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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