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CO2 is an environmentally friendly heat transfer fluid and has many advantages in thermal energy and power systems due to its peculiar thermal transport and physical properties. Supercritical CO2 (S-CO2) thermal energy conversion systems are promising for innovative technology in domestic and industrial applications including heat pump, air-conditioning, power generation, renewable energy systems, energy storage, thermal management, waste heat recovery and others. Both S-CO2 and transcritical CO2 thermodynamic cycles have been extensively investigated in order to improve the efficiencies of thermal and power systems and achieve net zero carbon emissions. This paper focuses on the progress and prospects for current research and technology development of S-CO2 thermal energy conversion systems and their applications including power generation, energy storage and waste heat recovery. First, the CO2 thermal transport and physical properties and benefits using CO2 as a heat transfer fluid in thermal energy and power systems are discussed. Then, classification of CO2 thermodynamic systems is presented. Next, S-CO2 for power generation, energy storage and waste heat recovery systems are presented. Finally, research needs of subcritical and supercritical CO2 heat transfer, fluid flow and heat exchangers for the development of various thermal energy and power systems are discussed. [ABSTRACT FROM AUTHOR]

Methods and instrumentation for measuring grout quality in heat pump boreholes, including the measurement of groundwater flow through boreholes outside partly grouted borehole exchanger pipes, have been developed in the Czech Republic. A Semtex charge has also been developed to repair rock massifs, which reliably disconnects borehole exchanger pipes without severely harming the surrounding rock environment or buildings. The resulting hole can then be used for regrouting, thus preventing undesirable vertical water flow through the borehole. [ABSTRACT FROM AUTHOR]

Ground heat pump systems (GHPSs) are esteemed for their high efficiency within renewable energy technologies, providing effective solutions for heating and cooling requirements. These GHPSs operate by utilizing the relatively constant temperature of the Earth's subsurface as a thermal source or sink. This feature allows them to perform greater energy transfer than traditional heating and cooling systems (i.e., heating, ventilation, and air conditioning (HVAC)). The GHPSs represent a sustainable and cost-effective temperature-regulating solution in diverse applications. The ground heat exchanger (GHE) technology is well known, with extensive research and development conducted in recent decades significantly advancing its applications. Improving GHE performance factors is vital for enhancing heat transfer efficiency and overall GHPS performance. Therefore, this paper provides a comprehensive review of research on various factors affecting GHE performance, such as soil thermal properties, backfill material properties, borehole depth, spacing, U-tube pipe properties, and heat carrier fluid type and velocity. It also discusses their impact on heat transfer efficiency and proposes optimal solutions for improving GHE performance. [ABSTRACT FROM AUTHOR]

The accurate optimisation of absorption chillers is often impeded by idealised models that overlook system interactions and machine complexities. This study introduces a validated mathematical description for predicting the primary indicators of non-idealised absorption chillers, accounting for factors such as the electrical work of the Solution Circulation Pump, entropy changes within the refrigerant cycle, and exergy losses. Validation against 13 years of data (2008–2021) from the University of Debrecen's absorption chiller indicated close agreement, with deviations within acceptable limits. The use of a solution heat exchanger shifted cooling indicators towards their minima. Sensitivity analyses indicated that a 2.5% reduction in condenser temperature increased COP by 41.3% and Cooling Exergetic Efficiency by 15.5%, while a 2.5% reduction in the Heat Fraction Factor improved both by 34%. Adjusting absorber temperature and Heat Fraction Factor down by 2.5%, alongside a 2.5% rise in generator temperature, resulted in a 100.8% increase in COP and a 52.8% boost in Cooling Exergetic Efficiency. These insights provide a solid foundation for future optimisation strategies in real-life absorption chiller systems. [ABSTRACT FROM AUTHOR]

The performance of heat pump systems for heating and cooling heavily relies on the thermal conditions of their reservoirs. This study introduces a novel thermal reservoir, detailing a 2017 project where the Municipality of Stavanger installed a heat exchanger system on the wall of a main wastewater tunnel beneath the city center. It provides a comprehensive account of the system's design, installation, and performance, and presents an Artificial Neural Network (ANN) model that predicts heat pump capacity, electricity consumption, and outlet temperature across seasonal variations in wastewater temperatures. By integrating domain knowledge with the ANN, this study demonstrates the model's capability to detect anomalies in heat pump operations effectively. The network also confirms the consistent performance of the heat exchangers from 2020 to 2024, indicating minimal fouling impacts. This study establishes wastewater heat exchangers as a safe, effective, and virtually maintenance-free solution for heat extraction and rejection. [ABSTRACT FROM AUTHOR]

This study proposes a novel onboard carbon capture system (OCCS) with reduced fuel consumption. The proposed system included a heat pump with an intermediate heat exchanger, a parallel compressor, and a steam compressor. The proposed system consumed 43% less fuel than the boiler for producing the same amount of steam, which was required for CO2 stripping. In addition, a blended solvent of amino methyl propanol (AMP) and piperazine (PZ) was applied to the OCCS. A rate-based process simulation indicated that this solvent resulted in 22% lower reboiler duty, compared to a monoethanolamine (MEA) solvent. Further, it was shown that the proposed OCCS with the heat pump and the AMP/PZ solvent achieved a reduction of approximately 50% in both fuel consumption and CO2 emissions along with 26.9 USD reduction for capturing one ton of CO2, compared to the OCCS with a boiler and MEA solvent. [ABSTRACT FROM AUTHOR]

The use of geothermal borehole heat exchangers (BHEs) in combination with ground-source heat pumps represents an important part of shallow geothermal energy production, which is already used worldwide and becoming more and more important. Different measurement techniques are available to examine a BHE field while it is in operation. In this study, a field with 54 BHEs up to a depth of 120 m below ground level was analyzed using fiber optic cables. A distributed temperature sensing (DTS) concept was developed by equipping several BHEs with dual-ended hybrid cables. The individual fiber optics were collected in a distributor shaft, and multiple measurements were carried out during active and inactive operation of the field. The field trial was carried out on a converted, partly retrofitted, residential complex, "Lagarde Campus", in Bamberg, Upper Franconia, Germany. Groundwater and lithological changes are visible in the depth-resolved temperature profiles throughout the whole BHE field. [ABSTRACT FROM AUTHOR]

