There is a prevalent
on increasing data center temperature to improve PUE and lower power usage, but when does it go too far? While it may be common knowledge that raising data center air temperature to above 70°F saves power, finding the sweet spot and exploring higher temperatures with free cooling takes some experimentation.
Even if you aren’t considering raising your data center set point, consider that inlet air temperature varies significantly from top to bottom of the rack. Airflow engineering attempts to even out airflow across the room, but a variation of 10°F is still not uncommon.
To find the effect of higher temperatures, GRC decided to measure the power of a server with varying input air – and you should, too. Using a power meter and thermocouple, we gradually increased the amount of recirculation to increase the input temperature into the server.
*Note: Raising the air set point is to save power on the chiller. We can’t test that affect because GRC data centers are chiller-less.
The following data is taken from a 2009 Dell R410, populated with a single, low power processor. Since the chassis is lightly loaded, the fans aren’t working strenuously. Fan power in other chassis is shown in
Table 1: Dell R410 (2009) lightly loaded with a single processor, representing relatively low fan power
Table 2: Distributed Computing Load and Air Temperature
|Ambient Temperature (ºC)
||Ambient Temperature (ºF)
||Increase (∆ 27ºC)
We found the server power increased logarithmically with input temperature. We also measured the difference between servers in air versus servers submerged in GRC cooling equipment.
Table 3: Power Savings from Submerging in Oil
*Compared to 75-80ºF inlet air temperature
||Power Savings in Oil*
||1950, gen III
||2U, 8 CPU
With your servers, how much power could you save by running the fans slower? How much if you submerged the servers and removed the fans altogether?
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