MIL-HDBK-1011/2
desirable. In the extreme case, the best "structure" consists of only an
insulated roof-canopy to provide shade and protection from the rain and while
allowing maximum ventilation. In practice, careful siting and orientation,
narrow elevated buildings, open plans, and use of exterior wingwalls,
overhanging eaves, verandahs, and large windows are prevalent elements of
naturally ventilated buildings in warm-humid climates (see Figure 2).
2.2.2
Structural Cooling. Structural cooling in which the building mass
smooths out the daily temperature variation, is effective in climates which
large daily temperature variations (i.e., hot-arid climates). During the day,
the building interior is unventilated and the high thermal capacity of the
building structure serves as a heat sink for the interior gains. At night,
the mass is cooled by longwave radiation to the sky. Cooling may be enhanced
by "flushing" the building with cool night air removing the stored structural
heat and prechilling the mass for the next day. Night air must be cool enough
to receive the stored heat (i.e., the nighttime outdoor air temperatures must
be lower than indoor air temperatures, and dip into or below the comfort
zone).
Traditional architecture has achieved structural cooling through
natural ventilation by means of small closable windows and various forms of
wind scoops or wind towers. Ventilation is often enhanced by using pools of
water or evaporative screens to cool the incoming air (see Figure 3).
Nocturnal ventilation can lower daytime indoor temperatures below that of
similarly thermally massive but unventilated buildings by an amount equal to
15 percent of the outdoor temperature range. Therefore if the outdoor
temperature range is 59deg.F (15deg.C), an additional 8 to 9deg.F (2 to
3deg.C) indoor
daytime temperature reduction can be expected in the nocturnally ventilated,
thermally massive building as compared to an unventilated building.
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