Re: Is liquid cooling really "greener"?
Exactly this. Water conducts heat much more readily than air, and can hold a lot more of it, requiring significantly less flow of the cooling medium (in this case water vs. air). So instead of using 100W/server or more on spinning fans (which are also contributing to the heat load), you can spend 4.3kW to move warm water for an entire row of cabinets (using something like the CoolIT CHx750 CDU, which claims to handle up to 750kW heat load). So, if you figure 4.3kW to cool 750kW of server load, that's about 0.06% of power going to cooling, vs. 100W of fans to cool a 600W server, being about 16.7% of power going toward cooling. This is only looking at the server side of things; the facility side is similar as they only have to pump water through mostly-passive coolers, vs. moving around a lot of air through active chillers. Due to the thermal characteristics of water it can operate as a sufficient coolant at much higher starting temperatures than air, adding to the efficiency. I believe something like up to 45C is allowed on the *inlet* side of the server, outlet side can go up significantly from there, which means a passive cooling tower in outdoor ambient air can bring it back down to useful temp in most climates (maybe not in Arizona in the summer, but in most northern climates it's perfectly reasonable).