Decrease In Energy Efficiency Research Articles

A multi-valve flexible heat pump system with latent thermal energy storage for defrosting operation

There has been growing interest in using air-source heat pumps as an alternative to potentially replace fossil-fuel-based heating technologies for heat decarbonisation. One of the technical issues that hinders the wide uptake of air source heat pumps is the decreasing energy efficiency caused by frequent defrosting operations under low ambient temperatures. Currently, the most widely used defrosting method is the reverse-cycle defrosting but this operation would have to interrupt the heating supply during the defrosting process. The authors recently proposed, developed, and demonstrated a flexible heat pump concept that recovers partial of the subcooled heat from the hot refrigerant exiting the condenser and stores it in an integrated thermal storage. The stored heat could later be used to save compressor power and defrosting applications. In this paper, we proposed an innovative method by using a multi-valve design of the flexible heat pump to achieve the defrosting function. In this new concept, defrosting is achieved by condensing the refrigerant inside the evaporator and simultaneously ensuring uninterrupted heating during the heat storage discharge process. A model has been established to study the heat pump performance during a full charge/discharge cycle of the storage. Results indicated that with R410a, R134a and R1234yf, the proposed flexible heat pump has the potential to respectively save up to 11.2%, 10.8% and 13.2% of compressor power, in comparison with a heat pump using the conventional reverse cycle defrosting method. Concurrently with the defrosting operation, the same heating capacity is ensured without interruption by the flexible heat pump.

Evaluation of the high-robustness nuclear power cycle against lunar surface environmental threat

Heat sinks exposed to the lunar surface environment cause fluctuations in the energy cycle due to variations in lunar thermal conditions, leading to non-design operations of the energy system. Such suboptimal operations decrease energy efficiency and shorten the lifespan of system components. This paper introduces an innovative design for a highly robust lunar nuclear power cycle that mitigates environmental threats on the lunar surface. A reverse closed Brayton cycle increases the waste heat discharge temperature. Higher waste heat temperatures allow the heat sink panels to have greater heat radiation per unit area, countering the negative disturbances from lunar environmental changes on the energy system. Under the dual threats of lunar dust toxicity and intense solar radiation, the output reduction of this robust nuclear cycle is only 0.96% that of traditional nuclear power cycles with the same thermoelectric parameters. Moreover, even under severe environmental threats, the power quality of this robust nuclear cycle remains 10.8 times better than that of conventional designs with the same nighttime output design baseline. In conclusion, employing a reverse Brayton cycle to increase waste heat emission temperature effectively enhances the robustness of the nuclear power cycle. This paper proposes a new nuclear thermoelectric system framework to withstand threats from the lunar surface environment.

Analyzing Safety Factors and Predicting Fatigue Life of Weak Points in an Electrically Driven, Multi-Purpose Cultivation Tractor

The advancement of agriculture and a shortage of labor have led to an increased use of agricultural machinery. However, the resulting environmental issues have prompted a shift from internal combustion engines to electric drivetrains. The electric drivetrain includes the installation of batteries, which can lead to decreased energy efficiency and significant loads on the vehicle due to their heavy weight. Consequently, the importance of ensuring the safety of agricultural machinery is being increasingly emphasized. The load on the frame of agricultural machinery is not consistent during off-road driving, and the accumulation of load cycles can lead to the destruction and failure of components. Therefore, it is necessary to ensure a level of safety and to predict the fatigue life. In this study, we estimate the safety factor and predict the fatigue life of weak points in an electrically driven, multi-purpose cultivation tractor based on working conditions (width, soil, and drive). Strain gauges were attached to these weak points to measure the strain, which was then converted to von Mises stress. Fatigue life was predicted using the rainflow counting method and the Palmgren–Miner rule. The results showed that the safety factor measured under various working conditions was greater than 1. The estimated minimum fatigue life was 124,176 years. Considering that the cultivator is used for 29.7 h annually and has a durability lifespan of 5 years, it is expected to be safely usable throughout its service life.

