Q: Which of the following configurations lend themselves to becoming potentially viable applications of variable speed drives?
A. One pump feeding one user
B. One pump feeding multiple users
C. Two operating parallel pumps feeding one user
D. Two operating parallel pumps feeding multiple users
Installing a variable speed drive to operate one pump that feeds one user (Answer A) allows the variable speed drive to manipulate that flow as part of a feedback control loop. This configuration lends itself to being viable when the energy savings associated with operating with the variable speed drive sufficiently offsets the cost of the installation. Similarly, using two operating parallel pumps (Answer C) can be viable, although two variable speed drives will likely be required to operate the system.
Installing a variable speed drive to operate one pump that feeds multiple users (Answer B) allows the variable speed drive to manipulate the header pressure. This configuration may lend itself to being viable when header pressure reductions (as compared to the existing header pressure) result in energy savings that offset the cost of the installation. Similarly, using two operating parallel pumps (Answer D) can be viable while two variable speed drives will likely be required to operate the system.
Additional complicating factors
These configurations generally focus on energy savings. Making process improvements as a result of applying variable speed drives in other configurations can reduce operating costs significantly.
David W. Spitzer is a regular contributor to Flow Control magazine and a principal in Spitzer and Boyes LLC, which offers engineering, seminars, strategic, marketing consulting, distribution consulting and expert witness services for manufacturing and automation companies. Spitzer and Boyes is also the publisher of the Industrial Automation INSIDER. He has more than 40 years of experience and has written more than 10 books and 350 articles about flow measurement, instrumentation and process control.
Spitzer may be reached at 845-623- 1830 or via spitzerandboyes.com. Click on the “Products” tab to find his Consumer Guides to various flow and level measurement technologies.