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Construction principles, foundations PDF. This can lead to air leaking out through the walls of the room or traveling into the attic or crawlspace. Similarly, if the return flow from a room is larger than the supply flow, the room can depressurize, drawing air in from outside.
Buildings that have central return systems can experience large pressure differences when certain interior doors are closed. This HVAC design delivers air to each room, but does not have a return in each room. When a door is closed it becomes a barrier between the return — located in the main body of the house — and the supply air delivered to the closed room.
The return attempts to draw this missing air from the rest of the house, depressurizing the main body of the home and possibly causing backdrafting problems with any fireplaces, wood stoves, or other combustion appliances.
Likewise, without any local returns, the closed rooms become pressurized, driving warm, moist, interior air into the walls and ceilings, possibly leading to mold growth and even rot in the structural assemblies.
In both cases, the magnitude of these pressure differences depends on the tightness of the rooms with reference to the main body of the house and to the outside, as well as the amount of air supplied to each room. Reduce the number of holes in the building, and you reduce the amount of uncontrolled air flow.
There are only two kinds of holes in buildings: undesigned holes and designed holes. Designed holes, as the name implies, are those necessary to allow the proper flow of air, such as vents and chimneys. Undesigned holes, though, allow uncontrolled air leakage and rob a home of its efficiency and healthy environment. Undesigned holes in the home are found in the attic, walls, and floors. Any of these holes that connect to the outdoors should be adequately blocked, caulked, gasketed, or otherwise adequately sealed.
Sometimes these holes are connected to floor, wall or ceiling cavities, or to spaces under bathtubs and stairs, around chimneys, above cabinets, etc. These spaces become pathways for air to move between the inside and outside of the building. Undesigned holes should be air-sealed and blocked to control the potential spread of draft, smoke, and fire. Designed holes include any hole or system that is designed to have air passing through it in a specific direction.
Designed holes should not be blocked, sealed, restricted, or have their direction of flow reversed. When examining air flow into and out of a building, applied building science addresses three areas of concern: effects on the occupants, effects on the durability and structural integrity of the building, and effects on the energy efficiency of the building.
Improper air flow can have severe effects on the health and safety of the people in the building by promoting mold growth, spreading pollutants, and possibly creating backdrafting of combustion appliances. Negative pressure can cause backdrafting and prolonged spillage from fireplaces, gas-fired water heaters, furnaces, boilers, or any other device that uses house air for combustion. It can also cause flame roll-out from the bottom of residential water heaters and increased carbon monoxide production in both water heaters and furnaces.
During the summer months, negative pressures inside the home can draw in warm moist air from outside. When this moist air comes in contact with surfaces that are below the dew-point temperature, condensation often forms, providing an excellent breeding ground for mildew and other molds, which are known respiratory irritants.
The same is true during the winter if the house is pressurized, driving moisture-laden air out of the building. The air in a home often contains many pollutants, such as smoke, pollen, dust mites, animal dander, radon, and fumes from cleaning supplies. Particulate pollutants and volatile organic compounds VOCs are drawn from one area of the home to another by undesigned air flow. Soil gases such as radon can be drawn up from the crawlspace or basement in to the building by negative pressures.
Combustion devices and fireplaces can backdraft, causing carbon monoxide gases to enter the home. This air movement can be caused by either convection currents or by mechanical means. Air naturally rises when heated and falls when cooled; such movements are known as convection currents. These currents can occur whenever air in a building is heated or cooled in an uncontrolled fashion by improperly insulated surfaces i. Convection currents can also occur within building cavities found in the building.
Examples of this situation are:. Forced-air heating and cooling equipment is designed to move specific quantities of conditioned air throughout a building. If the air moves too quickly, it can have a noticeable cooling effect on the occupants. Proper design of HVAC equipment and ducts and proper orientation of the duct registers can help to reduce this effect. Improper air flow can draw in moist air from outside, or force moist interior air out into the walls, ceilings, and other structural assemblies.
In either case, this air-transported moisture can have serious effects on the durability of a building. Condensation forms when air with a high relative humidity RH either indoors or outdoors comes in contact with surfaces that are below the dew-point temperature.
The most effective approach to reducing air-transported moisture is to seal the building tightly against air infiltration or exfiltration. Unwanted air flow can reduce the energy efficiency of a building, even if the building is tightly sealed to the outside. Pulse and Digital Circuits by Millman and Taub. Power Electronics Handbook by Fraidoon Mazda. Control Systems Engineering. Semiconductor Optoelectronics McGraw Hill. Top 25 Strength of Materials Books Collection.
Building Science and Materials by John Elliott. Highway Engineering By S. Khanna and Justo. Signal processing and linear systems by B. The BSP Reference Guide is extremely readable and well-illustrated, a powerful resource for reminding yourself how buildings work and to fill in gaps in your knowledge.
The book was very well written. This could develop sales of higher end equipment, tools, and test equipment for us, while raising the bar for installations, resulting in less warranties for our organization to process. The industry wins, contractors win, we win, homeowners win.
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Text Resize. Building Science Principles Certificate Overview Ask yourself the following questions: Are you considering a career in green buildings, sustainability or energy efficiency? Do you already work in the residential building trades? Do you conduct home inspections?
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