Formulating Local Environment of Oxygen Mitigates Voltage Hysteresis in Li-Rich Materials.

Li-rich cathode materials have emerged as one of the most prospective options for Li-ion batteries owing to their remarkable energy density (>900Wh kg-1). However, voltage hysteresis during charge and discharge process lowers the energy conversion efficiency, which hinders their application in practical devices. Herein, the fundamental reason for voltage hysteresis through investigating the O redox behavior under different (de)lithiation states is unveiled and it is successfully addressed by formulating the local environment of O2-. In Li-rich Mn-based materials, it is confirmed that there exists reaction activity of oxygen ions at low discharge voltage (<3.6V) in the presence of TM-TM-Li ordered arrangement, generating massive amount of voltage hysteresis and resulting in a decreased energy efficiency (80.95%). Moreover, in the case where Li 2b sites are numerously occupied by TM ions, the local environment of O2- evolves, the reactivity of oxygen ions at low voltage is significantly inhibited, thus giving rise to the large energy conversion efficiency (89.07%). This study reveals the structure-activity relationship between the local environment around O2- and voltage hysteresis, which provides guidance in designing next-generation high-performance cathode materials.

Analysis of the influence of substitute fuels on properties operating conditions of military hybrid drive systems

The energy density of chemical batteries makes it difficult to rely solely on cheap and eco-friendly electricity for power in many applications, such as airplanes, long-distance trains, ocean vessels, and heavy equipment. Limited charging infrastructure and power generation capacity are also problematic. However, hybrid powertrains provide a solution by combining electric and internal combustion engines to achieve better fuel economy and similar operational characteristics to traditional engines. Hybrid systems can also use alternative hydrocarbon fuels , with all advantages of conventional engines. This study aimed to determine the impact of alternative fuels on the performance of a hybrid drive system for a military wheeled platform developed for operation in urban areas. The experiment found that substitute fuels, such as, F-34, and Jet A-1, were compatible but could result in increased fuel consumption, decreased energy efficiency, and negative environmental impacts due to higher exhaust emissions.

Effect of varying percentages of Co3O4 Nanoparticles on the Behavior of (ORR/OER) Bifunctional Co3O4/α-MnO2 Electrocatalyst

Among all type of batteries, Lithium Air Batteries (LAB) are considered to be the most effective due to their highest energy density of around 11900 Wh/kg but there are some major issues are being faced by LAB such as large overpotential, poor cycle life, low current density, and decreased energy efficiency. The solution to these issues is primarily dependent on the proper selection of an electrocatalyst. A new approach for using a bi-functional electrocatalyst produced excellent results. Here, Co3O4/α-MnO2 composite has been considered as a bifunctional catalyst because cobalt oxide performed well in the Oxygen Evolution Reaction (OER) process while manganese oxide performed well in the Oxygen Reduction Reaction (ORR) process. A simple two-step hydrothermal process is used in this work to synthesize Co3O4/α-MnO2. This work focuses on the behavior of the composite electrocatalyst when varying percentages of Cobalt oxide (5%, 10%, 15%, and 20%) are deposited on the alpha-Manganese Oxide nanorods. The primary characteristics of each sample with different percentages of Cobalt Oxide are examined, and the performance of each sample is compared to one another. Several testing techniques like Cyclic Voltammetry (CV), Linear Sweep Voltammetry (LSV), X-Ray Diffraction (XRD), and Scanning Electron Microscopy (SEM) are performed on the samples. The combination of cobalt oxide and manganese oxide showed a synergistic effect and work as a bifunctional electrocatalyst. As the percentage of Co3O4 deposited on the α-MnO2 nanorod increased, it behaves more like an OER electrocatalyst leading to a decrease in charging potential. This work will help in finding an optimum amount of Co3O4 that should be deposited on α-MnO2 nanorods to get an efficient (ORR/OER) bifunctional electrocatalyst.

