Demand Response for Reducing Coincident Peak Loads in Data Centers

Demand response is a key aspect of managing uncertainty and reducing peak loads in electric grids. This paper considers the capability of a datacenter to provide responsiveness to grid signals through cooling system control. The strategy is based on pre-cooling the center for provision of load reduction during demand response events, and is evaluated using a numerical model of a cooling system, validated against experimental data obtained from a small telecommunication data center. The pre-cooling strategy is applicable to a wide-range of demand response programs, but is illustrated on the example of an established critical peak pricing program; specifically the 4 coincident peak (4CP) program in the ERCOT ISO. Precooling reduced the annual cost of electricity used by the cooling system by 7.8% to 8.6%, while increasing the total energy use only by 0.05%. This translated into 2% to 2.6% reduction in the electric bill of the whole data center. The developed demand response strategy is suitable for data centers with power densities below 500 W/m2 which do not use server air containment systems

Technoeconomic Analysis of Biofuel Production and Biorefinery Operation Utilizing Geothermal Energy

A technoeconomic study is conducted to assess the feasibility of integrating geothermal energy into a biorefinery for biofuel production. The biorefinery is based on a thermochemical platform that converts low-value lignocellulosic biomass into biofuels via gasification and fuel reforming. Geothermal energy is utilized in the refinery to generate process steam for gasification and steam-methane reforming in addition to providing excess electricity via the organic Rankine cycle. A process simulation model is developed to simulate the operation of the proposed biorefinery, and corresponding economic analysis tools are utilized to predict the product value. The biorefinery uses 2000 metric tons of corn stover per day, and the products include gasoline, diesel fuel, hydrogen, and electricity. Implementation of geothermal energy into the proposed biorefinery is analyzed through two studies. In the first study, process steam at 150 °C with a flow rate of approximately 16 kg/s is assumed to be generated through a heat exchanger process by utilizing the heat from geothermal resources, producing a geothermal liquid at 180 °C and a total flow rate of 105 kg/s which is used to provide steam for gasification and steam-methane reforming within the biorefinery. In the second study, additional geothermal capacity of 204 kg/s is assumed to be available and is separated into two phases (liquid and steam) via a flash column. The steam produced is utilized in the same manner as the initial study while the geothermal liquid is used for electricity production via the organic Rankine cycle to add to the profitability of the biorefinery. This analysis considers that the technology is feasible in the near future with a high scope of technology development and the end products are compatible with the present fuel infrastructure. The total capital investment, operating costs, and total product values are calculated considering an operating duration of 20 years for the plant, and the data are reported based on the 2012 cost year. Simulation results show that the price of the fuel obtained from the present biorefinery utilizing geothermal energy ranges from $5.17 to$5.48 per gallon gasoline equivalent, which is comparable to $5.14 using the purchased steam. One important incentive for using geothermal energy in the present scenario is the reduction of greenhouse gas emissions resulting from the combustion of fossil fuels used to generate the purchased steam. Geothermal energy is an important renewable energy resource, and this study provides a unique way of integrating geothermal energy into a biorefinery to produce biofuels in an environmentally friendly manner

Design and optimization of standardized organic Rankine cycle power plant for European conditions

RES Master´s Thesis Verkefnið er unnið í tengslum við Háskóla Íslands og Háskólann á AkureyriThis paper investigates the possibility of introducing universally designed binary power plants into European energy markets. ORC cycles are found to be particularly useful not only for the production of electricity from geothermal water, but also for the recovery of waste heat from engine exhaust gasses, furnaces and drying ovens. In this dissertation, an analysis of market demand and thermodynamic characteristics of different heat sources is performed in order to find an optimal set of design boundary conditions maximizing unit performance for the most promising types of applications. A thermodynamic model of a power plant using a wet mechanical-draft cooling tower is created in EES software and a detailed analysis of component configuration and parameters of working fluids is carried out. Optimal plant configuration and size of components is found by thermoeconomic optimization. Exergy flow rates of all streams in the system as well as rates of exergy destruction and loss are quantified. Detailed economic analysis of the unit is made for four different applications: geothermal plants using water from conventional hydrothermal wells, former oil and gas boreholes, waste heat recovery plants coupled with diesel engines, and a clinker cooler in a cement plant. Finally, a sensitivity analysis shows the impact that changes in heat source characteristics and macroeconomic variables have on levelized cost of power

A Systems Approach to Development and Evaluation of Geothermal Energy Utilization Systems

