Air Duct Elbow Equivalent Length

The sum of all equivalent lengths of fittings used and the measured distances of all pipe and duct from room terminal to the air handler should be calculated for each conditioned room.

Air duct elbow equivalent length. If the installer uses the 4 or 5 piece elbow instead with 5 feet less equivalent length the actual duct system will be less restrictive than the designed duct system at least in that part. From the return grille to the supply register in that run it adds the lengths of the straight runs and the effective lengths of all the. Refer to table 2 3 for duct thicknesses and reinforcement methods changes to 2012 edition as follows. The weakness of the equivalent length method is that.

The two largest values i e. Ordinary heating ventilating and air conditioning duct systems read air pressures at 0 4 psi or less often much less. 23 offset starting collar 10 el no. δh 0 109136 q 1 9 d e 5 02 1.

Duct classification standard duct pressure classification tables found in the as 4254 such as low medium or high pressure as4254 explains duct thicknesses sealing reinforcement and functional requirements. The strength of the equivalent length method is that it is very simple to calculate. The longest supply and the longest return runs are added together to create a total called the critical path. It shows the duct layout with all vents fittings air flows and duct sizes.

Fittings such as elbows tees and valves represent a significant component of the pressure loss in most pipe systems. Q air volume flow cfm cubic feet per minute. A common duct pressure of 0 25 inches water column is equal to 0 25 divided by 27 7 in wc psi 0 009. From table a 2 the equivalent round size is 9 9 inches.

Air flow dynamics duct sizing reference guide supply or return duct size capacity 09 to 10 pressure drop per 100 el cfm round no. Typo circulation should be circular example. The total effective length tel is the sum of all those fitting equivalent lengths plus the lengths of straight duct. 1 psi equals 27 7 inches of water gauge.

20 straight starting collar 35 el no. D e equivalent duct diameter inches. 120sc snap collar round 35 el. Use the friction chart at 1000 cfm in 9 9 inch diameter to friction loss is 0 4 in water 100 ft.

To find those duct sizes the software we use rightsuite universal calculates the effective length of the most restrictive run. Duct system design guide first edition 2003 mcgill airflow corporation mcgill airflow corporation one mission park groveport ohio 43125 duct system design. Equivalent duct sizes for same friction loss from. The major loss or friction loss in a circular duct in galvanized steel with turbulent flow can for imperial units be expressed.

δh friction or head loss inches water gauge 100 ft of duct. For rectangular ducts the equivalent diameter must be calculated.