Actual Energy Efficiency Research Articles

Designing a Real-Time Implementable Optimal Adaptive Cruise Control for Improving Battery Health and Energy Consumption in EVs through V2V Communication

Battery electric vehicles (BEVs) face challenges like their limited all-electric range, the discrepancy between promised and actual energy efficiency, and battery health degradation, despite their environmental benefits. This article proposes an optimal adaptive cruise control (OACC) framework by leveraging ideal vehicle-to-vehicle communication to address these challenges. In a connected vehicle environment, where it is assumed that the Ego vehicle’s vehicle control unit (VCU) accurately knows the speed and position of the Leading vehicle, the VCU can optimally plan the acceleration trajectory for a short-term future time window through a model predictive control (MPC) framework tailored to BEVs. The primary objective of the OACC is to reduce the energy consumption and battery state-of-health degradation of a BEV. The Chevrolet Spark 2015 is chosen as the BEV platform used to validate the effectiveness of the proposed OACC. Simulations conducted under urban and highway driving conditions, as well as under communication delay and infused noise, resulted in up to a 3.7% reduction in energy consumption and a 9.7% reduction in battery state-of-health (SOH) degradation, demonstrating the effectiveness and robustness of the proposed OACC.

A Method and Metrics to Assess the Energy Efficiency of Smart Working

The paper discusses the energy efficiency of smart working (SW) as a solution to traditional work-approach issues, with a focus on evaluating benefits for both employers and employees. Remote working, while offering environmental advantages such as reduced commuting and office space use, poses challenges in assessing its true impact. The study presents results from a dynamic analysis on a real residential building, typical of an architectural style diffused in northern Italy, revealing a 15% average increase in energy consumption when all work tasks are performed from home. To address concerns about the environmental impact of SW, the research proposes a method and metrics for evaluation. Four novel indices (SWEET, SEE, SSEE, and 4E) are introduced, providing a structured approach to assess the energy efficiency of SW initiatives. The paper outlines a methodology for data gathering and metric application, aiming to acquire quantitative insights and mitigate disparities arising from a transfer of burdens to employees. This contribution not only signifies a ground-breaking methodology but also addresses an unresolved research question concerning the evaluation of the actual energy efficiency of smart working implementations for both employers and employees. The results underscore the importance of understanding the nuances of SW’s impact on household energy usage and its broader implications for sustainability goals.

Rational Management of Energy Efficiency in a Power Complex

The problem of energy efficiency management in the energy complex under stochastic conditions and taking into account the human factor is analysed. Undesirable activities of the Executive of complex subdivision associated with the presence of his own goals have been identified. Such unwanted activity can lead to a decrease in the energy efficiency of the complex. To improve this efficiency, a control system is proposed that uses a digital learning procedure for the Manager of the complex with the help of the Counsellor, who, in turn, learns to evaluate actual energy efficiency. In addition, this system includes digital procedures for planning and classifying the Executive, depending on the energy efficiency of the subdivision he heads. The task is to determine a control system in which the actual energy efficiency of the subdivision will be equal to the maximum possible under stochastic conditions. This problem is solved by synthesizing a control system that includes a set of decision-making procedures by the Manager (planning and classification) together with a set of advisory procedures used by the Counsellor (evaluation and judgment). The problems of forming such an energy efficiency management system in the energy complex are discussed.

Comparison of CO2 emissions during the operation of autonomous heating systems

The issue of CO2 emissions from heat generators in autonomous heating systems is one of the most important indicators of human technological impact on the Earth's atmosphere. Heat generation is carried out by heat pumps, gas and electric boilers, and systems using solid and liquid hydrocarbon fuels. The purpose of this work is to assess the CO2 emission rate per kilowatt of thermal energy for the specified generators of heating systems based on the actual energy efficiency of heat generators in heating systems with radiator-type heating devices. The study uses official data from Rosstat RF, reports from the Ministry of Energy, the Ministry of Economic Development, current GOST standards, and regulatory documents. CO2 emission values per kilowatt of thermal energy are determined for autonomous water heating systems when generating thermal energy with air-source heat pumps (ASHP), gas condensing and convection boilers, and boilers using solid and liquid fuels. The assessment of CO2 emissions from heat generators of autonomous water heating systems showed a dependency on the structure of electricity production and transportation, climate, and the heating devices used. All these parameters vary across different countries. Analyzing data for specific countries shows that different heating units have the minimal carbon footprint.

