Coefficient Of Performance Values Research Articles

Control strategy calibration of a direct-expansion solar-assisted heat pump

As known, the performance of a direct-expansion solar-assisted heat pump (DX-SAHP) is affected by environmental and operational parameters significantly, and the variable capacity system has distinct advantages. The calibration of the control strategy will be very useful for the thermal performance improvement of DX-SAHP systems. Based on the test rig which is used to supply domestic hot water, the original variable capacity control strategy has been calibrated with the quasi-dynamic mathematical model under different conditions. The calibration results show that the optimum range of the degree of superheat is 7–12 °C. For winter and spring/autumn conditions, the optimum range of operation duration are 360–420 min and 300–360 min, and the corresponding optimum range of average compressor speed are 3750–4500 r·min−1 and 2750–3750 r·min−1, respectively. Experiments prove that the actual operation parameters can be maintained at the optimum range well and the average coefficient of performance (COPm) during the whole heating process has been improved further. For winter and spring/autumn, the average operation duration and compressor speed are 395 min and 3970 r·min−1, 345 min and 3066 r·min−1, respectively. Moreover, the values of COPm could reach 3.44 and 4.67, respectively. Even at solar radiation intensity of 577.6 W·m−2 with ambient temperature of −9.1 °C, the COPm could reach 2.38.

Performance analysis of the temperature-upgraded flash-driven low-temperature advanced natural circulation heating reactor system

To address the current deficiencies in outlet temperature and thermal power of low-temperature heating reactors while ensuring safety and economic viability, this study introduces the Temperature-Upgraded Flash-driven Low-temperature Advanced Natural Circulation Heating Reactor (TU-FLANC). The FLANC system innovatively utilizes the flashing phenomenon of the coolant in the rising channel to significantly increase the coolant circulation flow rate and thus enhance thermal power at atmospheric pressure. The TU system employs an Absorption Heat Pump (AHP) to upgrade the temperature of the reactor’s output heat. The two systems are interconnected via a Coupled System Heat Exchanger (CSHEX), achieving an upgrade in reactor thermal power and outlet temperature at atmospheric pressure. To evaluate the performance of the TU-FLANC system, a mathematical model of the system was established, and a computational program was developed. The impact of key parameters such as evaporator temperature, condenser temperature, and solution concentration on system performance was analyzed. The results indicate that the evaporator temperature and solution concentration have the most significant impact on the system’s coefficient of performance (COP) and the coefficient of performance considering pump work (COPW). Through Differential Evolution (DE) algorithm optimization, the optimal solution concentration combinations were determined to maximize COP and COPW under different temperature upgrade demands. For a temperature upgrade demand of 50 °C, the optimal solution concentration combinations are 40.02 % and 57.48 %, with corresponding COP and COPW values of 0.5282 and 0.4886, respectively. The research findings highlight the significant innovative potential of the TU-FLANC system in enhancing heat power and outlet temperature.

Novel MOF-303/G coated wire-finned heat exchanger for dehumidification applications–Experimental investigation

Adsorption dehumidification outperforms other technologies regarding moisture removal rate, lower energy consumption, and environmental friendliness. The selection of desiccant material, the heat exchanger used, and the method of regeneration significantly impact the performance of desiccant dehumidifiers in terms of water vapour removal rate and energy consumption. Metal-organic framework materials are a new class of microporous materials with high water adsorption characteristics compared to conventional desiccants like silica gel. In this work, a novel MOF-coated electrically heated wire finned heat exchanger was developed, and its performance was experimentally investigated. Wire-finned tubes coated with MOF-303/G outperformed other wire-finned tubes coated with Aluminium fumarate, MIL-100(Fe), MIL-100(Fe)/G, MOF-801 and MOF-801/G, achieving water uptake of 22 %. Also, the addition of graphene nanoplatelets during the synthesis of MOF-303 resulted in a significant enhancement of its thermal diffusivity to reach 0.184–0.23 mm2/s at temperatures ranging between 25 °C and 115 °C. The Coefficient of Performance (COP) for the developed multi-tube MOF-303/G coated heat exchanger was experimentally tested and compared to other desiccant-coated heat exchangers. Results showed that COP values ranging from 0.6264 to 1.02 to 1.2 at the regeneration temperatures of 45 °C, 60 °C and 70 °C, respectively, were achieved, which are higher than those reported in the literature.

