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Author Topic: Engine Room Ventilation Fan  (Read 8724 times)

Geno

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Engine Room Ventilation Fan
« on: August 27, 2006, 12:23:28 PM »
I had 2 computer fans for engine room ventilation which were not big enough for summer use. I replaced them with the big military surplus blower seen here. It uses about 425 watts. When I partially block the exaust the watts consumed goes down and continue to go down as I block more flow.
1) Why doesn't the wattage go up as the motor struggles to maintain speed?
2) If I put an adjustable damper on it will I reduce the blowers lifespan? With a damper, maintaining engine room temp will be real easy.





Thanks, Geno

dkwflight

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Re: Engine Room Ventilation Fan
« Reply #1 on: August 27, 2006, 12:39:24 PM »
Hi The blower does not act like a positive displacement pump. By blocking the intake the blower wheel has less air to act against. This type of adjustment has been the standard in the havac industry for ages. I installed many hot air furnaces that needed the load adjusted in this manner. The direct drive motors would draw too much power and over heat and possibly be damaged,
Dennis
28/2 powersolutions JKSon -20k gen head
Still in devlopment for 24/7 operation, 77 hours running time

Geno

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Re: Engine Room Ventilation Fan
« Reply #2 on: August 27, 2006, 12:50:31 PM »
Hi The blower does not act like a positive displacement pump. By blocking the intake the blower wheel has less air to act against. This type of adjustment has been the standard in the havac industry for ages. I installed many hot air furnaces that needed the load adjusted in this manner. The direct drive motors would draw too much power and over heat and possibly be damaged,
Dennis

That makes sense. The pic is from the outside of the engine room. If I put the damper on the exaust will it make a difference? It would be a little more convienent to adjust it from inside the engine room
Thanks, Geno

dkwflight

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Re: Engine Room Ventilation Fan
« Reply #3 on: August 27, 2006, 01:26:53 PM »
Hi You have to throttle the intake. I think if you throttle the exhaust you might load the motor up a bit before the load decreases, but i never tried it.
Dennis
28/2 powersolutions JKSon -20k gen head
Still in devlopment for 24/7 operation, 77 hours running time

bitsnpieces1

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Re: Engine Room Ventilation Fan
« Reply #4 on: August 27, 2006, 02:30:17 PM »
 1) Since it's not positive displacement the motor and blade will stay at the same speed.  The reduction of watts is because you're moving less mass of air.  E = M V2
 2) You definitely need to throttle the intake.  If you throttle the discharge, all of the air coming in can't be pushed out and gets compressed, thus getting hot which can make the motor hotter than it should be.  Also, wastes energy hence higher power consumption.  If you throttle the intake all of the air coming does go out.  Which means no compression, which means no excess heat and keeps power usage down. 

  Also what you have is a type of blower that is intended to produce some increase in pressure, say 1 - 5 psi.  If you have 12vdc available you could go with an automotive electric radiator fan which is meant to move large masses of air with little compression thus even more power savings.  You could still rig up a suction side damper to regulate the amount of air moved to give best cooling with least power usage.  However you would need to buy it, If the fan you have is essentially free and the power to run it is the same, no problem staying with it. 
« Last Edit: August 27, 2006, 02:41:16 PM by bitsnpieces1 »
Lister Petter AC1, Listeroid 12/1, Briggs & Stratton ZZ, various US Mil. surplus engines. Crosley (American) 4cyl marine engine(26hp).

Geno

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Re: Engine Room Ventilation Fan
« Reply #5 on: August 27, 2006, 03:27:30 PM »
1) Since it's not positive displacement the motor and blade will stay at the same speed.  The reduction of watts is because you're moving less mass of air.  E = M V2
 2) You definitely need to throttle the intake.  If you throttle the discharge, all of the air coming in can't be pushed out and gets compressed, thus getting hot which can make the motor hotter than it should be.  Also, wastes energy hence higher power consumption.  If you throttle the intake all of the air coming does go out.  Which means no compression, which means no excess heat and keeps power usage down. 

  Also what you have is a type of blower that is intended to produce some increase in pressure, say 1 - 5 psi.  If you have 12vdc available you could go with an automotive electric radiator fan which is meant to move large masses of air with little compression thus even more power savings.  You could still rig up a suction side damper to regulate the amount of air moved to give best cooling with least power usage.  However you would need to buy it, If the fan you have is essentially free and the power to run it is the same, no problem staying with it. 

Throttling the intake is what I'll do. Your post makes sense but the wattage does go down when I throttle the exaust. I can make a linkage to bring the adjustment in the engine room.
The fan was free except for some new bearings and a couple hours. Military spec equipment is made to survive anything. Its heavy and well built.
Will the pressure increase give me any boost? ;)

Thanks, Geno

dkwflight

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Re: Engine Room Ventilation Fan
« Reply #6 on: August 27, 2006, 04:08:47 PM »
Hi I don't think so. You will probably want to run wide open if the motor is not overloaded. Check with amprobe.

