Calculating Duct Sizes

you can use a ductulater which is some thing like a sliderule to calculate duct sizes you can buy one from Trane USA .

May I suggest that you become a member of a professional association like ASHRAE or SMACNA?

There you will get useful information, books, training courses, links to suppliers of design software, tips, and so on.

You can't design a duct just using a software. Unless you fully understand the theory and practice of air movement and duct design, any help you might get from design software can easily lead you to disappointing results.

Mario

first if you know about the air movement and basic design thats the way if
you get the knowledge .

In addition to the other references mentioned, you can go to www.acgih.org where you will find the book Industrial Ventilation, now in its 25th edition, I believe. Many ventilation distribution systems have been designed with its simple equations. The more complete equations are, as mentioned above, available from ASHRAE and SMCNA. Have FUN.

With this being a library you will want to be sure there is no noise introduce. You would probably want the velocity to be in the 600 to 900 fpm range. That plus your cfm will get you started on the selection. You will want to get a ductulator if possible.

In a perfect world all this duct calculating works, but in practice it has several drawbacks, the biggest is in the designers and builders who build stuff that can't be ducted to flow well. Having been in the remodeling business, I can't tell you how many times I had to fix badly flowing AC/Heat systems that were supposedly designed by a specialist. It takes more than theory. You have to install what your calculations say and then modify for practibility. This may mean oversizing or undersizing different sections because of the air flow problems inherent to the project that can't be seen on paper. It also means when it says it needs 10 square feet of intake, it doesn't mean have a 10 square foot hole necked down to 3 square feet. duh! If you have a Westerly facing room at the far end of a house in Texas, with no trees for shade, it doesn't mean you keep a 50' long, 4 inch duct to cool it. You have to think of a house or building as a living entity. They breathe and you have to figure out how they do it best and help them. Roy Blizzard - Alphaterraengineering.com

Your library may have a copy of Ashrae's Handbook "Fundamentals" which has a chapter on duct design. The ductilator similarly takes rectangular duct dimensions and determines the equivalent round duct dimension and pressure loss for a given air volume and standard length. The Handbook has considerable information of transitions and elbow pressure drops.

The maximum recommended velocities for ducts in a library are:

Main supply 2000 fpm (feet/minute)

Main return 1500

Branch supply 1600

Branch return 1200

For a library, I would seriously consider sizing supply branches for no more than 1000 fpm, absolute max. You'll notice the air noise if any faster. Also, ensure the duct is internal (liner) insulation, even the inside of the return duct, which should have two blind 90 deg transitions prior to entering equipment.

Try a Google search and you are bound to find at least one free or free-trial download of software that will provide the same information as a "ductulator," but if not, find your nearest Commercial Trane (the HVAC equipment company) office and call them, ask if they will give you one.

Go to Bacharach site and they have a calculator maybe US $ 5.oo for duct sizing, Plus velocity/ cfm meters too.These are used for duct sizing