Hot Water Production Research Articles

Techno-economic assessment of co-pyrolyzed kitchen waste and rice straw for co-generation of heat and power

Increasing concerns relating to depletion of fossil fuels and global warming coupled with significant growth in waste-to-energy markets have propelled the need for ingenious and flexible technologies that can effectively transform waste biomass into fuels and power at high efficiency. In this study, a comprehensive techno-economic investigation was undertaken to investigate the economic potential of utilizing co-pyrolyzed kitchen food waste and rice straw in a waste to heat and power facility based on microwave pyrolysis and a combined heat and power system. The study involved microwave pyrolysis experiments to investigate the effects of blending proportions of kitchen food waste and rice straw on the evolution of synthetic gas components based on gas chromatography analysis. The optimal blending proportion was then used to run the Aspen Plus heat and power plant simulation. Boiler efficiency, steam cycle thermal efficiency, electrical efficiency, and overall system efficiency were 96.30 %, 36.46 %, 41.61 %, and 35.11 %, respectively. The model had an estimated annual power production of 744,576 kWh/year, hot water production capacity of 1,727,649 L/year, and annual biochar production of 162,045 kg/year. A positive net present value was observed for the project after the second year, coupled with an internal rate of return of 0.62 and a profitability index of 3.85 over ten years. The heat generated can meet rapidly increasing urban heating needs and the power will contribute to grid stabilization. Sensitivity analysis revealed that the greatest potential performance improvements can be achieved by increasing biochar selling price and reducing total investment costs and total annual operating costs. Overall, the study shows scaled-up microwave-based heat and power technology to be a profitable and effective waste management and renewable energy solution.

Development, experimental validation through infrared thermography and applications of a mathematical model of a direct-expansion solar-assisted heat pump with R290 based on energy, exergy, economic and environmental (4E) analyses

The application of renewable sources, such as solar energy, and the use of ecological refrigerants in refrigeration and heating systems contribute to more sustainable development and the reduction of global warming. With this perspective, the main objective of this work is to develop, validate and apply a mathematical model based on the energetic, exergetic, environmental, and economic analysis of a Direct-Expansion Solar-Assisted Heat Pump for the production of Domestic Hot Water operating with R290. Environmental analysis is based on Total Equivalent Warming Impact and economic analysis is based on payback. The proposed mathematical model was validated on an experimental bench with R290 through infrared thermography applied to evaluate the temperature distribution in the evaporator. The influence of environmental parameters on the system with R290 is investigated through simulations. Among the environmental parameters investigated, solar irradiance was the parameter that most contributed to the increase in energy (69.3 %) and exergy efficiency (8.72 %). In addition, the increase in ambient temperature contributed more to the reduction of greenhouse gas emissions (88.6 %) but promoted the longest payback time for the system. Finally, in the tests performed, heating the water at a lower temperature (45 °C) compared to the higher temperature (65 °C) increased energy (25.0 %) and exergy efficiency (2.86 %), contributed more to the reduction of emissions, but increased the payback time.

Impact of Stearic Acid as Heat Storage Material on Energy Efficiency and Economic Feasibility of a Vacuum Tube Solar Water Heater

The overheating of heat pipes, poor transfer of heat across the absorber and finned heat pipes, and inability to provide hot water in the late evening hours are major problems associated with conventional heat pipe vacuum collector systems. The amalgamation of highly conductive storage material between the absorber tube (heat collecting surface) and the heat pipe is an effective way to overcome these problems. In this study, a stearic acid amalgamated vacuum tube solar collector system was designed and fabricated and its thermal output compared with a conventional vacuum tube system without storage material under the same environmental conditions. The experimental results showed that the amalgamation of stearic acid as storage material enhanced the thermal output of the solar system compared to the conventional one. The desired heat gain of the solar system with storage material increased by 31.30, 23.34, and 18.78% for Test 1_40 °C, Test 2_45 °C, and Test 3_50 °C, respectively. The technoeconomic analysis showed that almost 118.80 USD in revenue could be earned by the proposed solar system at the end of 15 years. The total running cost of ELG and the developed solar system was observed to be 202.62 and 86.70 USD, respectively. On average, the cost of hot water production using the solar system and ELG was found to be 0.0016 and 0.004 USD/L, respectively. The value of LEC was found to be 0.062 USD/electricity unit, which was much lower than the LEC value of ELG (0.116 USD/electricity unit). The value of NPW (73.73 USD) indicated high acceptability of the proposed system. The payback time is lower than the life of the system, indicating its suitability for use in the commercial sector. Therefore, the proposed solar system is highly recommended over conventional water heating systems in urban and rural areas.

