Energy Performance Evaluation Research Articles

Seasonal energy performance evaluation with new perspective on partial-coupling ejection-compression solar cooling system for modern city buildings

Space cooling accounts for high percentage of energy consumption in modern city building. To improve energy utilizing efficient of space cooling, a new system based on solar partial-coupling ejection-compression refrigeration cycle is studied. Builds are assumed to be located at modern city of Shanghai, with area of 100 m2 for each floor. With a model combining cooling system, building, and weather information, comparative analysis is carried out hourly, using new perspective of total primary energy, during the whole cooling season. For the building with a common height of six-storey in modern city, partial-coupling ejection-compression refrigeration cycle reveals obvious superiority in electric coefficient of performance, solar factor, thermal coefficient of performance, total primary energy, with best value of 6.2, 1, 3.6, and 14 kW, respectively, which helps to reduce carbon dioxide emission. The remarkable difference in auxiliary heat between partial-coupling ejection-compression refrigeration cycle and traditional ejection-compression refrigeration cycle results in the great primary energy saving of partial-coupling cycle, which reveals significant superiority and good suitability of partial-coupling cycle used in multi-stroey buildings in modern city.

On the solar air heater thermal enhancement and flow topology using differently shaped ribs combined with delta-winglet vortex generators

A numerical investigation has been conducted to study the convective heat transfer enhancement and friction loss behaviors for turbulent flow by using arrays of differently shaped ribs combined with delta-winglet vortex generators (DWVGs) pair on the absorber plate of a solar air heater. Four transverse vortex generators arrays, i.e., 90° continuous ribs, 90° truncated ribs, 60° V-shaped continuous ribs, and 60° V-shaped truncated ribs, are studied to investigate the mixing effect with the DWVGs pair. The aspect ratio (AR = Lv/Hv) of the DWVGs is 2:1 while the geometrical condition of the ribs is height of 0.003 m and pitch of 0.028 m. The Reynolds number ranges from 4000 to 20,000. Results of temperature, Nusselt number, vortical structure, topological portrait, turbulent kinetic energy (TKE), friction factor and thermal performance evaluation are included. The results show that the adoption of DWVGs and the shape type of the ribs have great impact on the heat transfer and flow structure in the solar air heater. It is found that the DWVGs combined with the 60° V-shaped continuous ribs contributes the best heat transfer performance, and the heat transfer is enhanced by 39.4% compared with the only DWVGs case.

Quantitative evaluation of the building energy performance based on short-term energy predictions

Building energy prediction is a potential tool for benchmarking the future energy uses of individual buildings. However, inevitable gaps between predicted and actual energy uses and discrepancies between buildings make it challenging to quantify energy consumption. Therefore, this paper proposes a systematic methodology of quantitative building energy evaluation based on short-term energy prediction. First, the 24-h ahead building energy prediction model is developed based on a recurrent neural network via the Multi-Input Multi-Output strategy. Second, the quantitative energy evaluation strategy is proposed to quantify prediction gaps based on the 1-D k-means clustering. Third, case studies are conducted on five real buildings to verify the reliability of the proposed methodology. Results show that the energy prediction models achieved outstanding accuracies. Besides, it is necessary to analyze the absolute percentage error (APE) variation of each time step to deeply understand the building energy performance rather than the overall prediction performance evaluation index, such as CV-RMSE and MAPE. Further, customized energy quantification systems are established for buildings per their specific, individual energy performance. The building energy is quantified by labeling APEs into multiple levels. Moreover, building operation characteristics can be further understood by quantifying energy uses.

Utilising Open Geospatial Data to Refine Weather Variables for Building Energy Performance Evaluation—Incident Solar Radiation and Wind-Driven Infiltration Modelling

