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This paper introduces a novel a CO2 mechanical subcooling heat pump water heater (MSHPWH) to improve the heating performance in low temperatures. By utilizing a mechanical subcooling (MS) cycle, additional heat is supplied to cooling water, improving system efficiency. The study evaluates the heating COP (COPh), power consumption and temperature of hot water under various steady-state operating conditions. Results indicate that the COPh of the MSHPWH increases by 44% to 57% compared to conventional HPWH as ambient temperatures range from -25 ℃ to -5 ℃. The MS cycle proves beneficial, with a subcooling range of 4 ℃ to 20 ℃. Adjusting the refrigerant mass flow rate ratio enhances heating output and hot water temperature. Changes in the mass flow rate ratio impact COPh and the temperature of hot water concurrently. This research highlights the innovative MS cycle's significant role in enhancing CO2 heat pump water heater performance in cold climates, showcasing its potential as an eco-friendly and efficient heating solution. [ABSTRACT FROM AUTHOR]

Load shifting for existing electric resistance water heaters (EWHs) presents a potential solution to utility challenges caused by the temporal mismatch between solar generation and electricity consumption. A case study in the Florida Power & Light (FPL) territory for both an individual and a fleet of EWHs evaluates this potential. Two optimization problems are solved using mixed-integer linear programming to maximize solar self-consumption and minimize electricity cost for an individual EWH. Compared to default operation, the solar maximization strategy results in nearly twice as much heating electricity from solar (80% vs. 42%) and 14% increased electricity cost based on FPL rates. An energy balance approach shows the aggregate impact of all FPL EWHs on days of peak and minimal load, June 25th and December 3rd. Publicized goals of increased solar capacity by 2030 will cause changes to the FPL net load, total load minus solar generation. The four million EWHs in the territory can stabilize the net load in 2030 as shifting their load causes a 24% decrease in the standard deviation of the predicted load on both dates. These results encourage widespread adoption of retrofit devices that control EWHs based on solar generation profiles and water consumption schedules. [ABSTRACT FROM AUTHOR]

Thermoacoustic air-to-water air source heat pumps (TAWASHP) are the eco-friendly, simple, compressor less, low cost and likely looking future substitute for the existing compressor-based heat pumps. In this work, the design optimization of the 1-kW TAWASHP with helium for the temperature difference of 15 to 70 K for pumping heat from the atmospheric air to water using the linear thermoacoustic concepts was discussed. The optimized design can fit for both cooling and water heating applications without wasting the heat rejection to the surrounding atmosphere, rather supplied to the insulated hot water tank. The optimized one-fourth wavelength resonator TAWASHP shows the coefficient of performance of 1.1 to 2.34. The theoretical results are validated with the DeltaEC software results, and the results are in concurrence with each other. The DeltaEC predicts the TAWASHP can supply 1.55 to 3.35 kW of heat to water, which is equivalent to 37.3 to 80.3 kWh of heat energy per day. [ABSTRACT FROM AUTHOR]

This study focused on assessing the financial efficiency of investing in a horizontal shower heat exchanger. The analysis was based on net present value (NPV). The research also examined the possibility of using artificial neural networks and SHapley Additive exPlanation (SHAP) analysis to assess the profitability of the investment and the significance of individual parameters affecting the NPV of the project related to installing the heat exchanger in buildings. Comprehensive research was conducted, considering a wide range of input parameters. As a result, 1,215,000 NPV values were obtained, ranging from EUR −1996.40 to EUR 36,933.83. Based on these values, artificial neural network models were generated, and the one exhibiting the highest accuracy in prediction was selected (R2 ≈ 0.999, RMSE ≈ 57). SHAP analysis identified total daily shower length and initial energy price as key factors influencing the profitability of the shower heat exchanger. The least influential parameter was found to be the efficiency of the hot water heater. The research results can contribute to improving systems for assessing the profitability of investments in shower heat exchangers. The application of the developed model can also help in selecting appropriate technical parameters of the system to achieve maximum financial benefits. [ABSTRACT FROM AUTHOR]

