System Coefficient Of Performance Research Articles

Study on a novel hydrogen liquification process applying mixed-refrigerant for pre-cooling and cryogenics

Reducing the energy consumption of hydrogen liquefaction process is an urgent issue to improve the economy of liquid hydrogen transportation. A novel large-scale hydrogen liquefaction system, with a capacity of 100 TPD, is proposed in this paper. The pre-cooling system is composed of a mixed-refrigerant (MR) refrigeration cycle and a CO2–NH3 cascade refrigeration cycle. Due to the auxiliary pre-cooling effect of the CO2–NH3 cascade cycle, temperature of the pre-cooled hydrogen can be as low as −200.9 °C. A modified MR Joule Brayton cycle with an additional compressor is used as the cryogenic system to cool the hydrogen from −200.9 °C to −252.2 °C. Besides, a four-stage ortho-to-para conversion (OPC) process is utilized. Performance of the novel system is investigated and optimized using the Aspen HYSYS software. According to the results, the lowest specific energy consumption (SEC) of the proposed process is 6.15 kWh/kgLH2 and the exergy efficiency is as high as 67.4%. Based on the energy analysis, the best system coefficient of performance is 0.1751 with a 96.3% of p-H2 in the liquid hydrogen. In addition, compared to the initial conceptual system, the proposed system exhibits significant performance enhancements, a 20% reduction in SEC and a 27.9% increase in exergy efficiency. A sensitivity analysis is conducted to assess the impact of refrigerant composition and hydrogen pressure on the system, resulting in the determination of the optimal proportions of refrigerant components and the optimal inlet pressure. Results of the study can provide theoretical reference for the further development of large-scale hydrogen liquefaction technology.

Study on performance of direct-expansion heat pump water heater integrating uninsulated micro-channel PV/T solar collector

In this paper, a direct-expansion heat pump water heater system integrating uninsulated micro-channel PV/T solar collector is proposed. This system can realize storage for both thermal energy and electricity and complementary grade, ensuring the supply of domestic hot water. Based on the performance of the micro-channel PV/T heat pump water heater system, the theoretical models of micro-channel PV/T solar collector, hot water storage tank, compressor and electronic expansion valve are established where R134a is used as refrigerant. Theoretical simulation and analysis of system performance under different solar radiation intensities, ambient temperatures and different outdoor wind speeds are carried out with MATLAB. The results show that solar radiation intensity has the greatest influence on the system performance, followed by ambient temperature and wind speed. The basic-thermal system performance coefficient (COP) and the advanced system performance coefficient (COPpvt) will be enhanced, while the required operating time will be reduced, as solar radiation intensity and ambient temperature increase. This system removes the thermal insulation for the micro-channel PV/T solar collector that the convection heat transfer on the micro-channel evaporator is enhanced. Therefore, the system can absorb the thermal energy from the ambient air according to different solar radiation intensities, and maintain a high coefficient of performance, electric efficiency, thermal efficiency and overall energy efficiency. Even when the solar irradiation is 322 W/m2 and the ambient temperature is −18.6 °C, the thermal efficiency, electric efficiency and overall energy efficiency of UMC-PVT-SC and COPpvt can still remain at 0.718, 0.2442, 1.341 and 5.63, ensuring the heating capacity and high grade power output capacity.

A dynamic simulation study of temperature and humidity independent control system for temperate semi-humid continental monsoon climate regions

A temperature and humidity independent control (THIC) system is a promising solution for hot and humid indoor working environments. This study proposes a dual-source heat pump air-conditioning (DSHPAC) system composed of a dual-source heat pump (DSHP) and air handling unit (AHU) as a THIC system. The proposed THIC system indirectly adjusts the cooling capacity of the high-temperature evaporator (Eva1) and low-temperature evaporator (Eva2) by controlling the refrigerant mass flow rate of the system to meet the cooling and dehumidifying requirements under different operational conditions. The proposed THIC system can switch among three operational modes by using the designed operational strategy, ensuring that the requirements for indoor temperature and humidity are met. In addition, the mathematical model and equilibrium equations of the THIC system are established. This study uses an office building in Xi'an on a typical summer day as a simulation case in dynamic simulations. The coefficient of performance (COP), cooling capacity, and compressor power consumption of the proposed DSHP system are analyzed. The results demonstrate that the COP of the proposed system increases with the temperature of Eva1 (TEva1), the COP of the proposed system varies from 1.76 to 3.62, and the cooling capacity increases from 1.19 kW to 3.38 kW when TEva1 increases from 6.24 °C to 36.4 °C. The analysis of different values of φR (refrigerant mass ratio) shows that the highest COP is achieved at φR = 0.1. The results prove the application potential of the dual-source heat pumps to the THIC air-conditioning systems.

