Low-temperature Energy Sources Research Articles

Low temperature rotary Stirling engine: Conceptual design and theoretical analysis

The use of low-temperature energy sources for electricity generation demands a dual focus: a substantial enhancement in the efficiency of energy conversion devices and a reduction in system production costs. Particularly in scenarios where low-temperature energy sources are scarce, this factor can be pivotal in facilitating widespread adoption of such technologies. The Stirling engine emerges as a promising solution capable of meeting these articulated expectations, owing to its straightforward design and utilization of non-toxic, non-flammable, and cost-effective working mediums. This paper introduces a novel concept of a rotary Stirling engine, exhibiting significant potential for operation with low-temperature energy sources. Additionally, an analytical model of the engine is presented, enabling simulations of its operation under varying supply temperatures and geometric configurations. To analyse the impact of internal leaks on the net efficiency and net power of the engine, a modified adiabatic model was introduced. It was observed that utilizing identical heat exchangers for heat supply at 250 °C and 100 °C could lead to a decline in net efficiency from 8 % to 3 % for the worst case. Furthermore, an analysis was performed to assess the impact of the heater’s overall heat transfer coefficient and engine rotational speed on both net efficiency and net mechanical power for a heat supply temperature of 200 °C.

Simulating the Effects of Ammonia Crossover and Alternative Ligands in Thermally Regenerative Flow Batteries

There is a significant amount of low-temperature heat (< 100 °C) available globally from various sources such as geothermal energy, industrial processes, and thermal power plants. Electrochemical and membrane-based methods for harnessing this heat are becoming of greater interest due to their ability to utilize the low temperature energy sources and because they can be sized modularly to fit the power, energy, and spatial requirements of the application. The all-aqueous thermally regenerative ammonia battery (Cuaq-TRAB) is a leading technology in the waste heat to electrical power production space due to recent results showing operational power densities of 25 mW cm-2 with an estimated thermal energy efficiency of 7%, outperforming most technologies in this space. Previous research on the Cuaq-TRAB has shown that the battery suffers from the crossover of ammonia through the membrane which adversely impacts battery performance.To investigate these impacts, we developed a simple numerical model that simulates discharge curves using one fitting parameter to account for parasitic crossover instead of modeling species transport through the membrane. The model was able to replicate experimental data from Cuaq-TRABs with different membrane materials and for multiple applied current densities with < 5% error for average power and energy capacity. Results showed that there is a 20% loss in Cuaq-TRAB energy capacity due to ammonia crossover when compared to a discharge with no parasitic crossover losses. The model was then extended to demonstrate the impact of different changes to the electrolyte chemistry on the resultant power and energy capacities for Cuaq-TRABs. Using this model, we estimate that if chloride was the ligand for the positive electrolyte instead of bromide, it would decrease the power and energy capacity of the battery by 30%. However, considering that an economic analysis showed that chloride is 80% cheaper than bromide, it may be beneficial to consider the use of chloride ligands in this technology despite its worse electrochemical performance.

Multi-objective optimization and 3E analysis for solar-driven dual ejector refrigeration and phase change material as thermal energy storage

Ejector refrigeration cycles have garnered attention due to their inherent advantages, including simplicity, the ability to leverage low-temperature energy sources, and reduced reliance on high electrical power requirements. Optimizing these systems becomes pivotal, given the inherent challenges of low efficiency in ejector refrigeration cycles. This study explores an ejector refrigeration cycle incorporating a secondary ejector to recover expansion energy from the condenser. Solar collectors provide the necessary heat for the cycle, utilizing phase change materials for thermal storage. Initially, the impact of five key parameters, generator temperature, condenser temperature, evaporator temperature, collector area, and storage tank volume, on the cycle's performance is thoroughly investigated. Subsequently, a three-objective optimization is executed, resulting in optimal values for the mentioned parameters: 83.4 °C for the generator temperature, 35.8 °C for the condenser temperature, 6.8 °C for the evaporator temperature, 82 m2 for the collector area, and 4 m3 for the storage tank volume. The analysis of energy, exergy and exergeoeconomics for the optimal point showed that the exergy efficiency for the ejector and solar cycle is 6.78 % and 10.74 %, respectively. Also, the COP of the refrigeration cycle was obtained as 0.1858. The results showed that the solar fraction is equal to 65.4 %, and the highest amount of exergy destruction is related to solar collectors, which is equal to 8.136 kW.