Adaptive eco-cruising control for connected electric vehicles considering a dynamic preceding vehicle

Energy consumption and driving safety of a vehicle are greatly influenced by the driving behaviors of the vehicle in front (also termed the preceding vehicle). Inappropriate responses to unanticipated changes in the preceding vehicle can lead to decreased energy efficiency and an increased risk of rear-end collisions. To address this issue, this study proposes an innovative Adaptive Eco-cruising Control Strategy (AECS) for connected electric vehicles (CEVs) considering the dynamic behavior prediction of the preceding vehicle. The AECS, which is designed with a two-stage receding horizon control framework, can adapt to scenarios where the preceding vehicle cuts in or moves out in a safer and energy-efficient manner compared to traditional eco-cruising strategies, which merely focus on a constant preceding vehicle. In the first stage, a prediction model for characterizing the dynamic behavior of preceding vehicles is developed using the Bayesian network. This model is trained using real-world vehicle driving data, allowing it to anticipate the driving trajectories of vehicles changing lanes in front. In the second stage, an energy-saving, safety, and driving comfort-oriented optimization problem is formulated as a quadratic programming form. The eco-cruising speed is then optimized to adapt to the dynamic traffic environment, especially when the preceding vehicle changes over time. Finally, several simulations are conducted to validate the AECS. The results demonstrate that the AECS can improve the energy efficiency of CEVs by up to 11.80% and 19.53% on average compared to the existing cruise control strategies and ensure vehicle driving safety and comfort, without compromising travel time. Additionally, the vehicle cut-in position, the cut-in vehicle speed, and the ego vehicle speed affect the energy efficiency improvement performance of the AECS.

Study on the impacts of refrigerant leakage on the performance and reliability of datacenter composite air conditioning system

Refrigerant leakage occurring in the data center composite air conditioning system could decrease energy efficiency and even results to reliable risks like insufficient cooling and indoor air moisture condensation. In this study, the dynamic model of composite air conditioning system is built to research effects of refrigerant leakage on system performance. Further, influences of outdoor temperature, leakage area and leakage location on system reliability in different modes are investigated. Results indicate that in both modes obvious deviation of superheating degree and evaporating temperature manifest at least 40 % refrigerant has leaked. In vapor compression mode, the subcooling degree vanishes after around 15 % refrigerant has leaked and could detect the problem in early stage while condenser fan frequency in heat pipe mode. The vapor compression mode constantly meets insufficient cooling earlier than moisture condensation despite outdoor temperature, while heat pipe mode prompts to suffer indoor air moisture condensation when outdoor temperature is lower than around −8 °C. The vapor compression mode suffers indoor air condensation constantly later than heat pipe mode, and meets insufficient cooling later except in extremely low outdoor temperature. The results can provide guidance in refrigerant leakage detection as well as elevating system reliability in fault conditions.

Thermophotonic cells in self-sustaining parallel circuits

Thermophotonic (TPX) cells, which integrate a light-emitting diode (LED) and a photovoltaic (PV) cell, offer potential advantages over thermophotovoltaic (TPV) cells for low-grade waste heat utilization. While TPX cells traditionally operate in an independent circuit, which requires an external battery storage unit, the self-sustaining circuit presents an appealing alternative that eliminates the need for the storage unit. In this study, we conduct a comprehensive analysis of TPX cells operating in the self-sustaining circuit. We provide clear expressions for the electrical currents flowing through the LED and PV cell, considering the different bandgaps of the LED and the PV cell. Our results reveal that the bandgap energy of the LED must exceed that of the PV cell for the TPX cell to function in a self-sustaining parallel circuit. Furthermore, we demonstrate that the performance of the TPX cell in the self-sustaining circuit improves with a narrower bandgap energy for the PV cell and a wider bandgap energy for the LED, regardless of the far-field or near-field configurations. While near-field TPX cells exhibit higher power density, they also experience decreased energy efficiency compared to far-field TPX cells. Additionally, we explore the scenario where the bandgaps of the LED and PV cell are the same, analyzing the performance of a closed-structured self-sustaining parallel circuit with multiple LEDs and PV cells in the near-field configuration. We find that the near-field effect has a marginal impact on TPX cells with identical bandgaps, which means that the near-field TPX cell in the self-sustaining circuit will not be useful in practice. The insights gained from this work serve as valuable design guidelines for TPX cells operating in the self-sustaining parallel circuit, enabling practical operation without the need for an external battery storage unit.

