STEADY STATE THERMAL PERFORMANCE OF CONCRETE MASONRY WALLS

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CLEAR WALL AND OVERALL WALL THERMAL PERFORMANCE

 

Currently, the evaluation of the wall thermal performance is based on the thermal resistance value of the clear wall area.  The clear wall is a flat, uniform part of the wall, uninterrupted by wall details.  Traditionally, only this area is tested and most of the theoretical calculations are provided only for this area. Measured or calculated thermal properties of the clear wall area may not adequately depict the total wall system thermal performance.  For concrete masonry wall systems, intersections with other building elements, and perimeters of openings are often very different from the clear wall.  In the past, this fact has been ignored and omitted in wall thermal analysis.

 

The influence of wall details on the overall wall thermal performance is different for every structure because of the variety of architectural designs.  To allow comparisons, a standard building elevation was used.  The standard elevation selected for this purpose is a single-story ranch style house that has been the subject of previous energy efficiency modeling studies [Huang et al. 1987].  The house has approximately 1,500 ft² of living area (55 H 28 ft), 1,328 ft² of exterior wall area (elevation), 8 windows, and 2 doors (one door is a glass slider and is included with the windows).  The elevation wall area includes 1,146 ft² of opaque wall area (an overall wall), 154 ft² of windows, and 28 ft² of door area. Based on the computed wall detail R-values, the overall wall system R-value was calculated by combining the thermal resistance of the wall details, subsystems, wall intersections, and clear-wall area in a parallel, area-weighted method.

 

Very often, thermal performance of wall details are different from those of the clear wall area.  Distribution of heat losses through the wall details can be different from the wall area distribution.  For an ideal wall system (from a thermal performance perspective), the overall wall R-value should be equal to the clear wall R-value.