High-temperature geothermal energy is precious renewable resource for heating. Reducing the return temperature of geothermal water is an important way to maximize geothermal heating potential and expand the heating area. Considering that existing buildings generally use high-temperature radiators and other heating terminals, while newly constructed buildings mostly use low-temperature floor heating terminals, the required supply water temperatures for these two types differ. In response to this, a geothermal energy-driven dual-temperature district heating substation system with a single absorption heat pump and two heat exchangers is proposed. This system aims to produce dual-temperature hot water for both high and low-temperature heating terminals and reduce the return temperature of geothermal water. Simulation results shows that when the geothermal outlet water is 100 ℃, and the secondary network's high- and low-temperature terminal supply water temperatures are 50 ℃ and 35 ℃ respectively, the return temperature of geothermal water in the dual-temperature district heating substation can be reduced to 20. 1 ℃. Compared to a substation using two serial heat exchangers, the proposed can lower the geothermal water return temperature by 14. 9 ℃, reduce the geothermal water flow rate by 18. 6%, and improve COP by 11%, demonstrating significant energy-saving advantages. Variable working condition analysis indicates that promoting the use of low-temperature heating terminals helps further reduce the return temperature of geothermal water, increase the heat supply to users, and improve the COP of the dual-temperature heating substation. [ABSTRACT FROM AUTHOR]

• COP improvements of up to 16 % experimentally shown for high-glide mixtures compared to pure refrigerants. • COP of mixtures more robust against changes of operating conditions than pure fluids. Climate change necessitates the reduction of primary energy consumption. Industrial heat pumps can contribute by replacing oil and gas fired boilers in various applications. To cater the application, heat pumps must often impose temperature differences of 25 K or more to the heat source and heat sink, causing great irreversibility if evaporation and condensation occur at constant temperatures. Many theoretical studies suggest that high-glide refrigerant mixtures designed to match the temperature differences have a superior COP for such applications. In contrast to the numerous theoretical studies, systematic experimental studies are missing. This study tests high-glide mixtures at varying compositions at constant operating conditions. COP improvements of 16 % are shown comparing the best mixture against the best pure fluid. The improvement was established despite a significant degradation in the heat transfer coefficient, which could presumably be alleviated with larger heat exchangers. Additional parametric studies are conducted on the temperature differences of heat sink and source as well as the temperature level. The results show that mixtures not only outperform pure fluids at certain operating conditions but can maintain a higher COP across varying operating conditions. The binary and ternary mixtures in this study have glides between 10 and 40 K and consist of R1336mzz(Z), R1233zd(E), R1224yd(Z), R1234yf and R32. [ABSTRACT FROM AUTHOR]

The paper explores the performance of a sub-slab ground heat exchanger, coupled to a heat pump, and the ability of the system to provide space conditioning and domestic hot water (DHW) for a multi-unit residential building (MURB) located in Ottawa, Ontario. The parametric analysis conducted to optimize the design of the building, as well as the sensitivity analysis performed to optimize the configuration of the sub-slab ground heat exchanger is also presented. According to the simulated results, the ground layer can store some of the rejected energy over medium term, without reducing the long-term performance of the heat pump. The annual energy consumption per dwelling unit (including heat pump, all auxiliary equipment, appliances, and lights) was estimated to be 28.4 GJ, significantly lower than the average annual energy consumption for a low-rise apartment in Canada (46.7 GJ per apartment). To assess the sensitivity of the system to environmental conditions, the simulation was conducted using the weather files for other five locations in Canada. [ABSTRACT FROM AUTHOR]

• Two comparable high-temperature heat pumps at different scales are investigated. • Both heat pumps show similar COP trend lines depending on the temperature lift. • Differences in heat losses and heat transfer are related to volume-to-surface ratios. • Experimental data for a water-cooled compressor show promising results. • Analysis of over 200 data points shows the possibility of upscaling laboratory results. High-temperature heat pumps (HTHP) are crucial for decarbonizing district heating and industry. Hence, a reliable performance estimation considering effects of scaling is of interest for cost-efficient system integration. This study compares two laboratory HTHPs with the same refrigerant R1233zd(E). These systems have a similar plant design but a capacity scale factor of 3.2. The aim is to evaluate scale effects and make general valid statements about the challenges of upscaling laboratory test results. The analyses show that it is essential to distinguish between design effects like temperature differences at the pinch point or different heat exchanger surfaces and scale effects like relative heat losses and efficiencies of components and the system. At the component level, large surface reserves in the heat exchangers lead to 3–5 K smaller approach temperature differences in the lower capacity HTHP. At the system level, the relative heat losses are about 15 % higher than in the system with a larger capacity. The coefficient of performance of both HTHPs shows a similar trend as a function of the temperature lift from the heat source to the sink. Cross-referencing these performance results with over 200 data points from the literature, validated the possibility of upscaling. [ABSTRACT FROM AUTHOR]

This research investigates a polyvalent heat pump that simultaneously produces hot and cold water and uses natural refrigerants. The novelty of using a 48 V direct current compressor driven by solar photovoltaic (PV) energy and the staged retrofitting improvements to this heat pump are discussed. Empirical testing has indicated that using a suction line heat exchanger yields a 30% improvement in the heating Coefficient of Performance (COP). Rising ambient temperatures could positively and negatively impact its heating and cooling performance, respectively. In addition, an average COP of 3.8 was obtained after a one-hour simultaneous mode operation, with the average hot tank temperature rising from 32.7 to 58.9°C and the average cold tank temperature dropping from 18 to 14.4°C. Being capable of operating the polyvalent heat pump under renewable energy sources and utilizing all its generated heating and cooling energy contributes further to the electrification and decarbonization of residential buildings. [ABSTRACT FROM AUTHOR]

