Duct Sizing??? 1

[chbtech]

Help!!!!

I'm trying to design a simple duct system for a room that is 15' W X 25' L X 18' H. This room has 3 large Sullair LS1250 air cooled air compressors in it. I want to use the fans from the compressors to push the hot air in the winter into a the large factory adjacent to the compressor room and outside in the summer. The other catch is the duct work will need to have a relief in the case that if the compressor room gets to cold it will keep some of the hot air in the room to raise the compressor room temperature. Each compressor produces 5,200 cfm and 135,000 BTU/HR. I need to find out how large to size the ducts and the maximum lengths I can run so I don't load the compressor fans to much. I'm waiting on the fan data but I need to know what calculations to use to determine my duct size once I have the fan data???[\b]

 

[imok2]

This may be of use to you:

http://www.connel.com/cgi-bin/airduct.pl

 

[trashcanman]

First of all, what do you mean by, "the fans from the compressors"? Are these fans attached to the compressor? What is their function? If they are for cooling the compressors, how are you going to use them? What CFM & static pressure do they produce? Can ductwork be attached to them?

Assuming they are available for use, do a heat loss calculation of your compressor room. See if the waste heat generated by the compressors is enough to heat the space (it probably is). Assuming you have more than adequate heat for the compressor room, the system can be designed as follows:
Use motorized dampers, controlled by thermostats. If the minimum space temperature in the compressor room rises above a setpoint (say 68 Deg.F), AND the temperature in the factory is also below its setpoint,then the motorized damper directs the hot air from the room to the factory. If the factory themostat is satisfied, the damper directs the air outside though a discharge louver or wall cap or roof cap.

The duct sizing depends upon the static pressure available from the "compressor fans" (I am not really clear on what you mean). Generally, 0.10"/100' should work (unless you have to route the duct hundreds of feet).

Please clarify.

 

[imok2]

Axial flow propeller fans are not made to provide much flow with attached duct work beause propeller fans are used to move high air volume against low or no static pressure so unless the duct is very short and the static pressure is low you may not have enough air to meet the requirements and if you don't move the required amount of air across the heat xchanger then you have compressor over heat I'm not saying it can't be done only that you take precautions.

 

[chbtech]

Thanks for all your help!

 

[compressorprofessor]

Call your Sullair representative. Most manufacturers offer recommendations such as "the ducting must be sized so that there is only .12 inches of water drop in or out of the air ducts" or may be able to give you a recommended layout.
CompressorProfessor

http://www.compressoroils.com

 

[chicopee]

As a quick estimate- with an heat input of 405,000 btu/hr(135000x3), delat T= 20 dF, specific heat= .24 btu/lbm-dF and air density =.079Lb/ cuft, air flow at 1000 fpm, then calculated square duct size=4.2'x4.2'. Double your air velocity to 2000 fpm, calculated square duct size=3'x3'.