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Home Blog 400ZR Benefits of Low Power Consumption and Higher Operating Temperature in Modules

Benefits of Low Power Consumption and Higher Operating Temperature in Modules

By Marc Stiller on December 18, 2021 | Leave a Comment

In determining the cost to deploy optical modules, one of the often-overlooked factors is power consumption. Although it’s usually considered as a day 0 specification, it also manifests in long term operational expense (OpEx) through two factors, i.e., (1) direct cost (electricity), and (2) indirect costs (fan power, air conditioning) that may be significantly larger.

Figure 1. Fraction of U.S. data center electricity use in 2014, by end use. Source: Shehabi 2016, Energy Innovation.

The relationship between fan speed and power needed to drive it follows a relationship called an affinity law that establishes a cubic relationship between fan speed and power required (shown below using above as reference point).

Figure 2. 50% power savings with a 25% reduction in fan speed

Simply by reducing the necessary fan speed from 100% of maximum to 75% of maximum saves 50% of the power used by the fan, which is estimated at 20% of the total switch and transceiver power consumption. Factoring in the additional overhead of the datacenter, including air conditioning and power conversion efficiency, will be even higher, although the exact number depends on the Datacenter design and other factors.

Of course, there is a reason for the fans, if they are running slower, there is less airflow, and less cooling of the module case. In order to save power, the modules need to be able to sustain higher temperatures for extended periods of time. While the actual temperature varies depending on details of the switch and module designs, with the increased power consumption in ZR modules relative to the shorter reach LR4 and DR4 modules, operating case temps may rise as high as 80C over short periods of time when cooling capacity is insufficient (ie, air conditioning dropout), and 75C over long periods. If the modules and associated technology (e.g., laser or DSP) used to manufacture are capable of reliably operating in this range, the net savings to the datacenter operators will be significant.

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