Variable pressure differential fuzzy control method for the multi-split backplane cooling system in data center

In contrast to existing room-level cooling systems, rack-level cooling systems can solve local hot spot issues due to their on-demand cooling way with higher energy efficiency and higher supply cooling temperatures. However, the multi-split backplane cooling system, which is a typical rack-level cooling way, makes it easy to cause insufficient refrigerant supply problems due to higher evaporating pressure under the same ambient condition. To solve above problems, a suitable condensing pressure relative to evaporating pressure is a critical optimized parameter, which needs to follow with the change of ambient condition. Therefore, a variable pressure differential control method between the condensing side and the evaporating side is proposed based on online fuzzy inference. A Modelica-based simulation model is built to validate the proposed method. Results show that the proposed method can ensure the terminal cooling effect at different ambient temperatures. Compared with the fixed condensing pressure control method, the proposed method shows an increase of 13.3% in system coefficient of performance (COP) with lower condensing pressure.

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.

The effects of Multiwalled Carbon Nanotube to the performance of a refrigeration system

By incorporating nanofluid technology and nanolubricants into compressors, the performance can be enhanced while also lowering worldwide fuel consumption and aiming at developing cleaner, more efficient energy sources and uses. The globe is being confronted with energy security issues and heating, cooling and HVAC systems highly contribute to it. Hence, it is critical to save energy and improve the efficiency of the refrigeration cycle. This study presents experimental and theoretical findings in order to investigate the effect of Polyester (POE)-oil based multiwalled Carbon Nanotube (MWCNT) nanolubricant on the Coefficient of Performance (COP) of a refrigeration system. The objectives of this study is to analyze the stability of MWCNT nanofluids, to obtain the COP of a refrigeration cycle run with pure POE oil and MWCNT nanofluids with different concentrations respectively. The experiment was conducted by preparing 0.55, 0.65 and 0.70 g/l MWCNT nanofluid by using the two step method. The most effective concentration used in the refrigeration system was referred to the one that resulted in the highest COP. It was determined from the experiment that 0.55 g/l MWCNT nanofluid resulted in a higher COP of 5.766 as compared to the other two concentrations. Besides, it showed an improvement of 34.6% in COP as compared to the COP of using pure POE oil in the refrigeration system, which was found to be 4.285. The 0.65 g/l and 0.70 g/l concentration of MWCNT resulted in a COP of 5.618 and 5.617, respectively. The compressor work was also analyzed and was found to be reduced noticeably after adding MWCNT nanoparticles. Hence it can be concluded that the increment of MWCNT concentration in nanofluids increases the COP of the refrigeration system but only up to a certain limit of concentration.

Field experiment on performance of water source heat pump using underground rainwater tank as heat source

Research on heat sources for various heat pump (HP) systems is ongoing worldwide to achieve carbon neutrality and mitigate global warming. In this study, a rainwater (RW) tank HP (RWHP) using an underground RW tank as a heat source and heat sink was installed in an actual building and evaluated for its potential to provide cooling during the summer season. The water temperature of RW tank, the inlet and outlet fluid temperature, and the power consumption were measured. Using the collected data, the thermal stability of the RW tank and the performance of the RWHP were analyzed. In addition, the effect of the water level of the RW tank and precipitation was analyzed. As a result, the RW tank functioned as the heat sink for the HP during the cooling season. If the water level in the RW tank and the moisture content of the surrounding ground are high because of precipitation, the water temperature in the tank can be maintained at a relatively stable level. The coefficient of performance (COP) and system COP (COPsys) ranged 2.41–3.38 and 1.80–2.50, respectively. When the rainwater temperature in the RW tank increased, the COP and COPsys tended to decrease. Through this study, the data necessary for optimization through future mathematical modeling was collected. Also, the basic mechanisms of the temperature distribution of the RW tank and the performance of the RWHP were identified. Additionally, the operation method and means for improving the system were determined to increase the energy efficiency and broaden the applicability of the system.

