November 30, 2011

Present-Worth Comparisons

Engineering Economics Revision Article Series

Net present worth (NPW) or Net present value (NPV) is the difference between the present worths of benefits and costs of an engineering decision. It is the most widely used present-worth model.

Illustrative Problem

A single underground transmission circuit is needed immediately, and load studies indicate the need for a second circuit in 6 years. If provision is made for a second conduit when the conduit for the first circuit is installed, there will be no future need for reopening, trenching, backfillng, and repaving.

the cost of installing a single circuit wiht minimum preparation for the eventual second circuit is $850,000. the installation of the second circuit will be considered to cost $800,000 at the end of year 6 in order to be in operation by the beginning of year 7. If the second circuit is installed immediately, the total cost will be $1.4 million.

Constant annual operating and maintenance costs of the circuits are 8 percent of the first cost. The average life of a circuit is 20 years. The required rate of return on such investments is 10 percent before taxes.

To take a decision, Comparison of the deferred investment with the immediate investment needs to be made.
(Exercise Problem 3.25, Riggs)

Engineering Economics, 4th Edition, James L. Riggs, David D. Bedworth, and Sabah U. Randhawa, McGraw Hill, New York, 1996

Updated 21.4.2012

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