Practical example of right sizing
How efficient is it to size something 100 times larger than necessary? Will it use the same amount of energy as something that is sized precisely for the load it serves? A practical example is a glass of water. How much water will actually enter the glass if it is filled with a fire hose? Depending on how long you try to fill the glass, the entire area around the glass will be covered with the overspray which is essentially wasted water. The wasted water is a direct parallel to the wasted energy associated with mismatching the load and the cooling system capacity.

In the same glass example, what if the glass is filled with water from a sink faucet that is easily controlled; all the water enters and stays in the glass with no waste. This is an example of matching the supply with the need; "right sizing". Take the glass example still one more time. What if the glass is filled with a faucet that has an automatic shutoff? The glass will be filled but you have to move the glass around to re-engage the sensor so that the faucet does not prematurely shutoff. The net result is the glass will be filled but the automatic shutoff will keep the faucet running for a period of time after the glass is filled. This is an example of inadequate control and not synchronizing the cooling supply with the load. Right sizing is a good energy saver and is easily achievable.

Step 1 - Determine the actual maximum load
What is the maximum load for each piece of equipment? Especially in a multi-vendor environment, this can be quite an undertaking. Typically the terms used vary greatly resulting in inherent inaccuracies due to not using a common baseline and unit. For example, some terms used include:

-. Watts or kW
- Amps
Circuit Amps
DEG.. Wiring Amps - Nameplate Amps - Full Load Amps - Peak Amps - Measured Load

General Allowance in kW/Rack
Frequently the nameplate amps are used because it is a number that is readily available (attached to the equipment). Unfortunately, the nameplate information is a regulatory requirement and is focused on safety; not on accurately characterizing the load.

Typically the nameplate amps grossly overstate the load. To compensate for this, many apply an adjustment factor (e.g. 40-to-50%). There is great inconsistency in the measured load versus the nameplate value and therefore a standardized adjustment factor can be inaccurate (oversize or undersize).

The most effective approach to identifying equipment load is to request an ASHRAE Thermal Report for each piece of equipment. This report identifies the measured load (heat release) in watts and provides this information for multiple configurations of the equipment such as number of processors, amount of memory, or the amount of hard disks.

Figure 1 shows an ASHRAE Thermal Report for the IBM model 520. Where a Thermal Report is not available, simple measurements can be made to provide a general characterization of the piece of equipment and informal produce a Thermal Report.

Figure 1: 2004, ASHRAE Thermal Guidelines For Data Processing Environments adapted by DLB Associates, Consulting Engineers, P.C.

Step 2 - Determine the load profile
Imagine looking at the compute load or workload for an entire data center in five minute increments across an entire year. It is hard to imagine that there would be no fluctuation in load and easy to imagine significant fluctuation.
Typically within a data center, there is more than one software application running. Further, the activities and load on each application are often varying. This compute load profile is also complicated by software upgrades and applications that are installed but not serving load due to a delay in their integration into a worldwide operation. The cooling system is not only impacted by the compute load but by climate as well. It is very beneficial to produce annual load profile curves for the compute load, climate, and a composite of compute load and climate. The same profile curves should be provided for an hour period and day in addition to the annual. These profiles should be produced even if they are not much more than educated guesses using minimal input from IT operations, etc.

Step 3 - Determine the future load
ASHRAE has tables that identify the projected life of cooling equipment (10-to-25 years). IT equipment has a much shorter life. For ease of comparison, if the IT equipment life is two-to-five years, there will be five generations of IT equipment in one lifetime of cooling equipment.

As a result cooling system design and sizing should consider both the current load and the future load. Often, the data center must remain in operation during a partial or full upgrade/refresh of IT equipment. This means that upgrading the cooling system to add capacity or cooling interface points must occur with minimal to no disruption; this is very costly and difficult to accomplish.

Figure 2 is a chart from the ASHRAE book, Datacom Equipment Power Trends and Cooling Applications. This chart provides projections through to 2014. These loads are the highest loads for any single manufacturer for any given class of equipment. The intent is to apply an adjustment or derating factor to these loads to determine the future load for a specific facility.

Figure 2: ASHRAE Datacom Equipment Power Trends and Cooling Applications

Step 4 - Determine the operating conditions
The operating conditions (temperature and humidity) have a significant impact on:
�. Amount of cooling being accomplished by economizer (free cooling) - Pumping and fan horsepower since the larger the Delta T (temperature differential), the less the required flow. - Amount of humidification required and its associated energy ASHRAE Book, Thermal Guidelines for Data Processing Environments, provides both recommended and allowable ranges for temperature and humidity as well as temperature rate of rise.

ASHRAE Book, Thermal Guidelines for Data Processing Environments, provides both recommended and allowable ranges for temperature and humidity as well as temperature rate of rise.

Step 5 - Equipment and system selection
Develop several cooling alternatives based on the current and projected capacity needs as well as the operational load profiles. Optimize equipment selections based on operating ranges. Alternatives should include various degrees of scalability. For example, the current load may be significantly less than the ultimate load. A single piece of equipment or system may not be efficient at both the current or day one load and the ultimate or final load.

Summary
Data center energy usage is significant. Right sizing through the five step process or any other structured approach has the potential to yield significant energy savings.

About the author Don Beaty is Founder and President of DLB Associates Consulting Engineers; a firm providing international consulting on a selective basis for over 20 years. Don was Chair of ASHRAE Technical Committee TC 9.9 (mission critical facilities, technology spaces, & electronic equipment) from its inception through June 2006. His exclusive interest is in exposing the industry to the work of TC 9.9 (he does not solicit nor accept clients or projects from speaking engagements). His interest in educating the industry about ASHRAE being the unbiased source of data center cooling material has resulted in Don publishing over 50 technical papers and articles. He also is a frequent presenter on the subject including having presented in 9 countries on the topic of data center cooling. Under his committee leadership the plan of publishing an extensive series of small, reader friendly books was developed with the fourth book being published by the end of 2006. Don is currently International Chair TC 9.9 Committee-Liaisons, Alliances and International Activities. Previously, Don was with ASHRAE TC 90.1 (energy standards committee) from 1993 to the present serving in various roles such as Vice-Chair. Contact dbeaty@DLBASSOCIATES.com