Laboratory and operational analysis of air to water gas absorption heat pump cycle

Gas absorption heat pumps (GAHP) have significant potential to reduce fossil fuel consumption for space heating and hot water production and reduce CO2 emissions. The paper deals with laboratory and operational verification of GAHPs operating with air as a low-temperature energy source. The laboratory verification was used to specify and analyse the courses of one GAHP cycle in terms of cycle phases, outputs, and operating temperatures at different temperatures of the air supplied to the evaporator and heating water temperatures from GAHP. Comparative operational verification was conducted simultaneously in two identical buildings with the same technology and on two identical GAHPs A. The influence of interventions in GAHP control on the operating parameters and the average time of one cycle was monitored. The decrease in outdoor temperature and the transition from using the GAHP for water heating only to using it for space and water heating significantly affected the performance parameters and the average cycle time. Validation measurements were carried out for one year in twelve boiler rooms with GAHP connected in a cascade with gas-condensing boilers. The results showed that in the seasonal evaluation of GAHP operation for space and water heating, the average operation time of GAHP did not significantly affect the performance parameters. A fixed operation control to a higher required temperature of heating water when applying GAHP for space and water heating significantly negatively affected the performance parameters. Compared to heat production from a gas-condensing boiler (GCB), the monitored GAHP operation had lower emissions by 52 kg of CO2 per 1 MWh of heat produced.

Multi-objective study on an innovative system for domestic hot water production: A pilot building in Southern Europe

The present study deals with a multi-objective analysis of an innovative decentralised system to produce and store domestic hot water (DHW), emphasising on the combined effects of the technological aspect, control strategy and user’s behaviour. The proposed system, by relying on thermal energy storage, decouples energy production and demand while shaves peaks in the energy demand and, at the same time, provides more autonomy to users through local storages. To identify subtle interactions in components of DHW system, dynamic simulations are carried out by establishing a coupled TRNSYS-MATLAB code, calibrated and validated by experimental measurements. The energy analysis implies that the proposed system cuts the required annual electrical energy in half, of which up to 82% of needed primary energy is supplied from renewable sources, compared to previous electrical-decentralised system. The optimisation of the results through applying control strategies indicates that adopting a three-time charging scheme is advantageous in terms of providing a more stable temperature profile as well as a higher hot water temperature. Compared to an available-by-demand operation, this scheme reduces the required total annual electricity by 5.2 % and enhances total thermal loss from components up to 4.0%. Furthermore, a sensitivity analysis on the results emphasises the striking role of the user behaviour in electrical energy consumption either via draw-off temperature or adjusting the pre-defined temperature for activation of the built-in auxiliary heater.

Design, optimization and economic viability of an industrial low temperature hot water production system in Algeria: A case study

Solar energy has a great potential in many areas of industrial activity in Algeria. This is because most of Algeria has high levels of sustainable solar insulation. Unfortunately, few industries use solar energy for hot water generation, but some industrial processes require hot water at temperatures that can be easily obtained from solar thermal panels. This paper presents a case study to investigate the technical and financial feasibility of a solar-powered industrial agro-processing system in Algiers. Based on the solar collectors connection type for which the economic feasibility study was carried out, an appropriate design of the system was determined. The latter was actually done by analyzing the levelized cost of energy savings. The design of the thermo-solar process is carried out based on F-chart method with a new approach by integrating the incidence angle modifier and of using real and experimental data requirements to determine realistic achievable performance of the solar process. The results showed that, in comparison to the currently used electrical system, the electrical energy savings achieved by the solar-powered system make it an economically viable option with a solar coverage rate of 80%. The investment depreciation balance shows that the use of such a thermal solar energy system will be more competitive than fossil fuels system if the price of electricity in the country increases from 0.048 to 0.075 €/kWh.

