# Emergency Power Generator Over Heating



## Tuckahoe Sparkplug (Oct 3, 2008)

So, we recently had a 2 hour load test performed on the new 500kw generator in our facility. After adding resistive loads incrementally for about an hour, and at around 77% of full kw, the engine coolant temperature shot up to 220 degrees. The technician reduced the loads and got the temperature back down to 205 degrees before ending the test. 
The generator is situated in a room next to an outside wall with the vent for the radiator (vent has actuated louvers) in this wall. The intake vent on the opposite wall (which is an inside wall to the facility) has been covered with screen door type screening to keep insects out of the plant (we are a food manufacturing facility). It is apparent that this is restricting air flow because the room has negative air pressure when the generator is running, which is noticeable when opening the personnel door to this room. The technician suggested replacing this vent with one that has actuated louvers. This makes sense to me and should help with the over temperature problem.
Now my question: A 4" exhaust pipe runs off the turbo on the generator through the outside wall where it transitions to a 4" straight tee. The bottom of the tee is a cleanout and the top of the tee rises to a muffler. Off the muffler, it is a 6" pipe to the top of the building. The technician suggested that back pressure from the 4" pipe, that runs from the turbo to the muffler, could be contributing to the over heating. He also suggested that the tee should be a sweep tee rather than a straight tee to improve flow. Before we go consider making these modifications, I wanted to see if others think this might help.


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## McClary’s Electrical (Feb 21, 2009)

Tuckahoe Sparkplug said:


> So, we recently had a 2 hour load test performed on the new 500kw generator in our facility. After adding resistive loads incrementally for about an hour, and at around 77% of full kw, the engine coolant temperature shot up to 220 degrees. The technician reduced the loads and got the temperature back down to 205 degrees before ending the test.
> The generator is situated in a room next to an outside wall with the vent for the radiator (vent has actuated louvers) in this wall. The intake vent on the opposite wall (which is an inside wall to the facility) has been covered with screen door type screening to keep insects out of the plant (we are a food manufacturing facility). It is apparent that this is restricting air flow because the room has negative air pressure when the generator is running, which is noticeable when opening the personnel door to this room. The technician suggested replacing this vent with one that has actuated louvers. This makes sense to me and should help with the over temperature problem.
> Now my question: A 4" exhaust pipe runs off the turbo on the generator through the outside wall where it transitions to a 4" straight tee. The bottom of the tee is a cleanout and the top of the tee rises to a muffler. Off the muffler, it is a 6" pipe to the top of the building. The technician suggested that back pressure from the 4" pipe, that runs from the turbo to the muffler, could be contributing to the over heating. He also suggested that the tee should be a sweep tee rather than a straight tee to improve flow. Before we go consider making these modifications, I wanted to see if others think this might help.


 

I think both suggestions would probably help, with the first suggestion making the most difference. BUT,,,Who designed the intake system? Does it meet the requirements of the minimum amount of CFM to cool the motor? How many CFM is it flowing when cooling? Does that meet the manufacturers specs for that cooler?


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## MDShunk (Jan 7, 2007)

The exhaust flow slams straight into the wall of a tee? Wow, there's something I've never seen before. I think all these generators come with instruction to use sweeping bends. 

Plus, if you have negative pressure on the magnehelic for the whole room, you're not bringing in enough air. You can only push out as much air as you can bring in. 

I agree with the tech. Neither of these may be the "real" problem, but they're both a problem.


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## McClary’s Electrical (Feb 21, 2009)

MDShunk said:


> The exhaust flow slams straight into the wall of a tee? Wow, there's something I've never seen before. I think all these generators come with instruction to use sweeping bends.
> 
> Plus, if you have negative pressure on the magnehelic for the whole room, you're not bringing in enough air. You can only push out as much air as you can bring in.
> 
> I agree with the tech. Neither of these may be the "real" problem, but they're both a problem.


 
WOW,,,I didn't realize that's what he meant about the TEE until you wrote that.I pictured the exhaust going straight accross the TEE, and the bottom being the cleanout. This is gonna cause just as much problem as insufficient air flow through the cooler


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## Bob Badger (Apr 19, 2009)

Tuckahoe Sparkplug said:


> The intake vent on the opposite wall (which is an inside wall to the facility) has been covered with screen door type screening to keep insects out of the plant (we are a food manufacturing facility). It is apparent that this is restricting air flow because the room has negative air pressure when the generator is running, which is noticeable when opening the personnel door to this room.


Obviously the screen is restricting but once it is removed where would the make up air come from?

