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The relationship between pressure and leakage air flow rate is defined by the power law between the airflow rate and the pressure difference across the building envelope as follows: [16] q L =C L ∆p n. where: q L is the volumetric leakage airflow rate expressed in m 3 h −1; C L is the air leakage coefficient expressed in m 3 h −1 Pa −n
There are two major systems to classify ductwork airtightness, one based on European standards, the other based on ASHRAE standard 90.1-2010.Both are based on the leakage airflow rate at a given ductwork pressure divided by the product of the ductwork surface area and the same ductwork pressure raised to the power 0.65.
For residential buildings, which mostly rely on infiltration for meeting their ventilation needs, a common ventilation rate measure is the air change rate (or air changes per hour): the hourly ventilation rate divided by the volume of the space (I or ACH; units of 1/h). During the winter, ACH may range from 0.50 to 0.41 in a tightly air-sealed ...
Since passively designed buildings are essentially air-tight, the rate of air change can be optimized and carefully controlled at about 0.4 air changes per hour. All ventilation ducts are insulated and sealed against leakage. Some passive house builders promote the use of earth warming tubes. The tubes are typically around 200 millimetres (7.9 ...
Rooftop HVAC unit with view of fresh-air intake vent Ventilation duct with outlet diffuser vent. These are installed throughout a building to move air in or out of rooms. In the middle is a damper to open and close the vent to allow more or less air to enter the space. The control circuit in a household HVAC installation.
As the interior air dewpoint temperature is an important basis for such rules, buildings with high interior humidities during cold weather (e.g., museums, swimming pools, humidified or poorly ventilated airtight homes) may require different rules, as can buildings with drier interior environments (e.g., highly ventilated buildings and warehouses).
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Ventilation is present in buildings mainly for air quality reasons. It can be used additionally to remove both excess heat gains, as well as increase the velocity of the air and thereby widen the thermal comfort range. [3] Ventilative cooling is assessed by long-term evaluation indices. [4]
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