Rational Use of Energy in Sports Centres to Achieve Net Zero: The SAVE Project (Part A)

Sports centres constitute major energy consumers. This article presents the proposed energy performance upgrade process and the achieved results for the municipal sports centre in Arkalochori, Greece. The facility consists of a swimming pool centre, an outdoor 8 × 8 football court, and two tennis and basketball courts. It operates with considerably high energy consumption due to the lack of any measure towards its energy efficiency improvement since its initial construction in 2002. Due to the significantly high heating cost, the swimming pool centre remains operative only during the summer period. The energy performance upgrade of the facility was holistically approached through all possibly applicable passive and active measures: insulation of opaque surfaces and replacement of openings, construction of a new, bioclimatic enclosure for the swimming pool’s centre and conversion of the current outdoor facility to an indoor one, installation of heat pumps for indoor space conditioning and swimming pool heating, installation of a solar–combi system for domestic hot water production, upgrade of all indoor and outdoor lighting equipment and installation of a photovoltaic plant on the new enclosure’s roof for the compensation of the remaining electricity consumption. With the proposed measures, the municipal sports centre is upgraded to a zero energy facility. The payback period of the investment was calculated at 14 years on the basis of the avoided energy procurement cost. The swimming pool’s centre operation is prolonged during the entire annual period. This work has been funded by the Horizon 2020 project with the acronym “NESOI” and was awarded the public award of the “Islands Gamechanger” competition of the NESOI project and the Clean Energy for EU Islands initiative.

The role of individual metering in reducing domestic hot water consumption in residential buildings: A long-term evaluation

Within the residential sector, Domestic Hot Water (DHW) production represents the highest energy-intensive end-use after the space heating. Energy consumption for DHW production in residential buildings depends not only on the efficiency of the production, distribution and supply systems, but also on the occupants’ behaviour and characteristics. For this reason, it is crucial to increase users' awareness in order to induce virtuous behaviours and reduce excessive uses of DHW. In this context, individual metering and consumption-based billing can be extremely useful and low-cost tools for reducing energy and water wastes and increasing the end-use energy efficiency in buildings. This paper is aimed at investigating the effect of individual metering systems on DHW consumptions in the residential sector. For this purpose, the operating parameters of 16 substations of a high-temperature district heating (DH) network supplying 137 multi-family buildings were monitored daily for over 14 years, during which individual DHW meters were installed and consumption-based billing was introduced. It has been found that after the installation of individual DHW meters the average daily heat consumption for DHW production decreased by 14% and that the DHW volume withdrawn by the buildings decreased by 32%. Those variations were found to be statistically significant.

Persistent contamination of a hospital hot water network by Legionella pneumophila

We assessed the contamination with Legionella pneumophila (Lp) of the hot water network (HWN) of a hospital, mapped the risk of contamination, and evaluated the relatedness of isolates. We further validated phenotypically the biological features that could account for the contamination of the network. We collected 360 water samples from October 2017 to September 2018 in 36 sampling points of a HWN of a building from a hospital in France. Lp were quantified and identified with culture-based methods and serotyping. Lp concentrations were correlated with water temperature, date and location of isolation. Lp isolates were genotyped by pulsed-field gel electrophoresis and compared to a collection of isolates retrieved in the same HWN two years later, or in other HWN from the same hospital. 207/360 (57.5%) samples were positive with Lp. In the hot water production system, Lp concentration was negatively associated with water temperature. In the distribution system, the risk of recovering Lp decreased when temperature was >55°C (p<10-3), the proportion of samples with Lp increased with distance from the production network (p<10-3), and the risk of finding high loads of Lp increased 7.96 times in summer (p=0.001). All Lp isolates (n=135) were of serotype 3, and 134 (99.3%) shared the same pulsotype which is found two years later (Lp G). In vitro competition experiments showed that a 3-day culture of Lp G on agar inhibited the growth of a different pulsotype of Lp (Lp O) contaminating another HWN of the same hospital (p=0.050). We also found that only Lp G survived to a 24h-incubation in water at 55°C (p=0.014). We report here a persistent contamination with Lp of a hospital HWN. Lp concentrations were correlated with water temperature, season, and distance from the production system. Such persistent contamination could be due to biotic parameters such as intra-Legionella inhibition and tolerance to high temperature, but also to the non-optimal configuration of the HWN that prevented the maintenance of high temperature and optimal water circulation.

Optimization of Heat Pump Systems in Buildings by Minimizing Costs and CO2 Emissions

District heating systems are gaining global recognition as an essential tool for reducing greenhouse gas emissions and transitioning to a low-carbon-energy future. In this context, heat pumps are becoming an important technology, providing an effective solution for improving energy efficiency and reducing the reliance on fossil fuels in heating systems. Therefore, this study is focused on the optimal selection of heat pump systems for different types of buildings considering technical, economic, environmental, and social factors. This paper proposes a novel methodology based on mixed-integer nonlinear programming and multi-objective optimization that minimizes total costs and reduces CO2 emissions for heat production and supply systems over a desired period. The methodology is applied to various building types, including renovated and unrenovated apartment buildings, schools, kindergartens, and a supermarket. The study analyzes various types of heat pumps and electric heaters for space heating and domestic hot water production. Optimization results showed that the optimal heating system includes air-to-water heat pumps and electric heaters. Furthermore, for schools and a supermarket, these systems are combined with hybrid heat pumps. The goal of making the heating system neutral in terms of CO2 emissions was achieved for eight out of eleven buildings analyzed. The most profitable investments were in the heating systems of renovated five-story and unrenovated nine-story apartment buildings due to their low energy costs (0.0831 EUR/kWh), short payback periods, and high returns on investment.