A review of the integration of the copper-chlorine cycle with other systems for hydrogen production

There are different methods for hydrogen production, among which thermo-chemical cycles are particularly important. One of the most common thermochemical cycles is the copper-chlorine cycle. In this cycle, the water electrolysis process takes place during a thermo-chemical reaction, and copper chlorine is used as a thermochemical reaction intermediate. This cycle requires two factors to produce hydrogen: A heat source with a temperature of about 520 oC and electricity. For this reason, it is possible to use the hot waste gases of industries or parabolic through collector and heliostat field to provide its heat. To supply electricity for this cycle, various alternatives from the power grid and wind turbine to heat recovery in cycles that use low-temperature energy sources are considered. In this article, the integration of the copper-chlorine cycle with power generation systems has been discussed and investigated from the perspective of energy, exergy, and economics. This review is divided into two general parts using renewable and non-renewable resources. At the beginning of this article, various methods of hydrogen production focusing on the copper-chlorine cycle have been briefly discussed. In the following, the way this cycle works is explained along with energy, exergy, and economic equations, and the research done in this direction is explained. Finally, a strategy for how to integrate the copper-chlorine cycle with other systems is described. Studying this article, in addition to giving a better attitude in the field of integrating this cycle with other plants, is similar to a guideline for using the cycle along with other systems for better productivity. The conducted investigations showed that the recovery of hot industrial exhaust gas as a source of heat for the Cu-Cl cycle has a high potential for saving energy consumption and reducing environmental pollutants. To produce the required electricity, it is recommended to use cycles that work with a low-temperature energy source, such as the organic Rankine cycle and Kalina cycles. Also, if renewable energy sources are used, it is recommended to use parabolic through collectors and heliostats to produce the required heat. As in the case of non-renewable energy sources, cycles with low-temperature energy sources can be used.

Experimental characterization of an ammonia – water – hydrogen diffusion absorption refrigeration system

A diffusion absorption refrigerator (DAR) is a heat powered refrigeration system. It uses the ammonia-water mixture as a working fluid in addition to an auxiliary inert gas. In the present work, experimental investigation and dynamic analysis of the H2O-NH3-H2 diffusion absorption refrigeration system have been carried out using different values of thermal power input to the generator and evaporator load. Experimental results show that the temperature evolution of system components, transient response, amount of cooling below ambient, and coefficient of performance are significantly sensitive to the values of generator power input and evaporator load. Analysis of DAR system behavior for different start up conditions is used to estimate the time and energy required for the initiation of cooling effect. Steady-state experimental results obtained over a wide range of generator input power and evaporator load are used to characterize the unit performance. Performance maps useful for the design and integration of DAR systems with low-temperature energy sources are developed. These maps can be used to estimate the generator input power required for a given cooling load at a specified value of cooling temperature below ambient.

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.