Влияние дефектов распылителя форсунки на расход топлива и контроль топливной аппаратуры на современном уровне

The basis of improving the vessel energy efficiency is economical operation of its power units - the main and auxiliary diesel engines, steam boilers. There has been described the smart control system for ship operation. The main parameters listed below are under constant control: fuel consumption of the main and auxiliary steam diesel engines, auxiliary steam boiler, operating time of the main and auxiliary diesel engines, auxiliary steam boiler; fuel level in consumable, settling and bunker fuel tanks; vessel speed, vessel position, weather conditions. The system includes flow meters, temperature, speed, power, and pressure sensors, GPS-station, digital converters, controllers, marine computer industrial design, monitors for parameters in the engine control room and on the bridge, special software for ships and offices. There has been determined the main goal of developing and assembling the system: to develop a reliable working tool for the crew and the main ashore office, to evaluate and control the quality of the vessel operation, to supplement the existing control methods with an improved and more understandable scheme of monitoring various parameters of the ship's operation, including fuel consumption. The results of developing and introducing the system help increase the actual energy efficiency of the vessel operation. An example of real-time fuel consumption control using the smart control system - ShipSmartView - is presented. The functionality of the system is quite wide. Graphs of the current fuel consumption which indicated the defect in the fuel equipment are given. Based on the data, overhaul of the fuel equipment was carried out and a malfunction of the nozzle - a crack - was defined. It has been proved that due to untimely detection of a malfunction, a loss of fuel was allowed.

A Study of Coverage Probability-Based Energy-Efficiency Analysis for UAV-Aided THz-Enabled 6G Networks

Reliable and flexible emergency communication is a crucial challenge for search and rescue in the circumstance of disasters, specifically for the situation when base stations (BS) are no longer functioning. Unmanned aerial vehicle (UAV)-aided networking is becoming a prominent solution to establish emergency networks, which also should be energy-efficient. The Terahertz (THz) frequency-enabled communication system is also envisioned as enabling technology for Sixth-Generation (6G) communication systems. To this end, we consider a THz UAV network for our investigation. In this article, we study energy-efficiency (EE) analysis for UAV-Aided Terahertz-Enabled 6G Networks. The metric coverage probability (CP) is adopted as EE analysis given the QoS requirement. Using stochastic geometry tools, we derive a CP. Afterward, considering that CP, we study a network EE optimization method. Borrowing the idea from the existing literature, we reformulate the actual EE optimization problem into a solvable Dinkelbach nonlinear fractional programming. However, the optimization problem turns into a nondeterministic polynomial hard (NP-hard) problem. Eventually, we transform that NP-hard problem into a convex optimization problem using the ConCave-Convex procedure (CCCP), which is more tractable and feasible to find a solution for the optimization.

Policy pressure to retrofit Germany's residential buildings to higher energy efficiency standards: A cost-effective way to reduce CO2 emissions?

Germany's climate goals require over 75% of its housing stock to be retrofitted for energy efficiency. An important question for Germany and other countries is, what minimum energy efficiency standard should be mandated for housing retrofits so as to reduce CO2 emissions economically efficiently? It has long been known that the marginal costs of energy efficiency increase as standards are pushed higher, and therefore the marginal costs of CO2 abatement increase, but at the same time energy consumption reduces, thereby reducing CO2 emissions. This paper investigates where the social optimum lies between these two effects. In addition to a large database of house sale advertisements containing price and energy efficiency data, it uses two semi-official data sources of modelled and actual energy efficiency upgrades in Germany. It finds that retrofitting to a modestly high standard of about 70 kWh/m2/y entails marginal costs of CO2 abatement comparable to current CO2 prices. However, each step to a higher standard increases these by up to an order of magnitude, with absurdly high marginal costs of CO2 abatement for the highest standards. German policymakers are currently pushing for higher minimum standards, but money could better be spent retrofitting more houses to less stringent standards.

