MIL-HDBK-1011/2
3.1.2.9
Back-up Mechanical Systems. It may be necessary or desirable to
include backup ventilation using a whole-house fan, ceiling fans in the
interior spaces, or a mechanical ventilation system to ensure comfort when
wind-driven ventilation is inadequate. For a description refer to para. 4.6.
Ceiling fans are required in all major occupied spaces of naturally ventilated
buildings when comfort cannot be achieved by natural ventilation alone based
on the Climate Analysis Method in Appendix B.
3.1.3
Special Considerations
3.1.3.1
Mechanical System Integration. Naturally ventilated buildings may
not be completely compatible with conventional mechanical systems. Care shall
be exercised so that neither cooling strategy undermines the effectiveness of
the other. Automatic sensors to detect open windows or doors and to shut down
mechanically-conditioned air supply are recommended in naturally ventilated
buildings with backup air conditioning or closed-loop ventilating systems.
Natural ventilation of buildings with large openings in the
building envelope is inappropriate during months when appreciable heating or
air conditioning is required unless the openings can be closed to thermal and
infiltrative losses. In such cases, movable insulation shall be considered.
3.1.3.2
Condensation. Condensation may be a problem in buildings combining
natural ventilation with mechanical air conditioning. Note that planning and
design to minimize mechanical air conditioning loads does not always coincide
with planning for natural ventilation. If a combined (zoned) system is
desired, each shall be designed for maximum efficiency and the connection
between the zones should be carefully detailed.
3.1.3.3
Other Issues. Due to the "open" nature of naturally ventilated
buildings, special consideration shall be given to possible problems with
noise, privacy, and rain protection.
3.1.3.4
Building Types Considerations. High ventilation rates may not be
suitable for offices (where papers may be blown about) or for uses requiring
high security, or rigid environmental standards (such as computer and other
sensitive instrument rooms, toxic producing processes, hospitals, clinics).
In general, natural ventilation shall be considered for all housing projects,
recreation facilities, religious buildings, hangars and general purpose
storage facilities when climate analysis (refer to Appendix B) indicates that
natural ventilation is an acceptable strategy. Storerooms for hazardous
materials or for materials requiring humidity control are not addressed by
this handbook.
In buildings where natural ventilation
is indicated as an
acceptable strategy, mechanical cooling may still
be necessary for critical
areas, but the natural ventilation may be used to
reduce energy and mechanical
equipment costs in less critical areas. Refer to
para. 3.2 for a description
of zoned buildings.
Optimal Configuration to Encourage Ventilation. Each building
3.1.4
project and site will have a unique set of opportunities and constraints, and
shall be considered on a case-by-case basis. The following "ideal" set of
design conditions would produce one optimal configuration for ventilation.
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