Performance investigation and numerical evaluation of a single-effect double-lift absorption chiller

This study deals with innovative integrated absorption refrigeration systems. This cycle could be useful for converting low-temperature energy sources into useful outputs like cooling. The Single Effect Double Lift Absorption Chiller (SE-DL AC) was introduced and energetically evaluated. A detailed modeling based on the first law of thermodynamics is built to investigate the performance of this novel system. This model was initially validated considering a reference SE-DL AC from the Hitachi company with a nominal cooling capacity of 106.1 kW. This system is compared to a conventional single-effect absorption chiller while maintaining the same operating parameters and boundary conditions in both configurations to ensure a fair comparison in terms of the internal and external baseline operating conditions. A parametric study of the driving hot water inlet temperature, the solution mass flow rate, the effectiveness of the solution heat exchanger, and internal and external temperatures on the Coefficient of Performance (COP), Cooling capacity (CC), and Glide Temperature (ΔT) are conducted. The final results demonstrate that the cooling production capability of the SE-DL is increased by an average of about tenfold when compared to the conventional SE AC at a thermal source temperature of 88.7 °C and an inlet hot water mass flow rate of 1 kg/s. The COP results produced under the same operating conditions are quite similar. The cooling generation capability of the SEDL is, on average, 10 times greater than that of the traditional SE AC. This explains that the SEDL-AC is well suited for a wide range of low-temperature heat sources (e.g., solar energy). Furthermore, the SE-DL AC enables efficient use of low-grade heat with a high glide temperature in the driving heat stream of about 10 times (36 °C instead of 3.5 °C). This large temperature difference exemplifies that the SE-DL AC absorption chiller is an alternative for extracting as much heat as possible, thereby improving cold production.

Mass and Charge Transfer in a Polymeric NiSalen Complex at Subzero Temperatures

Electrochemical energy storage systems have a wide range of commercial applications. They keep energy and power even at temperatures up to +60 °C. However, the capacity and power of such energy storage systems reduce sharply at negative temperatures due to the difficulty of counterion injection into the electrode material. The application of organic electrode materials based on salen-type polymers is a prospective approach to the development of materials for low-temperature energy sources. Poly[Ni(CH3Salen)]-based electrode materials synthesized from different electrolytes were investigated by cyclic voltammetry, electrochemical impedance spectroscopy and quartz crystal microgravimetry at temperatures from -40 °C to 20 °C. By analyzing data obtained in various electrolyte solutions, it was shown that at subzero temperatures, the process of injection into the polymer film, together with slow diffusion within the film, predominantly limit the electrochemical performance of electrode materials based on poly[Ni(CH3Salen)]. It was shown that the deposition of the polymer from solutions with larger cations allow the enhancement of the charge transfer due to the formation of porous structures facilitating the counter-ion diffusion.

A competitive study of a geothermal heat pump equiped with an intermediate economizer for R134a and R513A working fluids

At temperatures below 60?C, the best way to use geothermal sources for heating is to use heat pumps. A heat pump can provide air conditioning for a residential, commercial, etc., all year round by heating in winter and cooling in summer using a low temperature source. Also, a heat pump can be used for water distillation through evaporation. The ground source heat pump with a high COP and low temperature thermal energy sources is one of the best technologies for using RES. In the present study, the effects of changing ambient temperature and soil temperature on a heat pump?s overall COP and energy efficiency are investigated using a simulated geothermal heat pump with an economizer. The system?s thermodynamic simulation is first performed in the engineering equation solver software for R134a and R513a working fluids. The exergy destruction of different components for both working fluids was calculated and displayed as a figure. The COP of the heat pump for R134a working fluid is equal to 3.916, equal to 3.729 for R513a working fluid, which indicates that R134a fluid has about 5% better performance. The COP of the system for R134a working fluid is equal to 3.662, which is equal to 3.504 for R513a working fluid, which indicates that R134a fluid has about 4.5% better performance.