Thermodynamic mechanism of high energy performance of air source heat pump with coupled liquid-storage to gas-liquid separator

This study proposed a novel air source heat pump system (NASHPs) with coupled liquid-storage and gas-separator to prevent an air source heat pump (ASHP) from frosting. Compared to the original air source heat pump system (OASHPs), the proposed system delayed frost by 30 min and shortened defrosting time by 72 s in a cycle. To further study the mechanism of NASHPs, coefficient of performance (COP), transient losses (heating loss due to frosting and recovery) and defrosting losses (heating loss due to defrosting) of NASHPs and OASHPs were analysed based on experimental data. Furthermore, the thermodynamic perfectibility was introduced to reflect the degree of deviation of the actual operation performance of NASHPs from the theoretical energy efficiency. The maximum reduction of thermodynamic perfectibility in the actual running condition for NASHPs was observed to be approximately 26.5%, which caused the actual continuous energy efficiency of NASHPs to exhibit a certain gap with the energy efficiency of the ideal cycle. The transient loss of NASHPs indicated that the heat loss in the frosting and recovery stages was mainly due to the irreversible loss of the compressor and condenser. Moreover, the defrosting loss of the NASHPs was mainly due to the longer defrosting time and high temperature difference between the supply and return during defrosting. The energy efficiency in the continuous operation of the NASHPs plays a crucial role in the actual operation, and the defrosting loss significantly impacts the actual energy efficiency of the NASHPs compared to transient loss. We believe the results of this study provide a basis for the design and energy efficiency improvement of ASHP systems.

An actual-performance-oriented study on the relationship between environmental efficiency and passive design factors for multi-family dwellings in cold areas

Performance during operation reflects the actual energy efficiency of the building. Therefore, when analyzing the relationship between passive design factors and building performance, using performance data in operation also makes the conclusion more in line with reality. In this study, winter and summer air temperature measurements were conducted in several multi-family dwellings in four cities in cold areas, and data on heating and cooling energy consumption of the dwellings were gathered as well. An environmental efficiency assessment method was devised to comprehensively describe residential energy consumption and environmental quality. The ratio of energy consumption to indoor-outdoor temperature difference (EDR) has been proposed as a new metric to measure the environmental efficiency of dwelling units. Through sensitivity analysis, the impacts of passive design factors on environmental efficiency were quantified and ranked. The two passive design factors that have the greatest impact on environmental efficiency in winter are northern window-to-wall ratio and surface area-to-volume ratio, while the floor number affects the environmental efficiency most significantly in summer. According to comprehensive analyses of winter and summer, the most important factors impacting environmental efficiency in a year are northern window-to-wall ratio and surface area-to-volume ratio. The study's findings can help architects filter design elements for focused design during the passive design process, increasing design effectiveness.

Experimental study on the energy flow of a commercial heavy-duty vehicle under the C-WTVC of cold and warm start

In order to improve the actual performance of China-VI heavy-duty vehicle (HDV), the energy flow test on a HDV was conducted under the C-WTVC (Chinese-World Transient Vehicle Cycle). Then, the transient energy distribution of heavy-duty diesel engine was compared with different start condition. Results show that, the energy flow is greatly affected by the variation of actual vehicle conditions. The percentage of coolant energy fluctuates between 6% and 76%. In the urban cycle, the exhaust energy is slightly higher under cold start condition due to the high engine speed at the beginning of this condition. In the expressway cycle, the coolant loss ratio fluctuates slightly and stabilizes around 20% and the percentage of exhaust energy is around 32% in the later constant speed stage. What’s more, idle and variable working conditions can cause a large energy loss, such as the acceleration and deceleration of C-WTVC. All those provide guidance for improving the actual energy efficiency of HDVs.

