Sediment Delivery Assessment for a Transboundary Mediterranean Catchment: The Example of Nestos River Catchment

Nestos River flows through Bulgaria and Greece and discharges into the North Aegean Sea. Its total catchment area is around 6,200 km², while the mean annual precipitation and runoff are 680 mm and 40 m³/s, respectively. The Hellenic part of the catchment has undergone a substantial hydroelectric development, since two dams associated with major hydropower pumped-storage facilities are in operation. The main objective of the paper is to assess the expected sediment delivery of Nestos R. at the uppermost Thisavros reservoir site. This has been carried out by implementing the Universal Soil Loss Equation in a GIS environment for determining the mean annual soil erosion in conjunction with a suspended sediment measurement program (114 measurements in total) accomplished between 1965 and 1983 adjacent to the dam site. The sediment discharge rating curve between sediment and river discharges in a power form has been constructed using five alternative techniques, namely (a) the linear regression of the log-transformed variables, (b) the same as (a) but with the Ferguson correction, (c) different ratings for the dry and wet seasons of the year, (d) the nonlinear regression, and (e) the broken line interpolation that utilizes different rating parameters for two discharge classes. It is shown that the mean annual sediment yield is almost equal for all rating curve formulations and varies between 178.5 t km⁻² and 203.4 t km⁻² and the highest value results from the broken line interpolation method. Accordingly, the sediment delivery ratios vary slightly between 17% and 19% of the upstream soil erosion.     

A roadmap towards intelligent net zero- and positive-energy buildings

Buildings nowadays are increasingly expected to meet higher and more complex performance requirements: they should be sustainable; use zero-net energy; foster a healthy and comfortable environment for the occupants; be grid-friendly, yet economical to build and maintain. The essential ingredients for the successful development and operation of net zero- and positive-energy buildings (NZEB/PEB) are: thermal simulation models, that are accurate representations of the building and its subsystems; sensors, actuators, and user interfaces to facilitate communication between the physical and simulation layers; and finally, integrated control and optimization tools of sufficient generality that using the sensor inputs and the thermal models can take intelligent decisions, in almost real-time, regarding the operation of the building and its subsystems. To this end the aim of the present paper is to present a review on the technological developments in each of the essential ingredients that may support the future integration of successful NZEB/PEB, i.e. accurate simulation models, sensors and actuators and last but not least the building optimization and control. The integration of the user is an integral part in the dynamic behavior of the system, and this role has to be taken into account. Future prospects and research trends are discussed.     

On the selection and design of the proper roof pond variant for passive cooling purposes

The present paper aims to fully summarize the current scientific and technological experience focusing on the comparative characteristics of roof pond variants. The design guidelines and pond characteristics provide the opportunity to make the proper decision of a roof pond variant for cooling purposes. The following systems are under detailed investigation: covered/uncovered pond with/without sprays, skytherm, energy roof, coolroof, walkable pond, wet gunny bags, cool-pool shaded and ventilated pond. A brief background of the motivation behind the creation of the above variants is provided. The advantages and disadvantages of ponds as well as the design considerations and state of the art are discussed. Additionally, in the present study a detailed comparison is performed in terms of effectiveness and cooling demand reduction. A complete set of criteria affecting the choice of the proper roof pond are also analyzed. Finally, a decision support flowchart, is provided based on the various criteria and parameters.     

Predictive control techniques for energy and indoor environmental quality management in buildings

The aim of the present paper is to present a model-based predictive controller, combined with a Building Energy Management System (BEMS). The overall system predicts the indoor environmental conditions of a specific building and selects the most appropriate actions so as to reach the set points and contribute to the indoor environmental quality by minimizing energy costs. The controller is tested using a BEMS installation in Hania, Crete, Greece.     

Reinforcement learning for energy conservation and comfort in buildings

This paper deals with the issue of achieving comfort in buildings with minimal energy consumption. Specifically a reinforcement learning controller is developed and simulated using the Matlab/Simulink environment. The reinforcement learning signal used is a function of the thermal comfort of the building occupants, the indoor air quality and the energy consumption. This controller is then compared with a traditional on/off controller, as well as a Fuzzy-PD controller. The results show that, even after a couple of simulated years of training, the reinforcement learning controller has equivalent or better performance when compared to the other controllers.     

