Airflow measurement

[Bernie Kopfer]

I recently enclosed my V-3000 into a closet lined with sound board and made it airtight. Obtained more than 10db reduction in noise!!!! Able to measure accurately with a professional sound meter I borrowed from a Audiologist friend. But i got to wondering if the rubber mat lined baffle was big enough to not impede airflow. Now I need some way of measuring airflow at a machine with the closet closed and with it open. Does anyone know of a easy way to do this or about a [cheap] flow meter? Thanks

[David L Morse]

Acquire or fabricate (easy!) a manometer. Make a port in your duct at a convenient spot not too close to the machine of interest. Pressure drop is proportional to the square of airflow. Take pressure readings with the door open and then closed. The square root of the ratio of the two pressures is the ratio of the two airflows. For example, door open reads -2.0"water and door closed is -1.8"water. (-1.8)/(-2.0) = 0.9. The square root of 0.9 is 0.95 so the baffle costs you 5% of your flow.

[John Lanciani]

Where are you located? I have everything you need to test your entire system, if you're nearby you're welcome to borrow it.

[Bernie Kopfer]

John Lanciani;2093105]Where are you located? I have everything you need to test your entire system, if you're nearby you're welcome to borrow it.

Hi John, I reside in Wenatchee, Wa. Great place tolive, work and retire!

[Bernie Kopfer]

I'll find a manometer and do as you outline. Thanks for the info, that's what makes this forum so grEAT

[Lee Schierer]

No need for a fancy meter. Open the door and start you DC. Then move the door as if to close it without engaging the latch. Let go of the door. Does the door swing open when you let go? Does the door get sucked shut? If the answer to both questions is NO, then you have no restriction to air flow.

[Chris Parks]

Lee beat me to it, keep it simple, I did this very thing with a customer's installation a few days ago to demonstrate that he needed to install vents in the enclosure.

[David L Morse]

No need for a fancy meter. Open the door and start you DC. Then move the door as if to close it without engaging the latch. Let go of the door. Does the door swing open when you let go? Does the door get sucked shut? If the answer to both questions is NO, then you have no restriction to air flow.
Good trick! I love that kind of use of available resources. Of course with his sound baffle (muffler?) we would expect some pressure loss and so might want a more quantitative answer than restriction or no restriction. Let's "calibrate" the door. Let's say we have 1"water pressure loss through the baffle and a standard 30" x 80" door. The door is 16.7sqft and 1"water is 5.2psf thus we have a total force on the center of the door of 1x16.7x5.2=87lb. At the edge of the door that's about 43lb. The total system pressure is approximately the zero flow pressure which, for the V3000, is 11.75" So, to estimate the flow loss estimate (or borrow your wife's kitchen scale and hold it against the door) the the amount of force, in pounds, it takes to keep the door shut. Divide by 43, divide by 11.75. Subtract from 1 and take the square root. That's the ratio of the flow with the door close to with the door open.

For example, say your door is 24"x80" and you measure 3lb to keep it closed. First your door "calibration": 24x80/144*5.2=69.3lb. Divide by two since the hinges carry half the force giving 34.7lb/(inH2O). Now 3/34.7/11.75=0.00736 1-.00736=.99264 SQRT(.99264)=.996 That's less that half a percent loss, certainly not noticeable. From the other direction, let's say you want to verify no more than 5% loss. .95x.95=.9025 1-.9025=.0975 .0975x11.75x34.7=39.75lb I don't know what you weigh but you'll probably have to lean in a bit to keep that closed. Oh, and DON'T use your wife's kitchen scale if you have to push that hard.

Also, if the outlet is in the door be sure to subtract it's area from the door's when you calculate the door factor.

[Michael W. Clark]

Two additional ways:
1) If you still have access to the sound meter, measure the sound in the room under both conditions. A change would indicate a change in flow.

2) check the amp draw on the fan motor for both situations.

Mike