In building thermal energy characterisation, the relevance of proper modelling of the effects caused by solar radiation, temperature and wind is seen as a critical factor. Open geospatial datasets are growing in diversity, easing access to meteorological data and other relevant information that can be used for building energy modelling. However, the application of geospatial techniques combining multiple open datasets is not yet common in the often scripted workflows of data-driven building thermal performance characterisation. We present a method for processing time-series from climate reanalysis and satellite-derived solar irradiance services, by implementing land-use, and elevation raster maps served in an elevation profile web-service. The article describes a methodology to: (1) adapt gridded weather data to four case-building sites in Europe; (2) calculate the incident solar radiation on the building facades; (3) estimate wind and temperature-dependent infiltration using a single-zone infiltration model and (4) including separating and evaluating the sheltering effect of buildings and trees in the vicinity, based on building footprints. Calculations of solar radiation, surface wind and air infiltration potential are done using validated models published in the scientific literature. We found that using scripting tools to automate geoprocessing tasks is widespread, and implementing such techniques in conjunction with an elevation profile web service made it possible to utilise information from open geospatial data surrounding a building site effectively. We expect that the modelling approach could be further improved, including diffuse-shading methods and evaluating other wind shelter methods for urban settings.

Energy performance evaluation of centralised ice-storage district cooling system

Centralised district cooling system equipped with ice storage has substantial advantages in comprehensive energy utilization and cost effectiveness. It facilitates cutting peak and filling valley of power load and helps saving energy costs by using the peak-valley electricity price. Despite such advantages, energy performance of ice-storage district cooling systems is still a controversial topic, especially there is a lack of effective evaluation methods and relevant evaluation standards in China. Therefore, this paper establishes a thorough index system to evaluate energy performance of ice-storage district cooling system. The index system covers all aspects of ice-storage district cooling systems, including the gradual evaluation of each process from equipment, via subsystem to whole system. Afterwards, the index system is used to analyse a real case, focusing on the eight most important energy performance indexes. The results show that the index system can adapt well to the evaluation requirements, help to find energy performance problems and facilitate to improve energy efficiency. In view of existing insufficiency, further efforts are needed to make in formulating reasonable benchmarks of such energy performance indexes.

Building energy performance assessment using linked data and cross-domain semantic reasoning

Cross-domain information is essential for building energy performance assessment. The heterogeneous nature of this information is a major source for inefficient assessments. The semantic web provides a flexible pathway for addressing recognised interoperability issues. However, further implicit knowledge in cross-domain information could provide meaningful solutions for such assessments. This paper aims to develop a conceptual framework that links cross-domain information, infers implicit knowledge, and empowers building managers with insightful assessments. The framework integrates Web Ontology Language (OWL) ontologies, Resource Description Framework (RDF) instances, and a set of predefined rules to infer implicit knowledge, which can satisfy data requirements of performance metrics and enable meaningful performance assessments. Then building managers can identify inefficient building operations and improve energy efficiency while maintaining desired building functions. This approach reduces burdensome intervention from the managers when compared with traditional solutions. A demonstration highlights the engineering value by evaluating energy performance of a university building.

The study of a highly efficient and environment-friendly scale inhibitor for calcium carbonate scale in oil fields

A highly efficient and environment-friendly scale inhibitor (MA-VA-VS) was synthesized via free radical solution polymerization method, where maleic anhydride (MA), vinyl acetate (VA) and vinyl sulfonate (VS) acted as monomers, while ammonium persulfate was used as initiator. The inhibition performance and the structure as well as properties was characterized using static jar measurement and dynamic test, Fourier transform infrared spectroscopy and thermogravimetric analysis. The surface morphology and composition of scale formed in the solution were examined using scanning electron microscopy and X-ray diffraction, respectively. The binding energies of inhibitor with calcite (104) face were calculated using Materials Studio 2017 (MS) at 323 K. The results show that the inhibition efficiency gradually increases with increasing inhibitor concentration. While as the Ca2+ concentration increases, the efficiency first increases and then decreases. With the increase in temperature or pH, the efficiency generally decreases. It is confirmed that the inhibition efficiency can reach 91.4% when 150 mg/L MA-VA-VS is used in a flow condition. Both the calculated binding energy and inhibition performance evaluation results demonstrate that the scale inhibition performance of MA-VA-VS is better than a commercial scale inhibitor (HPMA). The excellent inhibition performance of this inhibitor is due to its chelation and dispersion properties.