Virtual Building Dataset for energy and indoor thermal comfort benchmarking of office buildings in Greece

The knowledge of building stock energy data of a country is a very significant tool for energy benchmarks establishment, energy rating procedures and building classification boundaries determination, according to the Directive 2002/91/EC and its implementation in EU Member States. The lack of building energy databases in many EU Countries, including Greece, and the difficulties of collecting them lead to the investigation of other potential solutions. The aim of this paper is to present a method of a Virtual Building Dataset (VBD) creation for office buildings in Greece. The philosophy of VBD is based on the creation and simulation of random office buildings that could be found or built in Greece, taking into account the Greek constructional and operational characteristics of office buildings and Greek legislation. The VBD consists of 30,000 buildings (10,000 in each climatic zone) with their detailed constructional and operational data and of their simulation outputs: the annual specific energy consumption for heating, cooling, artificial lighting, office equipment and an indoor thermal comfort indicator. Based on VBD results the energy and indoor thermal comfort benchmarks for office building sector in Greece are assessed and presented.     

TCP-Aware Call Admission Control in High Altitude Platforms Using Cross-Layer Design

In this paper, a new cross-layer design is proposed employing the predictability of rain faded channels to guarantee QoS requirements in High Altitude Platform (HAP) networks. Both a centralized and a distributed scheme are proposed for call admission control of packet-switched HAP wireless networks using a cross-layer approach aiming at keeping the call dropping probability below a predefined threshold. In both schemes, a new call is accepted if there are sufficient resources for the ongoing calls and for the new one to guarantee their QoS requirements for their whole connection. The performance of the proposed schemes is investigated using markov chain analysis and bounds of the call blocking probability are determined analytically.     

Boiling on the surface of a rotating disc

An experimental unit to study heat-transfer characteristics while boiling at subatmospheric pressure of a horizontal smooth spinning disc was designed and built. Evaporation experiments were carried out with the speed of rotation varying from 0 to 1000 rpm and the feed flow rate from 1 to 5 litre/min. The boiling temperature varied between 40 and 50 °C. Water and corn syrup were used as test liquids. Results are presented from the experimental measurement of the heat flux on the disc as a function of the wall superheat. The heat-transfer coefficient for water, in the low range of heat flux (10–30 kW/m²), increased from about 2 to 9 kW/m²K when the speed of rotation increased from 0 rpm to 1000 rpm. In the upper range of heat flux (60–100 kW/m²), it increased from about 5 to 16 kW/m²K for the same increase in the speed of rotation. The feed flow rate between 1 and 5 litre/min had no significant influence on the heat-transfer coefficient in the range of 200–600 rpm. With the 60 °Brix corn syrup, the heat-transfer coefficient at 10 °C temperature difference increased from about 0.8 to about 2.3 kW/m²K when the speed of rotation increased from 0 to 1000 rpm. A simple theoretical relation was derived which predicts the heat-transfer coefficient for water at inlet Reynolds numbers 500–1000 relatively well, but underpredicts the results for corn syrup at inlet Reynolds numbers 10–100.     

E‐CLEMA: A cross‐layer design for improved quality of service in mobile WiMAX networks

In this paper, an efficient cross‐layer design that performs joint adaptation of the physical (PHY) and application layers of a mobile WiMAX network is proposed. The design takes into account channel state and performance information from the PHY and medium access control (MAC) layers, respectively. It uses a decision algorithm to evaluate this information, specify unfavorable conditions regarding low channel quality and increased congestion, and take measures by coordinating modulation order, transmission power, and media encoding rate, toward improved overall quality of service (QoS) offered to the user. Extensive simulation results show that the proposed design achieves considerably reduced packet loss and power consumption, combined with increased throughput as compared to a typical mobile WiMAX system. Copyright © 2008 John Wiley & Sons, Ltd.