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• The paper confirms the suitability of the design of the ITER Cryo-distribution (CD)components. • The paper suggests the use of the liquid helium baths present in the ITER CD system as one of the heat load mitigation schemes to the ITER cryoplant. • The paper suggests the minimum opening percentage of the liquid helium baths to minimize the helium inventory in the ITER CD system. • The paper presents the dynamics of the heat load, mass flow, and pressure on the ITER cryoplant interface with the ITER CD system. The ITER cryogenic system consists of the Liquid Helium (LHe) plant, the Cryo-Distribution (CD) system, and the cryo-lines. The Auxiliary Cold Boxes (ACBs) dedicated to cooling the superconducting (SC) magnet system and the Cryoplant Termination Cold Box (CTCB) of the ITER CD system are in the factory acceptance phase. The internal components of ACBs, e.g. , cryogenic valves, a cold compressor (CCp), heat exchangers, and a cold circulator (CCr), have been sized and assembled, ensuring their functionality. The interdependency of the functional parameters of one component over the others needs to be assessed, as their integrated performance under the dynamic heat load deposition from the SC magnets may impact the overall operation of the ITER cryogenic system. The ACBs are equipped with two helium baths having ∼ 1200 kg of He inventory and situated inside the Tokamak building. These baths act as a thermal buffer for the LHe plant, situated in the cryoplant building, allowing it to operate at a quasi-steady state despite heat load variation from the applications. Such a large helium inventory can challenge the secondary confinement system of ITER due to helium ingress accidental events and thus needs to be optimized. The integrated system-level simulation is therefore necessary for the safe and reliable operation of the cryogenic system under such demanding requirements. The present study summarizes the results obtained for ACBs dedicated to the magnet system, including CTCB for the enhanced ITER operation modes, and confirms the integrated performance of the system. The results show that the LHe baths inside the ACBs can be used as a thermal buffer with the proposed limit of initial filling and by keeping a constant opening of the respective J-T valves upstream of the LHe baths. The study outcome and the proposed recommendations would be beneficial to mitigate the pulsed heat load to the LHe plant while minimizing the helium inventory. [ABSTRACT FROM AUTHOR]

In this study, the year-round thermal performance of a qanat source heat pump in supplying the required cooling and heating loads of a case study building is investigated. Using TRNSYS software, dynamic simulation of the proposed system is performed in three climate zones including Hot/Dry, Cold/Dry, and Hot/Humid. The heat pump and helical coil heat exchanger inside the qanat water are mathematically modeled in MATLAB, and then, coupled to TRNSYS model to evaluate the system transient performance. It is found that the free energy ratio of the qanat source heat pump Hot/Dry climate zone is on average 21.6% higher than compared to that of the air source heat pump. In cold months, by increasing the temperature of the inlet fluid to the helical coil heat exchanger inside the qanat, the system coefficient of performance increases 15%. The increase of the energy efficiency ratio of the system in the warm months is 7.7%. It is also found the highest coefficient of performance and the lower energy efficiency ratio of the system is obtained in the Hot/Humid climate zone in comparison with the other zones; so that, the energy efficiency ratio of the system in the Cold/Dry and Hot/Dry zones is 48% and 58% higher than that in the Hot/Humid zone, respectively. The annual FER of 63.4%, 63.1%, 56.8%, and 53.3% are obtained in Hot/Dry (Kerman), Cold/Dry (Mashhad), Hot/Dry (Tehran), and Hot/Humid (Bandar Abbas), respectively. These findings suggest that the building energy consumption significantly reduces using the QSHP in all climatic conditions. [ABSTRACT FROM AUTHOR]

Closed-loop processes are widely used in the chemical industry, for example in separation processes to recycle waste streams. However, the recycled streams represent a source of instability, especially when the overall system suffers a (desirable or undesirable) change in the operating conditions. In this case, the time required to reach a steady state is significantly longer, because of oscillations encountered in the leaving stream characteristics. The dimensions of such oscillations can reach high and even hazardous values, even if the new steady state is reached in a safe operating condition. This is why the knowledge of the dynamic closed-loop process behavior is essential to prevent hazardous situations. In this work, a general rate-based model of a closed-loop chemical absorption process is presented and the results of dynamic simulations are compared with published experimental data on absorption of carbon dioxide with aqueous monoethanolamine solution. The periphery is considered using dynamic models of the liquid distributors, the liquid holdup in the bottom of the columns as well as of the relevant heat exchangers and pipelines. Based on the simulations, the influence of different closed-loop process elements on the dynamic behavior of the overall configuration can be evaluated, enabling a cause-effect analysis of hazardous situations. [ABSTRACT FROM AUTHOR]