Energy efficiency in transient surface runoff and sediment fluxes on hillslopes – a concept to quantify the effectiveness of extreme events

Abstract. Surface runoff over time shapes the morphology of the landscape. The resulting forms and patterns have been shown to follow distinct rules, which hold throughout almost all terrestrial catchments. Given the complexity and variety of the Earth's runoff processes, those findings have inspired researchers for over a century, and they resulted in many principles and sometimes proclaimed laws to explain the physics that govern the evolution of landforms and river networks. Most of those point to the first and second law of thermodynamics, which describe conservation and dissipation of free energy through fluxes depleting their driving gradients. Here we start with both laws but expand the related principles to explain the co-evolution of surface runoff and hillslope morphology by using measurable hydraulic and hydrological variables. We argue that a release of the frequent assumption of steady states is key, as the maximum work that surface runoff can perform on the sediments relates not only to the surface structure but also to “refueling” of the system with potential energy by rainfall events. To account for both factors, we introduce the concept of relative dissipation, relating frictional energy dissipation to the energy influx, which essentially characterizes energy efficiency of the hillslope when treated as an open, dissipative power engine. Generally, we find that such a hillslope engine is energetically rather inefficient, although the well-known Carnot limit does not apply here, as surface runoff is not driven by temperature differences. Given the transient and intermittent behavior of rainfall runoff, we explore the transient free energy balance with respect to energy efficiency, comparing typical hillslope forms that represent a sequence of morphological stages and dominant erosion processes. In a first part, we simulate three rainfall runoff scenarios by numerically solving the shallow water equations, and we analyze those in terms of relative dissipation. The results suggest that older hillslope forms, where advective soil wash erosion dominates, are less efficient than younger forms which relate to diffusive erosion regimes. In the second part of this study, we use the concept of relative dissipation to analyze two observed rainfall runoff extremes in the small rural Weiherbach catchment. Both flood events are extreme, with estimated return periods of 10 000 years, and produced considerable erosion. Using a previously calibrated, distributed physics-based model, we analyze the free energy balance of surface runoff simulated for the 169 model hillslopes and determine the work that was performed on the eroded sediments. This reveals that relative dissipation is largest on hillslope forms which relate to diffusive soil creep erosion and lowest for hillslope profiles relating to advective soil wash erosion. We also find that power in surface runoff and power in the complementary infiltration flux are during both events almost identical. Moreover, there is a clear hierarchy of work, which surface runoff expended on the sediments and relative dissipation between characteristic hillslope clusters. For hillslope forms that are more energy efficient in producing surface runoff, on average, a larger share of the free energy of surface runoff performs work on the sediments (detachment and transport) and vice versa. We thus conclude that the energy efficiency of overland flow during events does indeed constrain erosional work and the degree of freedom for morphological changes. We conjecture that hillslope forms and overland dynamics co-evolve, triggered by an overshoot in power during intermittent rainfall runoff events, towards a decreasing energy efficiency in overland flow. This implies a faster depletion of energy gradients during events and a stepwise downregulation of the available power to trigger further morphological development.

