Average Coefficient Of Performance Research Articles

Energy Simulation Module Development of Evaporative Condensing Chiller Based on TRNSYS

Evaporative condensing chillers have been widely used in rail transit, data centers, communication base stations and other fields, but the simulation of evaporative condensing chillers has not yet reached the stage of engineering design and application. Therefore, based on the DOE-2 model of the general chiller, considering that the energy efficiency of the evaporative condensing chillers is related to the inlet air wet bulb temperature, it is used to replace the inlet cooling water temperature, and the evaporative condensing chillers model is established. The evaporative condensing chillers model was combined with TRNSYS to develop an evaporative condensing chillers module that includes condensing fans and cooling water pumps using C++ compilation algorithm program. This module was used to simulate a subway station in Tianjin City. The results showed that the average coefficient of performance of the evaporative condensing refrigeration system during operation was 5.68, and the average system coefficient of performance was 4.76. To our knowledge, it is the first time proposed the evaporative condensing chillers energy simulation module and related the outlet chilled water temperature and the inlet air wet bulb temperature to refrigerating capacity as well. The development of the module provides convenience for the study and optimizes evaporative condensing chillers performance.

Evaluation of the efficiency of steam compression heat pumps of the "air-water" type as part of a combined heat supply system

Every year, increasing attention is paid to the use of unconventional and renewable energy sources for heating. Promising sources of heat supply are steam compression heat pumps, for which soil, atmospheric air, groundwater, ventilation emissions, etc. are used as low-potential heat sources. Due to its accessibility, air is one of the most common sources of heat for such installations. The efficiency of air heat pumps depends significantly on climatic conditions, and in practice they are used in conjunction with an additional energy source. This study evaluates the efficiency of such a combined system using the example of a heat supply system for a residential building under various climatic conditions in Russia. The coefficient of performance (COP) of a heat pump is considered as the main indicator of its efficiency. The load on the heating system for each region was determined using the thermal balance method. The study utilized the values of the COP obtained from testing. It is established that the average annual COP of the heat pump for the considered climatic conditions ranges from 1.76 to 1.98 when operating the heat supply system with a temperature schedule of 80/60°C, and it functions effectively at this temperature schedule down to an outdoor air of no lower than – 16°C; at lower temperatures, the load is covered by an additional source. In addition, the annual energy costs for operating the heat supply system are calculated, and the distribution of this component between the heat pump (48% – 97.6%) and the additional source is determined. The feasibility of using heat pumps in non-gasified areas is determined by the electricity tariff.

Enhancing the performance of plug-in refrigerated display cabinets using R290 refrigerant and grooved tube evaporator

ABSTRACT Plug-in refrigerated display cabinets (RDCs) are widely used in supermarkets but consume a lot of energy. This study aims to increase the label class of RDCs by using a new generation microchannel condenser, a grooved evaporator, R449A, and R290 refrigerants as alternatives to R404A and implementing modifications to the system. The created systems were tested according to the ISO 23,953-2:2023 standard and characterized in detail for both eco-design and energy labeling criteria. The study showed that the heat exchange efficiency of the grooved tube evaporator was higher than that of the regular tube evaporator. However, a 30% higher pressure drop was measured for the grooved tube evaporator than for the smooth tube evaporator. Performance analysis of the developed refrigerators was performed from energy, economy, and environmental perspectives. The average coefficient of performance (COP) of the RDC was calculated as 2.4, and the second law efficiency of the RDC was determined to be 45.2%. When using the R290 + grooved evaporator combination, CO2 emissions were reduced by 22.74% per year as compared to the R404A + smooth evaporator. With an energy efficiency index (EEI) of 43.4, RDC’s energy class was upgraded from “E” to “D.” It was found that the compressor consumed 80.3% of the total energy consumption. The resistance, employed in condensation pans and accounting for 8.2% of the overall energy consumption, was discovered to be the second crucial factor affecting the energy class. The improvements and upgrades to RDC may strengthen the understanding of enhancing performance and serve as the foundation for future studies.

Blade pitching in vertical axis wind turbines: A double multiple stream tube theoretical approach to performance enhancement.