The Path for Green Development and Utilization of Energy in China

The green development and utilization of energy is an important component for the new energy security strategy and the ecological civilization in China. To promote energy production and consumption revolution, this study first summarizes the development status and challenges of China’s energy sector, and elaborates the concept and principles of energy green development and utilization. Subsequently, an energy green development evaluation model and an energy utilization system evaluation index model are established to evaluate the economic and environmental benefits of the energy green development and utilization approach; development goals are then predicted for 2030 and 2050 using these two models. The energy green development and utilization can be implemented from two aspects. In terms of energy distribution, China should focus on the clean and efficient development and utilization of fossil energy, the large-scale development and utilization of clean energy, and the intelligentization of energy systems, particularly emphasizing green coal engineering, oil stabilization and gas enhancement, and energy intensification and conservation. In terms of scientific and technological innovation, China should promote breakthroughs for the safe, efficient, and clean utilization of coal; develop key technologies for deep-seated and unconventional oil and gas exploration and development; and advance scientific and technological innovation for large-scale development and utilization of clean energy. To build a clean, low-carbon, safe, and efficient energy system, suggestions are proposed in terms of energy management system innovation, energy price marketization, performance evaluation, and technology innovation system.

Energy Performance Evaluation of a Ventilated Façade System through CFD Modeling and Comparison with International Standards

Ventilated façades can help to reduce summer building thermal loads and, therefore, energy consumption due to air-conditioning systems thanks to the combined effect of the solar radiation reflection and the natural or forced ventilation into the cavity. The evaluation of ventilated façades behavior and performance is complex and requires a complete thermo-fluid dynamic analysis. In this study, a computational fluid dynamic (CFD) methodology has been developed for the complete assessment of the energy performance of a prefabricated timber–concrete composite ventilated façade module in different operating conditions. Global numerical results are presented as well as local ones in terms of heat flux, air velocity, and temperature inside the façade cavity. The results show the dependency of envelope efficiency on solar radiation, the benefits that natural convection brings on potential energy savings and the importance of designing an optimized façade geometry. The results concerning the façade behavior have been thoroughly compared with International Standards, showing the good accuracy of the model with respect to these well-known procedures. This comparison allowed also to highlight the International Standards procedures limits in evaluating the ventilated façade behavior with the necessary level of detail, with the risk of leading to design faults.

Evaluation of energy performance of dynamic overhang systems for US residential buildings

A novel dynamic overhang system is evaluated in this paper when applied to control solar heat gains through windows of US residential buildings. In particular, the energy performance of the dynamic overhangs is compared to static systems using various operation scenarios. The main objective for the control strategies evaluated in the analysis is to minimize annual heating and cooling energy consumption when dynamic instead of static overhangs are applied to US residential buildings. The operation of the dynamic overhangs is adjusted to account for the range of positions allowed as well as the setting frequencies. In particular, the dynamic overhangs can be set on hourly, daily, and monthly basis depending on the window orientation and the time of the year. The analysis has indicated that the performance of the dynamic overhangs depend on their design specifications as well as on the window glazing type. However, the energy saving potential for the dynamic overhangs compared to static devices depend largely on the window size and the climate with significant reduction in cooling energy use achieved in hot and mild US climatic zones. Indeed, the dynamic overhangs can save over 45% of the air conditioning needs for US homes with window-to-wall ratio of 30% located in Phoenix, AZ, and San Francisco, CA, when automatically operated on hourly basis.

Annual energy losses due to partial shading in PV modules with cut wafer-based Si solar cells

To further improve the efficiency of the wafer-based silicon photovoltaic (PV) module, producers are introducing new module designs with cut-cells. Since smaller solar cells might be affected by partial shading even more and earlier than full-size cells, the energy performance simulations of partially shaded modules are crucial. A detailed shading analyses of partially shaded modules with different cut cell designs are presented not only on a single case scenario but on annual energy yield simulations using Spice, where a shading scenario over the whole module by the use of a new 3D shading horizon profile of selected shading objects is calculated. The annual simulations reveal that regardless the module design almost all cells in the module are confronted by reverse bias, which can deteriorate the module performance significantly. Simulation results with three different shading objects on five different module topologies at five locations showed that the best cut-cell module design depends strongly by the micro location and shading objects; however, in general the string of solar cells connected in series should be aligned with the shading shape around noontime as much as possible. A comprehensive annual energy performance evaluation of partially shaded cut-cell modules revealed; that with a correct cell layout of cut-cells in a PV module, the shading losses can be reduced by 30–50% if comparing to the standard PV module design.