This article presents the performance estimation of a single-stage vapor adsorption system employing various carbon-based adsorbents with ethanol refrigerant, coupled with a small-scale biomass-based heating unit for space cooling, refrigeration, and heat-pumping applications. A detailed parametric investigation highlights the effects of operating temperatures, and heat exchanger to adsorbent mass ratio on specific cooling energy (SCE), coefficient of performance (COP), uptake efficiency (ηu), and mass of adsorbent to combustion fuel (mad/mcf) to identify the suitable adsorbent and sorption bed designs for each application. The numerical findings reveal that the flat-finned tube (FFT) adsorber outperforms traditional-finned tube (TFT) and tube & shell-type (T&S) adsorbers, achieving 19% and 30% higher COP, respectively, with biomass carbon-ethanol pair. The H2-treated Maxsorb-III shows the greatest optimal cooling COP (0.73), followed by the biomass-carbon (0.72) for refrigeration and space cooling. For heat pumping applications, biomass carbon-ethanol achieves the highest heat pumping COP (1.84) at a desorption temperature of 90°C, surpassing H2-treated Maxsorb-III. Further, the biomass-derived activated carbon requires the lowest amount of adsorbent per unit mass of combustion fuel in the biomass heating unit. The present thermodynamic analysis is a precursor for optimization of the potential heat-exchanger geometries and operating parameters, with the high-performance carbon adsorbents. [ABSTRACT FROM AUTHOR]

The deteriorating thermal environment of tunnels and the increase in energy consumption of environmental control systems has become highlights in the subway field. In existing research related to analysis of subway tunnel thermal environments and thermal accumulation; there is no predictive law that accounts for thermal accumulation or the long-term change in subway tunnel thermal environments. In this study, a combination of simulations and experiments is used. First, the long-term evolution of tunnel thermal environments with and without thermal interference are predicted and analyzed. Then, the changes in the tunnel thermal environment after the use of capillary heat exchangers are explored. The research results indicate that the model of the system has high accuracy and reliability. When there is a capillary heat exchanger installed in the subway tunnel, the anti-seasonal heat storage characteristics of the system result in the tunnel temperature increasing significantly in summer and decreasing significantly in winter, with a small decrease in the average annual temperature. This study provides a theoretical reference for environment-based subway tunnel construction and the comprehensive utilization of tunnel waste heat. [ABSTRACT FROM AUTHOR]

Model predictive control (MPC) is a promising approach for optimizing the performance of borehole heat exchangers (BHEs) in ground-source heat pump systems. The central element of MPC is the forward model that predicts the thermal dynamics in the ground. In this work, we validate the prediction accuracy of four BHE modeling approaches against real-world measurement data across various operational events and timescales. We simulate the fluid temperature leaving a BHE using a fully discretized 3-D numerical model, a resistance–capacitance model, a g-function model, and a hybrid model. The simulated temperatures are compared to measured temperatures using three validation metrics that quantify temperature offset, noise, and accuracy. The main reason for a mismatch between measured and modeled temperatures is a temperature offset of the simulated temperature. To remove this effect, the models were calibrated for their most sensitive parameter, the ground temperature, and their prediction accuracy over 4 years was evaluated. Thereby, model calibration seems to be a viable solution to account for an unknown load history. The results show that the resistance–capacitance model provides decent predictions in the short term and the g-function model in the long term. However, both models are strongly dependent on accurate calibration. The hybrid model provides the most accurate short and long-term predictions and is less dependent on calibration. Still, its integration into optimization syntax poses challenges compared to the other models. Although not yet applied in model predictive control, the hybrid model stands out as a promising choice for optimizing BHE field operations across various timescales. [ABSTRACT FROM AUTHOR]

This paper studies the optimization design of capillary heat exchangers and their innovative engineering applications in buildings. The purpose of this study is to use a capillary heat exchanger as the front-end device of the heat pump in coastal areas to extract energy to facilitate the application of renewable energy in buildings. Firstly, in this paper, the main factors of capillary heat transfer efficiency were explored in areas near the coast. Secondly, for the sake of improve the heat transfer efficiency of the capillary heat exchanger, numerical calculations were carried out on the heat transfer of the capillary in the case of inconsistent operating patterns in the summer and winter months, respectively. The results showed that when the daily working time of the capillary heat exchanger was 8 hours, the temperature difference of the capillary inlet and outlet was 2.1 ℃. And the heat transfer rate was 87.1 W/m² . In summer, the temperature difference of the capillary inlet and outlet was 2.6 ℃. And the heat transfer rate was 107.8 W/m² . This article helps to promote innovative and sustainable technologies in coastland development, such as capillary heat exchangers and heat pumps, which could used in renewable energy extraction and building utilization in near coastal areas. [ABSTRACT FROM AUTHOR]

A common belief is that any closed, counterclockwise cycle on a pV diagram represents a refrigerator or heat pump. It has been established that this is not the case, but previous papers on this topic have made unnecessary assumptions about the temperatures of the energy reservoirs and about how the system exchanges energy with the reservoirs. Relaxing these assumptions leads to a wide array of unexpected behaviors. In some cases, the same pV cycle can be a heat pump, a cold pump, or a Joule pump simply by changing how the system is connected to the reservoirs. This paper explores the strange world of counterclockwise cycles. Editor's note: In this paper, author Randall Knight explores the rich behavior of counterclockwise thermodynamic cycles. A counterclockwise cycle can function as a heat pump or refrigerator, but this is not the only possibility. The choice of thermal reservoirs and the choice of which reservoir heat is absorbed from and exhausted to during the cycle affect the coefficient of performance and even the basic function of the device. The author illustrates these possibilities through an analysis of counterclockwise Carnot, Kelvin, Brayton, and Stirling cycles. The analysis includes interesting possibilities, such as a cycle that operates with a single reservoir, as well as practical applications like the role of heat exchangers. The surprising results of this analysis will likely be of interest to anyone who has studied thermodynamics, and the material can easily be incorporated into any course that includes thermodynamics, from introductory physics to graduate study. [ABSTRACT FROM AUTHOR]

