Passive cooling techniques can be used to reduce, and in some cases eliminate, mechanical air
conditioning requirements in areas where cooling is a dominant problem. The cost and energy
effectiveness of these options are both worth considering by homeowner and builders. Contained
within this section are rules of thumb and an explanation or the essentials of passive cooling systems.
In many parts of the southwest, summer cooling is as important as winter heating. In the arid part of
the country, cooling is the primary design consideration.
Thermal comfort in summer means more than keeping the indoor air temperature below 75°. High
temperatures, or high humidity (or both) can lead to excessive discomfort. Fortunately, the regions of
high summer temperatures are quite arid (relative humidity is usually low). The only regions of fairly
high humidity, the coastal regions, are also among the coolest parts of the region in summer.
There are three major sources of unwanted summer heat: direct solar impacts on a building and
through windows and skylights; heat transfer and infiltration, of exterior high temperatures, through
the materials and elements of the structure; and the internal heat produced by appliances,
equipment, and inhabitants. Of the three, the first is potentially the greatest problem in the southwest,
but it is usually the easiest to control.
conditioning requirements in areas where cooling is a dominant problem. The cost and energy
effectiveness of these options are both worth considering by homeowner and builders. Contained
within this section are rules of thumb and an explanation or the essentials of passive cooling systems.
In many parts of the southwest, summer cooling is as important as winter heating. In the arid part of
the country, cooling is the primary design consideration.
Thermal comfort in summer means more than keeping the indoor air temperature below 75°. High
temperatures, or high humidity (or both) can lead to excessive discomfort. Fortunately, the regions of
high summer temperatures are quite arid (relative humidity is usually low). The only regions of fairly
high humidity, the coastal regions, are also among the coolest parts of the region in summer.
There are three major sources of unwanted summer heat: direct solar impacts on a building and
through windows and skylights; heat transfer and infiltration, of exterior high temperatures, through
the materials and elements of the structure; and the internal heat produced by appliances,
equipment, and inhabitants. Of the three, the first is potentially the greatest problem in the southwest,
but it is usually the easiest to control.
HEAT GAIN CONTROL
Many of the principles and techniques of passive solar heating are adaptable to natural cooling.
Insulation and weather-stripping that prevent heat loss in the winter will also retard heat gain during
summer. Movable insulating shutters for winter nighttime containment of heat gain can also be used to
reduce summertime daytime heat gains. Inside the house, thermal mass such as masonry walls and
floors, act as "heat sponges", absorbing heat and slowing internal temperature rise on hot days, and
can be cooled down by nighttime ventilating (at the beginning and end of the summer season) and by
use mechanical cooling during off-peak cost hours (nighttime). Suitably placed near a window,
skylight, or vent, the same thermal mass can be exposed to cool night air to release the heat
absorbed from the space earlier in the day. Finally, earth integrated buildings, embedded into the
ground, benefit from the lower difference between interior and exterior surface temperature.
Many of the principles and techniques of passive solar heating are adaptable to natural cooling.
Insulation and weather-stripping that prevent heat loss in the winter will also retard heat gain during
summer. Movable insulating shutters for winter nighttime containment of heat gain can also be used to
reduce summertime daytime heat gains. Inside the house, thermal mass such as masonry walls and
floors, act as "heat sponges", absorbing heat and slowing internal temperature rise on hot days, and
can be cooled down by nighttime ventilating (at the beginning and end of the summer season) and by
use mechanical cooling during off-peak cost hours (nighttime). Suitably placed near a window,
skylight, or vent, the same thermal mass can be exposed to cool night air to release the heat
absorbed from the space earlier in the day. Finally, earth integrated buildings, embedded into the
ground, benefit from the lower difference between interior and exterior surface temperature.
CONVECTIVE COOLING MODELS
The heat gain control methods discussed above should suffice to keep room temperatures
comfortable in houses built where mild summer temperatures are the rule. But there are many other
regions of the southwest, particularly the desert areas, where additional cooling will usually be
necessary. The next step in natural cooling is to take advantage of "convective" cooling methods -
those which use the prevailing winds and natural, gravity-induced convection to ventilate a house at
the appropriate times of the day.
