Infiltration is the introduction of accidental or intentional intentional air into the building, usually through cracks in the building envelope and through the use of doors for travel. Infiltration is sometimes called air leakage . Air leakage out of the building, intentionally or not, is called exfiltration . Infiltration is caused by wind, negative pressure from the building, and by known buoyancy forces generally as a stack effect.
Video Infiltration (HVAC)
Infiltration size
The infiltration rate is the volumetric flow rate of external air into the building, usually in cubic feet per minute (CFM) or liters per second (LPS). The exchange rate air , ( I ), is the amount of interior air volume changes that occur hourly, and has units of 1/h. The air exchange rate is also known as air change per hour ( ACH ).
ACH is the rate of ventilation every hour, divided by the volume of the building. This can be calculated by multiplying the building CFM by 60, and then dividing it by the volume of the building. (CFM x 60)/volume
The infiltration in the finished structure can often be measured directly by testing the gas tracer.
Maps Infiltration (HVAC)
Infiltration as air ventilation
In many smaller buildings, 'forced' or 'mechanical' ventilation is not used to introduce air vents. By contrast, natural ventilation, through open windows and other openings, fans, and infiltration is used to provide air vents. Typically, at least one-third of air changes per hour are considered minimum. ASHRAE Standard 62.2 was adopted in 2004; this explains the air vent requirements for low-rise occupancy. The standard specifies that forced ventilation is required at home with infiltration of less than 0.35 ACH. This is usually done with a heat recovery vent or exhaust fan that runs constantly or periodically.
Controlling infiltration
Because infiltration is uncontrolled, and acknowledging unconditioned air, it is generally considered undesirable except for ventilation air purposes. Typically, infiltration is minimized to reduce dust, to improve thermal comfort, and to reduce energy consumption. For all buildings, infiltration can be reduced through sealing cracks in building envelopes, and for new construction or major renovations, by installing sustainable air retarders. In buildings where forced ventilation is provided, their HVAC designers typically choose to slightly tap the buildings by admitting more air outside than tiring so that infiltration dramatically diminishes.
Energy savings
In typical US modern residences, about one-third of HVAC energy consumption is caused by infiltration. The other third is ground contact, and the remainder is to heat losses and profits through other windows, walls, and thermal loads . Thus, reducing infiltration can result in significant energy savings, with rapid returns. In cold climates, with a 15 MPH wind, residence often has an air exchange rate of from 1.0 to 1.5 ACH, far exceeding the air vent requirement and hence is called loose construction . It is easy to reduce the infiltration rate to less than 1.0 ACH. Smoke candles and penetrating door tests can help identify less obvious leaks. The Weatherization article describes methods for further energy savings. If infiltration is reduced below 0.35 ACH, it is recommended that mechanical ventilation (usually exhaust fan or heat recovery ventilation) is implemented.
See also
References
Source of the article : Wikipedia
0 Comments