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Temperature Rise Calculations for IP65 panels
Looking for temperature rise and cooling fan requirement calculations
By Anonymous on 22 April, 2003 - 8:41 am

i am an qualified instrumentation enginner. we are designing and building PLC panels. i would like to know the detailed calculations for the following:

- Temperature rise of sealed enclosure due to heat dissipation inside the panel.
- determine the cooling fan requirements to minimise temp. rise to allowable limits.

Interesting question!
The approach has IMHO 3 parts:
1. Calculate the heat generated inside the enclosure,
2. Obtain heat transfer data on enclosure,
3. Size heat removal device.

1 Calculate the heat generated inside the enclosure
Calculate / estimate the heat generated (Watts burned) by all the devices (exclude of course energy passing through the enclosure, i.e., switched by a device inside but burned by a device outside), then calculate / estimate the
diversity (simultaneity factor) - how many and which of them are ON at teh same time on the average.

2. Obtain heat transfer data on enclosure
That's the hard part - if not impossible - I haven't seen such data for enclosures (like Theta JA or JC for semiconductors). You can skip this step by assuming that you want to remove 100% of the heat generated (expensive assumption). If you can't - you need to know the max temp. rise you can afford = directly proportional to heat not removed.

3. Size heat removal device.
>From 1. and 2. above you have the figure of how much heat you want to remove (in W or BTU/hr) - find a heat removal device of that rating.

That was my 5 cents.
Meir Saggie

By Jamie Barrett on 22 April, 2003 - 4:40 pm

go to this site

Jamie Barrett

By Anonymous on 22 April, 2003 - 4:40 pm

Hoffman Enclosures has a progam on their website which can be downloaded free. It's been a while since I used it, but basically you enter the dimensions of the enclosure, the heat generated by the devices inside, and the ambient air temperature, and it will tell you how much cooling capacity is required.