Masonry Magazine April 1984 Page. 27
NBS Completes Field Tests of Brick and Concrete Block
Researchers at the Commerce Department's National Bureau of Standards have confirmed that walls of heavyweight construction—such as brick, concrete block and logs—exhibit an energy-conserving "mass effect" in residential buildings. This was the first extensive field testing of its kind. The testing was cosponsored by the Department of Energy and the Department of Housing & Urban Development.
The preliminary test results from six one-room structures at the bureau's headquarters in Gathersburg, Md., should help resolve a controversy over whether residences having heavyweight walls consume less energy for space heating and cooling than buildings having lightweight walls of equivalent thermal resistance, according to the NBS.
Most state and local building codes require specific "R-values," or thermal resistance values, for the walls, ceilings and floors of houses. R-values in these codes vary primarily with geographical location and climate. The masonry and log home home industries have objected to such R-value requirements for walls which ignore the theorized mass effect of heavyweight construction.
Commenting on the NBS test results, Doug Burch, a mechanical engineer with the bureau's Center for Building Technology, said, "We found that the heavyweight walls did exhibit a thermal mass effect and thus save significant amounts of energy both in the summer cooling season and the intermediate heating season representative of fall or spring in this area. For example, during the Washington. D.C., summer cooling season, the uninsulated masonry building with R-5 walls used only as much cooling energy as the insulated wood-frame building with R-12 walls.
"In an insulated wood-frame building, which is considered to have low mass, the maximum wall heat gain rate during this season occurs during the day when the cooling system is operating most often and working the hardest. In a masonry building, however, the heat transfer lag means the maximum wall heat gain rate generally occurs during the cool night period when the cooling plant is operating least often or not at all. Consequently, the cooling energy requirement is reduced in the masonry building," Burch said.
The NBS tests also provided data that confirm a previous NBS finding that thermal insulation used in conjunction with heavyweight walls is more effective during the intermediate heating season and the summer cooling season when it is placed outside the wall mass.
According to Burch, the NBS findings must be used carefully. "While these test data will help improve our understanding of the mass effect, they are not sufficient by themselves for making decisions about different construction operations," he said. "For instance, not only must economics be considered—our tests do not consider the costs of each type of construction—but it is especially important to take the particular climate conditions into account since mass effect will vary considerably with climate."
Burch added that a recently developed NBS computer model that predicts the energy consumption for multi-room structures will be validated and subsequently used to extend NBS test results to other locations and climates throughout the nation.
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MASONRY-MARCH/APRIL, 1984 27