Mechanical or Forced Ventilation

"Mechanical" or "forced" ventilation is used to control indoor air quality. Excess humidity, odors, and contaminants can often be controlled via dilution or replacement with outside air. But in humid climates, much energy is required to remove excess moisture from ventilation air.

Kitchens and bathrooms typically have mechanical exhaust to control odors and sometimes humidity. Factors in the design of such systems include the flow rate (which is a function of the fan speed and exhaust vent size) and noise level. If the ductings for the fans traverse unheated space, the ducting should be insulated as well to prevent condensation on the ducting. Direct drive fans are available for many applications, and can reduce maintenance needs.

Heat recovery ventilation systems employ heat exchangers to recover some heat from exhausted air, to preheat the incoming outside air.

Ceiling fans and table/floor fans circulate air within a room for the purpose of reducing the perceived temperature because of evaporation of perspirations on the skin of the occupants. Because hot air rises, ceiling fans may be used to keep a room warmer in the winter by circulating the warm stratified air from the ceiling to the floor. Ceiling fans do not provide ventilation as defined as the introduction of outside air

ВАРІАНТ III

Why Ventilate?

Fresh air is needed inside the home to help eliminate odors and pollutants harmful to human health. Fresh air also helps eliminate excessive moisture that harms the building structure and furnishings and is the source of mold and mildew growth. It is also important to replace the air that is expelled out of the home by kitchen range fans, clothes dryers, and other exhaust equipment. Failure to replace exhaust air decreases air pressure inside the home, causing outside air to be pulled into the home through leaks and other openings. In Minnesota, where many homes are fairly air tight, this depressurization can result in back drafting of the furnace and other combustion appliances: carbon monoxide and other dangerous gases are pulled back into the house rather than being expelled up the chimney. Although open windows are often relied on to supply fresh air, in a climate like Minnesota's this is not practical year round. Here, homes are "built tight" to ensure comfort and keep monthly energy bills as low as possible, especially during the winter. Although tightening up a home to prevent air leaks and then bringing in outdoor air through ventilation may seem like a contradiction, it is not. Tightening is essential for comfort and energy efficiency; controlled ventilation is necessary to ensure that the proper amount of fresh air is brought indoors in all seasons.

ВАРІАНТ IV

Recycled Building Materials

In an effort to lessen waste, many builders are seeking to reuse materials which would otherwise end up as trash. Many structures, especially in urban areas, can be effectively rehabilitated, saving immense amounts of new construction costs, maintaining important cultural links, as well as avoiding massive amounts of landfill waste. Other structures can be carefully dismantled, saving lumber, bricks and other recyclables for new projects. High quality old-growth timber has been salvaged from old barns, which is then used for new homes. Waste wood can be reused to create a number of board products. Many of these, unfortunately, depend on toxic binders, but efforts to make healthy alternatives continue. Additionally, sawdust and recycled plastic have been used to create long-lasting lumber substitutes. Efforts in these areas have been spearheaded by the Wood Reduction Clearinghouse. Windows, doors and other fixtures can be refurbished and reused, saving valuable architectural heritage and creating unique resources for owner-builders. Others use "junk" in innovative ways.

The advantage of this approach is the obvious environmental benefits as well as the aesthetic possibilities. Disadvantages include the time, labor and cost to build with old treasures because of refurbishment, special detailing necessary, and the time spent to find, dismantle and transport these resources.

ВАРІАНТ V

Wood

Wood is an ideal building material: strong, easily worked and beautiful. Its major disadvantage is that its use is unsustainable, with current clear-cutting practices leading to widespread deforestation. Natural builders are seeking alternatives to conventional stick-frame construction, where wood is used indiscriminately, and have begun to use wood in new ways.

Building with exposed timber-frames surrounded by materials such as straw-clay or straw bales can take advantage of the beauty and structure of wood while eliminating its unnecessary use. Innovations in bentwood truss construction in Nova Scotia shows ways to create strong members using smaller diameter trees. Other builders are finding uses for driftwood, and irregularly shaped trees which would otherwise go to waste. Innovative use of scraps and sawdust make the best use of wood for panels, hybrid products, etc. In addition, increased popularity of non-wood construction systems can lead to reduced wood use and ecosystem rehabilitation.

Appropriate timber use is closely tied to sustainable forestry practices. Selective cutting can provide ongoing sources of material while saving delicate ecosystems. Using smaller diameter or unmilled lumber can save large old-growth trees; innovative uses of non-traditional species or young, second growth trees can also be an effective strategy.