Comparison Of Energy Efficiency Research Articles

Assessing the Economic and Environmental Dimensions of Large-Scale Energy-Efficient Renovation Decisions in District-Heated Multifamily Buildings from Both the Building and Urban Energy System Perspectives

The European Union (EU) has introduced a range of policies to promote energy efficiency, including setting specific targets for energy-efficient renovations across the EU building stock. This study provides a comprehensive environmental and economic assessment of energy-efficient renovation scenarios in a large-scale multifamily building project that is district-heated, considering both the building and the broader urban energy system. A systematic framework was developed for this assessment and applied to a real case in Sweden, where emission factors from energy production are significantly lower than the EU average: 114 g CO2e/kWh for district heating and 37 g CO2e/kWh for electricity. The project involved the renovation of four similar district-heated multifamily buildings with comparable energy efficiency measures. The primary distinction between the measures lies in the type of HVAC system installed: (1) exhaust ventilation with air pressure control, (2) mechanical ventilation with heat recovery, (3) exhaust ventilation with an exhaust air heat pump, and (4) exhaust ventilation with an exhaust air heat pump combined with photovoltaic (PV) panels. The study’s findings show that the building with an exhaust air heat pump which operates intermittently with PV panels achieves the best environmental performance from both perspectives. A key challenge identified for future research is balancing the reduced electricity production from Combined Heat and Power (CHP) plants within the energy system.

EMPLOYING THIN PLANAR ELECTRODES TO EXPAND THE IONIC WIND FLOW COVERAGE AREA AND ACHIEVE ENHANCED HEAT DISSIPATION

The suboptimal photoelectric conversion efficiency of light-emitting diodes (LEDs) leads to increased temperature. There is a growing interest in using microstructure ionic wind pumps to regulate the chip temperature. But the ionic wind flow and thermal transfer characteristics of thin-plate electrode pumps used for cooling LED chips is unclear. This study proposes ionic wind pumps equipped with wedged and zigzag emitters to effectively manage the heat generated by high-power LED chips. Experimental investigations were conducted to analyze the electrohydrodynamic characteristics of pumps with different emitter types. A two-dimensional model with a wedged electrode and a three-dimensional model with a zigzag electrode were developed for flow distribution analysis and energy efficiency comparison. The cooling capacity of pumps with different configurations was examined. The results show that the pump equipped with a zigzag electrode exhibits improved stability in corona discharge and approximately 1.53 times higher energy efficiency compared to the pump with a wedged electrode. Moreover, the pump with the zigzag electrode covers a larger ionic wind flow area, generating a higher intensity of ionic wind. The angle between the emitter and the grounding electrode significantly affects the ionic wind flow characteristics. The optimal angle is 70° for pumps with wedged emitters and 30° for those with zigzag emitters. Both pumps can produce a steady wall jet at their optimal angle, causing significant disruption in the surrounding area. The pump with a zigzag electrode exhibits superior cooling performance and is more effective with low power consumption.

Effect of vehicle operating parameters on fuel consumption and the overall energy efficiency of the drive system

This article presents a research methodology that supplements known studies to solve the problem of a correct complementary analysis of vehicles with different drive units. This method can be used at the stage of selecting a car for specific tasks, as well as for in-service technical condition checks. A new method is proposed for analysing the impact of operating conditions on the mileage fuel consumption, unit fuel consumption and overall energy efficiency of vehicles. In the study, it was possible to determine the effect of changing the vehicle speed, road gradient angle and vehicle weight. Tests identifying fuel consumption and efficiency characteristics as a function of vehicle load were carried out using passenger cars with different drive designs. Carrying out tests under laboratory conditions on a chassis dynamometer bench enabled the precise determination of the change in operating conditions. The criteria adopted for the evaluation included fuel consumption and overall vehicle energy efficiency. The variable parameters included speed, vehicle weight, and the road gradient angle. The data for criteria calculation were acquired using a diagnostic tester with a functional parameter recording function. The application of the presented method enabled a comparison of the overall energy efficiency of two vehicles equipped with spark-ignition combustion engines, according to the criteria listed. The experiment showed that in a three-cylinder engine, unit fuel consumption is more sensitive to parameter changes under identical conditions (speed, vehicle weight, road gradient angle) than in a four-cylinder engine. To evaluate the drive units of the test vehicles, characteristics of changes in the overall energy efficiency were used as well. It was observed that in all testing variants, the value increased with increasing road gradient values, with the intensity of η increase not being constant. A car with a four-cylinder engine has a higher energy efficiency at low loads. The proposed methodology is relevant for evaluating vehicles with different drive systems (including hybrid) and adapting drive characteristics to the operating conditions. Partially the presented methodology can also be transferred to EV vehicles - in terms of energy efficiency.

