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Measuring airflow into large electrical enclosure

Measuring airflow into large electrical enclosure

Measuring airflow into large electrical enclosure

(OP)
Hi,
I need to measure flow rate through some approx. .5 m2 inlets that supply cooling air to some large, densely packed enclosures. Flow rate is around 500-2000 cfm per inlet, driven by backward curved radial blowers making up to 700Pa.
The inlets are basically rectangular holes through the outer skin of the enclosure, covered by some low restriction filters.

How would you measure flow rate through each inlet? I was thinking about using an anemometer with some ducting to straighten out the flow. Is there a better way?

Thanks!
Jon C

RE: Measuring airflow into large electrical enclosure

If you have to do it just once I'd call a HVAC service place. Have them deal with all that quickly and easily.

If this will be on-going then go to Amazon and get a hot-wire anemometer and go that route. You'll probably need charts to tell you how much air is going thru an entire square when the pressure is known in the center, etc. They might come with a hot-wire anemometer or the duct could possibly be programmed into the instrument and it will do the calcs and give you the CFM.

Hot-wire anemometers are small and long and especially useful for ducts.

Keith Cress
kcress - http://www.flaminsystems.com

RE: Measuring airflow into large electrical enclosure

Think you could use an annubar ( pitot tube type) flow element also for this application.

RE: Measuring airflow into large electrical enclosure

Any square opening has a non uniform flow.

To measure volume you would need to measure air flow/ velocity on a grid of min 5 x 5 to create a map and allow you to average the velocity over the whole opening.

The filter will cause the flow to very and will need dp sensors to avoid a lot of flow reduction as it gradually fouls.
 

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

RE: Measuring airflow into large electrical enclosure

(OP)
Are you saying take speed measurements right at the intake? I'm not expecting flow to be perpendicular to the inlet filter as there are so many obstructions inside the enclosure. Are there anemometers that will measure air speed regardless of direction? This is why I was considering using a duct to straighten the flow but I'm not sure if that would significantly reduce the actual flow rate.
Seems ,like if I do use a duct I should measure half way along it to be most likely to measure flow that's parallel to the duct? Or is that not an issue?

RE: Measuring airflow into large electrical enclosure

Photo?

Drawing?

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

RE: Measuring airflow into large electrical enclosure

You use one of these. https://tsi.com/products/ventilation-test-instrume...

Expensive to buy, but you can rent them, or as already suggested by itsmoked hire an HVAC testing a balancing company to make the measurement.

RE: Measuring airflow into large electrical enclosure

Google says consult the annubar supplier - (Rosemount or other) for applications in rectangular ducts.

RE: Measuring airflow into large electrical enclosure

(OP)
Littleinch what are you asking for drawings of? My questions above were aimed at you re. your previous post.

RE: Measuring airflow into large electrical enclosure

(OP)
Mintjuliep, do you know of a similar hood thats good for 2000 CFM or more? Also one large enough for my .5 m2 inlets?

RE: Measuring airflow into large electrical enclosure

What the entrance looks like and size.

If yo can measure airflow with any element at 90 degrees to the entrance then you can determine overall air flow.

Whatever you do will be no better than 10-20% accurate, but better than nothing.

Or just create a small box around the entrance to force the air into a small chamber.

but we can't see what you can see.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

RE: Measuring airflow into large electrical enclosure

(OP)
Littleinch, I'm having trouble understanding your post. Could you please elaborate?

If yo can measure airflow with any element at 90 degrees to the entrance then you can determine overall air flow.
I suggested that flow is unlikely to be perpendicular to the intake (filter surface). Are you suggesting I can ignore this?

Or just create a small box around the entrance to force the air into a small chamber.
What would be the purpose of this?

Also I'm curious what the 10 to 20% accuracy statement is based on as it contradicts the spec of the equipment recommended above.

Thanks!

RE: Measuring airflow into large electrical enclosure

If litteinch had said - with a precision calibrated built for purpose device - then that range of error would be high, but with a do-it-yourself pitot-static or a handheld anemometer trying to develop a velocity profile, 10-20% is pretty good and is probably good enough.

You could get a good estimate by looking at the heat-rejection wattage and the delta-T from the inlet to the outlet knowing that a certain heat gain of the air is a function of delta-T and the mass of the air.

Delta-T will also indicate fouling of the filter as the flow restriction will lead to the heat being taken by a smaller air mass flow.

RE: Measuring airflow into large electrical enclosure

I had solved this problem similarly to the other poster's suggestions by using a hot wire anemometer. You may want to consider building a wind tunnel as well to smooth out the airflow to get better readings if you expect there will be turbulence at the point of measurement. This article may also be helpful. Best of luck.

RE: Measuring airflow into large electrical enclosure

(OP)
I had kinda hinted at this method in my OP ;)

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