Thermodynamic study of zeolite and graphene nanoplatelet-based composites for adsorption cooling systems

The consolidated composite adsorbents containing AQSOA-Z02 zeolite and graphene nanoplatelets (GNPs), recently developed and exhibiting excellent thermophysical and water adsorption characteristics, are found to overcome the above-mentioned limiting factors. However, rigorous thermodynamic analysis has not yet been studied, which is crucial in the simulation of adsorption characteristics, system design, and ACS analysis. Therefore, this study aims to conduct a rigorous thermodynamic investigation and the assessment of performance parameters for various AQSOA-Z02 – GNPs–based composite/water pairs. In the thermodynamic analysis, the heat of adsorption (Qst) and the adsorbed phase-specific heat capacity (cp,a) are investigated theoretically. The study reveals that Qst decreases with adsorption uptake, while cp,a exhibits the opposite trend. The incorporation of H25-GNPs into zeolite leads to a reduction in both Qst and cp,a, contributing favorably to the design of an energy-efficient ACS. Additionally, the performance parameters such as specific cooling effect (SCE) and coefficient of performance (COP) are theoretically investigated with variations in desorption and evaporation temperatures. Both SCE and COP increase with evaporation and desorption temperatures. The composite containing 90 wt% AQSOA-Z02 and 10 wt% H25-GNPs exhibit the maximum COP value of 0.351 and the maximum volumetric cooling effect of 581.621 MJ m−3, which are almost 20% and 41% improvement over parent AQSOA-Z02 zeolite, respectively. All the findings of this study will greatly assist in the design of an energy-saving and eco-friendly adsorption cooling system.

Advancing sustainable cooling: Performance analysis of a solar-driven thermoelectric refrigeration system for eco-friendly solutions

The solar-powered thermoelectric refrigerator (SPTR) is an innovative approach that uses solar energy to cool spaces. Its effectiveness relies on solar insolation rates and an intelligent dual-axis solar tracking system (STS) that maximizes solar energy capture. Performance analysis of SPTR with the fixed panel solar system (WST) and dual-axis STS by keeping the SPTR at a standard ambient temperature of 25 °C was carried out under local climate conditions. The experimental test setup includes a thermoelectric refrigerator (TER), thermoelectric module (TEM), solar panels, and STS. The experimental findings showed that the coefficient of performance (COP) of SPTR depends on the solar irradiance, the system's input power, the surface temperature of the solar panels, and the cooling rate. The maximum and minimum values of COPs were 1.19 and 0.27 for directly coupled SPTR with a WST and 2.07 and 0.39 for STS, respectively. Compared with the stand-still solar system, a COP enhancement of 44–75 % is achieved. The results also show that the cooling load is a function of the refrigerated space, and the products are to be cooled, which is affected by the thermoelectric properties of the TEM. The cooling rate is recorded at its maximum when the system is operated using an STS on a clear sunny day with a maximum solar insolation rate. The SPTR has proven to be environmentally friendly, the best alternative to conventional cooling systems, and sustainable due to the independence of traditional energy resources.

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.

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.

Efficient cooling system design by using different shaped nanoparticles and rotating cylinders in channel system for photovoltaic thermal management

Research focusing on improving the efficiency and performance of renewable energy systems requires the development of cooling systems (CSs) with effective solutions, including photovoltaic (PV) thermal management. The current work proposes a unique cooling method that uses double rotating cylinders (RCs) and different shaped alumina nanoparticles (NP; spherical, blade, brick, and cylindrical) in water for conductive panel’s cooling channel. The numerical study is performed for different values of Reynolds number (Re: 100–600), rotational Re (Rew: 0–20), size of the cylinders (Rc: 0.01H–0.2H), and solid particle volume fractions (svf: 0–0.03). It is observed that vortex size and numbers behind the cylinders can be controlled by varying Re and Rew. A 16 °C temperature drop of the panel is achieved at the highest Re at svf = 0.03. When rotations are active, the average Nu increases 99% and 37% for water and nanofluid (NF) at Rew = 20 and Re = 250 while temperature drops of 15 °C and 7.5 °C are obtained. The highest performance coefficient (PEC) is obtained as PEC = 1.38 when NF is used at Rew = 15. Large cylinders results in lower PEC values. When rotations are not active, the average Nu rises by about 26.8%, 13.5%, 12.8%, and 3.5% for cylindrical, blade, brick, and spherical-shaped particles while average cell temperature drops by about 5.5 °C, 4.5 °C, 4.3 °C, and 1 °C. The highest PEC value is obtained as 1.23 when cylindrical particles at the highest loading are used for stationary cylinders. Proper orthogonal-based model is considered for estimation of spatially varying panel temperature.