A novel differential chaos shift keying system based on joint time slot and code index of carrier phase modulation

This paper proposes a novel differential chaos shift keying (DCSK) system that utilizes carrier phase modulation in combination with time slot and code index modulation, referred to as CP-TCIM-DCSK system, to achieve high data rate transmission. In the proposed CP-TCIM-DCSK system, the carrier modulated by the carrier phase is used to transmit the information-bearing signal. In addition to physically transmitted information bits, extra information bits are conveyed through time slot and Walsh code modulation, as well as carrier phase modulation, making full use of the benefits of multidimensional modulation. To successfully estimate carrier phase bits and code index bits, an effective joint detection algorithm for carrier phase and code index tailored for the CP-TCIM-DCSK system is introduced. The theoretical Bit Error Rate (BER) expressions for the CP-TCIM-DCSK scheme are derived for both Additive White Gaussian Noise (AWGN) and multipath Rayleigh fading channels. Furthermore, a comparison of data rates, energy efficiency, and complexity between the CP-TCIM-DCSK system and the most advanced systems in the same category at present is conducted. The results validate the accuracy of theoretical analysis through simulation and demonstrate that the proposed scheme outperforms its competitive systems in terms of BER performance.

Low-cost and durable polyvinyl alcohol modified polyethylene separator for vanadium redox flow battery

Porous separators are considered a viable alternative to the high cost Nafion membrane for vanadium redox flow battery (VRFB) commercialization. However, the porous separators suffer from high vanadium ion crossover due to the presence of large micron size pores, which leads to decay in capacity of the VRFB system. To tackle the same, a composite separator is synthesized wherein a cross-linked polyvinyl alcohol (PVA) layer is coated on to the porous polyethylene silica separator (PE separator) to mitigate the vanadium ion crossover rate and employed in the VRFB application. Scanning electron microscopy (SEM) analysis confirmed the successful coating of the PVA film on to the PE separator. Synthesized PE-PVA separator showed a significant decrease in the vanadium ion crossover by 31.44 times compared to the pristine PE separator. Consequently, the self-discharge time increases by 8 and 1.66 times compared to the pristine PE separator and the Nafion117 membrane, respectively. VRFB cell equipped with the synthesized separator showed better capacity retention with a capacity fade rate of 0.2 % Ah·cycle−1 than the Nafion117 membrane (0.5 % Ah·cycle−1). In-situ and ex-situ oxidative stability of the separator is explored in detail and a degradation mechanism of the cross-linked PVA membrane is proposed accordingly. The synthesized single side coated PE-PVA´ separator exhibits higher coulombic efficiency of 99 % and comparable energy efficiency of 71 % at a current density of 120 mA·cm−2 and demonstrated excellent lifetime durability tested up to 1600 charge-discharge cycles at 80 mA·cm−2.

Enhancing Energy Efficiency of Cumene Production Through Reactor Output Recycling Modification in a Heat Exchanger

Cumene production generally involves irreversible and exothermic reactions that leads to an increase in product temperature and needs to be cooled for further processes. The high temperature of reactor product can be utilized as a heat transfer fluid in heat exchanger. This modification process is essential for improving energy efficiency by recycling the reactor output with high temperature as a heat transfer fluid, so that the implementation of replacing the heater with a heat exchanger can be carried out for the process of increasing the initial feed temperature. In an effort to enhance energy efficiency in the cumene production process, simulations were conducted using HYSYS and the comparison of energy efficiency for both basic and modified processes can be evidenced by comparing the total amount of energy required during the process. The results shows that the total amount of energy required for the modified process is 39,814,003.7 kJ/h, while for the basic process is 40,588,937.4 kJ/h, with a difference of 774,933.7299 kJ/h. Since the total amount of energy required in the modified process is smaller than the basic process, then the modification process will increase the energy efficiency of cumene production. Copyright © 2024 by Authors, Published by Universitas Diponegoro and BCREC Publishing Group. This is an open access article under the CC BY-SA License (https://creativecommons.org/licenses/by-sa/4.0).

