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The flow is proportional to the absolute inlet pressure, so the flow in scfm would equal the C v flow coefficient if the inlet pressure were reduced to 2 psia and the outlet were connected to a vacuum with less than 1 psi absolute pressure (1.0 scfm when C v = 1.0, 2 psia input).
Ratings found in centrifugal fan performance tables and curves are based on standard cubic feet per minute (SCFM). Fan manufacturers define standard air as clean, dry air with a density of 0.075 pounds mass per cubic foot, with the atmospheric pressure at sea level of 29.92 inches of mercury and a temperature of 70°F.
Duct leakage test in the US. A duct leakage tester is a diagnostic tool designed to measure the airtightness of forced air heating, ventilating and air-conditioning (HVAC) ductwork. A duct leakage tester consists of a calibrated fan for measuring an air flow rate and a pressure sensing device to measure the pressure created by the fan flow.
Note that, in approximation, for a given value of flow volume, a step up in duct size (say from 100mm to 120mm) will reduce the friction loss by a factor of 3. Volumetric Flow Q of air at STP where friction loss per unit length Δ p / L (SI kg / m 2 / s 2 ) is, resp., 0.082, 0.245, and 0.816., for selected Nominal Duct Sizes [ 19 ] in smooth ...
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.
Some flexible duct markets prefer to avoid using flexible duct on the return air portions of HVAC systems, however flexible duct can tolerate moderate negative pressures. The UL181 test requires a negative pressure of 200 Pa. To use flexible ducting in a system, make sure to pull the duct tight so you get the full internal diameter.
Chapter 6 - Duct Systems; Chapter 7 - Combustion Air; Chapter 8 - Chimney and Vents; Chapter 9 - Installation of Specific Appliances; Chapter 10 - Boilers and Pressure Vessels; Chapter 11 - Refrigeration (Part 1: Refrigeration Systems; Part 2: Cooling Towers) Chapter 12 - Hydronics (Part 1: Steam and Water Piping; Part 2: Hydronic Panel Heating ...
Leakage area estimates can also be normalized for the size of the enclosure being tested, For example, the LEED Green Building Rating System has set an airtightness standard for multi-family dwelling units of 1.25 square inches (8.1 cm 2) of leakage area per 100 square feet (9.3 m 2) of enclosure area, to control tobacco smoke between units.
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