Innovative airspace reflective tool for different building applications, part I: tool development

Abstract

The current methods such as ISO-6946 provide thermal resistances for horizontal and vertical enclosed airspaces. Additionally, hot-box results from the U.S. National Bureau of Standards (now NIST) were used to provide the thermal resistances in the ASHRAE Handbook of Fundamentals (HOF) for horizontal, vertical and 45-degree angle airspaces. The thermal resistances in the HOF are available for three temperature differences and four values for mean temperatures. Thus, thermal resistances in the HOF include a limited number of climatic conditions and construction techniques that exist around the globe. The effect of the aspect ratio on airspace thermal resistances is not included in ISO-6946 or the ASHRAE HOF. Many studies including this one have shown that the aspect ratio of enclosed airspace has a significant impact on thermal resistance. This has motivated the development of a tool for accurately determining thermal resistances of enclosed airspaces for a wide variety of conditions. In this paper, a validated numerical model has been used to obtain the necessary thermal resistances values (about one million) of various enclosed airspaces, subjected to different operating conditions. Thereafter, the calculated thermal resistances were used to develop a tool, called “Airspace Reflective Tool, ART”. The capabilities of this tool for evaluation, optimization and design are explored in this paper.