R-Blocks: an Energy-Efficient, Flexible, and Programmable CGRA

Emerging data-driven applications in the embedded, e-Health, and internet of things (IoT) domain require complex on-device signal analysis and data reduction to maximize energy efficiency on these energy-constrained devices. Coarse-grained reconfigurable architectures (CGRAs) have been proposed as a good compromise between flexibility and energy efficiency for ultra-low power (ULP) signal processing. Existing CGRAs are often specialized and domain-specific or can only accelerate simple kernels, which makes accelerating complete applications on a CGRA while maintaining high energy efficiency an open issue. Moreover, the lack of instruction set architecture (ISA) standardization across CGRAs makes code generation using current compiler technology a major challenge. This work introduces R-Blocks; a ULP CGRA with HW/SW co-design tool-flow based on the OpenASIP toolset. This CGRA is extremely flexible due to its well-established VLIW-SIMD execution model and support for flexible SIMD-processing, while maintaining an extremely high energy efficiency using software bypassing, optimized instruction delivery, and local scratchpad memories. R-Blocks is synthesized in a commercial 22-nm FD-SOI technology and achieves a full-system energy efficiency of 115 MOPS/mW on a common FFT benchmark, 1.45× higher than a highly tuned embedded RISC-V processor. Comparable energy efficiency is obtained on multiple complex workloads, making R-Blocks a promising acceleration target for general-purpose computing.

베이지안확률변경분석을 이용한 국내 철강기업의 에너지효율성 분석

Steel companies, due to their production processes, emit a large amount of greenhouse gases. Therefore, improving the energy efficiency of them is a very important issue in responding to climate change. The starting point for effective management of energy efficiency improvements in steel companies is the objective measurement of their energy efficiency. Previous studies primarily utilized traditional Stochastic Frontier Analysis to estimate the energy efficiency of steel companies. Meanwhile, Bayesian Stochastic Frontier Analysis, which incorporates Bayesian Inference into Stochastic Frontier Analysis, offers the advantage of more accurate and flexible estimates by considering the uncertainty of parameters. Despite the advantages, there has been no research applying Bayesian Stochastic Frontier Analysis to analyze the energy efficiency of Korean steel companies. This study is the first to apply Bayesian Stochastic Frontier Analysis to Korean steel companies, using the Gibbs Sampling technique to estimate the energy efficiency of 22 major Korean steel companies from 2011 to 2019. The key findings of this study are as follows: First, the overall average energy efficiency of steel companies is 0.5450. Second, from 2011 to 2013, the yearly average energy efficiency of the steel companies analyzed shows an improving trend, peaking in 2013, followed by a decreasing trend. Third, a comparison of average energy efficiency across individual companies reveals the firms with relatively high energy efficiency, exceeding 0.8

Energy Efficiency Comparison in Heating Water Using Gas, Electric, and Induction Cooktops and Determination of Container Emissivity Coefficient

A 1.315 kg stewpan is used to boil 1 kg water using three different type of cooktops, that is, gas, electric, and induction. The power of the electric cooktop is 600 W, a gas cooktop uses the maximum setting (large burner in control knob), and the induction cooktop has maximum power of 1200 W. We have observed two different settings of power: 600 W and 1200 W. In the first setting, we compared induction and electric cooktops, while in the second induction and gas cooktops were compared. We obtained energy efficiency about 67.24% and 56.2% for the first setting and 74.03% and 38.55% for the second, which shows that induction cooktop always gives better performance compared to the other cooktops. Besides this, we also investigated the energy leak from the stewpan to the environment through radiation, which should be the same, since all four observations were using the same container to heat the water.
 Keywords: energy efficiency, heating water, induction cooktops, container emissivity coefficient

Improving energy efficiency: a highly efficient coaxial design for a laser ranging system with a splicing lens.

Light detection and ranging (LiDAR) systems have made significant contributions in different applications. The laser ranging (LR) system is one of the core components of LiDARs. However, existing coaxial LR systems suffer from low energy efficiency due to obstruction of the reflection mirror. In this study, we carefully design a laser transmitter and receiver subsystem and consequently propose a highly energy-efficient coaxial design for a time of light-based LR system, where a perforated mirror and splicing lens account for the promotion of energy efficiency. The small hole in the perforated mirror is located on the object focus of the focusing lens to ensure the laser beam will pass through the perforated mirror without obstructions. The ring-shape splicing lens, consisting of two parts, is used for laser collimation and laser reception simultaneously. Laboratory experiments proved that the proposed design eliminates the complex calibration process for noncoaxial LR systems while reaching a comparable energy efficiency, which is higher than 98%. We believe it is an economical yet efficient way to promote the energy efficiency of coaxial LR systems.

