Masonry Magazine December 1986 Page. 24
States, and the National Association of Home Builders (NAHB) Thermal Performance Guidelines (TPGs)
used to qualify buyers of energy efficient homes at lower debt-to-income ratios, also recognize thermal mass and insulation economics tradeoffs.
Momentum continues to grow for national standards including thermal mass(3), despite continued resistance from insulation marketing groups. As the thermal mass technical data base grows and continues to approach consensus, political resistance may stiffen. However, when ASHRAE adopts energy efficient standards which include heat capacity and insulation location effects, considerable added credibility should result.
Future technical analysis will use PEAR 2.0 to generate similar scenarios of more U.S. cities, and continue to refine our specific understanding of heat capacity and insulation tradeoffs.
Summary
Thermal mass saves considerable heating and cooling energy in most climates for all building types. These whole building energy savings can be "traded off" to help specify appropriate mass wall insulation levels providing similar annual total energy consumption, while boosting cost effectiveness.
The quantity of energy savings is related to many factors including: insulation position, wall heat capacity, overall wall U-value, use of passive solar heat or natural architectural cooling, HVAC operations, foundation type, and other envelope thermal protection levels including ceiling and floor insulation.
Analysis of thousands of computer runs verified by test house data show that climate, insulation position and wall U-values are the most influential parameters.
Buildings designed to use passive energy sources for heating and cooling will frequently exceed the conservative thermal mass benefits described in this TEK, and should be analyzed on a case by case basis.
Thermal envelope interactions have been accounted for by DoE researchers in production of the PEAR 2.0 program, a design aid for thermally efficient buildings with frame, masonry and log walls. This program is in use today by ASHRAE experts developing performance and economics based energy standards.
Mass walls are most effective in saving heating and cooling energy when insulation is located towards the exterior "skin" of a building. However, even interior insulation placement saves some energy in many climates.
Due to thermal mass effects, insulated cavity walls pre-insulated concrete block walls and those containing loose fill, (perlite and vermiculite) save more energy than than typical interior insulated block walls, improve fire and sound resistance and protect insulation for low maintenance.
Over-insulating masonry walls can boost annual energy costs in hot climates. Prescriptive energy standards and codes that create over-insulated, noncost-effective envelopes must be revised to reflect current technology.
U.S. DoE research has been completed verifying accuracy of the principal computer simulation programs in predicting mass effects. Further research into specific details of thermal mass is anticipated.
Thermal mass may be influential in reducing equipment size requirements. However, more systems research is required in this area. Until more is known, it is generally not advisable to down-size HVAC equipment in thermal mass buildings unless full year heating and cooling simulations are performed to support engineering judgements.
References Cited
1. Christian, J. "DoE/ORNL Thermal Mass Program Summary."
2. Howard, B. D. "Advances in Thermal Mass Assessment Data."
3. Howard, B. D. "Masonry Thermal Mass in the Energy Codes."
4. Byrne, S. and R. Ritschard. "Thermal Mass in Exterior Walls of Residential Buildings."
5. PEAR 2.0 (Program for Energy Analysis of Residences) developed by Lawrence Berkeley Laboratory, University of California.
6. Carroll, W. (unpublished) BLAST data on thermal mass.
NATIONAL CONCRETE MASONRY ASSOCIATION
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