MIL-HDBK-1003/19

If multiple storage elements are present, the appropriate correction factor

must be applied to each element individually. R-values for finish materials

are included in table III and solar absorptances are available in table VII

which, though not specfically directed at finish materials, does indicate

the variation of [alpha] with color. For convectively coupled mass

elements, set [alpha] equal to 0.8, the reference design value, regardless

of surface color.

5.1.3.2 Radiant panels. Three reference designs are available for

simple radiant panels. Double glazing is used in all cases. The distance

between the inner glazing and the metal absorber plate is 1-inch and the

plate has a solar absorptance of 0.95 and an infrared emittance of 0.9. The

thermal storage medium is high density concrete. The concrete thickness is

4 inches and the area ratio may be 3, 6, or 9. System parameters, including

the EHC are provided in Appendix A. Systems may be analyzed with other

thermal storage materials or configurations by employing the EHC as

described in 5.1.3.1. For radiant panels, however, the [alpha] in equation

5.4 is the infrared absorptance ([alpha]ir) rather than the solar

absorptance. Therefore, to correct for the presence of decorative

coverings, use the formula:

[alpha]ir/(1.48 [multiplied by] Rd + 0.9)

(Equation 5.10)

The infrared absorptance of most building or finish materials is about 0.9.

5.1.3.3 Thermosiphoning air panels. There are 18 reference designs for

TAP systems that include both single and double glazed apertures. The solar

absorptance of the metal panel is 0.95 and the infrared emittance is 0.9.

The thermal storage medium is high density concrete and all combinations of

2, 4, and 6 inch thicknesses with Am/Ac ratios of 3, 6, and 9 are

available. The flow channel depth is 3.5 inches and, for the backflow

systems, the absorber surface is 1 inch behind the inner glazing. The upper

and lower vents are 8 feet apart and have a total area equal to 6 percent of

the panel area.

The R-value of insulation between the back of the flow channel and the

room air (RTAP) is R-11. If any other value is desired for RTAP, one has

only to calculate the effective aperture conductance and the steady state

aperture conductance from the following equations:

G = 24/[RTAP + Kb + (NGL - 1) + 3.7]

(Equation 5.11)

Uc = G/24

(Equation 5.12)

where Kb is a parameter whose value is one for a backflow system and zero

otherwise. The scale factor (F) does not vary with RTAP or Kb but is

dependent on NGL. Note that the correlations presented in Appendix A are

for frontflow systems with RTAP = 11. For backflow systems, ed = 0.58 for

single glazed systems and ed = 0.69 for double glazed systems.

5.1.3.4 Trombe walls. The Trombe wall reference designs are split into

two subcategories: vented and unvented. For both subcategories, the

parameters that are varied among the Trombe wall reference designs are the

thermal storage capacity (expressed also in terms of wall thicknesses

varying from 6 to 18 inches), the number of glazings (1, 2, or 3), the wall

surface (flat black or selective), night insulation (none or R-9), and the

masonry

64

Integrated Publishing, Inc. |