Low Coefficient Of Performance Research Articles

Efficient portable thermoelectric refrigerator developed with a temperature control system mode at best COP for different seasons and conditions of the year

ABSTRACT Global energy scarcity and pollution resulting from excessive energy consumption are among the most important causes of global warming, in addition to using Freon, which poses a danger to the environment. This led to searching for sustainable alternatives that use less energy to alleviate environmental difficulties and are eco-friendly. The portable thermoelectric refrigerator was developed to control the temperature required in different seasons of the year, for those who live in rural areas in Egypt (such as deserts). The main control unit has five modes (Economic, Minimum, Medium, Fast and Fast not Economic) based on the best coefficient of performance (COP) and minimum energy. The results showed the highest COP, for the economic mode with an 8°C difference in temperature, and the lowest COP with a 26.4°C difference in temperature for the fast not economic mode. On the other hand, the difference temperatures of 12.5°C,18.2°C and 23°C of the mode minimum, medium and, fast, respectively.

Performance research of a solution cross-type absorption-resorption heat transformer using NH3/H2O work fluid

Absorption-resorption heat transformer (ARHT) can realize the efficient utilization of low-grade heat under lower operating pressure than traditional absorption heat transformer (AHT), but the application is limited by the low coefficient of performance (COP). In this paper, an ammonia-water solution cross-type absorption-resorption heat transformer is proposed to improve the performance. The rectifier can be eliminated because the component can be balanced with the adjustment of solution's mass flow rate between the absorber and resorber. A thermodynamic model is established to investigate the influences of different parameters on the coefficient of performance. The results reveal that: When the high/low pressure pair is 1.5/0.48 MPa and the temperatures of generator, absorber, resorber and desorber are 105 °C, 80 °C, 80 °C and 4 °C, the COP of the proposed system can reach 0.4049, which is 19 % higher than traditional ARHT, resulting in a corresponding gross temperature lift (GTL) is 25 °C. Besides, the proposed system has wider working temperature ranges than the traditional system. The advantages of the proposed system also include the lower optimal low-pressure values. Therefore, the ammonia-water solution cross-type absorption-resorption heat transformer is appropriate for working in larger pressure differences and makes waste heat recovery more economical and efficient.

Performance boost of a commercial air-to-air plate heat recovery unit by mesh-net insert; thermal-frictional, economic, and effectiveness-NTU analysis

This research proposes, tests, and comprehensively investigates the application of mesh-net to increase the efficiency of any air-to-air plate heat exchanger (mainly as a building heat recovery unit). The idea is tested through a commercial heat-recovery unit and all parameters including Nusselt number, pressure drop, friction factor, thermal performance factor, effectiveness, number of thermal units, pumping power and economical profitability are comprehensively investigated and reported with and without mesh-net insert. In economic evaluation the price of electricity and type of building heating system (resistance heater, heat pump and so on) are considered. In the maximum air flow rates, the overall heat transfer coefficient is enhanced from 24 to 36 W/m2K. Nusselt number increases up to 75 % depending on air flow rate. The economic results were found very interesting, and even by paying further fan power due to the higher pressure drop, the economic profitability is positive when the building heating system is resistance heater or heat pump with lower coefficient of performance. The profitability of the mesh net insert is higher for the region with higher electricity price. This means the gained recovered heat overcomes the further energy required for pumping power. Nonetheless, final decision making from pure economic viewpoint depends on the desired supply air flow rate, type of heating system and local price of electricity.

An advanced exhausting airflow photovoltaic curtain wall system coupled with an air source heat pump for outdoor air treatment: Energy-saving performance assessment

