Section 3: DESIGN CRITERIA
Building Design for Natural Ventilation
Introduction. Continuous ventilative cooling is suitable in
hot-humid climates such as Hawaii where the high atmospheric humidity limits
the daily swing of temperature. In such climates, buildings cannot cool off
sufficiently at night to reduce daytime internal temperatures substantially
below the outdoor daytime temperature. The best buildings for such zones have
continuous ventilation day and night, both for cooling the occupants directly
and for dissipating any internal gains. The indoor temperatures remain close
to the outdoor temperatures. These buildings are usually open, relying on
their connection to the outside wind environment to achieve the most
comfortable interior conditions.
The primary comfort requirements for buildings using natural
ventilation are to protect occupants from the sun and rain without obstructing
the airflow that cools both the occupants and the building structure.
Minimizing heat gain and promoting maximum ventilation are of primary
Requirements and Recommendations
Climate Analysis. Perform the Climate Analysis located in Appendix
B to determine the number of months that natural ventilation will provide
comfort and the air velocity required to achieve comfort in the given climate.
This method also examines possible seasonal variations that may affect the
Required Air Changes. An outside air exchange rate sufficient to
remove internal heat gain must be provided to prevent a rise in interior
temperature. Calculate the required air changes to keep the building's
interior temperature below the top of the comfort zone at the 98 fpm (0.5
m/sec) internal air movement boundary (refer to Appendix C, Section 2).
Site Selection. Sites in which the slope, elevation, orientation,
vegetation and wind pattern act to increase summer and winter cooling by wind
large bodies of water may be preferable if cooling breezes can be directed
into the building(s).
To minimize heat gains from solar radiation, south, south-
southeasterly and northern slopes are preferable. West and east facing slopes
should be avoided due to the difficulty of providing adequate shading. The
most desirable wooded sites have high tree canopies and open trunk areas,
permitting air movement while providing shade. Avoid sites with dense low
canopy trees which block breezes and trap humidity in dead air pockets.
Site Planning and Landscaping. Buildings must be spaced to allow
winds to reach the ventilation openings. In general, it is not desirable to
site buildings within the wake of surrounding structures or landscaping. In
most cases dense development should be avoided. The terrain, surrounding
vegetation and other nearby structures may be used positively to "channel" or