A Ground Coupled Heat Pump (GCHP) is a highly energy efficient heating, ventilation, and air conditioning (HVAC) system that utilises the ground as the heat source when heating and as the heat sink when cooling. This paper investigates GCHP systems with horizontal Ground Heat Exchangers (GHEs) in the rural industry, exemplifying the technology for poultry (chicken) sheds in Australia. This investigation aims to provide an Artificial Neural Network (ANN) model that can be used for GCHP design at various locations with different climates. To this extent, a Transient System Simulation Tool (TRNSYS) model for a typical horizontal GHE applied in a rural farm was first verified. Using this model, over 700,000 hourly performance data items were obtained, covering over 80 different yearly loading patterns under three different climate conditions. The simulated performance data was then used to train the ANN. As a result, the trained ANN can predict the performance of GCHP systems with identical (multiple) GHEs even under climatic conditions (and locations) that have not been specifically trained for. Unlike other works, the newly introduced ANN model is accurate even with limited types of input data, with high accuracy (less than 5% error in most cases tested). This ANN model is 100 times computationally faster than TRNSYS simulations and 10,000 times faster than finite element models. [ABSTRACT FROM AUTHOR]

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Based on air-, water-, and ground-source heat pump systems, a novel type of heat pump system, named the heat-source tower heat pump system (HSTHPS), has recently been developed in the southern area of China. The HSTHPS overcomes the evaporator frosting problems of the air-source heat pump system (ASHPS) when the ambient temperature is lower, and it avoids the geological condition constraints of the water- and ground-source heat pump systems. However, studies on the HSTHPS are insufficient, thereby limiting its development and applications. Thus, the present review provides a detailed literature review on the advancements of HSTHPSs in China, including the HSTHPS operation principle, heat-source tower (HST) structure, heat and mass transfer characteristics, HSTHPS performance, antifreeze solution use, and antifreeze solution regeneration. Studies on the heat and mass transfer characteristics of HSTs are sufficient for guiding the application. Regarding open systems, the solution drifting to the air needs to resolved, and future studies need to focus on structure optimization for heat exchangers in closed systems. Moreover, advanced defrosting technology should be applied to closed-type HSTs, and a suitable operation strategy for HSTHPSs should be developed. Future priorities should involve integrating HSTHPSs with additional renewable energy in order to achieve continuous, stable, and efficient heating in winter based on the characteristics of local climate and renewable energy. [ABSTRACT FROM AUTHOR]

This research was carried out to compare selected forecasting methods, such as the following: Artificial Neural Networks (ANNs), Classification and Regression Trees (CARTs), Chi-squared Automatic Interaction Detector (CHAID), Fuzzy Logic Toolbox (FUZZY), Multivariant Adaptive Regression Splines (MARSs), Regression Trees (RTs), Rough Set Theory (RST), and Support Regression Trees (SRTs), in the context of determining the temperature of brine from vertical ground heat exchangers used by a heat pump heating system. The subject of the analysis was a public building located in Poland, in a temperate continental climate zone. The results of this study indicate that the models based on Rough Set Theory (RST) and Artificial Neural Networks (ANNs) achieved the highest accuracy in predicting brine temperature, with the choice of the preferred method depending on the input variables used for modeling. Using three independent variables (mean outdoor air temperature, month of the heating season, mean solar irradiance), Rough Set Theory (RST) was one of the best models, for which the evaluation rates were as follows: CV RMSE 21.6%, MAE 0.3 °C, MAPE 14.3%, MBE 3.1%, and R2 0.96. By including an additional variable (brine flow rate), Artificial Neural Networks (ANNs) achieved the most accurate predictions. They had the following evaluation rates: CV RMSE 4.6%, MAE 0.05 °C, MAPE 1.7%, MBE 0.4%, and R2 0.99. [ABSTRACT FROM AUTHOR]

By constructing the heat transfer model of the buried tube heat exchanger, using the mathematical method and numerical calculation software, the temperature of the buried tube heat exchanger is calculated numerical, so as to better understand the temperature effect of the buried tube heat exchanger on the surrounding soil. This paper establishes a mathematical model of a vertically buried heat transfer system based on the principle of thermal equilibrium and the thermal conductivity differential equation. Conduct research on the temperature field around single pipes in different soil (geological conditions), temperature field under different drilling backfill materials, and the temperature around buried pipe-lines in both short-term and long-term operation of the system. The experimental results show that the simulation results of the system's short time (10 days) and long time (90 days) performance show that the cooling and temperature cycles in different areas directly affect the heat radius of the buried pipe and the heat accumulation near the buried pipe. The thermal action radius of the short-term operation system is about 1.8 m, and the long-term operation reaches 4.5 m. [ABSTRACT FROM AUTHOR]

The heat transfer capacity of ground and soil energy sources is the key factor that affects the performance of the ground source heat exchanger. The heat storage capacity of soil is related to various factors. The author proposes a multi-component heat pump system which combines solar energy, waste heat, and air, and designs a new type of dual channel finned tube evaporator for defrosting. Based on different weather conditions, the operation mode of the system was provided, and performance tests were conducted on the system under no light conditions and with or without waste heat utilization. The results show that the seepage speed of buried tube ground source heat pump system geographic tube heat exchanger and soil heat transfer influence is larger, the groundwater seepage speed of 15 m per annual, running 3-4 years later, the heat transfer well area of the soil temperature field will be stable, which can judge in the groundwater seepage is sufficient area, the buried tube ground source heat pump conditional soil winter and summer heat balance. [ABSTRACT FROM AUTHOR]

In order to understand the application of frost measurement of air source heat pump heat exchanger, a research on frost measurement of air source heat pump heat exchanger based on image recognition processing technology is put forward. In this paper, the scheme design of defrosting control system based on image processing technology is introduced, and the frost degree coefficient of outdoor heat exchanger fin surface is introduced to characterize the frost degree of fin surface. Secondly, the experimental environment room was built, and the conventional defrosting control method of the existing heat pump unit was tested on the spot. It was found that in the air temperature of -6~0 °C and the air relative humidity of 86~92%, the unit appeared the phenomenon of "defrosting in time" and "defrosting without frost". Finally, the change of frost layer on the surface of the outdoor heat exchanger fin during defrosting is analyzed, and the coefficient of frost degree on the surface of the fin is calculated and analyzed. At the beginning of defrosting, due to the large degree of frost, the P-value of the frost degree coefficient on the surface of the fin is close to 1, when the defrosting is carried out for 125 seconds, the P-value of the frost degree coefficient on the surface of the fin decreases sharply to 0.09, when the defrosting is completed, the P-value of the frost degree coefficient on the surface of the outdoor heat exchanger is maintained at about 0.04. The defrosting control method of air source heat pump based on image processing technology is proposed in this paper, and its technical feasibility and effect are verified by experimental tests, which lays a foundation for future popularization and application. [ABSTRACT FROM AUTHOR]