Energy, exergy, economic, and environmental analysis of a high-temperature heat pump steam system

Industrial steam is widely recognized as a valuable form of heat currency, possessing considerable social and economic significance. As the industry shifts to low carbon emissions, there is an urgent need to reduce CO2 emissions from industrial steam generation. The analysis of a high-temperature heat pump steam system (HTHPSS), which recovers industrial waste heat to produce high-temperature steam at 170 °C, includes evaluations of its energy, exergy, economic, and environmental (4E) to determine whether it can replace a coal-fired boiler. The economic analysis considered the recovery value of waste heat and the effect of CO2 trading prices. Optimization calculations were performed to investigate changes in the waste heat temperature and condenser outlet temperature. The study also offers recommendations for operational conditions and optimization strategies for the HTHPSS. The results indicate a positive correlation between the system coefficient of performance (COP) and the waste heat utilization rate with waste heat temperature and condenser outlet temperature. The maximum COP value is 2.73. The total exergy efficiency initially increases and then decreases as waste heat temperature increases. It also decreases as the condenser outlet temperature increases, reaching a peak value of 43.26 %. The waste heat temperature needs to be at least 59 °C to generate a net profit, with a corresponding payback period (PBP) of 4.40 years. The minimum PBP is 0.03 years, independent of waste heat temperature. The annual emission reduction increases as waste heat temperature increases and decreases as condenser outlet temperature increases. These results indicate that a HTHPSS could replace a coal-fired boiler and offer guidance for design optimization.

Analysis and optimization of a medium-depth ground source heat pump heating systems with heat storage and borehole heat exchangers

The medium-depth ground source heat pump (MD-GSHP) heating technology is considered a clean energy solution with the potential to mitigate air pollution issues attributed to winter heating in northern China. However, it currently suffers from problems such as a mismatch between heat supply and demand and a lack of optimal operation. To overcome these limitations, this study focuses on a 3000 m2 residential building in Xi’an and implements two configurations: coupling MD-GSHP heating systems with heat storage tank and shallow borehole heat exchanger (BHE). Additionally, an optimization strategy based on the improved particle swarm algorithm is proposed, integrating chaos optimization and dynamic parameters. Finally, noteworthy outcomes were revealed by optimizing the MD-GSHP heating systems under different objective functions. In system coupled with shallow BHE, the variation trend of flow in the medium-depth BHE was similar to that of heating load when the heating cost was taken as the objective function. After the optimization, heating cost reduced by 10.02%, while system coefficient of performance (COP) and medium-depth geothermal utilization coefficient increased by 10.43% and 2.00%, respectively. For system coupled with heat storage tank, the optimized flow exhibited a generally decreasing-increasing-decreasing trend, with the peak preceding the heating load curve. This resulted in a 12.82% reduction in heating cost, along with increases of 10.35% and 1.96% in system COP and the medium-depth geothermal utilization coefficient, respectively. Comprehensive consideration of heating cost and system COP suggested a favorable weight of 2.8 for continuous system operation. In conclusion, when prioritizing heating cost, the system coupled with heat storage tank yields greater economic benefits compared to the system coupled with shallow BHE. The findings of this study can provide a guidance for the applications of the MD-GSHP heating technology.

