effects of using 4" fan on 6" vent

[TurboDog]

I was wondering if I use a 4" high velocity fan like HTG's to blow air threw a 6"cool tube connected to a 6" vent(cool tube will have 4"reducer so fan can connect securely to it), what effect will that have on pressure, the vent length will be 6 feet long with 2 90 degree bends, the blower is rated at 170cfm. I want to make sure the cool tube will still have the airflow being pulled threw. when air comes out of High velocity fans it kinda "spreads" a bit right and it wont be a solid 4" stream of air will it? I want to make sure it "fills" the cool tube and has enogh force to thoroly push the hot air threw 2 90 degree bends and out the 6" duct work. please don't suggets a bigger fan as this is THE ONLY fan I will be running/can run, i simply want to know what effect running this fan will have on the above variables. Thanks for any input.

 

[nycjb]

It shouldnt be a problem, I have HTG's 4" and I had to get a speed control because this thing is LOUD and moves a lot of air, I have it at about 70% without a cool tube and Im HOPING to go lower when I get one since the fan gets nice and quiet at 50% and still blows plenty of air.

 

[messn'n'gommin']

All things being equal, going from one size fan orifice to a larger diameter duct has the benefit of less resistance for the fan to overcome and (somewhat) quieter operation of the system as a whole. Always a good idea!

But, there are a couple of other things you need to consider.

How many watts? Typically, HPS lamps emit about 30% (about 25% for MH) of energy consumption as usable light and the other 70% as heat. It will directly affect how much fan you need to use. e.g. A 1000w HPS lamp will generate about as much heat as a 700w space heater. If you can only use one fan for the whole system; it may limit how much light you can use and still maintain temps. However, something to consider for future reference, if it is used exclusively for cooling just the light on a closed circuit with its own intake and exhaust port, a smaller fan can remove a lot of heat and that translates to a smaller fan for exhausting just the cab/tent/room.

How much area of intake ports do you have to draw from for ventilation? This is related to how hard/easy the fan will have to work in order to draw cooler, fresh air to replace the expelled hot air. A 4" fan will work best at about 25/sqin of intake.

hth

 

[TurboDog]

I have 1, 1000 watt light that the 4" fan will be cooling off. The cooltube has a insulated duct attached that runs to the outside, the enclosed growing chamber has a 6"x8" intake area and the room has 2 vents that draw cool ac air in to the main room(the grow chamber is enclosed in a smaller area in the room. so the growing chamber can draw cool air in, and the fan Will be blowing air from the growing chamber threw the cool tube to the outside. so cool air enters room-then into growing tent-then threw the fan into the cool tube and out to the outside.

 

[Don Dump]

this thread probably has the answer http://www.icmag.com/ic/showthread.php?t=112862

 

[TurboDog]

thnaks

 

[qbert]

a 4" fan blows plenty of air to cool a 1kw in a tube or hood. Hooking it up to 6" duct will slow the air velocity and consequently reduce noise (most likely, and possibly lower its tone).