INTRODUCTION In the mission critical environment reliability has been the cornerstone of the industry. This has been the priority almost at the exclusion of any other issue@ especially efficiency. The general consensus seemed to be that because of the critical nature of data centers; efficiency was not much of a priority and in fact seemed a hindrance to reliability. With rising energy costs and the fact that virtually every large business and government branch has a critical data center@ the mindset is shifting quite rapidly. There are a number of reasons for this shift; mainly increasing energy demand and rising cost@ but also public pressure and pressure from utilities. The energy per square foot required for the typical data center has increased dramatically over the last 10 to 15 years. This increase in load density is due primarily to the increased speed and processing power of the computer microchip (processor). As the size of the chip is reduced and the power is increased the load per square foot has skyrocketed. There are many papers written on this subject with varying projections on the rising cost of the average data center's monthly utility bill. But the general consensus seems to be about 50% of the Information Technology (IT) budget is spent on costs directly related to energy for the IT environment. In addition to the above@ new IT system designs@ which include more efficient interconnects and high performance data bus design@ create a significant increase in memory and higher utilization percentage amongst other devices. The new trend of system miniaturization@ dense packing within racks@ and the increase in power needed for power conversion on system boards have caused an order of magnitude rack power increase. This means that the data center will experience significant reductions in populated area on the raised floor while pushing their UPS and critical power systems to the limit. The recent introduction of high density blade servers substantially complicated the cooling system requirements. This triggered the introduction of new technologies such as the utilization of chilled water or refrigerants directly in the IT racks with more advanced air management methods at the rack level. Power is considered the major hurdle in data center flexibility and expansion. Between 1999 and 2005@ electricity consumption by US data centers rose more than 39% and its cost can no longer be ignored. In 2006@ data centers' power consumption including supporting mechanical and electrical infrastructure consumed over 1.5% of the United States (U.S.) national power consumption (EPA 2007). Indeed@ environmental consciousness is vital for survival in today's world where more and more emphasis is underway to control the global warming which results from green house gas emissions such as CO2. Data center owners and operators are only now beginning to accept the concept that reliability and energy efficiency are compatible. Now@ new standards for the design and operations of new and existing facilities are emerging around the world. Silicon Valley is the hub of this activity for both IT and facilities based solutions. Future rules and regulations regarding data center energy consumption will clearly be lead by the federal government. The Department of Energy (DOE) (DOE 2007@ 2008) and the Environmental Protection Agency (EPA) are currently recommending legislation to Congress which they in turn will enforce as may be required by law. EPA's Report to Congress (2007) sent a clear message to the public that they wish to develop collaborative solutions with the data center industry. However@ the extent to which they plan to enforce those solutions remains to be seen. Data centers consume immense amounts of power to perform functions reliably and effectively@ but efficiency in a data center is extremely beneficial. Efficiency conserves energy@ reducing the costs of operation while also lowering the environmental impact of the facility. Presently@ many changes are taking place that affect data center operations: energy costs are rising@ government organizations such as the EPA and DOE are working to implement new initiatives that could eventually regulate and tax massive energy consumers@ as well as advancing technologies that are more compact and give off a greater amount of heat in relation to size. These changes only increase the benefits of creating a data center with efficiency in mind. With the ever rising cost of energy@ efficiency will only become increasingly financially beneficial.