Using fins on the inner and outer surfaces of pipes is one method to improve the heat transfer rate of ground heat exchangers (GHEs), thereby reducing the borehole depth and construction and operation costs. Results of 3D numerical studies of simple and finned U-tubes with outer and inner fins are evaluated for GHEs under similar physical conditions. Dynamic and static simulations show the effects of longitudinal fins on the thermal performance of borehole heat exchangers (BHEs) and heat transfer rate between circulating fluid and soil around pipes, while the dynamic tests include short timescale and frequency response tests. The results indicate that the maximum fluid temperature change is about 2.9% in the external finned pipe and 11.3% in the internal finned pipe compared to the finless pipe. The effects of the inlet velocity on temperature profiles, the patterns of the velocity and temperature contours due to the borehole curvature and the response times of the systems under various frequencies are also investigated in detail. [ABSTRACT FROM AUTHOR]

Shell & Tube heat exchanger is the most often used equipment for heat transfer between fluids in chemical plants, refineries, power generation stations and many other industries. The fluid cooled and the fluid heated are often operated at very different pressures: in this case design standards require an analysis to verify the maximum pressure surge that could be generated by an accidental fluid leak from the high-pressure side of the heat-exchanger into the other. The analysis of such accident is very complex due to a number of interacting phenomena such as vapor-liquid equilibrium, large enthalpy effects, large changes of fluid density and the formation two-phases (vapor and liquid) fluid flows. With reference to a real project case, this article presents the simulation of the pressure increase due to the full-bore rupture of a tube. This evaluation is required to assess if a rupture disk must be installed on the shell side to protect both the equipment and the operating personnel. The analysis is performed using a state-of-the-art dynamic simulation tool. [ABSTRACT FROM AUTHOR]

The temperature control loop of the actuating air following the heat exchanger is considered. The control loop consists of a heat exchanger, adjustable air intake, circulation fan, temperature sensor, and temperature controller. A dynamic model of the control loop that takes into account the automatic control system is created. Transient processes that arise in the control loop as a consequence of variations of the altitude of the aircraft are considered. Results of the variation in the actuating air temperature at a temperature control point are obtained. Partial optimization of the coefficients of the controller is performed. Optimal coefficients of the controller are selected. [ABSTRACT FROM AUTHOR]

In this study, a cryogenic turbo-based refrigerator, with high-speed foil gas bearing turboexpander and plate-fin heat exchanger, was presented. For the cooling process of a cryogenic refrigerator is long and complex, the efficient simulation of the dynamic performance is vital for its evaluation and operation. It is difficult to achieve this purpose. Because the cryogenic refrigerator will go through great temperature changes, resulting in dynamic performances of components going to complexity. In this article, the turboexpander was simulated using CFX, and the matching models with expansion works of consumption and utilization were unified and modified. With numerical calculation of heat exchanger, the dynamic simulation model of the refrigerator was improved via MATLAB code. The calculation method of the required input energy of the refrigerator in cooling processes was proposed based on the simulation and integration. The energy efficiency and economy cost of the refrigerator were evaluated under different operation modes. The refrigerator with a motor was more stable than the one with a blower. The refrigerator was tested under different conditions, the results of which agreed well with simulation data. The simulation method is efficient to serve practical applications, improve energy efficiency and reduce costs. [ABSTRACT FROM AUTHOR]