Techno-economic analysis of green energy resources for power generation & direct use by preserving near-wellbore geothermal gradient

Closed-loop fluid circulation in wellbores has gained considerable attention for harnessing the earth's thermal energy. Recent studies with analytical and numerical models show that geothermal gradient and well depth constitute the two most consequential variables in fluid output temperature at the surface. This study presents a new strategy for managing geothermal-gradient cooling to ensure more prolonged operation by adopting another energy source, such as solar or wind, with a day/night cycle over the years. In other words, the fluid circulation will occur at night, while the solar or wind source will operate in the daytime. Well-depth and geothermal gradients dictate which geographic area provides the best opportunity for power generation or hot water production to meet various industrial needs. Economic tools, such as Net Present Value and Levelized Cost of Electricity, helped gauge their strengths and limitations, thereby offering business decisions objectively.Considering a 20-year power generation period, this study provides some pragmatic lessons. For example, retaining the near-wellbore geothermal gradient is essential for assuring about 130 °C for the binary cycle. We can attain this objective with a 12-h fluid-circulation cycle by juxtaposing a second well or a solar/wind source for a day/night cycle. Also, besides being a safety net, a power grid can aid the economic value proposition in this energy-transition phase. The generation of hot water for direct industrial usage for low-geothermal prospects also becomes economically viable, particularly in repurposing abandoned wells. These industries include food and agriculture, requiring 60 to 85 °C.

A novel and versatile solar Borehole Thermal Energy Storage assisted by a Heat Pump. Part 1: System description

The paper reports a system combining Solar Thermal Collectors (STC), Borehole Thermal Energy Storage (BTES), a Heap Pump (HP) and a backup boiler for space heating and Domestic Hot Water (DHW) production. The integration of the components and the overall control strategy are described. The system is flexible, being able to select the best thermal source and to use it directly or through a HP, while only the excess solar heat is stored into the BTES. The contribution of every subsystem to the energy mix is discussed. For a “reference configuration” combining the three subsystems (“Design D”) and characterized by heating and DHW needs of 510.5 MWh.y−1 and 226.7 MWh.y−1 respectively, a BTES volume of 15000 m3, a distance between boreholes of 3 m, a STC area of 2500 m2, and a solar tank volume of 100 m3, the system uses 274 units of gas and electricity to provide 1000 units of heating and DHW. This reference configuration outperforms any alternative design: Design A (STC only), Design B (STC and HP) and design C (STC and BTES) would respectively require 612, 480 and 591 units of gas and electricity to do so. A one-at-a-time analysis reveals that the STC area, azimuth and inclination, the solar tank volume, the BTES volume, the borehole density and the HP power are key parameters to the overall system performance.

Particle-Size Effect of Nanoparticles on the Thermal Performance of Solar Flat Plate Technology

One of the cleanest and most efficient solar collector systems is the flat plate collector, which has applications in hot water production, drying, among others. Flat plate collectors have improved in terms of both their structural configurations and working fluids. Several studies have verified the comparatively higher efficiency of nanofluid-based flat plate collectors, relative to that of water and other thermal oils. Additionally, the influence of several nanofluid synthesis factors, such as volume fraction, pH, type of base fluid, hybridization, surfactants, and sonification, on the performance of these collectors has been highlighted in the literature. However, the effect of nanoparticle size on collector performance has received minimal research interest, despite its significant effect on both the cost of synthesis and the thermophysical properties of nanofluids. The uncertainties regarding the effect of nanoparticle size on thermal collectors have limited their practical applications. This study numerically investigates the effect of the nanoparticle size of silver (Ag) nanofluid with nanoparticle sizes between 20 nm and 100 nm on the performance of flat plate collectors. The effect of nanoparticle size on the mean fluid temperature resulted in a maximum temperature of 45.8 °C for the Ag-100 nm. An increase of 0.25 °C for the Ag-20 nm was recorded, relative to the Ag-100 nm. In addition, the Ag-100 nm was calculated to have resulted in the highest reduction in collector size (18.30%), relative to that of water.

