Install Instructions

2
SELECTING THE PROPER COMMERCIAL DRYER DUCT BOOSTER DUCT SIZE
Dryers operate most efficiently when exhaust velocities between 1200-2200 feet-per-minute (FPM) are maintained. The number of
co-ducted dryers operating, exhaust fan model selection and the diameter and length of the common exhaust duct can dramati-
cally affect exhaust velocity. Follow the recommendations below to maximize the efficiency of the Tjernlund exhaust system and
connected dryers.
Over sizing the exhaust manifold will reduce velocities and allow more opportunity for lint to drop out of the exhaust stream.
Undersized or excessively long exhaust manifolds will increase drying time and operating costs. COP controller set point adjust-
ments will allow velocities to be fine tuned.
Common exhaust manifold sizing and Dryer Booster Fan selection
1. Based on the CFM total for all connected dryers find the Total Dryer CFM value in the left column of the table equal to or
greater than that CFM and determine the common manifold minimum or maximum duct diameter.
2. Trace to the right to select the Dryer Booster and determine the maximum equivalent length of common duct based upon your
choice of either the minimum or maximum duct diameter.
Example:
4 Dryers @ 225 CFM/ea.
4 x 225 = 900 Total Dryer CFM
Minimum duct diameter at 900 CFM is 9 inches
Maximum duct diameter at 900 CFM is 12 inches
Installing a common duct sized between 9” and 12” is the optimal size range for maintaining a proper velocity across all operating
conditions. Trace to the right to select the desired Dryer Booster and maximum equivalent feet of common duct based on your
duct diameter choice.
Important Common Manifold Construction Recommendations
Always install a capped length of straight pipe at least 1 pipe diameter long behind the dryer farthest from the exhaust termination
for a stable place to measure exhaust pressure. Always connect individual dryers to the common manifold using wye connectors
pointed towards the exhaust termination. Do not use straight tee connections.