Ambient room temp for xfrmr

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VALZ

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Okay, I have a question if anyone can point me in the right direction. Does anyone know if there Is a cheat calc for estimating a rise in ambient temperature in a closet space after an 80c rise dry tranny has been installed? So basically I’m not asking about the calculation of factory rise at 40c. What I’m looking for is if you brought a thermometer into a closet and the ambient temperature was 60*F before you installed a class 130, 80c rise dry tranny in that room. The calculation of amb temp + max temp rise + hot spot it works out to 40+80+10=130c or 266*F. Since the closet was at 60*F before the tranny was installed, what would the room ambient temperature of the closet be after? 70,80,90*F? I am asking this as a way to figure out how how many transformers I can place in a closet before the ambient temperature gets too high for the tyranny’s to be efficient without ducting extra ventilation. And yes it’s a super old building that has no room to build other rooms.

In the same vein, regarding the NEMA chart. Why does the math not add up for maximum allowable operating temperature for all classes except for Class 130 and 155? Makes it confusing.
 
You have to go back to basic thermal calcs.
First, you have to know how much heat the transformer is generating. This depends on efficiency and load. For example, a 100 KW transformer that’s 95% efficient and fully loaded will reject 5KW into the closet.

Then you need to know the R value of the closet walls and the temperature outside the closet.

The temperature inside will rise until the delta T will conduct 5 KW of heat through that R value.

A bit oversimplified, but it should get you headed in the right direction.
 
In my opinion, if the heat dispersed from the transformer does not be evacuated any way in the open air the temperature will rise to infinite.
You have to know how the heat will be evacuated by convection through tiny opens in the door or windows, through walls, ceiling and ground.
 

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Julius Right said:
In my opinion, if the heat dispersed from the transformer does not be evacuated any way in the open air the temperature will rise to infinite.
You have to know how the heat will be evacuated by convection through tiny opens in the door or windows, through walls, ceiling and ground.
Click to expand...
it can't become infinite because the temp difference between the inside and outside of the closet walls will cause heat to flow through the walls.
 
Julius Right said:
In my opinion, if the heat dispersed from the transformer does not be evacuated any way in the open air the temperature will rise to infinite.
You have to know how the heat will be evacuated by convection through tiny opens in the door or windows, through walls, ceiling and ground.
Click to expand...
Conduction will also be a major contributor, hence the need to know R values. Radiation is probably neglegible.

Sent from my Pixel 4a using Tapatalk
 
Julius Right said:
In my opinion, if the heat dispersed from the transformer does not be evacuated any way in the open air the temperature will rise to infinite.
You have to know how the heat will be evacuated by convection through tiny opens in the door or windows, through walls, ceiling and ground.
Click to expand...

If that were true, you could make your 5000 square foot house airtight and heat it with a light bulb.
 
In a closet room of 10*10 feet area and 8 ft height of concrete wall 2.5 inches thickness, the outside air temperature of 30 degrees C no sun 250 W will produce 40 oC interior air
 
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