Building integrated photovoltaic (BIPV) and air source heat pump (ASHP) technologies have emerged as promising solutions for building energy conservation. However, traditional solar buildings face limitations such as overheating, limited efficiency, and singular functionality; additionally, ASHPs suffer from a low coefficient of performance (COP) due to high condensing temperatures or low evaporating temperatures; the process of outdoor air handling proves energy-intensive. To address these challenges, this study proposes an innovative exhausting ventilation PV curtain wall system coupled with ASHP units (EVPV-HP) for outdoor air treatment. This system features a fine combination of PV cooling, supply air reheating, and heat recovery from both the PV facade and exhaust air. The mathematical model of the BIPV curtain wall, based on energy balance equations, is developed and solved using Matlab programming. This model is then combined with the ASHP system model established in TRNSYS to predict the year-round energy performance of the hybrid system. The findings demonstrate that the EVPV-HP system achieves seasonal energy efficiencies of 5.08 for cooling and 4.06 for heating operation modes. Compared to a conventional system, the EVPV-HP system enhances yearly energy efficiency by 17.05 % owing to increased PV production, reduced air-conditioning load, and improved COP. Furthermore, parametric analysis suggests that the system exhibits improved performance under higher solar irradiation and hotter weather conditions during summer. Conversely, in winter, the system performs better under lower ambient temperatures with incident radiation around 800 W/m2.

Waste heat upgrading with high-temperature heat pumps for assisting steam generation in ships: Performance, cost and emissions benefits

An alternative waste heat recovery technology is examined based on a high-temperature heat pump (HTHP) for heat upgrading in ships. This solution exploits the low-temperature heat of the cooling water of marine engines at 85 °C with two integration options, for either preheating the water before entering the auxiliary (steam) boiler or directly generating 6-bar steam for a vessel’s needs. An electric-driven heat pump cycle is used with an economizer for increasing the Coefficient of Performance (COP) and the heating capacity, while reducing the discharge temperature of the compressor. An ultra-low GWP refrigerant (R1233zd(E)) with a high enough critical temperature is considered. The sizing parameters of the HTHP are examined with the use of a validated numerical model attempting to find the best match between high performance and short discounted payback period (PBP). The latter is estimated with appropriate cost correlations that relate the component sizing with the equipment cost, in order to calculate the total capital cost. The operating costs on the other hand depend on the net fuel savings, i.e. fuel savings minus the fuel required to generate the electricity for the heat pump, the fixed operating cost such as for maintenance and service and the fuel price. The net emissions savings of the HTHP are also examined in a variety of ship types and sizes, based on their typical specific factors. The results show that the proposed solution leads to significant net fuel savings especially in oil tankers and cruise ships, reducing the boiler’s fuel consumption by up to 2.5%. But due to the low COP of the steam generation HTHP case of around 2, a very long PBP is achieved of over 20–30 years, whereas the preheat case always leads to a very short PBP of 2–6 years in all ship types, even though its capacity is low. Moreover, the net total emissions savings are significant especially for the preheat case, although additional fuel is consumed for producing electricity to drive the HTHP, while NOx and CO emissions are increased with the steam generation HTHP.

Thermal performance of three horizontal ground heat exchanger systems: comparison of linear-loop, spiral-coil and slinky-coil arrangements

Ground source heat pumps (GSHPs) are highly efficient for heating and cooling buildings. Among the different types of ground source heat pumps, horizontal ground heat exchangers (HGHEs) gaining popularity due to their cost-effectiveness, ease of installation and high regeneration capacity. However, studies on the interaction and influence of the local environment with the HGHE and the thermal performance influenced by the arrangement and performance of the HGHE are insufficient. This study uses a three-dimensional numerical model to simulate three types of HGHEs, including linear-loop, spiral-coil, and slinky-coil arrangements. Instead of just one unit, three units are connected in series or parallel. The model considers the energy balance and the heat transfer and exchange processes between the heat exchanger and the soil. Simulation of cooling and heating for 1 year revealed that the slinky-coil arrangement is the most affected by heat fluxes at the ground surface, because of its maximum length, which leads to its lowest coefficient of performance (COP) value. The thermal performance of linear-loop and spiral-coil arrangements is similar, but considering the material cost, the linear-coil arrangement has the lowest installation cost and operating cost for 30 years.

