Superior indoor air quality, greater thermal comfort, lower heating costs, and lower air conditioning costs are achieved by sealing air leaks in the building envelope and using a heat recovery ventilator , energy recovery ventilator, or one of the lower-cost ventilation systems.
Mechanical Ventilation - Controlled air exchange through a ventilation system
Natural Ventilation - Intentional air exchange through open doors and windows
Infiltration - Uncontrolled air exchange through unintentional openings driven by wind, pressure, and temperature differences
Infiltration is a function of the buildings air tightness, wind, pressure and ambient temperature. If the building is constructed poorly with a large number of small openings, there will be a high amount of air flowing through the house.
- Wind pressure on the exterior walls will cause increased infiltration as well. Wind will produce a positive pressure on the windward side of the building, forcing air into the building. At the same time, a negative pressure is produced on the leeward side, which forces air out of the building.
- Temperature differences between conditioned space and ambient produce pressure gradients at the top and bottom of external walls. This is called the Stack Effect. If the internal temperature is greater than ambient (heating season), the warm internal air will rise and produce a higher pressure at the top of the wall compared to the outdoor pressure. This pressure differential will force air out the top of the building. At the same time, there is a lower pressure at the bottom, and air is forced in at the bottom of the building. The air pressure is equal at the midway point on the exterior wall, this is called the neutral point. The taller the building, the more pronounced the stack effect will be. The opposite will occur during the cooling season.
If all indoor air pollutants had an unpleasant smell, you and I could easily recognize and avoid them.
The average American spends about 90% of the time indoors. Air pollution in the average American home, as measured by the EPA, is usually 2 to 5 times worse than outdoors because of the chemicals we use indoors and the entry of unfiltered air.
The American Lung Association and the EPA recommend filtering the incoming fresh air to block entry of dust and pollen. Well-sealed buildings are more comfortable and less expensive to heat, air condition, and ventilate because you, not the wind, get to control your fresh air supply.
Poor indoor air quality causes or aggravates 50% of all illnesses and can lead to a host of health problems for people of all ages.
Mechanical ventilation can make it safe to seal unwanted air leaks and install as much insulation as you want. Adequate insulation helps to control indoor temperature and humidity.
Beginning in 2004, ASHRAE Standard 62.1 "Ventilation for Acceptable Indoor Air Quality" requires proper pressurization of buildings. Maintaining a small positive pressure, relative to the outdoors, limits the entrance of outdoor moisture and is a very common strategy to prevent mold and mildew formation in a building.
The American Society of Heating, Refrigerating and Air Conditioning Engineers (ASHRAE) develops national consensus standards. ASHRAE's Internet address is www.ASHRAE.org
The eave vents on the underside of roof overhangs gradually become clogged and reduce essential attic ventilation.
Eave vents should be checked at least every five years. Clogged eave vents should be cleaned or replaced.
Building codes typically require a net free ventilating area equal to 1/300 of the total area to be ventilated, one-half of the ventilation to be provided in the upper portion of the space to be ventilated with the balance provided by eave or cornice vents.
Houses Need a Breath of Fresh Air
Donald Pellerin
Home Inspection
Many modern homes are sealed tighter than a drum. While that is a good thing for
anyone trying to stay warm in the winter and cool in the summer, it also means
such a house will have no fresh air.
To avoid "sick house syndrome" and other problems cause by stale and
contaminated indoor air, many well sealed homes now employ HRV (Heat Recovery
Ventilators), resulting in lower energy bills and eliminating poor indoor air
quality.
To enlarge the picture, click
on it.
HRV systems bring fresh air in from the outside, circulate this fresh air
throughout the house at the same time heating or cooling this air as required
using a heat exchanger. Such systems usually operate year round, revving up when
the air in the house is unusually humid.
A common mistake made by homeowners with such systems is turning the system off
thinking the system loses precious heat, or that it's cooling the house too
much.
Fresh air is important for the health and comfort of the inhabitants. But it is
also necessary for the safe operation of combustion appliances such as gas/oil
furnaces, gas water heaters and fireplaces. A frequent cause of deadly carbon
monoxide gas is incomplete combustion due to an inadequate supply of oxygen.
It is also vital household air be flushed to get rid of pollutants that built up
and irritate humans and even threaten the health of people living in homes
lacking proper air circulation. These irritants/contaminants may originate in
building materials, furniture fabrics, cooking odors and yes, the family pet.
Some contaminants, such as carbon monoxide, radon gas, old formaldehyde,
tobacco, and even dust and smoke can become deadly.
The only sure way to have fresh air is to have god ventilation, even more so in
today's highly insulated, sealed virtually air-tight (R-2000) homes.
In winter, HRVs extract the heat from the stale air being exhausted from the
house and use it to heat the incoming fresh, outside cold air. It takes less
effort and fuel for the furnace to heat this fresh air up to room temperature.
In summer, heat is transferred from the warm incoming air to the outgoing air,
so the air conditioner has less work to do. HRVs are necessary in today's
air-tight homes, and may be a good idea for older homes where these older homes
have had added insulation, installed energy efficient doors and windows and
plugged and sealed all cracks and crevices found.
It is important these HRVs function properly and be well balanced. If the system
does not function as intended, either due to dirty filters, blocked ductworks,
or blocked airflow, this may result in a pressure difference causing serious
problems.
These HRVs are excellent devices for our North American homes. They do require
regular maintenance. If properly installed, properly maintained, and left to
function as intended, they can greatly improve the air in the home, reduce the
cost of energy, resulting in a safer and healthier home to live in. Proper
ventilation is the key word.