cross and stack ventilation strategies

Natural ventilation uses windows and other openings to bring outside fresh air into the house - typically during the coolest parts of the night.

Natural ventilation can remove heat from our homes for free or at a very small fraction of the cost of air conditioners. They are great for energy savings.

Cross ventilationBesides cross ventilation - involving windows and openings in opposite sides of the house (image at right) - you can also consider stack or convective ventilation (image below).

Strategies with cross and Stack Ventilation

Consider placing window fans in upstairs rooms. It will draw off the heat and push the heat outdoors; the inside hot air will tend to rise to the top of the home, and you just have to open a door or a window in the first floor, on the shady side of the house, to draw fresh air into it (that’s convective or stack Stack Ventilationventilation).

Obviously, you can also create stack ventilation in single-storey homes, and you don't have necessarily to use windows-fans.

You just have to have high and low openings, in your house: in favorable conditions, breezes and cool air will enter through the lower openings, while the inside air is exhausted through the upper openings.

Note: In hot climates you may need dedicated openings (inlets, outlets, clerestories...) to provide convective air movements

Strategies for Two-Storey homes

Stack ventilation is mostly used in two-story homes, and is based on the tendency of hot air to rise. Typically, it uses windows (or other openings) in the windy side of the house, to bring outside fresh air into it, and high windows (or other openings) on the leeward side, to exhaust stale air.

You just have to find the right openings and do some experiments to figure out what works best. Experiment with different patterns of window venting, until you find the most effective one for moving outside fresh air through your rooms. You will have to leave some windows open, and to keep other windows closed.

Sophisticated Stack Ventilation Methods for Hot Climates

Besides these common strategies, there are other more sophisticated methods to induce stack ventilation, in hotter climates; they are especially useful when the outside air is not fresh enough, or when there are no breezes or they are rare, and theu can use turbine vents, solar chimneys and trombe walls. To improve the results of stack ventilation, the inlet and the outlet vents/openings should be located on opposite corners. The outlet openings should also be significantly larger than those bringing fresh air in (50 to 100% more). Pay also attention to the height difference: the greater the difference, the more effective the ventilation can be…

Turbine vents

New turbine vents are cheap and not very different from millenary units.

They are installed at the top of the roof, and use wind and high breezes to spin and to exhaust inside air; they are mostly used in hot and windy or breezy areas.

New units are all-aluminum and rust-free, and require very little or no maintenance.

Though cheap, durable and easy to install, they may be rather useless in non-windy weather conditions (they require minimum wind speeds to be effective: 5 mph or more) and may provide too much ventilation in windy periods.

Solar ChimneyInducing stack ventilation with Solar Chimneys, Trombe walls and attached sunrooms

A solar chimney is a narrow structure built on top of the house, exposed to the sun.

The chimney uses glass and heat absorbing materials to gather solar heat and generate high temperatures, able to create a strong updraft of air in the chimney, that will exhaust the stale air from the rooms below; and as it happens, fresh air will enter through any windows or other openings at the bottom of the house.

1) The air current can be reversed in cold-sunny days, in cold and moderate climates, to heat the house.
2) Attached sunrooms and trombe walls use the same mechanism and principles of thermal chimneys. For technical details: AIA Advanced Cooling Architectural Solutions for Hot Climates and Arizona Solar Center Cooling Strategies.

Underground air chamber

Bringing underground cooling into the home

Another convective cooling method relies on fresh air created with the help of underground chambers (ventilation tubes buried deep enough in the ground). See image.

To be effective, these systems require a proper design: the intake end of the tubes should be properly screened and placed in a shady location; the tubes should be buried at a proper depth; the ground should have convenient temperatures; the soil should not pose drainage problems...




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