Enhancement of an air conditioning system performance utilizing a PCM-based heat exchanger: Impact of aspect ratio

This research emphasizes enhancing air conditioning (AC) system performance through the integration of a phase change material (PCM)-based annulus heat exchanger (HEX) within the condenser unit. The present study delves into how aspect ratio (AR), inlet velocities, and inlet air temperature impact the coefficient of performance (COP) and melting rate. Moreover, it considers the variable specific heat of the PCM, a less-explored aspect in AC-integrated PCM systems. Results have revealed that the AR notably affects the complete melting time. Specifically, an increase in the AR from 15 to 21 has led to a noteworthy reduction of 30.07% in the total melting time under fixed velocity conditions at 2.55 m/sec and θ = 0.429. The present study has also established a correlation to demonstrate how total melting time is influenced by AR, inlet air temperature, and inlet velocity. Also, modifying AR and inlet velocity to the HEX could lead to lower outlet temperatures from the HEX. Initially, at a given velocity of 2.55 m/sec and θ of 0.429, increasing the AR from 15 to 18 leads to a 1.61% decrease in the outlet air temperature from the HEX, while increasing AR from 15 to 21 results in a 3.12% decrement. PCM-enhanced AC systems consistently exhibit improved COP values, especially in low-velocity scenarios, outperforming systems without PCM. At the onset of melting, for a given velocity of 2.55 m/sec and θ of 0.429, the percentage increase in the COP for the altered system compared to a system without the PCM is found to be 11.28%, 12.84%, and 14.01% for ARs of 15, 18, and 21, respectively. Configurations with higher ARs are found to be more suitable for higher cooling loads with shorter working periods.

Thermodynamic analysis of adsorption cooling system using composite halide salts

AbstractIn the development of an adsorption cooling system, it has been observed that halide composites exhibit less hysteresis than pure halide salts. Therefore, it is important to thermodynamically analyze the composite salt‐based adsorption cooling system (ACS) to understand its performance. In this study, we conduct a thermodynamic first‐law and second‐law analysis of ACS using reactive salts such as BaCl2, BaCl2‐ENG, CaCl2‐ENG, SrCl2‐ENG, and MnCl2‐ENG, with ammonia as the refrigerant. We compared the coefficient of performance (COP) with that of a pure halide salt‐based ACS. The theoretical COP of the ACS at a mass ratio of 4 is estimated as 0.45, 0.4, 0.27, 0.37, and 0.22, and the second‐law efficiency is estimated as 44.28%, 38.76%, 20.71%, 16.26%, and 6.92% for BaCl2, BaCl2‐ENG, CaCl2‐ENG, SrCl2‐ENG, and MnCl2‐ENG reactive salts, respectively. Among the different salts, BaCl2 shows the highest COP. However, the COP values are lower than the maximum theoretical coefficient of performance (COPmax) due to the sensible mass of the reactor, and COP values decrease with an increase in the mass ratio due to an increase in sensible mass. It is noteworthy that the COP of the pure salt‐based ACS is higher than that of the composite salt‐based ACS because the ammonia uptake of pure salt is greater than that of the composite salt.

Operating characteristics and evaluation of air source heat pumps in cold regions during heating season in China

The mismatch between the actual heat production of an air source heat pump (ASHP) and the instantaneous load of the building it heats is a critical cause of low energy efficiency. Research on the measured heating effect provides an effective approach to improve the energy efficiency of an ASHP. This study therefore focused on two small office buildings to explore the operating data describing the ASHP system source and load sides during the heating season. A sensitivity analysis was employed to explore the actual operational effects of the ASHP. Common problems associated with system operation were comprehensively identified, including the operation characteristics, energy efficiency coefficients, load characteristics, and energy consumption characteristics of the transmission and distribution systems. The effects of these problems were evaluated from three perspectives: integrated part load value (IPLV), system performance loss, and indoor environmental parameters. The results shows that the highest coefficient of performance (COP) of the ASHP in Building A was 3.27 while the IPLV was 2.68, operating status reached the standard. The COP value of the ASHP in Building B was 1.55 while the IPLV was 2.45. Poor value shows the low performance in operating phase, which can be further optimised by matching the building instantaneous load to the heat production of the ASHP, improves the operating effect of two buildings comprehensively.

