Coefficient Of Performance Research Articles

An experimental study exploring heat transfer enhancement in tube in tube heat exchanger with pulsating flow

Rationalizing power consumption is crucial in air conditioning and refrigeration design. This study focuses on improving the coefficient of performance (COP) by applying pulsating flow. Experimental trials compared continuous counter and counter pulsating flow to continuous parallel flow, showing a 10% reduction in fluid temperature with continuous counter flow and a 20% reduction with counter pulsating flow. Sensible water heat rejection increased by 10.03% and 19.78% with continuous counter flow and counter pulsating flow, respectively. Overall heat transfer coefficient improved by 57.5% and 75% with continuous counter flow and counter pulsating flow. Effectiveness increased by 4.55% and 10.6%, while COP increased by 4.52% and 13.4% with continuous counter flow and counter pulsating flow, respectively. This research demonstrates the potential of pulsating flow techniques to enhance air conditioning and refrigeration efficiency.

Parametric analysis for nanolubricant in vapor compression refrigeration cycle

With the escalating global energy crisis and the consequential surge in energy consumption, particularly attributed to air conditioning (AC) systems in buildings, there arises a pressing need for sustainable solutions to mitigate this escalating demand. Vapor compression refrigeration (VCR) cycles, ubiquitous across residential, commercial, and industrial sectors, represent a significant portion of global electricity consumption, exceeding 10%. This demand is further exacerbated in regions characterized by hot climates. Consequently, there is a critical imperative to address the environmental impact of these systems, particularly in terms of reducing their Global Warming Potential (GWP). In response to this imperative, this study aims to develop a comprehensive numerical model for VCR systems, focusing on the implementation of nanolubricants. The primary objective is to assess the impact of integrating Al2O3 nanoparticles into the lubricating oil (referred to as nanolubricant) on the performance of the VCR cycle. The scope of the study encompasses the investigation of nanolubricants within refrigeration systems, aiming to enhance their efficiency and environmental sustainability. Utilizing the Engineering Equation Solver (EES), a numerical model of a VCR cycle utilizing R-410A refrigerant is developed. The model specifically emphasizes the compressor component, which is flooded with a polyolester (POE) oil base. The study explores various parameters, including ambient conditions, refrigerant-to-oil dissolving ratio, and mass concentration of nanoparticles, to evaluate their influence on system performance. The results indicate a significant enhancement in performance when flooding the base oil before introducing Al2O3 nanoparticles, with further improvements observed upon nanoparticle integration. Specifically, the coefficient of performance (COP) of the VCR system exhibits a notable increase compared to the base case configuration. Additionally, the adoption of eco-friendly refrigerants, such as R-32, demonstrates promising COP values following nanoparticle implementation by up to 4%. Moreover, the study reveals a reduction in compressor discharge temperature by up to 20% with higher oil mass concentrations during nanolubricant implementation, indicating enhanced durability and longevity of the VCR system’s compressor. These findings underscore the potential of nanolubricants to contribute to both the efficiency and environmental sustainability of refrigeration systems. In conclusion, the findings of this study offer valuable insights into the utilization of nanolubricants in VCR cycles, highlighting their potential to enhance system performance and mitigate environmental impact. These advancements hold promise for the development of more sustainable refrigeration technologies in the face of mounting energy challenges.

Thermodynamic Simulation of Cascade Cooling System for Vacuum Freeze Drying

Vacuum freeze drying (VFD) is a drying method carried out at pressures and temperatures below the triple point of water. Drying occurs by sublimation. The results of the VFD method are able to maintain the quality of dry ingredients (taste, colour, nutrient, etc.). To achieve a condition below the triple point of water, it is conditioned so that the pressure is under a partial pressure of 6.11657 mbar at a temperature of 0.01°C. The refrigeration system is simulated using refrigerants R-134a and R-22. The purpose of the simulation is to obtain the optimum system conditions. The variables varied were the saturated temperature of the LTC (Low-Temperature Circuit) evaporator, the saturation temperature of the HTC (High-Temperature Circuit) evaporator, the difference in the temperature of the pinch point between the LTC condenser and the HTC evaporator and the temperature of the HTC condenser. The simulation results are the saturated temperature of the LTC evaporator -30°C, the saturation temperature of the HTC evaporator -15°C, the difference in the temperature of the pinch point between the LTC condenser and the HTC evaporator 10°C and the temperature of the HTC condenser 40°C. The highest Coefficient of Performance (COP) of the cascade cooling system with these parameters is 2.55 using a combination refrigerant R22 in HTC and R134a in LTC.

