 Abstract-Modern data centers are characterized by large sizes, high energy consumption and complexity involving IT, power supply, ventilation and cooling. Data center energy efficiency is a major concern for data center design and operation. To improve data center energy efficiency through efficient cooling and ventilation, advanced process control and optimization, process models to describe the process power consumption are required. In this work, data center power consumption models are investigated. A concept of distributed air flow control is presented. The objective is to develop a comprehensive data center power consumption model to describe IT room, computer room air handling (CRAH), data center ventilation and cooling characteristics as well as distributed air flow control. Data center operation scenarios with uneven IT load are simulated. Results show that the distributed air flow control can save the cooling energy significantly.

The design-point performance of various gas turbine cycles such as simple, regenerative, and intercooled-regenerative, is well understood. It is also understood that more elaborate shaft arrangements such as one, two, or three concentric or nonconcentric shafts, and a separate power turbine shaft, provide better starting and operational flexibility, and wider plateaus of high off-design performance. However, the types of different off-design performance one can obtain with these different shaft arrangements has not been previously reported. In this paper we use a computer program to investigate the design-point and off-design-point performance of engines with the following: one single shaft joining the compressor, turbine and load; one shaft joining compressor and turbine, and one shaft for the power turbine; two shafts for compressor and turbine, and one shaft for the power turbine; and three shafts joining the compressor and turbine, and one shaft for the power turbine. This is done by specifying typical compressor and turbine maps, and computing various aspects of off-design performance. The advantages and disadvantages of the various arrangements are investigated and discussed.

The design-point performance of various gas turbine cycles such as simple, regenerative, and intercooled-regenerative, is well understood. It is also understood that more-elaborate shaft arrangements such as one, two or three concentric or non-concentric shafts, and a separate power turbine shaft, provide better starting and operational flexibility, and wider plateaus of high off-design performance. However, the types of different off-design performance one can obtain with these different shaft arrangements has not been previously reported. In this paper we use a computer program to investigate the design-point and off-design-point performance of engines with: one single shaft joining the compressor, turbine and load; one shaft joining compressor and turbine, and one shaft for the power turbine; two shafts for compressor and turbine, and one shaft for the power turbine; and three shafts joining the compressor and turbine, and one shaft for the power turbine. This is done by specifying typical compressor and turbine maps, and computing various aspects of off-design performance. The advantages and disadvantages of the various arrangements ore investigated and discussed.