VEnt a Hood says their hood is 1 1/2 times as efficient--true?

needinfo1February 4, 2013

We've had several different sales people tell us that due to its unique design VAH works at 1 1/2 times the capacity of their competitors. In other words, their 300 cfm is the equivalent of someone else's 450 cfm. Is this true? If it is, it certainly seems that if someone is interested in the lower end of the cfm spectrum so as to avoid the expense and hassle of installing make-up air, then VAH would be the way to go. Thanks.

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john_com

I'm not familiar with the numbers you mention, but they are on the right track. the VAH has no obstructions of filters which will reduce the flow rate. With the VAH, what you see is what you get. With others, you would need to calculate the inefficiencies of the filter material to determine flow rate, duct work being the same.

    Bookmark   February 4, 2013 at 9:55AM
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eleena

Not true according to a recent discussion on this forum.

FWIW, a local kitchen design company that has been in business *forever* is of the same opinion.

    Bookmark   February 4, 2013 at 10:55AM
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needinfo1

eleena--I can't get that link to work.

So, there definitely are differences of opinion here.

    Bookmark   February 4, 2013 at 11:01AM
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kaseki

Efficiency is a different kettle of fish. Flow rate (cfm) depends on the fan power and design, the losses in the baffles, ducting, transitions thereto, and house negative pressure due to insufficient make-up air.

At best, VAH claims apply only to their hood as an entity, versus someone else's fan without a hood. But all fans have a fan curve, and as the pressure losses grow, the cfm achieved is reduced.

I have never seen a fan curve from VAH, so I don't know how their fans behave when inevitable additional pressure losses are present. Some other fan with a more convex fan curve could have better flow in a given situation, even if not as good in the open air.

Properly designed fans, whether squirrel-cage, axial-propeller, or radial propeller, will at their designed operating point be similarly efficient. Power in times efficiency equals work per unit time out.

kas

    Bookmark   February 4, 2013 at 11:08AM
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needinfo1

What is squirrel cage?

    Bookmark   February 4, 2013 at 11:40AM
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eleena

OP,

I did not post a link b/c I didn't bookmark it. Just search the forum.

It is hard to explain the cage. VAH pix don't make it quite clear either, IMHO. I had to go to a showroom to look.

    Bookmark   February 4, 2013 at 1:18PM
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weedmeister

A squirrel cage fan is one that looks like that wheel that hamsters run around in. Except it is a fan.

Here is a link that might be useful: automotive squirrel cage fan

    Bookmark   February 4, 2013 at 2:45PM
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eleena

OP,

Here is the link to that thread:

http://ths.gardenweb.com/forums/load/appl/msg0120474018028.html?4

But it was kaseki who explained it there as well as in response to you.

    Bookmark   February 4, 2013 at 4:30PM
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needinfo1

eleena--
Thanks. I hadn't seen that posting.

    Bookmark   February 4, 2013 at 6:02PM
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