Generator room ventilation and winding temperature

[chaterpilar]

There is an installation where they have 8 CAT 3512BTA 1600 kva engines in sync.

They run at around 60% load each.

The ambient ( room temperature is 55 deg C) and the alternator winding temperature is rising upto 115 deg C.

Now, the question is is this winding temperature is acceptable ( It is Class H insulation) but alternator name plate specifies 105 deg C rise at 40 deg C ambient.

Will increasing the ventilation,reduce the problem this high temp rise?

Presently there is a substantial negative pressure in the room...it takes effort to open the door of the room.

Is there any formula to calculate the ventilation for a generator room?

Any thoughts..

 

[weressl]

There is an installation where they have 8 CAT 3512BTA 1600 kva engines in sync.

They run at around 60% load each.

The ambient ( room temperature is 55 deg C) and the alternator winding temperature is rising upto 115 deg C.

Now, the question is is this winding temperature is acceptable ( It is Class H insulation) but alternator name plate specifies 105 deg C rise at 40 deg C ambient.

Will increasing the ventilation,reduce the problem this high temp rise?

Presently there is a substantial negative pressure in the room...it takes effort to open the door of the room.

Is there any formula to calculate the ventilation for a generator room?

Any thoughts..

The temp rise may be within limits of the insulation rating, but I think you may be exceeding the operating limits of the generator and the controls, so you may expect them to be malfunction and 'cooked' prematurely.

In the installation manual/planning guide they usually specify the air supply duct size, provide exhaust and insulate the combustion exhaust. Gravity louvers will do the job, no forced exhaust or supply is usually needed.

 

[Ragin Cajun]

If the negative pressure on the room is that much, sounds like either there are not enough inlet vents or they are closed.

As for the 105 degC, that's 131 degF!!! You are frying all the generator controls. How does anyone even go in that room much less work in there.

Get that temperature DOWN!

RC

 

[barclayd]

As for the 105 degC, that's 131 degF!!! You are frying all the generator controls. How does anyone even go in that room much less work in there.

Get that temperature DOWN!

RC

105 C is actually 221 F.
Conductors have to be derated for any ambient above 30 C (86 F), and most motors & generators are designed for 40 C ambient (104 F).
Like the man said "Get that Temperature DOWN". An installation that big should have a Mechanical Engineer available. Cool that room down, or in a short while you will have 8 very expensive boat anchors.
Also - if the engines use batteries for starting, they won't last very long, either.
db

 

[weressl]

105 C is actually 221 F.
Conductors have to be derated for any ambient above 30 C (86 F), and most motors & generators are designed for 40 C ambient (104 F).
Like the man said "Get that Temperature DOWN". An installation that big should have a Mechanical Engineer available. Cool that room down, or in a short while you will have 8 very expensive boat anchors.
Also - if the engines use batteries for starting, they won't last very long, either.
db

It helps to actually read the posts, so that you can 'stay on message'. The OP ambient temperature was indicated to be 55C NOT 105C. I have also made prior comments about derating.

I understand that you may not want to wade through gazzilion posts when you come to a discussion late - I am guilty of such - but we only had 4 posts here and the subject is already skewed...:roll:

 

[steveng]

The temp rise may be within limits of the insulation rating, but I think you may be exceeding the operating limits of the generator and the controls, so you may expect them to be malfunction and 'cooked' prematurely.

In the installation manual/planning guide they usually specify the air supply duct size, provide exhaust and insulate the combustion exhaust. Gravity louvers will do the job, no forced exhaust or supply is usually needed.

chat, sounds like weressl has good advice,

how long has this installation be in operation?

 

[steveng]

duplicate post

 

[steveng]

chat, sounds like weressl has good advice,

how long has this installation be in operation?

can you leave the door open a while and recheck the temps,

sound like you may need more fresh air inlet to the mech/gen room.

 

[Ragin Cajun]

If the negative pressure on the room is that much, sounds like either there are not enough inlet vents or they are closed.

As for the 105 degC, that's 131 degF!!! You are frying all the generator controls. How does anyone even go in that room much less work in there.

Get that temperature DOWN!

RC

I ment to write "As for the 55 degC, that's 131 degF!!!"

Can't type worth a #$%^&

RC

 

[barclayd]

It helps to actually read the posts, so that you can 'stay on message'. The OP ambient temperature was indicated to be 55C NOT 105C. I have also made prior comments about derating.

I understand that you may not want to wade through gazzilion posts when you come to a discussion late - I am guilty of such - but we only had 4 posts here and the subject is already skewed...:roll:

Nowhere in my post did I say the ambient was 105 C. I was pointing out an error in the calculation. I see nothing in your post about derating.

If recommending that a qualified Mechanical Engineer be consulted to design proper ventilation for a room containing several million dollars worth of equipment "skewes" the discussion, then I must not fully understand the purpose of this forum.

db

 

[coulter]

...Any thoughts..

