• John Straube
    RDH Building Science
  • Joe Simonji
  • Chris Schumacher
    RDH Building Science

Thermal bridges, localized areas of building enclosures that allow higher heat flow, are recognized as an important source of heat loss/gain. Computer
models are now widely used to quantify the impact of thermal bridges. However, few full-scale measurements of heat flow through thermal bridges have been undertaken to confirm and validate computer models. To allow for the measurement of specimens with complex 2D and 3D heat flows (i.e. thermal bridges) a special large-scale guarded hot plate apparatus based on ASTM C177 was designed and constructed. This apparatus is capable of accepting specimens measuring 4 ft (1219mm) by 4 ft (1219mm) and up to 16 inches (406mm) thick. This paper describes the apparatus, its design, and the results of commissioning tests.
Computer modelling was used to estimate heat flow errors describing the characteristics and limitations of the apparatus. Once constructed, the apparatus was validated against a heat flow meter calibrated using a NIST-traceable calibration specimen. The capability of the guarded hot plate to measure layered specimens with thermal bridges was demonstrated through the measurement of three specimens resembling typical wall assemblies. Measurements from the apparatus were compared against results from computer models and good agreement was found.

Note: This article was published in Proceedings of Buildings XIV, 2019. Copyright 2019 ASHRAE. Reprinted by permission at rdh.com. This article may not be copied and/or distributed electronically or in paper form without permission of ASHRAE. For more information about the Buildings XIV Conference, visit this page.