Air Duct Elbow Equivalent Length

From table a 2 the equivalent round size is 9 9 inches.

Air duct elbow equivalent length.

12 x 7 rectangular 1000 cfm solution. 20 straight starting collar 35 el no. This article details the calculation of pressure losses through pipe fittings and some minor equipment using the equivalent length method. Air flow dynamics duct sizing reference guide supply or return duct size capacity 09 to 10 pressure drop per 100 el cfm round no.

A common duct pressure of 0 25 inches water column is equal to 0 25 divided by 27 7 in wc psi 0 009. Ordinary heating ventilating and air conditioning duct systems read air pressures at 0 4 psi or less often much less. The strength of the equivalent length method is that it is very simple to calculate. Equivalent duct sizes for same friction loss from.

Fittings such as elbows tees and valves represent a significant component of the pressure loss in most pipe systems. Equivalent lengths plenum duct fittings no. For rectangular ducts the equivalent diameter must be calculated. 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 longest supply and the longest return runs are added together to create a total called the critical path. δh friction or head loss inches water gauge 100 ft of duct. 23 offset starting collar 10 el no. D e equivalent duct diameter inches.

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. The total effective length tel is the sum of all those fitting equivalent lengths plus the lengths of straight duct. The weakness of the equivalent length method is that. Use the friction chart at 1000 cfm in 9 9 inch diameter to friction loss is 0 4 in water 100 ft.

Q air volume flow cfm cubic feet per minute. δh 0 109136 q 1 9 d e 5 02 1. 120sc snap collar round 35 el. It shows the duct layout with all vents fittings air flows and duct sizes.

Refer to table 2 3 for duct thicknesses and reinforcement methods changes to 2012 edition as follows. 1 psi equals 27 7 inches of water gauge. 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. Duct system design guide first edition 2003 mcgill airflow corporation mcgill airflow corporation one mission park groveport ohio 43125 duct system design.

The major loss or friction loss in a circular duct in galvanized steel with turbulent flow can for imperial units be expressed. The two largest values i e.