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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