ESTIMATING SAVINGS TO JUSTIFY A VSD
ESTIMATING SAVINGS TO JUSTIFY A VSD
(OP)
Is there a "rule of thumb" or a formula used to estimate energy savings (by implementing a VSD) based on motor loading?
I was given the following formula to calculate the predicted energy use with a VSD but it makes no sense to me (I have no idea where it came from)
Energy used = (full load power / VSD rated eff) * (% rated speed)^3 * (# operation hours)
* I'm not 100% sure what the (% rated speed) is......or where to get the (VSD rated eff).
I'm looking at several pumping systems inorder to determine if implementing VSD technology is feasilbe and economical. I am lacking most of the necessary system and pump information in order to make accurate energy saving calculations.
I'm a recent graduate (way over his head) and would greatly appreciate your help.
I was given the following formula to calculate the predicted energy use with a VSD but it makes no sense to me (I have no idea where it came from)
Energy used = (full load power / VSD rated eff) * (% rated speed)^3 * (# operation hours)
* I'm not 100% sure what the (% rated speed) is......or where to get the (VSD rated eff).
I'm looking at several pumping systems inorder to determine if implementing VSD technology is feasilbe and economical. I am lacking most of the necessary system and pump information in order to make accurate energy saving calculations.
I'm a recent graduate (way over his head) and would greatly appreciate your help.





RE: ESTIMATING SAVINGS TO JUSTIFY A VSD
RE: ESTIMATING SAVINGS TO JUSTIFY A VSD
Another resource: Adjustable Speed Drives Applications Guide, TR-101140, pg 106, Electric Power Research Institute, c. 1992
RE: ESTIMATING SAVINGS TO JUSTIFY A VSD
For typical pump or fan applications, the energy savings results from operating the punmp at a reduced speed and not throwing away energy across a throttling valve or damper.
The motor will also be less efficient when operating from a VFD than operating across the line.
I haven't looked lately, but many of the drive manufacturers have some "tools" that will provide a rough estimate of possible energy savings for pump and fan applications. Actual savings will probably be somewhat less than these programs indicate.
RE: ESTIMATING SAVINGS TO JUSTIFY A VSD
One precaution: I've seen people estimate the new speed based soley on the required flow using the affinity law. Many processes have a minumum pressure requirement for adequate damper/valve control or system distribution requirements. If so, this needs to be considered dring these calculations. It's possible that the drive speed that's adequate for your flow requirement won't meet your minimum pressure requirement.
RE: ESTIMATING SAVINGS TO JUSTIFY A VSD
There are lot of case studies on VSD implementation in www.greenbusinesscentre.com. Please go thro.