MIL-HDBK-1011/2
APPENDIX A (continued)
Section
2:
CLIMATE AND MICROCLIMATE
2.1
Climatic Elements Affecting Natural Cooling. The local climate
affects the building's energy efficiency, the comfort of its occupants, and
its resistance to weathering. The climatic elements important to natural
cooling in buildings are: temperature, wind, humidity and radiation. Records
of these climatic elements exist in many forms. The Air Forces' RUSSWO
(Revised Uniform Summary of Surface Weather Observations) or the Navy's SMOS
(Summary of Meteorological Observations, Surface) Part C "Surface Winds" and
Part E "Temperature and Humidity" summaries, available from the National
Climatic Center in Asheville, North Carolina, are the most complete weather
data available, generated from long-term hourly records taken from weather
bureau and military weather stations.
Climatic elements must be examined in conjunction with each other.
The wind is a good illustration of the need to relate climatic elements to
each other. In humid climates it is a blessing and dominates the layout,
orientation and shape of buildings. In arid climates it carries dust, brings
little relief from heat and must be excluded during the daytime.
2.2
Extrapolating Regional Weather Data to Specific Sites. The weather
at the building site may differ from that at the weather station providing the
climatological data used in design. The climatic differences tend to increase
with larger distances between the two locations. Because there are relatively
few first-order weather stations providing the detailed climate data needed
for natural ventilation design, the distance between any given building site
and its closest or most appropriate weather station will tend to be large.
This can introduce error in the predicted building performance.
To reduce this error, estimates can be made of the differences
between the climates of the weather station and the building site, and, if
they are significant, adjustments may be applied to the weather station data
to account for the differences. The climatic differences are estimated from
two sources of information. First, if one has access to a more local climate
record of limited detail or limited period of measurement, one may compare
this record with the more distant detailed record to estimate the overall
differences between the sites. Second, the local terrain and ground cover
may have predictable effects on the climate.
Of the important climate elements for the design of natural cooling
in buildings, humidity and solar radiation data are not generally subject to
extrapolation, reasons given in paras. 2.2.1 and 2.2.2.
Humidity. There is usually very little humidity data available
2.2.1
from local second-order weather stations, and there are few generalizations
that can be made about the amount of atmospheric moisture above a site, based
on a description of the site's physical characteristics.
2.2.2
Solar Radiation. Solar radiation data are usually not available
from local sources, either measured directly or extrapolated from cloud cover
observation. It is possible to quantify the very local effects of site
obstructions blocking solar radiation on site hour by hour. This information
is important for accurate computer simulations of building performance, but
is not a primary requirement for determining or evaluating natural cooling
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