PM Engineer

Watt Are You Talking About? Part 2 – The Summer Version

by Anthony Shupenko , Jr., P.E.

June 25, 2009

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As stated in a previous blog, I am a person who looks at numbers. “Do the numbers made sense?” is a question that often bounces through my head.

This question has once again been raised – this time with full-page ads for “…a home cooling breakthrough that uses 96% less electricity than air conditioners.” Wow, I thought, no more high rates to cool my home!

Then I looked a little further at the ad – some of the people in the photos looked suspiciously like the ones in the ads last winter claiming “revolutionary” electric heaters to slash heating bills. Can it be that the same shenanigans at work?

The Web site provided in the ad listed the following engineering miracles:

* Cooling power of 80 watts (a fan).

*The system comes with four containers that hold a total of 1.45 gallons (or 12 pounds) of water. The purchasers must supply the water and put them in the refrigerator to freeze (somehow the cost of doing this is not mentioned).

*These contains are placed in the fan chamber for the cooling effect.

*The ice containers last 4 to 6 hours.

This system yields a total cooling power, based on the following calculation:

^Latent heat of ice melting; 12 lb. x 143 Btu/lb. = 1,716 Btu

^Sensible heat (say from 0°F to 75°F) = 12 x (75-0) = 900 Btu

^Total heat removal (or cooling) = 2,616 Btu

^LESS HEAT GENERATED BY FAN THAT WILL BE ADDED TO THE ROOM (NOT INCLUDED IN WEB SITE): 80 watts x 3.4 Btu/watt x 4 hours of operation to get full cooling = 1,088 Btu

^Net heat removal: 2,616 – 1,088 = 1,528 Btu

^Net heat removal rate (over 4 hours, based on rate): 1,528/4 = 382 Btu/hr.

All of this for $298 and, if you act now, a second one will be provided for free!

Unless one is cooling a closet, this amount of cooling is inconsequential, since most rooms require a cooling rate of several thousand Btu/hr.

In essence, the same can be accomplished by putting a $20 fan next to a plastic bag filled with ice cubes – wait, this can be considered retro, since that is the way it was done back in the early 1900s!

Not much of a “breakthrough” is it?

Anthony Shupenko , Jr., P.E.
shupenko@optonline.net
Anthony Shupenko, Jr., P.E., is a professional engineer in New Jersey, as well as a licensed plumbing and building inspector in the state. He has been the president of Shupenko Engineering, Inc., located in Garfield, NJ, since 1984. Firm services include commercial, industrial, and residential building inspections and evaluations; forensic engineering; and structural and mechanical-system design. Shupenko is also an adjunct instructor at the Stevens Institute of Technology’s  engineering design laboratory. Contact him at shupenko@optonline.net.

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