Immune, metabolic, and renal effects of post-wean BPF exposure in BUF/Mna female rats

Exposure to endocrine-disrupting chemicals (EDCs) increases the risk of obesity and related cardiometabolic disorders. Bisphenol F (BPF), an EDC that affects the thyroid, reproductive health, and immune cell function, is a common substitute for bisphenol A (BPA) and is used in manufacturing polycarbonates and consumer products. EDC exposure effects likely vary in the population, indicating gene x EDC interactions; however, genetic risk factors interacting with EDCs are unknown. In vivo toxicity studies performed in isogenic or genetically undefined outbred models may obscure or overemphasize exposure outcomes and do not address significant variability in population-level effects. These limitations can be avoided by studying the N/NIH Heterogeneous Stock (HS) rats, an outbred population derived from eight founder inbred strains readily amenable to genetic study. We hypothesize that BPF-induced metabolic disease has underlying genetic risk, which can be identified using HS rats and their founding inbred strains. We previously demonstrated that post-wean BPF exposure increases body growth and adiposity in male HS rats. We evaluated the metabolic impact of post-weaning BPF exposure in BUF/Mna rats, one of the HS-founding inbred strains that has genetic risks for thymic hyperplasia and focal segmental glomerulosclerosis. Weanling littermate pairs of male and female BUF rats were randomly exposed to either vehicle (0.1% EtOH) or 1.125 mg BPF/L in 0.1% EtOH for 10 weeks in drinking water. Metabolic measures, tissues, urine, and feces were taken. Males exposed to BPF did not differ from vehicle control. In females, BPF exposure did not change body composition or body weight gain; however, examination of two metabolic cage time points found that BPF females had decreased energy efficiency (weight gained/calorie absorbed) compared to vehicle control. There was an energy balance disruption in BPF females with increased 24 hr distance traveled and decreased resting metabolic rate compared to vehicle females. Also, BPF females had increased thymus and kidney mass compared to vehicle females. Our preliminary data indicate that post-wean BPF exposure affects immune, metabolic, and renal phenotypes in BUF rats in a sex-specific manner. These results suggest that BPF exacerbates inherent organ dysfunction in a genetically susceptible HS-founding inbred strain. This work supports BPF exposure as a metabolic disease risk factor and indicates that the HS rat will be a useful model for dissecting gene x BPF interactions on metabolic health. NIH T32 GM008629, NIH P30 ES005605, NIH R24 OD024617. This is the full abstract presented at the American Physiology Summit 2023 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.

Impact of Prolonged working hours, work stress and fatigue among Nurses

Job stress can endanger the physical and mental health of nurses, decrease energy and work efficiency, and fail to provide proper nursing care, which ultimately has a negative impact on patient outcomes. Therefore, it is required to investigate the stressors and effective planning to eliminate these factors. Fatigue can impair the ability to think clearly, make sound judgments and act decisively. While it is the nurse's and employer's responsibility to find the right balance between work and time off, only the nurse can determine her or his tolerance level for stress, anxiety and fatigue. Prolonged and Extended working hours and those periods without rest can seriously impair cognitive and motor performance at work, decrease alertness and productivity and increase risk of adverse events and outcomes such as tiredness, fatigue, poor performance, and safety and health care errors. A study conducted across many countries has revealed that chronic psychosocial work stressors such as low job control (low skill discretion and low decision authority), high level of psychological job demands, lack of supervisor and co-worker support at work, bullying or harassment at work, a lack of social interactions with co-workers, job insecurity, and long working hours per week, etc. cause severe adverse effects on both physical and psychological health of the workers, which sometimes even could lead to suicidal ideation in the workers.

