The aperture sizes given in figures 14 through 22 are for single family
detached residences with 1500 ft2 of heated floorspace. For larger or
multi-story buildings, the ratio of collector area to floor area should be
scaled according to the following formula:
Ac/Af = 1/3 (Ae/Af)(Ac/Af)o
where Ae is the external surface area of the building and (Ac/Af)o
is the reference area ratio read from the appropriate contour map. This
building size correction is intended to compensate for the fact that heat
from internal sources provides a higher fraction of the building heat load
in larger buildings.
The sizing rules presented above are intended for apertures facing due
south but may be applied to cases involving departures of up to 30 degrees
without incurring serious error. Generally, the performance penalty for a
passive solar system that is thirty degrees off south is about 10 percent.
These initial values should, as previously stated, be checked by design
analysis calculations before proceeding to construction documents.
4.3.8 Thermal storage mass. The amount of thermal storage mass
required per square foot of solar aperture depends primarily on the solar
availability at the building site. The relative solar availability in the
continental United States is given by the contour map in figure 8.
Masonry thermal storage walls and sunspaces with masonry common walls
generally employ a wall thickness of about 12 inches of high density
material. This thickness is quite appropriate in the sunny region and to a
large extent, in the adjacent cloudy and very sunny regions. However, in
the most sunny region a wall thickness of 18 inches should be employed to
protect against overheating and fully utilize the available resource. In
the very sunny region, wall thicknesses may range from 12 inches to 18
inches depending on which boundary the building site is nearest. At the
other extreme, mass walls in the very cloudy region need only be 6 inches
thick and in the adjacent cloudy region, thicknesses may range from 6 inches
to 12 inches depending on position relative to the boundaries. When water
containers are used for thermal storage, either in sunspaces or thermal
storage walls, equivalent thicknesses comparable to those recommended for
masonry walls are appropriate in all solar availability regions; however,
because the heat capacity of water is roughly twice that of high density
masonry, significant downward revisions may be permissible.
Direct gain apertures, radiant panels, and TAPs all use interior mass
for heat storage. Ideally, the interior mass should have a high density and
be distributed in thicknesses of 2 inches to 6 inches. Appropriate area
ratios (Am/Ac) are 3 in the very cloudy region, 3 to 6 in the cloudy
region, 6 in the sunny region, 6 to 9 in the very sunny region and 9 in the
most sunny region. Equivalent or somewhat smaller volumes of water may be
used instead of masonry in lightly constructed buildings.