Proposal of a tri-generation system by co-combustion of groundnut shell biomass and synthesis gas exiting from a solid oxide fuel cell: Environmental assessment and multi-objective optimization

Developing tri-generation energy systems is of interest, and in this regard, a novel tri-generation system of electrical power, distilled water and hot water was proposed in this study. The system composed of a solid oxide fuel cell, a combustion chamber, a supercritical carbon dioxide Brayton cycle, a desalination unit and a heat recovery system. Groundnut shell biomass was co-combusted with the synthesis gases exhausted from the solid oxide fuel cell and the resulted stream drove the supercritical carbon dioxide Brayton cycle and the desalination unit. Its waste heat was recovered to produce the hot water. Central composite design and analysis of variance were used to evaluate the system performance. Current density most contributed on the electrical power and the distilled water and the mass flow rate of biomass had the first rank on the hot water production. The electrical power and the distilled water were promoted when the current density increased and increasing mass flow rate of biomass boosted the hot water. The system performance was tri-objectively optimized using response surface methodology and the tri-generation system has 27.4% of electrical energy efficiency and 69.08% of thermal energy efficiency in the optimal conditions.The environmental assessment shows that the CO2 emission rate of the system is 2653 kg/KWh.

Effects of helical condenser coil designs on the heating process of the domestic refrigerator for hot water production: A numerical study

Enhancement of heat transfer characteristics in helical condenser coils by modifying the coil shape has been reported by many researchers. While the influence of different types of condenser coil designs on the operating performance of refrigeration machines for hot water production unit is available in the literature, there exists no published numerical or experimental analysis of the impact of geometric parameter of immersed helical condenser coil on heat transfer characteristics and water velocity distribution during water heating process, which is the subject of our article. With using CFD methodology, a numerical study was carried out to present the water velocity distribution with varying coil parameters such as pipe diameter, tube pitch, and turns number. After validating the numerical model by the experimental ones, the effect of coil parameters on water velocity distribution was examined. The results confirm that by reducing the coil pitch and increasing the tube diameter, an increase of the water velocity and a higher natural convection is obtained. On the other hand, the results indicate that with reducing the turns number, the water velocity and the heat transfer coefficient is also increasing. Indeed, the average water velocity of condenser coil with N = 11 turns is higher than the other two condenser coil structures, which presents 21.34% and 63.56% higher than that of N = 13 turns and N = 15 turns, respectively. Thus, this investigation could provide some guidance to obtain the optimum condenser coil structure for water heating process.

Experimental Performance and Cost-Effectiveness of a Combined Heating System under Saharan Climate

The solar water heater can be integrated into future residential buildings as the main energy source, which will subsequently reduce the energy cost of water heating. An original configuration for an efficient Domestic Hot Water (DHW) storage tank is developed and experimentally evaluated under Saharan climate. This novel DHW configuration includes a hybrid (solar and electric) energy system with a flat plate solar collector coupled with an electric heater. Additionally, a phase change material (PCM) mixture that is composed of paraffin wax and animal fat with a melting temperature between 35.58 °C and 62.58 °C and latent heat between 180 and 210 kJ/kg is integrated into this novel tank configuration. The experimental results indicated that hot water production by using latent heat storage could be economically attractive. By evaluating the cost of water heating expressed in Algerian dinar per liter (DZD/L), it was found that one liter of hot water may cost around 0.1362 DZD/L (i.e., 0.00096 USD/L) compared to 0.4431 DZD/L for the conventional water heater, an average energy cost savings of 69.26%. On a yearly basis, the average energy cost savings may reach up to 80.25% if optimal tilt for the solar collector is adopted on a monthly basis. The flat plate collector may be vulnerable to convective heat transfer; therefore, other solar collectors, such as vacuum tube collectors, may provide enhanced energy performance.