Numerical investigation on the thermal performance of energy tunnels under groundwater flow and tunnel airflow

The integration of underground tunnels with ground heat exchangers (GHEs), also known as energy tunnels, is a promising technology that has gained attention in energy geotechnics research. This study investigates the coupled effects of groundwater and tunnel-air flows on the energy tunnel system via 3D thermo-hydraulic numerical modelling. It is found that the combination of groundwater flow parallel to the tunnel and limited airflow velocity results in reduced operational efficiency of ground source heat pump (GSHP) due to the strong thermal interference along the tunnel. The study also highlights the importance of real-scale modelling to evaluate the thermal yield of long energy tunnels, particularly when dealing with parallel groundwater flow in geothermal tunnel design.
 The use of shallow geothermal energy is a renewable solution towards net-zero carbon emissions. In recent years, a variety of conventional geotechnical structures, such as piles, retaining walls and tunnels, have been transformed into energy geostructures to also serve as GHEs to harness renewable energy for space heating and cooling purposes [7]. The thermal performance of energy tunnels is significantly affected by the presence of groundwater flow [1, 6] and the airflow in the tunnel [2, 4]. The groundwater flow and tunnel airflow can both be present in the field, however, their coupled effects on the energy tunnel system are hardly explored in the literature. This study aims to bridge this gap via real-scale numerical investigations.
 This study uses 3D thermo-hydraulic numerical modelling developed with the finite element package COMSOL Multiphysics [3]. The numerical model was successfully validated against an energy tunnel model-scale laboratory experiment [5]. Figure 1 shows the overall geometry and boundary conditions of the numerical model. A 48 m long tunnel section is thermally activated with the embedment of HDPE pipes (outer diameter of 25 mm and 2.3 mm thickness) placed in the lining segments at a spacing of 200 mm. A single tunnel ring consists of six segments with absorber pipes joined between them. Every four adjacent rings are connected in series to form a complete loop (with a single inlet and outlet), which is then connected in parallel to a flow and return header pipe(s). The entire thermally activated section comprises six loops, with identical fluid inlet temperature and flow rates, as they are fed by the same flow header pipe. The outlet fluid from each loop is mixed along the return header pipe to the GSHP. A constant 36 kW cooling thermal load is applied, and the simulation is run for ten years to allow the system to reach a steady state condition considering the minimum groundwater flow and airflow. The thermal properties of the ground are prescribed as 2 W/(m·K) and 1100 J/(kg∙K) for thermal conductivity and specific heat capacity, respectively.
 Figure 2 shows the entering water temperature (EWT, header outlet) and the coefficient of performance (COP) of the GSHP after 10 years of operation for different groundwater flow velocities and directions for tunnel air velocities = 0.05 m/s and 2 m/s.
 Results show that an increase in and leads to a decrease in EWT and an increase in COP. However, the effect of groundwater direction and velocity is more significant when airflow is limited ( = 0.05 m/s). The parallel groundwater flow leads to a higher EWT and lower COP than when the flow is inclined and perpendicular to the longitudinal tunnel axis. Consequently, the thermal performance of the system under parallel flow with a higher can be even worse than the perpendicular and inclined flow with a lower . When = 0.05 m/s, the EWT of parallel flow increases by 15% to 20% compared to the perpendicular flow, resulting in a maximum decrease of 15% in the COP. The effect of groundwater flow is much less significant when airflow is fast ( = 2 m/s): for increases from 0.05 to 2 m/d, EWT and COP change by no more than 13% and 5%, respectively, and the impact of groundwater flow direction is minor.

Exergetic and energetic evaluation of a modified tc-CO2 refrigeration system assisted with an absorption chiller using natural refrigerants

Transcritical CO2 (tc-CO2) refrigeration system is a pertinent option for refrigeration at low temperature, but it has high energy consumption with low coefficient of performance (COP) and exergetic efficiency. Thermodynamic properties of CO2 are favorable to be used as refrigerant with zero ozone depletion potential (ODP) and very low global warming potential (GWP). The tc-CO2 system rejects a huge amount of energy at higher temperature in the gas cooler which can be utilized to run the absorption chiller and produce desired cooling effect, in various combinations. The current research focuses on the energy and exergy analysis of a tc-CO2 refrigeration system that aspires to accomplish low-temperature refrigeration. A single-effect absorption chiller is used to give subcooling to the tc-CO2 refrigeration system, which is powered by the heat available at high temperatures and pressures at the exit of the compression process of the former system, rather than any other external heat source. A work recovery turbine is also used as the expansion device to reduce throttling losses and electricity consumption to power the integrated system. The parametric study reveals that there is a significant improvement in the refrigerating capacity, COP and exergetic efficiency of the system.