As Marc pointed out you cannot remove more air then you replace and unless your facility is usually wide open to the the outside there should be a specific plan for getting this make up air into the building. A 500 KW generator moves and consumes a ton of air.


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## MDShunk (Jan 7, 2007)

Bob Badger said:


> Obviously the screen is restricting but once it is removed where would the make up air come from?
> 
> As Marc pointed out you cannot remove more air then you replace and unless your facility is usually wide open to the the outside there should be a specific plan for getting this make up air into the building. A 500 KW generator moves and consumes a ton of air.


If the intake air opening isn't the same size as the fan-forced outlet, it could benefit from fan-forced intake air. 

The fact that this intake opening communicates with the interior of the plant bothers me a little bit too. I'm not sure how big the plant is, but I can see that thing actually making negative pressure in the whole plant if it runs long enough. I'd rather favor getting the makeup air from a roof penetration.


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## McClary’s Electrical (Feb 21, 2009)

Bob Badger said:


> Obviously the screen is restricting but once it is removed where would the make up air come from?
> 
> As Marc pointed out you cannot remove more air then you replace and unless your facility is usually wide open to the the outside there should be a specific plan for getting this make up air into the building. A 500 KW generator moves and consumes a ton of air.


 

I cannot picture a 500 kw with a 4" exhaust:no:


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## MDShunk (Jan 7, 2007)

mcclary's electrical said:


> I cannot picture a 500 kw with a 4" exhaust:no:


I think he said that the 4" was the bypass exhaust coming off the turbo. It sounds like it has 6" off the main exhaust, and 4" off the turbo. I could be wrong, though, since I've never seen such a setup.


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## Southeast Power (Jan 18, 2009)

Tuckahoe Sparkplug said:


> So, we recently had a 2 hour load test performed on the new 500kw generator in our facility. After adding resistive loads incrementally for about an hour, and at around 77% of full kw, the engine coolant temperature shot up to 220 degrees. The technician reduced the loads and got the temperature back down to 205 degrees before ending the test.
> The generator is situated in a room next to an outside wall with the vent for the radiator (vent has actuated louvers) in this wall. The intake vent on the opposite wall (which is an inside wall to the facility) has been covered with screen door type screening to keep insects out of the plant (we are a food manufacturing facility). It is apparent that this is restricting air flow because the room has negative air pressure when the generator is running, which is noticeable when opening the personnel door to this room. The technician suggested replacing this vent with one that has actuated louvers. This makes sense to me and should help with the over temperature problem.
> Now my question: A 4" exhaust pipe runs off the turbo on the generator through the outside wall where it transitions to a 4" straight tee. The bottom of the tee is a cleanout and the top of the tee rises to a muffler. Off the muffler, it is a 6" pipe to the top of the building. The technician suggested that back pressure from the 4" pipe, that runs from the turbo to the muffler, could be contributing to the over heating. He also suggested that the tee should be a sweep tee rather than a straight tee to improve flow. Before we go consider making these modifications, I wanted to see if others think this might help.


Did someone professionally design this job or is this a random installation?


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## Bob Badger (Apr 19, 2009)

MDShunk said:


> I'd rather favor getting the makeup air from a roof penetration.


Agreed, right in the generator room if at possible. Bring the air in where it is needed no need to condition the supply air so what if the generator room gets cold or hot while in operation. (Of course you may need to consider freezing pipes if it is a real cold area.)

I used to work in a 6 story coffee factory and until they addressed the make up air for all their exhaust fans there would be times you could barely open swinging doors to the outside and once you did it was like a hurricane.


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## micromind (Aug 11, 2007)

I agree with the tech on both items. 

It doesn't take much restriction to cause the radiator airflow to be reduced to the point of overheating.

If the exhaust of a 500KW gen is indeed 4", that would likely be an even larger problem. In my experience, 6" is on the small side, 8" would be more normal, especially if the pipe is longer than a few feet. Most of the 500s I work with have two turbos, each one has a 5" or 6" exhaust. 

Rob


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## william1978 (Sep 21, 2008)

Bob Badger said:


> I used to work in a 6 story coffee factory and until they addressed the make up air for all their exhaust fans there would be times you could barely open swinging doors to the outside and once you did it was like a hurricane.


 That reminds me of a job we did that had a 275KW generator that would do the same thing you could not open the door when it was running. When we did startup on it the start up guy left the room and he could not open it back up it took 4 of us to open it.:laughing:


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## Tuckahoe Sparkplug (Oct 3, 2008)

jrannis said:


> Did someone professionally design this job or is this a random installation?