This research delves into the performance enhancement of Vertical Axis Wind Turbines (VAWTs) through the innovative approach of variable blade pitching based on Double Multiple Stream Tube theory principles. VAWTs, known for their potential in urban and low-wind environment, often face efficiency and energy yield challenges. This study addresses these challenges by proposing a novel variable blade pitching mechanism that dynamically adapts to changing wind conditions, optimizing the aerodynamic performance, and enhancing the torque and overall performance of VAWT rotor. The efficiency of two pitching models is investigated on 3-bladed NACA0015 rotors, where the blade's local angle of attack is cyclically adjusted below the stall angle to maximize the lift force and torque throughout full revolution. In Model 1, the angle of attack experiences cyclic variation as a sinusoidal function providing smooth pitching, whereas in Model 2, the peak value of angle of attack was fixed below the stall condition forming linear function. The investigation showed substantial improvement in the VAWT performance using both pitching models. The variable blade pitching strategy significantly enhances the lift-to-drag ratio and thus improving the torque output across diverse wind scenarios/tip speed ratios, demonstrating its effectiveness in maximizing the operational efficiency of VAWTs. Blade pitching model 1 and 2 were found to be effective across all lower Tip Speed Ratio (TSR) values, suggesting its robustness in variable wind conditions. A peak average coefficient of performance (Cp) of 0.568 was achieved at TSR=5 using pitching Model 1 with a maximum angle of attack of 8.5°, compared to a Cp of 0.48 for the fixed blade configuration, near to Betz's limit (Cp=0.593). The findings confirm that integrating variable blade pitching would substantially improve VAWT performance and offer a clear direction for revolutionary future wind turbine aerodynamic design enhancements.

Performance Evaluation of a Solar Assisted Dual Condenser Heat Pump System for Drying of Pandan Leaves (Pandanus Amaryllifolius)

The solar-assisted heat pump drying (SAHPD) system uniquely incorporates solar-heating refrigerant through hot water from solar evacuated tubes, offering distinct advantages. This study analyzed three experimental setups: a heat pump dryer (HPD) without solar assistance, SAHPD configuration 1 (C1-SAHPD) with solar-heated refrigerant at the discharge line, and SAHPD configuration 2 (C2-SAHPD) with solar-heated refrigerant between condensers, both for performance and economic viability. The experiments maintained consistent parameters, including 5.5 kg of Pandan leaf (Pandanus amaryllifolius), an airflow rate of 0.135 kg/s, and a refrigerant operating pressure of 9.65 bar. The SAHPDs operated when the hot water temperature in the storage tank reached between 70°C and 90°C, with a daily average radiation intensity ranging from 0.670 to 1.102 kW/m² for heating the water. The study revealed average coefficients of performance (COP<sub>avg</sub>) of 5.34, 5.43, and 6.53 for HPD, C1-SAHPD, and C2-SAHPD, respectively. The specific moisture extraction rate (SMER) for HPD was 2.64, while C1-SAHPD and C2-SAHPD had SMERs of 1.88 and 2.71 at solar fractions of 0.34 and 0.45, respectively. Notably, C2-SAHPD reduced electricity consumption by 46%. The payback period for drying 11 kg of Pandan leaves per day was 4.56 months for HPD, 4.32 months for C1-SAHPD, and 3.84 months for C2-SAHPD. The study concluded that C2-SAHPD was the most efficient dryer system for Pandan leaves based on its higher efficiency, SMER, and cost recovery. Additionally, the performance optimization presented in this study contributed to developing a novel technique for classifying dryer technologies.