The Impact of Solar Radiation at Different Colombian Thermal Floors on an Adsorption Refrigeration Cycle

The process of energy transition in Colombia has sparked an exploration into appropriate geographical areas for the utilization of solar energy. The country’s rugged terrain and significant climate variability pose challenges for implementing standardized technologies uniformly across all regions. Consequently, this study aims to develop and apply a mathematical model to characterize the performance of a solar adsorption cooling system under the environmental conditions found in six distinct Colombian cities, taking into account different thermal profiles and extreme weather periods such as the El Niño and La Niña phenomena. The selected mathematical model was simulated in these cities, considering ambient temperature and solar radiation variables over a twelve-month period during these extreme weather phenomena and an additional twelve-month period representative of a typical year with minimal influence from these phenomena. The results indicated that despite a lower coefficient of performance (COP) compared to the other cities, Riohacha demonstrated a greater number of ice production days owing to its high levels of solar radiation.

Energy Performance and Thermal Comfort Delivery Capabilities of Solid-Desiccant Rotor-Based Air-Conditioning for Warm to Hot and Humid Climates—A Critical Review

There has been considerable research worldwide on desiccant-based air-conditioning during the past 30 years. The rationale for the push for this new research focus has been twofold: (a) the need to provide an alternative to conventional refrigerative air-conditioning systems which rely heavily on fossil fuels as their energy sources, and (b) the need to provide better thermal comfort in air-conditioned spaces in warm to hot and humid climates. A desiccant air-conditioning system consists of several components to cool and dehumidify the air before it is supplied to a conditioned space. Earlier research work has identified the potential advantages of this technology, which include the following: (1) working fluids that do not impact on the ozone layer, (2) reduced electricity consumption, (3) improved indoor air quality, (4) simpler construction and less maintenance, and (5) integral provision of heating and cooling for cold/temperate climates. On the other hand, the authors of this paper identified the following drawbacks: (1) inevitable heating of air while being dehumidified, (2) the need for desiccant regeneration and low thermal COP paradox, (3) limited options for regeneration heat sources, (4) limited options for reliable cooling, and (5) low electrical coefficient of performance (COP). This paper presents a critical review of the energy and thermal comfort performance of solid-desiccant rotor-based air-conditioning systems, and discusses in detail their potential advantages and drawbacks. This critical review found that the drawbacks of the systems outweigh their identified advantages. The main reason for this is the inevitable heating of air while being dehumidified and counterintuitive addition of moisture to air during the evaporative cooling process. During the past 30 years of research and development efforts, no significant innovations have been discovered to resolve these crucial issues. Unless future research and development is directed to find a breakthrough, this technology will have limited commercial application.

Experimental study of refrigerator truck cold box for a constant temperature of 10oC based on variations in condenser dimensions

Transportation equipment equipped with a cooler box is needed for food delivery to keep the product fresh until it reaches its destination. Evaluation is carried out to determine the cooling temperature performance through testing using variations in condenser dimensions. The test was carried out to achieve a cold temperature in the cooler box of 10oC. The condenser used includes three variations, namely the 1st dimension is (P 23 x H 14) inch2 x 19 mm, the 2nd dimension is (P 23 x H 14) inch2 x 26 mm, and the 3rd dimension is (P 23 x H 14 ) inch2 x 44 mm. The test gives the result that the condenser in dimension-3 gives time to cool down at a temperature of 10oC faster than the condenser in dimensions-2 and 1. The condenser in dimension-1 can produce a cold time of 660 seconds, while the condenser for dimensions-2 and 1 is 960 seconds and 1320 seconds respectively. In addition, the lowest compression work occurs in the condenser with the 3rd dimension of 33.408 kJ/kg when compared to the 1st and 2nd dimensions of 38.984 kJ/kg and 35.923 kJ/kg. The smaller the dimensions of the condenser have an impact on the higher the compressor outlet pressure. This condition has an influence on the coefficient of performance (COP) in the refrigeration system, namely the condenser with dimension-3 gives the highest COP of 4.622 compared to dimensions-1 and 2, respectively 3.531 and 4.081. It was found in this study that the condenser at the largest dimension produces the most optimum performance, that is, an efficient refrigeration system has low compression power and high COP.

