scope:

INTRODUCTION

This work was done to support efforts by the American Society of Heating Refrigeration and Air-Conditioning Engineers (ASHRAE) Standing Standard Project Committee (SSPC 90.1) Envelope Subcommittee Metal Buildings Task Group (MBTG) to provide accurate thermal performance data for insulated metal building enclosure systems. ASHRAE's Envelope Subcommittee recognized that descriptions and characterizations of metal building insulation systems in ASHRAE Standard 90.1 (Energy Standard for Building Except Low-Rise Residential Buildings) did not reflect commonly installed assemblies and were based on largely unavailable or incomplete data. It appeared that most of the inaccuracies were from insulation mock-ups and assumptions on insulation cross-sectional profiles in computational modeling that were not representative of common or practically achievable field installations.

Traditional construction methods for metal building roofs and walls result in non-uniform insulation thicknesses and require non-insulating materials in the plane perpendicular to the dominant heat flow. Because the systems result in nonuniform insulation thicknesses (i.e., insulation thermal resistances), and because there are structural members with low thermal resistance (e.g., purlins and bracing) and different types of insulation (e.g., fiberglass batts plus extruded polystyrene spacer blocks), it is challenging to determine the overall insulation effectiveness in typical metal building roofs and walls.

Each of the above systems may be installed with standing seam or through-fastened roofs. Only through-fastened walls were tested and included in Standard 90.1 as they represent the most common insulation installation method for metal building walls-mainly for structural reasons. Thermal spacer blocks of different thicknesses and material properties can also be used in these systems. Continuous (e.g., uninterrupted constant thickness insulation systems) can be installed in series with the metal building systems described in this paper, and the effective thermal resistance can be determined by adding the thermal resistance values of the two systems.

The MBTG's charge from the Envelope Subcommittee was to review and, if necessary, modify the thermal resistance values in Standard 90.1 for insulated metal building assemblies. We did not attempt to characterize proprietary systems or any other systems not currently included in the Standard. The objectives addressed within this paper are:

1. Define the insulation profiles for commonly installed metal building insulation systems.

2. Verify laboratory data with field measurements and observations.

3. Determine the effective thermal resistance for the metal building systems currently included in Standard 90.1 by calculation methods for single layer (Choudhary and Kasprzak 2010b) and double layer (Gavin and McBride 2010) systems.

The data, analyses and discussions in the remainder of this paper are for metal frame buildings and for the non-continuous insulation systems commonly installed in these buildings.