Masonry Magazine June 1966 Page. 7
The Engineering Center is an all-glass building. Glass throughout is so-called Grey Glass. The company claims conductivity and resistance to be superior to those of common glass. Transmittance of solar heat is claimed at about 50 per cent.
Komkov tests indicated clearly that due to aluminum frames and aluminum structural members, heat transfer through the glass was not uniform. Increased loss was noted as far as five or six inches for the frame. Furthermore, heat transfer was considerably greater than the rate that would be shown from the usual "U" calculations. (The "U" calculations would simply have noted that there was 15 times more glass than aluminum. They would not have taken into account the influence of the aluminum on the glass.)
What If Conditions Are Not Standard?
All experiments were done when the wind velocity was between 10 and 15 miles an hour. This is the velocity assumed in the "U" tables. But what if the conditions are not "standard" as assumed in the "cook-book" approach? What if the wind is 30 miles an hour instead of 15? What if the design positions the air conditioning grilles right on the outside wall (usually under the windows) so that instead of the assumed no-air movement inside we have a 15-mile-an-hour average velocity of air in the vicinity of the wall surface? Findings were that heat flow through the aluminum frame will increase more than 300 per cent. The loss through double thermal glass some distance from the frame will be increased 50 per cent. The loss in a solid masonry wall will be increased only 14 percent.
Masonry vs. Glass
The Komkov study also took into consideration the effects of solar radiation on heat transfer. Heat flow meters were placed on both sunlit and shaded areas of buildings.
It was found that where non-transparent materials, like masonry, are used air conditioning need only follow the correction of outside temperatures recommended by the ASHAE.
However, where vertical glass walls were used, the additional air conditioning load can be as great as 500 BTU's per square foot per day. For example: at one "all glass" building studied the air conditioning has been required in February on the southern exposure despite 20-degree temperatures outside. Rooms on the northern exposure have had to be heated at the same time. Radiant heat penetrating an all-glass building will create an excessive demand on the air conditioning equipment. The expense of air conditioning will be partly compensated by lower heating bills in winter, when radiation through glass puts less demand on heating equipment. But this doesn't help at all in ordering the size of heating equipment, which must be designed for either sunny or cloudy weather, for day or night conditions. It does boost the size of the air conditioning installation.
HEATING COSTS TRIPLED
Roughly three times as much heat must be added (or subtracted) for the same temperature difference when using double thermal glass as when using a 12-inch brick wall with no insulation. To the owner of a building with a wall area of 50,000 square feet this could mean a difference of $1,500 each summer for average Intermountain West or Midwestern conditions.
And this does not include depreciation, maintenance, insurance, and other costs, which again would favor a smaller air conditioning plant. A similar picture emerges when trying to compare heating costs.