An investigation on potential use of ice thermal energy storage system as energy source for heat pumps

It has been crystal clear to everyone that ice storage systems provide significant advantages in reducing cooling costs, balancing energy supply and demand profiles, and shaving peak loads. As the main purpose of ice storage systems is for cooling purposes, separate heating systems, such as furnaces, heat pumps, electrical heaters, etc., are required for buildings with heating demands. This work offers to use an ice storage system in the heat pump as the energy source. Comprehensive thermodynamic and economic analyses are conducted to assess the proposed system. The proposed system is implemented in an office building in Istanbul, Turkey. Thermodynamic studies indicate that while the overall energetic and exergetic coefficient of performance (COP) values for the ice storage integrated air conditioning (AC) are calculated to be 4.57 and 2.04, respectively, they are 3.99 and 2.12 for the ice storage integrated heat pump. While the yearly operating cost for the traditional AC is 1.9 million TL, it is 0.5 million for the ice storage integrated AC. The annual natural gas consumption cost for heating is 295,000 TL, and 375,000 TL for the ice storage integrated heat pump. The payback period of the ice storage integrated AC and heat pump system is observed to be 4.5 years. It may provide almost 8 million TL savings at the end of 10 years. At the end of the present study, it is reached that the ice storage system has a promising potential to use in heat pumps as a low-temperature energy source. Also, it provides a more environmentally friendly heating operation as it does not require fossil fuels by removing the furnaces or provides higher COP for heat pumps.

Експериментальні дослідження термоакустичних двигунів з двофазним робочим тілом

A distinguishing feature of these days is the general tendency to decrease the temperature level of the waste heat of engines for power plants in industry, transport, and energy. These circumstances complicate the usage of traditional energy-saving technologies designed to transform this heat into mechanical work. Given the lack of effective technologies, large volumes of such heat emissions are lost. As an example, we can consider ship power engineering. On ships that are equipped with dual-fuel medium and low-speed engines, the thermal emissions of the cooling systems have a temperature of 355…365 K. Given the small exegetical potential, the use of such low-temperature waste energy sources by any heat engines is a difficult problem. Therefore, the task of improving existing energy-saving technologies or developing new ones remains relevant. Thermoacoustic technologies can be useful in solving this problem. A significant advantage of thermoacoustic heat machines is the ability to use any external heat source, in this case low-temperature sources, and produce mechanical work. There are known cases of thermoacoustic oscillations at small temperature differences between heat sources under conditions of high humidity of the working environment. This phenomenon can be used to create low-temperature energy-saving systems based on thermoacoustic engines (TAE) with a wet two-phase working environment. The practical use of thermoacoustic systems as part of ship power plants requires additional research to solve low-level issues, in particular, increasing the specific power of the TAE. This work provides a description of the experimental equipment, design of experimental TAE with a wet working body and research methods. The results of the experiments showed that in experimental TAEs with a two-component (moist) working environment, the temperature of spontaneous thermoacoustic oscillations was 355…359 K, while the longitudinal temperature gradient in the matrix was 1.19…1.30 K/m. The specific power of TAE with a moist environment increased by 1.7…7 times, and the acoustic pressure increased by 2…4.7 times compared to the operation in dry air. It is shown that in the existing TAEs, the condensation of water vapor in the ceramic matrix and on the surfaces of the heat exchangers can lead to a loss of power, roughly up to 25 %, while maintaining the operational capacity.

Combined heat pump heating and ventilation system using heat of soil, sewage water and ventilation emissions

Currently, one of the main energy consumers in many countries is the communal sector. In this case, the bulk of the energy is supplied by fossil sources. In this regard, studies in the field of alternative energy sources that can help solve not only the problem of energy saving, but also the problem of environmental pollution and prevent the approaching environmental collapse deserve special attention. One of the most promising sources of alternative energy in the field of communal utilities is heat pump that use the low-temperature heat of renewable sources and the heat of the upper layers of the soil. Soil, as an energy source, has an almost constant and sufficiently high temperature level, which determines the sufficient efficiency of using its heat. However, the widespread occurrence of this type of heat pump is hindered by the high cost of the ground heat exchanger and its installation. In this regard, the development of new heat supply schemes having higher energy efficiency is relevant. To solve this problem, a combined heating and ventilation scheme based on ground heat pump was developed. The feature of this scheme is the use of additional low-temperature energy sources, such as the heat of ventilation emissions and wastewater of a heat supply facility. On the basis of the scheme the thermodynamic model in which the equation of the basic balance of separate elements and the scheme as a whole found the defining parameters characterizing work of system is developed. An algorithm for determining parameters at the nodal points of the chain is proposed, on the basis of which a numerical analysis of the circuit is performed. The results of the analysis are presented in the form of graphical dependencies. Features of operation of the scheme depending on the set initial parameters and ambient temperature are shown. Conclusions are made on the possible reduction of capital and operating costs for heating and ventilation due to the proposed solution.