An experimental investigation of vapor compression refrigeration cooling and energy performance for CPU thermal management

This case study experimentally investigates a R134a charged Vapor Compression Refrigeration (VCR) assisted liquid cooling of high-powered CPUs. In this hybrid system, water-based liquid cooling of the CPU is achieved in a pumped loop with a commercial cold plate affixed to the simulated CPU. The heat is then transferred to the evaporator heat exchanger of a miniature VCR system that rejects the energy to ambient air. Tests are performed at room temperature over a range of operating conditions, including CPU heat loads (12 W/cm2 - 75 W/cm2), liquid volumetric flow rates (0.5 Litre/min - 8 Litre/min), fan air speeds (2.1 m/s – 4.2 m/s), and compressor speeds (2540 rpm–6500 rpm). Both cooling performance and additional energy consumption implications are considered. Overall, it is shown that the miniature hybrid VCR system can cool the primary liquid to below ambient temperature, even at the highest tested heat load. As a result, cooling levels that far exceed both a conventional Fan-Fin Air Cooled heat exchanger and a Hybrid Liquid-Air Cooled system are achieved. Finally, optimal combinations of liquid flow rate and compressor speed are identified for minimum energy consumption of the cooling system to maintain a setpoint CPU die temperature. It is shown that management and control of pump, compressor and fan speeds can result in significant improvement in the overall system Coefficient of Performance (COP).

Performance Evaluation Of Refrigerated Pickup Truck Using Hydrocarbon Refrigerants

HFCs group refrigerants are still widely used in refrigerated pickup trucks. This refrigerant is a synthetic chemical and has a high potential to cause global warming and damage the ozone layer. This study aims to obtain performance data from the use of HCs as refrigerant in refrigerated pickup trucks. The research was conducted experimentally on a pickup truck with a 1500 cc engine capacity. The size of the refrigerated room is 2300 mm long, 1500 mm wide and 1400 mm high. A commercial refrigeration system (C-250e MAX, Thermo King Europe, Belgium). The size of the evaporator, which consists of a cold air supply fan and an intake fan, is 133 mm long, 985 mm wide and 525 mm high. The cooling capacity is 2770 W. The volumetric flow rate of cold air is 1100 m3/hr. The test started at 9 am and the temperature value in a gallon of water was measured for 120 minutes. The results showed that the optimal refrigerant filling was the use of R290 (35%) and R1270 (20%). The value of the coefficient of system performance obtained from the use of the two variations of HCs is 4. Thus, refrigerant HCs R290 and R1270 can replace refrigerant HFCs in refrigerated pickup trucks with refrigerant mass variations of R290 (35%) and R1270 (20%).

Experimental Investigation of the Performance of a Household Refrigerator Using Phase Change Material

A household refrigerator represents an essential device for all houses nowadays. The electric energy consumed by the refrigerator and the fluctuation of the temperature inside the fresh food cabin is the main two problems affecting its performance. Incorporating phase change material (PCM) inside the refrigerator is one of the solutions for the previous mentioned problems. In the present study, a water PCM is added to the cabinet of 220-litters double door refrigerator. The PCM (0.5 ml of water) is added at three different locations, touch the front of the evaporator part inside the cabin, touch the rear of the evaporator part in the cabin, and far away from the evaporator part inside the cabin. The location of the PCM determines how much energy is released and stored from the evaporator. The use of phase change material (PCM) touch to the evaporator increases the rate of heat transfer due to the conduction method being used throughout the whole heat transfer process from the evaporator to the phase changematerial (PCM), which raises the refrigeration system's COP (coefficient of performance). The experimental test period is 24 hours for each day. Firstly, the refrigerator is tested without using PCM, and the power consumption, the temperatures at different points for the refrigerator, suction pressure, discharge pressure, the ambient temperature, and the time on period and time off period of the compressor are measured. Secondly, for same testing period all previous parameters are measured with using PCMat different locations inside the refrigerator. The results show that, adding the PCM (water) behind the evaporator led to increase the COP by 21.97%, increase the compressor off time by 73 minutes, reduction in power consumption of 14.4%, decrease of exergy losses of the system by 8% and temperature fluctuation reduced inside the fresh food cabin, that enhance the quality of stored food. Adding the PCM front the evaporator improve the previous parameters but less than that of the first case. The third location, adding the PCM far away from the evaporator has no improvement on the refrigerator's performance.