Wet brewers’ grains as a source of protein for feedlot lambs: Impacts on intake, apparent nutrient digestibility, ruminal fermentation, and nitrogen balance

The aim of this study was to evaluate the effect of wet brewers’ grain (WBG) as an alternative ingredient replacing soybean meal (SBM) and ground corn (GC) on nutrient intake and apparent digestibility, ruminal fermentation characteristics, and nitrogen balance in feedlot lambs. Five ruminally cannulated ½ Dorper × ½ Santa Inês lambs, castrated with 48.3 ± 2.0 kg of initial BW and 8.3 ± 0.68-month-old (mean ± SD), were assigned in a 5 × 5 Latin square design. The experimental diets were composed of 10% roughage (Coastcross hay) and 90% concentrates, in which 85.9% of the diet was composed of GC (71.3%) plus SBM (14.6%) in the control diet. Treatments consisted in WBG inclusion levels of 7.6%, 15%, 23% and 30% replacing GC+SBM in control diet with the aim to maintain isonitrogenous concentrations. The data were analyzed using a linear or quadratic polynomial contrast in SAS. There was no effect of WBG inclusion on DMI, OM nor CP intake, but a linear increase was observed for NDF (P < 0.001), ADF (P < 0.001), EE intake (P < 0.01), and linear decrease (P < 0.001) on NFC intake. Inclusion of WBG decrease linearly NFC, while DM, OM, and CP digestibility were being lower for lambs fed a diet contained 23% WBG (quadratic component, p < 0.05). The replacement of SBM and corn grain by WBG, linearly increased the molar ratio of acetate (P < 0.01), and linearly decreased propionate (P < 0.01), resulting in a linear increase in the acetate:propionate ratio (P = 0.04). In addition, increasing the inclusion of WBG linearly increased the molar proportion of isovalerate (P < 0.05). Ruminal pH increased linearly (P < 0.001) by dietary WBG inclusion, as consequence, ruminal pH was maintained less time below 5.5 as WBG inclusion increased. Although nitrogen excretion was greater with 23% inclusion of WBG in diet (quadratic component, P < 0.05), there was no effect (P > 0.10) on retained N. Based on diet acceptability, digestibility, N retention, and ruminal fermentation parameters, it is concluded that, WBG can be used as feed ingredient up to 7.6% in diets, replacing partially SBM and GC in finishing diets for lambs. Inclusion WBG replacing SBM and partially GC, minimize the risk of acidosis in lambs fed high-concentrate diets during fattening. Inclusions beyond 23% decreased significant diet digestibility and increased ruminal acetate: propionate molar ratio, decreasing energy efficiency, increasing methane losses.

Effect of varying percentages of Co3O4 Nanoparticles on the Behavior of (ORR/OER) Bifunctional Co3O4/α-MnO2 Electrocatalyst

Among all type of batteries, Lithium Air Batteries (LAB) are considered to be the most effective due to their highest energy density of around 11900 Wh/kg but there are some major issues are being faced by LAB such as large overpotential, poor cycle life, low current density, and decreased energy efficiency. The solution to these issues is primarily dependent on the proper selection of an electrocatalyst. A new approach for using a bi-functional electrocatalyst produced excellent results. Here, Co3O4/α-MnO2 composite has been considered as a bifunctional catalyst because cobalt oxide performed well in the Oxygen Evolution Reaction (OER) process while manganese oxide performed well in the Oxygen Reduction Reaction (ORR) process. A simple two-step hydrothermal process is used in this work to synthesize Co3O4/α-MnO2. This work focuses on the behavior of the composite electrocatalyst when varying percentages of Cobalt oxide (5%, 10%, 15%, and 20%) are deposited on the alpha-Manganese Oxide nanorods. The primary characteristics of each sample with different percentages of Cobalt Oxide are examined, and the performance of each sample is compared to one another. Several testing techniques like Cyclic Voltammetry (CV), Linear Sweep Voltammetry (LSV), X-Ray Diffraction (XRD), and Scanning Electron Microscopy (SEM) are performed on the samples. The combination of cobalt oxide and manganese oxide showed a synergistic effect and work as a bifunctional electrocatalyst. As the percentage of Co3O4 deposited on the α-MnO2 nanorod increased, it behaves more like an OER electrocatalyst leading to a decrease in charging potential. This work will help in finding an optimum amount of Co3O4 that should be deposited on α-MnO2 nanorods to get an efficient (ORR/OER) bifunctional electrocatalyst.

