Yes but not in much detail TBH, we usually size the ductwork and then send the information out to a few sub-contractors.
I haven't really done much else on ductwork, I do remember a job that was 'value engineered' where instead of insulating with a thin later of phenolic insulation they used vast quantities of mineral wool instead which took up lots of space in the risers.
In message , fred writes
Must have been concentrating on the t on the end of 100
If you are talking about a duct that is the same diameter all the way, then the air must move at the same speed all the way. Otherwise at some point there will be a high or low pressure area.
If first fan gets it to 20, then the second can only get it to 40 if the diameter reduces commensurately. If it does not reduce diameter you are somehow getting air going past the first fan at 20, the second at 40 - which would need twice the amount of air!
So what stops the suction of the 2nd etc fan doing that to some degree?
Jim K
A fan has a P-Q curve, pressure/airflow.
- Fan A has max airflow X at ZERO static resistance (free air)
- Fan A has max pressure Y at ZERO airflow (blowing against a sealed duct
A duct (and terminal and prevailing wind) imposes static resistance.
- Corrugated duct has very high static resistance
- Smooth duct has much lower static resistance
Fan A will produce say 50% of max airflow in a duct. Putting 2 such fans in series may get you to 67% of max airflow, 3 in serie s getting you to 75% of max airflow.
If you want more airflow you use a mixed flow fan - &/or bigger fan - or fa n on the outside of the building (Ebay/Google, 4", 5", 6").
A mixed mode fan has both axial (high airflow) & radial (higher pressure) q ualities, but often sticking a 6-8" diameter fan on a 4-5" duct so joist de pth needs consideration.
3 fans in parallel, that is to say 3 fans supplying 3 individual ducts will get you 3x the airflow of any one... ASSUMING there is sufficient airflow at low resistance into the room! This last point is often missed (and solve d by chimneys which is not an ideal solution re mildew and so on).No...
A fan has a P-Q curve, pressure/airflow. - Fan A has max airflow X at ZERO static resistance (free air) - Fan A has max pressure Y at ZERO airflow (bl owing against a sealed duct
A duct (and terminal and prevailing wind) imposes static resistance. - Corr ugated duct has very high static resistance - Smooth duct has much lower st atic resistance
Fan A will produce say 50% of max airflow in a duct. Putting 2 such fans in series may get you to 67% of max airflow, 3 in series getting you to 75% o f max airflow.
If you want more airflow you use a mixed flow fan - &/or bigger fan - or fa n on the outside of the building (Ebay/Google, 4", 5", 6").
A mixed mode fan has both axial (high airflow) & radial (higher pressure) q ualities, but often sticking a 6-8" diameter fan on a 4-5" duct so joist de pth needs consideration.
3 fans in parallel, that is to say 3 fans supplying 3 individual ducts will get you 3x the airflow of any one... ASSUMING there is sufficient airflow at low resistance into the room! This last point is often missed (and solve d by chimneys which is not an ideal solution re mildew and so on).End quote/
Many thanks for a comprehensive answer.
If only more wiki authors were so informed.
Compliments of the season.
Jim K
After recommendation here, I bought one of these:
Admittedly not cheap, but I was amazed by how quiet it was, I had to feel the air to be sure it was running. The airflow is far better than the (failed) cheap Manrose one it replaced. It can push-fit into the pipework, and is readily removable for cleaning.
Chris
After recommendation here, I bought one of these:
Admittedly not cheap
End quote/
Tho istr even a noisy cheapie off ebay was £50 odd so not too bad
Jim K
Now that is a very good point!
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