ZEN Industries' February 2012
e-Newsletter |
Understanding HVAC Air Flow Efficiencies
Pressure Loss with Duct Size Changes
For
those calculating HVAC duct sizes the equation Quantity = Area X
Velocity should be familiar. By using it you can calculate duct
size changes while maintaining the same quantity (CFM) and velocity
(FPM) in the duct.
Unfortunately, the equation does not take pressure loss due to friction
into account.
Pressure loss is the result of friction as the air moves along the
inside of the duct. Keep air quantity and velocity equal and a
duct with greater duct/air contact area will suffer greater friction
loss.
How
to compensate? While Q = A X V remains an important tool, there's
more to consider, and SNIPS Magazine has covered what you need to know
in an informative article titled
Understanding airflow: ductwork sizing explained.
SNIPS Magazine delivers in-depth, insightful journalism that covers the
sheet metal industry, heating, air conditioning, ventilation, indoor air
quality, architectural sheet metal, and more.
Learn why round duct has the least friction loss, why next to round duct
square duct is best, and why you should avoid using duct with an aspect
ratio greater than 3 to 1.
Read the
Snips Magazine article and then
contact ZEN
Industries to learn how we can better meet your HVAC project needs.
Joining Equivalent Sized Duct
Challenges
in Joining Round to Square Duct
Sometimes the job site and the engineering specs just don't see eye to
eye.
What happens when the duct specified by the engineer simply won't fit in
the ceiling space? You may be forced to consider switching from
the preferred round duct to rectangular duct under the circumstance.
To keep the air flow calculations valid, you consider that the
cross-sectional area of the rectangular substitution needs to remain
within 1% of the area of the original round duct. That should work
out OK, right?
Unfortunately, this is another instance where friction loss rears its
ugly head. The greater the surface area of the duct, the greater
the friction loss.
To get out of this sticky situation correctly, you need to consider both
the math and your contract very carefully. First, you need a
better formula when calculating the equivalent diameter of rectangular
duct. Second, you want to get written approval of the size change
before fabricating the replacement duct.
To walk through the math and review a few good examples, you can read
the article
Taking the mystery out of equivalent size of duct
on the Snips Magazine website.
At ZEN Industries, our goal is to help your business succeed. No matter
how big or small your project, ZEN can provide all or part of your HVAC
needs.
No matter how big or small your project:
ZEN Industries provides all or part of your HVAC
needs. HVAC ductwork manufactured according to your schedule,
meeting 3rd Edition 2005 SMACNA standards. Contact Heather Rodehaver -
Business Development Representative at 877-600-0274.
Success is about Service
Success in our business is about service. The quality of our HVAC duct
work is of the highest caliber and our price competitive with the best
in the industry. Nonetheless, quality and price are default items today
in sheet metal fabrication. They give us access to the playing field.
Service is where ZEN Industries Inc. gains its edge, and service means
people - it's about our experienced personnel and the relationships we
build with each and every customer.
Contact ZEN Industries today.
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