Development and evaluation of a solar based integrated hydrogen energy system for mobile applications

Sustainable and nature-friendly energy systems are critical in playing a key role in meeting the needs for better energy security and reduced environmental impacts which appear among the primary concerns of today’s modern society in the 21st century. The present study, in this regard, undertakes the development and thermodynamic investigation of a unique solar energy-based multigenerational energy system for modular and transportable applications. Electricity, heat, hot water, hydrogen and clean water are the useful commodities generated by this uniquely integrated energy system. This system employs a photoelectrochemical reactor stack for wastewater treatment and hydrogen production. The hydrogen generated from the photoelectrochemical water splitting process is employed within a proton exchange membrane fuel cell providing electricity and heat for hot water. The system’s energetic and exergetic efficiencies under different operational conditions are investigated and comparatively evaluated. The key effects of varying prime operational conditions and state properties on the system performance and hence the efficiency, as considered in the system analysis, are parametrically investigated, and the obtained results are comprehensively discussed along with explanations about the main drivers. The integrated system provides 1.026 kW electrical power along with, 2.1 kW space heating, 0.6 kW heat for hot water, and hydrogen and clean water production rates of 22.97 mg/s and 9.79 g/s, respectively. An overall energy efficiency of 16.79 % and an overall exergy efficiency of 17.31 % are obtained and discussed. The presently developed system is capable of operating as a self-standing system in an off-grid manner. Furthermore, the number of PEC reactors required to sustain the system needs to be maintained, which can be achieved by potential improvement in PEC water splitting process.

A novel two-stage compression air-source heat pump cycle combining space heating, cooling, and domestic hot water production

To improve the efficiency of HVAC system, a novel air-source heat pump based on the two-stage compression cycle is proposed. The heat pump shows the multi-function of producing the domestic hot water year-round, space cooling water in summer, and space heating water in winter. The theoretical model is developed to analyze the performance of heat pump under various conditions. Four high GWP refrigerants, including R134a, R32, R407, R410A, and four low GWP refrigerants, including R1234ze(E), R600a, R152a, R290, are compared and analyzed under various conditions. Besides, the effects of environment and system operation parameters, such as domestic hot water demand ratio, evaporating and condensing temperatures, on system performance are investigated. The major results are concluded: A multi-functional air-source heat pump shows high annual efficiency by switching both the four-way valve and tee valve. The low GWP refrigerant R152a shows the best performance among the selected refrigerants, especially for summer conditions, and the COP is higher than the R1234ze(E), R134a, R600a, R32, R407C, R410a, and R290, R152a by 10.4 to 9.0 %, 8.3 to 7.9 %, 5.6 to 4.0 %, 9.1 to 13.0 %, 20.9 to 23.3 %, 29.8 to 36.5 %, and 11.0 % under the selected condition, respectively. Compared with summer conditions, R152a improves COP slightly under winter conditions, especially for R600a and R134a (less than 5 % under the selected conditions). Besides, under the summer conditions, the system performance increases first and then decreases with the increasing domestic hot water demand. The maximum COP reaches 6.7 while the summer domestic hot water load ratio (SLR) equals 0.5 and the environment air temperature equals 25 °C. The heat pump also shows a good performance under winter conditions. The minimum COP reaches 2.4 with the air temperature of −25 °C and the winter domestic hot water load ratio (WLR) of unity. The result of this study hopes to promote the further improvement of the air-source heat pump and HVAC system.

Dynamic thermal analysis of a coupled solar water heaters-thermal storage tank for solar powered district heating networks

The integration of solar thermal and energy storage systems into district heating networks (DHNs) has been considered as one of the most advantageous solutions to reduce the use of fossil fuels and carbon emissions. In this context, this work deals with the numerical investigation of a coupled solar water heaters-thermal storage unit for urban heating networks. The studied system contains flat plate solar collectors (FPCs) for hot water production, a shell-and-tube thermal storage unit with phase change material (PCM) for latent storage or water for sensible storage, hydraulic pumps and a mass flow rate regulation system. The functioning of the coupled system is simulated using a detailed dynamic model based on transient energy and mass balances. The reliability of the developed model is verified through comparing numerical results with measurement data from the literature and a good agreement is obtained with a maximum relative error of about 4.5 %. The validated model is used to investigate the system thermal performance under the weather conditions of the city of Pau, France, and the effects of multiple parameters such as the FPC area, the DHN target thermal power, and the storage medium type (latent or sensible) during both charging and discharging processes are presented and analyzed. Results show that the use of FPCs is beneficial for DHNs during summer as they allow the production of thermal energy for both the DHN use and the storage process. It was also shown that increasing the DHN target thermal power from 30 kW to 50 kW leads to a reduction in the thermal storage process duration by up to 40 %. For both charging and discharging operations, the use of PCM (latent storage) as a storage medium is more suitable than water (sensible storage) as it leads to an increase in the storage density and extends the duration of hot water production with constant thermal power by about 65 %.

Compressor control strategy for CO2 heat pump toward efficient and stable domestic hot water production: An experimental investigation

Compressor control strategy for CO2 heat pump toward efficient and stable domestic hot water production: An experimental investigation