Trophic Positions of Sympatric Copepods across the Subpolar Front of the East Sea during Spring: A Stable Isotope Approach

We investigated the trophic relationship between particulate organic matter (POM) and sympatric copepods within the epipelagic zone (~200 m depth) in the East Sea during spring based on stable isotope analysis (SIA). The SIA indicated that interspecific differences in the prey size and vertical segregation of feeding migration range among copepods may promote niche partitioning among sympatric copepods in each region of the subpolar front (SPF). Additionally, our results showed remarkable differences in the copepod community structure and resource utilization across the SPF. The south region of the East Sea showed higher species richness of copepods than the north region, while copepods that fed mainly on POM in the surface and subsurface chlorophyll maximum layers showed smaller body sizes in the south region. These results revealed that the food chain between primary producers and higher trophic levels was longer in the south region than in the north region. Additionally, δ13C and δ15N values of copepods increased gradually with the body size increase whereas δ15N values in the north region showed the reverse trend. Latter results could be attributed to the consumption of deep-layer POM in small copepods. Therefore, we suggest that northward shifts in the distribution of copepods under global warming may decrease energy efficiency in the pelagic ecosystem of the East Sea.

Securing energy while mitigating climate change

Mainstream energy policy emphasizes the exploitation of domestic sources to secure energy. Since readily available, many nations focus on fossil fuels, so they lack investment in the alternatives. The result is increasing atmospheric partial pressure of carbon dioxide, and energy security is still an issue. This study analyzes the impact of different variables on securing energy and reducing carbon emissions and attains this aim by econometrics. Energy-related data for 47 countries have been compiled from the IEA webpage, WDI, and BP databases, covering the period between 1990 and 2017. The results indicate that electricity generation by solar and wind globally helps both securing energy and climate change mitigation as anticipated. The dataset confirms that coal- and gas-based power generation does not contribute to global energy security. The dataset does not cast any distinct role on energy efficiency in terms of energy intensity. Increasing energy intensity, i.e., decreasing energy efficiency releases more carbon as anticipated. However, increasing energy intensity, i.e., decreasing energy efficiency, contributes to the energy security of the countries with wind power in the energy mix. One interesting result is that having a large population promotes energy security, but increasing urban population brings risks.

E-BATCH: Energy-Efficient and High-Throughput RNN Batching

Recurrent Neural Network (RNN) inference exhibits low hardware utilization due to the strict data dependencies across time-steps. Batching multiple requests can increase throughput. However, RNN batching requires a large amount of padding since the batched input sequences may vastly differ in length. Schemes that dynamically update the batch every few time-steps avoid padding. However, they require executing different RNN layers in a short time span, decreasing energy efficiency. Hence, we propose E-BATCH, a low-latency and energy-efficient batching scheme tailored to RNN accelerators. It consists of a runtime system and effective hardware support. The runtime concatenates multiple sequences to create large batches, resulting in substantial energy savings. Furthermore, the accelerator notifies it when the evaluation of an input sequence is done. Hence, a new input sequence can be immediately added to a batch, thus largely reducing the amount of padding. E-BATCH dynamically controls the number of time-steps evaluated per batch to achieve the best trade-off between latency and energy efficiency for the given hardware platform. We evaluate E-BATCH on top of E-PUR and TPU. E-BATCH improves throughput by 1.8× and energy efficiency by 3.6× in E-PUR, whereas in TPU, it improves throughput by 2.1× and energy efficiency by 1.6×, over the state-of-the-art.