ОПЫТ ИСПОЛЬЗОВАНИЯ ГЕОТЕРМАЛЬНОЙ ЭНЕРГИИ ПРИПОВЕРХНОСТНОГО МАССИВА ДРЕВНИХ ГРАНИТОИДОВ ДЛЯ ЦЕЛЕЙ ТЕПЛОСНАБЖЕНИЯ (ЮГ ЗАПАДНОЙ СИБИРИ)

An example of transition of the heating- and hot-water supply system to a low-temperature geothermal energy source from the Paleozoic granitoid massif is given for a secondary school building in Novosibirsk. The necessity for change the source of heat supply arose in 2018 due to wear and tear of the coal boiler house old equipment, which has provided the school with heat since it was built in 1964. At the time of the geothermal project implementation, there were already several cases of successful use of underground heat-producing probes arranged in specially drilled geothermal wells for heating public facilities in neighboring Siberian cities (Tomsk, Barnaul). However, loose sedimentary rocks there served for the source of heat energy, that greatly simplified and accelerated the tasks implementation. The described experience of heating – and hot-water supply of building due to the low energy from a shallow lying massif of ancient rocky grounds with intrusive genesis is unique for Russia and can serve as a platform for the implementation of geothermal projects in regions with complicated ground conditions and moderately cold climate.

Liter-scale atmospheric water harvesting for dry climates driven by low temperature solar heat

This experimental study demonstrates a thermodynamic cycle based on isothermal regeneration to enhance the exploitation of sorbents and low temperature energy sources, such as solar energy, for atmospheric water harvesting in dry climates. An experimental setup based on silica gel has been designed to produced liquid water with low regeneration temperatures for dry climates with dew points in the range of 2 to 8 °C and ambient temperatures between 20 and 35 °C. Experimental results demonstrate daily water production from 1.5 to 3.3 L day−1 per square meter of solar field, with a maximum regeneration temperature of 57 °C, and ambient temperatures up to 35 °C. The thermal energy required to activate the cycle is between 1 and 3 kWh per liter of condensed water.

Techno-economic control strategy optimization for water-source heat pump coupled with ice storage district cooling system

Incorporating low-temperature renewable energy sources such as geothermal energy, solar energy, and waste heat into district heating and cooling systems is expected to be an effective solution for reducing fossil energy consumption and carbon emissions. This study aims to propose an optimal intelligent control strategy for the water-source heat pump coupled with an ice storage district cooling system, which can fully maximize the economic potential of renewable energy and ice storage systems. The proposed control strategy treats the ice melt cooling rate, water supply temperature, and cooling ratio of the water source heat pump as three independent control variables. The minimum operating cost per unit of cooling supply is identified as the optimal objective function of the genetic algorithm. An integrated heat transfer model of the water-source heat pump coupled with an ice storage district cooling system was developed, and experimental test data verified its accuracy. Compared with the ice melting priority control strategy and the water-source heat pump priority control strategy, the GA-based optimal control strategy saved 8.7–9.3% of the operating cost while maintaining a relatively good energy-saving performance. This proposed intelligent control strategy can stimulate the tremendous economic potential of the ice storage district cooling system coupled with renewable energy sources.