Highlights • Double U-tube borehole heat exchangers are studied by 3D finite element simulations. • Simulation results are validated by comparing 3D and 2D borehole thermal resistance. • Equations to evaluate the mean fluid temperature of a double U-tube borehole are given. • Results hold for any borehole length, shank spacing, conductivity and working condition. • Results improve thermal-response-tests evaluation and borehole-fields hourly simulation. Abstract The design of ground-coupled heat pump systems requires the knowledge of the mean temperature T fm of the working fluid in borehole heat exchangers. This quantity is usually approximated by the arithmetic mean of inlet and outlet temperature. The approximation yields an overestimation of the thermal resistance of the heat exchanger in thermal response tests, as well as errors in the estimation of the outlet fluid temperature in the dynamic simulation of ground-coupled heat pumps. Recently (Applied Energy 206, 2017, 1406–1415), Zanchini and Jahanbin determined, by finite element simulations, correlations that allow an immediate evaluation of T fm in any working condition, with reference to double U-tube boreholes with length 100 m and shank spacing 85 mm. In this paper, the analysis presented there is extended to double U-tube boreholes with any length, between 50 and 200 m, and any shank spacing, between 65 and 105 mm. The results hold for every thermal conductivity of the sealing grout between 0.9 and 1.6 W/(m K), every volume flow rate between 12 and 24 L per minute, every diameter of the BHE and every working condition (heating, cooling, thermal response test), both in quasi-stationary and in transient regime. [ABSTRACT FROM AUTHOR]

A novel method combined signal flow graph of a single heat exchanger with the transfer function of streams is developed for the dynamic behaviors of heat exchanger networks problems, which are determinate factors of the process control and operation optimization in the processing industries. The transfer functions between any two nodes of heat exchanger networks including the inlet and the outlet are obtained based on the signal flow graph of the networks by block-diagram reduction, Mason's rule and the seeking-up method. The developed method is solved by a numerical inverse Laplace transform and the analytical solution to the dynamic behavior of heat exchanger networks is presented in the time domain. The numerical results demonstrate that the presented method is more efficient and more accurate for the dynamic behaviors of heat exchanger networks problems. [ABSTRACT FROM AUTHOR]

In this article, the dynamic responses of heat exchanger networks to disturbance and setpoint change were studied. Various control strategies, including: proportional integral, model predictive control, passivity approach, and passivity-based model predictive control were used to monitor all outlet temperatures. The performance of controllers was analyzed through two procedures: 1) inducing a ±5% step disturbance in the supply temperature, or 2) tracking a ±5°C target temperature. The performance criteria used to evaluate these various control modes was settling time and percentage overshoot. According to the results, the passivity-based model predictive controllers produced the best performance to reject the disturbance and the model predictive control proved to be the best controller to track the setpoint. Whereas, the ensuing performance results of both the PI and passivity controllers were discovered to be only acceptable. [ABSTRACT FROM AUTHOR]

A physical model and dynamic simulation models of a solar phase-change heat storage heating system with a plate solar collector, phase-change material (PCM) storage tank, plate heat exchanger, and auxiliary heat sources were established. A control strategy and numerical models for each of seven different operation modes that cover the entire heating season of the system were developed for the first time. The seven proposed operation modes are Mode 1: free cooling; Mode 2: reservation of heat absorbed by the solar collector in the PCM storage tank when there is no heating demand; Mode 3: direct supply of the heating demand by the solar collector; Mode 4: use of the heat absorbed by the solar collector to meet the heating demands, with the excess heat stored in the PCM storage tank; Mode 5: use of heat stored in the PCM storage tank to meet the heating demands, Mode 6: combined use of heat stored in the PCM storage tank and the auxiliary heating sources to meet the heating demands; and Mode 7: exclusive use of the auxiliary heat sources in order to meet the heating demands. Mathematical models were established for each of the above seven operation modes, taking into consideration the effects of the outdoor meteorological parameters and terminal load on the heating system. The real-time parameters for the entire heating season of the system with respect to the different operation modes can be obtained by solving the simulation models, and used as reference for the optimal design and operation of the actual system. [ABSTRACT FROM AUTHOR]

Large-scale commercial buildings served by ground source heat pump (GSHP) systems generally require a large land area for ground heat exchanger (GHE) installation. However it is difficult to provide such large area around the buildings, especially in urban area. Additionally, a large-scale GHE may consume more energy consumption compared with a medium or small GHE system because of the significantly large transmission energy consumption in the closed GHE loop. This study takes a commercial building located in northern China as a case study and proposes three different design schemes: chillers plus municipal central heating system, a single GHSP system and a hybrid GSHP system with chiller and municipal central heating as supplemental heat source and sink. The simulation models of the three systems have been established in the platform of TRNSYS. An optimal control strategy has been found with the aim of lowest annual operating cost. The results show that the municipal heating system can be put in operation when the outlet water temperature from GHE is less than 4℃ in winter; the cooling tower would be open to assist heat dissipation when the outlet water temperature from GHE is above 33℃ in summer. In this case the GSHP can provide 42% of the cooling and 83.5% of the heating loads, respectively. [ABSTRACT FROM AUTHOR]

