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This paper addresses the energy conservation problem in computing systems. The focus is on energy-efficient routing protocols. We formulated and solved a network-wide optimization problem for calculating energy-aware routing for the recommended network configuration. Considering the complexity of the mathematical models of data center networks and the limitations of calculating routing by solving large-scale optimization problems, and methods described in the literature, we propose an alternative solution. We designed and developed several efficient heuristics for equal-cost multipath (ECMP) and Valiant routing that reduce the energy consumption in the computer network interconnecting computing servers. Implementing these heuristics enables the selection of routing paths and relay nodes based on current and predicted internal network load. The utility and efficiency of our methods were verified by simulation. The test cases were carried out on several synthetic network topologies, giving encouraging results. Similar results of using our efficient heuristic algorithm and solving the optimization task confirmed the usability and effectiveness of our solution. Thus, we produced well-justified recommendations for energy-aware computing system design to conclude the paper.

Abstract The supercritical power plant analyzed in this paper consists of the following elements: a steam turbine, a hard-coal-fired oxy-type pulverized fuel boiler, an air separation unit with a four-end-type high-temperature membrane and a carbon dioxide capture unit. The electrical power of the steam turbine is 600 MW, the live steam thermodynamic parameters are 650°C/30 MPa, and the reheated steam parameters are 670°C/6 MPa. First of all the net efficiency was calculated as functions of the oxygen recovery rate. The net efficiency was lower than the reference efficiency by 9–10.5 pp, and a series of actions were thus proposed to reduce the loss of net efficiency. A change in the boiler structure produced an increase in the boiler efficiency of 2.5–2.74 pp. The range of the optimal air compressor pressure ratio (19–23) due to the net efficiency was also determined. The integration of all installations with the steam turbine produced an increase in the gross electric power by up to 50.5 MW. This operation enabled the replacement of the steam regenerative heat exchangers with gas–water heat exchangers. As a result of these alterations, the net efficiency of the analyzed power plant was improved to 5.5 pp less than the reference efficiency.

Abstract. Design of an optimal wind farm topology and wind farm control scheduling depends on the chosen metric. The objective of this paper is to investigate the influence of optimal wind farm control on the optimal wind farm layout in terms of power production. A successful fulfilment of this goal requires: 1) an accurate and fast flow model; 2) selection of the minimum set of design parameters that rules the problem; and 3) selection of an optimization algorithm with good scaling properties. For control of the individual wind farm turbines, the two most obvious strategies are wake steering based on active wind turbine yaw control and wind turbine derating. The present investigation is a priori limited to wind turbine derating. A high-speed linearized CFD RANS solver models the flow field and the crucial wind turbine wake interactions inside the wind farm. The actuator disk method is used to model the wind turbines, and utilizing an aerodynamic model, the design space of the optimization problem is reduced to only three variables per turbine – two geometric and one carefully selected variable specifying the individual wind turbine derating setting for each mean wind speed and direction. The full design space spanned by these (2N + Nd Ns N) parameters, where N is the number of wind farm turbines, Nd is the number of direction bins, and Ns is the number of mean wind speed bins. This design space is decomposed in two subsets, which in turn define a nested set of optimization problems to achieve the fastest possible optimization procedure. Following a simplistic sanity check of the platform functionality regarding wind farm layout and control optimization, the capabilities of the developed optimization platform is demonstrated on the Swedish offshore wind farm. For this particular wind farm, the analysis demonstrates that the expected annual energy production can be increased by 4 % by integrating the wind farm control in the design of the wind farm layout, which is 1.2 % higher than what is achieved by optimizing the layout only.

Quantitative reliability, availability, and maintainability (RAM) assessments are of fundamental importance at the early design stages, as well as planning and operation of marine renewable energy systems. This paper presents an RAM framework adaptable to different offshore renewable technologies, conceived to provide support in the choice of the device components and subsequent planning of the O&M strategies. A case study, characterizing a pilot farm of oscillating water column (OWC) wave energy converters (WECs), is illustrated together with the method used to obtain reliable estimate of its key performance indicators (KPIs). Based on a fixed feed-in-tariff for the project, economic figures are estimated, showing a direct relationship with the availability of the farm and the cost of maintenance interventions. Consequently, the probability distributions of the most relevant output variables are presented, and the mutual correlations between them investigated using principal components analysis (PCA) with the aim of discovering the relationships influencing the performance of the offshore farm. In this way, the contributions of the individual factors on the profitability of the project are quantified, and generic guidelines to support the decision-making process are derived. It is shown how this type of analysis provides important insights not only to ocean energy farm operators after the deployment of the devices, but also to device developers at the early design stage of wave energy concepts.