What are your plans to recycle heat in upstate NY.
I had a chance at 120 acres for $20k a long time ago. My wife at the time backed out. She was afraid of being in the outback ;D
That was when I first became interested in slow speed diesels. Her brother was living off a small Briggs generater and suffering because the gen wouldnt last long and the refrig didn't work right only running a few hours a day.
Dennis
28/2 powersolutions JKSon -20k gen head
Still in devlopment for 24/7 operation, 77 hours running time

bitsnpieces1

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Re: Engine Room Ventilation Fan
« Reply #7 on: August 27, 2006, 04:57:28 PM »
1) Since it's not positive displacement the motor and blade will stay at the same speed.  The reduction of watts is because you're moving less mass of air.  E = M V2
 2) You definitely need to throttle the intake.  If you throttle the discharge, all of the air coming in can't be pushed out and gets compressed, thus getting hot which can make the motor hotter than it should be.  Also, wastes energy hence higher power consumption.  If you throttle the intake all of the air coming does go out.  Which means no compression, which means no excess heat and keeps power usage down. 

  Also what you have is a type of blower that is intended to produce some increase in pressure, say 1 - 5 psi.  If you have 12vdc available you could go with an automotive electric radiator fan which is meant to move large masses of air with little compression thus even more power savings.  You could still rig up a suction side damper to regulate the amount of air moved to give best cooling with least power usage.  However you would need to buy it, If the fan you have is essentially free and the power to run it is the same, no problem staying with it. 

Throttling the intake is what I'll do. Your post makes sense but the wattage does go down when I throttle the exaust. I can make a linkage to bring the adjustment in the engine room.
The fan was free except for some new bearings and a couple hours. Military spec equipment is made to survive anything. Its heavy and well built.
Will the pressure increase give me any boost? ;)

Thanks, Geno

  UHM let's see:  Throttling the exhaust does reduce the mass of air being moved which will reduce the wattage required.  However, some power is needed to compress the air which shows up as heat in the air.  Continued throtling will build up enough heat to fry the motor.  I have a similar situation occur in sewage pumps with a partially (or fully) plugged discharge.  Evrey bit of power fed into the
motor ends up heating the water to a temp that is sifficient to finally build up enough steam pressure to blow the steel pump into pieces. 

SAY, If you throttle on the intake side you can reduce the air being moved by 1/2.  The energy needed to move it will go down.  With no compression no power goes into heating the air.  If you throttle the discharge to the same 1/2 air flow you get the same energy savings for the mass of air that you are moving.  HOWEVER, since you are now compressing the air some energy goes into heating it.  Now you wattage only goes down by 40% instead of 50%.  The extra 10% goes into heating the air.  Without the hot air moving out of the blower you get an increase in temp which gets added to and added to continuosly until the air temp inside the blower is high enough to fry the motor. 

 NOW,  you could throttle the suction to reduce the airflow enough to reduce the power use to 250 watts.  If you throttle the discharge to obtain the same amount of air (mass) being moved it will only go down to say 300 watts.  250 to move the air and 50 to heat it up.  + another 50, + another 50, until the air gets to say 400-500 degress F.  If this helps great, if not I'll  keep trying. 
  Since the blower is essentially free I'd also go right ahead and use it. 
Lister Petter AC1, Listeroid 12/1, Briggs & Stratton ZZ, various US Mil. surplus engines. Crosley (American) 4cyl marine engine(26hp).

Geno

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Re: Engine Room Ventilation Fan
« Reply #8 on: August 27, 2006, 07:23:24 PM »
bitsnpieces1: I fully agree that throttling the intake (within reason) is the way to go and understand your posts completely. Earlier I didn't get the non-positive displacement thing. I did not block the exhaust long enough during testing to heat up the motor so current draw may have gone up after it went down. I have a killawatt, Fluke multimeter, and amp meter. Thank you for the help.

dkwflight: That land must have been in some real boondocks. It’s not that cheap around here. My future plans, after everything else is sorted out is to put some kind of heat exchanger on the hot side of the rad and wrap up the muffler in copper coils for another one. I will not compromise the primary coolant loop and want it to remain as simple as possible. My main problem is getting that heat to the house economically, having it hot enough to do some good when it gets there and keeping it from freezing when not in use. The engine is 40' from the house with a concrete slab, a deck and a leach field to contend with down low. If I can’t do it economically it will take years (maybe never) to recover the $. I know there are solutions, I'll think about it for a while, ask some questions and come up with a KISS solution.

