Published on 9th October 2009 by
Originally Posted by smc8788I'd like to see how multiple smaller fans compare to supersize ones where cases have the option for it (i.e. 2x140mm or 4x120mm).
Originally Posted by SchizoFrogThat would be a totally unfair comparison with 280x140mm2 (39200mm2) compared to 240x240mm2 (57600mm2) which would have a 46% area increase.
(Not exactly true as really you would have to work out the circumfrance area of each individual fan and then time that by 2 or 4 depending on which set up you are looking at... but you get the idea.)
Originally Posted by KyoceraThe number of tested fans is too low to give any valid conclusion;
the site here recommends ATCS 840, which has one front 230 x 30 mm fan x 1 / 700 RPM / 19 dBA ; one does not know if to change it, with which one.....
The piece on the classic dimensioned fans was great, this here is just to no avail.
Originally Posted by Otto69Bit Tech continues to use the Ghetto fan testing methodology, Until they actually get some real test equipment, and a tester who has some clue as to use it, any further "fan tests" are invalid.
Originally Posted by Otto69More to the point: this is like doing CPU heat sink tests using your finger tip as the thermometer.
Originally Posted by Otto69As I said in the thread for the last fan "test" using this method; at the very least the fans pressure has to overcome the weight of most of the bag, and of the captive air pushing back against the incoming pressurized air. NEITHER of those things should be present in an actual computer case.
Originally Posted by SchizoFrogWhy not? Does the air inside your case not push back like the rest of ours?
Instead of just complaining like little girls, why not tell us how to do it better? Oh thats right... YOU DON'T KNOW!!! So STFU!!!
Originally Posted by http://ezinearticles.com/?Fan-Calculations---Measure-Airflow-with-CFMA standard measurement of airflow indicates how many cubic feet of air passes by a stationary point in one minute. The higher the number, the more air is being forced through the system. The volumetric flow rate of a liquid or gas in cubic feet per minute equals the CFM, and one CFM equals approximately 2 liters per second.
Fan manufacturers base their measurements on a standard measurement with clean, dry air at a density of 0.075 pounds mass per cubic foot, barometric pressure at sea level of 29.92 inches of mercury, and a temperature of 70°F. These standard measurements are used to determine SCFM: Standard Cubic Feet Per Minute.
Originally Posted by http://hvac-talk.com/vbb/showthread.php?t=116330
>>Research so far indicates the "garbage bag" method of measuring system airflow at registers is actually comparable...
I've gotta ask you what is this research. I have heard of this method from a Canadian source but have never heard anything good supporting it from this forum. And I think whenever you have a concensus on this board, they tend to be right. For one thing you must measure the seconds to fill, and the precision of your stopwatch will limit the precision (and therefore accuracy) of your CFM figure. If you go ahead and do some measurements this way, I am sincerely eager to hear how it turns out! But in the meantime I have to wonder if there could be better methods.
The one super-amateur method I know of, would use a cardboard box placed over the supply vent, with a measured hole for air to exit. You need the hole large enough that it won't disrupt total airflow much, and small enough that you have a measurable pressure difference between the box and atmospheric. Then you might use a manometer to measure that pressure, and there are equations relating that to airflow. Everything has its drawbacks and this method would certainly be more complicated than the fill-a-bag method. And I have not done it myself, so who knows whether your method might be more practical.
Dwyer makes a pitot tube for use with its manometers, which could be used to measure air speed. By taking various measurements you could get a semi-good measurement of CFM, the pros have a method for this and I better let them describe it. If you are interested of course.
But to get really *good* measurements, the pros use flow hoods costing thousands and those must be calibrated frequently. I really don't think they would do this if a gas-bag method could be developed that would give good enough results.
Originally Posted by Bufo802Does it really matter if the cfm figures are completely accurate (compared to some perfect testing method) if the method provides results which are consistent and able to be compared?
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9th October 2009
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