In a picturesque spot overlooking San Francisco Bay, the US Department of Energy's Berkeley Lab has begun building a new computing center that will one day house exascale systems. The DOE doesn't know what an exascale system will look like. The types of chips, the storage, the networking and programming methods that will go into these systems are all works in progress. DOE is expected to deliver to Congress by the end of this week a report outlining a plan for reaching exascale computing by 2019-2020 and its expected cost. But what the DOE does have an idea about it is how to cool these systems.