Cooling efficiency

Cooling efficiency is important because an inefficient mechanical system indicates that cooling is available but cannot be supplied to the load.

Calculating cooling efficiency is not as simple as calculating space or power efficiency; however, here is a guideline:

Cooling Efficiency =IT Equipment Power (kW) / Data Center Cooling Usage (kW)

First, determine what the IT Equipment Power is. This is identical to the IT Equipment Power used in calculating power efficiency.

The next step is to determine what the Data Center Cooling Usage of the CRAC units is (in tons)--not taking into consideration redundant units. Newer CRAC units display the percentage of capacity being used. To calculate the cooling usage of older chilled-water units, you must first determine the total capacity and determine the capacity of each compressor. Then, determine what percentage the control valve is open. This tells you the percentage of capacity being utilized. To calculate the cooling usage of older air-cooled/glycol units, you must also first determine the total capacity and the capacity of each compressor. Next, remove the side panel and determine how many compressors are operating.

The current cooling usage of a data center fluctuates over time and is often difficult to determine. In addition, any measurement taken will be a point-in-time measurement. Because of this, we recommend having your data center service provider gather the measurements on several occasions.

Once the Data Center Cooling Usage (in tons) has been determined, multiply it by 3.5 to convert to kW.

Finally, divide the IT Equipment Power by the Data Center Cooling Usage (in kW).

While a result of 1 is ultimately the goal because it represents perfect efficiency, it is more realistic to achieve a cooling efficiency in the range of .75 to .85. Anything lower than this target range indicates the need to evaluate the operation of the data center.

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When calculating space, power, and cooling efficiency, it is important to measure with the same methodology every time. Otherwise, the information is inaccurate. When you make a change to the data center environment, recalculate the space, power, and cooling efficiency to determine whether the action was an improvement.

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Bick Group has subject matter experts in this and many other topics. Talk to our experts by going to Bick Group’s mcfsolutions Let’s Talk webpage, located at

http://www.bickgroup.com/mcfsolutions/talk.htm.

800 295 BICKwww.bickgroup.com

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tedIn the data center environment, efficient operations translate into doing more with less. By understanding how to calculate space, power, and cooling efficiency, a data center professional can evaluate his or her existing facility and discover where improvements can be made---and thus stretch the original investment.

Space efficiency

It is important to utilize data center space efficiently because, quite frankly, it’s expensive real estate. What’s more, we have seen clients who were able to avoid a risky expansion project by re-designing the space layout.

Space Efficiency = Square Footage of Raised Floor Area / Total Rack Count

To calculate the space efficiency of an existing data center, first determine how many racks are in the facility. Establish a rack equivalent unit for equipment that is not in racks--for example, for every two access floor panels that a piece of equipment consumes, consider it as one rack. Then divide the square footage of the raised floor area by the total number of racks. This is your square-foot-per-rack calculation.

Reasonably efficient data centers will be between 30 and 35. Highly efficient data centers will be below 30. If you are over 50 square feet per rack, you should consider redesigning the space layout.

Power efficiency

The amount of power that data centers consume has recently become the subject of countless discussions, and the efficient use of that power has become the agenda of many organizations. Gartner, AFCOM, the Environmental Protection Agency (EPA), Alliance to Save Energy, Green Grid, Lawrence Berkely National Laboratory (LBNL), and others are working independently as well as collectively to not only educate data center professionals on the growing concern for data center power, but also to develop a standard set of metrics that will enable the industry to understand efficiency of data centers, improve the performance of equipment, and make smarter IT purchases.

Data Center Efficiency (DCE) is one metric that can be used to measure the power efficiency of your data center. It is defined as:

DCE = IT Equipment Power (kW) / Data Center Power (kW)

IT Equipment Power is the equipment that is used to manage, process, store, or route data within the raised floor space. The measurement is taken from the output of all of the PDUs and distribution points in the data center.

Data Center Power is the power measured at the utility meter--the power dedicated solely to the data center. It is inclusive of all power, including lighting and power required to run the CRAC units.

If the data center is separately metered, the measurement is taken from the meter. If the data center is not separately metered, it can be taken from the ATS reading (provided that it is available). You may need to contact your data center service provider to gather these measurements. In addition, these measurements presume that the generator is dedicated to the data center. If it is not, you will need to factor out ancillary loads.

A DCE value of .5 suggests that the IT equipment consumes 50 percent of the total power required in the data center. While it can never be one, the higher the DCE (or the closer the value is to one), the more efficient the facility is operating. According to Christian Belady with HP, a ‘good’ DCE is .625 and a reasonable target for facilities just beginning to address power efficiency is .5. Anything less than .5 indicates a need to make improvements.

data center efficiency

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