A ventilation method that works well even when there is very little air movement outside is called Stack Ventilation which utilizes the “stack effect” which relies on the principle that hot air rises due to its relative buoyancy creating lower pressure in the lower areas of the house which causes cold air to be sucked in through lower spaces. For Stack Ventilation to work in a residence you need plenty of low operable windows combined with high operable clerestory windows, ventilation stacks or wind scoops on or above the roof.
Night purging is a method of passive ventilation that works especially well in climates with significant temperature differentials between night and day. Typically night purging is achieved by keeping the windows closed during the day to maintain relatively cool temperatures during hot days, and opening all of the windows during the night to allow cool air to flush out the hot air that has built up throughout the day. Night purging works especially well when paired with thermal mass such as an exposed concrete floor, since the mass will remain at lower temperatures for longer periods than other materials and can help to bring down the average temperature in the house.
As insulation and glazing technology has drastically improved over the years, reliance upon passive cooling and heating strategies has become less critical to moderating the temperature of a house. A well insulated modern envelope has the ability of maintaining a constant temperature, and window and door technology has improved drastically with the introduction of double and even triple-glazed units, gas fills between panes, and Low-E films with heat and UV blocking properties. Super insulated homes combined with low air infiltration (R60 roofs, R-40 walls for example) reduce both heat gain and loss in modern homes.
The first and simplest strategies we bring to the design of every home is a combination of reducing house size, simple passive heating and cooling strategies, and good orientation on the land, along with a well insulated and sealed house that is designed in response to the local climate and site specific characteristics. Part II of this series will discuss the potential “active” or more complex mechanical-electrical systems that can be used to supplement a “sustainable house”
Josh Meharry, RA. LEED AP.
Rhodes Architecture + Light