Or, How a Bad Hair Day Can Save You Thousands Of Dollars...
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| Airflow Pattern From An Air Curtain |
You have probably walked through a doorway some time in your
life that totally messed up your hair…you had just experienced an “air
curtain”. So why would someone want to
install one of these things if they can be so annoying? The reason, as is most often the case, is to
save money.
“Air curtains” or “air doors” have been around for
decades. You find them on some
commercial buildings up north in entry vestibules as a way to help isolate the
cold outdoors from the heated indoors.
You also find thousands of them on industrial and warehouse buildings
because of the large number of “dock doors” that are constantly being opened
and closed. Every time one of those
doors opens, the building has the potential to lose heat to the cold
outdoors…and that costs money. Most
facility managers realize this instinctively (or it was passed down from one
generation to the next) but I am not sure how many have actually tried to
calculate just how much energy and money is lost through a single dock door.
Here at Mestex we produce a number of “air curtain” products
under brand names such as King, Applied Air, and LJ Wing. All of our “air curtains” are intended for
use on the large dock or ramp doors that you find in industrial or warehouse
buildings. The purpose of this little
article, though, is to highlight the operating cost savings from using an “air
curtain” rather than to tell you which one to use. In order to do that we turned to one of our
engineering analysis tools that we employ for more complicated application
studies…Computational Fluid Dynamics, or “CFD”.
In some of our other blog articles we talked about CFD and
how it works so I won’t go into that in detail but suffice to say that we can
predict the temperature and airflow impact of HVAC equipment in a building…and
do so with surprising accuracy.
For this study we created a model of a 20,000 square foot
warehouse with a 20 foot height. We then
added a 14 foot wide by 16 foot tall dock door.
The model included R-13 wall construction and R-11 roof construction. Our target inside design temperature in
winter was set at 68 degrees F. We threw
in a few storage racks and a heating system on the opposite wall of the
building from the dock door…about as far away as we could put it. We then ran the CFD software with winter
weather conditions from Syracuse, Chicago, and Atlanta. (The little video above shows the airflow patterns in the warehouse and around the open door.)
Our CFD study showed a heating requirement of 3.5 million
btuh in Syracuse without an “air curtain” and only 2.4 million btuh with an
“air curtain”. In Chicago it was 3.75
million versus 2.5 million, and in Atlanta it was 2.25 million versus 1.75
million. You can see that the savings in
btuh were significant in each case…even in Atlanta.
Converting this into dollars and cents translates into a
savings of almost $21,000 per year in Syracuse, $19,000 dollars per year in
Chicago, and $3,600 per year in Atlanta. When you consider that a typical “air
curtain” for a 14x16 dock door only costs about $18,000 completely installed
and operational you can see why facility managers in cold climates can easily
justify the investment…I mean, who doesn’t want a 1-year payback? Even in “Hot-Lanta” the payback is 5 years
just for heating…and the concept also helps with cooling. We have also calculated the internal rate of
return with various hours per day of door opening but that analysis is too
lengthy for this already lengthy blog article.
If you want more information about the IRR or want information for your
city just contact us at www.appliedair.com
using the “contact us” selection under the “support” tab.
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