The objective of this paper is to describe an energy-based approach to visualize, identify, and monitor faults that may occur in a water-to-water transcritical CO ${}_2$ heat pump system. A representation using energy attributes allows the abstraction of all physical phenomena present during operation into a compact and easily interpretable form. The use of a linear graph representation, with heat pump components represented as nodes and energy interactions as links, is investigated. Node signature matrices are used to present the energy information in a compact mathematical form. The resulting node signature matrix is referred to as an attributed graph and is populated in such a way as to retain the structural information, i.e., where the attribute points to in the physical system. To generate the energy and exergy information for the compilation of the attributed graphs, a descriptive thermal–fluid model of the heat pump system is developed. The thermal–fluid model is based on the specifications of and validated to the actual behavioral characteristics of a physical transcritical CO ${}_2$ heat pump test facility. As a first step to graph-matching, cost matrices are generated to represent a characteristic residual between a normal system node signature matrix and a faulty system node signature matrix. The variation in the eigenvalues and eigenvectors of the characteristic cost matrices from normal conditions to a fault condition was used for fault characterization. Three faults, namely refrigerant leakage, compressor failure and gas cooler fouling, were considered. The paper only aims to introduce an approach, with the scope limited to illustration at one operating point and considers only three relatively large faults. The results of the proposed method show promise and warrant further work to evaluate its sensitivity and robustness for small faults.

Research in nuclear engineering focusses on improving the safety of light water reactors (LWRs), driven by accidents like Fukushima in 2011. The severity of this accident was a result of active cooling system failures and cladding material oxidation resulting in hydrogen explosions. To this end, efforts concentrate on the improvement of passive safety in LWRs and the development of accident tolerant fuel (ATF). Natural circulation small modular reactors (SMRs) are new reactor concepts designed around passive safety. One such SMR called the NuScale SMR was chosen for this study. This study aimed to evaluate the combination of one selected passively safe reactor system with two selected ATF cladding materials, namely FeCrAl alloy and a silicon‐carbide (SiC) composite, to determine if this combination would greatly increase the safety of LWRs. The use of ATF cladding materials in the NuScale for possible mitigation of a potential worst‐case scenario accident has not been evaluated. A model of the SMR was developed using ASYST 3.4 thermal–hydraulics code and validated for steady state operation and one worst‐case scenario accident transient using data taken from the NuScale final safety analysis report (FSAR) and literature. Results indicated minimal impact on steady state operation when employing ATF cladding materials. FeCrAl and SiC caused minor changes in peak cladding temperature (PCT) and peak fuel centerline temperature (PFCT). The worst‐case scenario accident transient involved the inadvertent opening of one reactor vent valve (RVV) with subsequent failure of the emergency core cooling system (ECCS) and decay heat removal system (DHRS). In the current model, this led to failure of the Zr‐alloy cladding after 6.42 h. This coping time was increased with the use of ATF cladding, with FeCrAl and SiC providing an increase of 0.5 and 4.35 h, respectively.

Energy and exergy interactions in industrial systems hold meaning across physical domains. This paper builds on the notion that capturing the energy and exergy interactions of a system, while retaining physical structural context, enables fault detection and isolation. To this end, three energy graph-based visualisation methods were developed for the purpose of fault detection and isolation. This paper presents a comparative study of the three analysis methods designated the 1) distance parameter method, 2) eigenvalue decomposition method, and 3) residual method. The study utilises data from a physical lignite plant in Janschwalde, Germany, in combination with simulation data of specific faults in order to compare the sensitivity and robustness of the three methods. The comparison is done firstly in terms of detection and secondly in terms of isolation. The distance parameter and eigenvalue decomposition methods showed high sensitivity and robustness for fault detection, while the residual method showed moderate comparative performance. In terms of fault isolation, the distance parameter method showed high sensitivity and robustness, while the eigenvalue decomposition method had irregular isolation performance. The residual method isolation results proved inconclusive.

The South African industrial sector has a high energy demand, accounting for 1167 PJ/annum (37.8%) of the country’s total energy demand, and accounts for 80% of the thermal demand. Consequently, the sector exhibits a significant opportunity for the integration of high-temperature CO2 heat pumps within the South African context. For this paper, the industrial heat demand for South Africa below 100°C was determined. From the data, one can determine which divisions have the highest theoretical potential for integrating CO2 heat pumps. The authors investigated 12 industrial divisions to determine the sectors with the highest theoretical potential below 100°C. From the investigation, South Africa has a theoretical potential of 266.1 ±49.1 PJ/annum under 100°C. The non-specified industry has the largest theoretical potential for heat below 100°C, with a share of 64.1% or 170.6 ± 44.8 PJ/annum. The division is too diversified to make any substantial conclusions. The second largest sector was the mining and quarrying division, with a share of 20.6% or 54.8 ±6.7 PJ/annum. The food, beverage, and tobacco division has a low theoretical heat demand below 100°C of 1.8±0.2 PJ/annum, which contradicts the literature research. However, the fraction of heat demand below 100°C is 21.3% ±1.8% and this sector may still be a feasible option for integrating CO2 heat pumps. The results facilitate the prioritized application of CO2 heat pumps in industrial sectors and processes in South Africa. Furthermore, the technique can be used for other countries that do not have thermal heat demand per sector.

The South African industrial sector has a high energy demand, accounting for 1167 PJ/annum (37.8%) of the country’s total energy demand. Additionally, the sector also accounts for 80% of the thermal demand. Consequently, the sector exhibits a significant opportunity for the integration of high-temperature CO2 heat pumps within the South African context. For this paper, the industrial heat demand for South Africa below 100°C was determined. From the data, one can determine which divisions have the highest theoretical potential for integrating CO2 heat pumps. The authors investigated 12 industrial divisions to determine the sectors with the highest theoretical potential below 100°C. From the investigation, South Africa has a theoretical potential of 266.1 ±49.1 PJ/annum under 100°C. The study showed that the non-specified industry has the largest theoretical potential for heat below 100°C, with a share of 64.1% or 170.6 ± 44.8 PJ/annum. The division is too diversified to make any substantial conclusions. The second largest sector was the mining and quarrying division, with a share of 20.6% or 54.8 ±6.7 PJ/annum. Even though the food, beverage and tobacco division has the 7th highest theoretical heat demand below 100°C, the sector is the division that has the highest potential from literature. Based on the investigation's data, it's possible to identify industrial divisions with the greatest potential for integrating CO2 heat pumps.

The primary heat rejection cycle, which is critical for the stability and integrity of the metal production process and equipment, involves the transfer of heat from flue gas to a fluid circulated through a gas-cooler. The rate of heat transfer from the flue gas is influenced by several parameters, including the temperature of the cooling fluid. Heat transfer rates that are too high or too low can negatively impact equipment’s life, emphasising the need for a temperature operational envelope in the cooling fluid prior to entering the gas-cooler. Rejected heat is used for power generation, transferred to the environment, or both. This study examines the impact of control philosophies on both temperature and power generation, while maintaining the exit temperature within the desired range as the highest priority. A more advanced philosophy that combines bypass control with feedforward parameters can maintain temperatures within safe operating limits at all times, while improving the power generation, compared to a typical works approach which is used as a baseline. This study presents a formulation that increased power generation from an average of 6.11 MW for a typical works philosophy to 10.68 MW, while maintaining the temperature within the operating temperature envelope.