MIL-HDBK-1003/19
4.2.3.5 Very cloudy region. The very cloudy region includes only the
extreme Pacific Northwest and the central to eastern Great Lakes area. The
Great Lakes area, where the very cloudy region overlaps the very harsh
region, is the poorest location in the continental United States for passive
solar heating. The Pacific northwest area overlaps the Harsh climate
region and is slightly better suited for passive solar applications.
Schematic design guidelines that are related to the climate regions
appearing in figures 7 and 8 are presented in 4.3.
4.3 Guidelines for schematic design. The objective during schematic
design is to develop a rough idea of what the final building will be like.
The designer is not concerned with detail at this point but seeks only to
establish the basic shape, dimensions, materials, window areas, and
insulation levels that will characterize the design; in these procedures,
the characteristics of the passive solar heating system are added to the
list of more traditional architectural concerns.
The guidelines in this chapter provide starting point values for the
basic passive solar design parameters; if the user already has a good idea
what his building will be like he may skip to 4.4 where the fundamentals of
design analysis are introduced.
4.3.1 Building shape and orientation. Passive solar buildings are
usually elongated in the east-west direction so that a large south-facing
surface is presented to the low winter sun for solar heating, and small east
and west-facing surfaces are presented to the northerly rising and setting
summer sun to reduce unwanted solar gains. The aspect ratio (east-west
dimension divided by north-south dimension) should be at least 5/3, and
much larger values are appropriate for large dormitory-like structures.
Ideally, passive solar buildings should be no more than two zones deep
in the north-south direction. The two zone limit on depth generally allows
solar heat collected on the south side of the building to be transported for
use to the north side, thereby improving thermal performance. Multi-story
buildings are well suited to passive solar design, particularly if the above
recommendations on aspect ratio and depth are observed, because of the
large vertical surface that may be presented to the winter sun for solar
absorption.
Orientations that depart from true south by up to 30 degrees are
permissible; performance penalties will usually be less than 10 percent. An
easterly bias is preferred in applications that require a rapid warm up in
the morning, whereas a westerly bias will sometimes improve the performance
of buildings that are occupied in the evening because of the improved
phasing of heat source and heat load.
4.3.2 East, west, and north windows. Windows not facing south should
be kept small while complying with local building codes. Particularly in
the colder climates, it is best to place most of the nonsouth window area on
the east or west side of the building to take advantage of winter solar
gains available during the early morning and late afternoon.
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