Some. Possibly even useful:smile:

...Will increasing the ventilation,reduce the problem this high temp rise?

Presently there is a substantial negative pressure in the room...it takes effort to open the door of the room. ...

http://www.cat.com/cda/components/securedFile/displaySecuredFileServletJSP?x=7&fileId=303767

This is the closest I could find to your application. Note this sheet list the heat rejection from the engine to atmosphere and the gen to atmosphere. You need enough air changes to get rid ot that heat. You could need exhaust fans.

The sheet also list the air intake for the engine. You need enough inlet area to keep the pressure drop down to the mfg specs. Considering that you have enough negative pressure to make it tough to open the doors, I suspect you need more inlet louvers.

A question: where is the radiator? Outside? If not, you need a bunch of air for the radiator. That spec is also listed on the link.

This type of data is with the mfg literature that came with the gen sets. If not available, I'd suggest calling Cat. They have been pretty helpful to us.

A lot of times the equipment is not from Cat, but rather bought from a packager/builder - I have not found any packager/ builder to be helpful. But Cat will generally still pitch in and help.

carl

 

[chaterpilar]

This is the second summer it is enduring....i agree with all that size of room is less.

i actually did some calulation based on the data given in Caterpillar website for these ( eight 3512BTA engines in a room) and came to a ventilation figure of 94 m3/sec for each generator at 5 deg F Delta T betwen outside temperature and engine room temperature.

By the way, the ambient temperature in peak summer here in the desert is 119 Deg F and engine room temperature goes to 131 deg F.

The formula i have used is


Ventilation air ( M3/min) =

Heat load
__________________
1.099 X 0.017 X Delta T

to this is added the total combustion air

Hence total air (ventilation + combustion )required for 8 engines is 752 m3/sec


The available opening is 115 sq metres hich gives a windspeed of 6.53 metres/sec, which is high.

Carl,

Thanks for the link, the radiator is flush with the wall and sucks out the air from the room.

Cheers.

 

[mivey]

Some. Possibly even useful:smile:


http://www.cat.com/cda/components/securedFile/displaySecuredFileServletJSP?x=7&fileId=303767

This is the closest I could find to your application. Note this sheet list the heat rejection from the engine to atmosphere and the gen to atmosphere. You need enough air changes to get rid ot that heat. You could need exhaust fans.

The sheet also list the air intake for the engine. You need enough inlet area to keep the pressure drop down to the mfg specs. Considering that you have enough negative pressure to make it tough to open the doors, I suspect you need more inlet louvers.

A question: where is the radiator? Outside? If not, you need a bunch of air for the radiator. That spec is also listed on the link.

This type of data is with the mfg literature that came with the gen sets. If not available, I'd suggest calling Cat. They have been pretty helpful to us.

A lot of times the equipment is not from Cat, but rather bought from a packager/builder - I have not found any packager/ builder to be helpful. But Cat will generally still pitch in and help.

carl

This just seemed a little surreal: a guy in snow giving temperature advice to a guy in the desert.

 

[coulter]

This just seemed a little surreal: a guy in snow giving temperature advice to a guy in the desert.

(Caution: Weirdness attack ahead)

"Surreal" That's a neat word. But some how apparitions of Salvador Dali clash with my vision of the icedog assisting the sandman.

Yeah, does seem odd. Amazing what knowledge we gather.

carl

 

[petersonra]

sounds to me like whoever designed the room needs a stern talking to.

i agree with getting someone a little more competant involved.

with the high ambient temperatures you have, it is not necessarily going to be trivial to get enough cooling air, especailly since the combustion air is coming from inside the room.

 

[coulter]

From chater's data (which is consistent with similar Cat gen specs) the combustion air is not as much an issue as the radiator cooling air.

carl

 

[coulter]

sounds to me like whoever designed the room needs a stern talking to.
...

That won't fix anything. That was yesterday's problem.

I'm guessing chater is more concerned with today's problem - dealing with the existing installation with the resources he has available.

carl

 

[chaterpilar]

Yes, Carl. I need to get that figure of free area opening ( square metres ). At present the total louvered area is 177 sq meter but effectively it is only 115 square metres as Free area = 0.65 x louvered area.

If i get that opening area i can add further openings to the room.

cheers.

 

[Pierre C Belarge]

I could be way off here, but it seems as though there may even be a need for chilled air/AC just to keep the room temperature to a level that you do not cause long term issue with those very expensive 8 Generators. I base this on the temperatures you have posted.

 

[mivey]

I could be way off here, but it seems as though there may even be a need for chilled air/AC just to keep the room temperature to a level that you do not cause long term issue with those very expensive 8 Generators. I base this on the temperatures you have posted.

It will eventually all come down to air movement. I suspect the radiator will probably be the best combination of economic and efficient.

[edit: unless you can find another heat sink, like the aquifer]