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The relationship between ambient temperatures and temperatures at full load

post #1 of 14
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I think it's the consensus opinion that ambient temperatures have a significant influence on CPU/GPU/chipset cooler performance. I can't recall who it was who worked out a rudimentary mathematical formula defining this relationship (my apologies to this intrepid OCNer), but my observations in testing more or less coincided with his.

However, as I recall, his observations and calculations were only for ambient temperature readings (I may be wrong about this, of course). I'm therefore left wondering about whether the same mathematical relationship would apply to all temperature readings across the whole thermal range experienced by the processor. In other words, given all other factors being the same, would observed maximum load temperatures also rise as the ambient temperature rises? Or is there a definite peak temperature your cooling equipment will allow the chip to scale to?

I'd test these questions right now, but ambient temperatures where I live have been consistent lately.

This line of questioning is actually based on another thought, namely, that perhaps evaluations of cooler equipment performance should not be based on observed maximum temperature readings (if there is indeed also a direct relationship between ambient temperatures and observed temperatures all along the thermal range).

All thoughts and inputs are welcome!
    
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post #2 of 14
Too many variables.
vDroop, voltage sway, voltages for different parts, heatsinks used, mounting styles, testing method, etc.

Hell, just by having my computer on the lower part of my desk, my temps rise 2C.

Too many variables to get an accurate number.
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post #3 of 14
When it comes to a cpu, I don't know, but I work at a car stereo shop, and I may have relitave info on this subject. During the summer I see multiple customers come in with blown fuses for sub amp's. The number of people are increased on a really hot day. A car amp will pull more current when it is hot, and thus pop the fuse. This is not thermal protection this is the main fuse at the battery. It is possible that since the power wire is hot it is having trouble delivering dc current over a 12-15ft line. I never see this problem in the winter, except on cd decks in dash, because the heater core is right behind most radios. So I think that temps can change performance, and the higher the ambient temp the more likely you are going to have a higher load temp, due to current flow droping.
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post #4 of 14
Quote:
Originally Posted by odie View Post
When it comes to a cpu, I don't know, but I work at a car stereo shop, and I may have relitave info on this subject. During the summer I see multiple customers come in with blown fuses for sub amp's. The number of people are increased on a really hot day. A car amp will pull more current when it is hot, and thus pop the fuse. This is not thermal protection this is the main fuse at the battery. It is possible that since the power wire is hot it is having trouble delivering dc current over a 12-15ft line. I never see this problem in the winter, except on cd decks in dash, because the heater core is right behind most radios. So I think that temps can change performance and the higher the ambient temp the more likely you are going to have a higher load temp, due to current flow droping.
From what I understand, that has more to do with humidity than temps when dealing with fuses.
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post #5 of 14
Quote:
Originally Posted by odie View Post
When it comes to a cpu, I don't know, but I work at a car stereo shop, and I may have relitave info on this subject. During the summer I see multiple customers come in with blown fuses for sub amp's. The number of people are increased on a really hot day. A car amp will pull more current when it is hot, and thus pop the fuse. This is not thermal protection this is the main fuse at the battery. It is possible that since the power wire is hot it is having trouble delivering dc current over a 12-15ft line. I never see this problem in the winter, except on cd decks in dash, because the heater core is right behind most radios. So I think that temps can change performance, and the higher the ambient temp the more likely you are going to have a higher load temp, due to current flow droping.
What is actually happening is the wire heats up, which reduces the resistance, which allows more current to flow.
post #6 of 14
Quote:
Originally Posted by thealmightyone View Post
What is actually happening is the wire heats up, which reduces the resistance, which allows more current to flow.
When the wire heats up it increases resistance and allows less current to flow, but that is not what really happens, the electrical system delivers the proper current, but works harder to do it. Eventually something overheats "hopefully the fuse".
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post #7 of 14
This is why it is often to provide the temperature delta or difference between ambient and loaded processor. Instead of saying, this HSF is better than that since it can do 30C under full load (but at different ambient air temps.) It is more informative to just provide the delta to compare cooling. For example, my room is around 24C and my CPU is 30C under load. Hence, my delta is 6C.
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post #8 of 14
Quote:
Originally Posted by The Pook View Post
From what I understand, that has more to do with humidity than temps when dealing with fuses.
Not here, I live in the high desert no humidity, just dry dust, and dry heat.
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post #9 of 14
Thread Starter 
Quote:
Originally Posted by DuckieHo View Post
This is why it is often to provide the temperature delta or difference between ambient and loaded processor. Instead of saying, this HSF is better than that since it can do 30C under full load (but at different ambient air temps.) It is more informative to just provide the delta to compare cooling. For example, my room is around 24C and my CPU is 30C under load. Hence, my delta is 6C.
DuckieHo's idea is precisely what I was trying to hint at when I said that perhaps there's a better way to evaluate cooling equipment performance. If indeed cooler performance across the entire possible thermal range is directly related to ambient temperatures, you'd never get repeatable results unless you precisely control ambient temperatures (impossible except in a dedicated testing laboratory). What DuckieHo and I are thinking (if I may presume as much) is that it's far more useful to think in terms of temperature deltas, specifically from idle processor conditions to maximum load.
    
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post #10 of 14
Quote:
Originally Posted by txtmstrjoe View Post
DuckieHo's idea is precisely what I was trying to hint at when I said that perhaps there's a better way to evaluate cooling equipment performance. If indeed cooler performance across the entire possible thermal range is directly related to ambient temperatures, you'd never get repeatable results unless you precisely control ambient temperatures (impossible except in a dedicated testing laboratory). What DuckieHo and I are thinking (if I may presume as much) is that it's far more useful to think in terms of temperature deltas, specifically from idle processor conditions to maximum load.
Don't most server rooms have an ac unit to controol ambient temps. If you think about it the best bang for the buck cooling upgrade if you live in a high temp area would be an ac unit for the room.
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