Numerical and Experimental Investigation of Supersonic Binary Fluid Ejector Performance

Ejectors are simple mechanical devices with no moving parts which convert the pressure energy of a motive fluid to kinetic energy and generate suction of the secondary fluid. The ability to recover waste heat, to operate using solar power and the ability to use geothermal energy make ejector-based systems attractive in different industrial applications. The main challenge of ejector-based refrigeration systems is their relatively low coefficient of performance (COP). In order to increase the ejector performance, two chemically distinct fluids can be used in the refrigeration cycle. It is suggested that a higher molecular mass be used for the motive fluid to improve the entrainment ratio of the binary fluid ejector (BFE) and thus the system COP. Inert gas combinations of argon–helium and krypton–air are studied in this paper using computational fluid dynamics (CFDs) and experimental measurements. All CFD cases were axisymmetric and the appropriate turbulence model was selected based on experimental validation. Specifically, the entrainment ratio and the static pressure along the ejector wall were measured to validate the CFD predictions. It was found that the molar entrainment ratio was significantly higher in argon–helium compared to krypton–air. The static pressure measurements along the wall, in addition, exhibited good agreement with the results obtained via computational fluid dynamics (CFDs).

Thermodynamic appraisal of utilizing compressor in double effect absorption heat transformer

In the current appraisal, three various designs of employing compressors in double-effect heat transformers are presented and evaluated from exergy and energy standpoints and collated with the simple configuration of mentioned designs. Water-LiBr is utilized as an operating fluid in noticed systems. As a function of the unit temperatures, the gross temperature lift, pressure ratio (R),and the efficiency of the economizer, a numerical model is also introducedto prognosticatethe irreversibility, exergy coefficient of performance (ECOP),coefficient of performance (COP), and the exergy destruction in each and every one of the key components (EF). The findings show that the generator has the highest exergy destruction, accounting for around 46.06% of the total exergy destruction. Additionally, a decrease in the temperature of the absorber increases the ECOP and COP. The outcomes indicate that systems utilizing water-LiBr as operating fluid have a higher outlet temperature of the absorber as well as higher condenser temperature and lower coefficient of performance (COP). the results showed that, Regarding the simple DEAHT curve, the COP slowly diminishes at low absorber-evaporator temperatures and rapidly at absorber temperatures more than 144.5 °C. Also, Utilizing the compressor in the basic design of the DEAHT unit results in improving the absorber temperature.

Analysis of a solar-assisted heat pump system with hybrid energy storage for space heating

Insufficient heating capacity and low coefficient of performance have always been obstacles that inhibit the application of air source heat pump systems in cold regions. This study proposes an indirect expansion solar-assisted air source heat pump system to improve the heating performance of the air source heat pump. The indirect expansion solar-assisted air source heat pump system consists of solar collectors, a hybrid thermal energy storage tank, and a dual-source heat pump. An optimized control method is proposed to tackle the refrigerant redistribution problem for the dual-source heat pump. An experiment is carried out to study the thermodynamic performance of the indirect expansion solar-assisted air source heat pump. The experimental results indicate that the average coefficient of performance of the solar heat pump mode is increased by 50.0% compared to the air source heat pump mode due to the higher evaporating temperature. Based on the experimental results, a techno-economic and environmental analysis of the indirect expansion solar-assisted air source heat pump system for space heating is conducted in six northern cities in China. The indirect expansion solar-assisted air source heat pump system has the highest annual average coefficient of performance of 2.53 in Jinan, which is increased by 18.8% compared to Harbin. The payback period of the indirect expansion solar-assisted air source heat pump system is shortest in Xining and is reduced by 53.45% compared to Jinan. Applying the IX-SAASHP system in the northwest region is suitable for improving its energy and economic performance. The analysis results indicate that the IX-SAASHP system is beneficial for reducing carbon emissions from space heating systems in the northeast region.