Thermodynamic analysis of a solar-driven vapor compression refrigeration system using R1234ze for cooling applications in Ghardaïa region (Southern Algeria)

This study presents a thermodynamic analysis of a solar-driven vapor compression refrigera-tion (VCR) system designed for use in the region of Ghardaïa (Southern Algeria) which is lo-cated in a desert with a semi-arid climate where the demand for cooling is high, and the solar radiation is abundant. Two working fluids are tested and compared, the HFC high GWP going to phased out, R134a and the low GWP, HFO refrigerant recently introduced R1234ze. The performance of the solar VCR system was evaluated using a numerical model developed in MATLAB software, based on thermodynamic properties of R1234ze and R134a refrigerants. The results showed that coefficient of performance (COP) and thermodynamic efficiency of the solar VCR system increased with decreasing ambient temperature due to the increase in the compressor power consumption. The COP during the 21st day of July month is obtained in the range of 4.37–5.77 for R1234ze refrigerant which are close and more than 90% of the maximum COP value, while it is in the range of 2.56–3.17 for R134a fluid. The lowest COP values are found around noon hours during 12:00 AM and 15:00 PM. In addition, the greatest amount of the PV power production for R134a and R1234ze refrigerants occurs in the middle of the day (12:00 PM) as 2.8 and 1.6 kWh, respectively.

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.

Research on geothermal-driven single-effect absorption refrigeration systems with different working fluids: energy and exergy analysis

Abstract Geothermal energy is not only environmentally friendly and has low carbon but also represents a nonintermittent technology. It is anticipated that its utilization in human society will experience rapid growth in the coming decades. Absorption refrigeration can be employed for the recovery of geothermal resources. However, the low performance of absorption refrigeration systems has hindered their development. In order to advance absorption refrigeration technology suitable for geothermal energy recovery, this study developed a mathematical model for an absorption refrigeration system using 55% lithium bromide (LiBr) and 35% lithium chloride (LiCl) solutions as working fluids. The impact of various parameters, including cooling water conditions, chilled water conditions, heat source parameters, and working fluid concentration, on the thermodynamic performance, system efficiency, and exergy efficiency of a single-effect absorption refrigeration system was analyzed. The results reveal that the cooling water inlet temperature and flow, chilled water inlet temperature, heat source inlet temperature, and working fluid concentration are the primary factors affecting the thermodynamic performance and exergy efficiency of the absorption refrigeration system. The coefficient of performance (COP) of the system increases with higher cooling water flow, chilled water inlet temperature, and working fluid concentration, but decreases with higher cooling water inlet temperature. Within a certain temperature range, the COP increases with higher heat source temperature. The effective COP (ECOP) increases with higher cooling water inlet temperature, cooling water flow, chilled water inlet temperature, and working fluid concentration, while it decreases with higher heat source temperature. The highest COP values for the LiBr and LiCl solution single-effect absorption refrigeration systems are 0.795 and 0.785, respectively, while the highest ECOP values are 0.694 and 0.684, respectively.

Dynamic simulation of a novel liquid desiccant air-conditioning system for greenhouse cooling and water recovery

We present dynamic, hour-by-hour modelling of a multi-stage nanofiltration regeneration system for liquid desiccant air-conditioning (NF-LDAC) of horticultural greenhouses in 17 locations covering four climate types. Four technologies are compared: fan ventilation, evaporative cooling (EvapC), conventional air-conditioning (AC), and NF-LDAC. The comparison is based on acceptable conditions for cultivation and coefficient of performance (COP). On average, fan ventilation and EvapC achieve acceptable conditions for 2 months per year, compared to 5.4 and 10.5 months for AC and NF-LDAC respectively. The highest COP value of 7.6 for NF-LDAC is reached at Colombo (Sri Lanka), followed by 5.3 at Mecca (Saudi Arabia). The permeate of the multi-stage regenerator can be recycled for irrigation, providing water savings. The highest water saving of 63% is at Mecca. These results are inferior but more realistic than those from an earlier idealised and steady-state model, which predicted a COP of 12.4 and water savings of 100% at Mecca. Nevertheless, in hot desert climates, NF-LDAC maintains acceptable conditions for year-round cultivation and saves water that is scarce in such climates. Future advances in nanofiltration membrane fabrication could increase the COP of NF-LDAC to 12.1 at Colombo and 7.4 at Mecca.

