David J. CappuccioThis post is the third in a series of questions that need to be asked before embarking on a data center build project.
How much energy will I need?
Great question. Somebody always asks the obvious, especially when there is no way to definitively answer the question. In the old days (you know, 8 or 10 years ago), a data center was built with a single power footprint – meaning a consistent watts per square foot design. This was done historically with data centers because IT equipment generally followed a fairly obvious and linear energy consumption growth path and projecting future growth was at least feasible. Not so much in today’s world. Both server and storage energy growth has skyrocketed over the past 8 years due to the introduction of newer technologies (blades, 2u and 1u servers, higher density cores etc). Couple that with a rapid rise in the use of virtualization and we have exceeded the physical capacity of the facilities mechanical and electrical equipment to deliver power to support IT loads in many data centers around the world.
So what can you do? You can plan for the unknown (and I wish you luck with that boardroom funding request), or you can design for the most logical expected energy loads, but with the flexibility to shift loads and usage patterns as needed. From a basic design point today a 3 zone structure might support high density racks at 10-12kW, medium density at 6-8kW and low density up to 5kW. The size (percentage) of these zones obviously depends on you (your mileage will truly vary) but these zones can shrink or grow as workloads demand.
Ok, let’s say we’ve done that and 8 years from now things are getting a bit hot in the data center and power demands continue to rise, one option would be to refocus my cooling efforts away from forced air, especially as power requirements for equipment begin to exceed the 6 to 8kW per rack range. Augmenting traditional air cooling with in-rack cooling, either water or refrigerant, will fee up a significant amount of power for other uses. The general rule of thumb is that for each watt of power for IT load you should assume at least an additional watt of power for cooling the same equipment. For low utilized equipment this could be less (below 4kW per rack), but as you move into the higher density zones above 8kW the ratio begins to shift towards cooling needing more power than IT load (sometimes as much as 2 to 1). However, if you decide to cool inside the rack with refrigerant based systems the cooling to IT load ratio never changes – as air leaving the rack is approximately the same temperature as that going in and the room air conditioning workload does not change.
There are other options as well which we will explore in other posts, things like bringing in outside air instead of just using the mechanically cooled variety, or refocusing what loads actually need the UPS and which ones don’t. The bottom line though is that with flexible designs, scalable PDU’s, and a willingness to use alternative cooling techniques the energy question is not quite as critical as one might think.
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Category: Data Centers Food for Thought Tags: Data Centers, Power and Cooling