Terrain mobility performance optimization: Fundamentals for autonomous vehicle applications. Part I. New mobility indices: Optimization and analysis

Based on an analysis of vehicle mobility performance indices in use, it is shown that an index for the optimization of autonomous vehicle mobility performance should be constituted as a set of technical parameters that result directly from the interactive dynamics of tires and terrain and should be measurable and controllable in real-time. In addition, the combination of the parameters should characterize the vehicle’s technical productivity/efficiency (not energy efficiency), and thus, enable the estimation and control of vehicle mobility performance. If such requirements are satisfied, the index can be optimized and optimization results can facilitate autonomous control design. This article provides results of a study to address the above-formulated requirements in the proposed mobility performance index.In Part I of this article, wheel mobility performance is characterized first by the wheel circumferential force and the actual linear velocity. The proposed wheel mobility performance (WMP) index mathematically relates the wheel circumferential force and velocity to the theoretical maximum performance. Thus, the actual performance can be evaluated in terms of the theoretical maximum performance in a similar manner that the actual energy efficiency is compared to its theoretical maximum, i.e., to unity. The WMP-index is then extended to multi-wheel vehicles. The proposed vehicle mobility performance (VMP) index relates the traction and velocity characteristics of all wheels to a theoretical maximum performance.Founded on the circumferential force and velocity characteristics of the wheels, the VMP-index mathematically reflects the influence of the power distribution among the wheels on the vehicle mobility performance. Hence, the VMP-optimization is formulated as an examination for the optimal tire slippages. Essentially, their combination characterizes the optimal wheel power split, and consequently, the best set of the wheel circumferential forces and the vehicle actual velocity for the maximum mobility performance in a given terrain condition. The tire slippages are subject to lower and upper bound constraints. The lower bound ensures positive tire slippages, and thus, positive traction of the wheels. The upper bound is imposed in the form of characteristic slippages such that exceeding them drives the wheels into an extremely nonlinear zone of the traction characteristic. In this zone, the wheel mobility margins drop significantly and some or all wheels can easily be immobilized. Further, the optimization is subject to the vehicle longitudinal dynamics, which sets the summation of the wheel circumferential forces equal to the motion resistance forces.By applying Lagrange Multipliers (LMs) to the objective function, a system of equations is arranged to compute the optimal tire slippages that correspond to the necessary conditions of an extremum of the objective function. The strict monotonicity property of the LM-based equations is then examined and the uniqueness of the solution is exhibited. Finally, the Hessian theory for a constrained optimal problem is used to prove that the solution is globally minimum.Part II discusses the computational results of mobility performance optimization for a 4x4 vehicle simulated on three homogeneous terrains and split terrains on flat surface and on slopes, with and without drawbar pull. Additionally, the vehicle with three conventional driveline systems is simulated in the same terrain conditions, and a detailed analysis establishes dependences between the optimal tire slippages and optimal circumferential forces of the wheels and their correlation to those provided by the driveline systems. Advantages of the mobility optimization for control design are explained and discussed. It is also concluded that the use of energy efficiency indices in mobility performance assessment can be considered as a supplementary, but not the primary subject-heading of the vehicle mobility performance.The mobility performance optimization directly contributes to mobility design that is illustrated by conceptual implementation of the optimization results in two driveline systems of the 4x4 vehicle: a driveline with positive engagement of the power-dividing units and a virtual driveline that serves for fully electric vehicles with in-wheel motors.Finally, a verification of the mobility optimization results and validation of the proposed mobility performance index is conducted through statistics-based assessment against experimental wheel circumferential forces and tire slippages.

Evaluation of the Effects of Tunnel Lighting Environment on Energy Consumption and Drivers’ Reaction Time

