Letters: Reader Feedback

Observations on VFDs In "Saving Energy and Water with VFDs" (CSE 2/06, p. 57) author Jeff Lovelace uses the cube of the horse power to determine the reduction in energy. This may be true in a perfect world, but in applications with closed-loop pumping and VAV air handlers, it's not true, since one needs to maintain a pressure.

04/01/2006


Observations on VFDs

In "Saving Energy and Water with VFDs" (CSE 2/06, p. 57) author Jeff Lovelace uses the cube of the horse power to determine the reduction in energy. This may be true in a perfect world, but in applications with closed-loop pumping and VAV air handlers, it's not true, since one needs to maintain a pressure. On many chilled-water applications you're lucky to achieve two instead of the three in theory. VAV applications are better in the 2.4 to 2.6 range. It is possible to improve performance at lower speeds by reducing the system pressures at lower loads as a chilled-water delta pressure reset schedule or for duct static. So to avoid confusion, cubing is not universally applicable. The reality can be shocking if you are basing your decision on a system payback and you miss the mark because of the application limitations.

LEONARD ROZEKE CUBE, INC., BOULDER, COLO.

Jeff Lovelace responds:

Mr. Rozek is correct in the applications he mentions. These types of applications cannot be adjusted in the same way a simple water pumping system can. Again, you can contact your local motor manufacturer or the U.S. Dept. of Energy. Both offer several free software programs and articles to help you reduce energy costs in your particular application. My article was targeted to pumping water to homes/businesses using the graphs and calculations directly from DOE's software.

Daylighting and retail

In the article "Shopping Smarts" (CSE 2/06, p. 38) Turner Construction's Rod Wille comments that "...studies have shown that shoppers tend to buy more in a daylit environment, as sunlight contributes positively to their mood, and the natural light lends greater appeal to merchandise." In addition, Arup's Alisdair McGregor makes a similar statement: "Customers don't enjoy being flooded with undifferentiating fluorescent lights. We've found that it's not a good environment for people to be in for a long time, and it doesn't help sales."

Is it possible to get access to these studies, as well as information supporting Mr. McGregor's comments?

SHAWN E. MEYER, TARGET CORPORATION, MINNEAPOLIS

Alisdair McGregor responds:

There are two studies that I am aware of, both conducted by Heschong-Mahone. The first has the often-quoted statement that there was a 40% increase in sales due to daylighting. The second is more comprehensive and uses better filters to filter out other factors affecting sales. The conclusion was that sales increases with daylighting ranged from 8% to 40%.





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