Improved energy management of chiller system with AI-based regression

This research aims to enhance energy management in commercial building air-conditioning systems, specifically focusing on chillers, which are significant energy consumers. This study evaluates various regularized regression models using comprehensive time series operating data from a system comprising five chillers of two distinct capacities. Compared with lasso and elastic net regression, ridge regression exhibits superior performance metrics when optimized with the appropriate hyperparameter. This makes it the most suitable method for modeling the system coefficient of performance (SCOP), thereby facilitating the development of an effective energy management plan. Key variables that strongly influence SCOP include the part load ratios of operating chillers, the operating numbers of chillers and pumps, and the temperatures of chilled water and condenser water. This study further identifies July as the month with the highest potential for performance improvement based on the predicted benchmark regions. This study introduces a novel approach that balances feature selection, model accuracy, and optimal tuning of hyperparameters. It highlights the significance of a generic and simplified chiller system model in evaluating energy management opportunities for sustainable operation, taking into account the distinct performance characteristics and time series features of individual system components. The findings from this research can guide future efforts towards more energy-efficient and sustainable operations in commercial buildings.

Experimental performance analysis of evacuated tube type direct-expansion solar-assisted heat pump system

ABSTRACT The direct-expansion solar-assisted heat pump (DX-SAHP) have proven to be one of the strategies in reducing energy consuming for domestic hot water supply. The poor pressure resistance of the collector, high heat loss from radiation for the traditional bare-plate type DX-SAHP limits its popularization and application. To solve this problem, a DX-SAHP system using evacuated tube type collector-evaporator was proposed in this post. System optimization can not only reduce operating costs, but also results in energy savings. Thus, a DX-SAHP prototype was established and tested under various running conditions to obtain the optimal running parameters. Based on experimental data, the impacts of refrigerant charge, solar radiation intensity, and ambient temperature on the performances of evacuated tube type DX-SAHP system are investigated and evaluated. The outcome indicates that this system coefficient of performance (COP) increases by 73.4% with the decrease of charge amount of refrigerant in the range of 5.66–6.67 kg. And, the average collector efficiency is 0.71 with a refrigerant charge of 5.66 kg. And, the optimal COP of this presented system is 5.27 when an ambient temperature, solar radiation intensity, and refrigerant charge are 26.3°C, 954.37 , and 5.56 kg, respectively.

Organic Rankine cycle-ejector heat pump hybrid system using low GWP zeotropic mixtures for trigeneration application

This paper presents a comprehensive study focused on improving the thermal efficiency and performance of an organic Rankine cycle (ORC) combined with an ejector heat pump (EHP) for trigeneration application. The utilization of zeotropic mixtures with low global warming potential (GWP) was proposed as a solution to address the inherent inefficiencies of the ORC at low-temperature heat sources and to enhance the coefficient of performance (COP) of the ejector refrigeration cycle. A thermodynamic model was developed to predict system performance, utilizing low-temperature heat sources such as solar or geothermal energy, along with zeotropic mixtures. The model was validated with the available literature data, demonstrating very good agreement. Five zeotropic fluid mixtures were preliminary studied, and the optimal mass fractions identified. Detailed investigations were then carried out for two of these mixtures, R1233zd(E)/propane and butane/propane, which exhibit low GWP and ozone depletion potential (ODP). The influence of generator temperature and entrainment ratio on system efficiency metrics, exergy, and COP were evaluated for these mixtures. Conclusions are drawn based on the two optimized zeotropic mixtures for maximum thermal efficiency. For R1233zd(E)/propane mixture with mass fractions 0.75/0.25 and butane/propane mixture with mass fractions 0.5/0.5 at generator temperature of 75 °C and entrainment ratio of 0.5, the systems achieved a heating capacity of 1607.9 kW and 2847.9 kW, a cooling capacity of 1037.5 kW and 1280.3 kW, and a net power output of 59.2 kW and 136.3 kW. Other related performance and efficiency parameters are included in the paper. These findings indicate the feasibility of utilizing these systems for trigeneration application. Additionally, a comparative analysis with a regenerative ORC highlighted the ORC-EHP hybrid system's advantages, including enhanced heating efficiency, cooling capacity, and overall COP.This research contributes valuable insights to advance the efficiency and sustainability of combined cooling, heat, and power systems, fostering the progression of innovative energy solutions.

