In dust collection, one of the critical decisions to be made is in selecting a fan. With many different ways to go about this, we've distilled 23 years of experience and hundreds of successful installations to put together our approach and these recommendations when it comes to selecting your next fan.
We prefer to use a highly efficient, direct-driven fan installed on the clean side without system errors with a premium efficiency inverter duty motor and preferably without an inlet box with a piezometer ring for measurement of air volume.
As a first step, calculate Total Air Volume for all workstations connected to the system: use 4,500 FPM drop air velocity for general dust for smaller machines; use 6,000 FPM for all CNC machines, as well as all machines producing a high volume of sawdust. For other materials use recommended air velocity drops per the latest version of the Industrial Ventilation - A Manual of Recommended Practice (by ACGIH).
Next, ask the customer if he is planning to add, remove, replace, or relocate workstations within the next 12 months. Include these planned changes in air volume calculations.
Then calculate total pressure losses at Peak Air Volume (usually 100% of Design Air volume as calculated in the previous step) to the last workstation in the duct system = highest pressure losses in the system. Include hood losses based on information from the manufacturer or measured value from the same or similar workstation, duct system losses calculated at peak air volume, abort gate losses, dirty filter losses, duct and elbows between filter and fan inlet, fan silencer losses (if used), return air losses (if used). Be sure to include all pressure losses in the calculations. If the fan is to be installed without an inlet box there must be a minimum of three to five duct diameters between the elbow and fan inlet, and the same at the fan outlet to eliminate “system error”. Use evasé (stack) at the fan outlet for best fan efficiency.
Ask the supplier of the fan to propose a direct driven fan for air volume not less than 85% of total design air volume and for calculated total pressure losses at elevation ASL (Above Sea Level in feet) where the fan will be installed, and at the highest temperature, the fan will be operated. If the customer or installer of the fan prefers the fan with the inlet box, the supplier must provide the fan curves with the inlet box. We prefer a fan where the pressure on the left side of the fan curve from the standard operating point is higher than at the operating point.
If the supplier cannot provide the fan curve with the inlet box - Ecogate will not use this fan. If a customer is requesting the fan for lower air volume than 85% of the total design air volume - we will need written confirmation of such a request to proceed.
Author: Ales Litomisky