Tunable Low-Pressure Water Adsorption in Stable Multivariate Metal-Organic Frameworks for Boosting Water-Based Ultralow-Temperature-Driven Refrigeration.

The green water-based adsorption refrigeration is considered as a promising strategy to realize near-zero-carbon cooling applications. Although many metal-organic frameworks (MOFs) have been developed as water adsorbents, their cooling performance are commonly limited by the insufficient water uptakes below P/P0 = 0.2. Herein, the development of multivariate MOFs (MTV-MOFs) is reported to highly modulate and boost the low-pressure water uptake for improving coefficient of performance (COP) for refrigeration. Through ligand exchange in the pristine MIL-125-NH2 , a series of MTV-MOFs with bare nitrogen sites are designed and synthesized. The resulting MIL-125-NH2 /MD-5% exhibits the significantly improved water uptake of 0.39g g-1 at 298 K and P/P0 = 0.2, which is three times higher than MIL-125-NH2 (0.12g g-1 ) and comparable to some benchmark materials including KMF-1 (0.4g g-1 ) and MIP-200 (0.36g g-1 ). Combined with its low-temperature regeneration, fast sorption kinetics and high stability, MIL-125-NH2 /MD-5% achieves one of the highest COP values (0.8) and working capacities (0.24g g-1 ) for refrig-2 under an ultralow-driven temperature of 65°C, which are higher than some best-performing MOFs such as MIP-200 (0.74 and 0.11g g-1 ) and KMF-2 (0.62 and 0.16g g-1 ), making it among the best adsorbents for efficient ultralow-temperature-driven refrigeration.

A validated model for variable-speed multi-chillers to assess different operation modes

Environmental protection drives the replacement of environmentally harmful refrigerants with potentially flammable alternatives, necessitating efficient cooling strategies for varying loads. Legislation limits flammable refrigerant charge, leading to the adoption of multi-chiller systems with smaller charges and therefore also smaller loads per chiller. However, operating such systems requires complex strategies, addressable through fast and reliable models. This study presents a semi-empirical model predicting the behaviour of variable-speed multi-chiller systems. The model focuses on predicting cooling capacity and coefficient of performance (COP) for cooling, with input parameters of evaporation and condensation temperatures, and compressor speed. Experimental validation of the parameterized model shows COP predictions within 3 % for a two-module system using R-290 (propane) under different conditions and compressor speeds. The model assesses various operation strategies, including the conventional mode with fewer chiller modules running at high speed, compared to modes where all chillers run but at reduced speeds. Comparing COP values in these modes reveals energy-saving potentials of up to 14.57 % for constant condensation temperatures. Moreover, strategies involving condensation temperature reduction, or a combination with compressor speed reduction are analysed for energy-saving potentials. Reducing the condensation temperature by 3 K results in savings of up to 13.25 % and combined with the compressor speed reduction savings of up to 23.54 % are feasible. These findings emphasize the importance of considering compressor speed when operating multi-chiller systems to maximize energy savings. The presented model effectively evaluates various strategies and implements variable-load control in multi-chiller systems, serving as a valuable tool for optimising energy efficiency and promoting environmentally friendly cooling practices.

Investigating New Environmentally Friendly Zeotropic Refrigerants as Possible Replacements for Carbon Dioxide (CO2) in Car Air Conditioners