Research on renewable energy coupling system based on medium-deep ground temperature attenuation

Medium-deep geothermal has large reserves, a high temperature, a high heat flow density, and other characteristics, but the traditional medium-deep ground heat pump system have long relied on heating from the ground, and soil temperature decreases annually. Using a community building heating system as an example, from a point of view of heat accumulation or not, this article examines the design of a photovoltaic photothermal coupled medium-deep ground source heat pump system (PV/T-GSHP) and a photovoltaic-assisted medium-deep ground source heat pump coupled air source heat pump system (PVGSHP-ASHP). First, the operational performance of a typical GSHP system was compared to that of the PV/T-GSHP and PVGSHP-ASHP systems, both of which were built using TRNSYS. Second, the energy balance and electrical consumption of each system were compared. Finally, the effect of the PV/T-GSHP system’s key parameters and the different ASHP load ratios in the PVGSHP-ASHP system on soil temperature were analyzed. The results showed that after 20 years of operation, the average soil temperature decreased from 38.29 °C to 36.89 °C for the GSHP system, resulting in a decrease in the performance coefficient of the ground source heat pump and the system performance coefficient. The PV/T-GSHP system can address the issue of declining soil temperature with an increase in soil temperature of 0.09 °C. The PVGSHP-ASHP system can mitigate the issue of decreasing soil temperature. The PVGSHP-ASHP system is better than the PV/T-GSHP system in terms of electricity economy. In the PV/T-GSHP system, the larger PV/T component area of similar structures, the smaller flow rate of the heat collector pump, and the volume, inclination, and set temperature of the heat storage tank that are more suitable for the system can achieve higher soil temperatures. As the air-source load ratio increases, the rate at which the soil temperature in the PVGSHP-ASHP system decreases progressively decelerates.

Effect of drying air supply temperature and internal heat exchanger on performance of a novel closed-loop transcritical CO2 air source heat pump drying system

A novel closed-loop transcritical CO2 air-source heat pump drying (HPD) system with a relatively simple structure, higher drying temperature, and internal heat exchanger (IHX) for the drying of medical equipment was proposed and built. With or without the IHX in the system, the effects of different drying air supply temperatures on the performance of transcritical CO2 HPD system were studied experimentally. The results showed that the maximum drying air supply temperature (DAST) in the designed system could reach 72.9 °C. As the DAST raised, whether with or without the IHX in the system, the coefficient of heating performance (COPh), coefficient of system performance (COPsys), and specific moisture extraction rate (SMER) decreased gradually and moisture extraction rate (MER) increased continuously. When the DAST was 70 °C, COPh, COPsys, MER and SMER were respectively 3.68, 6.07, 3.27 kg/h and 1.68 kg/(kW·h) in the HPD system without the IHX, and were respectively 4.00, 6.89, 3.67 kg/h and 1.97 kg/(kW·h) in the HPD system with the IHX. In contrast, the compressor discharge pressure decreased 4.26 %–5.99 %, COPh increased 1.39 %–8.65 %, COPsys increased 1.89 %–13.57 %, MER increased 4.68 %–14.01 %, SMER increased 6.93 %–17.18 % in the HPD system with the IHX.

Experimentally investigating and numerically simulating the performances of various low-temperature hydronic heating/cooling systems connected to a vertical closed-loop ground-coupled heat pump

