Variable Freq Drive on a Fan?
Variable Freq Drive on a Fan?
(OP)
Is there a significant energy savings when installing a VFD on a variable pitch axial fan? The folks at the VFD company tell me this would be similar to having a fixed blade fan and inlet guide vanes, but I suspect they're opinion is a little slanted.
Is there an easy way to calculate this?
Thanks!
Is there an easy way to calculate this?
Thanks!





RE: Variable Freq Drive on a Fan?
I am reading them myself.
http://www.saftronics.com/pdf_fils/CaseStudy/CS_VFD_001.pdf
http://www.greenbusinesscentre.com/casestudies/paper/Paper-Case%20Study%2011-Installation%20of%20VFD%20in%20place%20of%20VFC%20in.pdf
http://www.drives.com/industry/default.asp?np=/industry/HVAC/ESP.htm
My company (Siemens Building Technologies) recently evaluated a customer site for a Variable Volume, Variable Pressure program. If you email me, robert.okamura@siemens.com I will put you in contact with an engineer. When properly implemented, the savings equates to about $50 per horsepower each month.
RE: Variable Freq Drive on a Fan?
RE: Variable Freq Drive on a Fan?
Energy savings for fan and pump applications using VFDs are very well documented for HVAC applications. Generally, energy savings will pay for the installed cost of the VFD within one year.
Suggest you deal with a vendor that has a significant presence in your local HVAC market, local support is very important.
RE: Variable Freq Drive on a Fan?
In general, I would prefer to use VSDs wherever possible. There are drive losses as mentioned above, but the basic fan laws say that if you start with a 50 HP fan and cut the speed in half, the power required will reduce to 6.25 HP (a cubic relationship).
Without diving too deep on this and if I were to make a decision based on current knowlege, I would first fix the blade pitch to the optimum efficiency angle and set the motor sheave to give the optimum RPM at maximum anticipated system flow. Then I would use a VSD to control the fan to maintain the right static pressure in the duct to account for varying conditions.
Gut feel is that variable pitch is a lower level application that could cover up design sloppiness - VSD does likewise, but with more first cost and a more substantial energy savings potential.