This paper presents an open standards-based information system supporting the democratization and consumer empowerment through flexibility activation. The paper describes a functional technical reference infrastructure: a secure, standard-based and viable communication backbone for flexibility activation. The infrastructure allows connection, registering, activation and reporting for different types of granular consumer flexibility. The flexibility sources can be directly controllable set points of chargers and stationary batteries, as well as controllable loads. The proposed communication system sees all these flexibility provisions as distributed energy resources in a wider sense, and the architecture allows consumer-level integration of different energy systems. This makes new flexibility sources fully available to the balancing responsible entities in a viable and realistically implementable manner. The proposed reference architecture, as implemented in the FLEXCoop project, relies on established open standards as it is based on the OpenADR and OAuth2 / OpenID standards and the corresponding IEC 62746-10 standard, and it covers interfacing towards other relevant standards. The security and access implications are addressed by the OpenID security layer built on top of the OAuth2 and integrated with the OpenADR standard. To address the data protection and privacy aspects, the architecture is designed on the least knowledge principle.

Aerodynamics of the Darrieus wind turbine is an extremely complex issue requiring the use of very advanced numerical methods. Additional structural components of this device, such as, for example, a rotating shaft disturb the flow through the rotor significantly impairing its aerodynamic characteristics. The main purpose of the presented research is to validate the commonly-used unsteady Reynolds averaged Navier–Stokes (URANS) approach with the shear stress transport (SST) k-ω turbulence model based on the particle image velocimetry (PIV) studies of a two-bladed rotor operating at the moderate tip speed ratio of 4.5. In the present numerical studies, a two-dimensional turbine rotor with a diameter of 1 m was considered. The following parameters were evaluated: instantaneous velocity fields; velocity profiles in the rotor shadow and aerodynamic blade loads. The obtained numerical results are comparable with the reference experimental results taken from the literature. The second purpose of this work was to examine the influence of the rotating rotor shaft/tower on the wind turbine performance. It has been proven that the cylindrical shaft reduces the power of the device by 2.5% in comparison with the non-shaft configuration.

Abstract Efficiency of the earth-to-air heat exchangers depends not only on their thermal performance but also on the total pressure losses that are the cost of harvesting a geothermal heat. In this paper the sensitivity analysis of the flow characteristics to the change of multi-pipe exchanger geometry is presented. Experimental investigation and CFD simulation results present total pressure losses in the considered exchangers and airflows in each branch-pipes. Considered geometrical structures varies in the number of parallel pipes, pipes length, main pipes diameters and supply type. The experimental investigations were conducted on the exchangers models in a scale 1:4. To investigate the real size exchangers, validated CFD flow performance model was used. A costless modification of heat exchanger supply-type from Z-type to U-type structure (change in air inlet location) is verified as a simple method of decreasing total pressure losses by 6–36% and improving airflow division uniformity by 11–80%. It is shown that main pipes diameter that are 1.4 times bigger than parallel pipes diameter can result in diminished total pressure losses by 56–73% and improved airflow division uniformity by 6–59%. The least significant effect on the flow characteristics has the branch-pipe length. Total pressure losses of long branch-pipes exchangers can be 15–32% higher than for short ones and the airflow division uniformity can be 8–35% higher. Results can be used for choosing the proper geometry of multi-pipe earth-to-air heat exchangers from the flow performance point of view. Presented flow characteristics can be used in detailed analysis and energy assessment of exchangers cooperating with the mechanical ventilation system in building.

Passive buildings compared to the standard ones require significantly less energy for heating, so the correct models of every “energy using” building's components are very important. This paper analyzes how various models of the internal heat and moisture gains, as well as natural airflows between building zones, influence the accuracy of the calculation of the energy performance, indoor temperatures and absolute humidity in a single-family passive building. A simulation environment used a detailed twelve-zone TRNSYS model of a house with HVAC system. The model included natural airflows between zones, and internal heat and moisture gains, defined as precisely as possible. The gains were allocated on the basis of special protocols of use filled by the occupants during the two-week measurement. The measurement data were also used for validation of the model. The verified model constituted a basis for calculation of energy performance and simulation of air temperature and absolute humidity change in a building with significantly limited airflow between zones, and heat and moisture gains defined according to standards. The standardized values of heat and moisture gains were defined on the basis of the standard ISO 13790 and national regulations in Poland. The simulations have shown that precise methodology of calculation of heat gains and airflows between building zones is very important for proper computation of energy performance and simulation of indoor temperatures and absolute humidity in passive buildings. Results of carried out analysis have shown that the difference in energy need for heating calculated using precise and simplified methods of internal heat gains determination was 30.1%.