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Rightsizing
Rooftop Equipment
Like an automobile in stop-and-go traffic, a rooftop package unit suffers
as a result of excessive cycling. Starts and stops accelerate wear and tear
on equipment, which can lead to premature failure. Compared with their
"rightsized" counterparts, oversized systems cost more, do not
dehumidify as well, use more fan power, and can have more duct leakage
because of higher duct pressure. Oversized air conditioners greatly aggravate
peak kilowatt demand on hot days. Rooftop units in smaller sizes have one
compressor and operate in an "on" or "off" mode.
Equipment usually is selected to provide the needed capacity on the hottest
afternoon of the hottest summer. Because those conditions occur infrequently,
a single compressor is more or less oversized for all conditions less severe
than maximum design. This excess capacity causes short-cycling and higher
operating costs. Dual refrigerant circuits, each with its independent
compressor, can more closely provide the right amount of cooling needed.
Unless conditions require the second circuit, only one compressor is
used—consuming less energy than a single-compressor air conditioner would
use.
The presenter:
A member of HPAC Engineering's Editorial Advisory Board,
Mike West, PhD, PE,
is a principal building-systems scientist with Advantek Consulting Inc. in
Melbourne, Fla. His expertise includes HVAC problem solving, design
consulting, and HVAC-equipment development.
The Webcast will take place Wednesday, Aug. 22, at 2 p.m. ET. It will run for
one hour and include a valuable Q & A session.
Register
Today!
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Event Title:
Rightsizing Rooftop Equipment
Date:
Wednesday, Aug. 22, 2007
Time:
2 p.m. ET / 11 a.m .PT
Duration:
60 Minutes
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