Fan Selection HVAC

Hi ,

the static pressure depends on diameter and total length of your duct and number of fittings ( elbows,tees,dampers,......)

you will find all these data in tables and charts for your duct

hi thanks for the reply. The pipe is 6in diameter and 1.4m high. there are three 60mm diameter outlet fittings, that are 250mm in length, and at 90 degrees to the pipe. How do i calculate the static pressure for these, or the pressure drop? Stupid question probably but i am bewildered by fluids.The duct is also vertical and made from polypropylene.

Hi ,

i'm sorry I haven't tables or charts for polypropylene ducts

I would urge you to take a look at this if you are not familar with various ideas concerning UFAD It may helpyou to consider alternatives to your concept

http://www.price-hvac.com/content/flash/ptm/ptm.asp?Section=Underfloor%20Air%20Distribution

Is it awkward? Nah that's not the word? Oh backwards engineering; that's it! But - Why? Why is the air flow rate through the plenum too low? Or is it an assumption? What would be a causation of this predicament?

So let's address the symptom and not the problem...Is it cost effective? What is the goal? Not efficiency; what then? H?

backwards.

The point of it is to provide airflow above desk level, thereby improving personal control of airflow. It is purely conceptual. the pipe is intended to provide flowrate to 3 people, hence the requirement of 360m3/h, providing 33l/s to each individual.when selecting th fan i am unsure of how to work out the static pressure for the fan characteristic curve.so any help would be sweet.just to point me in the right direction

dear ufadnewbie,

can you give a layout for your issue to explain the location of plenum,outlets ,suction side ,.....? so , what is the benefit of plenum?

The required airflow will be equal to the average velocity times the duct area. Therefore the first selection item is outlet velocity of the 6" fan. However as you increase the velocity to match the volume required the static pressure resistance will increase exponentially.

Your problem would be much easier if you picked one system of measurement to work with (SI or IP).

Since the pressure information on the fittings and configuration is not easy to come by, and since your not dealing with large size equipment, it might be simpler to build a prototype system in your lab or workshop with measurement devices and run tests at various settings. One of my suspicions is you will have to deal with fan and air velocity noise issues. Make adjustments until you are happy with the configuration, and then make the real thing.

ufadnewbie,

First correct the plenum

flow rate then provide an point of use adjustable vent to each individual.

http://tjernlund.com/retail/ductboosters.htm

http://process-equipment.globalspec.com/Industrial-Directory/booster_duct