samedi 14 janvier 2012

Principles of bioclimatic design

Bioclimatic design strategies are effective for
“envelope-dominated” structures, to provide
 a large portion if not all of the energy required
to maintain comfort conditions.
“Internal load dominated” buildings— such as
 hospitals, offices, commercial kitchens,
windowless stores— experience high internal

gains imposed by the heat of  occupancy, lights ,and equipment. In such cases, the external climatic conditions mayhave a more complex influence on achieving comfort and low energy utilization.
 However, as internal loads are reduced through energyefficient design—that is, low-wattage equipment and lighting, occupancy scheduling and zoning—the effects of climate become more obvious and immediate. All buildings can benefit from available daylighting, so that its related heating and cooling impacts and means
of control are essential for all buildings.
The “resources” of bioclimatic design are the natural flows of energy in and around a building—created by the interaction of sun, wind, precipitation, vegetation, temperature and humidity in the air and in the ground. In some instances, this “ambient energy” is useful immediately or stored for later use, and in other cases, it is best rejected or minimized.
There is a limited number of “pathways” by which heat is gained or lost between the interior and the external climate (Fig. 1).

These can be understood in terms of the classic definitions of heating energy transfer mechanics, and from these, the resulting bioclimatic design strategies can be defined (Fig. 5).

Conduction—from hotter object to cooler object by direct contact.
- Convection—from the air film next to a hotter object by exposure to cooler air currents.
- Radiation—from hotter object to cooler object within the direct view of each other regardless of the temperature of air between.
- Evaporation—the change of phase from liquid to gaseous state:
The sensible heat (dry-bulb temperature) in the air is lowered by the latent heat absorbed from air when moisture is evaporated.
- Thermal storage—from heat charge and discharge both diurnally and seasonally, a function of its specific heat, weight, and conductivity.
Although not usually listed alongside the four classic means of heat transport, this role of thermal storage is helpful in understanding the heat transfer physics of building climatology.

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