MIL-HDBK-1011/2 1990 Edition, January 31, 1990
COOLING BUILDINGS BY NATURAL VENTILATION
Includes all amendments and changes through Cancellation Notice 1, December 5, 2006
Additional Comments: CNCL REFER TO MIL-STD-3007
This handbook provides guidance and criteria for the design of buildings to be totally or partially cooled by natural ventilation and supports the planning and design process as outlined in Figure 1. This handbook describes a variety of natural cooling techniques and the climatic conditions under which they should be considered. Comfort criteria and a manual design method for determining and implementing appropriate cooling strategy(s) and are described. Building design features and practices are presented for the designer's use. Special considerations related to the integration of mechanical systems and other design issues that will influence comfort and safety are noted. Recommendations for the development of occupant and maintenance manuals are given.
Appendix A includes fundamental principles related to people and comfort, climate, and information on predicting airflow. Appendix B contains a method of climate analysis, weather data sources, methods for analyzing the weather information and extrapolating it from weather station data to specific sites. Appendix C gives information on window and fan sizing, stack effect and wind tunnel testing, field and computer modeling. Appendix D is a worked example of the climate analysis and window sizing procedure. A selective bibliography and glossary are also included.
When natural ventilation can supplant some or all of a building's mechanical cooling requirements, two types of cost savings may result:
a) The energy costs of operating the air conditioning system.
b) The first cost of unnecessary mechanical equipment. As a result, the Navy is requiring that the potential for natural ventilation be examined in the design of all applicable projects in tradewind and tropical regions.
This handbook provides state-of-the-art information on natural ventilation, and a manual procedure for the design of ventilated buildings. Its use will facilitate the design of buildings that save energy by substituting natural ventilation for mechanical cooling. Although "natural ventilation" strictly refers to ventilation induced by external wind or interior thermal buoyancy, the meaning usually includes ventilation from low-powered equipment such as whole-house fans and ceiling fans.
The external climate (temperature, radiation, humidity, and wind) determines the heating and cooling requirements of the building. Since the building envelope acts as a mediator between the external and internal environment, its design and composition affect the interior conditions of the building, its energy consumption and life-cycle cost. The design of naturally ventilated buildings attempts to adjust to the regional and site-specific sun and wind patterns on a daily and annual basis to maximize occupant comfort at minimum energy cost.
Because building site has a strong influence on how well natural ventilation will function, it is important that such ventilation be a primary design parameter from the very beginning of the design process. The siting of the building will influence the ease or difficulty with which solar shading may be achieved, how much insulation is required, etc. Ventilation should also be considered throughout the design of the building. This handbook provides guidelines and suggested practices at both of these scales.
This handbook provides a procedure to evaluate the success or failure of a building design by examining the expected percentage of time that human thermal comfort will be achieved. The choice of building cooling strategy (i.e., natural ventilation, evaporative cooling, thermal mass, nocturnal ventilation, or mechanical air conditioning) is determined from the climate data for the site and an evaluation of what strategies work in different climates. Methods are given for determining and achieving the interior ventilation rates required for comfort. When wind or buoyancy-driven ventilation alone cannot provide adequate interior wind speeds for comfort, mechanical fan backup systems shall be used.
Because naturally ventilated buildings respond to the site conditions and microclimate, there is no one set of specific criteria applicable to every naturally ventilated building. However, general building design criteria are included whenever possible. A description of the "optimal configuration" for achieving continuous natural ventilation is presented in para. 3.1.4.
The choice of general site, building program, and cooling strategy is performed by the planner. The designer is responsible for the specific site planning within the given general site and for the design of the building and the site.
This handbook is intended for use both by planners (for assessing the potential for ventilative cooling in a particular climate) and by designers (for establishing the design features of the particular site and building).
To take maximum advantage of the opportunities for natural ventilation of buildings, and thus energy savings, planners and designers shall:
a) Be sensitive, at all levels of design, to the opportunities for natural ventilation.
b) Be flexible in their approach to site planning and design.
c) Perform analysis early in planning, site, and design studies.
d) Be aware of the significance of specific microclimatic differences and unique constraints of each site.
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