GRC & Minimus Servers Blog

Experiment: Temperature Set Point vs Server Fan Power

Posted by Alex McManis on June 17, 2016
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There is a prevalent industry focus 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 3 below.


Table 1: Dell R410 (2009) lightly loaded with a single processor, representing relatively low fan power
Ambient Temperature (ºC) Ambient Temperature (ºF) Power (Watts) Increase (∆ 27ºC)
27ºC 80.6ºF 137.7 -
29ºC 84.2ºF 139.4 +1%
31ºC 87.8ºF 141.5 +3%
33ºC 91.4ºF 144.0 +5%
33ºC 91.4ºF 144.1 +5%
35ºC 95.0ºF 148.4 +8%
37ºC 98.6ºF 154 +12%


Table 2: Distributed Computing Load and Air Temperature
R410 Watts vs Temp

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
Brand Model Size Power Savings in Oil*
OpenCompute Winterfell 2U 9%
Dell 1950, gen III 1U 30%
Dell R410 1U 8%
Dell C6100c 2U, 8 CPU 17%
Supermicro 1026 1U 20%
IBM X3550 1U 8%
HP 585 G5 4U 18%
CoinTerra Miner 4U 29%
*Compared to 75-80ºF inlet air temperature

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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Topics: fans, temperature, Servers, components, hardware, cost, cost optimization