User requirements serve as the primary reference content in product design. The effective capture of crucial user requirements, followed by the development of a product technical solution aligned with these requirements, stands as a pivotal approach to enhancing design efficiency. In order to explore the problem of generating and decision-making of product technical solutions in the case of complex user demands, this study constructs a user requirements driven product optimization design model, which is used to complete the generation and decision-making of product design solutions in a more reasonable way. The model unfolds across three key stages: Firstly, a user requirements importance ranking system is crafted leveraging Kano Model and Pairwise Analysis. Next, employing the Functional Analysis System Techniques (FAST) theory and the Quality Function Deployment (QFD) theory, user requirements undergo transformation into technical solutions. Finally, these technical solutions are amalgamated into diverse technical combinations, with decisions facilitated by a game theory model to yield the optimal overall design solution. The new optimal design model reduces the influence of subjectivity and ambiguity in the process of user requirements analysis, increases the reliability of the transformation of user requirements into technical solutions, and improves the efficiency of the generation and decision-making of product design solutions under multiobjective situations. The model proposed in this study is exemplified through the development of a medicated bath water heater. Results indicate that the technical solution derived from the model surpasses similar products in terms of user satisfaction, thereby validating its feasibility. [ABSTRACT FROM AUTHOR]

Featured Application: The main application of this paper is to review and improve a model that enables the use of water heaters by small electricity customers in electricity markets and services in the short and medium term. For this goal, it is necessary to review the service of loads to avoid customer discomfort and the way control mechanisms work, usually thermostats. To guarantee a minimum level of accuracy in the flexibility of the response, the understanding of heat and electric processes in the load is a cornerstone for the participation of these appliances. This must be done by comprehensive validation of the model in different conditions, including water draws, temperature, and load control. To exemplify the potential of the model, an application in a prosumer scenario is presented. Residential segments are of the greatest interest from the point of view of Demand-Side Resources and Decarbonization. Main end-uses such as water heaters, heating, and cooling have interesting opportunities: first, they can store energy, and this is relevant for the integration of renewables. Second, they are candidates for efficiency and electrification, increasing their demand share and the flexibility of demand. This paper aims to formulate an elemental Physical-Based Heat Pump Water Heater model that will enable the use of these energy-efficient appliances through aggregation in complex products, considering the advantages for demand and supply sides. Simulation results show that the individual performance is quite accurate and that the proposed model is flexible enough to be used to take more profit from energy markets or to easily respond to fast-occurring events. The model can be easily aggregated and used to obtain baselines, an important point for Demand Response evaluation. Results also demonstrate that demand–supply coordination and balance can be improved using these models to reduce or mitigate the risks and volatility of renewables without inducing a noticeable loss of service. Consequently, the contribution of this responsive load can be modelled through this methodology, making the engagement of more customer segments in Demand Response policies more credible and deploying new segments, such as prosumers. [ABSTRACT FROM AUTHOR]

Steam Rankine cycle (SRC), which is mainly utilised in power generation sector, faces external irreversibility in its daily operation causing inefficiency in the system. To address this issue, reheat Rankine cycle (RHRC) and regenerative Rankine cycle (RRC) have been widely studied and implemented in power plants to improve thermal efficiency and reduce external irreversibility of Rankine cycle. This study investigates the implementation of different RRC configurations in a combined heat and power plant, including RRC with modified thermal deaerator, RRC with open feed water heater (OFWH) and closed feed water heater (CFWH). A base case simulation model was first constructed using commercial simulation software Aspen HYSYS for the basic SRC system based on actual plant data. Various scenarios were then evaluated for their profitability and sustainability through techno‐economic analysis (TEA) and carbon footprint analysis (CFA). From both analyses, the scenario of RRC with CFWH showed the greatest long‐term potential, generating the highest annual profit of $ 771 691 and carbon footprint reduction of 14.63%, while RRC with modified thermal deaerator showed the greatest potential in the short run with the highest return of investment (ROI) of 201.51% and shortest payback period (PBP) of 0.50 year. [ABSTRACT FROM AUTHOR]

Domestic hot water heaters are considered to be easily integrated as flexible loads for demand response. While literature grows on reproducible simulation and lab tests, real-world implementation in field tests considering state estimation and demand prediction-based model predictive control approaches is rare. This work reports the findings of a field test with 16 autonomous smart domestic hot water heaters. The heaters were equipped with a retrofittable sensor/actuator setup and a real-time price-driven model predictive control unit, which covers state estimation, demand prediction, and optimization of switching times. With the introduction of generic performance indicators (specific costs and thermal efficiency), the results achieved in the field are compared by simulations to standard control modes (instantaneous heating, hysteresis, night-only switching). To evaluate how model predictive control performance depends on the user demand prediction and state estimation accuracy, simulations assuming perfect predictions and state estimations are conducted based on the data measured in the field. Results prove the feasible benefit of RTP-based model predictive control in the field compared to a hysteresis-based standard control regarding cost reduction and efficiency increase but show a strong dependency on the degree of utilization. [ABSTRACT FROM AUTHOR]