Combined Solar Air Source Heat Pump and Ground Pipe Heating System for Chinese Assembled Solar Greenhouses in Gobi Desert Region

Chinese Assembled Solar Greenhouses (CASGs) in the Gobi Desert region face significant diurnal temperature variations, with excessively high temperatures during the day and low temperatures at night, which adversely affect crop growth. Traditional temperature regulation technologies are hindered by high energy consumption, high costs, and severe pollutants. To address these issues, this study designed a heating system suitable for CASGs in the Gobi Desert region, integrating solar air source heat pump technology with underground pipe systems. The power consumption and performance of the system were assessed by comparing temperature and humidity in an experimental greenhouse (with the system), a control greenhouse (without the system), and outdoor environments under various typical climate conditions. The results indicated that the system exhibited excellent performance in both daytime heat absorption and nighttime heat release. Specifically, during operation, the maximum daytime temperature in the experimental greenhouse was reduced by up to 5 °C, while the minimum nighttime temperature increased by up to 8 °C, effectively preventing crop frost damage. The system achieved heat absorption rates of 14 to 16 KJ s−1 and heat release rates of 36.5 to 37.5 KJ s−1, with average coefficients of performance (COP) of 4.33 and 4.81. Compared to traditional heating methods using coal, gas, and electricity, the system reduced energy consumption by 84.7%, 81.3%, and 79.1%, respectively, and decreased greenhouse gas emissions by 8.24 t, 6.52 t, and 5.67 t, respectively. This system exhibits outstanding thermal efficiency, energy savings, and environmental benefits, while also showing promising economic benefits with a payback period of four years, providing a reliable heating solution for CASGs in the Gobi Desert region.

Comparative study on a solar-assisted ground source heat pump with CPC solar collector and phase change heat storage

Comparative study on a solar-assisted ground source heat pump with CPC solar collector and phase change heat storage

Thermodynamic analysis of a solar-fed heat upgrade system using the reverse air brayton cycle

Thermodynamic analysis of a solar-fed heat upgrade system using the reverse air brayton cycle

Study and optimization of the influence of the water tank temperature on the performance of a solar assisted multi-source heat pump drying system

Study and optimization of the influence of the water tank temperature on the performance of a solar assisted multi-source heat pump drying system

Numerical simulation and experimental study of medium and deep ground source heat pump system in a cold and arid region

Numerical simulation and experimental study of medium and deep ground source heat pump system in a cold and arid region

A quasi-two-stage trans-critical CO2 heat pump with in-cycle thermal storage for performance enhancement

A quasi-two-stage trans-critical CO2 heat pump with in-cycle thermal storage for performance enhancement

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

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

Analysis of Chiller Machine Energy Efficiency in the Paint Shop Air Handling Unit (AHU) Process

Abstract The Energy Efficiency in Industrial, Commercial, and Public Sector (EINCOPS) program is the result of a collaboration between the Indonesian Ministry of Energy and Mineral Resources and Danida (Danish International Development Assistance), which began in 2008 to support Indonesian government policies in achieving development goals in the field of sustainable environmental management. Energy users have gradually adopted energy efficiency measures in the industrial, commercial, and public sectors, starting with a large class. This research aims to obtain the optimal temperature range for using a chiller machine so that it continues to run efficiently. The method used is to calculate the coefficient of performance and energy efficiency ratio of each chiller when it is used. The number of chillers can be affected by the temperature range of the air handling unit (AHU), which uses wind from the environment as the main source for processing, and the temperature range is linear with weather conditions. This research found that in the environmental temperature range of 26°–29° Celsius taken by AHU for distribution to production areas, chiller performance is still not optimal. In the previous operation, three chillers were used out of the four available units, so after knowing the results of the chiller load analysis in this temperature range were still below standard or not optimal, the number of chillers could be reduced from three units full time to only two units when the temperature environment was in the range of 26°–29° Celsius. The results of calculating the average Coefficient of Performance and Efficiency Energy Ratio using two chillers when the temperature range of 26°–29° Celsius is still included in the standard, namely by increasing 0.15, the pre-improvement value is 5,833, and the chiller efficiency load increases to 14 percent.