The 24-hour artificial lighting of the tunnels consumes a large amount of electricity, which means increased environmental damage and carbon footprint for China, which is dominated by thermal power. In order to alleviate the above problems, the effects of the tunnel lighting environment on energy consumption and drivers’ reaction time were evaluated by the finite element method and laboratory test to optimize the lighting environments. In this study, based on the Wanxichong extra-long tunnel in Yunnan Province, a 3D tunnel model using DIALux software is established first. Then, the effects of climate conditions, layout method of the lamps, and layout height and reflection of the sidewall material on the average luminance and uniformity on the pavement, the efficiency ratio per unit length, and the actual energy efficiency value were investigated. Finally, the indoor lighting environment simulation experiments were conducted to examine the effect of the type of sidewall materials, contrast, background luminance, and eccentricity on drivers’ reaction time. Simulation results show that, under the same climate condition and layout method of lamps, the average luminance and luminance uniformity on the road surface are positively correlated with the reflectivity of the sidewall material. On the clear days, the efficiency ratio per unit length corresponding to the 2 m high sidewall material is the largest, while the efficiency ratio per unit length on cloudy days and mixed days corresponding to the 2.5 m high sidewall material is the largest. In addition, the staggered layout of the lamps at the entrance of the tunnel consumes less power, which is more conducive to energy saving. Experimental results show that, with the increase of background luminance, the reaction time of drivers decreases. Meanwhile, applying energy-storage reflective coating on the sidewalls of the tunnel has a better visual performance than using light yellow ceramic tiles and cement mortar on the sidewalls. This conclusion would provide a lower energy consumption lighting design method and higher drive comfortable for highway tunnels.

Comparison of energy efficiency and costs related to conventional and LED road lighting installations

Comparison of conventional (usually high-pressure sodium (HPS)) and LED luminaires in street/road lighting is not often based on photometrically equivalent lighting solutions and/or correct economic analysis, which may lead to either overestimation or underestimation of savings of any kind. Therefore, this paper presents a correct methodology for the determination of actual energy efficiency and cost indicators in street/road lighting. Both neutral white (NW) and warm white (WW) LEDs, all relevant street/road lighting classes and pole layouts were considered. Analyzing optimal lighting solutions, characterized by the lowest installed power, it was shown that when considering mesopic effects the average energy savings achieved comparing LED (NW and WW) with HPS lighting solutions amounted to 41–62% and 29–59%, respectively, while the ratio between the total costs of the comparable LED (NW and WW) and HPS lighting solutions belonged to the ranges 0.59–1.26 and 0.61–1.14, respectively. An expanded sensitivity analysis of the costs, carried out considering not only the usually taken discount and electricity cost rates, but also the LED package lifetime, showed that the last only slightly influences the total costs. The effects of the use of more efficient LED packages expected in the near future were also analyzed.

A Study of the Performance of Ship Diesel-Electric Propulsion Systems From an Environmental, Energy Efficiency, and Economic Perspective

Abstract Climate change and air pollution that are enormously impacted by ship emissions have become an intriguing issue, drawing consideration from the shipping industry. The ship's propulsion system is the main contributor to energy efficiency and ship emissions. This research paper presents a solution to this issue through propelling the ship by using a diesel-electric propulsion system instead of the conventional one. As a case study, a passenger ship is investigated. The results showed that the proposed electric propulsion system has lower emission rates than the conventional one by 10%, 21%, and 88% for Carbon dioxide, Nitrogen oxides and Sulfur dioxide emissions, respectively. From an energy efficiency point of view, the diesel-electric propulsion system enhances the energy efficiency and complies with the required International Maritime Organization (IMO) values, as actual energy efficiency is about 66%, 70%, 83%, and 95% of the required IMO values at baseline, Phase 1, Phase 2, and Phase 3, respectively. From the economic point of view, the annual costs are $2.5 and $3.05 million for both diesel-electric and conventional propulsion systems, respectively. This shows that the annual cost of the diesel-electric option is less than that of the conventional by 22%.

ЭКОНОМИЧЕСКИЕ МЕХАНИЗМЫ ОЦЕНКИ ЭНЕРГОЭФФЕКТИВНОСТИ КРУПНЫХ ЭНЕРГЕТИЧЕСКИХ КОМПАНИЙ КАК ФАКТОР ИХ ИНВЕСТИЦИОННОЙ ПРИВЛЕКАТЕЛЬНОСТИ