The high energy consumption of water bath heaters in city gate stations due to heating the passing gas is always a significant concern. A suggested approach is to apply a shell and tube heat exchanger to raise efficiency or utilize heat losses. This study first examined the impact of the geometrical parameters of a heat exchanger, e.g., baffle cut, baffle number, tube pitch, and tube diameter, on heat transfer, pressure drop, and exchanger price as objective functions and estimated the optimal point of the exchanger's geometry based on the TOPSIS algorithm. Then, the feasibility of replacing a shell and tube exchanger with a water bath heater in city gate stations was probed. The shell and tube exchanger was simulated and analyzed by Ansys Fluent software. The results showed that increases in the baffle cut from 20 to 50%, tube pitch from 1.3 to 1.9, and tube diameter from 21.3 mm to 42.2 mm reduced heat transfer by 10, 3, and 7% and pressure drop by 9, 10 and 11%, respectively, while a surge in the number of baffles from 2 to 5 raised pressure drop and heat transfer by 14 and 12%, respectively. The outcomes associated with the economic analysis of replacing an exchanger revealed that this replacement decreased fuel consumption and led to reduced contamination, on the one hand, and cost conservation, on the other hand, such that the net present value index zeroed in less than 5 years. [ABSTRACT FROM AUTHOR]

• Heat pump water heater with liquid-separation condensation is modelled and verified. • A 7.43 % improved COP and a 13.1 % shorter time with same condenser area is achieved. • A 22.22 % reduced condenser area and a 4.1 % shorter time with similar COP is obtained. • Optimized cases are superior at early stage of transient heating-up process. Heat pump water heater (HPWH) offers great potential to reduce energy consumption in water heating applications. But its performance enhancement and/or initial cost deduction are the main challenges to promote market penetration. In this paper, a heat transfer improvement technology, i.e., liquid-separation condensation (LSC), is implemented to HPWH and screen to achieve the maximized COP (E-HPWH) or reduced condenser area (R-HPWH). A model of HPWH with LSC is developed and validated, and its predictions are in good agreements with tested results from the baseline (B-HPWH) with an average deviation of 4.92 % at most. By using this validated model, E-HPWH and R-HPWH are obtained by adjusting the path arrangement and separation efficiencies. With the same heat transfer area, the COP of E-HPWH reaches 4.48, which is 7.43 % higher than that of B-HPWH, and the heating time is shortened by 13.1 %. With the same COP of B-HPWH being 4.17, the heat transfer area of R-HPWH is reduced by 22.2 % and heating time is shortened by 4.1 %. Then transient heating-up process of three HPWHs are comparatively investigated. Results indicate that E-HPWH has the highest compressor power as well as pressures and temperatures at the inlets of condenser and evaporator, followed by R-HPWH and B-HPWH. E-HPWH and R-HPWH overperform B-HPWH in terms of heat capacity before 4220s, due to the increased mass flowrate. Compared to B-HPWH, E-HPWH and R-HPWH have averagely 15.02 % and 7.29 % higher COP before 2790s and 1860s, respectively. Their states are less differentiated as the water temperature increases. [ABSTRACT FROM AUTHOR]

A calcium phosphate solid formed as an unintended consequence of a novel high-pH orthophosphate lead corrosion control strategy in Providence, RI, resulting in some consumer complaints and clogged plumbing. Investigations were carried out at pH levels of 8.9–10.4, at temperatures of 5–60°C, and with orthophosphate concentrations ranging from 0 to 4.0 mg/L as orthophosphate (PO4) to examine this phenomenon. During field testing, the calcium phosphate initially precipitated at orthophosphate doses above about 2 mg/L as PO4, and the extent of precipitation increased with water age and higher temperature. Laboratory-scale tests confirmed that doses above about 2 mg/L as PO4 were required to form the precipitate in the absence of preexisting calcium phosphate solids and that the solid formed quickly at 60°C (upper range for hot water heaters) and tended to dissolve at lower pH. Solubility studies and solids characterization indicate that the particles are a mixture of noncrystalline compounds containing calcium and phosphate. For water systems currently practicing a high pH/low alkalinity corrosion control strategy, orthophosphate dosing can enhance plumbosolvency control without the risk of pH reduction, but formation of this solid can place an upper limit on the maximum orthophosphate residual level in the distribution system. [ABSTRACT FROM AUTHOR]

