STEADY STATE THERMAL PERFORMANCE OF CONCRETE MASONRY WALLS

 

Jan Kosny and Jeffrey E. Christian

Oak Ridge National Laboratory

Building Thermal Envelope Systems and Materials Group

 

 

ABSTRACT

 

Several new materials and modern building masonry technologies are now available in the building marketplace. Also, unique and more accurate, methods of thermal analysis of wall systems create an opportunity to design and erect buildings where thermal envelopes that use masonry wall systems can be more efficient.

 

Current techniques for the evaluation of the wall thermal performance are focused on the thermal resistance value of the clear wall area.  The clear wall is the 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. Finite difference two-dimensional and three-dimensional computer simulations were utilized in this paper, for clear wall and whole wall thermal analysis.

 

Thermal performance of six masonry wall systems is analyzed below. Since most existing masonry systems are modifications of these analyzed technologies this paper can be used for approximate energy evaluations of most of concrete masonry technologies. A wide range of concrete densities (represented by thermal resistivities) was analyzed in this paper. This enables energy performance comparisons for lightweight and normal weight structural conctretes used in masonry units.

 

In the design of thermally efficient masonry wall systems, it is important to know how effectively the insulation material is used and how the insulation shape and its location affect the wall thermal performance. For some shapes of the insulation and concrete components, hidden thermal shorts can cause considerable heat losses.  In this study, the thermal analysis of the clear wall was enriched with the quantity defined here as the “Thermal Efficiency” of the insulation material. Also, the evaluation of the thermal effects generated by mortar and grout were included in the clear wall thermal analysis.

 

In addition, the examination of thermal properties of wall details was performed for three wall systems. The total wall system thermal performances were determined for a typical single-story ranch house. At present, building energy codes and standards, and many residential building designers do not include the effects of building envelope details such as corners, window and door openings, and structural joints with roofs, floors, ceilings, and other walls. This simplification can lead to errors in determining the energy efficiency of the building envelope.  In masonry wall systems, wall details may have a different structure than the clear wall area. Also, highly conductive grout, and reinforcement are used very often.  These cause additional thermal bridges, which should be incorporated in the thermal performance analysis.

 

 

KEYWORDS: BUILDING ENVELOPE, MASONRY, CONCRETE, THERMAL PERFORMANCE