However, offsetting this initial expense was a savings of

$123,000 in initial costs for the heating and cooling equipment, ductwork and the like. (A 64.7 percent reduction in the capacity of the central refrigeration system, a 53.2 percent reduction in the capacity of the central heating equipment and a 67.9 percent reduction in the capacity of the distribution system). The pay-off is the fact that the design chosen results in an energy consumption savings of 729.4 kilowatts per hour (translates to a savings in yearly operating cost of approximately $40,000).

The architect today has a wide choice of transparent surfaces to install. Heat absorbing glass hit the market in the late 50's and early 60's and can absorb as much as 45 percent of the solar energy striking it. Combining it with external shading such as sunscreen can be very effective, blocking up to 75 percent of the available solar energy. The effect of air movement between the screen and window offers further

reductions. The big change in glass, however, has come in the past three or four years with the advent of reflective metallic coatings. They can block any desired amount of solar light and heat, with the standard transmittance ratings being 8, 14, and 26 percent; combined with dual insulating glass, the result is glass that keeps heat where it is wanted outside depending on the weather conditions.

or inside

The individual home owner would generally not consider the kind of glass mentioned above but indeed might be interested

in double pane or storm windows. They offer a reduction in solar transmission for the cooling season of 10 to 15 percent (excluding the use of internal shading devices) but more importantly the glass area becomes at least twice as resistant to normal conduction transmission losses in the winter time. These losses can be significant as shown in figure 15 for a typical one story concrete slab house located in the center of the United States.5/

It should be noted that the window framing itself is important from a thermal standpoint. In a recent study by the

Hittman Associates of Columbia, Maryland on the energy consump6 tion of typical residences in the Baltimore-Washington area, they found that aluminum windows lose approximately 25 percent of the total window loss through the frame assembly. In contrast, wood assemblies lose only approximately 13 percent of the total window loss. The accompanying two figures, 16 and 17, show a comparison of total loss (winter) and gain (summer) for the two kinds of window frames.

It appears feasible that in both commercial and residential dwellings it is possible to reverse the trend of large expanses of glass to minimize their poor thermal efficiency and yet allow for a sufficient amount of visual communication.

In a recent study completed at NBS on a federal government building in Manchester, New Hampshire (this will be described more fully in a later section), the effect of amount of glass