High-temperature heat pumps are a key technology for enabling the complete integration of renewables into the power grid. Although these systems may come with several variants, Brayton heat pumps are gaining more and more interest because of the higher heat sink temperatures and the potential to leverage already existing components in the industry. Because these systems utilize renewable electricity to supply high-temperature heat, they are particularly suited for industry or energy storage applications, thus prompting the development of various demonstration plants to evaluate their performance and flexibility. Adapting to varying load conditions and swiftly responding to load adjustments represent crucial aspects for advancing such systems. In this context, this study delves into assessing the transient capabilities of Brayton heat pumps during thermal load management. A transient model of an emerging prototype is presented, comprising thermal and volume dynamics of the components. Furthermore, two reference scenarios are examined to assess the transient performance of the system, namely a thermal load alteration due to an abrupt change in the desired heat sink temperature and, secondly, to a sudden variation in the sink mass flow rate. Finally, two control methodologies—motor/compressor speed variation and fluid inventory control—are analyzed in the latter scenario, and a comparative analysis of their effectiveness is discussed. Results indicate that varying the compressor speed allows for a response time in the 8–20 min range for heat sink temperature regulation (first scenario). However, the regulation time is conditioned by the maximum thermal stress sustained by the heat exchangers. In the latter scenario, regulating the compressor speed shows a faster response time than the inventory control (2–5 min vs. 15 min). However, the inventory approach provides higher COPs in part-load conditions and better stability during the transient phase. [ABSTRACT FROM AUTHOR]

In the ever-evolving landscape of technology and industry, there's a growing awareness of the need for environmentally friendly solutions. This survey marks a pioneering investigation into utilizing eco-environmentally friendly organic mixtures within indirectly integrated heat pump-driven humidification-dehumidification desalination systems. Its primary objective is to determine the most effective approach for enhancing the performance of the integrated cycles: employing organic blends or implementing structural modifications. The proposed layouts for distilled water production are structured around two distinct scenarios: the first scenario involves a basic heat pump, and the second incorporates a vapor injection heat pump. To scrutinize the devised systems' performance, an exergoeconomic analysis is performed, taking into account a meticulous heat exchanger modeling approach. In addition, extensive sensitivity analysis and NSGA.II optimization are conducted based on the most efficient mixture in terms of electricity consumption at a consistent feed-water flow rate. The findings highlight a notable enhancement in the efficiency of the two developed systems when organic blends are employed instead of pure working fluids, resulting in a substantial reduction in electricity consumption. Specifically, replacing R134a with R22/R142b increased the Gain-Output-Ratio (GOR) by 42.26% for the first scenario and 29.06% for the second scenario. As a result of the cost assessment, distilled water unit costs have decreased by 12.87% and 14.32%, respectively, for the first and second scenarios. Notably, using a ternary blend slightly enhances the performance of the proposed systems compared to when a binary blend is employed. Specifically, the highest Gain-Output-Ratio (GOR) of 12.28 was achieved for the second scenario when using R142b/R22/R236fa, representing a modest 3.2% increase compared to the case where R22/R142b was utilized. Furthermore, optimizing the first and second scenarios and utilizing R22/R142 leads to an improvement of 7.31% and 12.55% in exergetic efficiency and 7.36% and 16.21% in UCDW, respectively. Ultimately, it is evident that incorporating eco-environmentally friendly organic blends in the simple heat pump, alongside their minimal ecological footprint and their role in promoting sustainability and adhering to environmental mandates, stands out as a remarkably efficient choice. In fact, the GOR of the first scenario is approximately 27.66% higher when using R142b/R22/R236fa compared to the second scenario employing a pure working fluid. Also, PP of the second scenario increases from 7.76 years to 9.66 years. [ABSTRACT FROM AUTHOR]

The main objective of this study is to model variable speed water-to-water heat pumps ( VSHP) and to examine the impact of the operation of such devices on ground heat exchanger sizing and energy consumption when they are used in ground-source applications. In the first part of the paper, a complete physics-based steady-state model of a variable-speed water-to-water heat pump is briefly presented. A performance map approach is also used by modifying an existing TRNSYS variable speed heat pump model to provide a minimum speed of operation and a better representation at part load. Simulation results over a heating season on a residential ground source VSHP indicate that the energy coverage (i.e., percentage of annual heat supplied by the heat pump) increases at a faster rate than the effect coverage (i.e., percentage of peak building heat supplied by the heat pump) for a small value of the effect coverage. For example, for effect coverage of 60%, the energy coverage is ∼ 93%. It is also shown that the normalized length of the ground heat exchanger varies linearly up to effect coverage of 60% where it is equal to 75% of the value encountered for effect coverage of 100%. [ABSTRACT FROM AUTHOR]

Flowrate control can have a significant positive impact on the thermal performance and economic profitability of ground-source heat pump systems. Including dynamic advective processes in the design phase, however, remains a challenging task, as few computationally efficient modeling tools allow for their adequate and accurate representation. The present work addresses this issue by presenting new formulations of non-stationary convolutions, an efficient simulation algorithm that relies on the theory of linear time-variant systems for predicting the thermal response of a ground heat exchanger to both dynamic heat loads and flow rates. First, the new original formulations are presented, which include (1) a simple time-domain expression and (2) a fast frequency-domain expression. Then, the efficiency and validity of the new formulations are verified using experimental multi-flowrate thermal response tests involving dynamic circulation, pumping and bleed flow rates in closed-loop and standing column well ground heat exchangers. Results show that the new formulations can reproduce the outlet fluid temperature of both experimental test cases with good accuracy ( MAE = 0.06 ∘ C and 0.26 ∘ C , respectively). At last, the high efficiency of the new frequency-domain expression is demonstrated, with the computing times (0.04 s and 0.01 s) being 100 and 8 times faster than the original formulation in both scenarios. [ABSTRACT FROM AUTHOR]