Computational fluid dynamics investigations over conventional and modified Savonius wind turbines

Wind turbines are devices that convert the kinetic energy present in the wind into clean, sustainable, and effectively renewable energy that could be used to generate electricity. A Savonius wind turbine is a drag-based vertical axis wind turbine (VAWT) that is known to have low noise levels and good starting characteristics even at low wind speeds. Its disadvantage lies in its low efficiency or low coefficient of performance. Exploring ways to increase the coefficient of performance, numerical investigations were carried out on different modified Savonius VAWT configurations, having different curvatures, different overlap percentages, added mini blades, and fitted out with extended surfaces. These investigations were computationally executed on Ansys Fluent™ using the sliding mesh technique. Two-dimensional simulations, on a Bach blade curvature with zero overlap as well as a half-circle and a polynomial curvature with overlap, showed that for a wind speed of 5 m/s and a tip speed ratio of 0.8, the half-circle blade curvature having an overlap of 20% performs best, yielding the highest net (average) coefficient of moment, equal to 0.3065. Results also show that the addition of mini blades to this optimal configuration produces a slight improvement in the coefficient of moment. However, the addition of extended surfaces onto the blades caused the minimum coefficient of moment to be a substantial negative value and thus resulting in a much lower value for the turbine's average coefficient of moment.

A parametric study and performance investigation of thermoelectric refrigeration system using computational fluid dynamics

Global commercial market forecasted around 45 billion US dollars for refrigeration equipment in 2021. Currently used refrigerants have high global warming potential (GWP); hence, environment-friendly refrigeration system using the Peltier effect is being considered for this research. The thermodynamic refrigeration system has a low coefficient of performance (COP), when compared to chlorofluorocarbon (CFC) and hydrofluorocarbon (HCFC) refrigeration systems. The design of various models of the thermoelectric refrigerator (TER) is created using ANSYS workbench. Each new design is analysed with computational fluid dynamics (CFD) analysis tool by altering insulating materials such as nickel with aluminium foil and polyurethane foam in airflow streamline of thermoelectric refrigeration. Temperature differences obtained between 7.5 and 9.4 °C are tabulated after each run using the finite volume method. Optimization of inner design and insulation material is done by using computational fluid dynamics analysis in the ANSYS FLUENT software. The results of sharp edge design have proved better when compared to partially round edge design and fillet design, 7.85 °C for the cold region and 54.85 °C for the hot region. Further research is expected using the multistage Peltier module and smart temperature control unit to improve the COP of the TER system.

Assessing the Potential of Heat Pumps to Reduce the Radiator Size on Small Satellites

Future small satellites will demand high-performance on-board electronics, requiring sophisticated approaches to heat rejection beyond simply increasing the radiator surface area. An interesting alternative approach is to increase the surface temperature of the radiator, using a heat pump. In this study, calculations were carried out to compute the theoretical radiator size reduction potential enacted by having a heat pump as part of a satellite’s thermal management system. The practical likelihood of a ‘typical’ vapor compression cycle (VCC) heat pump satisfying theoretical requirements was considered. In agreement with theoretical calculations, employing a ‘typical’ VCC heat pump could either increase or decrease the required radiator surface area. The choice of heat pump and its design is therefore crucial. A heat pump with a large temperature lift is essential for satellite radiator cooling applications, with the coefficient of performance (COP) being less important. Even with a low COP, such as 2.4, a ‘typical’ heat pump providing a large temperature lift, close to 60 °C, could reduce the satellite’s radiator surface area by a factor close to 1.4. This is a significant potential reduction. The decision on whether to pursue this approach compared to alternatives, such as deployable radiators, should consider the relative complexity, cost, weight, size, reliability, etc., of the two options. The focus of this study is VCC heat pumps; however, the results provide performance targets for less mature heat pump technologies, e.g., caloric devices, which could ultimately be applied in space.