Analysis of a refrigeration system using carbon nanotubes (CNTs) lubricant and a combination of R290/R600 refrigerants

A combination of R290/R600 refrigerants with low global warming and zero ozone-depleting potential refrigerant was tested with a based lubricant and CNTs nanolubricant in a refrigeration system to improve its performance efficiency and minimise the environmental impact of refrigerants and energy demand by refrigeration systems. CNTs-nanolubricant, an alternative lubricant for the refrigeration system, was made by dispersing CNTs in the based lubricant. By connecting measuring devices at each system component, temperatures and pressures were determined. The experiment’s measured outputs were used to determine the system’s performance. When compared to a 290/600 in the based lubricant, CNTs nanolubricant showed a reduction in work input ranging from 39.8%, a shorter pulldown time, a lower evaporator temperature, an increased coefficient of performance (COP), and a higher cooling capacity of 9.1%. Therefore, the lubricant made of carbon nanotubes (CNTs) presents a viable substitute for based lubricant in a vapour compression system.

Study on drying characteristics of sludge under different conditions based on the low-temperature sludge heat pump drying model

The study established a model for a closed low-temperature heat pump drying (HPD) system and structured a sludge drying experimental platform to validate it. The effects of incoming air temperatures of the drying cabinet, circulating air volume, and ambient temperature on both drying rate and system performance were investigated. The findings revealed that the drying rate and specific moisture extraction rate (SMER) rise with higher incoming air temperatures of the drying cabinet and circulating air volume, while the coefficient of performance (COP) exhibited a contrasting trend. The sludge dried the fastest with a drying rate of 6.01 kg/h when the incoming air temperatures of the drying cabinet and circulating air volume were set to 65 °C and 900m³/h, respectively. At the incoming air temperature of the drying cabinet was 65 °C and the circulating air volume was set to 850 m3/h, the SMER reached the maximum value, 2.782kg/(kW·h). In addition, the COP increased as the ambient temperature rose, while the drying rate and SMER both decreased gradually. The drying rate demonstrated an average decline of 0.29 kg/h for every 2 °C rise in ambient temperature, while the SMER exhibited an average decrease of 0.148kg/(kW·h). These works offer guidance for the practical implementation of the sludge HPD system.

Optimizing R152a/R600 and R290/R600 mixtures for superior energy performance in vapor compression systems: Promising alternatives to Isobutane (R600a)

This study presents an experimental investigation into the optimal composition of R152a/R600 and R290/R600 mixtures as potential alternatives to isobutane (R600a) in a single-stage vapor compression cycle. The research involved testing eight different mass compositions for R152a/R600 and ten mass compositions for R290/R600, comparing their performance with that of R600a. After careful analysis, the “optimum” mass compositions were identified as (10/90)% for both R152a/R600 and R290/R600, achieving a balanced trade-off among coefficient of performance (COP), volumetric cooling capacity (VCC), and cooling output (Q̇o). Further tests were conducted on the “optimum” compositions at nine different secondary fluid temperature inlets. The results indicated an average COP increase of + 7.3 % for the R152a/R600 mixture, with decreases of −11.4 % in VCC and −9.7 % in Q̇o. Similarly, the R290/R600 (10/90)% mixture showed a COP increase of + 10.3 %, accompanied by VCC and Q̇o decreases of −8.8 % and −6.6 %, respectively. Notably, both mixtures exhibited superior energy performance compared to isobutane while maintaining similar thermodynamic properties, particularly the R290/R600 (10/90)% mixture. These findings suggest that the R152a/R600 and R290/R600 mixtures could serve as long-term, high-efficiency alternatives to R600a in vapor compression cycles.