The electrification of process industries is one of the main challenges when building a low-carbon society since they consume huge amounts of fossil fuels, generating different emissions. Heat pumps are some of the key players in the industrial sector of the carbon-neutral market. This study proposes an approach to improve the economic feasibility of heat pumps within process plants. Initial energy targeting with grand composite curves was used and supplemented with the detailed design of an evaporator and a compressor for different condensation and evaporation pressures. The trade-off between the capital cost of the heat pump and the electricity cost was investigated, and optimal configurations were selected. This case study investigates the gas fractioning unit of a polymer plant, where three heat pumps are integrated into distillation columns. The results demonstrate that the heat recovery is 174 MW and requires an additional 37.9 MW of electricity to reduce the hot utility by 212 MW. The selection of the evaporation and condensation pressures of heat pumps allows 21.5 M EUR/y to be saved for 7 years of plant operation. The emission-saving potential is estimated at 1.89 ktCO2/y. [ABSTRACT FROM AUTHOR]

Ground source heat pump systems are one of the renewable energy heat utilization technologies that can reduce the energy for HVAC and hot water supplies and consequently mitigate the progression of global warming. On the other hand, the development of ground heat exchangers that can be installed in small buildings with low installation costs is an important challenge for increasing the installation number of ground source heat pump systems in Japan. This study proposes H-shaped PC pile ground heat exchangers to reduce installation costs. The installation test and installation cost estimation of H-shaped PC pile ground heat exchangers showed that installation costs could be reduced to less than half compared to the conventional borehole double U-tube ground heat exchanger. The coefficient of heat extraction/injection of H-shaped PC pile ground heat exchangers was evaluated as 2.2–2.4 W/(m K) from the results of actual measurements during the heating and cooling operation of the GSHP system, and this was slightly high compared to the borehole single U-tube ground heat exchanger. In addition, the GSHP system with an 8 by 8 m long H-shaped PC pile ground heat exchanger could supply adequate heating output for the heating load of the residential house and operate with an SCOP of more than 3.0. Finally, the authors have confirmed that the GSHP system with H-shaped PC pile ground heat exchangers can reduce installation costs by 40% or more while maintaining the same running cost compared to conventional GSHP systems. [ABSTRACT FROM AUTHOR]

This study investigates the optimal refrigerant flow path for a fin-tube heat exchanger used in the indoor unit of a mini VRF heat pump. Optimal circuitry can significantly enhance the performance of fin-tube heat exchangers. Its performance according to various refrigerant circuitry is evaluated by the developed finite-element-calculation simulation model. The refrigerant circuitry was optimized by maximizing the heat transfer rate for given refrigerant and air conditions during cooling and heating seasons by adopting an optimization algorithm. A four-circuit circuitry has a higher capacity than the six-circuit circuitry and two-circuit circuitry because of the balancing effect of pressure drop and heat transfer. The best circuitry, which contains split/merge tubes, has a higher capacity and a significant pressure drop reduction compared to the two-circuit circuitry. It is found that compared to the reference circuitry, the best circuitry for the indoor unit of the heat pump has a 13 % increase in capacity. [ABSTRACT FROM AUTHOR]

Heat pumps are currently one of the most frequently applied heat sources in residential buildings. Ground source heat pumps are more reliable than air source heat pumps in terms of energy efficiency, especially in colder climates. However, they are more expensive and involve increased material inputs; therefore, multi-criteria analyses taking into account environmental and economic aspects seem necessary for the green design of these systems. The aim of this work was to analyze the environmental and economic impacts of the ground source heat pump providing heating for a family house located in eastern Poland, cooperating with three types of ground heat exchangers (each in two sizing options): helix, vertical and horizontal. The multi-criteria analysis was based on the life cycle assessment methodology using IMPACT 2002+ and life cycle costs methods. The lowest environmental impact was reported for the variants with vertical ground heat exchangers, mainly due to their high efficiency in the operation stage. On the other hand, the lowest economic impact was observed for the horizontal heat exchangers, which are not demanding in terms of material and construction costs. Final recommendations based on multi-criteria analysis propose the vertical probes as a sustainable solution, with a weighted sum indicator in the range 0.085–0.297 on 0–1 scale. [ABSTRACT FROM AUTHOR]

The performance of high temperature heat pumps (HTHPs) is highly dependent on the efficiency of its main components, which need to be optimally matched especially in closed cycles. The design process is therefore a challenging task as many disciplines and varying modeling depths need to be considered. Consequently, this is usually a sequential procedure beginning with cycle definition and raising the fidelity for component design. Fundamental design decisions are made based on assumptions for component performance. Mistakes in the phase of cycle definition are hard to reverse in later design stages. Therefore, this work introduces holistic approaches to the multidisciplinary design of closed Brayton cycles. Aerodynamic compressor design with two-dimensional throughflow analysis and geometry-based heat exchanger sizing are simultaneously optimized with thermodynamic cycle parameters. The presented methodologies make use of highly sophisticated design tools drawing on many years of experience in gas turbine design. The results demonstrate that holistic heat pump optimization can be successfully performed with reasonable computational effort. The advantages compared to conventional sequential design are elaborated. A comparison of two optimization concepts indicates that splitting up the design vectors of cycle and components shows the tendency to improve robustness. Finally, the tradeoff between system compactness and performance is demonstrated with a multi-objective optimization study. [ABSTRACT FROM AUTHOR]