Efisiensi Energi Berkelanjutan: Strategi Desain dan Perhitungan Optimalisasi Efisiensi Energi pada Selubung Bangunan

Global warming is an increase in the temperature of the Earth's surface over the last few decades. Building energy consumption is the number two contributor to global warming. About 5-13% of the energy consumed during construction and the remaining 87-95% occur during the lifetime of a building, mainly for heating, cooling, and lighting purposes. This requires the selection of building materials that are certified green or environmentally friendly to help reduce energy consumption. The aim of this study is to evaluate the energy efficiency of a variety of designs of the building cover best in the glass protector as a building wall material. The research method uses comparative research that involves comparing energy efficiency between 4 different designs and materials with the calculation of OTTV on the facade of the building. Overal Thermal Transfer Value (OTTV) is a design parameter used to measure the level of energy efficiency of a building in reducing the heat from sunlight entering through walls and roofs. The results of the study showed massive walls with a 0.8 m high parapet and 1.2 m sharpening (Aluminum 4 mm with semi-flash white paint + 30 mm airspace + 150 mm precast concrete), along with window walls using the Stopray Vision 52 T (8 mm (#2) +12 mm Anti-Shatter+6 mm Clear Glass) and horizontal shading as high as 0.4 m, as well as openings with a configuration of 8 mm (No2) + 12 mm anti-shatter + 6 mm Clear glass, showing that the Overall Thermal Transfer Value (OTTV) reached its peak with a 29% decrease from the standard value. It states the combination of these elements provides optimal thermal performance, minimizing overall heat transfer.

Energy Efficiency in Brazil: Policies, Motivators, Barriers

This paper discusses energy efficiency in thermal processes of chicken slaughterhouses in Brazil, as they are large consumers of electricity and have few indicators to system monitoring. The article reviews energy efficiency in Brazil’s industry, global policies, motivations and barriers to the adoption of an energy management system in the refrigeration circuit. The government lack of regulations towards the development of energy efficiency in the industry, also, that is not the concern of industries managers. That industry is losing competitiveness, as well, the country has an energy inefficient industry. This work compares the production indicator commonly monitored by the chicken slaughterhouses: the Unit Cost which indicates that a slaughterhouse consumes 218.33% of energy in relation to another chicken slaughterhouse. It represents the energy consumed per kilogram of chicken processed, thus the second slaughterhouse uses more than the double of energy to produce the same amount of product. Thus, the disclosure of information for energy efficiency comparison may help the national industry to become more efficient and competitive.

ИССЛЕДОВАНИЕ ЭНЕРГОЭФФЕКТИВНОСТИ АВТОМАТИЗИРОВАННЫХ ПРОЦЕССОВ АДДИТИВНОГО ПРОИЗВОДСТВА

This study is devoted to a comparative assessment of energy costs when implementing additive manufacturing processes. The structure of modern production is constantly being improved. Traditional technological processes are being replaced by completely new ones, based on different principles and having their own characteristics. This primarily concerns additive technologies. In many industries, additive technologies are actively used to produce higher quality, more reliable products. But the question of their comparative energy efficiency arises. The purpose of this work is to calculate energy costs, compare and search for optimal materials for implementing the selective laser sintering (SLS) process. The study was carried out using a modular system for the additive production of polymer parts EOSINT P760, and two types of powders: polymer powder PA 2200 with different thicknesses 0, 12 and 0.15 mm and glass powder PA 3200 GF 0.15 mm thick. The technological process is divided into three main stages. Auxiliary steps include heating and cooling the powder, as well as cleaning and preparing the machine. Calculations were carried out: the number of layers to form the required height of the product, the power of the technological process, the cost of time and energy for main and auxiliary operations. The results are presented in the form of histograms. As a result, it was concluded that in addition to working processes, which include laser sintering and powder coating, the total energy costs are also quite actively influenced by non-production processes: cleaning and preparation of the machine, preheating, powder cooling. When implementing SLS technology, it is necessary to take into account the total costs of time and energy.

