Let’s start with the first question… how much power can my IT space support? Often times, the available power feeds (the input voltage and breaker size) are constraints within the IT space of a data center. These power feeds determine the maximum power capacity provided to each IT pod (a pod is generally defined as 2 rows of racks being fed from a common distribution point).
For instance, if I have 208/120V 3-phase power coming into my IT space, and my input breaker is rated at 225A, I can get 65 kW of power out of that breaker.
Here’s the math: Power (kW) = [3-ph voltage x 1.732 x the breaker rating in amps x the derating of the breaker] / 1,000; so [208 x 1.732 x 225 x 0.8] / 1,000 = 65 kW
On the other hand, if my input voltage was 415/240V, with the same input breaker size, I can get 130 kW of power. (415/240V distribution allows you to get twice the power.)
The amount of power you can get from a particular breaker is one of the key outputs of our IT Pod Sizing Calculator. We developed this TradeOff Tool to help data center designers understand the electrical and physical attributes of an IT pod based on key constraints. Another key factor is the rack density, which leads us to the second question…
Expected rack density impacts how many racks I can specify and deploy in each pod. But this is a tricky parameter to forecast, especially with the rapid changes we’re witnessing in IT, such as hyper-convergence. The more uncertain you are of the density, the more additional space you should reserve to avoid stranding power and/or cooling capacity. Generally, it is a better financial decision to strand space vs. stranding power and cooling infrastructure. The IT Pod Sizing Calculator helps illustrate the effect of expected density and density confidence on the overall pod and room size.
An additional electrical consideration for determining pod size is the number of available breaker positions. This can become a constraint for low density pods with a higher number of racks for a given power feed. The calculator helps you see these implications.
In our supporting White Paper 260, Specifying Data Center IT Pod Architectures, we explain how to specify the physical infrastructure for an IT pod and describe optimum configurations based on available power feeds, physical space, and targeted average rack power densities.
Check out the tool and the paper when you’re facing these data center decisions. Experimenting with “what-if” scenarios will help you feel confident in the impact it has on your data center.