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Centrifugal Blower Static Pressure

 
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doninmedford



Joined: 03 Aug 2016
Posts: 26
Location: Oregon

PostPosted: Sat Oct 14, 2017 12:23 pm    Post subject: Centrifugal Blower Static Pressure Reply with quote

I found this thread here that gives a little information on the use of the larger HVAC blowers as the main cooling fan for a chassis dyno. http://www.efi101.com/forum/viewtopic.php?t=2509

I did not want to bump an old thread, but the manufactures of the blowers give charts for horsepower draw/fan rpm/cfm at certain static pressures. My thoughts are that if the blower does not have the restriction of the ducts and vents, it's not going to be able to see any static pressures. When people build these for Dyno use I am guessing they use the lowest pressure in the table (.25" WC) to get their specs? Or is there some other advice I need to follow?
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doninmedford



Joined: 03 Aug 2016
Posts: 26
Location: Oregon

PostPosted: Thu Oct 19, 2017 7:06 pm    Post subject: Reply with quote

Instead of building something right now when there is so little info. I went ahead and got a american made 1.5 hp PPV fan for reasonable. It puts out a decent amount of air and was in fairly good shape after I cleaned the soot and tar off it. They are made for firefighters, and they move the air. I still would like to try experimenting with a HVAC blower, but this does the job.
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doninmedford



Joined: 03 Aug 2016
Posts: 26
Location: Oregon

PostPosted: Sun Jun 10, 2018 3:52 pm    Post subject: Reply with quote

Anyone have more information on putting together a scroll style blower? What air pressures are you looking for as it affects the pulley size and hp. My PPV fan actually works really well. IAT is good most runs. Just looking to add a larger fan to my setup for even better cooling. Being mobile, a 20hp requirement just is out of the question, but a 3hp 220v blower would be worth experimenting with.
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Pantera EFI



Joined: 12 Feb 2005
Posts: 1718
Location: So. California

PostPosted: Mon Jun 11, 2018 7:49 am    Post subject: Brown Boveri VTR 454D Reply with quote

Hi, I would NEED to know your flow requirement ?
MY GUESS is to use repair parts for a Brown Boveri VTR 454D.

I can supply a 20HP PMM and speed controller.

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doninmedford



Joined: 03 Aug 2016
Posts: 26
Location: Oregon

PostPosted: Tue Jun 12, 2018 10:38 am    Post subject: Reply with quote

Thank you for the feedback. I got to email with Tim May, an application engineer with Lau fans, they make a lot of the blowers used in HVAC. He did not like the idea of using a centrifugal type of air mover at all for dyno use. I even sent him the propaganda from Dastek Dyno listed in the earlier thread linked above.

Quote:
These type blowers are not usually used at free delivery, that is the highest horsepower operating condition and least efficient. An axial flow fan would be a better product for this application.

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JimK



Joined: 30 Aug 2005
Posts: 77
Location: Denver

PostPosted: Wed Jun 13, 2018 8:09 am    Post subject: Reply with quote

If you change the blower shaft speed, the air flow varies directly with the ratio of the new speed/old speed. The hp varies with the ratio of the old speed/new speed cubed, i.e. New hp = old hp x (new speed/old speed)^3
So you can easily overload the motor with speed changes. You are not concerned with the pressure rise, but it varies with the speed ratio squared.
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doninmedford



Joined: 03 Aug 2016
Posts: 26
Location: Oregon

PostPosted: Wed Jun 13, 2018 9:45 pm    Post subject: Reply with quote

Its actually a lot more complicated than that. Each centrifugal housing fan assembly that Lau Fan, and others make has a tested efficiency chart. Pulling numbers out of the air with generic formulas will be a sure miss - I was not even considering doing that. My original question was the charts do not cover free air discharge, nor does the situation show up on any of the charts, so I had no rpm and hp numbers. After emailing with the engineer at Lau, I found the reason for the lack of info on the charts for this situation is that centrifugal fans are NOT recommended for this use as there are more efficient ways to move air that is not in a duct. I sent him all the ads listed on the other thread, saying how great these fans were. He just said the point was not that they wont move air, they do its just not very efficient use of the power and there were better solutions that can move the same amount of air with lower requirements. He referred me to their axial fan engineers.
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JimK



Joined: 30 Aug 2005
Posts: 77
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PostPosted: Thu Jun 14, 2018 6:02 am    Post subject: Reply with quote

No argument with the fan guy, but for you application, he is talking way above what you need. I am a retired Professional Engineer who worked 40+ years in the electrical power plant design/installation business. The last fans I specified, approved and designed the system for were 4000 hp variable speed centrifugals. The fan shaft and wheel weight was 45000 lb with bearings 29 feet apart. These are custom designed fans and so I went thru all the performance data from several mfrs. The catalog info you get on the small fans suck and yes the efficiency is poor for moving free air. Unless you want to save a few watts, it isn't worth the effort.
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doninmedford



Joined: 03 Aug 2016
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Location: Oregon

PostPosted: Wed Jun 20, 2018 11:37 am    Post subject: Reply with quote

OK thank you for the feedback. I was really surprised to read what the engineer said because of the way the centrifugal fans were talked up here for use with a dyno. I have a PPV axial fan already. It does a good job for what it is. I will probably just pickup a second when I find them on a fire dept auction.
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doninmedford



Joined: 03 Aug 2016
Posts: 26
Location: Oregon

PostPosted: Thu Apr 25, 2019 2:47 pm    Post subject: Reply with quote

Just some fan feedback. Last year I used a tiny 1.25 hp PPV fan made by unifire. It actually did well! It was made to pressurize houses for fire fighting and is very expensive new, but I got it used. The biggest draw back was the armchair quarterbacks on social medial who know nothing about fans, bad mouthing the business because of course bigger has to be better when it comes to fans and the fan did not look like what they saw in the magazines. So this year I purchased a 30" Patterson H30A fan, also sold by different dyno companies here in the USA under their names. That thing is huge and heavy, not very mobile friendly. They are both rated at 1200 cfm. In comparison the Patterson fan shows no decrease in IAT and more air flows around the vehicle. The tiny Unifire fan can be directed so most of the air flows through the radiator. It does shut up the keyboard warriors though and with a small business word of mouth is important.
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