Experimental investigation of heat pipe thermoelectric generator

Thermoelectric generators can generate electricity directly from low-temperature energy sources, such as solar and geothermal energy. Because of the low heat flux of the heat source, heat pipes are used to increase the hot end temperature of the thermoelectric module, and thus improve its conversion efficiency. We developed a heat pipe thermoelectric generator and quantitatively studied the effects of the heating power of the heat pipe evaporator and the number of modules used in the condenser, on the thermoelectric performance, heat transfer characteristics, and temperature uniformity of the generator. As the heating power increased, the heat pipe thermal resistance decreased, and the thermoelectric conversion efficiency increased. As the number of thermoelectric modules increased, the proportion of heat pipe thermal resistance increased and became dominant, which caused the hot end temperature of the modules to decrease. The system attains maximum efficiency when there is only a single module at the condenser. The temperature of the evaporator can be effectively increased to improve the output power. When the temperature of the evaporator remained constant, increasing the number of modules reduced the temperature of the hot end slightly, however, the output power was greatly improved, and the maximum output power reached 10.85 W with four modules used in the experiment. The non-uniformity of the module output performance was obvious at a low heat flux, and the module output power was high near the evaporator. These results contribute to understanding the working characteristics of heat pipe thermoelectric generators and provide some guiding significance for the optimization of generator operations.

The future role of energy geostructures in fifth generation district heating and cooling networks

Energy geostructures are novel dual use engineering sub-structures that can be used for heat transfer and storage as well as original structural function. Their use is becoming increasingly popular in delivering cost-effective shallow geothermal energy. Currently, they are mostly used as a part of ground-source heat pump (GSHP) systems for supplying partial or full heating and cooling demands of different types of buildings. The recent introduction of fifth generation district heating and cooling (5GDHC) networks can pave the way for the exploitation of energy geostructures as ground-coupled low-temperature energy sources and stores for providing energy demands of a wider range of energy users in districts rather than single buildings. In this article, the capability and feasibility of the novel concept of integration of energy geostructures into the 5GDHC networks are evaluated through reviewing different aspects of thermal performance of operating energy geostructures and 5GDHC networks. The potential advantages and challenges along with the knowledge gaps in such integration are discussed, and some practical recommendations are provided concerning dealing with some implementation challenges. It is highlighted that the incorporation of energy geostructures in 5GDHC networks can enhance the sustainability, flexibility and resilience of the network. There is the potential to exploit a greater share of cost-effective geothermal energy, and the ability to act as both thermal energy sources and stores for efficiently supplying both heating and cooling demands. However, since the development of fifth generation thermal networks and energy geostructures, particularly energy walls and energy tunnels, are still in their infancy, further research is required to assess the magnitude of the opportunities and quantify the advantages of integrating energy geostructures into the 5GDHC networks.

Energy Benefits of Heat Pipe Technology for Achieving 100% Renewable Heating and Cooling for Fifth-Generation, Low-Temperature District Heating Systems

