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Author Topic: Electric cooling fans for bus engine  (Read 2836 times)
bevans6
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« Reply #30 on: April 10, 2014, 06:29:31 AM »

Clifford, I was assuming that the cooling system was a stand-alone system and the alternator was dedicated to it, but of course there is no reason it wouldn't also run the AC.  At the same time the AC on these buses is different from anything I have ever seen, a big roof-mount package.  I have to think the reasoning and payback is in fuel savings and lower emissions plus being able to specify a lower power engine to obtain the same performance.  Modern manufacturers are highly competitive when it comes to long term costs.  I think that system could be very low maintenance, to be honest.  Just an alternator, a controller - both are highly proven technology - and 8 fans.  8 fans gives great redundancy, they are swappable in minutes and they are new on Ebay for $300 each.

I know that when I spoke to people who put S-50's in MC-9's they were able to cool that engine with one stock MC-9 radiator.  My understanding is that CNG engines run hotter than 4 stroke engines, so they might be in the middle between a 4 stroke diesel and a 2 stroke in terms of how much cooling they need.

Edit:  I went in and read the powerpoint presentation in the link I posted earlier.  Kind of neat to see how they have engineered it.  They document 4% to 10% fuel savings depending on the fleet, and $2,000 - $4000 reduced maintenance cost compared to hydraulic fans annually per bus.  Fun to learn new things!

Brian
« Last Edit: April 10, 2014, 06:46:39 AM by bevans6 » Logged

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« Reply #31 on: April 21, 2014, 11:01:19 PM »

Just want to share my experience of a working electric fan bus.

Can the work? Sure, but only for buses with smaller engines and low heat rejection - 6-71 and 6V71s. Unless you are willing to go for a relatively expensive system like the one shown by Brian.

So what's my setup? A radiator from an F350 (7.3 PSD) and two sets of fans of a Nissan Altima. Most people would be laughing thinking that would never work, but living in BC dealing with one hill climb after another I can tell you it works flawlessly in my 27,000 lbs bus.

Sure, a 250hp F350 has a fan of roughly 20 hp. But, big but, it's designed to work with 3 sets of heat exchangers stacked in series - the intercooler, AC condenser, and finally that rad. The air is already hot by the time it hits the rad, and the fan has to overcome the resistance of 3 layers. Where as my air is nice fresh cool air, and the fans has a single two-row fin worth of resistance.

Some simple fluids math would tell you I need less than a tenth the power of the F350. And I was proven right. Even on sustained 6 - 10% climbs in summer, my fans rarely even hit high speed. In the worst case, I do have a set of misters.

Why did I do it? I had no choice. The factory fan was long gone, and the previous owners already had a set of electric fans on the original copper rad. That didn't work so well because the factory rad was 4" thick, and electric fans are not very good at static pressure. By going with a much thinner F350 aluminum rad, I solves that problem.
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chessie4905
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« Reply #32 on: April 22, 2014, 04:10:41 AM »

   Is this setup in a school bus with a front mount radiator?
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« Reply #33 on: April 22, 2014, 10:32:59 PM »

No, it's a 35' Prevost with a side mount radiator. There are louvers / semi-scoop on the side. At a 50 mph slow cruise in cool weather, natural draft is enough to cool the engine.

At higher speeds / hotter weather the fans kick in roughly once every 3 - 5 minutes for about 15 - 20 seconds. I can tell by watching the ammeter.
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bevans6
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« Reply #34 on: April 23, 2014, 02:37:11 AM »

After studying the details of the engineered system I became of the opinion that electric cooling fans can indeed work for us, but with caveats.  The biggest one is that electric fans are unlikely to work with the stock radiator(s).  You need to increase the cooling capacity and lower the airflow resistance of the radiator as one step in the conversion.  Then you need good natural airflow - in the nose or at the rear side are both natural high pressure points, and the engine compartment can be a nice low pressure area to dump the hot air into.  Very good shrouding will help a lot.  Then you need good fans, and enough electricity.  I'm no longer as against the idea as I was.

Brian
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1980 MCI MC-5C, 8V-71T from a M-110 self propelled howitzer
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« Reply #35 on: April 23, 2014, 07:00:18 AM »

I am convinced keeping the fan belt system intact is the most reasonable thing to do, but had my OTR heater/AC 24 volt fan motor worked, I would have tried to fit it to the squirrel cage engine cooling fans, or use the fans attached to it, to get maximum cfm, even in city traffic at low rpm, lvmci...
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MCI5A 8V71 Allison MT643
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« Reply #36 on: June 07, 2014, 08:32:40 PM »

Well I'm new here but I'll take a chance and add to this thread...

I researched the same thing because my rig (not a bus) has a hydraulic motor driven and I hate the thing.  It's so loud with hydraulic motor noise, and surely pulling more hp than a direct drive.

What I found can be seen here: http://www.electricfanengineering.com/app_truck_turbine_electric_fans.html

They seemed confident in my application (which has a front mounted radiator).

For reference, these things weigh about 60lbs vs some of the other lightweight solutions mentioned in this thread.
They are designed for over the road trucks.

In case you're wondering, the one for my 6-71 is about a grand, which if it saved fuel, might be worth it.

Cheers!
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TomC
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« Reply #37 on: June 09, 2014, 12:05:43 PM »

That electric system is only for front ram radiators and for engines that don't overheat. Good Luck, TomC
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Tom & Donna Christman. '77 AMGeneral 10240B; 8V-71TATAIC V730.
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« Reply #38 on: June 09, 2014, 03:42:25 PM »

That electric system is only for front ram radiators and for engines that don't overheat. Good Luck, TomC

True. 
Being unfamiliar with buses, are almost all of them pushers with rear or side radiators?
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oldmansax
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« Reply #39 on: June 09, 2014, 05:02:38 PM »

True. 
Being unfamiliar with buses, are almost all of them pushers with rear or side radiators?

Yes


TOM
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