Natural Cooling & Ventilation
Finding the Whole-House Fan That Fits
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It doesn't make much sense to use an air conditioner to cool the air in a home when the outside air is cooler than the inside. So in areas with hot summer days and cool nights, people often use whole-house fans to clear out hot indoor air once the outside temperature drops below about 80 F. High-velocity whole-house cooling fans operate at night during summer months to cool the house. These whole-house cooling fans should not be confused with low-velocity whole-house ventilation fans, which operate continuously to provide fresh air and to control levels of indoor polllutants.
The dramatic cooling potential of whole-house fans has been well established (see "Florida Cooling, the Natural Way," HE Nov/Dec '91, p. 32). Whole-house fans are installed in the ceiling, in an opening that is cut into the attic. They flush indoor air out through the attic, replacing it with outside air drawn in through the open windows. Residents turn on the fan and open windows when the outside temperature drops below the inside temperature, and for best results, they leave the fan on for several hours--preferably overnight. This cools the house down almost to the outside temperature and also flushes built-up heat (much of which would otherwise find its way back into the home) out of the attic.
Finding the Whole-House Fan That Fits |
How to Stay Cool in the Hot Desert
When the thermometer starts to hit 90 F nearly every day, even though "it is a dry heat" as we say here in the desert , we start thinking seriously about ways to stay cool. More than 14 years ago when we were planning to build a renewable energy powered home, cooling our home was the big question.
We had no doubt our new home, to be constructed on a 20 acre hilltop near Vail, Arizona, would be powered with wind and solar. We chose the site with wind power in mind. The domestic hot water system would be a passive solar system. We would use solar for space heating the structure, but how do we cool the home using alternative energy?
How to Stay Cool in the Hot Desert |
Innovative Design Eliminates Cooling Equipment
Davis, California is hot--with a summer design temperature of 103 degrees F. So, researchers at Pacific Gas & Electric Co. made a bold move when they proposed to build an experimental house without an air conditioner. The project was called ACT Squared.
"The goal was to apply an integrated package of the latest technologies to a house design to see how far we could go with energy efficiency," says Lance Elberling, research associate at PG&E. "The result was a building shell so effective at resisting summer heat gain that no air conditioning equipment was required."
Designers at Davis Energy Group were hired to help. They started with an energy package that complied with California's Title 24 energy code. Then, they evaluated 86 energy efficiency measures. Twenty-seven of these were selected for the project. The first demonstration house was built in Davis in 1993. Another house was completed in Rockland, California early this year.
Innovative Design Eliminates Cooling Equipment |
Maximize Natural Ventilation
Often windows required for view and day-lighting are not in appropriate locations for effective natural ventilation. Here, it may be appropriate to incorporate operable vents specifically located and designed to admit controlled amounts of ventilation air.
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Natural Cooling
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.
Natural Cooling |
Natural Ventilation- World Building Design Guide
Almost all historic buildings were ventilated naturally, although many of these have been compromised by the addition of partition walls and mechanical systems.
With an increased awareness of the cost and environmental impacts of energy use, natural ventilation has become an increasingly attractive method for reducing energy use and cost and for providing acceptable indoor environmental quality and maintaining a healthy, comfortable, and productive indoor climate rather than the more prevailing approach of using mechanical ventilation. In favorable climates and buildings types, natural ventilation can be used as an alternative to air-conditioning plants, saving 10%-30% of total energy consumption.
Natural ventilation systems rely on pressure differences to move fresh air through buildings. Pressure differences can be caused by wind or the buoyancy effect created by temperature differences or differences in humidity.
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Passive Air Conditioning
A cool tower requires no blowers or fans to move the cool air. The only power required is for a small 12 volt DC pump to circulate water over the cooler pads. Below you will find three different designs for cool towers in a graphic format. In general all three work on the same principles.
Passive Air Conditioning |
Which Passive Cooling Strategy Is Right for You?
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Before refrigeration technology first appeared, people kept cool using natural methods: breezes flowing through windows, water evaporating from springs and fountains as well as large amounts of stone and earth absorbing daytime heat. These ideas were developed over thousands of years as integral parts of building design. Today they are called "passive cooling." Ironically, passive cooling is considered an "alternative" to mechanical cooling that requires complicated refrigeration systems. By employing passive cooling techniques into modern buildings, you can eliminate mechanical cooling or at least reduce the size and cost of the equipment.
Passive cooling is based on the interaction of the building and its surroundings. Before adopting a passive cooling strategy, you must be sure that it matches your local climate.
In his book Sun, Wind and Light, G.Z. Brown identifies four passive cooling strategies: natural ventilation, evaporative cooling, high thermal mass and high thermal mass with night ventilation. (See the sidebar for descriptions of these strategies.) All these passive cooling strategies rely on daily changes in temperature and relative humidity. You can identify the passive cooling strategies that are appropriate for your building site by using a bioclimatic chart.
Which Passive Cooling Strategy Is Right for You? |
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