This paper addresses the challenges the policymakers face concerning the EU decarbonization and total electrification roadmaps towards the Paris Agreement set forth to solve the global warming problem within the framework of a 100% renewable heating and cooling target. A new holistic model was developed based on the Rational Exergy Management Model (REMM). This model optimally solves the energy and exergy conflicts between the benefits of using widely available, low-temperature, low-exergy waste and renewable energy sources, like solar energy, and the inability of existing heating equipment, which requires higher exergy to cope with such low temperatures. In recognition of the challenges of retrofitting existing buildings in the EU stock, most of which are more than fifty years old, this study has developed a multi-pronged solution set. The first prong is the development of heating and cooling equipment with heat pipes that may be customized for supply temperatures as low as 35 °C in heating and as high as 17 °C in cooling, by which equipment oversizing is kept minimal, compared to standard equipment like conventional radiators or fan coils. It is shown that circulating pump capacity requirements are also minimized, leading to an overall reduction of CO2 emissions responsibility in terms of both direct, avoidable, and embodied terms. In this respect, a new heat pipe radiator prototype is presented, performance analyses are given, and the results are compared with a standard radiator. Comparative results show that such a new heat pipe radiator may be less than half of the weight of the conventional radiator, which needs to be oversized three times more to operate at 35 °C below the rated capacity. The application of heat pipes in renewable energy systems with the highest energy efficiency and exergy rationality establishes the second prong of the paper. A next-generation solar photo-voltaic-thermal (PVT) panel design is aimed to maximize the solar exergy utilization and minimize the exergy destruction taking place between the heating equipment. This solar panel design has an optimum power to heat ratio at low temperatures, perfectly fitting the heat pipe radiator demand. This design eliminates the onboard circulation pump, includes a phase-changing material (PCM) layer and thermoelectric generator (TEG) units for additional power generation, all sandwiched in a single panel. As a third prong, the paper introduces an optimum district sizing algorithm for minimum CO2 emissions responsibility for low-temperature heating systems by minimizing the exergy destructions. A solar prosumer house example is given addressing the three prongs with a heat pipe radiator system, next-generation solar PVT panels on the roof, and heat piped on-site thermal energy storage (TES). Results showed that total CO2 emissions responsibility is reduced by 96.8%. The results are discussed, aiming at recommendations, especially directed to policymakers, to satisfy the Paris Agreement.

Thermo-economic analysis of working fluids for a ground source heat pump for domestic uses

Ground source heat pump, due to high coefficient of performance (COP) and use of low-temperature thermal energy source, is one of the best technologies to use renewable energy resources. In this work, at first, a geothermal heat pump for heating with an economizer is simulated, and then the effects of the variations in different parameters such as evaporator pressure, condensation pressure, and intermediate pressure on heat pump and total COP and exergy efficiency are analyzed. Initially, the thermodynamic simulation of the system is performed for different working fluids (R134a, R-12, R152a, R1234yf, and R1234ze(E)) in the EES software programming environment. The COP and exergy efficiency are calculated for different working fluids and obtained optimal values. The best overall coefficient of performance of the system is related to fluid R134a with a value of 3.663 and the best overall exergy efficiency of the system is related to fluid R1234ze(E) with a value of 0.5517. The lowest PCEU value is for fluid R152a with 0.01247$ per kilowatt. It can be concluded that by reducing the evaporator pressure of the cycle, the cost of producing an energy unit will be cheaper and by reducing the middle pressure of the cycle, the cost of producing an energy unit will be more expensive.

Multi-objective optimization of an ORC power plant using one-dimensional design of a radial-inflow turbine with backswept rotor blades

Organic Rankine cycle (ORC) power plants are a promising technology for converting low and medium temperature energy sources into electricity. In order to fully exploit the potential of an ORC, the components of the system should be designed appropriately. One of the key elements of the ORC installation, substantially affecting the system efficiency, is a turboexpander. This study concerns a multi-objective optimization of an ORC coupled with a one-dimensional radial-inflow turbine (RIT) model. Particular attention is given to determination of optimal parameters which have an impact on the turbine geometry of the nozzle and the rotor. The nozzle pitch to chord ratio and the blade angle at the rotor inlet are investigated as one of the decision variables. The first parameter is rarely discussed in most studies and it is either a fixed value or its optimum is determined using correlations developed for axial-flow turbines. Applying the blade angle as a variable is associated with the use of backswept rotor blades, which is achievable in the ORC and results in higher turbine efficiency. By means of Non-dominated Sorting Genetic Algorithm-II (NSGA-II) and Technique for Order Preference by Similarity to Ideal Solution (TOPSIS), the optimal design point has been determined. It was found that by applying the blade angle at the rotor inlet as the decision variable, the optimal blade sweep design featuring a 0.00% incidence enthalpy loss can be obtained. Based on the parametric analysis, it was reported that by making wrong design choices with respect to the RIT decision variables, the turbine efficiency may be decreased by almost 8.00%, leading to a decrease in the net power output by more than 8.00% and an increase in the electricity production cost of more than 7.00%.