64 Prevost, NEED (not want) custom cooling!

[kyle4501]

Pay attention to what is done by the manufacturers - that is usually the most reliable & cost effective solution.

If you must use electric fans, you must have the performance curve before you'll know if it will work. My experience with Flex a lite fans was sufficient enough that I won't ever spend a dime in that direction.

It takes HP to move air & if the factory setups use over 20 HP, you will too - else you will overheat . . . .

My suggestion/ advice is to stick with as big a radiator as you can fit in there & either belt or hydraulic drive the fan. (Get familiar with the heavy duty vehicle wrecking yards & you may find one that will fit nicely. Lots of ideas to drive the fan too. . . .)
Then you can watch the road & not the temp gauge.  

Enjoy the ride!

[kyle4501]

Could a unused ac condensor be used to supplement cooling??have wondered???or heater core?

Short answer = yes

Longer answer = efficiency & heat rejection rate will depend on coolant flow rate, air flow, cross section, fin count, tube diameter, material, etc.

[Len Silva]

There is a reason that Flex-a-light does not make a heavy duty electric fan, only medium duty truck fans.

[RoyJ]

Welcome to our wild and crazy world !!

I am in the process of removing my A/C condenser which uses a hydraulic fan, which I will no longer need, if the deal gets done.

It cools a 36" X 36" X 6" condenser, so I imagine it might be helpful in your application.

If you are unable to get the situation resolved with the radiators and fans, let me know and we may be able to work out a deal for the fan.

I also have the two condensers that are just collecting dust !!

Keith
PCC

Roy,

Lots of buses have large DC motors that ran both the evaporator & condenser fans. The venerable DN50 alternator that was original equipment has a plenty of power to drive the motors. Some bus nuts here have removed the original equipment setup & installed other options. You should be able to pick up the discarded components & fabricate what you need.

TOM

Thanks for the info on condenser fans Keith and Tom.

This does seem like a good option, though I'm sure a lot of custom fabrication is required to fit my specific radiator. A new alternator at 24V would be necessary as well if the fan is electric. If an electric setup is used, I'd probably go high voltage, as even at 24V, it's hard to power a reasonable sized motor. A 300am 24V alternator would be cost prohibitive for me at this point as well.

[RoyJ]

As far as model call prevost car with serial number or I just saw site that has prevost listed by serial number and tells to whom they were sold and spec. Hydraulic fans can be easily driven by a belt operated auto power steering pump.one large fan blade easier to put shroud around and control air flow.unlimited blade configur around...Just a thought. need pictures.....possible a prestiage (sp)model...need pictured of rad area...being a engineer you can apreciate the KISS principle it does well in our hobby especially  when trying to get part on the road...Welcome and fyi there is no age requirements..we are all crazy Bus Nuts

I'll probably call Prevost one day and find out exact what my model is called. Chances are there were only a handful ever made, but I do know that I can still get some parts from Prevost.

A lot of people have suggested hydraulic for me at this point, and I'm definitely keeping that open as an option. I'm a little concerened about the high-loss transmission of hydraulic power, as the 6V71 is definitely not overpowering for the coach! The bus has no power steering (will save me on gym membership), so I'll need a full hydraulic system.

Are hydraulic fans only on-off? If so I'd go with a 2 speed clutch.

[RoyJ]

My instinct would be to use an engine driven fan, either belt or hydraulic, since the power levels can be pretty high.  I'm not sure if letting an alternator run at high voltage is a long-term reliable thing to do, if you are going to pull 16hp out of it you have to put more than that into it, and they just aren't designed for that loading.  I also don't know how to figure the hp load to accomplish the air flow, but at a guess and looking at some charts put out by Caterpillar on their engines, you might need 20 hp.  I use a rule of thumb of 1,000 watts for 1 HP output of electric motor, so 20,000 watts?  That's a lot of electricity, but it's not a lot of mechanical power.

I also have this idea that an alternator may be power limited, in other words it can be designed for 100 amps at 12 volts for 1,200 watts, or 50 amps at 24 volts, or 10 amps at 120 volts.  Certainly the literature on alternators that come in various voltages implies that sort of relationship.

