Some recent studies have defined a metric called TPUE, which stands for “true PUE” or “total PUE.” TPUE is defined as PUE * SPUE.
PUE, the power utilization effectiveness, is defined in Section 6.4 as the ratio of the total facility power over the total IT equipment power. SPUE, or server PUE, is a new metric analogous to PUE, but instead applied to computing equipment.
SPUE is defined as the ratio of total server input power to its useful power, where useful power is defined as the power consumed by the electronic components directly involved in the computation: motherboard, disks, CPUs, DRAM, I/O cards, and so on. In other words, the SPUE metric captures inefficiencies associated with the power supplies, voltage regulators, and fans housed on a server.

a. Consider a design that uses a higher supply temperature for the computer room air conditioning (CRAC) units. The efficiency of the CRAC unit is approximately a quadratic function of the temperature, and this design therefore improves the overall PUE, let’s assume by 7%. (Assume baseline PUE of 1.7.) However, the higher temperature at the server level triggers the on-board fan controller to operate the fan at much higher speeds. The fan power is a cubic function of speed, and the increased fan speed leads to a degradation of SPUE. Assume a fan power model:

where ns is the normalized fan speed=fan speed in rpm/18,000 and a baseline server power of 350 W. Compute the SPUE if the fan speed increases from (1)
10,000–12,500 rpm and (2) 10,000–18,000 rpm. Compare the PUE and TPUE in both these cases. (For simplicity, ignore the inefficiencies with power delivery in the SPUE model.)

b. Part (a) illustrates that, while PUE is an excellent metric to capture the overhead of the facility, it does not capture the inefficiencies within the IT equipment itself. Can you identify another design where changes to the TPUE are potentially lower than the changes to traditional PUE?

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Fan power 284*ns*ns*ns-75*ns*ns, =