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
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