MIL-HDBK-1011/2
APPENDIX B (continued)
CLIMATE ANALYSIS
This appendix presents a method for determining the most suitable
natural cooling strategy for a particular site. The method also determines
the need for an open or an infiltration-resistant envelope, and whether a
backup mechanical system is required.
STEP 1:
DETERMINING POTENTIAL FOR NATURAL COOLING
1.1
Building Bioclimatic Chart Transferred Onto Four Overlays. The
overlays (Figures B-1, B-2, B-3, and B-4) plot the range of temperatures and
humidities for which the natural cooling strategies should be used in building
design. They must be copied onto clear acetate by the user and carefully
checked for exact size reproduction prior to use as described below.
Several strategies allow design of building envelopes for climate
control. The appropriateness of a building's climate control strategy under
any set of ambient temperature and humidity conditions is determined by an
analysis of weather data and the requirements for human comfort, as given on
the bioclimatic chart (Figure B-5). Plotting the climatic limits for each
climate control strategy onto the bioclimatic chart produces a new diagram,
the Building Bioclimatic Chart (Figure B-6). The Building Bioclimatic Chart
indicates that whenever ambient outdoor temperature and humidity conditions
fall within the designated limits of a control strategy, then the interior of
a building designed to effectively execute that strategy will remain
comfortable. The boundaries indicated on Figure B-6 are appropriate for
residences and other buildings with small internal gains. For buildings with
large internal gains, such as offices and some factories, the boundaries need
to be shifted to the left. Different strategies may be used alone or in
conjunction with air conditioning and conventional heating. They are:
a)
solar heating,
b)
solar gain controls,
c)
ventilation, shown at 100 and 200 fpm (0.5 and 1.0 m/sec),
d)
thermal mass (low levels of ventilation),
e) thermal mass with nocturnal ventilation (low ventilation in the
daytime and high ventilation at night), and
f)
evaporative cooling.
1.1.1
The Natural Ventilation Boundary. The natural ventilation boundary
(Figure B-1) is based on the assumption that indoor air temperature and water
vapor pressure are identical indoors and out, and that the mean radiant
temperature of the building interior is approximately the same as that of the
air. Both assumptions are sufficiently valid if the interior is well
ventilated, the building envelope is well insulated and well shaded, and the
exterior is light colored to restrict solar heat gain.
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