Originally Posted by
Rich Harman
I'm not going to argue your experiences, but I am confident that your reasoning is flawed - since it is in conflict with know physical properties. Restricting a duct will increase velocity but it will reduce efficiency and cfm. A larger inlet (and ducting) would not require a larger blower to draw the same cfm. Just the opposite, the same blower will evacuate more air with a larger duct and inlet. That is just physics.
Gravograph may very well have designed a better cabinet. I know my machine's designer has put zero effort into making it evacuate smoke efficiently - it is a box with a hole in it where you hook up a tube, lots of room for improvement there.
I agree, that scenario would not provide a benefit. You would need to replace the entire 4" line going to the blower with 6" to realize the increased efficiency.
Actually high velocity air distribution systems exist, in older homes or a building where space for ductwork is extremely limited they use PCV or steel tubing about 2 inches in diameter to deliver the air to the rooms. The outlets or supply registers are usually installed in the corner of the room discharging the air, out of direct contact with the occupants. Its also common practice to reduce the inlets in exhaust systems to pull the air in rapidly and in a certain direction. After the reduced inlet the duct is the normal size for the calculated CfM.
Retired Guy- Central Iowa.HVAC/R , Cloudray Galvo Fiber , -Windows 10