MIL-HDBK-1003/19
4.
GENERAL REQUIREMENTS
4.1 Basic concepts. The concepts introduced herein are limited to
those that are further developed within the remainder of the design
procedures. Thus a comprehensive treatment is rejected in favor of one that
is directed at areas of particular interest to the Navy in which our
understanding is sufficient to warrant a quantitative treatment.
4.1.1 Direct gain heating. Direct gain buildings are passive solar
heating systems in which sunlight is introduced directly to the living space
through windows or other glazed apertures as indicated schematically in
figure 1. As with all passive solar systems, it is important that the
apertures face south or near south in order to achieve high solar gains
during the winter heating season and low solar gains during the summer
cooling season.
Thermal storage mass is essential to the performance and comfort of
direct gain buildings. A building that has inadequate mass will overheat
and require ventilation, which entails a loss of heat that might otherwise
have been stored for night time use. Generally, it is desirable to employ
structural mass as a storage medium in order to take advantage of the
improved economics associated with multiple use. Insulation should always
be placed on the outside of massive elements of the building shell rather
than on the inside in order to reduce heat Losses without isolating the mass
from the living space. Concrete floor slabs can contribute to the heat
capacity of a building provided they are not isolated by carpets and
cushioning pads. Heat losses from the slab can be limited by placing
perimeter insulation on the outside of the foundation walls. If the
structure is fairly light, the heat capacity can be effectively increased
by placing water containers in the interior. A variety of attractive
containers are available commercially.
An overhang, also illustrated in figure 1, is used to shade the solar
aperture from the high summer sun while permitting rays from the low winter
sun to penetrate and warn the inside of the building. In climates having
particularly warm and sunny summers, an overhang may not be sufficient to
prevent significant aggravation of the summer cooling load. Sky diffuse and
ground reflected radiation enter the living space despite the presence of an
overhang and must be blocked by external covers or internal shades. Using
movable insulation on direct gain apertures has the advantage of reducing
night time heat losses during the winter-as well as eliminating unwanted
solar gains during the summer.
Direct gain buildings involve less departure from conventional
construction than other types of passive solar systems and are therefore
cheaper and more readily accepted by most occupants. However, they are
subject to overheating, glare, and fabric degradation if not carefully
designed; these problems can be minimized by distributing the sunlight
admitted to the building as uniformly as possible through appropriate window
placement and the use of diffusive blinds or glazing materials. When
properly designed for their location, direct gain buildings provide an
effective means of reducing energy consumption for space heating without
sacrifice of comfort or aesthetic values.
10
Previous Page