Comparison of the effectiveness of stabilizing quasi-resonant and inertial influences on the parameters of a controlled Lorentz system with dynamic chaos

Problem statement. The article is devoted to determining the comparative energy efficiency of stabilizing quasi-resonant and inertial effects on the parameters of a controlled discrete-nonlinear Lorentz system with dynamic chaos. Currently, information transmission systems based on the use of chaotic dynamics effects are developing extremely intensively. The need to ensure reproducibility of parameters and statistical characteristics of pseudorandom signals generated on the basis of nonlinear systems with dynamic chaos makes the task of stabilizing chaotic modes of nonlinear devices and systems urgent. Goal. Determination of the comparative energy efficiency of stabilizing quasi-resonant and inertial effects on the parameters of a controlled discrete-nonlinear Lorentz system with dynamic chaos. Results. It is shown that fluctuations causing deviations of the discrete-nonlinear Lorentz system from equilibrium states lead to changes in the quasi-resonant frequency and the effectiveness of inertial stabilizing effects. It is established that the effectiveness of stabilizing inertial effects on parameter b of a controlled discrete-nonlinear Lorentz system increases with an increase in the fluctuation deviation of the system from equilibrium states. The conditions under which stabilizing inertial effects become energetically more advantageous than quasi-stationary effects on the parameters of a discrete-nonlinear system are determined. Practical significance. Ensuring the required regular behavior with the transfer of nonlinear electronic and quantum devices and systems from stochastic to regular mode.

Energy-Efficient Computing and Green Computing Techniques

Energy-efficient computing and strategies for environmentally sustainable computing have become indispensable in the contemporary world, given the escalating demand for computing power and the growing emphasis on ecological conservation. This summary delves into diverse facets of energy efficient computing and green computing methodologies, elucidating their significance, hurdles, and potential remedies. The primary objective of energy-efficient computing is to curtail the energy consumption of computing systems while either maintaining or enhancing their performance. This proves pivotal in alleviating the ecological ramifications of computing, especially as data centers and similar facilities consume substantial amounts of energy. Green computing techniques encompass a broad spectrum of practices geared towards diminishing the environmental footprint of computing. These encompass the utilization of renewable energy sources, the crafting of energy-efficient hardware, the optimization of software algorithms, and the cultivation of energy consciousness among users. Despite the advantages associated with energy-efficient computing and green computing methodologies, various challenges necessitate attention. These encompass the delicate balance between energy efficiency and performance, the intricacies involved in designing energy-efficient systems, and the absence of standardized metrics for gauging and comparing energy efficiency. Exploration in this domain propels technological progress, resulting in the creation of more effective hardware, software, and systems. These advancements not only positively impact the environment but also propel the overall evolution of computing technology. The Information and Communication Technology (ICT) sector substantially adds to worldwide carbon emissions. Energy-efficient computing and environmentally conscious computing approaches can play a crucial role in mitigating this impact, decreasing energy usage, and advocating for the adoption of renewable energy sources. The aim of this research is to investigate the complexities associated with multiple attribute decision-making when confronted with intuitionist fuzzy information. In this context, the weights of attributes are not entirely known, and the attribute values are expressed using intuitionist fuzzy numbers. To ascertain the attribute weights, an optimization model is formulated based on the foundational principles of traditional grey relational analysis (GRA). The proposed approach entails computing the grey relation degree between each alternative and the positive-ideal solution as well as the negative-ideal solution. This degree is subsequently utilized to establish a relative relational degree, facilitating the simultaneous ranking of all alternatives concerning both the positive-ideal solution (PIS) and negative-ideal solution (NIS). From the result Efficient Algorithms is ranked at first position and Green Data Centers is ranked at fifth position.

A series electric hybrid wheel loader powertrain with independent electric load-sensing system

Electric hybrid powertrain is a promising way for wheel loader electrification. However, the widely used centralized load-sensing working hydraulic system has low efficiency with imbalance load. A novel electric hydraulic system configuration making good use of the electric drive is needed. An independent electric load-sensing hydraulic system for series hybrid wheel loaders is proposed in this study. The lift/tilt functions are powered by speed-controlled fixed displacement pump and controlled by proportional control valves. The independent electric load-sensing hydraulic system eliminates the system inherent power losses of the multi-actuator hydraulic system and combines the high efficiency of variable speed fixed displacement pump and high dynamic performance of valve control. Simulation study on energy efficiency comparison among the proposed powertrain, the existing hybrid powertrain and the non-hybrid powertrain is carried out to check its potential on fuel saving. Results show that the independent electric load-sensing system improves the working hydraulic system efficiency from 34.0% to 54.9% compared to the centralized load-sensing system. The proposed hybrid powertrain saves 11.8% of the fuel consumption compared to the existing hybrid solution, and 41.9% lower than non-hybrid powertrain.

