MIL-HDBK-1003/19
It is usually not necessary to account for the heat storage contribution
of all surfaces in a direct gain zone. Frequently, the thermal storage
effect is dominated by one or two relatively thick layers of high density
masonry material. A wooden frame structure on a concrete floor slab, for
example, can be accurately modeled by including only the concrete slab in
the EHC calculation. For the special case in which one thermal storage
element dominates the building reponse, the EHC given by equation 5.2
reduces to:
-0.22 (Am/Ac)
EHC = 45.5 [1 - e
] [multiplied by] s [multiplied by] EF
(Equation 5.6)
The diurnal heat capacity of a building is given by:
N
DHC =
[SIGMA] Ai [multiplied by] si [multiplied by] DFi
i=1
(Equation 5.7)
where, again, the summation is carried out over the N thermal storage
elements in the building. The quantity DFi is the DHC thickness function
and is plotted as a function of x in figure 26. When the DHC is used to
determine the time constant of a particular building or set of rooms
comprising a single thermal zone, all massive elements contained in the
zone, whether in a solar room or not, should be included in the summation.
In applications that involve determination of temperature swings in solar
rooms, all elements that are radiatively coupled to the solar source (as in
rooms having direct gain apertures or radiant panels) should be included in
the summation; contributions from mass elements that are convectively
coupled to the solar source are included in the summation only after
multiplying their DHC thickness functions by 0.4. If only one radiating
coupled mass element is contained in the thermal zone of interest, the DHC
given by equation 5.7 reduces to:
DHC = Am [multiplied by] s [multiplied by] DF
(Equation 5.8)
5.1.3 System parameters. Tables of system parameters for a large set
of reference designs are presented in Appendix A. The reference designs
include direct gain buildings, radiant panels, thermosiphoning air panels,
unvented Trombe walls, vented Trombe walls, water walls, concrete block
walls, and sunspaces. The system parameters include the scale factor (F),
the effective aperture conductance (G), the steady state aperture
conductance (Uc) and the effective aperture absorptance ([alpha]). For
those systems with interior mass, DHC/Ac is included and, for direct
gain buildings and radiant panels, EHC/Ac is also specified. The user
must select the reference design that most closely resembles his own and
use the associated parameters from Appendix A in the subsequent design
analysis.
The characteristics of the reference designs will be discussed by system
type in the subsections that follow. However, some of the design
characteristics are common to all systems and these common properties are
listed in table V.
5.1.3.1 Direct gain buildings. A set of 81 reference direct gain
designs are included in Appendix A. The 81 designs were selected by choosing
three appropriate values for each of the four principal design variables and
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