Energy analysis of a simple PV/T system for heating using a variable speed vapor compressor system

The use of photovoltaic/thermal (PV/T) modules reduces the losses in the photovoltaic cells and, in addition, uses the waste heat in the panel. This paper presents the simulation results of a PV/T system for domestic hot water supply using a vapor compression system during the four seasons of the year in the conditions of Salamanca, Mexico. The results obtained from the simulation indicate that the cooling of the panel causes an increase of approximately 7% in PV efficiency. During the spring, when there is greater solar radiation and, therefore, greater electrical power generation, despite the average temperature of around 36 °C, the lowest efficiency is found. On the other hand, the highest efficiency is achieved in winter, reaching up to 22%. As for the performance coefficient, the highest value is observed during the spring, with a coefficient of performance (COP) of 6.63, while the lowest value is recorded in summer, with a COP of 5.11. It is concluded that this system can satisfy the domestic hot water demand for the conditions under study.

Performance investigation of solar ejector cooling system: Case study area-Addis Ababa, Ethiopia

This study investigates the performance of a solar ejector cooling system under both on-design and off-design operating conditions, focusing on the case study area of Addis Ababa, Ethiopia. Data crucial to the analysis were gathered from the Ethiopian National Meteorology Agency (ENMA) over six consecutive years (2013-2018). The system's performance was evaluated through hourly and monthly analyses under on-design conditions, yielding promising results. Under on-design conditions, the system demonstrated favorable performance metrics. Specifically, at noontime in March, when the design points were set at Tg = 90°C, Tc = 30°C, and Te= 12°C, the system achieved a total hourly maximum coefficient of performance (COP) of 0.2049 and a cooling capacity of 186.9 W/m². Furthermore, the study determined that a collector area of 22.3 m² per ton of cooling capacity is required during noontime for all cooling seasons in Addis Ababa, Ethiopia. Additionally, an off-design operating condition map was developed for the system. The findings indicate that the solar ejector cooling system can effectively provide cooling during office hours (8:00-15:00) in Addis Ababa, Ethiopia.

Optimal discharging of solar driven sorption thermal battery for building cooling applications

In this study, optimal discharge conditions of sorption thermal battery (STB) are determined for stable supply of the building cooling load based on different load patterns. Parametric analysis is conducted to ascertain the influence of heat source temperature and the mass flow rate ratio between the solution and the heat transfer fluid on the performance of the STB. The maximum values of energy storage density (ESD) and coefficient of performance (COP) are estimated as 207.73 kWh/m3 and 0.74, respectively. The daily transient behaviors of STB are examined in detail, and the optimal solution charge and the solution flow rate are quantified based on the building types (residential, hospital, hotel, and office). For a building with an air conditioning floor area of 181.63 m2, the most suitable cooling load response is observed in the hotel scenario. The minimum deviated cooling output from the building load is 8.69%. Concurrently, COP and ESD are estimated of 0.69 and 101.99 kWh/m3. This paper demonstrates the cooling load responsiveness and optimal operating point of STB based on building load pattern. Additionally, a dimensionless number is defined to generate the discharge trend and enable to predict COP and ESD.

R290 Refrigerant Performance in a Commercial Refrigerator

In this study, we investigated the impact of the environmentally friendly R290 refrigerant, which has a higher Coefficient of Performance (COP), on the operating performance of the cooling system, as an alternative to the commonly used R404A refrigerant, which has a negative effect on global warming. The boundary conditions in the refrigeration cycle were designed to be -10°C evaporation and +45°C condensation, and the performance of the system referenced in the TS EN ISO 23953-2 standard was experimentally compared for both refrigerants. The temperature and energy consumption values of the M-packs, whose location and quantity are specified in the relevant standard, have been evaluated in terms of the cooling performance of the cabinet. As a result of the study, the heat removal performance of the system using R290 fluid in the condenser showed better results compared to R404A. According to the relevant standard, the system using R290 is in the C and D classes in the energy consumption evaluation.