Brian

You bring up a good point Brian. I'm not to worried about the alternator itself, but chances are, the belts and pulleys were not designed to transmit more than 5 hp.

I'm no an expert on alternators, but have done my share of research. From what I know, as long as the diodes can handle the higher voltage, the alternator itself is of low concern. The heat generated in a conductor is determined by current (amperage) only, and not power. A wire conducting 600V at 25 amps will have the same heat generation as 12V and 25 amps. Alternator windings are also the same as motor windings, so reasonable voltage (120v) should be no problem.

At 120V, a 5 hp motor (the highest I'd go for) would only consume 35 amp or so. The alternator internals would be working a lot LESS than at 12V full capacity. However, the mechanical components would be working as if producing 350 amps!

[RoyJ]

Thanks for all the replies guys. I'll quickly breif on what I think of the power issue.

Upon research, I found the following regarding the hp consumption and CFM for a typical Class 8 truck:

http://www.drivetrainindustries.com/kitmas2sp.pdf

Take a look on the chart on page 2. In summary, for the fan, it takes:

- 1 hp to induce 3300 cfm flow over the rad fins
- 2 hp to induce 10,000 cfm
- 70 hp to induce 30,000 cfm !!!

Like most fluid work, the relationship of power vs speed is to the 3rd power!

From this, we can conclude that the 20 - 40 hp the OEM fan consumes falls in the ultra-inefficient region, akin to 70hp on a truck. OEMs have to design at this level to pass durability testing at maximum duty cycle - full throttle hill clim in 100 degree weather.

As a private owner, I don't have to follow such strict requirements. The current fans on my bus probably represent the very first step on that curve - 1 hp and 3300 cfm. I'd like to improve this to atleast the 2 hp/10,000cfm level, which would be a vast improvement over current. Anthing over this is a bonus for me, but by no means am I trying to cover the 100% percentile operating conditions of a stock fan.

Keep the suggestions coming guys, they're of great help to me. So far, I think the hydraulic and condenser fan / motor is the best best solution. The hard part would be the custom fabrication, and tailoring the rad and shroud to such a fan setup. I'll probably have to find such a fan first before going to a rad shop.

Thanks again everyone.

[Just Dallas]

Removed

[Kenny]

Found this website that describes the many factors involved in a successful cooling system.

http://www.arrowheadradiator.com/14_rules_for_improving_engine_cooling_system_capability_in_high-performance_automobiles.htm

Kenny

[RoyJ]

Found this website that describes the many factors involved in a successful cooling system.

http://www.arrowheadradiator.com/14_rules_for_improving_engine_cooling_system_capability_in_high-performance_automobiles.htm

Kenny

Kenny, I have read that article, and it's the exact reason why I though of putting two F150 radiators, at 1.42" thick and 1200 in^2, instead of my current radiator, at 3" thick and 600 in^2.

With electric fans, the current fins are too dense and reaching the point of diminishing returns. Following the logic in that article, using two thinner F150 radiators in parallel should increase both the coolant flow within the radiator cores, as well as the effective CFM and active fin area. My concern is the uncertainty of automotive radiators in a bus, and the fabrication involved in fitting a fan and shroud to such a setup.

[RoyJ]

Something wrong with those numbers.

I think I wuld do some more research if I were you. That company is trying to sell you something and I would take their graph with a box of salt(s).

According to that, I should be able to use 2 fans and at 4HP supply 20K CFM.

And then there is the problem of their RPM figures.

To be honest I'm not believing the numbers 100% either, and I will keep on researching for sure, but I think it does illustrate an important point.

95% of te driving can probably accomplished by a much lower powered fan, but to design to the 100 percentile, you'll need a very powerful fan. This is the same reason why a typical family sedan requires 8 - 9 hp at 55 mph, but most are equipped with 250+ hp.

I believe the catch is that, while you can use 2 fans to produce 20,000 cfm, it will be much less effective than a single fan at 20,000 cfm because the single fan would be producing much higher pressure (and therefore consuming much more power).