In this paper, a combined air/water source heat pump water heater is presented. At ordinary time, the heater can be used for hot water heating in water-source mode to improve the energy efficiency. While in cold season, it gives priority to air-source mode for water heating to improve operational safety. Experiments were conducted to investigate the thermodynamic performance of the heater in each operation mode, and the experiment results were analyzed. The research indicated that its operation was reliable during the long-time running. This paper offers a promising energy-saving method in future. [ABSTRACT FROM AUTHOR]

Against the backdrop of increasing global demand for reducing greenhouse gas emissions, promoting the use of energy-saving and environmentally friendly products has become a crucial aspect of low-carbon economic development. Customer satisfaction plays a vital role in the promotion of these products. To address the challenges of dealing with big data in the conventional customer satisfaction analysis tool, Importance Performance Analysis (IPA), a machine learning-based method is proposed to improve IPA. Firstly, the Latent Dirichlet Allocation (LDA) model is used to capture users' opinions on different product topics. Then, the Support Vector Machine (SVM) and Random Forest (RF) algorithms are employed respectively to assess the satisfaction and importance of product attributes, enabling an objective measurement of customer satisfaction and adapting to the current trend of big data. The proposed method is applied to the analysis of water heater satisfaction on the JD platform, obtaining satisfaction levels for 10 topics. The research findings demonstrate that the improved IPA method based on SVM-RF effectively explores customer satisfaction and can provide some improvement strategies for platform managers and manufacturers. [ABSTRACT FROM AUTHOR]

Purpose: The aim of the study was to present the actual efficiency of a gas-fired instantaneous water heater for the production of domestic hot water. Design/methodology/approach: The object of the study was a gas-fired instantaneous domestic hot water heater located in a flat in Krakow. Measurements with a suitable device were carried out for three basic variants of hot water preparation, defined as showering, washing hands and washing dishes. Findings: The tests and analyses carried out have revealed that the current efficiency (average efficiency based on 3 measurements – 77.61%) differs radically from that indicated on the water heater data sheet. Such a drop in efficiency may be caused e.g. by fouling of the surface of the heat exchanger on the flue gas side and scaling of the exchanger on the heated side. Research limitations/implications: The tests proved that the heater did not reach its nominal efficiency during the tests, but on the other hand, simulations of different intensities and durations of water consumption did not drastically change the efficiency of hot water preparation. Practical implications: Regular cleaning of the exchanger would probably reduce the difference between the efficiency declared by the manufacturer and the one achieved during the tests. A clean heater will also ensure a sufficiently low level of carbon monoxide in the flue gas, which has a real impact on the safety of the appliance. Social implications: The values obtained from the measurements for each operating mode can help occupants understand how to prepare water most efficiently with this particular appliance, which will have a real impact on the bills they pay. The user will be provided with information on what percentage of energy they use from the volume of gas burned. Originality/value: Gas-fired instantaneous water heaters provide an efficient and energy37 saving solution, especially in situations where the demand for hot water is low, and immediate access to it is crucial. [ABSTRACT FROM AUTHOR]

To preheat water for moistening a sinter charge, it is proposed to use a recuperative water heater installed in the gas collector of a sinter machine in the zone of the last wind boxes where the temperature of the exhaust gas reaches the maximum, which allows the maximum effect of water heating. The established dependence of the difference between the final and initial temperature of the charge on its initial temperature indicates that the water heating system in sinter production will be the most efficient at sinter charge temperatures close to 0 °C. Finite-element models for analysis of gas dynamics, heat transfer, and water heating in recuperative water heaters by the exhaust gas in the collector of a sinter machine have been developed. Diagrams of the distribution of the temperature of the fluids and the flow-average temperature of water at the collector outlet in planes located along and across the flow of the exhaust gases are plotted. It is established that the heating of the heat-transfer fluid in the water heater with the tubing parallel to the gas flow from the wind box is more intensive, the outlet water temperature being higher by 12.6 °C compared with the case where the tubing is perpendicular to the gas flow in the collector. The developed method of simulating water heating by the heat of the exhaust gas is intended to determine the rational parameters and design features of the recuperative water heater installed in the collector of a sinter machine. [ABSTRACT FROM AUTHOR]

