Infiltration (HVAC)
Infiltration is the unintentional or accidental introduction of outside air into a building, typically through cracks in the building envelope and through use of doors for passage.
Infiltration measures
The infiltration rate is the volumetric flow rate of outside air into a building, typically in cubic feet per minute (CFM) or liters per second (LPS). The air exchange rate, (I), is the number of interior volume air changes that occur per hour, and has units of 1/h. The air exchange rate is also known as air changes per hour (ACH).
ACH is the hourly ventilation rate, divided by the building volume. It can be calculated by multiplying the building's CFM by 60, and then dividing by the building volume. (CFM x 60)/volume
Infiltration in finished structures can often be measured directly by using tracer-gas leak testing.
Infiltration as ventilation air
In many smaller buildings, 'forced' or 'mechanical'
Controlling infiltration
Because infiltration is uncontrolled, and admits unconditioned air, it is generally considered undesirable except for ventilation air purposes. Typically, infiltration is minimized to reduce dust, to increase thermal comfort, and to decrease energy consumption. For all buildings, infiltration can be reduced via sealing cracks in a building's envelope, and for new construction or major renovations, by installing continuous air retarders. In buildings where forced ventilation is provided, their HVAC designers typically choose to slightly pressurize the buildings by admitting more outside air than exhausting so that infiltration is dramatically reduced.
Energy saving
In typical modern U.S. residences, about one-third of the
See also
- Vapor barrier
- Ventilation (architecture)
- Natural ventilation
- Indoor air quality
- Thermal comfort
- Sick building syndrome
- Heating, Ventilation and Air-Conditioning
- Psychrometrics
- Mechanical engineering
- Architectural engineering
- Green building
References
- ^ Fundamentals volume of the ASHRAE Handbook, Ch. 27, ASHRAE, Inc., 2005
- ^ Ventilation for Indoor Air Quality, ASHRAE Standard 62-89, American Society of Heating, Refrigerating and Air Conditioning Engineers, Atlanta, GA.
- ^ Ventilation for Indoor Air Quality, ASHRAE Standard 62-89, American Society of Heating, Refrigerating and Air Conditioning Engineers, Atlanta, GA.