No, not a random installation. It's a very large facility designed by a major engineering firm and the emergency power layout was part of that design. The insect screen that was installed over the intake vent was probably installed after initial construction, and I don't know who was responsible for installation of the generators exhaust system. The facility interior temperatures, humidity, and pressures are closely controlled because they will affect product and the air flow involved with running the generator has not caused issues. I suspect the area of the plant adjacent to the generator room, which is walled off from production areas, has roof intakes. 
I did get some good information for consideration, though, and I appreciate the input. :thumbsup:


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## sparky.jp (May 1, 2009)

In my job I work with EG rooms, and there are specific formulas for intake and exhaust air openings (I'm an EE but I get involved in a lot of design reviews where I am looking at the entire design not just the wiring). In general, the air intake opening should be 2 - 2.5 times the area of the exhaust opening.

From your description, I'd say that there is a significant problem with the cooling system design. I just came from a 300kW EG startup at my main project two weeks ago, we were running full-load for a couple of hours (Kohler EG with Detroit Diesel 14 liter 675HP motor HOOAH!) and our coolant temp never exceeded 182 degrees F. Amazing to be in the room with that thing running full-load, even with hearing protection the turbo whine was head-splitting. Running 26psi of intake manifold boost (this was in Colorado at 5900' elevation) at full load, wowee!

For a 500kW EG, I think the cooling airflow is somewhere between 20,000 and 25,000 cfm, plus about another 1500cfm for combustion air. That's a LOT of airflow!

If you're in an area of the country that could see well-below-freezing temperatures, you must consider some means of controlling the generator room temperature if you have wet-pipe sprinklers in the room (most do). Or switch to a dry-pipe sprinkler system (we are doing this at three facilities right now).

Or, the best solution is to install a remote-mounted radiator outside--this makes it very easy to control the temperature of the EG room. With 20K+ cfm at whatever the outside temp is, the EG room will drop to that temp within a few minutes after the EG starts, and there is no heater big enough to keep the room above freezing with that kind of airflow.

The optimum solution is to install a recirculation plenum between the EG radiator and the outside wall, with modulating dampers on the plenum which control the amount of (heated) air that gets recirculated back into the room.

The problem is that most engineers forget about the low-temp issue until well after the design is done and the EG is set in place and the ducting installed, and then you have to do some kind of band-aid fix (like alter the sprinkler piping).

Sorry for getting a bit OT there, but this issue is near & dear to me right now because I'm dealing with it every day.


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## MDShunk (Jan 7, 2007)

What's 25,000 CFM equate to in terms of the physical size (square feet) of a non-fan-forced intake damper?


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## sparky.jp (May 1, 2009)

MDShunk said:


> What's 25,000 CFM equate to in terms of the physical size (square feet) of a non-fan-forced intake damper?


 I'm at home right now so don't have my notes handy, but from memory it's in the range of 75-100 square feet. Some of our EG rooms have multiple intake openings. We also use filtered openings in some cases and this tends to increase the overall size due to the pressure drop across the filters.

The mechanical engineers that I work with can rattle this stuff off the back of their hand because they do the actual CFM calculations, so don't quote me on the numbers but I think they are in the ballpark.

I ran the numbers on the project I am working on now and with the EG running, it completely exchanges the entire room air volume three times a minute!


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## frenchelectrican (Mar 15, 2007)

As far you know I dealt alot of generators I know few of you may know I am used to work on larger units.

Ouais { yeah } .,, let cut to the chase.


First thing can you tell me what brand this 500'er is and 4 inch single exhaust is way too small for this type of engine.

Second thing someone broke the carndial rules about the tee fitting on exhaust that is complety wrong set up it must have sweep ell if you have to use the tee fitting for clean out port or drain then go with Wye pipe that have much wider sweep than straight tee's.

Normally with 500'er if single turbo they will come in at least 6 inch most case 8 inch is the most common but with vee format engine or two tubochargers at least 6 inches is the smallest.

Third thing the amount of air flowage on 500 KW units you will need a minuim of 28,000 CFM if engine mounted fan remote raditors verison will need 10,000 CFM.

As far for engine mounted raditor fan ,. Oui you will need louvers or shutter but make sure you sized them very well and sized them at the max air flowage.

The last one I did deal with it it was 3 MW meduim speed diesel engine you should see how big the raditor is 3.5 meter across plus 3.5 meter up 

The air flow of that unit is insane when the fan kick in high speed { yeah it have 30 CV (HP) VSD electric cooling fan }

Merci,Marc


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