Improving Efficiency of Heat Pump Dryer Using R32 Refrigerant by Nanofluid

Drying process are important in many areas in the agriculture and food sectors, including increasing shelf life, improving transportability by reducing product weight or adding value to products. However, the main problem in the drying process is the relatively high energy consumption. Therefore, the development of energy-saving dryers is necessary. Based on the above reasons, this research aims to study the performance enhancement of heat pump dryers using R32 refrigerant by using heat recovery and nanofluid. The heat that is exhausted from the refrigerant by a heat exchanger. In this work, a Nano titanium dioxide (Ti2O3) was selected. Pork was dried under the conditions of drying temperature of 45, 50 and 55 °C and water flow rate in the heat exchanger at the front of the drying chamber of 2, 3 and 4 L/min. Criteria for evaluating heat pump dryer performance include drying rate, specific moisture extraction rate, specific energy consumption, heat pump dryer performance coefficient compared to heat pump dryers without nanofluid. The results showed that increasing the drying temperature and water flow rate in heat exchanger increased the drying rate, power and specific moisture extraction rate in the heat pump dryer using nanofluid. Whereas, the specific energy consumption was lower than the case without nanofluid. Increasing the drying temperature and the water flow rate in the heat exchanger had relatively little effect on the coefficient of performance (COP) of the heat pump dryer. Moreover, the study found that the coefficient of performance of heat pump dryer with nanofluid was in the range of 4.33 - 4.42.

Improving adsorption materials properties for renewable energy-driven cooling systems

Considering addressing global warming and energy crises, this work presents an alternative cooling system based on adsorption technology. The novelty of this work lies in the improvement of the adsorption properties of the commercial adsorbent AquaSorb2000 (AS2000) for the first time by a chemical method. The AS2000 is improved by mixing with ammonium carbonate and thermally treated at 500 °C in a nitrogen gas flow. The raw AS2000 and the modified (MAS2000) adsorbents were characterized by X-ray powder diffraction, FTIR spectroscopy and N2 gas adsorption/desorption techniques. It was found that the modification led to significant surface changes. Adsorption isotherms of HFC-404A gas were investigated over AS2000 and MAS2000 adsorbents. Experimental results are fitted with Dubinin–Astakhov (D-A) and Sun-Chakraborty (S-C) equations for the isotherms and linear driving force and Fickian diffusion models for the kinetics. Moreover, the performance of the two materials is investigated for adsorption cooling systems (ADSs) using transient simulation modeling. The results showed improvement in the adsorption uptake from 0.50 kgR/kgAC of AS2000 to 0.99 kgR/kgAC of MAS2000 adsorbent. At the optimum conditions of the modified sample, the ADS performance parameters estimated by 124 W/kg specific cooling power (SCP) and 0.17 of coefficient of performance (COP) improved by 63 % and 70 %, respectively, compared to using the indicated original activated carbon material.

Thermal Performance of Earth Air Heat Exchanger for Geothermal Energy Application in Hot Climate using CFD Simulation

The Ground Air Heat Exchanger (GAHE) is a sustainable, environment friendly, and efficient device that can be used for both heating and cooling applications. Careful design of GAHE enables efficient exploit of the earth interior energy. The design of a GAHE relies on the constant temperature of the earth interior which allows consistent and reliable source of geothermal energy. By harnessing this renewable energy, a sustainable solution for heating and cooling needs is attained while minimizing the impact on environment. In this study, the performance of GAHE was examined using ANSYS Fluent 19 R1 and SOLID WORK 16.0 software. The efficiency and Coefficient of Performance (COP) of the ETHE have been investigated. The effect of air flow rate and operation conditions on the outlet air temperature have been studied. GAHE is made of Polyvinyl Chloride (PVC) pipe of 0.1 m diameter, 0.005 m thickness and 18 m horizontal length. Computer simulations were carried out for five different air velocities (1, 2, 3, 4, and 5 m/s) at various operation conditions. Results show that the 18 m pipe length is adequate to attain useful air outlet temperature giving COP values between 0.5 and 1.3. The length of the horizontal part of GAHE can be further increased for air velocities between 3 and 5 m/s. Comparison between the results obtained by the CFD model and experimental work demonstrated that the CFD model is capable of producing results with acceptable accuracy. This suggests that the CFD software can accurately model the performance of the GAHE under different operation conditions. Increasing the length of the horizontal part of the GAHE can improve its COP when higher air velocities are used.