The widespread use of automobiles and the increased duration spent within automobiles equipped with air conditioning systems have prompted various countries to enforce regulations that advocate for eco-friendly cooling substances (refrigerants) characterized by a slight global warming potential (GWP) and the absence of an ozone depletion potential (ODP). The imperative for automobiles to possess air conditioning systems that are both high-performing and eco-conscious has emerged as a means to mitigate their ecological impact, reduce fuel usage, and minimize carbon emissions. Zeotropic refrigerants, with a lower GWP than traditional alternatives, contribute to sustainability in car air conditioning by reducing the environmental impact and enhancing the energy efficiency, aligning with global regulations and fostering innovation in the automotive industry. This shift signifies a commitment to mitigating climate change and adopting environmentally conscious practices. The objective of the present study is to introduce blends of zeotropic refrigerants based on CO2 (R-744), namely R455A (a blend of R-744, R-32, and R-1234yf), R469A (a blend of R-744, R-32, and R-125), and R472A (a blend of R-744, R-32, and R-134a), to enhance the thermodynamic performance of pure CO2 refrigerant. Through the utilization of the Aspen HYSYS V11 software, an investigation is carried out involving thermodynamic energy and exergy analyses, as well as system optimization for an automotive air conditioning (AAC) system utilizing these novel zeotropic refrigerant blends, in comparison with the use of R-744 as the refrigerant. The study delves into the impact of parameters such as average evaporator temperature, condenser/cooler pressure, refrigerant flow rate, and condenser/cooler outlet temperature on AACs’ output parameters and subsequently presents the findings. The outcomes reveal that, under equivalent operational circumstances, the adoption of R455A, R469A, and R472A offers improvements in coefficient of performance (COP) by 35.4%, 18.75%, and 2%, respectively, when compared to R744. This shift is advantageous as it mitigates leakage-related issues stemming from the elevated operational pressure of R744 and eliminates the need for cumbersome equipment. R455A and R469A obtain the greatest COP and exergy efficiency (ηex) values, measuring 4.44 and 4.55, respectively, at the identical operating conditions with optimal condenser/cooler pressures of the examined blends. Furthermore, eco-friendly refrigerants R455A and R472A are recommended for integration into AAC systems in vehicles, as they help combat global warming and protect natural surroundings and leakage issues.

Research on heat pump air conditioner compressor speed control strategy based on whale algorithm

Accurate control of compressor speed is crucial for enhancing the heating performance of heat pump air conditioning systems and extending the driving range of electric vehicles. Based on traditional PID control and fuzzy PID control strategies, a control system utilizing the WOA-PID (Whale Optimization Algorithm)fuzzy control strategy is proposed to regulate the compressor speed and achieve optimal passenger compartment temperature control.The results demonstrate that, compared to traditional PID control and fuzzy PID control, the WOA-PID fuzzy control strategy results in significantly reduced overshooting of the passenger compartment temperature, as well as increased COP (Coefficient Of Performance)values. Specifically, when the target temperature is set at 18 °C, the WOA-PID fuzzy control strategy achieves a temperature overshoot amount of only 0.01 °C, and increases the COP by 0.10 and 0.01 compared to traditional PID control and fuzzy PID control, respectively. Similarly, when the target temperature is set at 25 °C, the WOA-PID fuzzy control strategy achieves a temperature overshoot amount of only 0.08 °C, and increases the COP by 0.14 and 0.07 compared to traditional PID control and fuzzy PID control, respectively. These improvements optimize the maximum overshooting amount and adjustment time of the passenger compartment temperature, effectively enhancing the heating performance of the system.

Thermal analysis of operating a solar-powered diffusion absorption refrigerator with a parabolic collector

This study investigates the use of solar energy, one of the leading renewable energy sources, to power a diffusion absorption refrigerator, thereby demonstrating the feasibility and practicality of renewable energy applications without relying on electrical energy or fossil fuels. Two mini refrigerators with identical power and features were employed in the experimental study. The aim is to evaluate the performance of two refrigerators, one powered by electricity and the other by heat from a parabolic solar collector. The heat transfer oil circulating in the parabolic solar collector was transferred to the generator of the solar refrigerator through a special apparatus. Various parameters such as mass flow rates, system pressure, solution concentrations, and thermal and COP values of diffusion refrigerators were meticulously analyzed. Experimental results obtained from both refrigerators were compared for a comprehensive evaluation. While the Coefficient of Performance (COP) of the electric refrigerator was determined as 0.398, the COP value of the solar refrigerator was determined as 0.380. These findings highlight the potential of solar energy in sustainable cooling applications and provide valuable information on comparing electric and solar cooling systems. The study contributes to the ongoing efforts to promote eco-friendly and energy-efficient technologies, emphasizing the role of solar energy in reducing dependence on traditional energy sources.