Heat exchangers, as essential devices for facilitating heat transfer, have found a variety applications in various industries. However, the occurrence of corrosion-related failures in real-world scenarios remains a prevalent problem that can lead to catastrophic incidents. This paper investigates the problem of corrosion perforation on the outlet flange of a heat exchanger in a sour steam stripper from a petrochemical company. Failure analysis was performed using physical testing and chemical analysis, metallographic examination, microscopic observation, and energy spectrum analysis. Intergranular corrosion experiments and flow calculations were performed to verify the analysis. The results indicate that the main cause of the flange corrosion perforation was the formation of a highly concentrated NH4HS aqueous solution during the cooling process of the NH3, H2S, and water vapor in the fluid passing through the heat exchanger, and the velocity was too high, which triggered alkali-sour water washout corrosion. To prevent the recurrence of similar corrosion perforations, recommendations for material and process optimization are proposed to effectively reduce the safety production risks in refinery units and provide valuable information for the safe long-term operation of a sour steam stripper. [ABSTRACT FROM AUTHOR]

Shutdowns of photovoltaic installations are a problem that has been increasingly affecting private investors who have built home installations of several to a dozen kWp over the last few years. This problem, most often caused by outdated infrastructure, appears in many countries and impacts energy production. This work focuses on three aspects of the problem. The first one answers the question of how shutdowns of the photovoltaic installation affect production, and how significant the energy loss happens when the PV inverter is not working or is in the restart phase. The second aspect proposes an original, low-cost method that reduces the number of shutdowns. This method relates to the auto-consumption mechanism associated with domestic water heaters and the system for measuring voltage and energy consumption from the electrical network. The solution is based on constant monitoring of the network voltage and the switching of heaters based on a dedicated algorithm. Additionally, continuous analysis also allows for reporting observed irregularities to the electricity supplier. The third and final factor corresponds to the real impact of shutdowns on the long-term aspect of the investment and the extension of its payback period, and to what extent the proposed solution shortens this period. Through a detailed analysis on the issue of shutdowns, the proposed solution allows for a reduction in the number of shutdowns by over 40%. However, due to the fact that it discusses a specific case, this solution requires a calibration and adjustment process, which is discussed in the article. [ABSTRACT FROM AUTHOR]

• A vapor-liquid adjustment evaporator is pioneered to heat pump water heater. • Serials experiments are conducted for performance comparisons. • Current vapor-liquid adjustment evaporator cannot ensure its superiority for each period. • A 6.35 % higher COP and 16.18 %−63.37 % lower evaporator pressure drops are found. Adjusting vapor and liquid in the evaporator could lead to heat transfer enhancement and pressure drop reduction simultaneously. Its benefits in the steady system, such as air conditioning and heat pump, have been confirmed extensively, but its effectiveness in the dynamic system is not explored yet. In this paper, a vapor-liquid adjustment evaporator is implemented to heat pump water heater (HPWH-AE) featured by a dynamic water heating process. Comprehensive comparisons to the heat pump water heater with a conventional evaporator (HPWH CE) are experimentally investigated and discussed. Firstly, the matching test reveals that the optimized HPWH-AE has a 6.35 % higher COP than HPWH CE. Secondly, the detailed comparisons indicate that HPWH-AE has less evaporator pressure drop, smaller compressor ratio, higher refrigerant mass flowrate and decreased power consumption than HPWH CE. Thirdly, the divided tests are carried out with an increment of half hour. The results suggest that HPWH-AE outperforms HPWH CE in terms of heating capacity and COP at the first one and half hours, which becomes inferior afterwards. However, HPWH-AE has always lower power consumption relative to HPWH CE. The images from FLIR camera show that the vapor-liquid adjustment evaporator is featured by effectively utilizing heat transfer area, resulting from more evenly distributed temperatures. Finally, the feasibility is examined at various operating conditions. HPWH-AE could have higher heating capacity and lower power consumption than HPWH CE simultaneously when ambient temperature is between 18 °C and 26.5 °C. HPWH-AE always has higher COP of 4.92–6.35 % than HPWH CE. [ABSTRACT FROM AUTHOR]