The oldest, straightforward convective method admits cool night air to drive out the warm air. If
breezes are predominant, high vents or open windows on the leeward side (away from prevailing
breeze) will let the hottest air, located near the ceiling, escape. The cooler night air sweeping in
through low open vents or windows on the windward side will replace this hot air and bring relief.
The heat gain control methods discussed above should suffice to keep room temperatures
comfortable in houses built where mild summer temperatures are the rule. But there are many other
regions of the southwest, particularly the desert areas, where additional cooling will usually be
necessary. The next step in natural cooling is to take advantage of "convective" cooling methods -
those which use the prevailing winds and natural, gravity-induced convection to ventilate a house at
the appropriate times of the day.
The oldest, straightforward convective method admits cool night air to drive out the warm air. If
breezes are predominant, high vents or open windows on the leeward side (away from prevailing
breeze) will let the hottest air, located near the ceiling, escape. The cooler night air sweeping in
through low open vents or windows on the windward side will replace this hot air and bring relief.
RADIATIVE COOLING METHODS
The exterior water wall and roof pond systems mentioned earlier are also very effective summer
cooling strategies. In the cooling cycle (Fig. 27), insulating panels remain closed by day to reject
unwanted solar heat. The cool ponds act as "thermal sponges", absorbing room heat conducted
through the interior ceiling (metal deck) supporting them. At night panels are rolled back, exposing
the ponds to the black body of the night sky and to the cooler night air and breeze. The ponds lose
heat by radiation to the night sky and by natural convection to the air. Roof pond systems are
particularly effective in regions of low humidity and clear summer nights. The conditions exist in most
of the southern tier, where the cooling demand is greatest. If conditions are less than ideal,
augmented heat dissipation by evaporation can be integrated
The exterior water wall and roof pond systems mentioned earlier are also very effective summer
cooling strategies. In the cooling cycle (Fig. 27), insulating panels remain closed by day to reject
unwanted solar heat. The cool ponds act as "thermal sponges", absorbing room heat conducted
through the interior ceiling (metal deck) supporting them. At night panels are rolled back, exposing
the ponds to the black body of the night sky and to the cooler night air and breeze. The ponds lose
heat by radiation to the night sky and by natural convection to the air. Roof pond systems are
particularly effective in regions of low humidity and clear summer nights. The conditions exist in most
of the southern tier, where the cooling demand is greatest. If conditions are less than ideal,
augmented heat dissipation by evaporation can be integrated
Trees offer excellent natural cooling. They throw shade over the walls and
roof. They also will shade driveways, sidewalks and patios that can bounce
heat onto the motorhome or building. Since big trees give more shade than
little ones, find a site that has as many existing trees as possible.
roof. They also will shade driveways, sidewalks and patios that can bounce
heat onto the motorhome or building. Since big trees give more shade than
little ones, find a site that has as many existing trees as possible.
Outside shade screens prevent sun from entering a window. Put these
only on windows exposed to direct sunlight.
Interior window shades, such as roller shades, blinds and drapes, can
reduce heat gain. However, interior shades don't block sunlight as well as
exterior shades. Interior shades work in three ways. They reflect sunlight
back out the window before it can turn into heat. They block the
movement of hot air from the area around the window into the room.
They insulate the room from the hot surfaces of the window glass and
frame. To give you the most benefit, interior shades should:
* have a light colored surface on the side that faces the window;
* fit tightly to prevent air movement into the room;
* be made of an insulating material;
* cover the whole window.
only on windows exposed to direct sunlight.
Interior window shades, such as roller shades, blinds and drapes, can
reduce heat gain. However, interior shades don't block sunlight as well as
exterior shades. Interior shades work in three ways. They reflect sunlight
back out the window before it can turn into heat. They block the
movement of hot air from the area around the window into the room.
They insulate the room from the hot surfaces of the window glass and
frame. To give you the most benefit, interior shades should:
* have a light colored surface on the side that faces the window;
* fit tightly to prevent air movement into the room;
* be made of an insulating material;
* cover the whole window.
Awnings work like the visors on baseball caps by blocking high-angle
sunlight. On buildings, awnings can cover individual windows or sections
of outside walls. They are most effective on the south side of the building.
sunlight. On buildings, awnings can cover individual windows or sections
of outside walls. They are most effective on the south side of the building.
Natural Cooling
Natural Cooling