Today, institutional and private investors face the problem of an objective investment assessment of companies when investing their funds. Fundamental financial indicators of companies do not always fully reflect their efficiency, including when using fuel and energy resources. This problem is especially relevant for energy companies that consume a significant amount of fuel and where excess fuel losses are often included in the tariff to the consumer. In this work, the object of the research is various energy companies in Russia, whose shares are traded on the Moscow Exchange. The subject of the research is the investment attractiveness of large energy companies with an emphasis on their energy efficiency. The purpose of the research is to develop a new way to assess the investment attractiveness of large energy companies, taking into account their actual energy efficiency. The main research tasks are to analyze existing methods for assessing the financial efficiency of heat generating companies, as well as to develop a new method for assessing the investment attractiveness of heat generating companies, taking into account their actual energy efficiency. For the analysis of key fundamental financial indicators, three heat generating companies located in different regions of Russia and using different energy production cycles, as well as using different types of fuel have been selected. The methodology and research methods are based on a fundamental financial analysis of the indicators of heat generating companies. A comparative analysis of the profitability of three heat generating companies, as well as the average indicators for the industry, revealed the most inefficient company. For this company, an analysis of other financial indicators for the last ten reporting years has been performed. A comparative analysis of the specific fuel consumption for the generation of heat and electricity in these companies has also been performed. Based on the results of the results obtained, it is proposed for an objective investment assessment of heat generating companies to adjust their revenue and profitability, taking into account the indicators of their actual energy efficiency

Verification and Improving the Heat Transfer Model in Radiators in the Wide Change Operating Parameters

Laboratory measurements and analyses conducted in a wide range of changes of water temperature and mass flow rate for different types of radiators allowed to provides limitations and assessment of the current radiators heat transfer model according to EN 442. The inaccuracy to determinate the radiator heat output according to EN 442, in case of low water mass flow rates may achieve up to 22.3% A revised New Extended Heat Transfer Model in Radiators NEHTMiRmd is general and suitable for different types of radiators both new radiators and radiators existing after a certain period of operation is presented. The NEHTMiRmd with very high accuracy describes the heat transfer processes not only in the nominal conditions—in which the radiators are designed, but what is particularly important also in operating conditions when the radiators water mass flow differ significantly from the nominal value and at the same time the supply temperature changes in the whole range radiators operating during the heating season. In order to prove that the presented new model NEHTMiRmd is general, the article presents numerous calculation examples for various types of radiators currently used. Achieved the high compatibility of the results of the simulation calculations with the measurement results for different types of radiators: iron elements (not ribbed), plate radiators (medium degree ribbed), convectors (high degree ribbed) in a very wide range of changes in the water mass flow rates and the supply temperature indicates that a verified NEHTMiRmd can also be used in designing and simulating calculations of the central heating installations, for the rational conversion of existing installations and district heating systems into low temperature energy efficient systems as well as to directly determine the actual energy efficiency, also to improve the indications of the heat cost allocators. In addition, it may form the basis for the future modification of the European Standards for radiator testing.

Methods and techniques for energy efficiency assessment of geotechnological facilities at opencast mines based on the in-depth analysis

The article addresses energy efficiency of geotechnological facilities at opencast mines. The energy intensity of basic processes in solid mineral mining by the opencast method using the cyclical technologies takes up to 60–70% of the total mining and haulage cost. Given the mining technology is selected, and the stripping and excavations directions and procedures are determined, the potential for reduction in the geotechnology energy intensity lies in a proper choice of models of mining/haulage equipment, its duty and operation conditions. First of all, it is required to develop an energy efficiency methodology. This article reveals the possibility and potential of actual energy efficiency improvement in mines using the most widespread opencast method. The proposed approach assumes the in-depth analysis as an essential factor of the energy efficiency improvement of geotechnology facilities at opencast mines. The in-depth analysis should ensure real-time monitoring and assessment of energy consumption governed by the duty and operation conditions of the main mining and haulage equipment. The implementation of the proposed approach requires appropriate methods and techniques to take into account all factors that affect the mining and haulage equipment performance. This makes it possible to evaluate energy efficiency with due regard to the energy consumption and the nature of this energy integration by shares in the energy flows within the technology process. The studies emphasize that energy saving is a conventional key objective in mining. To this effect, it is required to ensure mechanical availability of mining and haulage machines, to monitor fuel consumption, to plan and control energy intensity based on the expected extraction volume per planned period. In the meanwhile, the research implemented reveals that opencast mines can essentially improve their energy efficiency in case of an appropriate backup with the relevant methods and techniques.

