Masonry Magazine March 1981 Page. 24
New Heat Flow Measurement System for Perimeter Foundation Insulation Introduced
The Dow Chemical Co. has announced a new, two-dimensional heat flow calculation which it claims provides the "most accurate method yet devised" for measuring heat transfer in the foundations and perimeters of commercial buildings.
First presented by Dr. Frank Wang, a senior research associate for Dow, at the ASHREA/DOE Conference on Thermal Insulation in Orlando, Fla., this finite element computer analysis considers the heat flow in two directions.
"Until recently, heat loss through the foundation has been of little concern for commercial buildings because of large heat losses in other areas," said George Mackey, Dow research specialist. "With the ever rising cost of energy and increasingly stringent state conservation codes, however, vulnerable locations such as the roof, walls and windows have become better insulated.
"The uninsulated foundation represents a significant part of a building's total energy loss. The basic assumption of ASHRAE 90-75, a voluntary set of design standards developed in 1975, and adopted, for the most part, by 45 states, is that heat flow is circular and one-dimensional between the basement and the ground surface."
Dr. Wang's mathematical modeling and computer simulations analyze two-dimensional heat flow through the perimeter foundation, while taking into account many more variables such as the freezing and thawing of ground soil and the most effective placement of the insulation for maximum thermal efficiency. The accuracy of the program has been verified in underground applications on the Alaskan pipeline.
To analyze the computer program more carefully, three different temperature zones were chosen representing a wide range of weather conditions: Atlanta, Ga., with a heating season of 3,000 degree days; Columbus, Ohio, with 5.300 degree days, and Madison. Wis.. with 7,600 degree days.
Four methods of construction were then used to investigate the effect of foundation and perimeter insulation. In each case, the walls were insulated. Heat loss that passes through the perimeter foundation or from the exposed foundation only was considered. The insulation used for testing purposes was 1"-thick Styrofoam SM brand used in a vertical position down 2'6" from grade. The board-form insulation, manufactured by Dow, has an R-value at 1 thickness of 5 at 75° mean, and 5.4 at 40° mean.
CAVITY WALL CONSTRUCTION WITH INTERIOR WALL INSULATION:
Calculations show that heat flows through the slab and wall joint to the perimeter foundation, as well as from the slab downward into the foundation and, eventually, to the ground. Styrofoam insulation was run vertically between the slab and wall joint down inside the foundation, thus placing a thermal break at all the major heat flow paths. The result was a 41% reduction in energy loss through the perimeter. This represented an annual savings of 27,000 BTUs per linear foot per year in Atlanta, or $95 per 10,000 sq. ft. of building space; 44,000 BTUs in Columbus, with a savings of $155 per 10,000 sq. ft., and 59,000 BTUs in Madison, with a monetary savings of $207 per 10,000 sq. ft.
CAVITY WALL CONSTRUCTION WITH INSULATION IN THE CAVITY:
In this type of construction, heat flows from the slab into the interior wythe of the wall, and downward into the foundation and the ground. By installing Styrofoam on the interior of the perimeter, heat flow from under the slab is reduced. Because there is still a pattern of heat transmission into the interior wythe, energy loss figures for this method of construction are not as dramatic as the previous.