Heat pumps can be switched between cooling and heating mode, requiring accurate charge modeling capabilities to enable the design of heat exchangers for near optimum efficiency in both operating modes. The charge modeling tools also require high-fidelity experimental validation data to tune their predictions. However, little experimental charge validation data is available in the open literature. This study addresses this need by providing complete, high-fidelity, experimental charge data of Round-Tube-Plate-Fin Heat Exchangers (RTPF) with ±2.2% of relative charge-measurement uncertainty and 0.8% of charge-measurement repeatability. In addition to R410A, charge data on two low-Global Warming Potential (GWP) refrigerants, R1234yf and R468C, is additionally collected. Furthermore, an accurate data-driven charge model is developed, tuned by the high-fidelity experimental charge data, with 12.3%, 12.8%, and 12.9% of the Mean Absolute Percentage Error (MAPE) based on the Taitel–Barnea, the Zivi, and the Baroczy void-fraction model, respectively. This experimentally validated charge model can contribute to enabling effective designs of heat pumps with high-accuracy charge predictions. [Display omitted] • High-fidelity experimental charge validation data with ±2.2% uncertainty. • Low-GWP refrigerants, R468C and R1234yf, as well as the baseline R410A. • The accuracies of popular void-fraction correlations are experimentally evaluated. • Tuning methods for a charge model are presented. • The model predicts the refrigerant charge in a heat exchanger with a MAPE of 12.3%. [ABSTRACT FROM AUTHOR]

• Experimental investigation of a natural refrigerant blend in a household heat pump dryer. • Successful drop-in with minor adjustments to the system. • Increased drying performance that result is a shorter drying time. Due to their high global warming potential (GWP), fluorinated refrigerants are being replaced in many heat pump and refrigeration systems. Especially in small systems such as heat pump tumble dryers (HPTD), the replacement of the globally used working fluid in this application, R134a, appears to be manageable. One established alternative is the use of hydrocarbon refrigerants. Within this research project, new zeotropic refrigerant blends of hydrocarbons are theoretically evaluated as retrofit substitutes for R134a in heat pump tumble dryers. The aim is to use the temperature glide inherent to zeotropic mixtures during phase change to increase the heat transfer efficiency and thus, the COP of the system. A mixture of R290 (propane) and RE170 (dimethyl ether) was selected and experimentally investigated in a commercially available HPTD. To assess the new mixture, parameters relevant to the cycle such as pressure, temperature, compressor power, and the dryer moisture extraction rate are compared to those values achieved using the refrigerant R134a. Retaining the heat exchanger and compressor from the R134a system, the system charge with the new mixture was 40 % lower, while the thermal capacity was equal to or higher than that of the R134a system. The increased temperature level supplied by the mixture reduced the drying time and the energy consumption of the HPTD. The investigation showed that the heat exchanger design needed to be adapted to the temperature glide properties of the mixture in order to realize meaningful heat transfer efficiency gains. [ABSTRACT FROM AUTHOR]

This investigation delves into the enhancement of heat exchange efficiency in heat exchange stations employing large temperature differential absorption (LTDA) heat pumps, a challenge often attributed to suboptimal operational adjustments. The focus is placed on LTDA heat pump systems within these stations, where operational adjustments are meticulously modified. The criterion for evaluation, energy efficiency, is rigorously applied throughout. A comprehensive approach combining experimental research with data simulation has been adopted, leading to the establishment of a mathematical model for the unit. Utilizing Matlab software, the simulation of adjustment methods for both the primary and secondary sides of the system is conducted in a phased manner, aiming to identify the most favorable operating conditions across various adjustment methods. Findings from this study reveal that the activation of lithium bromide absorption heating units for volume adjustment on the system's secondary side markedly underperforms in terms of heat exchange efficiency when compared to both mass adjustment and massvolume adjustment strategies. Crucially, it is identified that superior operating conditions under varying adjustment methods are achieved when the primary side supply water temperature is maintained at 110℃, coupled with a 20% ratio of temperature-driven heat exchanger flow to the actual flow on the secondary side, culminating in a peak heat exchange efficiency of 2.18. These results guide LTDA heat pump operational strategies in heat exchange stations, stressing strategic adjustments for better energy efficiency. [ABSTRACT FROM AUTHOR]

Spacecraft commonly dissipate heat into space through radiation. In the current development of spacecraft radiators, two major challenges are encountered: effective dissipation of heat in high-temperature environments and the heat waste by the thermal control system. Thermoacoustic heat pumps have emerged as a promising solution, capable of increasing the dissipating temperature of the radiators and reusing the waste heat. This paper presents a novel work-recovery thermoacoustic heat pump (WRTAHP) that incorporates a displacer, which serves the function of phase shifter and acoustic power recovery. One-dimensional numerical simulations are conducted to investigate the influence of the regenerator, thermal buffer tube, heat exchangers, and displacer on the system performance. The results reveal that WRTAHP can raise the temperature of waste heat sources from 50 °C up to 120 °C and obtain 511 W heating capacity with an overall relative Carnot efficiency of 56.4%. Furthermore, with the utilization of the heat pump, the surface area of the radiator is reduced to 60% of its original size. This work demonstrates the potential of WRTAHP for space applications. [ABSTRACT FROM AUTHOR]

Formation of frost on outdoor evaporators poses a significant challenge for air source heat pumps operating in cold climates. It is widely recognized that uneven air-flow across an evaporator can have a negative impact on both the evaporator's performance and the overall efficiency of the heat pump. This study investigates the influence of non-uniform air-flow distribution on a V-shaped outdoor evaporator as a component of an air-source transcritical CO 2 heat pump when subjected to frosting conditions. To this end, we developed and validated against independent experiments a numerical frost-formation model, and used it to study a multi-circuit evaporator of interest under different ambient conditions. It is shown that the uneven air-flow distribution results in varying frost formation patterns across different circuits of the heat exchanger, including differences in the amount of frost accumulated and its distribution among the individual tubes; the circuit with the largest frost weight accumulates 18% more frost compared to the one with the smallest in one hour under the sever frosting condition. Non-uniform frost formation also leads to air-flow distribution changing over time, and the rate at which this change occurs depends on the ambient conditions. For the presently investigated case, frost formation suppresses the non-uniformity of air-flow distribution. Moreover, evaporators with non-uniform and ideal uniform air-flows are compared and it is revealed that the difference in their capacities is more noticeable at the beginning of the frosting period. • Effect of non-uniform airflow on frosting behavior of a V-shape evaporator studied. • Different amounts of frost among circuits due to non-uniform airflow quantified. • Effect of ambient humidity on frost non-uniformity investigated. • Response of air-flow to frost formation over time investigated. • Drop in the evaporator capacity compared to the case of an ideal uniform airflow. [ABSTRACT FROM AUTHOR]

