Abstract

With the increasing availability and affordability of building-integrated Heat Pumps (HPs), the number of heat pumps installed in residential buildings has risen significantly in recent years. When coupled with conventional District Heating (DH) systems in a hybrid setting, HPs provide higher energy reliability and cost-effective solutions for domestic heating. The operation of such systems, however, requires a sophisticated control system that simultaneously considers the dynamics of energy pricing and building energy needs. In this paper, we propose a nonlinear economic model predictive control to determine the optimal share for a hybrid DH-HP heating system. A resistor-capacitor thermal building model is utilized to capture the system dynamics. The results indicate that the proposed controller in the hybrid DH-HP system has a cost saving between 29% and 57% compared to the baseline scenario.

Abstract

In desert, Gobi, and barren regions, while wind resources are abundant, the harsh environment presents challenges for the deployment of maintenance personnel and the safe operation of equipment. This significantly increases the maintenance costs of wind turbines(WTs). Therefore, a more effective control strategy is needed to reduce fatigue loads on critical components, thereby extending the lifespan of WTs and ensuring longer, safer operational periods. For WTs operating above rated wind speeds, wind shear, wake effects, and yaw movements can cause uneven mechanical loads on the turbine blades, resulting in power fluctuations. By adopting active load reduction technology, these uneven mechanical loads can be effectively minimized, thereby extending the turbine’s lifespan. This paper establishes a linearized model of the WT system to achieve coordinated optimization of mechanical load and power. A coordinate transformation is performed to obtain an independent pitch prediction model suitable for model predictive control (MPC). A multi-input-multi-output independent pitch model predictive controller for the WT is then designed. Comparisons between the proposed strategy and traditional gain scheduling PI controllers demonstrate the effectiveness of the proposed method.

Abstract

This paper investigates the event-based secure control problem for networked power system subject to stochastic cyber-attacks. In order to make more effective use of network resources, an adaptive event-triggered mechanism (AETM) is developed, which differs from previous deterministic ETMs in that the designed trigger mechanism herein is based on stochastic dynamic variables. Moreover, the communication channel is contemplated for potential false data injection (FDI) attacks, while also considering the security performance of the networked power system. Then, the sufficient conditions for the system to satisfy the ℋ∞ performance index and mean-square exponential stable are given by using the Lyapunov stability theory, and the solvability of the security controller is obtained based on linear matrix inequalities (LMIs). Finally, the effectiveness of the proposed control method is verified by a simulation example.

Abstract

Wind turbines located in the Gobi Desert and other arid regions are subject to extreme environmental conditions, including frequent sandstorms and significant temperature fluctuations. These factors complicate maintenance and elevate operational costs, necessitating enhanced adaptability and performance in wind turbine controllers. Traditional controllers, which rely on linearized models, often require extensive adjustments and may deliver suboptimal performance. This study introduces a novel collective pitch controller for output power regulation and an independent pitch controller for reducing structural loads. By integrating these controllers into a robust, nonlinear system model, we developed a full-power preset time controller specifically tailored for the challenging conditions of the Gobi Desert. The proposed controller significantly enhances output power stability and reduces turbine loads. Comparative analysis with a gain-scheduled proportional-integral controller demonstrates the superior performance of our proposed solution.

Abstract

Capacity Expansion Models (CEMs) are widely used in the academic literature to understand the needs and dynamics of highly renewable energy systems. Due to computational constraints, it is common to aggregate time-series data such as hourly power output from Variable Renewable Energy Sources (VRES) using clustering algorithms. However, there is evidence that the presence of wind data leads to increased clustering errors and biased investment decisions. With the above motivation, we combine two approaches from the literature and compare them against the state-of-the-art approach. For a small number of clusters, the proposed approach recovers 95% of the original variance and correlation. This leads to more robust investment decisions. However, we stress the increased computational burden involved.

Abstract

Hydrogen combustion reactions produce nitrogen oxides as a byproduct. They can be reduced by exploiting the catalytic combustion of hydrogen in a monolith. However, some nitrogen oxides can still be produced in the gas-phase of the catalytic combustor. The present work numerically investigates the production of nitrogen oxides as a by-product of the combustion of a lean airhydrogen mixture in a catalytic monolith with an equivalence ratio lower than 0.3. The analysis is carried out with a 2D dynamic numerical model implemented in MATLAB. The model solves mass and energy balances in
a domain describing a single channel of the monolith. The model involves a detailed reaction mechanism for the gas-phase combustion, including the subsets that model the production of nitrogen oxides. As a result, the model indicates that the catalytic combustor does not produce nitrogen oxides with an inlet hydrogen fraction lower than 9%vol. Furthermore, the maximum value of nitrogen oxide at the outlet of the channel is lower than 0.4 ppm, obtained with the highest hydrogen fraction simulated in this work (12%vol inlet hydrogen fraction).