Despite many studies that were found in the literature regarding the modelling of the short-time-step (STS) behaviour of the borehole ground heat exchangers, reported investigations of its effect on the long-term dynamic simulation of a ground-source heat pump (GSHP) system were sparse. Hence, in this study, the dynamic performances of a GSHP system applied to an office zone in Hong Kong over a period of 10 years were compared with both the long-time-step (LTS) and STS approaches for the boreholes. It was found that with the adoption of the more appropriate STS approach, the simulated fluid temperature leaving the ground heat exchanger borefield was lower by at most 1.62 °C over a range of ground and grout thermal conductivities investigated. This also allowed the design borehole length to be reduced by at most 14.4% while the resulting energy consumption was still better than those based on the LTS approach. In this regard, the STS approach should be employed in the long-term dynamic simulation of GSHP systems. [ABSTRACT FROM AUTHOR]

• Finnish building energy system with deep coaxial boreholes studied. • Four-step modelling approach combining simulation and hourly optimization applied. • Improved economic feasibility compared to reference district heating configuration. • Economic benefits from increasing the borehole depth decreased nonlinearly. • Deeper boreholes enable increased operating flexibility. Deep coaxial borehole heat exchangers (CBHEs) have been considered to enable cost and energy savings in building energy systems. However, achieving improved performance requires optimal design and operation of the CBHE. This work presents a case study for a building energy system in Finland, for which a hydraulic diagram was developed to incorporate a number of deep CBHEs (800 m to 2400 m) with multiple operating modes. To evaluate the techno-economic feasibility with optimized operating strategies, a four-step methodology is introduced, combining steady-state modelling, dynamic simulation and system optimization. The systems with a CBHE were found economically feasible compared to a district heating connection, enabling lower annualized total system cost (18.3–26.3%) and operating costs (49.1–53.5%). With deeper CBHEs, the main cost reductions originated from improved heat pump performance, increased operating flexibility and decreased capacity requirements of process components. However, the benefits partly decreased non-linearly with increased CBHE depth. Economic feasibility displayed the highest sensitivity to the price of electricity, with a relatively smaller impact for deeper CBHEs. Furthermore, maximizing the heat pump performance was found economically more significant than achieving a high borehole heat extraction rate. [ABSTRACT FROM AUTHOR]

Modelling and simulation is presented for a finned cross-flow heat exchanger with the aim to heat cold air to be fed to air conditioning batteries for marine purposes. The model employed in this paper is finalized to simulate the dynamic behavior of air and water temperatures fed to the air conditioning batteries operating in cold environments, in order to predict possible troubles owing to the change in input parameters, such as unwanted flow rate variations due to system malfunctions. In the investigated model, heat balance equations are presented and discretized by Laplace transform, which has the advantage to easily account for the different structures of heaters used for the purpose of validation. The model was implemented in the Matlab-Simulink environment for its high capacity of dealing with dynamic systems. The results of the model are satisfactory, as the dynamic behavior of the air stream temperature is correctly reproduced, as compared to experimental data, providing a suitable parameter for malfunctions prediction. [ABSTRACT FROM AUTHOR]

This study evaluates low-temperature district heating (LTDH) networks with different geothermal heat sources under thermo-economic criteria. In particular, the heat and cold supply of modern neighbourhoods are taken into account in a dynamic simulation model built on the modelling language Modelica. Both horizontal and vertical ground heat exchangers (GHE) were investigated in respect to the load profiles of the consumers, depending on dimension as well as location. The selected base case represents a LTDH network near Stuttgart (Germany). The corresponding results of an annual simulation show that a horizontal GHE is suitable for pure heat supply and can reduce costs by up to 12% compared to a vertical system. This economic advantage remains when the cooling demand is considered. Subsequently, a variation of the system location was carried out. It is shown that horizontal GHEs operate more economically in northern regions, whereas vertical ones are more advantageous in regions with increased cooling demand. For both cases, possible savings of between 3.0% and 4.2% resulted from the simulations. The heating-to-cooling demand ratio was used as a first decision criteria to weigh-up between the two systems. Vertical GHEs were more economical than horizontal systems as soon as the ratio dropped below 1.5. [ABSTRACT FROM AUTHOR]