Achieving Energy Self-Sufficiency in a Dormitory Building: An Experimental Analysis of a PV–AWHP-ERV Integrated System

In this study, we investigated the performance of air-to-water heat pump (AWHP) and energy recovery ventilator (ERV) systems combined with photovoltaics (PV) to achieve the energy independence of a dormitory building and conducted an analysis of the energy independence rate and economic feasibility by using energy storage devices. Our data were collected for 5 months from July to November, and the building energy load, energy consumption, and system performance were derived by measuring the PV power generation, purchase, sales volume, AWHP inlet and outlet water temperature, and ERV outdoor, supply, and exhaust temperature. When analyzing representative days, the PV–AWHP integrated system achieved an energy efficiency ratio (EER) of 4.49 and a coefficient of performance (COP) of 2.27. Even when the generated electrical energy exceeds 100% of the electricity consumption, the energy self-sufficiency rate remains at 24% due to the imbalance between energy consumption and production. The monthly average energy self-sufficiency rate changed significantly during the measurement period, from 20.27% in November to 57.95% in September, highlighting the importance of energy storage for self-reliance. When using a 4 kWp solar power system and 4 kWh and 8 kWh batteries, the annual energy self-sufficiency rate would increase to 67.43% and 86.98%, respectively, and our economic analysis showed it would take 16.5 years and more than 20 years, respectively, to become profitable compared to the operation of an AWHP system alone.

Comparative evaluation of experimental ejector refrigeration system for different operating configurations

In this study, a comparative performance evaluation of an experimental ejector refrigeration system was conducted for various operating modes. The experimental setup was operated in different modes: conventional vapour compression refrigeration (CVCR), conventional dual-evaporator system (CDES), and dual-evaporator ejector system (DEES). The system was tested under different operating conditions, including varying condenser temperatures and mass flow rates. The results of the evaluation showed that the highest total cooling capacity and coefficient of performance (COP) were achieved in the DEES mode, while the lowest total cooling capacity was observed in the CDES mode. The lowest compressor power was calculated when the system was operated in DEES mode. When the condenser temperature was 33°C, the compressor power obtained in the DEES was 22.7%, 5.4%, and 17.7% lower than that of the CVCRA, CVCRB, and CDES modes, respectively. In conclusion, the performance of the ejector-operated system was found to be superior to the other configurations, and the ejector contributed positively to the system performance.

An Approach to Capturing Residual Energy From the Subway System: Methodological Considerations

Abstract Urban heating and cooling demands account for a significant portion of global energy consumption. It is crucial to explore new energy resources and innovative solutions to meet environmental targets. Urban infrastructures like data centers, water networks, and tunnels move and collect energy, in some cases residual energy, that is valuable because of its proximity to consumers. The novelty of this work lies in the exploration of utilizing the accumulated residual heat that is not used in subway air to improve the energy efficiency of urban areas. The work focuses on the potential use of this residual heat by the installation of heat pumps in subway platforms or tunnels. By installing a heat pump on subway platforms or tunnels, this residual heat can be efficiently utilized for heating demand or producing domestic hot water. A general methodology for assessing the performance of such air source heat pumps in the subway context is presented. The calculation of the coefficients of performance (COP) and seasonal coefficients of performance (SCOP) calculation is outlined, with a detailed example illustrating the methodology. The paper emphasizes a comparative analysis between the proposed system and a traditional heat pump using ambient air, highlighting the advantages of the proposed approach. Finally, the paper concludes with a brief analysis of the different effects of refrigerants on the system performance for the same boundary conditions. Results are promising, increasing the energy efficiency of big cities and reducing CO2 emissions.

Theoretical and experimental research on the performance of new building environment control systems based on cooling dehumidification under positive pressure

A significant amount of energy consumed by building environment control systems is used for dehumidification. However, the conventional cooling dehumidification method is energy-intensive as the low required dew-point temperature and reheating. In this paper, two different new building environment control systems based on cooling dehumidification under positive pressure are proposed, which can realize dehumidification with a natural cooling source at ambient temperature. The cooling dehumidification model under positive pressure is proposed and verified by experiments, and the errors are within ± 4.16 %. Influences of pressure ratio and cooling source temperature on system performances are analyzed by simulation. The result shows that proposed systems can achieve the dehumidified air with a humidity ratio of 8.18 g/kgDA and a temperature of 20℃, and the dehumidification energy efficiency of new systems can achieve 6.11 kg/kWh. At a cooling source temperature of 18 °C and pressure ratio of 1.6, the total dehumidification rate of the system can reach 19.49 g/s. Reheating in front of the expander can reduce the detrimental dehumidification proportion to 0 %. The coefficient of performance (COP) of the new system can reach 6.26, which is superior to other dehumidification methods.

