This Web Exclusive article has been contributed by Carl Cottuli, vice president of products and services at Wright Line, an American manufacturer of air flow management systems based in Worcester, MA.
Data Center Air Flow: Measure It, Then Manage It
Per square foot, a data center within a larger facility is the most expensive portion of a modern building complex. This expense is due to evolving data center energy costs. Often it is the facilities manager who is asked to manage the data center’s energy needs.
Many data center managers understand that cooling improvement is always possible, but it is never clear to know how much improvement is possible without having to tear down and build new. The following is a short, simple, yet definitive, method of quantifying the energy/air flow status of your data center.
To improve cooling, you’ll need to identify four critical temperatures.
- Temperature 1 — A/C Outlet: Gather and average all air conditioning outlet temperatures at a given time.
- Temperature 2 — IT Inlet: Gather and average the lowest, mid-level, and uppermost rack inlet temperatures for a good statistical sampling for the rows in the data center.
- Temperature 3 — A/C Inlet: Gather and average the warm air stream returning for all air conditioning units in operation.
- Temperature 4 — IT Outlet: Gather and average the lowest, mid-level, and uppermost rack outlet temperatures for a good statistical sampling for the rows in the data center.
Subtract the Temperature 1 from Temperature 2. The result or “delta” is the average temperature rise in the supply chain of cool air entering the data center. This indicates how much heat is entering into the cool air stream before it gets to the IT equipment. Controlling this type of waste is important and will drive an improved performance for cooling the IT equipment.
If your Supply Path delta temperature is high, such as 15 degrees, for example, this represents a potential amount of energy to save and use elsewhere—such as for new IT equipment roll-outs—after an air flow management strategy is employed to eliminate some or all of the waste.
Next, subtract Temperature 4 from Temperature 3. This number will show the return path delta temperature, and will indicate the amount of cool air that is bypassing the IT equipment and returning directly to the air conditioning unit without cooling any IT equipment.
A significant change in the return path temperature above a few degrees indicates that some amount of chaos cooling is present in the data center and can lead to significant unpredictability in cooling performance.
These quantitative readings should be evaluated as pairs of delta temperatures in the supply and return path. A data center with many times more cooling capacity than demand would yield a very low delta in the supply path, but a very high delta in the return path. Consequently, there would be an opportunity to improve air flow management in the system. Also, when making any improvements, it is always very important to be mindful of the impact any air flow changes have on both supply and return optimization.