Abstract: Waste heat recovery by means of a Rankine Cycle is a promising approach for achieving significant reductions in fuel consumption and, as a result, exhaust emissions of passenger car engines. This approach is already well established in industrial applications such as gas and steam power plants or ship propulsion systems. While these systems are mainly designed for stationary operation, the behaviour in highly dynamic operating conditions becomes more important when the principle is transferred to a passenger car engine. Knowledge of the dynamic response of the employed heat exchangers plays an important role in performance prediction and control system design of the steam cycle. Hence, a dynamic model of the exhaust gas heat exchanger employing the moving-boundary principle was developed and is presented in this paper. The model describes both design operation and the heat-up procedure of the component. For achieving high model accuracy in the resulting broad range of operating conditions, new approaches for modelling wall temperature distribution and zone switching were developed. Simulations of stationary operating points as well as the response to typical disturbances of the system’s input variables are in good agreement with test bench measurements. The model is used to develop a control system for dynamic operation on the test bench. Further studies of the operating characteristics reveal varying dynamic behaviour depending on the heat flow rate from exhaust gas to working fluid as well as coupling of evaporation pressure and outlet steam temperature. [Copyright &y& Elsevier]

Abstract: A 1 kW solid oxide fuel cell (SOFC) balance of power (BOP) system is analyzed using experiments and simulations to optimize the design and operating conditions. The system consists of an autothermal reformer, combined heat exchanger and afterburner, and dummy stack. Thermolib program is used for the simulations. The system exhibits stable operation during a two cycle on/off experiment. The simulated results obtained by zero-dimensional modeling are similar to the experimental results although a discrepancy appears early in operation owing to the simplified modeling. The system''s characteristics are also investigated in terms of the fuel utilization, presence or absence of internal reforming and external heat transfer coefficient. [Copyright &y& Elsevier]

The dynamic simulation of a sub-scale ITER Central Solenoid (CS)/STRucture (STR) cooling loop has been performed to investigate the cryogenic control strategies against pulsating heat loads. HELIOS facility has been modified for this particular study, which consists of a Liquid Helium (LHe) reservoir with two immersed heat exchangers, a circulation pump and an approximately 130 m long piping with three evenly distributed heated sections. The setup provides the equivalent thermo-hydraulic configuration of the ITER CS/STR, cooled by the forced-flow Supercritical Helium (SHe). The dynamic simulator, C-PREST, has been utilized to model the HELIOS test loop and to compare the results with the experimental data sets. This paper presents the dynamic simulation results and discusses the control strategy to minimize the cooling power requirements, to have high reliability. [ABSTRACT FROM PUBLISHER]

Abstract: In this paper, the regulation problem of convection governed dynamical processes described by linear distributed parameter models with position-independent inputs is addressed by combining the method of characteristics (MC) and the Malek-Zavarei and Jamshidi theorem. In this approach, the MC is used to transform the first order partial differential equations model of such processes into a set of time-delayed ordinary differential equations whose elements are used to generate certain matrices that satisfy linear matrix inequalities that render the proportional integral (PI) control parameters that guarantee the process stability. The performance of the proposed PI controller is tested via numerical simulations in the temperature regulation of a linear heat exchanger and compared to a tightly tuned classical PI controller. The application of the proposed controller is extended to regulate the outlet concentration in a nonlinear non-isothermal plug flow reactor. It is shown that the proposed controller is able to handle the infinite dimensional nature of the process model yielding smooth and unsaturated responses around the predetermined set-point trajectory in the face of load changes, time varying boundary conditions and set-point changes. [Copyright &y& Elsevier]