The use of capillary heat exchangers with a large area means the lowest heat carrier temperature – typically less than 30 °C for heating. This determines the very efficient use of the installed heat pump due to an increase in the coefficient of performance (COP) with a decrease in the provided water temperature. The aim of the study was to find out whether renewable energy sources and radiant capillary heat exchangers increase energy efficiency. In order to achieve the maximum energy efficiency during the renovation of the existing apartment, a combination of two green approaches was used. One of them is the replacement of the existing high-temperature radiator heating system with radiant capillary mats. The same system is also used for cooling, which was not possible with the existing system. The necessary energy is provided from renewable aerothermal energy by installing a heat pump together with PV panels to ensure electricity consumption. The measurements were made in the apartment to determine the thermal transmission properties of all boundary structures and an air exchange rate using long-term monitoring. Experimental data were used to create the heat balance, to estimate the heating and cooling powers, as well as the seasonal energy needs. The amount of capillary heat exchangers and the size of the heat pump were chosen accordingly. The very first energy consumption data allow concluding that the planned improvement of the energy efficiency has been successfully achieved by using technology combination described without improvement of the thermal properties. [ABSTRACT FROM AUTHOR]

A number of parameters and characteristics of geological formations have a major influence on the long-term performance of ground heat exchangers. Some of these parameters can be measured, others in the laboratory and their evolution over time can be modelled using dedicated software. One of the commonly used software is EED (Earth Energy Designer) which can model, based on characteristics measured in the field and/or laboratory, the evolution over time of the temperature taken from geological formations, the evolution of loads, cooling, heating versus load introduced/extracted from geological formations over certain periods of time. [ABSTRACT FROM AUTHOR]

Geothermal energy is a kind of green and renewable energy. Conventionally, ground source heat pumps can be used to harvest geothermal energy from the subsurface. To reduce the initial investment, a good solution is to use tunnel linings as heat exchangers to extract/dump heat. This special infrastructure is called an energy tunnel. In addition to the thermal performance, the impact of pipe network configuration on thermal efficiency is still challenging in the design of energy tunnels. To solve this problem, this study makes the first attempt to carry out research on the optimization of pipe circuits in energy tunnels by a series of numerical analyses. A fully coupled thermo-hydraulic 3D finite element model is established to investigate the response of tunnel-soil interaction under cyclical thermal loading (initial soil temperature varies from 8 ℃ to 18 ℃), as well as the thermal transient interactions among air, absorber pipe, tunnel linings and ground, to quantify the amount of useful heat that can be extracted from the tunnel and the ground. On the other hand, the influence of 3 various heat-carrying pipes layout is also investigated. It is found that higher heat transfer efficiency can be obtained when the entrance and exit of pipelines are located below the tunnel in the study. The spatial location of pipelines will also affect the exchanged heat output. [ABSTRACT FROM AUTHOR]

This article deals with improving waste heat transformation in heat-using thermotransformers. Based on the directives of the European Commission on refrigeration equipment requirements, the possibility of using carbon dioxide (R744) in heat-using thermotransformers was evaluated. The possibility of the effective use of heat-using thermotransformers operating within the Chistyakov–Plotnikov cycle in the heat pump mode was assessed. As a result, a comparative analysis was performed with existing modern plants for combined cycles with an expander, for the expansion of CO2 in saturated steam, a suction gas heat exchanger (SGHE), and a compressor–expander unit. The design schemes with a throttling device and an SGHE were selected for a comparative analysis. As a result, calculation models for evaluating the operating parameters for the initial and proposed design schemes were developed. These models allow for evaluating thermodynamic and mode parameters for heat-reducing thermotransformers. They also allow for ensuring energy efficiency indicators and conversion factors for each cycle. Overall, the dependencies for the cycle conversion ratio for the pressure increase stage in the compressor were obtained for various under-recovery rates. Moreover, the cycle conversion ratios for the proposed design schemes were obtained depending on the discharge pressure of the first compressor. The proposed design schemes allow for increasing the energy efficiency of heat-using thermotransformers by an average of 23%, depending on the suction pressure in the compressor. [ABSTRACT FROM AUTHOR]

• Pure, binary, and ternary refrigerants of 14 refrigerants are analyzed. • Different refrigeration systems are considered. • Pareto fronts of the COP and volumetric heating capacity are obtained. • Binary refrigerants have similar advantages to ternary refrigerants. Mixed refrigerants are widely used in heat pumps; thus, it is necessary to analyze the performance advantages of pure, binary and ternary refrigerants. In this paper, 14 kinds of pure refrigerants were selected, and 24,024 kinds of pure, binary and ternary refrigerants were obtained and analyzed. The refrigerant performance in terms of the COP and volumetric heating capacity were compared in normal, vapor injection with internal heat exchanger and with flash tank systems. In this paper, 40 °C was used as the temperature lift, and four cases with heating production temperatures of 70, 80, 90 and 100°C were analyzed. The Pareto fronts for the different refrigerant types and compositions were obtained by using exhaustive method. The COP and volumetric heating capacity exhibited contradictory trends in all cases. The results showed that mixed refrigerants had significant advantages over pure refrigerants in achieving the Pareto fronts. However, in all cases, when the COP was higher than 5, the binary refrigerants had similar advantages to ternary refrigerants; thus, ternary refrigerants were not necessary. When the COP was lower than 5, it was difficult to further increase the volumetric heating capacity by sacrificing the COP. [Display omitted] [ABSTRACT FROM AUTHOR]

The average difference between hot and cold heat carrier temperatures, the amount of transferred heat, and the hydraulic resistance for a patented plate heat exchanger having plates with drop-shaped relief and for a heat exchanger having typical corrugated plates were calculated using a computational hydrodynamic module built into the software for 3‑D modeling. It was found that less energy is consumed in the patented heat exchanger for pumping heat carriers with the same amount of transferred heat. [ABSTRACT FROM AUTHOR]