MIL-HDBK-1003/19

is convectively coupled to the solar heat source rather than radiatively

coupled. If we assume that only 50 percent of the floor slab area is

located in direct gain rooms, then the surface area available for storage

is:

0.5 x 6,800 + 0.4 x (0.5) x 6,800 = 4,760 ft2

.

Dividing this number by Ac = 791 ft2 from Worksheet 1 yields a mass to

collector area ratio of:

Am/Ac = 6.02

.

If the concrete slabs are covered with dark brown ([alpha] = 0.88 from table

VII) linoleum tile (Rd = 0.05 from table III) the floor covering

correction factor has a value of 1.01 (see equation 5.9). This correction

factor is close to 1 because the thermal resistance of the tile is offset by

the enhanced solar absorptance. The effective area ratio of the thermal

storage mass therefore remains very nearly equal to 6, which is a reference

design value.

Employing the four digit numbering system used for direct gain buildings

in Appendix A, the first digit, which corresponds to the Am/Ac ratio, is

taken as 6. The floor slab thickness has already been specified as 4 inches

(of high density concrete), so the second digit in the system is 4.

Finally, selecting a night-insulated system with an R-value of

4deg.F-ft2-hr/Btu and two glazing layers, we obtain a system number of

6442 and record that number on the worksheet. Since the four-plex unit

corresponds closely to this reference design, we are able to obtain an

EHC/Ac of 53.93 Btu/deg.F-ft2 and a DHC/Ac of 56.76 directly from

Appendix A. These numbers also are recorded on Worksheet 3. Finally, the

worksheet is completed by locating and recording the values of F, G, Uc,

and alpha specified for direct gain system number 6442 in Appendix A. The

aperture size, 791 ft2, is also recorded to facilitate analysis of mixed

systems.

In some instances a building might employ two different system types;

Worksheet 3 allows for this possibility. To analyze a mixed system, repeat

the above procedure for the second system and enter the component areas in

the indicated blanks. The mixed system parameters are then calculated using

the weighting procedure indicated on the worksheet.

5.3.5 Base temperature. Worksheet 4 for the base temperature is

divided into two parts. The first part is used to calculate the base

temperature when a constant thermostat setting is employed during the

heating season. The second part is used to calculate the base temperature

when a night time setback is employed in the building. For this example

we shall adopt a setback strategy.

The daytime setting shall be 70deg.F and is assumed to be in effect from

5 a.m. to 10 p.m. for a duration of 17 hours. The night time setpoint shall

be 60deg.F and has a duration of 7 hours. After entering these values on

the worksheet, the indicated formulas are used to calculate the average

setpoint of:

Tave = 67.1deg.F

.

78

Integrated Publishing, Inc. |