Letters to the Editor

No More GiantsI can't help but to express my thoughts regarding August's "Giants Report."I am against these kind of rankings because most of the time they are misleading and do not reflect actual firm status. More so, they are totally unnecessary and useless.If we want to classify or rate engineering companies, we should find different methods to do so—one in which the result can be...

10/01/2001


No More Giants

I can't help but to express my thoughts regarding August's "Giants Report."

I am against these kind of rankings because most of the time they are misleading and do not reflect actual firm status. More so, they are totally unnecessary and useless.

If we want to classify or rate engineering companies, we should find different methods to do so—one in which the result can be used by the public for a good purpose.

For example, why not base the rating on the number of claims received? Or perhaps an annual engineering competition could be conducted, such as designing a 30,000-sq.-ft. medical facility, including a research lab, office, cafeteria, work shop and fitness center. The team that completes the project with the least amount of time and with the most accurate set of drawing wins. Let us know, where and when!

It is sad to see firms rated based on revenue. Some may rank high, despite the fact that their work may be defective or has been defective—believe me we really know our competitors!

Here's another good rating method: ask clients what they think of the work performed and the quality of services.

In addition, when comparing my firm to those cited in the Detroit metro area, I discovered, according to your results, that if we divided the total revenue per employee, the result is plus or minus $100,000 per employee. This is the average revenue of sales for my firm, yet we were not mentioned.

I strongly believe that engineering is a serious science, and a team should not be picked based on its marketing capabilities or how successful they are at taking a client out to the golf course.

An engineering team should be picked based on performance, knowledge and integrity. Accordingly, this was not reflected in your report. Rather your report undermined the excellent work of good people who offer a lot more to their clients.

FABRIZIO PESCE, President and CEO, Engineering Specialty Group, Redford, Mich.

Editor's reply: We agree that "Giants" rankings aren't necessarily the only, or best, way to rate firms or even projects for that matter, but they have become a regular staple of our magazine, and something many of our readers look forward to seeing. CSE tries to be very fair in creating numbers that mean something, by breaking revenues down to reflect the M/E community, as opposed to a firm's overall revenues which may include architectural, structural, environmental or other work. But your idea is duly noted. I don't think it's feasible to conduct an engineering competition—I don't think anyone would put in the time to be frank—but we will certainly try to think of another way to examine top firms that, in the future, we can perhaps run as a companion piece. We're certainly open to suggestions.

Math is off

In the August Specifier's Notebook, "Do the Math: Efficient Motors Alone Don't Add Up," it looks like the author (Ken Lovorn, P.E., Lovorn Engineering) didn't do the math:

A 10-hp motor driving 10 hp at the shaft—fully loaded—with a 92.8% efficiency would draw 8.04 kW total: (10 hp) x (.746 kW/hp) x (1/.928) = 8.04kW.

The lower efficiency version (.89 efficiency) would draw 8.38 kW: (10 hp) x (.746 kW/hp) x (1/.89).

It appears that the author used a 10-kW motor to base his calculations rather than a 10-hp motor. Otherwise his ideas make perfect sense.

PAT BUNN, P.E., Matrix Engineering, Spartanburg, S.C.

Correct Calculations?

Do the Math: Efficient Motors Alone Don't Add Up," was surprising, as the author did not appear to do the proper calculations.

He states that the standard 10-hp motor uses 10.4 kW of electricity and only 1.17 kW will be lost to heat due to motor inefficiencies. My book shows that 1 hp = 745.7 watts or 0.7457 kW. Thus a 100% efficient motor would draw only 10 x 0.7457 = 7.457 kW of electricity. Thus, the true efficiency of the motor is not the 89% as stated in the second paragraph, but 7.457/10.4 = 0.717, or 71.7%. Thus, the waste motor heat would be 10,400 - 7,457 = 2,943 watts.

Since this shows a large amount of losses, the waste heat may also be detrimental to other adjacent hardware.

The author then speaks of using a more efficient pump to do the task. This would increase the efficiency of the pump from 50% to about 66%, resulting in a savings of 1,700 watts .

As an engineer who tests pumps, I would say that he would have to be very careful in selecting the right pump to increase the efficiency. If the duty were constant—same head and flow—the task is relatively straightforward. However, higher efficiency pumps typically run faster and tend to wear out more quickly, ultimately meaning that they're less reliable and produce a higher life-cycle cost.

Lost reliability may not make up for pump savings.

In general, higher speed pumps cannot be turned down as much, i.e. they don't work well unless the flow is above 70%.

BILL PHALEN, Palo Verde Nuclear Generating Station Engineering Services, Inservice Testing Group, Phoenix

Author's response: Both of these letters contain a similar flaw that is typically seen with most mechanical engineers and numerous others, i.e. a one horsepower motor does not utilize 746 watts! In short, 746 watts is the theoretical equivalent of 1 hp, but in reality, a 1-hp motor requires 2.1 amps at 460 volts— or about 1,540 watts—and a 10-hp motor uses 14 amps at 460 volts. With a 0.92 power factor, the 10-hp motor will require 14 amps x 460 volts x 1.732 x .92 or 10,261 watts (See table 430-150 of the 1999 NEC under the 460-volt column).





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