Abstract: Tokamaks and Stellarators generate heat loads that are pulsating in nature. The helium refrigerators employed for cooling these fusion devices are, however, designed for a steady heat load. Unless they are appropriately adapted and controlled, process parameters under pulsed load may vary to such an extent which may lead of plant instability. In this paper, performance of a J–T stage as a part of modified Claude cycle based helium refrigerator has been analyzed subjecting it to a pulsed heat load for understanding of the behavior of the components. Pulsed heat load results in the fluctuation of mass flow rate in the return stream that needs to be mitigated. The analyses focus both on the equipment and their interactions in the cycle and a concept of parallel heat exchangers has been applied. There is a steady decrease in liquid level in Dewar when the plant is designed with a capacity equal to the time-averaged heat load. Introduction of parallel heat exchanger mitigates mass flow rate fluctuation by 15% with only one additional heat exchanger at the last stage. There is promise for a higher mitigation effect when more heat exchangers are used in parallel in more number of stages. The study may be extended to entire helium plant used in fusion devices. [Copyright &y& Elsevier]

Abstract: Ground coupled heat pump systems can offer high energy efficiency for heating and cooling of buildings. The coupling of the ground loop with system and building represents a complex system and system performances can vary over long periods, in the range of 10–15 years due to the charge or discharge of the ground loop. In order to correctly concept, size and optimise these systems, numerical simulation is a perfect tool. The assessment of the global performance of such systems through simulation relies on several parameters, from the physical model validity to the operating conditions and control of the system. Typically, a GCHP system is simulated with a 1-h step. Transient phenomena inside the borehole are often neglected since ground models are mainly developed to characterise long term phenomena. However, detailed system simulations considering a realistic control of the system require much smaller time steps. In these cases, the validity of simulation models has to be verified. This paper proposes a hybrid approach combining experiments and simulation to highlight and quantify the impact of borehole short-time response on the system efficiency and system operation. First, a comparison between steady state and transient models as well as measurement is carried out. It reveals significant influence of dynamic effects inside the borehole. The comparison is then extended a parametric study with annual simulations for different European climates. [Copyright &y& Elsevier]

• A microchannel heat exchanger made by the fluidic oscillators array was designed. • The oscillation modes of two parallel fluidic oscillators were studied. • The time-resolved pressure field and velocity field were analyzed. • The heat transfer performance of the fluidic oscillators array was evaluated. Impinging jet played an important role in cooling technology. The steady-state jet could be transformed into an oscillatory one based on the intrinsic flow instability mechanisms by using self-oscillating fluidic oscillators. In this paper, a high-performance microchannel heat exchanger based on a fluidic oscillator array was presented. The fluidic oscillators were tilted at an angle of 30° above the impinging surface to extend the influence area of the jets. The unsteady RANS turbulence models were adopted to study the fluid dynamic and heat transfer performance of the jet array. The time-resolved pressure field and velocity field were calculated to show that the parallel oscillators would produce three modes, including co-directional oscillation, reverse oscillation, and irregular oscillation, under synchronous and asynchronous output phases. The sweeping jets improved the heat removal performance by increasing the average Nusselt number and enlarging the influence range on the external flow field. The heat removal performance of the sweeping jets was almost equivalent under different oscillation modes. [ABSTRACT FROM AUTHOR]

In order to describe the dynamic behaviour of a fuel cell system its components are modelled by the help of 1D dynamic models which are implemented in Matlab Simulink. The fuel cell system consists of an autothermal gasoline reformer (ATR) which for the realisation of a high system efficiency is thermally coupled to the other system components (gas purification, heat exchangers). Dynamic simulations of load changes show that the dynamic behaviour of such a system is primarily dominated by the response times of the liquid water flowing through the heat exchangers, the volume of which should consequently be reduced to a minimum in order to achieve shorter response times. In contrast, the dynamic behaviour of the reactors is not critical. The composition of the product gas at the ATR-outlet is however influenced by the moisture content of the gas at the ATR inlet, which in turn is negatively influenced for a short transition period by the residence times of the water flowing through the heat exchangers during a load change.According to the results obtained, the system is able to adjust to load changes within 20 s for a load increase (10–90% of full load) and within 3 s for a load decrease (90–10% of full load). [Copyright &y& Elsevier]

