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Actual cubic feet per minute (ACFM) is a unit of volumetric flow. It is commonly used by manufacturers of blowers and compressors. [1] This is the actual gas delivery with reference to inlet conditions, whereas cubic foot per minute (CFM) is an unqualified term and should only be used in general and never accepted as a specific definition without explanation.
Round duct is made using a continuous spiral forming machine which can make round duct in nearly any diameter when using the right forming die and to any length to suit, but the most common stock sizes range evenly from 4" to 24" (10-60 cm) with 6"-12" (15-30 cm) being most commonly used. Stock pipe is usually sold in 10' (300 cm) joints.
In 1973, in response to the 1973 oil crisis and conservation concerns, ASHRAE Standards 62-73 and 62–81) reduced required ventilation from 10 CFM (4.76 L/s) per person to 5 CFM (2.37 L/s) per person. In cold, warm, humid, or dusty climates, it is preferable to minimize ventilation with outdoor air to conserve energy, cost, or filtration.
Q = Volumetric flow rate of air in cubic feet per minute (cfm) Vol = Space volume L × W × H, in cubic feet; In metric units = where: ACPH = number of air changes per hour; higher values correspond to more ventilation; Q = Volumetric flow rate of air in liters per second (L/s)
Duct plate 3/16", or thinner, may dishpan, or make noise, and should be avoided. Rectangular duct section properties are calculated from the distance between the upper to lower duct corners of the ductwork The flanges areas are based on the size of corner angles plus duct plate width based on the plate thickness ratio of 16*t.
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.
The higher the CADR number, the more air it filters per minute for that particle size range. Consumers can use these ratings to compare air cleaners from the various manufacturers. [3] The defined particle size ranges are 0.09–1.0 μm for smoke, 0.5–3 μm for dust, and 5–11 μm for pollen. AHAM recommends following their '2/3' rule.
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.