The method used in this study consists of evaluating different terminal heating/cooling systems in an experimental office at the Polytechnic University of Timișoara, Romania, through experimentation and numerical simulation. This paper is focused on the energy efficiency exploratory research of various low- and very low-temperature hydronic radiant heating/cooling systems (floor, wall, ceiling, combined floor-ceiling) and of the medium-temperature radiator heating system, connected to a vertical ground-coupled heat pump (GCHP) in double U-tube borehole heat exchanger (BHE) configuration. The main performance parameters are obtained for five weeks of operation in heating mode and three weeks in cooling mode, and a comparative analysis of these parameters together with indoor thermal comfort is carried out. The four simple heating systems (radiator, floor, wall, ceiling) have relatively small differences (maximum 7.4 %) in their coefficient of performance (COP) values, but the number of starts/stops in the case of radiator heating is twice that of floor heating, which leads to greater wear and tear on the heat pump equipment. Under the same operating conditions, the CO2 emission of the radiator heating system are 0.7–16 % higher than those of the heating system with radiant panels (floor, wall, and ceiling). The floor-ceiling combined radiant heating system has the highest COPsyst of 5.45 as well as the lowest CO2 emission value of 2.15 kg. The predicted mean vote (PMV) index (pair 1.1 met-0.29 clo) has values approximately equal to 0 only in the case of the floor-ceiling heating, when the percent of likely dissatisfied with the thermal comfort is 5 %. The three cooling radiant systems show differences in their energy performance, namely the radiant ceiling cooling system has the best COPsyst, 39.8 % higher than that of the radiant floor and only 5.9 % higher than that of the radiant wall. The values of the PMV index (pair 1 met-0.9 clo) for the radiant wall cooling system are 31–41 % lower than those of the radiant floor and 10.4–14.2 % lower than those of the radiant ceiling. Finally, numerical simulations of the useful thermal energy and the system COP in heating and cooling modes are performed with TRNSYS software for a duration of 8760 h and then analysed and compared with the experimental tests to validate the simulation models.

Thermodynamic analysis of a hybrid energy system coupling solar organic Rankine cycle and ground source heat pump: Exploring heat cascade utilization

The demand for efficient utilization of renewable energy is growing and the hybrid energy system driven by solar and geothermal energy is a significant way to achieve carbon neutrality. This paper presents a hybrid energy system coupling solar organic Rankine cycle (S-ORC) with ground source heat pump (GSHP) for heating and power supply to explore the heat cascade utilization. In the hybrid energy system, the ground heat exchanger (GHE) is shared by the S-ORC and GSHP systems and the waste heat from the condenser of S-ORC is recovered to enhance the coefficient of performance (COP) of GSHP. A mathematical model is optimized to analyze the parametric effects on thermodynamic performance. The results indicate that the COP of the hybrid energy system can be improved up to 6.5 which shows the obvious advantage compared to 2.8 of the stand-alone GSHP system. Furthermore, the hybrid energy system can obtain optimum exergy efficiency by matching ground source temperature and condensation temperature in the ORC unit. For a building of 3000 m2 with heating and power supply, multi-objective optimization is carried out to obtain the optimal design performance that the net power output, thermal efficiency and exergy efficiency are 180.0 kW, 27.5%, and 9.2% respectively.

Superhydrophobic Microchannel Heat Exchanger for Electric Vehicle Heat Pump Performance Enhancement

Battery-powered electric vehicles (EVs) have emerged as an environmentally friendly and efficient alternative to traditional internal combustion engine vehicles, while their single-charge driving distances under cold conditions are significantly limited due to the high energy consumption of their heating systems. Heat pumps can provide an effective heating solution for EVs, but their coefficient of performance (COP) is hampered by heat transfer deterioration due to frost accumulation. This study proposes a solution to this issue by introducing a microchannel heat exchanger (MHE) with superhydrophobic surface treatment (SHST) as a heat pump evaporator. A computational fluid dynamics MHE model and a dynamic heat pump model are developed and rigorously validated to examine the detrimental impact of frost accumulation on heat transfer, airflow resistance, and heat pump performance. When the frost layer thickness is 0.8 mm at a given air-side velocity of 1.0 m/s, the air-side heat transfer coefficient can be reduced by about 75%, and the air-side pressure drop sharply increases by 28.4 times. As frost thickness increases from 0 to 0.8 mm, the heating capacity drops from 3.97 to 1.82 kW, and the system COP declines from 3.17 to 2.30. Experimental results show that the frost thickness of the MHE with SHST reaches approximately 0.4 mm after 30 min, compared to that of 0.8 mm of the MHE without SHST, illustrating the defrosting capability of the superhydrophobic coating. The study concludes by comparing the performance of various heating methods in EVs to highlight the advantages of SHST technology. As compared to traditional heat pumps, the heating power consumption of the proposed system is reduced by 48.7% due to the defrosting effect of the SHST. Moreover, the single-charge driving distance is extended to 327.27 km, an improvement of 8.99% over the heat pump without SHST.