This study investigates the long-term thermodynamic performance of a direct-expansion solar-assisted (DX-SAHP) system for hot water production in an average Canadian household. Performance is evaluated using realistic time-varying demand profiles and DX-SAHP with and without glazing under cold climatic conditions. A mathematical model for determining the system's long-term thermodynamic performance based on the first law of thermodynamics and heat transfer fundamentals is developed and thoroughly validated. The solution is implemented in MATLAB®. The CoolProp® database is coupled with MATLAB® and used to determine the working fluid's thermal physical properties. Besides, the thermodynamic performance of the DX-SAHP throughout the year, operating with low global warming potential (GWP) and class A safety refrigerants, was evaluated. Moreover, the influence of solar irradiation and ambient air temperature on the DX-SAHP's thermodynamic performance is studied. Results indicate that the monthly average coefficient of performance (COP) varies between 2.5 and 3.8, while the monthly average energy consumption of the system varies between 170 and 275 kWh. The obtained figures for COP and power consumption demonstrate the high-efficiency potential of the DX-SAHP system, making it an attractive alternative to reduce energy costs and CO 2 emissions in residential water heating. In addition, results show that R1233zd gives the highest COPs, followed by R152a, R1234ze, R134a, R1234yf and R32. Besides, the long-term simulation results indicate that the DX-SAHP water heater without glazing has superior thermal performance compared to one with glazing. Also, results show that the COP rises as the ambient temperature or solar radiation level increases. [ABSTRACT FROM AUTHOR]

We present an example of one of the modelling projects we assign to students in our differential equations classes. Students are asked to determine how to run a cost-efficient hot water heating system. We consider a cylindrical tank filled with water and heated by a heating element immersed in it. Together with students we discuss physical laws governing the process and make assumptions necessary to build a model. One of the goals of the modelling activity is to compute the time needed for water to reach the desired temperature given the power of the heating element and the size of the water tank. Several different scenarios can be discussed. Assuming the cost of heating the water is directly related to the time for which the power is ON, students can choose the most cost-efficient scenario. We provide the description of several modelling activities and obtained results. [ABSTRACT FROM AUTHOR]

Climatic changes, exhaustion of resources, air and water pollution are the detrimental consequences of mismanaging the use of fossil fuels. Likewise, the low performance of the traditional energy-conversion plants encourages scientists to replace these plants with hybrid systems. Accordingly, this study suggests a biomass-based combined system encompassing a gasifier, a gas turbine, a S–CO 2 unit, along with a hot water heater. This system will be analyzed from exergy, and economic point of view also using the genetic algorithm optimization tool multi-objective optimization is carried out. The parametric analysis to evaluate the influences of various variables on the plant operation. It was found that the changing r p of the compressor have a small impact on the efficiencies while it increases the total exergy efficiency and cost. The largest exergy destruction rate of the plant was for the compressor unit with 7391 kW. After that the combustion chamber with 2124 kW represents the worst performance from exergy destruction rate point of view. The optimization is done according to five decision parameters of moisture content, compressor pressure ratio, T 9 , T 14 , and P 36. The objective functions were energy efficiency, exergy destruction rate, and total product cost rate. According to the results of multi-aspect optimization in the optimum point the energy efficiency, exergy destruction and cost of electricity are 33.44%, 12448.1 kw and 130.57 $/h, respectively. • Introduce a multi-generation plant integrated with biomass-feed gasifier. • Gasifier among all components has the highest exergy destruction with 7391 kW. • ANN optimization of system suggests different optimize states for introduced plant. • The optimized system efficiency and cost rate determined as 33.44% and 130.57 $/h. [ABSTRACT FROM AUTHOR]

This paper reviews the stability, heat transfer efficiency and photothermal conversion efficiency optimization studies of solid-liquid phase change materials (PCM) applied to water heaters. Suggestions and prospects were proposed. The study shows that the solid-liquid PCM are mostly filled in the water tank, thermal storage devices or solar thermal collector heater system with paraffin wax, and the addition of solid-liquid PCM can significantly improve the water heater performance. Further in-depth research is needed on PCM dosage and system economics of their application in heat pump water heaters, and the application of photothermal conversion PCM in solar water heater systems. [ABSTRACT FROM AUTHOR]

Conventional control strategies usually employed in tankless gas water heaters present difficulty in controlling the hot water temperature when subjected to sudden changes in water flow rate. Inadequate control leads to temperature overshoots and undershoots with long settling times that severely affect the user comfort, increasing water and energy wastage and associated gas emissions. A strategy based on model predictive control is presented to reduce the impact of changes in hot water demand. A semi-empirical model, parameterized with experimental data and compatible with real-time simulation, is used for the heat cell. A tailored state observer is proposed, considering time-varying delays characterizing this thermal process. An automatic code generation software tool was developed for the embedded implementation of gas water heater predictive controllers. Numerical simulations and hardware-in-the-loop experiments were established to evaluate conventional and predictive control strategies. It was demonstrated that embedded model predictive control could be successfully implemented on computationally limited microcontrollers, even for thermal systems with extensive varying time delays. Predictive control has shown significant performance improvements, with decreased temperature fluctuations, a gain in comfort index from 36% to 75% and a reduction of up to 32 s in the settling time. [ABSTRACT FROM AUTHOR]