Experimental performance comparison of various expansion devices for small-capacity subcritical R744 vapour-compression refrigeration units

The target of this study is to experimentally compare the performance of three different expansion devices for small-capacity subcritical R744 vapour-compression refrigeration units. The first considered expansion device was the conventional high-pressure expansion valve, which was selected as the baseline. The second assessed expansion device was a two-phase ejector for expansion work recovery whose refrigerant flow was modulated via the pulse-width modulation (PWM) strategy. Finally, the PWM approach was employed for controlling the refrigerant flow of the ejector motive nozzle while the refrigerant was not permitted to be drawn by the ejector suction nozzle. The results showed that the motive nozzle controlled via PWM effect offers similar effectiveness to a conventional high-pressure expansion valve in the subcritical regime. Furthermore, it was observed that the PWM ejector is able to control the high pressure effectively while increasing the coefficient of performance (COP) by up to 5.3 % without and by up to 7.9 % with overfed evaporator compared to the baseline in the transition regime. The results also showed that the installation of the conventional high-pressure expansion valve is not necessary. Finally, the yearly performance of the aforementioned expansion devices was assessed in five different locations, i.e., Athens (Greece), Phoenix (USA), New Delhi (India), Riyadh (Saudi Arabia) and Bangkok (Thailand). The outcomes revealed that the PWM ejector allows for a higher in yearly average COP (COPyearly avg) from 4.9 % (in Athens) to 11.8 % (in Bangkok) over the baseline.

Evaluation of a solar-driven adsorption desalination system for Brazilian semiarid region

In this study, the effect of using a hybrid solar thermal-activated adsorption desalination system for brackish water is evaluated under the climatic conditions of the Brazilian semiarid region. The proposed theoretical model utilizes climatic data from the meteorological station in Campina Grande, PB, and adsorptive kinetics data of Fuji Davison RD 260 silica gel to predict the performance indices of the specific daily water production (SDWP), specific cooling power (SCP), and coefficient of performance (COP) performance coefficients over a characteristic day. The SDWP value of 6.26 m3/ton, SCP ranging from 50 to 300 W/kg, and an average COP of 0.5 were obtained, considering variations in global horizontal irradiance in the ACDS system and transient ambient temperature. It was observed that both the production of desalinated water and the refrigeration effect increase with the rise in daily solar irradiance. The variation in the number of solar collectors used in the system and their optimality, as well as the variation in the salinity index of the feed source, impacted the evaluated performance coefficients.

CFD-based shape optimization of flashing converging-diverging nozzles in pelton turbines for domestic carbon dioxide heat pumps including off-design conditions

A path to enhance the coefficient of performance (COP) of domestic heat pumps is to replace the throttling valve with a turboexpander. Designing this component requires addressing supersonic flashing flows localized within the nozzle. In particular, two-phase flows prevent the application of the method of characteristics to design efficient converging–diverging shapes. To overcome this issue, we propose a shape optimization combined with a homogeneous equilibrium flow model as a design tool. Kriging models are used as surrogates of the objective function and constraint to reduce the overall computational burden associated with shape optimization. The infilling criterion to improve surrogate accuracy involves the maximization of the constrained expected improvement. A multi-point optimization is formulated, including design and off-design conditions in both objective and constraint, for a total of four relevant operating conditions. The off-design conditions are derived from system analysis, accounting for variations in the evaporator temperature and outlet gas-cooler temperature. The optimized nozzle results in a COP improvement of 7.6%, compared to a 6.6% increase when replacing the throttling valve with a baseline geometry designed as recommended by the literature. The adoption of a multi-point optimization strategy ensures that this enhancement in design conditions is not offset by off-design performance decay, which is 0.3 percentage points over the three off-design conditions. Overall, replacing the throttling valve with the optimized expander leads to an average COP improvement of 8.6%.

Experimental investigation of a new defrosting technique for sustainable refrigeration system

Experimental investigation of a new defrosting technique for sustainable refrigeration system

Simulation study on thermal performance of solar coupled air source heat pump system with phase change heat storage in cold regions

Simulation study on thermal performance of solar coupled air source heat pump system with phase change heat storage in cold regions

Feasibility investigation on a novel data center cooling system based on cross-seasonal soil cool storage in severe cold area

Feasibility investigation on a novel data center cooling system based on cross-seasonal soil cool storage in severe cold area

Thermodynamic characteristics of a novel solar single and double effect absorption refrigeration cycle

Thermodynamic characteristics of a novel solar single and double effect absorption refrigeration cycle