hi, im trying to find out what voltage to set my ruck200l at,
i want to move only 150m2 of air at night time. does anyone know a way or a rogh giuide to workin out the resistance of spiral ducting and bends,
if i know this i can try and work it out approx using the fans charts/graphs, many thanks
Full Version: Duct resistance ,pressure drops etc,
There is no rough way to calculate resistance to air flow. Resistances are contained in pressure drop-Vs air volume flow rate graphs found in vent books, but generally only for ducting to what is called DW 144, the current spec. For all other ducting, including flexible ducting, the unit rate for a given diameter and given flow rate is specified by the manufacturer. find a trade name or stamp on the ducting and contact them.
If you can't do that, the below taken from vent graphs may be used.
I would allow 6pa per metre for 150 dia flexible ducting, at a flow rate of 150m3 hour. For the loss at each bend, I would calculate at five times the straight ducting metre rate. That is to say, each straight metre run of 150 flexi, at 150m3/hr will be 6pa, and each turn through 90 deg will be (5 * 6) 30pa.
For 200 dia flexi ducting and bends, the loss will be about 1.4pa per metre run, and for each change in direction, (5 * 1.4) 7pa.
Bends are normally calculated by using a velocity pressure factor multiplied by flow rate, that factor dependent on the whether the bend is 'tight' or slow. The above 5 times straight is adequate for a rough guide.
It is always better to get the manufacturers figures/pressure loss graph.
If you can't do that, the below taken from vent graphs may be used.
I would allow 6pa per metre for 150 dia flexible ducting, at a flow rate of 150m3 hour. For the loss at each bend, I would calculate at five times the straight ducting metre rate. That is to say, each straight metre run of 150 flexi, at 150m3/hr will be 6pa, and each turn through 90 deg will be (5 * 6) 30pa.
For 200 dia flexi ducting and bends, the loss will be about 1.4pa per metre run, and for each change in direction, (5 * 1.4) 7pa.
Bends are normally calculated by using a velocity pressure factor multiplied by flow rate, that factor dependent on the whether the bend is 'tight' or slow. The above 5 times straight is adequate for a rough guide.
It is always better to get the manufacturers figures/pressure loss graph.
QUOTE(daviie @ Oct 25 2008, 10:12 PM) 
There is no rough way to calculate resistance to air flow. Resistances are contained in pressure drop-Vs air volume flow rate graphs found in vent books, but generally only for ducting to what is called DW 144, the current spec. For all other ducting, including flexible ducting, the unit rate for a given diameter and given flow rate is specified by the manufacturer. find a trade name or stamp on the ducting and contact them.
If you can't do that, the below taken from vent graphs may be used.
I would allow 6pa per metre for 150 dia flexible ducting, at a flow rate of 150m3 hour. For the loss at each bend, I would calculate at five times the straight ducting metre rate. That is to say, each straight metre run of 150 flexi, at 150m3/hr will be 6pa, and each turn through 90 deg will be (5 * 6) 30pa.
For 200 dia flexi ducting and bends, the loss will be about 1.4pa per metre run, and for each change in direction, (5 * 1.4) 7pa.
Bends are normally calculated by using a velocity pressure factor multiplied by flow rate, that factor dependent on the whether the bend is 'tight' or slow. The above 5 times straight is adequate for a rough guide.
It is always better to get the manufacturers figures/pressure loss graph.
If you can't do that, the below taken from vent graphs may be used.
I would allow 6pa per metre for 150 dia flexible ducting, at a flow rate of 150m3 hour. For the loss at each bend, I would calculate at five times the straight ducting metre rate. That is to say, each straight metre run of 150 flexi, at 150m3/hr will be 6pa, and each turn through 90 deg will be (5 * 6) 30pa.
For 200 dia flexi ducting and bends, the loss will be about 1.4pa per metre run, and for each change in direction, (5 * 1.4) 7pa.
Bends are normally calculated by using a velocity pressure factor multiplied by flow rate, that factor dependent on the whether the bend is 'tight' or slow. The above 5 times straight is adequate for a rough guide.
It is always better to get the manufacturers figures/pressure loss graph.
thanks davie,
great info, 200mm duct, 1.4pa per meter, 7pa per bend,, that l do me, nice one
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