[jartelt]

One reason cooling is used is to protect the Li-ion or lead acid batteries in the uninterruptible power supplies that provide backup power to the servers. Both Li-ion and lead acid lose calendar life and reliability when operated at 40 C. So, you have extra battery replacement costs and reliability concerns at higher temperature.

I also would imagine that you need some type of cooling system even to keep the ambient temperature at 40C. Otherwise the servers are just continuously pumping out heat and the temperature may get high enough to the point where you have equipment issues. It could be the case that the equipment needed to cool to 25C is not that different or more expensive that the equipment needed to maintain a temperature of 40C.

[terafo]

My impression is that these power supplies are usually in separate rooms or even buildings, so you can have different temperatures there.

> *It could be the case that the equipment needed to cool to 25C is not that different or more expensive that the equipment needed to maintain a temperature of 40C. *

From what I've heard, cost difference is quite large.