How many of you have heard that very soon, we MUST have liquid directly to racks to cool them? To me, I attribute this to the same hysteria of, "the sky is falling".
How many skyscrapers will you be building?
Today, the average in the industry for rack heat loads is between 4-6kw. For datacenters, the racks that have loads >15kw are the minority. This is analogous to having a small number of sky scrapers in a city, with a huge amount of smaller buildings surrounding it. While, there are many new boxes coming out that are increasing the load per rack, the average load will still only increase in 2-4kw increments over time. Skyscrapers aren't buit overnight. There will not be a rapid replacement to drive racks to an average of 20kw unless you are running a computation hungry facility that uses uniform equipment that is >90% optimized. The standard replacement of equipment in asset life cycles will drive the average load per footprint up, but the majority of companies will not have the average load per rack at these levels. The ramp is getting steeper, but It will take time, and money, to happen.
Future rack trends
With that said, there will, and are configurations that are requiring cooling for >30kw per footprint. You can use traditional localized cooling for racks up to 30kw in a mixed environment. But when you pass this point, you can no longer force enough air for this equipment to be cooled. The economics also start to hurt. Fans and chiller plants forcing air to extract heat, account for 33% of the datacenter operational costs. Liquid cooling really is the next step. But, I believe the liquid will be refrigerant, not water. Refrigerant is more efficient across coils, giving even cooling distribution to components. It is also much less risk in a datacenter since it changes to a gas if there is a leak. In conjunction with the cooling, power capacities will also need to increase. I believe it will be 480V direct, rather than 208V. This is the coming trend for racks in datacenters. My projection is 2 years for racks like this to be readily available from numerous vendors, but >7 years for the average load per rack getting to these levels.
My opinion is that companies do not need to consider liquid cool racks until the average load breaks 15kw. With tightly coupled air cooling and containment, you can achieve very efficient solutions for these skyscrapers, as well as the other racks in the datacenter. Here is a picture of our highest density datacenter that is currently cooling loads with an average of 12kw/cabinet. This design can scale to an average of 18kw per rack. Keep in mind, that we can roll in 30kw racks to this solution. The key here is the average is 18kw. So you can have a wide range of rack loads in the same datacenter and still achieve cooling efficiencies. This 2,132 square foot room will have 720kw of equipment load. And...it is on a SLAB! It is the highest density, and highest efficiency datacenter in our portfolio of 1.3M square feet.
So, don't believe the hype or doomsday projections. The sky is not falling. This is a very predictable curve that doesn't require you to take drastic action to solve your datacenter cooling loads. You just need to keep it simple. Our Santa Clara Datacenter design has covered the current equipment loads and scale for the next gen equipment, today.