  High-performance computing installations, which are at the basis of web and
cloud servers as well as supercomputers, are constrained by two main
conflicting requirements: IT power consumption generated by the computing nodes
and the heat that must be removed to avoid thermal hazards. In the worst cases,
up to 60% of the energy consumed in a data center is used for cooling, often
related to an over-designed cooling system. We propose a low-cost and
battery-supplied wireless sensor network (WSN) for fine-grained, flexible and
long-term data center temperature monitoring. The WSN has been operational
collecting more than six million data points, with no losses, for six months
without battery recharges. Our work reaches a 300x better energy efficiency
than the previously reported WSNs for similar scenarios and on a 7x wider area.
The data collected by the network can be used to optimize cooling effort while
avoiding dangerous hot spots.