Rotary heat exchangers have been widely used in paint shops, combustion power plants, and in heating, ventilation, and air conditioning systems in buildings. For these processes, many types of heat exchangers are available in the market: Tube-shell heat exchangers, plate heat exchangers, and rotary heat exchangers, among others. For the rotary heat exchangers, the problem is that there is no net present value method and lifecycle assessment method-based optimization found in the literature. In this work, we address this issue: An optimization is carried out with help of an empirically validated simulation model, a life-cycle assessment model, an economical assessment, and an optimization algorithm. The objective function of the optimization simultaneously considers economic and environmental aspects by using different CO2 pricing. Different CO2 pricing scenarios lead to different optimization results. The ambient air empty tube velocity v a ,   2.1 optimum was found at 1.2 m/s, which corresponds to a specific mass flow m s p of 5.4 kg/(m2·h). For the wave angle β , the optimum was found in the range between 58° and 60°. For the wave height h * the optimum values were found to be between 2.64 mm and 2.77 mm. Finally, for the rotary heat exchanger length l , the optimum was found to be between 220 mm and 236 mm. The optimization results show that there is still potential for technical improvements in the design and operation of rotary heat exchangers. In general terms, we recommend that the optimized rotary heat exchanger should cause less pressure drop while resulting in similar heat recovery efficiency. This is because the life cycle assessment shows that the use phase for rotary heat exchangers has the biggest impact on greenhouse gases, specifically by saving on Scope 2 emissions. [ABSTRACT FROM AUTHOR]

• Comparison of thermal performance between single and double U-tube BHEs was made. • Numerical model that governs unsteady heat transfer in and outside BHE was applied. • Dynamic simulation was made to examine the effect of parameters on BHE performance. • Double U-tube BHE has better performance and lower resistance than single U-tube. • CaCl 2 (25%) solution showed better thermal performance than other working fluids. In the ground coupled heat pump system that delivers space heating and cooling to the buildings, often questions are raised as to which borehole heat exchanger configuration (single or double U-tube) provides higher thermal performance. To answer this question, in this paper, detailed comparative transient heat transfer analysis between single and double U-tube borehole heat exchanger (BHE) with two independent circuits (that can operate with the same or different mass flowrate and inlet fluid temperature) is conducted. Validated numerical heat transfer model was applied to perform the dynamic simulation and analysis. The two borehole heat exchangers are compared from the perspectives of their thermal performance in the heating and cooling mode of operation. Detailed sensitivity analysis of the BHE has also been performed by investigating the impact of the important borehole parameters, thermal properties and working fluids on the thermal performance of the double U-tube BHE. The simulation result revealed that the heat injected and extracted by the double U-tube BHE at steady state is 21.8 (77%) and 10.2 W/m (71.8%) more than that of the single U-tube BHE respectively. The simulation results also indicate that the thermal effectiveness of the single and double U-tube BHE at steady state are 0.24 and 0.31 respectively. The single U-tube BHE showed higher borehole thermal resistance than that of the double U-tube BHE with values of 0.47 and 0.31 m.K/W, respectively. The results of the study also revealed that among the studied working fluids, CaCl 2 (25%) solution showed better thermal performance than other anti-freeze solutions with thermal effectiveness of 35.6%. The simulation result of this work is crucial as an input for the optimization studies made to obtain a single set of optimal borehole paramaters and thermal properties that results in the best performance of BHE coupled to ground source heat pump system designed to provide space heating and cooling of buildings. [ABSTRACT FROM AUTHOR]

The adoption of micro-scale renewable energy systems in the residential sector has started to be increasingly diffused in recent years. Among the possible systems, ground heat exchangers coupled with reversible heat pumps are an interesting solution for providing space heating and cooling to households. In this context, a possible hybridization of this technology with other renewable sources may lead to significant benefits in terms of energy performance and reduction of the dependency on conventional energy sources. However, the investigation of hybrid systems is not frequently addressed in the literature. The present paper presents a technical, energy, and economic analysis of a hybrid ground-solar-wind system, proving space heating/cooling, domestic hot water, and electrical energy for a household. The system includes vertical ground heat exchangers, a water–water reversible heat pump, photovoltaic/thermal collectors, and a wind turbine. The system with the building is modeled and dynamically simulated in the Transient System Simulation (TRNSYS) software. Daily dynamic operation of the system and the monthly and yearly results are analyzed. In addition, a parametric analysis is performed varying the solar field area and wind turbine power. The yearly results point out that the hybrid system, compared to a conventional system with natural gas boiler and electrical chiller, allows one to reduce the consumption of primary energy of 66.6%, and the production of electrical energy matches 68.6% of the user demand on a yearly basis. On the other hand, the economic results show that that system is not competitive with the conventional solution, because the simple pay back period is 21.6 years, due to the cost of the system components. [ABSTRACT FROM AUTHOR]