Empirical Comparison of Energy Efficiency Between 3-Tier and High-Speed 3-Tier Network Topologies

The high levels of energy use for cloud computing affect carbon emissions and climate change. This research thoroughly compares the energy utilisation of conventional and high-speed three-tier data centres (DCs). The green cloud simulator (GCS) was used to compare network configurations and energy-saving algorithms for each cloud's energy consumption in 10 trials. The power saver schedule algorithm used the least server energy, while the green and RR schedule algorithms used more. Despite the testing of several energy conservation approaches, core switch and aggregate switch energy usage remained unchanged. Although the high-speed three-tier DC architecture used more energy than the standard design, this is a key difference between the two network topologies. The authors discuss the power saver schedule algorithm's benefits for server energy utilisation. This study shows how three-tier DC architecture can save money by reducing core switch and aggregation switch energy use. These evaluations should include the make span coefficient, and future research should focus on DC transform energy-saving techniques.

A free piston engine generator powered hybrid wheel loader with independent electric drive

Series hybrid powertrain is a practical way for wheel loader electrification. Conventional internal combustion engine (ICE) technique is mature but the efficiency is limited. Free piston engine generator (FPEG) is regarded as a promising technology that can be applied as decarbonized range extenders attributed to its high thermal efficiency and ultimate fuel flexibility. In this study, a FPEG-based series hybrid powertrain is proposed for wheel loaders to reduce fuel consumption. Multiple FPEG units are parallel connected to power the electric powertrain. The optimal unit commitment of the FPEG set is investigated via dynamic programming. A rule-based strategy called discrete power follower (DPF) is proposed. The influence of FPEG unit number on powertrain performances is studied. Energy efficiency comparison between the FPEG-based and the ICE-based series hybrid powertrains is carried out. Results show that the fuel consumption of the proposed FPEG-based series hybrid powertrain is 10.5 % lower than the ICE-based powertrain. The mean efficiency of wheel loader powertrain improves from 31.7 % to 35.1 %.

Comparative Performance and Energy Efficiency Analysis of JVM Variants and GraalVM in Java Applications

Java has dominated the ICT market for almost thirty years with various applications in nearly every sector all over the world. One of Java's main drawbacks comes from its heavyweight core - the Java Virtual Machine (JVM). Therefore, several JVM distributions have been developed to address this issue. GraalVM is the most promising amongst the recent distributions, providing better performance, low power consumption, and reduced carbon footprint emissions. In this research, a comparative analysis based on performance and energy efficiency metrics was conducted to assess this JVM distribution in light of three other classic JVM distributions: Amazon Corretto, Adopt OpenJDK, and Zulu. Findings showed that, although there was no significant difference between the test candidates, GraalVM seemed to be the leading JVM distribution. It is recommended that programmers and technology businesses consider adopting GraalVM in their future Java applications because of its energy efficiency.

Assessing dynamic energy efficiency in the organization for economic Co-operation and development (OECD) countries and China during COVID-19

According to the October 2021 Glasgow Climate Agreement reaffirming the cooling goals of the Paris Agreement and the Glasgow Leaders Declaration on Forests and Land Use, this research applies the Super-D-DDF model to non-oriented variable returns to scale to evaluate the Organization for Economic Cooperation and Development (OECD) and China (38 countries in total), collect important production and energy variables from 2016 to 2020, and measure the total efficiency of energy dynamics and its changes during COVID-19. The empirical results are as follows. (1) Comparing energy efficiency from 2016 to 2018 and 2019 to 2020 (during COVID-19), we find that most countries (22 countries) changed from high efficiency to low efficiency, showing a decrease in energy efficiency. (2) The emissions of carbon dioxide in China in 2020 are close to the sum of OECD carbon dioxide emissions, highlighting that the energy policy in China should be adjusted appropriately. (3) From 2016 to 2020, the forest area of various countries has a significant impact on overall energy efficiency performance. In line with the United Nations’ policy goals, countries should adjust forest protection policies to effectively reduce carbon emissions.