Abstract

Absorption thermal storage technology has emerged as a viable option for both long and short term energy storage applications. Aqueous sodium hydroxide (NaOH) water pair has shown potential for high storage density and long-term storage. The present study experimentally investigates the impact of various design and operating conditions on the absorption performance of an aqueous sodium hydroxide storage system. The heat and mass transfer characteristics are further analysed and compared for two finned heat exchangers with various aspect ratios along with their energy and exergy performance characteristics. It has been observed that the solution depth is more critical to the system
performance over the heat exchanger surface area, with a storage density reduction of up to 41.2% for the heat exchanger with higher fin height. Higher exergy efficiency is also observed for the heat exchanger with lower fin height owing to its better absorption characteristics. The performance of NaOH-H2O based heat exchangers is finally compared with that of the LiBrH2O pair over a microchannel membrane heat exchanger design from the literature. It is seen that the LiBr-H2O pair offers a lower storage density by around 55% compared to the NaOH-H2O pair. The findings of the present study suggest significant potential for the NaOHH2O pair and can assist in identifying better heat exchanger designs for thermal storage applications.

Abstract

The calcium looping (CAL) process is a cost-effective method for post-combustion CO2 capture, using CaO as a sorbent in the carbonator and CaCO3 for CO2 regeneration in the calciner. A pilot-scale cold model dual fluidized bed (DFB) reactor system was constructed at the Waste-to-Energy Research Facility (WTERF) at Nanyang Technological University (NTU). This system includes a bubbling fluidized bed (BFB) as a carbonator to capture CO2 from WTERF’s flue gas, and a circulating fluidized bed (CFB) as a calciner to regenerate CO2 for storage. The hydrodynamics of the pilot-scale system
were investigated through a series of cold model experiments. The effects of various operating conditions—such as gas velocities in loop seals, the carbonator and calciner, and solid inventories—on pressure distribution and solid circulation rates were studied. The preliminary objective of these cold model studies was to assess the feasibility of the design for
developing a hot model capable of continuously capturing CO2 from real flue gas. The results indicated that changes in gas velocities caused variations in the pressure profile and axial solid holdup within the system. Gas velocities in the calciner significantly influenced the total solid circulation rate. Stable operation was maintained throughout the system, as determined by the pressure drop between the reactors. These studies contribute to the development of an efficient hot model for carbon capture and lay the groundwork for scaling up the calcium looping process for industrial applications.

Abstract

Vertical borehole heat exchangers are the main method for utilizing shallow geothermal energy and are more suitable for small to medium-sized cities and town buildings with both heating and cooling demands. The imbalance of heating and cooling loads is a common issue during the operation of borehole heat exchanger systems, therefore, an appropriate arrangement of borehole heat exchanger arrays is crucial for alleviating thermal accumulation of the system. This paper constructs a heat transfer model for borehole heat exchanger arrays and selects Harbin, Tianjin, and Guangzhou as typical cities to discuss the differences in heating and cooling load ratios. Based on the analytical solution of the ground temperature field under dynamic loads, the study investigates the impact on the ground temperature field of sequentially arranged ground heat exchangers within square and rectangular areas. The results show that for a group of 16 borehole heat exchangers arranged in a 45 m × 45 m square configuration, after 10 years of system operation, the ground temperature in Guangzhou, which has a higher cooling demand, increased by 15.45°C; in Harbin, which has a higher heating demand, the ground temperature decreased by 18.55°C; and in Tianjin, where the heating and cooling loads are more balanced, the ground temperature fluctuated by about 2.06°C, showing relatively minor changes. When the borehole heat exchanger group is arranged in a rectangular configuration, the ground temperature in Guangzhou increased by 12.50°C, in Harbin, the ground temperature decreased by 15.45°C, and in Tianjin, the ground temperature changed by 1.55°C, which is significantly less than the changes observed with the square configuration. Therefore, the rectangular arrangement of ground heat exchangers is superior to the square arrangement. The research results can provide theoretical guidance for the arrangement of borehole heat exchangers in practical engineering applications.

Abstract

The intelligent water control sleeve can measure water cut and flow rate in real-time, remotely control the sleeve opening, and adjust the flow rate from different formation segments into the wellbore. To enhance the water control efficiency of the intelligent sliding sleeve, a multi-segment well reservoir model was established based on Well A01H in the M oilfield of the Bohai Sea. Reservoir numerical simulations were conducted for the water control process during the water-free period, low and medium water cut period, and high water cut period to study the adjustment strategies for the intelligent sliding sleeve valve opening. The results indicate that during the water-free period, targeting the liquid production profile, the duration of water-free oil production can be extended by reducing the sleeve valve opening in high production sections and increasing the opening in low production sections. During the low to medium water cut periods, with water cut as the control target, the rate of water cut increase can be reduced by decreasing the sleeve valve opening in high water cut sections and increasing the opening in low water cut sections. In the high water cut period, the focus shifts to maximizing daily oil production. Cumulative oil production can be increased by further extracting liquid production within the permissible range of production pressure difference. This study proposes control objectives and methods for each stage of intelligent sliding sleeve adjustment in horizontal wells, providing theoretical and practical guidance for water control development in CNOOC oilfields.