# Calculating CFMs for HPC Power and Cooling

Dell’s John Fragalla is out with Part IV of his post on HPC Power and Cooling, this time talking about how to requirements for cooling air delivery in terms of Cubic Feet per Minute (CFMs):

CFMs = (3412*W/1000) / (1.085 * ∆T)

In the above formula, W represents the peak measured power consumption in watts when stressing the components with a particular benchmark, such as Linpack discussed in Part 2 of my blog, and ∆T is the change in temperature between the air entering the system components and air existing the system components. When the change in temperature is large, typically seen when the inlet temperature is low, the CFMs are lower. But if the change in temperature is small, typically seen if the inlet temperature is high, than the resulting CFMs is higher because the fan speed increases to remove the hot air quickly from the components. Typical measured change of temperature I personally seen at customer sites is anywhere from 20F to 30F, and can be as high as 40F to 50F, but this depends on each customer’s data center, the inlet temperature, and how well the hot aisle is contained to avoid hot air leaks into the cold aisle.”