Since the temperature at the top of the rack drives the cooling strategy for the whole data center, creating a measurement that factors in this reading seems only logical. And, since the temperature supplied by the CRAC unit is our cooling source, creating a measurement that evaluates the integrity of the air as it moves through the floor and to the server seems logical as well. The Airflow Utilization Efficiency (AUE)© calculation provides us with a way of evaluating the thermal loss in our airflow system. We compare the temperatures at the top of the rack to the supply air temperature.

Here is an example

55 degree supply air
85 degrees top of rack
AUE = 30
58 degree supply air
83 degrees top of rack
AUE = 25

In other words

1 degree = 4% reduction in energy costs
12 degrees = 48% reduction in energy costs
River systems quite often support an AUE of 10.
That is:
70 degrees supply air
80 degrees top of rack
AUE = 10


This is a simple way to determine if the cool air coming out of the CRAC unit experiences thermal loss leading to a low set point and higher energy usage. The smaller the AUE number, the more efficient your airflow system is working. In addition to the supply air temperatures, we would offer that the CRAC unit / supply air, should be optimized to have airflow temperatures at the top of the rack as close to 80 as possible. Lastly, since the difference is shown in temperature by degree, you can compare the difference and determine the reduction in energy costs.

River systems can do this with half the CRAC units utilized in a lake system. Additionally, the impact on energy consumption is improved as well. In the end, the reduced impact on capital expense and recurring costs make the “River Cooling System” an extremely compelling solution for any data center.


Temperature at upper Server


Supply temperature at CRAC


That is an Average AUE Of: