Temperature Rise Calculations for IP65 panels

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Anonymous

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
 
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