I've already realized that electric can never fully replace an engine driven fan; I am simply trying to cover more driving situations than the previous owner did. If I can find a suitable hydraulic unit, I will definitely put on a 2 speed clutch to preserve the limited power of my 6 cylinder.

[Iceni John]

Are hydraulic fans only on-off? If so I'd go with a 2 speed clutch.

Nope, they are (or can be) two-speed.   At 190 degrees my fan goes to full speed, and drops to half speed at 180 degrees.   A solenoid flow-restrictor is triggered by a coolant temperature switch, and is fail-safe so if the switch or solenoid fail the fan will run at full speed.   Simple and very effective.

I'm thinking of replacing my original 6-blade fan with a newer multi-blade fan, more like those on newer OTR buses.   If I can pull more air through my radiator I may not need to have it recored instead, and a fan is cheaper than a new radiator.   Other folk here have had success with this approach, so I may give it a try.

John

[kyle4501]

When moving a compressible fluid (like air), power is required to 1) create the pressure differential, 2) actually move a volume, 3) overcome the efficiency losses.

Actually moving the air takes the most power, so the manufacturers use shutters to reduce air flow -OR- they use a variable speed fan.
Also you will want to seal between the fan & the radiator to ensure all that air you are paying to move goes thru the radiator.

BTW, the engine is providing power to move the air - be it to drive an alt or hyd pump or v-belts, so don't casually discount the stock method.
It is damn difficult to get reliable & satisfactory cooling with electric fans on heavy vehicles. It can be done, but it ain't easy or cheap.
There are reasons the factory did it the way they did - If it was simple & cheap to do it otherwise, they would!

I've had things in the past with marginal cooling systems - that is an inconvenience I'd rather not deal with again - it always cost more to do it over & over than it would have to do it right the first time.

Good luck with your project.

[RoyJ]

Actually moving the air takes the most power, so the manufacturers use shutters to reduce air flow -OR- they use a variable speed fan.
Also you will want to seal between the fan & the radiator to ensure all that air you are paying to move goes thru the radiator.

BTW, the engine is providing power to move the air - be it to drive an alt or hyd pump or v-belts, so don't casually discount the stock method.
It is damn difficult to get reliable & satisfactory cooling with electric fans on heavy vehicles. It can be done, but it ain't easy or cheap.
There are reasons the factory did it the way they did - If it was simple & cheap to do it otherwise, they would!

Thanks Kyle, good points for me to consider.

I hear you about the seal between the fan shroud and radiator. In an ideal situation, if the fan is freely turning in vacuum, then it's consuming no power. Unfortunately though, my bus does not have shutters.

If I owned the bus since day one, I would have NEVER changed the cooling system. But now that the parts are all gone, and with such a rare coach, any attempt to rebuild to factory spec would involve tons of custom fabrication.

A little off topic, but the only reason an electric system can have less parasitic power loss is because of the battery. It acts as a power storage / buffer. On an uphill climb, the alternator can support only 25% of fan power, and the twin 8D batteries provide the rest. Once the hill is over, the batteries can slowly recharge.

[RoyJ]

Are hydraulic fans only on-off? If so I'd go with a 2 speed clutch.

Nope, they are (or can be) two-speed.   At 190 degrees my fan goes to full speed, and drops to half speed at 180 degrees.   A solenoid flow-restrictor is triggered by a coolant temperature switch, and is fail-safe so if the switch or solenoid fail the fan will run at full speed.   Simple and very effective.

I'm thinking of replacing my original 6-blade fan with a newer multi-blade fan, more like those on newer OTR buses.   If I can pull more air through my radiator I may not need to have it recored instead, and a fan is cheaper than a new radiator.   Other folk here have had success with this approach, so I may give it a try.

John

Yeah I just did some browsing on the web, and realized that hydraulic can get really fancy indeed.

By varying or reversion the displacement of the pump and / or motor, they have systems that can be continuous variable in speed, stop all together, and even reverse the fan for debris cleaning! The challenge is for me to locate a cheap hydraulic system at a bus yard / auction (which I don't know of any in my area).

New fan blades are probably a good idea also. With computer fluid simulation and 50 years of fluid research, I'm sure they've come up with more efficient ones than the 60's.