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We changed the default IT Equipment airflow assumption from 125 cfm/kW (212 m^3/hr/kW) to 100 cfm/kW (170 m^3/hr/kW). Though seemingly a minor tweak, this can have a large impact on your designs. With 20% less IT airflow, fewer coolers may be required and those remaining coolers may be operated at lower airflow rates - while still ensuring good cooling performance.
It is important to keep in mind that we are simply estimating airflow as a function of power; good airflow data is hard to find while power is typically known. Actual server airflow varies from model to model and even between different configurations of the same model. Servers may also automatically increase their airflow above an inlet-temperature threshold, e.g., 27 C (80.6 F).
Over the years, IT airflow has trended downward as data-center best practices have improved (e.g., hot/cold aisle, containment) and IT vendors reduce IT fan power. As the IT airflow goes down, the temperature rise across the IT equipment goes up. However, maximum exhaust temperatures are limited by inlet temperature thresholds and maximum safe "touch" temperatures. As a result of these constraints, IT airflow per power has become more consistent in recent years. The best overall source of IT airflow data that we have found is IT Equipment Design Impact on Data Center Solutions by ASHRAE. Below is a plot from that reference. Looking at the plot, we see that the average airflow per power is actually closer to 75 cfm/kW (125 m^3/hr). The default value in EcoStruxure IT Advisor CFD is a bit larger to give us some conservative margin and account for non-server IT equipment like storage products and networking gear which typically has more airflow on a per-power basis.
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