when does ducting become detrimental?

[daybreamer]

hey guys, having a few heat/extraction issues and one of my buddys thinks it could be the 10 metres of 6" acoustic ducting up in my attic? ive been running two 5" td silents to a y piece in the ceiling and then the acoustic duct

ive been running 1x600 hps with both fans on and still hitting 33oc!

 

[Sam the Caveman]

thats too much ducting for that type of fan

I'd cut it down to 2 meters and make sure there are no bends in it, straight duct.

 

[daybreamer]

thats too much ducting for that type of fan

I'd cut it down to 2 meters and make sure there are no bends in it, straight duct.

cool, so even tho its up int he attic and just to slow the air down its too much for the two 5's?

 

[jgrow]

Exactly what you just said, its slowing the air down. So your two 5" fans are not performing at the stated CFM with that much ducting.

 

[daybreamer]

thanks dude thats the first port of call then, reduce the duct down by half for a start,

thanks again guys

 

[Granger2]

Day,
Yes, way too much ducting, but that's not all. You've got 2 5s bottlenecking into a 6. Each 5 is nearly 20 sq in., and the 6 is less than 30. Good luck. -granger

 

[daybreamer]

does that mean theyll be fighting one another with pressure? i guessed it would help, like squeezing a hose the water comes out quicker?

 

[DiscoBiscuit]

smooth (sheet metal) ducting carries more air than flex

 

[DiscoBiscuit]

hey guys, having a few heat/extraction issues and one of my buddys thinks it could be the 10 metres of 6" acoustic ducting up in my attic? ive been running two 5" td silents to a y piece in the ceiling and then the acoustic duct

ive been running 1x600 hps with both fans on and still hitting 33oc!

If you're growing in a tent or enclosed area, you may have to increase your intake. A 6" fan is ~28 square inches. You need approximately 2x or 56 square inches of passive intake. Example, one 7" x 8" hole would work for a tent or enclosed area like a closet, etc.

 

[DiscoBiscuit]

does that mean theyll be fighting one another with pressure? i guessed it would help, like squeezing a hose the water comes out quicker?

depends on the configuration. if you're air flows from the 6" duct into the 5" Y, you're ok. The 5" Y combines for ~39 square inches and the 6" duct is less than 30

the 5" Y flowing into the 6" duct would cause drag

 

[daybreamer]

sorry, no the set up goes two tents each with a 600hps, 5" carbon filter, 5" td ilent, 1.5metres of regular duct, the y piece (which sits in the ceiling) then the 10metres of 6" acoustic duct, prior to this grow i ran 2x5" rucks with no problems but the dB rating of 2xtd's equals that of one ruck!

eta- but there was no duct in the attic jus the reg stuff to the y piece

 

[DiscoBiscuit]

You might could slow the fans speed with controllers, otherwise you have considerable back pressure from the reduction in air flow. Does the Y cause the fans to run faster and louder? This could prematurely wear out the bearing(s). Harbor freight has controllers for less than $20 each.

Do you have the tent intake flaps open? If they're not all open, try opening them all before doing anything more troublesome.

 

[festivus]

smooth (sheet metal) ducting carries more air than flex

Flex ducting with the reinforcing metal wire rib causes something called the "eddy effect". The peaks and valleys inside the duct dramatically reduce the airflow.

 

[daybreamer]

ok problem seems to be sorted, removed all but 40cms of the acoustic duct in the attic, had the 600 runnin or 7 hours with the the td-silent and cf and the max temp was 26.5 considering the ambient temp is around 20oC im pretty pleased! thanks for all the advice guys : )

 

[Granger2]

I'm unclear as to why you need to combine them with a y. You'll get much better exhaust by not combining them. -granger

 

[nugghead]

Agree combining the streams makes little sense. Anything that creates turbulence in the flow is bad. Trying to combine two 5" ducts into one 6" duct means that two laminar flow streams, each with a cross sectional area of 25 square inches, have to try to combine into a single stream with a cross sectional area of 36 square inches. That won't work well; as the two streams combine they will jostle each other and create areas of high and low pressure: turbulence. Your fans' energy is now being used to create turbulence instead of pushing laminar flow.

If the receiver duct was bigger than the sum of both input ducts, there would be less turbulence - the so-called "white Nile, blue Nile" effect where two laminar flows run next to each other, never mixing. In practice this would mean changing out your 6" duct (36 square inches) for an 8" duct (64 square inches). It is simpler just to run two separate ducts in my opinion.

Turns also create turbulence and disrupt laminar flow; the sharper they are, the worse it is. Two 45 degree turns separated by a short straight run are better than one 90 degree turn; three 30 degree turns with two short straights in between can be even better. Turbulence worsens not only efficency but also contributes noise, which it seems like is also an issue for you.

If this post was annoying, just ignore it; I'm trying to get up to fifty posts.

 

[daybreamer]

the y piece is because im in a rental house and thought one hole is easier to conceal/hide than two if i get an inspection, also easier to repair when we move out!