MIL-HDBK-1003/19
Having determined the heat to load ratio, QA is found as indicated on
Worksheet 6, and the annual solar heating fraction, SHFa, is calculated
from the equation given on Worksheet 10. Then, the annual utilization
efficiency, (eu)a, can be calculated using the indicated equation.
Next, calculate Tact, the actual indoor temperature (the annual
average) from the equation provided on the worksheet. Use the previously
determined value for (eu)a. Then, using Tact in place of Tset,
obtain a new base temperature from Worksheet 4. Enter the weather tables in
the column indicated by the new base temperature and read the actual heating
degree days, DDact, from the row marked MONTHLY DD. Enter this quantity
on the worksheet.
Finally, calculate Qact, the actual annual heating load, from the
equation provided on Worksheet 10, and then evaluate QI by subtracting
Qact from the sum of QD and QA. Thus, the incremental cooling load is
the difference between the amount of heat put into the building (solar plus
auxiliary) and the amount actually lost to the outside.
5.2.4.3 Reducing the incremental cooling load. The incremental cooling
load can be reduced by employing systems with higher utilization
efficiencies, smaller apertures, or more thermal storage mass. During the
heating season and early and late in the cooling season, ventilation can be
employed to remove most of the excess heat. Overhangs can reduce delivery
of unwanted solar heat to the living space as can drapes and shades in
direct gain buildings. However, external shutters or covers are by far the
most effective means of reducing or even eliminating the incremental cooling
load.
5.3
Example calculations for a four-plex family housing unit.
5.3.1 Description of the building. In this section an example is
presented that illustrates use of the schematic design guidelines in 4.3 and
the design analysis procedures in 5.1 and 5.2. To illustrate the special
problems associated with multizone design, a four-plex family housing unit
was selected for consideration.
A sketch of the four-plex unit to be solarized is presented in figure
28. The long dimension of the structure is oriented 15 degrees east of true
south, the departure presumably resulting from some constraint at the
building site. Each individual two story family section has a length of 37
feet and a depth of 23 feet. The heated floorspace of each section is
therefore about 1700 ft2 and the total floorspace of the building is 6800
ft2. In the following sections this family housing unit will be solarized
as a direct gain system located in Norfolk, Virginia.
5.3.2 Schematic design parameters. Begin by filling out Worksheet 1 as
illustrated in the example. Using the dimensions given in figure 28 and the
formulas on the worksheet, it is an easy matter to obtain the "Building Size
Parameters" and determine that the external surface area to floor area ratio
is 2.91. Note that the total heated floorspace of the four-plex unit is
being used in the analysis; this approach will yield the total solar
aperture size and auxiliary heat requirement for the building. (An
approximate procedure for partitioning the aperture area between inner and
outer sections of the unit will be discussed later, as will section by
section analysis.)
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