuit method that provides a means of achieving higher-order approximate solutions and a basis for quantifying the ASHRAE criterion for identifying situations for which either the upper- or lower-bound method can be used with reasonable confidence.