Uncertainty and sensitivity analyses of operational errors in air handling units and unexpected user behavior for energy efficiency and thermal comfort

Resource scarcity and anthropogenic climate change require the reduction of performance gaps in existing buildings. In addition to unexpected user behavior, performance gaps are primarily caused by the technical gap due to operational errors in building technology. The main objective of this paper is to quantify model input uncertainty incorporating uncertain boundary conditions in terms of operational errors using thermo-dynamic building performance simulations and to identify the most relevant input parameters for the performance gaps in air conditioning systems by means of sensitivity analyses. Model input uncertainty is stochastically determined using Monte-Carlo Simulations to calculate the target values “primary energy demand” as well as “over- and under-temperature degree hours” for an office building. Selected parameters are simulated in a specific uncertainty and sensitivity analyses using the Sobol’ and Jansen estimators, which distinguish between a direct influence on the target variables and interactions between the parameters. The methodology requires a selection process, which is carried out as part of relative uncertainty and relative sensitivity analyses. Furthermore, the operational errors are compared with construction factors as well as building physics inputs and design parameters for building technology systems to show their reciprocal effects as part of a comprehensive investigation. The main findings of this paper are that operational errors in air conditioning systems play an essential role in decreasing energy efficiency and thermal comfort, but do not warrant the significance of certain construction factors as well as setpoints in building technology. Moreover, the impact of operational errors on thermal overheating of the building investigated is minor compared to other targets that cause greater model input uncertainty.

The impact of city commercial banks’ expansion on China’s regional energy efficiency

This paper investigates whether city commercial banks’ expansion can boost energy efficiency to achieve regional carbon-neutral in China spanning the period from 2003 to 2017, including local expansion and cross-regional expansion. We find a significant positive association between the expansion of city commercial banks and energy efficiency. Specifically, the expansion of city commercial banks improved energy efficiency by easing financing constraints. However, the local expansion of city commercial banks worsens credit allocation and the relationship between government and market and decreases energy efficiency. In contrast, cross-regional expansion, which improved credit allocation and the relationship between government and market, increased energy efficiency. This contrasting effect on energy efficiency is pronounced in the eastern region. Our study suggests that the nature of city commercial banks’ expansion crucially affects its potential benefits to energy efficiency improvement.

Prospective of Upfront Nitrogen (N2) Removal in LNG Plants: Technical Communication

Conventional natural gas (NG) liquefaction processes remove N2 near the tail of the plant, which limits production capacity and decreases energy efficiency and profit. Engineering calculations suggest that upfront N2 removal could have substantial economic benefits on large-scale liquefied natural gas (LNG) processes. This article provides an overview of the most promising technologies that can be employed for upfront N2 removal in the LNG process, focusing on the process selection and design considerations of all currently available upfront N2 removal technologies. The literature review revealed that although adsorption has proven to be a huge success in gas separation processes (efficiency ≥ 90%), most of the available adsorbents are CH4-selective at typical NG conditions. It would be more encouraging to find N2-selective adsorbents to apply in upfront N2 removal technology. Membrane gas separation has shown growing performance due to its flexible operation, small footprint, and reduced investment cost and energy consumption. However, the use of such technology as upfront N2 removal requires multi-stage membranes to reduce the nitrogen content and satisfy LNG specifications. The efficiency of such technology should be correlated with the cost of gas re-compression, product quality, and pressure. A hybrid system of adsorption/membrane processes was proposed to eliminate the disadvantages of both technologies and enhance productivity that required further investigation. Upfront N2 removal technology based on sequential high and low-pressure distillation was presented and showed interesting results. The distillation process, operated with at least 17.6% upfront N2 removal, reduced specific power requirements by 5% and increased the plant capacity by 16% in a 530 MMSCFD LNG plant. Lithium-cycle showed promising results as an upfront N2 chemical removal technology. Recent studies showed that this process could reduce the NG N2 content at ambient temperature and 80 bar from 10% to 0.5% N2, achieving the required LNG specifications. Gas hydrate could have the potential as upfront N2 removal technology if the is process modified to guarantee significant removals of low N2 concentration from a mixture of hydrocarbons. Retrofitting the proposed technologies into LNG plants, design alterations, removal limits, and cost analysis are challenges that are open for further exploration in the near future. The present review offers directions for different researchers to explore different alternatives for upfront N2 removal from NG.