A successful design and operation of geothermal energy systems require a multidisciplinary approach combining engineering, geoscience and economics. The complex interactions between individual geothermal system components can be captured using techno-economic models. An example of such model is the GEOPHIRES software developed at the Cornell Energy Institute, which allows users to determine the optimal configurations of geothermal systems and quantify their technical and economic performance. The main objective of this work was to improve the competitiveness of geothermal energy by developing improved energy conversion and distribution technologies and by providing well cost models used for the GEOPHIRES software. The first part of this work focused on the development of organic Rankine cycle (ORC) power plants used in geothermal applications. This goal was addressed in multiple ways. First, the efficiency of ORCs was correlated with the molecular structure of working fluids. The developed methodology can be used to evaluate performance of ORCs using less common working fluids, for which no accurate equations of state (EOS) exist. This dissertation also supported the development of more accurate EOS models for next-generation working fluids by providing measurements of isobaric heat capacity (Cp) of pure fluids and mixtures. To expand the thermodynamic data library for these fluids, a flow calorimeter for measuring Cp in liquid, vapor, and supercritical phases was developed. Lastly, this work evaluated the ways to effectively incorporate geothermal utilization systems into the existing energy infrastructure. A feasibility study of a hybrid geothermal-biomass-natural gas energy system for Cornell University campus was done to analyze the opportunities for improving the integration of low-temperature geothermal systems. In addition to the work on geothermal utilization systems, this dissertation quantified the costs and uncertainties associated with drilling and completion of geothermal wells. The well cost correlations were developed using a predictive well cost model and the records of recently drilled geothermal wells. The presented analysis can reduce the financial risk involved in geothermal systems by quantifying the well cost uncertainty and its impact on the project economics

Technoeconomic Analysis of Biofuel Production and Biorefinery Operation Utilizing Geothermal Energy

A technoeconomic study is conducted to assess the feasibility of integrating geothermal energy into a biorefinery for biofuel production. The biorefinery is based on a thermochemical platform that converts low-value lignocellulosic biomass into biofuels via gasification and fuel reforming. Geothermal energy is utilized in the refinery to generate process steam for gasification and steam-methane reforming in addition to providing excess electricity via the organic Rankine cycle. A process simulation model is developed to simulate the operation of the proposed biorefinery, and corresponding economic analysis tools are utilized to predict the product value. The biorefinery uses 2000 metric tons of corn stover per day, and the products include gasoline, diesel fuel, hydrogen, and electricity. Implementation of geothermal energy into the proposed biorefinery is analyzed through two studies. In the first study, process steam at 150 °C with a flow rate of approximately 16 kg/s is assumed to be generated through a heat exchanger process by utilizing the heat from geothermal resources, producing a geothermal liquid at 180 °C and a total flow rate of 105 kg/s which is used to provide steam for gasification and steam-methane reforming within the biorefinery. In the second study, additional geothermal capacity of 204 kg/s is assumed to be available and is separated into two phases (liquid and steam) via a flash column. The steam produced is utilized in the same manner as the initial study while the geothermal liquid is used for electricity production via the organic Rankine cycle to add to the profitability of the biorefinery. This analysis considers that the technology is feasible in the near future with a high scope of technology development and the end products are compatible with the present fuel infrastructure. The total capital investment, operating costs, and total product values are calculated considering an operating duration of 20 years for the plant, and the data are reported based on the 2012 cost year. Simulation results show that the price of the fuel obtained from the present biorefinery utilizing geothermal energy ranges from $5.17 to$5.48 per gallon gasoline equivalent, which is comparable to $5.14 using the purchased steam. One important incentive for using geothermal energy in the present scenario is the reduction of greenhouse gas emissions resulting from the combustion of fossil fuels used to generate the purchased steam. Geothermal energy is an important renewable energy resource, and this study provides a unique way of integrating geothermal energy into a biorefinery to produce biofuels in an environmentally friendly manner.Reprinted with permission from Energy Fuels, 2013, 27 (3), pp 1381–1390. Copyright 2013 American Chemical Society.</p

Isobaric Heat Capacity Measurements of Supercritical R1234yf

R1234yf (2,3,3,3-tetrafluoropropene) is a low global warming potential (GWP) replacement for R134a, a fluid commonly used as a refrigerant in domestic and automotive air conditioning systems and as a working fluid in organic Rankine cycles. The use of R1234yf in energy conversion cycles requires an accurate determination of its thermophysical properties, including the isobaric heat capacity (<i>c</i>_P). Using a custom-made flow calorimeter, experimental <i>c</i>_P measurements of supercritical R1234yf were made at temperatures <i>T</i> = 373.15 to 413.5 K and absolute pressures <i>P</i> = 3.5 to 10 MPa. The experimental apparatus was calibrated using R134a to increase the measurement accuracy. The heat capacity measurements of R1234yf were compared to available published experimental data and to values obtained from a multiparameter equation of state (EOS). The measured <i>c</i>_P values agreed well with the EOS, providing an average absolute deviation (AAD) of 1.6%