Air Duct Elbow Equivalent Length

20 straight starting collar 35 el no.

Air duct elbow equivalent length.

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. D e equivalent duct diameter inches. The total effective length tel is the sum of all those fitting equivalent lengths plus the lengths of straight duct.

12 x 7 rectangular 1000 cfm solution. 120sc snap collar round 35 el. The weakness of the equivalent length method is that. The longest supply and the longest return runs are added together to create a total called the critical path.

Equivalent lengths plenum duct fittings no. Q air volume flow cfm cubic feet per minute. From table a 2 the equivalent round size is 9 9 inches. 1 psi equals 27 7 inches of water gauge.

For rectangular ducts the equivalent diameter must be calculated. Use the friction chart at 1000 cfm in 9 9 inch diameter to friction loss is 0 4 in water 100 ft. Duct system design guide first edition 2003 mcgill airflow corporation mcgill airflow corporation one mission park groveport ohio 43125 duct system design. This article details the calculation of pressure losses through pipe fittings and some minor equipment using the equivalent length method.

Refer to table 2 3 for duct thicknesses and reinforcement methods changes to 2012 edition as follows. Equivalent duct sizes for same friction loss from. 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. It shows the duct layout with all vents fittings air flows and duct sizes.

The two largest values i e. 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. Fittings such as elbows tees and valves represent a significant component of the pressure loss in most pipe systems. 23 offset starting collar 10 el no.

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. The major loss or friction loss in a circular duct in galvanized steel with turbulent flow can for imperial units be expressed. δh 0 109136 q 1 9 d e 5 02 1. Ordinary heating ventilating and air conditioning duct systems read air pressures at 0 4 psi or less often much less.

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. The strength of the equivalent length method is that it is very simple to calculate.