Information technology (IT) is becoming increasingly pervasive throughout society as more data is digitally processed, stored, and transferred. The infrastructure that supports IT activity is growing accordingly, and data center energy demands have increased by nearly a factor of four over the past decade. Data centers house IT equipment and require significantly more energy to operate per unit floor area than conventional buildings. The economic and environmental ramifications of continued data center growth motivate the need to explore energy-efficient methods to operate these buildings. A substantial portion of data center energy use is dedicated to removing the heat that is generated by the IT equipment. Using economizers to introduce large airflow rates of outside air during favorable weather could substantially reduce the energy consumption of data center cooling. Cooling buildings with economizers is an established energy saving measure, but in data centers this strategy is not widely used, partly owing to concerns that the large airflow rates would lead to increased indoor levels of airborne particles, which could damage IT equipment. The environmental conditions typical of data centers and the associated potential for equipment failure, however, are not well characterized. This barrier to economizer implementation illustrates the general relationship between energy use and indoor air quality in building design and operation. This dissertation investigates how building design and operation influence energy use and indoor air quality in data centers and provides strategies to improve both design goals simultaneously. As an initial step toward understanding data center air quality, measurements of particle concentrations were made at multiple operating northern California data centers. Ratios of measured particle concentrations in conventional data centers to the corresponding outside concentrations were significantly lower than those reported in the literature for office or residential buildings. Estimates using a material-balance model match well with empirical results, indicating that the dominant particle sources and losses -- ventilation and filtration -- have been characterized. Measurements taken at a data center using economizers show nearly an order of magnitude increase in particle concentration during economizer activity. However, even with the increase, the measured particle concentrations are still below concentration limits recommended in most industry standards. The research proceeds by exploring the feasibility of using economizers in data centers while simultaneously controlling particle concentrations with high-quality air filtration. Physical and chemical properties of indoor and outdoor particles were analyzed at a data center using economizers and varying levels of air filtration efficiency. Results show that when improved filtration is used in combination with an economizer, the indoor/outdoor concentration ratios for most measured particle types were similar to the measurements when using conventional filtration without economizers. An energy analysis of the data center reveals that, even during the summer months, chiller savings from economizer use greatly outweigh the increase in fan power associated with improved filtration. These findings indicate that economizer use combined with improved filtration could significantly reduce data center energy demand while providing a level of protection from particles of outdoor origin similar to that observed with conventional design. The emphasis of the dissertation then shifts to evaluate the energy benefits of economizer use in data centers under different design strategies. Economizer use with high ventilation rates is compared against an alternative, water-side economizer design that does not affect indoor particle concentrations. Building energy models are employed to estimate energy savings of both economizer designs for data centers in

In the US, data center operations currently account for about 61 billion kWh/y of electricity consumption, which is more than 1.5percent of total demand. Data center energy consumption is rising rapidly, having doubled in the last five years. A substantial portion of data-center energy use is dedicated to removing the heat generated by the computer equipment. Data-center cooling load might be met with substantially reduced energy consumption with the use of air-side economizers. This energy saving measure, however, has been shown to expose servers to an order-of-magnitude increase in indoor particle concentrations with an unquantified increase in the risk of equipment failure. An alternative energy saving option is the use of water-side economizers, which do not affect the indoor particle concentration but require additional mechanical equipment and tend to be less beneficial in high humidity areas. Published research has only presented qualitative benefits of economizer use, providing industry with inadequate information on which to base their design decisions. Energy savings depend on local climate and the specific building-design characteristics. In this paper, based on building energy models, we report energy savings for air-side and water-side economizer use in data centers in several climate zones in California. Results show that in terms of energy savings, air-side economizers consistently outperform water-side economizers, though the performance difference varies by location. Model results also show that conventional humidity restrictions must by relaxed or removed to gain the energy benefits of air-side economizers.

Data centers greatly impact California’s natural environment and economy. These buildings host computer equipment that provide the massive computational power, data storage, and global networking that is integral to modern information technology. The concentration of densely packed computer equipment in data centers leads to power demands that are much higher than those of a typical residence or commercial office building. Data centers typically consume 15 times more energy per square foot than a typical office building and, in some cases, may be 100 times more energy intensive (Greenberg et al. 2003). Nationally, data centers consumed 61 Terawatt hours in 2006; equivalent to the practical power generation of more than 10, 1 Gigawatt nuclear power plants (Brown et al., 2007). This is approximately equal to annual electricity consumption for the entire state of New Jersey (EIA, 2006). California has the largest data center market in the U.S., indicating that a significant portion of this energy is consumed within the State (Mitchell-Jackson, 2001).

This research project focused on identifying how data centers are currently designed and exploring potential energy saving associated with alternative building design options. The energy savings were quantified to understand when design changes resulted in significant benefits and when the benefits from alternative designs were minimal. The potential energy savings benefits were juxtaposed against changes to the environmental conditions in data centers and evaluated within the context of computer reliability concerns. The objective of this research is to provide data center designers and other decision makers with a better understanding of the benefits and concerns associated with data center energy efficiency, thereby reducing the unknown consequences that may hinder attempts to shift away from conventional design practices.