A high-fidelity digital twin predictive modeling of air-source heat pump using FCPM-SBLS algorithm

This paper proposes an innovative Digital Twin (DT) model to predict air-source heat pumps' (ASHP) coefficient of performance (COP) using a combination of fuzzy (c + p) means clustering (FCPM) and the stacked broad learning system (SBLS) algorithm (FCPM-SBLS). The SBLS algorithm is adopted to establish the structure of the DT model, considering the imperative of tracking real-time performance changes in ASHP applications. To enhance the fitting and generalization ability of the DT model, FCPM is employed to partition the dataset into subclasses, allowing for the creation of sub-models specifically tailored to each subclass. Moreover, an incremental-full evolution strategy of the DT model is proposed to track changes in ASHP performance. The DT model's validation is conducted using data collected at a railway passenger station. Results demonstrate that the FCPM-SBLS method has commendable predictive performance, with respective mean absolute error (MAE), mean absolute percentage error (MAPE), and root mean square error (RMSE) values of 0.045, 0.012, and 0.252. Additionally, the proposed evolution strategy ensures timely updates for tracking ASHP performance changes. Through analysis of the evolution performance of DT model straddling over years, the updated model shows a 63.1% decrease in MAPE compared to the non-updated model. This study is not only conducive to advancing DT modeling in the field of HVAC systems, but also has practical significance for improving the energy efficiency and performance monitoring of ASHP.

Experimental and numerical investigation of a novel high-temperature heat pump for sensible and latent heat delivery

This paper investigates, both experimentally and numerically, the performance of a high-temperature heat pump (HTHP) prototype for steam production and thermal energy storage applications using R-1233zd(E) as a refrigerant. The main novelties of this prototype are the incorporation of an external subcooler to separate the sensible and latent heat production. Other novel points are the testing of a new variable-speed piston compressor that endures a discharge temperature of up to 160 °C, and the development of an advanced numerical model based on the components’ specifications. In this temperature range there are very few detailed studies up-to-date. The proposed HTHP was tested experimentally in 50 different working points selected based on the compressor’s limits and on the general requirements for industrial applications requiring heat at high temperatures, up to 150 °C. The results show that the proposed HTHP can deliver a total heat of 38.6 kW at 148.5 °C, within a temperature lift of 66.8 K, with an electric power consumption of 10.7 kW, and with a heating coefficient of performance (COP) of 3.6. Moreover, using the external subcooler resulted in a substantial increase in the COP, which can reach 33 % compared with similar HTHPs without a subcooler. After successfully validating the HTHP model with the experimental results, extended performance maps were developed based on more than 500 possible operating conditions covering the most common steam generation and energy storage applications. Finally, four performance correlations were obtained, with an accuracy of ±10 %, hereby providing a black-box model to ease the integration of such HTHPs into dynamic simulations of industrial processes.

Study of a Thermochemical Heat Storage Reactor Filled with Polyaluminum Sulfate for Low-Temperature Application

This paper investigates comprehensively the operational dynamics of a thermochemical heat storage (TCHS) reactor for low-temperature applications using polyaluminum sulfate and takes into consideration a developed simulation model with an experimentation validation. Significant concordances were found between the developed simulation model and the experimental results. Results reveal optimized conditions for the charging process using an electrical heater, with a heating temperature of 120°C at 10 K/min over 500 minutes. This achieves full material charging, with stabilized pressure drops at an equilibrium of 80 mbar, corresponding to a temperature of approximately 108°C, and yielding a thermal power of 950 W. An inlet vapor pressure of 18 mbar at 10°C for 5 hours is sufficient to completely discharge the bed, with pressure drops reaching around 30 mbar and a thermal power of 300 after reaction completion. Insights into conversion extents during both processes are provided, along with a remarkable thermal efficiency of 90% and a coefficient of performance (COP) of 97%, surpassing recommended theoretical values (50%). The study suggests further enhancing system performance through the design and implementation of a dedicated heat exchanger. The achievement of 75% of the targeted thermal power specification represents a significant milestone, offering valuable contributions towards the realization of sustainable technological advancements of both the reactor technology of TCHS and state-of-the-art thermal energy storage solutions. From the research, it is possible to infer further suggestions for enhancing this performance by designing and implementing a dedicated heat exchanger for both heat supply and retrieval mechanisms.