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
Previous Page
