There are many aspects that go into running a data center successfully, but I think we would all agree that uniform, consistent temperature on the critical floor is certainly one of the most important. Customer equipment likes to have a reasonable temperature (we target 72* F), that does not vary - no matter what time of the day, or day of the year that it is.
What many customers do not realize is that from a facilities perspective, computer gear makes for wonderful space heaters. Typically, for every watt of power used by a piece of equipment, roughly 99% of that watt is converted into thermal energy (heat), and we are tasked with removing that heat from the datacenter. In our application, we have chosen to use closed-loop chilled-water cooling systems. Essentially, we use a chiller which makes cold water (about 54* F) and pump it through a coil in the environmental control rooms of the datacenter, and push the air that is coming from the computer gear through that same coil.
The problem is that these chillers consume considerable power, sometimes using upwards of 50 watts for every 100 watts of heat generated by customer equipment (thus, a Power Usage Effectiveness (PUE) rating of 1.50).
So, you ask, what does this have to do with 15* F outdoor temperatures?
Well, when we send the water out to be cooled by our chiller units, we first send them through what is known as a drycooler, which uses outside air to cool the water before we put it through the chiller. In our application, whenever the outside air temperature is about 50*F or cooler, we are able to cool the chilled water to our desired temperature of 58* F without using any chiller power whatsoever.
Consider the diagram below, which shows realtime operation of one of our many cooling modules in our Parsippany 2 (WBR) data center:
We know most people complain about the cold, but we are more than willing to put up with these low temperatures for a while longer!