Thanks, Geno

dkwflight

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Re: Engine Room Ventilation Fan
« Reply #9 on: August 27, 2006, 08:15:55 PM »
Hi  YEa it was one mile from power lines to the nearest border of the land I tried to buy. Needless to say the power co wanted A BUNCH of $ to run a line to a place where I wanted to build.
This was logged off land in 1973-4. The logging co. would buy defunct farms, some times for back taxes and take the good trees and sell the land  cheap to get rid of it. Tioga co. NY.

Don't over estimate what you can get for waste heat from the Lister-type engine. You probably could get your domestic hot water with not too much trouble. You will want some kind of heat exchanger to keep your antifreeze solution separate from the house water. The problem will be burying insulated pipe. Most insulation will soakup water and become ineffective.
Good luck
Dennis
28/2 powersolutions JKSon -20k gen head
Still in devlopment for 24/7 operation, 77 hours running time

binnie

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Re: Engine Room Ventilation Fan
« Reply #10 on: August 28, 2006, 03:29:25 AM »
Geno
Take a look at http://www.frontierheatingconcepts.com/downloads/bro-ThermoPEX-2496.pdf  pex tubing from frontierheatingconcepts.com  It looks like a doable solution to get the water 40' to where you want it. Not cheap. The supplier up here in Cda. was asking 18.00 per foot and wouldn't sell under 50' min. I like the idea of the 2 way single insulated pipe. Worth checking into binnie
Listeroid 12/2 Jkson with 10kw head, for backup now on diesel. Future interests: WVO, bio,  Cogen - Heat exchangers - solar.

slowspeed1953

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Re: Engine Room Ventilation Fan
« Reply #11 on: August 28, 2006, 05:04:11 AM »
Geno
Take a look at http://www.frontierheatingconcepts.com/downloads/bro-ThermoPEX-2496.pdf  pex tubing from frontierheatingconcepts.com  It looks like a doable solution to get the water 40' to where you want it. Not cheap. The supplier up here in Cda. was asking 18.00 per foot and wouldn't sell under 50' min. I like the idea of the 2 way single insulated pipe. Worth checking into binnie


Check out Pex-Flex its virtually the same product. There is a auction on ebay right now selling it for 10$US a foot

Peace&Love :D, Darren

Geno

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Re: Engine Room Ventilation Fan
« Reply #12 on: August 28, 2006, 12:15:33 PM »
slowspeed1953, binnie: I appreciate the suggestions. Both products look real nice. Its 40' to the nearest house wall, 25' more to the basement, etc, etc. I'm not off grid, I can still make a lot of hot water with 1 gallon of fuel oil. Firewood is free except for my time. 6 gallons an hour at 100° ambient isn't much. I might get a few more gallons with a heavier load and an exaust heat exchanger.

Its' been over a hundred here and mine is running 'hot water to waste' with an auto fill ten gallon tank for cooling water.
  You'll find fuel effeciency and performance go WAY UP when the temperature of the engine goes up.
    Mine runs at 198 degrees and uses 6 gallons of water an HOUR.

If I can’t do it economically it will take years (maybe never) to recover the $.
Thanks, Geno

What I'll probobly do is rig up something temporarily to see how much hot water I get and how hot it is after a 60-70' run in the winter.

Thanks, Geno

bitsnpieces1

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Re: Engine Room Ventilation Fan
« Reply #13 on: August 28, 2006, 04:27:36 PM »
 I do tend to get pedantic and longwinded.  It's better face to face.  It's a part of my wanting to learn everything I can. 
Lister Petter AC1, Listeroid 12/1, Briggs & Stratton ZZ, various US Mil. surplus engines. Crosley (American) 4cyl marine engine(26hp).

timgunn1962

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Re: Engine Room Ventilation Fan
« Reply #14 on: September 19, 2006, 10:27:30 PM »
You can run a damper on either the blower inlet or outlet and it's not likely to make much difference to either the temperature rise or the power consumed, at the sort of pressure differential you can expect from the fan.

Broadly speaking,  throttling the flow to half its unthrottled value will halve the power consumed. The "volume to power" ratio is constant.

With 425 watts absorbed, the fan probably represents a fair chunk of the output of the generator it is intended to cool. It may be worth considering a speed controller instead.

The "fan laws" give the relationship between flow, pressure, absorbed power and fan speed for any given fan.
Flow varies with the fan speed.
Pressure varies with the square of the fan speed.
Power varies with the cube of the fan speed.

If your fan uses 425 watts at maximum flow, it will use 212 watts when throttled to half flow.
It would only use 53 watts if the speed (and therefore flow) were halved.

The cube relationship between speed and power means that very little torque is needed at low speeds, so a very cheap, simple speed controller can be used.

Obviously, speed control is an added complication and goes against the KISS philosophy. The simple fan speed controllers may also play merry hell with  power quality from a small generator (I don't know, it would need checking), but if output is tight, it could be worthwhile.