A computational and experimental study of conjugate heat transfer through composite thermal envelopes in post-frame buildings

• Published in: Computers and electronics in agriculture 2018-06, Vol.149, p.139-149
• Main Authors: Holstein, Andrew J., Bohnhoff, David R., Choi, Christopher Y.
• Format: Article
• Language: English
• Subjects: Agricultural buildings; Computational fluid dynamics; Energy efficiency; Post-frame buildings; Rotatable guarded hot box
• ISSN: 0168-1699; 1872-7107
• DOI: 10.1016/j.compag.2017.09.003

•A two-dimensional CFD model was developed for post-frame thermal envelopes.•The model was validated experimentally by a Rotatable Guarded Hot Box.•Neglecting radiation and natural convection leads to significant errors in R-value.•A more efficient wall design was proposed and evaluated. The thermal performance of eight post-frame thermal envelopes was studied and optimized using a computational fluid dynamics model validated experimentally with a rotatable guarded hot box. In addition to providing thermal performance values for typical wall designs, this study proposed a new wall design that greatly increased thermal performance without sacrificing material efficiency. Study variables included structural geometry, level of insulation, and the presence and placement of radiant barriers. To reduce computational demand, modeling was primarily conducted using an area-weighted average of two-dimensional slices to represent three-dimensional assemblies. After modeling a portion of the assembly in three dimensions and comparing it with its two-dimensional counterpart, this simplification was found to result in less than a 6.7% error. Significant error (up to 57%); however, was determined to be integral to the simplifying assumptions commonly used by building designers, especially in envelopes common to the agricultural industry. This error was estimated to underpredict energy costs for a 2200m2 cold-storage warehouse in Wisconsin by approximately $1700ayear.