The share of renewable energy share in India's energy mix of India has been increasing recently owing to the promotion and implementation of various government policies that promote the use of renewable sources of energy, depleting fossil fuel levels, increasing fuel prices, and stringent laws for emission reduction worldwide. The increase in the use of solar-evacuated-tube-collector-based domestic water heating is the result of this transition from conventional to nonconventional sources of energy. The recent urban agglomeration is challenging to install these solar water heaters in every household because the roof space is limited. Space reduction can be achieved by reducing the collector area by varying the diameter of the evacuated tubes. This study used a single tube and tank arrangement model with a fixed inclination to achieve a thermosyphon effect in a solar water heating system with three different diameter configurations of 48 mm, 54 mm, and 72 mm, with a tube measuring 1800 mm in length. Thermal assessment of the thermosyphon-based evacuated tube-solar water heater using the ANSYS CFD simulation software involves measuring the temperature at three different positions in the tank to study the thermosyphon initialization. This study signifies that the 72-mm-diameter evacuated tube is more capable of initializing the thermosyphon effect in the system. Nevertheless, the final temperature of the system is better achieved in the 48-mm-diameter evacuated tube. [ABSTRACT FROM AUTHOR]

The single-flash geothermal cycle (SFGC) is not without its limitations, featuring drawbacks like diminished efficiency, restricted power generation capacity, and the incapability to yield multiple outputs concurrently. Furthermore, the SFGC requires a substantial water supply, potentially leading to adverse environmental consequences. In a concerted effort to enhance overall performance and facilitate the concurrent production of multiple valuable products, this study introduces a multigeneration system (MGS). By integrating additional subsystems into the SFGC framework, including a branched GAX cycle enabled by a thermoelectric generator (TEG), a domestic water heater (DWH), and a reverse osmosis unit, the objective is to surmount these limitations effectively. A thermodynamic and exergoeconomic analysis of the system is conducted and a bi-objective optimization is employed to minimize system cost and maximize exergy efficiency. The parametric study reveals that when degassing ranges are in the range of 0.2–0.37, the system product cost varies from $27.07/MWh to $28.44/MWh. In the optimized scenario there is a decrease of 67.7% in cooling provided by the system. This leads to an increase of 3.5% in generated electricity and a 3% increase in water purification compared to the base scenario. Through optimization the exergy efficiency of the system improves from 61.84% to 62.90% while the multigeneration gain output ratio (MGOR) decreases from 1.40 to 1.38. [ABSTRACT FROM AUTHOR]

The goal of the paper is twofold: a) following the identification of the merits of Distributed Energy Resources (DERs) by FERC 2222 for the flexibility they bring to the grid, we recognize water heaters and thermostats as mini-batteries and introduce volumetric/swing options that the Aggregator can sell by shifting consumers' consumption while rewarding them; b) We propose to address the pricing complexity of these volumetric options - which are in our setting very general in terms of number of exercises and quantities constraints - by a novel approach that combines Monte Carlo simulations and Recurrent Neural Networks (RNN). [ABSTRACT FROM AUTHOR]

To achieve the flexible operation of the active distribution network (ADN), an optimal control method for the ADN considering the soft open point (SOP) and thermostatically controlled loads under distributed photovoltaic (PV) access is proposed. First, the mathematical model of the SOP and thermostatically controlled loads are constructed based on the flexibility of the SOP and the thermal storage characteristic of thermostatically controlled loads, respectively. Then, the mathematical model of theADNconsidering the SOP and thermostatically controlled loads are further constructed. The optimal control of the ADN is realized by adjusting the transmission power of the SOP and the switching state of the electric water heater. Finally, the optimal operation analysis of the SOP and thermostatically controlled loads under various control methods is carried out, and the impact of the SOP and thermostatically controlled loads on the economic and secure operation of the ADN is further investigated. The results show that the proposed method taps the demand response potential of thermostatically controlled loads while satisfying the water consumption habits of different customers, and utilizes the network reconfiguration with the SOP to further improve the security and economy of the ADN operation. [ABSTRACT FROM AUTHOR]