Multidimensional performance-based evaluation method of high-performance cold source in green building

In the design stage of green buildings, there is a lack of a set of systematic performance-based evaluation methods for high-performance cold sources to evaluate whether the selected cold sources match the load characteristics of buildings, which leads to inappropriate selection of cold sources in the design stage. Due to this problem, this study proposes a multi-dimensional performance-based evaluation method. Data were collected from a public building in the cold region of China, and a set of calculation tools were developed to simulate the actual operation performance of cold source units. Considering its energy and economic efficiency, the multi-dimensional comprehensive evaluation index is put forward. Finally, taking a green building located in Tianjin, China as an example, the feasibility analysis of the multi-dimensional performance-based evaluation method is carried out. Results indicate that: 1) the prediction error of hourly performance coefficient prediction model based on Fuzzy clustering and Back-Propagation (BP) neural network algorithm is less than 10%, which can accurately predict the actual operation energy efficiency of cold source; 2) compared with the actual cold source, the improved cold source of the case building has the seasonal power consumption decreased by 34.0%, and the average load rate increased by 16.9%, which proves the feasibility of multidimensional performance-based evaluation method. The method proposed in this study can provide reference and help for the selection and performance evaluation of cold source units in green buildings at the design stage.

Field performance of household room air conditioners in Yangtze River Region in China: Case studies

The field performance of room air conditioners (RACs) directly affects energy consumption. In this study, a long-term field test was conducted in six residential rooms in the Yangtze River Region, China. Using specially developed test equipment, the occupancy pattern, control level, and energy performance factors for constant frequency and inverter RACs were investigated. The field test results showed that the performance of RACs was dependent on the behavior of the occupants and the properties of the service space. The occupancy pattern for RACs was classified as part-time-part-space basis. The control level for constant frequency and inverter RACs indicated that their respective hourly operation ratios and compressor frequency distributions were quite different. Furthermore, based on the compressor energy conservation – compressor volumetric efficiency method, the part load and annual performance were calculated. The results showed that the energy efficiency of inverter RACs was relatively higher with a steady evaporating temperature and small capacity loss. In addition, the actual annual energy efficiency ratios were between 2.38 and 3.83, and the gap between laboratory tests and field test APF ranges from 8.4 to 32.0%, which shows a large difference in the cooling/heating seasonal performance efficiency compared with the laboratory tests.

Power consumption and energy efficiency of VRF system based on large scale monitoring virtual sensors

Space cooling energy consumption is a significant component of building energy consumption, and in recent years it has attracted much attention worldwide owing to its significantly increasing usage. The variable refrigerant flow (VRF) system is one common type of cooling equipment for buildings in China and is applied extensively to residential and office buildings. The performance of VRF systems significantly influences the cooling energy consumption of buildings. The system energy efficiency and electricity consumption are the main indicators employed to evaluate the performance of VRF systems. It is hard to obtain the actual energy efficiency and electricity consumption of VRF systems in buildings because of the high cost of the required complicated measurements. This study proposes a virtual sensor modeling method to determine the actual energy efficiency and electricity consumption of 344 VRF systems in residential buildings. Statistical and clustering analyses are conducted to determine the energy efficiency and electricity consumption to obtain distributions and typical operation load patterns of VRF systems in residential buildings in China. The main findings are as follows: the main range of the Seasonal Energy Efficiency Ratio (SEER) for the cooling season is from 2.9 to 4.4; the median SEER in the Hot Summer and Cold Winter zone is lower than in another climate zones; the longer cooling duration may lead to greater electricity consumption, and the electricity load for VRF systems electricity load is periodic for each day. The oversizing issue is common for VRF systems in the dataset, which also led to the lower energy efficiency of VRF systems. The high usage of VRF systems appeared from July 27th to August 26th. The findings provide recommendations for designing VRF systems in residential buildings.