Look Before You Leap

For projects with a life expectancy over 10 years, the operating costs of the mechanical system will most likely exceed the initial installation cost. In addition, the initial selection of a cooling system will define all future options for cooling upgrades and expansions.

It is important to properly evaluate all cooling system options at the start of each project. At the plant level, the annual energy consumption of chilled water, water-cooled and air-cooled systems must be evaluated. At the terminal level, the selection of underfloor, overhead, or in-row cooling equipment should be considered. Fortunately, there are several energy modeling software packages on the market to make sense of this.

Modern energy modeling software can calculate system performance and energy consumption on an annual basis at various geographic locations and load profiles. For example, a free-cooling chiller plant in Miami will not have the same annual performance as a similar system located in Chicago. In addition, a system that is optimized for full-load performance may be highly inefficient when operated at partial load. Finally, a system that is highly efficient may not pay back if the project life expectancy is five years or less.

System selection must be carefully coordinated with the client expectations for installation cost, operating costs, and project life-cycle. Only when considering both energy and financial considerations together can the best decision be made.

Proper Air Flow

The quantities of CRACs and CRAHs required is initially calculated based upon nameplate data, but Computational Fluid Dynamics (CFD) is the best way to verify the design selections and quantities. CFD provides companies with a detailed 3-D analysis of how cold air is moving through the aisles and racks, identifying potential "hot spots" where equipment is receiving too little airflow. Thermal mapping can also find areas in a data center that are receiving more cold air than needed, wasting cooling and energy. For example, the selection of 50 ton CRAH units for a room with a 24" raised floor may look good on paper, but may result in uneven airflow distribution when installed.

CFD is the best way to verify and optimize CRAH and IT rack layouts and densities. Not all computer rooms are the same; CFD modeling helps to significantly improve in-room designs and aid in maximizing utilization of existing facilities.

For high density environments, it's important to know that blade servers consume, typically 10 times more total power than conventional rack servers, and require at least a four-fold increase in cooling capacity. As a result, according to an Uptime Institute study, power consumption in data centers has increased sevenfold (over 600 percent) in just seven years. As the graph from ASHRAE demonstrates (Fig. 2, next page), the trend for increased heat load will increase exponentially in the future.

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