To improve the heat transfer coefficient of a condenser, this paper proposes using a fin-tube condenser to replace a smooth-tube condenser in a domestic heat pump water heater. The finite element method is used to analyze the heat transfer coefficient of fin-tube condensers with different design parameters. By comparing the results of experiments with those obtained using CFD methods, it has been determined that the CFD method used in this study is feasible. Simulation results showed that the heat transfer coefficient enhanced clearly. The total thermal resistance of the fin-tube condenser decreased by 7% through increasing fin thickness. The total thermal resistance of the fin-tube condenser increased by 1–1.3% when fin spacing was increased. The heat transfer coefficient decreased severely and the maximum total thermal resistance of the fin-tube condenser increased by 8.7% with increasing fin height. In 600 s, when the fin spacing, fin height, fin thickness and inner diameter were 14 mm, 12.5 mm, 1.2 mm and 22.5 mm, respectively, compared to the smooth-tube condenser, the fin-tube condenser could increase the final water temperature by 18.37%, and the heat transfer coefficient would increase by about 95%. This research could provide a low-cost way to improve the heat transfer coefficient of condensers in domestic heat pump water heaters. [ABSTRACT FROM AUTHOR]

Technically, residential energy management systems are fundamental sectors in the smart grids for implementing demand response programs in the layer of households for managing energy consumption and reducing energy bills. The paper proposes a novel energy management scheme that takes production and usage into account based on a heuristic searching operation. In addition to modelling the grid, renewable energy sources, batteries, and electric vehicles, various kinds of electrical and thermal devices have been examined, including air conditioners, water heaters, vacuum cleaners etc. A method is developed for solving the objective constraint issue in a smart home in order to reduce energy consumption and determine feasible operation states among the various loads. Moreover, this paper proposes a grey wolf optimization method for solving the issue over a longer simulation period. Various cases were examined to evaluate the effectiveness of this suggested robust optimization algorithm. The outcomes show that the suggested model could not only reduce energy costs significantly but has also shown good performance for energy management purposes. [ABSTRACT FROM AUTHOR]

Evaluations of nonintrusive load monitoring (NILM) algorithms and technologies have mostly occurred in constrained, artificial environments. However, few field evaluations of NILM products have taken place in actual buildings under normal operating conditions. This paper describes a field evaluation of a state-of-the-art NILM product, tested in eight homes. The match rate metric—a technique recommended by a technical advisory group—was used to measure the NILM's success in identifying specific loads and the accuracy of the energy consumption estimates. A performance assessment protocol was also developed to address common issues with NILM mislabeling and ground-truth comparisons that have not been sufficiently addressed in past evaluations. The NILM product's estimates were compared to the submetered consumption of eight major appliances. Overall, the product had good performance in disaggregating the energy consumption of the electric water heaters, which included both electric resistance and heat-pump water heaters, but only a fair accuracy with refrigerators, dryers, and air conditioners. The performance was poor for cooking equipment, furnace fans, clothes washers, and dishwashers. Moreover, the product was often unable to detect major loads in homes. Typically, two or more appliances were not detected in a home. At least two dryers, furnace fans, and air conditioners went undetected across the eight homes. On the other hand, the dishwasher was detected in all homes where available or monitored. The key findings were qualitatively compared to those of past field evaluations. Potential areas for improvement in NILM product performance were determined along with areas where complementary technologies may be able to aid in load-disaggregation applications. [ABSTRACT FROM AUTHOR]

Heat pump water heaters (HPWH) are a proven method of reducing water heating energy use over prevailing electric resistance systems (ERWH). Both technologies lend themselves to enhanced control for peak load reduction. Laboratory tests were conducted in Central Florida using the CTA-2045 standard to evaluate load shifting strategies with connected water heaters. Four HPWHs from three manufacturers, including two different tank volumes, were tested alongside an ERWH in a garage-like environment. Tests aimed to shift energy use away from utility peak load periods to off-peak times when excess renewable energy resources are often available. Two load-shifting strategies were shown effective, Shed and Critical Peak, with variation by manufacturer. Beyond draw volume, other factors influenced HPWH load shifting: Florida winter conditions, which increase the energy used per draw, provided the greatest challenges to complete load shift. Inlet water temperature had a large impact on the success of load reduction. Ground temperatures in which water pipes were buried largely determined inlet water temperatures. HPWH efficiency setting: Heat pump water heaters often default to a "hybrid" mode that may use some electric resistance heat to minimize risk of running out of hot water. Operational mode can impact load shifting potential. [ABSTRACT FROM AUTHOR]