[HoosierDaddy]

https://www.prevostcar.com/news-and-medi...re-prevost

[Fulltiming]

Very interesting. Thanks Dean.

[Nebster]

Not unlike what almost all cars are moving to.

I am working on a similar variable-speed electric fan setup for the generator on my coach, but really just to reduce noise. More to come...

[77newell]

I've thought about this route for my 93 with the 8V92 with rear radiator in order to reduce the power consumed by the single big direct drive fan. The design would involve some kind of controller that would stage multiple fans just as Prevost has done based upon some engine parameter such as engine power and/or coolant temperature. I've noticed a lag between increased engine power and coolant temperature rise so coming up with an algorithm that would kick in additional fans as power increases, assuming the engine is near operating temperature, would reduce the need for even more fans if we wait until the coolant temperature rises.

I've noticed the current radiator fan design is less than optimal with part of the fan outside the shroud and with the shroud doing little to distribute the air evenly over the radiator surface. This less than optimal design is due to lack of space behind the engine to install a more efficient shroud which would be longer than the current shroud.

While the electric fan design reduces power required to force cooling air through the radiator, it does not eliminate the drag on the drive engine completely if/when the electricity is produced by an engine driven alternator.

I'm still interested in the challenge of getting my coach to average above 7mpg and the cooling system is definitely an area of opportunity.

[kyleb]

It seems the 8V92 requires LOTS more cooling than almost any other engine making comparable HP.
I agree that the fan shrouding leaves lots to be desired. Not much efficiency to be had when the air isn't captured at the blade tips. . . .
At full capacity, a direct drive fan is more efficient - due to losses when mechanical is converted to electrical & back to mechanical. However, being able to trim the fan speed to only what is needed definitely has benefits.

I would think more radiator would allow more cooling for the same amount of air flow.
I have toyed with the idea of placing an additional radiator is on the roof - but, that brings some issues too. . . . .

Easiest solution is for me to plan to take it a little slower - but that is also the hardest for me to implement!

[HoosierDaddy]

I found the Prevost system interesting. I was thinking that the real benefit would be to the side mount radiators. The machinery required to drive a side mounted fan would be eliminated possibly giving the edge in efficiency to the electric fans.
I don't understand how an electric fan can be more fuel efficient than a direct engine driven clutch fan. I suppose the peak engine loads would be lowered since the battery could offer additional stored energy for the fan when needed.

[kyleb]

Electric fans can be more fuel efficient if they operate only when needed and move only the amount of air needed.

It is easier to control the speed of an electric fan than the speed of a clutch fan.

I have often wondered why you couldn't drive a side mounted radiator fan with a belt and direction change pulleys. The fan wouldn't be moving with the engine, so the shroud clearances could be really close to improve the efficiency. . . . .

My '87 coach came with a thick stack of tech talk bulletins. I remember one of them was from Newell & said that their testing showed the rear radiator cooled better than the side mount.
Also saw that as Newell designed it, a properly functioning cooling system had a steady state temp rise above ambient of 125F when the 8V92 was making full power.

[77newell]

A mechanical fan has to push enough air to provide the needed cooling for the maximum heat generated at each engine RPM. A 2 speed fan or an on/off fan can provide savings over an always on fan. Multiple fans provide even greater variability and the electrical controls can more easily provide further variability.

On top of that, Prevost has designed the electrical system so that it tries to charge the batteries preferentially when the engine is at zero fuel (coasting) so that the electricity is produced by gravity. On the flat roads you only gain when stopping or slowing down. On the hills, lots of free juice. They also put electronic controls on the air compressor for this same benefit. They have proven this works, the question is, can something like this benefit us in a retrofit situation?

[bikestuff]

Wait.....gravity? Do they have some sort of axle mounted generator?

This is super intriguing! Since pretty much all cars nowadays have electric fans, sourcing a fan should be no problem....and I bet the current draw would be fairly low. In my coach, I have a honking big oil cooled alternator / generator (what’s the difference anyway?). I bet it has the supply capacity to run a bank of fans.

Also, in terms of cooling efficiency....A round fan and a square radiator? By utilizing a bunch of fans, you could push air through the entire surface making it more efficient.

Also x 2. We have a bank of house batteries that are wasted weight when traveling (other than the refrigerator and occasional microwaved sammich). Why not tie the fans to the house batteries and use them as a kind of low pass filter for the demand.

Is there any restriction on the width of the coach? If we could leave the radiator where it is, and could just move the door out a few inches, it would lower the cost of a retrofit.

[77newell]

The Prevost design of the system is such that if the batteries need charging and the coach is coasting (engine in "no fuel") then the smart electronics will ask the alternator to put out the maximum amperage it can. So, if the coach is coasting down hill (gravity pulling the coach instead of the engine) then the system will use the alternator to max out its power which provides a two-fer: it slows the coach a bit and generates "free" power. The system is designed to wait to charge the batteries as long as possible hoping for coasting to occur, so it isn't charging the batteries any time they need charging. It's making sure there is enough charge to do what needs to be done at the moment and then waiting for coasting to really charge up the batteries. Since the tolerance of AGM batteries to persistent undercharge is greater than standard batteries they use AGM. If you really wanted to juice the system you could do a design using lithium batteries and a monster alternator. Since they chose not to do that I assume the economics are not yet there. However, since we are lugging around a bunch of house batteries, it would be interesting to consider, as Bill suggested, the enlarged storage capacity we have.

One factor that probably makes multiple electric fans more efficient than a single big'un is that the electric fans require less changes in air direction in order to cover the area of the radiator, more of the air can take a straight line from the fan into the radiator. Also, the electric fans have tip shrouds that enhance efficiency.