The use of smart technologies and the Internet of Things (IoT) is becoming more and more popular in order to enhance the overall building performance by monitoring parameters related to occupants’ comfort and health in the built environment. A new modular, custom-made and replicable IoT system is proposed based on an Arduino development board (MKR WiFi 1010) connected to the Arduino IoT Cloud. An Application Programming Interface (API) enables the integration of this system with other possible ones, thus making the system modular, custom-made and replicable. A series of parameters were simultaneously monitored over a 7-day period in two office spaces and a photovoltaic (PV)-testing laboratory. While the meteorological and comfort parameters (temperature, relative humidity, CO₂) were monitored in all three spaces, the health parameters (total volatile organic compounds—TVOCs; formaldehyde—HCHO; particulate matter—PM; and radon—²²²Rn) were monitored only in an office setup located right next to a Chemical Analysis and Testing Laboratory. Generally, the registered values of the health parameters fell within the recommended thresholds. However, the thermal comfort parameters were constantly exceeded: over 90% of the working time in the two office spaces and 83.33% in the PV-testing laboratory. Still, the optimal relative humidity values in the monitored spaces contributed to the discomfort reduction in the occupants. Also, CO₂ and TVOCs had some exceptions in particular conditions. CO₂ values of up to 1500 ppm due to poor ventilation and TVOC levels of up to 1000 ppb related to chemical experiment development were registered. Also, several other peaks were recorded when monitoring HCHO as well as PM. Thus, special attention must be paid to natural ventilation or to the improvement of building characteristics. Also, the time intervals when experiments in the Chemical Analysis and Testing Laboratory are carried out should be communicated to other personnel from the nearest offices. The testing of the monitoring system over a one-week period showed that the proposed solution operated adequately, representing a reliable tool for data acquisition via the Arduino IoT Cloud.

The research presented in this paper involves the design of a power control system for a hydrokinetic turbine previously tested in real operating conditions. A maximum power point tracking (MPPT) algorithm was designed and simulated using the required parameters for a specific electric generator. The proposed system consists of a generator connected to the hydrokinetic turbine, a three-phase uncontrolled rectifier, a direct current (DC) boost converter with MPPT control to extract maximum available power, and a buck converter to control the amount of power delivered to the load. In order to test the MPPT algorithm, we built the individual blocks on the basis of the corresponding equations of each component. The algorithm considered the specific parameters of the previously tested turbine as input data and simulated the same water velocities for which the turbine had been tested. Thus, the simulation predicted a power output of 105 W for a water velocity of 1.33 m/s, 60 W for 1 m/s, and 30 W for 0.83 m/s. The efficiency of the control system was demonstrated when the instantaneous power value was maintained at a maximum point, regardless of the rotational speed according to the experimental power curves of the driving rotor obtained for certain water velocities.

This paper describes the experimental study of a behavioural barrier consisting of a bubble curtain placed near an ecological river water intake, aiming to assess the bubble curtain’s influence on the velocity field of water flowing in the water intake proximity. The scientific novelty is given by the water intake solution operating in tandem with the dedicated bubble curtain generator used for avoiding fish entrapment. The water intake solution used in the present research is based on a run-of-river intake without a dam in the riverbed, maintaining the mountain rivers longitudinal connectivity. An experimental setup was designed and built to study the behavioural barrier for ecological water intakes in different operating conditions. Thus, tests were performed for two water velocities (0.33 m/s and 0.535 m/s) in the experimental setup, two water depths (92 mm and 119 mm) and two air flow rates (10.5 LPM and 15 LPM). The results were compared with the case when no air is injected through the bubble curtain generator. The assessment of the bubble curtain influence on the water flow inside the channel was made by measuring and analysing the velocity variation in vertical and horizontal direction. The results showed a significant velocity gradient in the bubble curtain proximity, which can contribute to influencing the behaviour of the fish by deterring them from the water intake area.

The results of a pilot-scale study on the influence of electric field use for stimulating the active sludge in the biological purification tank of a small capacity wastewater treatment plant (up to 600 m³/day) are presented. Through specific comparative chemical tests (DO, COD, N-NH₄, and Pt) it was found that, by applying a sinusoidal electric field of 5 Vrms/m at 49.9 Hz on the active sludge suspension, the overall pollutant denitrification process speed is doubled compared with the reference case when no stimulation is used. Also, under identical operating conditions, the residual pollutant content of the biological treatment tank outlet water is reduced approximately three times for COD and approximately two times for N-NH₄ and P_t compared to the reference tank. These findings lead to the conclusion that, by stimulating the active sludge microbial activity of the wastewater treatment plants by a sinusoidal electric field of 5 Vrms/m at 49.9 Hz, the time of the biological purification treatment can be reduced by approx. 50%. This leads to a corresponding decrease in energy consumption, which usually represents more than 30% of a wastewater treatment plant’s specific electricity consumption.

The protection of fish habitat near water diversion or hydrotechnical facilities is of particular interest for researchers working in various fields. The chapter is focused on an experimental study of a fish behavioral barrier consisting of a bubble curtain operating along a river water intake scale model. It approaches elements of fish hydrodynamics, river water intakes, as well as physical and non-physical barriers for fish diversion from hydrotechnical facilities. The design, development, and testing of the fish behavioral barrier as well as the results of the experimental analysis are discussed. The proposed experimental setup was based on a barrier placed in the proximity of a river water intake scale model fitted and tested in a closed-circuit hydraulic stand. The intake chamber is provided with perforated orifices which communicate through an inlet with a lower tank for discharging the water into another tank located beneath. A certain water velocity within the hydraulic stand was set to assess the tandem operation of the bubble curtain and water intake. A sharp velocity gradient was found in most cases, indicating local velocity changes and creating the premises for impacting the fish behavior. Conclusions and future research development are also envisaged in the chapter.

The article emphasises both the advantages and disadvantages of photovoltaic power plant deployment, assessing the current stage of development as well as the deficient characteristic criteria, such as the occupied specific surface area or the associated unpredictability. The authors consider that current technologies related to photovoltaic plants provide a maximum efficiency of approximately 28%. Consequently, management methods must be applied in order to improve efficiency and eliminate the reported deficiencies. When assessing a medium- to high-power PV plant, the initial investment, projected efficiency, and parameters of the desired plant are correlated, and sometimes, a cheaper and less efficient power plant can be recommended. Although solar trackers may represent a viable solution in certain scenarios, their effectiveness is strongly influenced by various factors, including panel orientation, climatic conditions, installed capacity, and the specific technologies. These variables can significantly affect such systems’ overall efficiency and suitability. The present study proposes a statistical approach to assessing the economic efficiency of photovoltaic systems equipped with solar trackers, aiming to enhance energy production performance. The results are correlated and validated using field data obtained from existing literature studies to ensure the reliability and accuracy of the analysis. For a better analysis, the paper presents two methods, ANOVA and STEM, which are derived from quality control. The novelty aspect of this proposal consists of the combination of specific data obtained from the PVGIS platform with a new approach for optimisation of energy production in photovoltaic systems based on geographical coordinates. The STEM statistical method provides a high degree of novelty because, although it is a well-known method, it has not yet been applied to analyse the technical and economic efficiency of photovoltaic systems. One of the main advantages of this method is its ability to incorporate a wide range of technical and economic performance parameters. A case study is provided to evaluate the benefits of implementing the STEM method.