Research and application of park multi-source synergistic and complementary heating system and its coordinated control method

The integration of solar thermal collectors (STC) and air source heat pump (ASHP) heating systems has been widely used for building heating. However, these systems have the problems that the STC cannot fully utilize the solar energy at weak radiation, and the ASHP has insufficient output as well as low coefficient of performance (COP) under extreme cold conditions. In this study, a multi-source synergistic and complementary heating system (MSSCHS) with a heating mode selection model based on belief rule base and evidential reasoning (BRB-ER) method is designed. First, the MSSCHS composed of the STC and the ASHP as the main heat sources, and the water source heat pump as the auxiliary heat source, along with its three heating modes under different operating conditions were proposed. Then, a system heating mode selection model based on the BRB-ER method was establish to achieve mode switching. Finally, the MSSCHS with BRB-ER heating mode selection model was tested experimentally. The results show that compared with the conventional ASHP + STC heating system, the solar energy utilization rate of the MSSCHS had increased by 19.3 %, 16.6 % and 8.2 % respectively in three typical days, and the ASHP's COP had increased by 37.7 %- 55.6 % under extreme cold conditions. The high efficiency and stability of the MSSCHS were verified through operational tests during the heating period. Furthermore, by applying in different types of buildings, it is verified that the MSSCHS can meet different heating requirements and has a good applicability. It was demonstrated that the proposed MSSCHS has more efficient heating mode and more accurate mode selection method, which can provide a new research idea for building heating.

An experimental investigation of the effects of the number of capsules and operating conditions on the performance of encapsulated ice storage system

It is crystal clear to everyone that ice thermal energy storage (ITES) systems provide significant advantages in reducing cooling costs, balancing energy supply and demand profiles, and shaving the peak loads. When the thermodynamic performance of the ITES is compared with conventional AC, the following two points are critical: (i) ITES tends to increase the coefficient of performance (COP) of the system thanks to the lower ambient temperature during the nighttime (the charging period of ITES). (ii) It may cause a lower COP as a lower operating temperature is required to produce ice. In numerous papers, it has been reported that ITES can increase or decrease COP. This experimental study deals with the influences of the number of ice capsules and operating temperatures on the thermodynamic performance of the ITES-integrated cooling system. Results indicate that nighttime operation with the ITES provides higher COP and lower energy costs due to lower ambient temperature and no solar radiation. The highest COP value of the chiller is observed as 13.55. The highest COP during the charging period is found to be 8.99 when the storage medium is 0.3 m3, the charging temperature is −10 °C, and the ambient temperature is about 8 °C. The efficiency of discharging period is calculated to be 99.97 %. The best overall COP is observed to be 17.53 for the case at a storage medium volume of 0.3 m3 and a charging temperature of −12 °C. This is about three times higher than a conventional cooling system that works under ordinary daytime runs. Consequently, nighttime operations with ITES can reduce electricity consumption by 30 % and cooling costs by 62 %.

Highly efficient desiccant-coated heat exchanger-based heat pump to decarbonize rail transportation

In the rail sector, air conditioning accounts for 30% of the total operational energy consumption, thus, it is crucial to enhance the efficiency of air conditioning units (ACUs) to reduce overall energy consumption. Traditional ACUs for train vehicles usually have a low coefficient of performance (COP), often less than 2, because of condensation-based dehumidification and a consequent reheating process and also the restricted spaces to install ACUs on the rooftop of the cabinet. Herein, we present a novel ACU with an integrated structural design that uses desiccant-coated heat exchangers (DCHEs) coupled with heat pumps, providing comfortable air conditioning on the metro or high-speed trains. This approach provides a direct method for reducing the air temperature and humidity simultaneously, thus realizing the decoupling of temperature and humidity treatments on a single heat exchanger. Using this design, experimental results show that the proposed system can improve the COP by ∼40% under standard conditions compared with existing ACUs (2.5 vs. 1.8). In addition, the proposed system achieves the highest COP of 2.8 under Shenzhen ground conditions (high humidity and temperature conditions) and exhibits high adaptability to various climate zones. The application of the DCHE-based system in the rail sector can significantly contribute to the decarbonization of the sector and make rail transportation sustainable and ready for a green transformation.