Thermal Performance and Comfort Conditions Analysis of a Vernacular Palafitic Timber Building in Portuguese Coastline Context

The palafitic timber constructions of the central Portuguese coastline are an example of the adaptation to site-specific conditions (climate and sand landscape morphodynamics) using the available endogenous resources. Thus, in a context of environmental awareness and climate change, it is relevant to understand their features/strategies and how they perform. This work analyses the energy performance and thermal condition evaluation of a vernacular timber building–palheiro–from Praia de Mira, through in situ measurements, subjective analysis and energy simulation provided by DesignBuilder/EnergyPlus. The results show a good or satisfactory thermal performance during most of the seasons by passive means only. Despite, it was not possible to guarantee thermal comfort conditions for the occupants during winter. In the energy performance analysis, five scenarios, with different external walls, were compared. In the two scenarios that satisfy the maximum U-value for the climate zone, the current conventional building had a slightly better performance on heating and cooling (less 1.1 and 1.4 kWh/m2, respectively) than the timber building. However, the difference between the two construction solutions is not substantial in the annual energy demand (2.5 kWh/m2, 7.3%), indicating that timber structures are suitable in this mild climate area.

Need for integrated approach for energy efficiency assessments and material evaluation of historic buildings

Abstract Concerns about the energy sustainability of the existing building stock and about changes in both climatic conditions and comfort requirements, in recent years have put a lot of research focus on energy performance evaluation of buildings, which also need detailed assessment of material properties. Most often, historic masonry buildings present both structural and material typicality owing to local material availability and technical know-how at time of construction. Further, the available energy efficiency assessment methodologies demand a detailed diagnostic of the material behaviour. Along with this, the heritage status and the conservation policies attached to these buildings pose special requirements of on-site measurement and non-invasive analytical tools. Presently, as carried out, commonly the evaluation of all these aspects is undertaken separately. The paper highlights the need for an integrated investigative approach considering the need of material investigations and input requirements of advanced analytical tools like the simulation software systems. The paper also highlights the available literature references and practices presently followed in the energy efficiency studies for documenting material properties and identifies a vast scope for further study in the domain.

Circular Economy Initiatives through Energy Accounting and Sustainable Energy Performance under Integrated Reporting Framework

The financial reporting plays a significant role in sustainable development, as it contributes greatly to providing the information required to assess sustainable development performance. In order to achieve the sustainable development, accurate information should be provided to stakeholders on the energy consumed and the impact of energy consumption on the environment. Information on sustainable energy performance needs providing both of financial and non-financial information. However, the traditional financial reporting system is unable to provide information that helps measure and promote sustainable energy performance, as the current accounting system provides financial information only. It is therefore important to adopt an appropriate reporting framework to support the evaluation of sustainable energy performance. This paper proposes an approach to the measure the sustainable energy performance based on the integrated reporting framework. A unique feature of the approach is the selection of corporate energy performance indicators that cover both financial and non-financial information. This paper therefore sets out indicators for assessing sustainable energy performance based on the Integrated Reporting Framework. Furthermore, the application of the indicators proposed in this paper helps regulators and economic policy makers to develop sustainable development strategies at national level. Moreover, the adoption of the proposed indicators can provide accurate information on the real and future of sustainable energy in the country.

RACH in Self-Powered NB-IoT Networks: Energy Availability and Performance Evaluation

NarrowBand-Internet of Things (NB-IoT) is a new 3GPP radio access technology designed to provide better coverage for a massive number of low-throughput low-cost devices in delay-tolerant applications with low power consumption. To provide reliable connections with extended coverage, a repetition transmission scheme is introduced to NB-IoT during both Random Access CHannel (RACH) procedure and data transmission procedure. To avoid the difficulty in replacing the battery for IoT devices, the energy harvesting is considered as a promising solution to support energy sustainability in the NB-IoT network. In this work, we analyze RACH success probability in a self-powered NB-IoT network taking into account the repeated preamble transmissions and collisions, where each IoT device with data is active when its battery energy is sufficient to support the transmission. We model the temporal dynamics of the energy level as a birth-death process, derive the energy availability of each IoT device, and examine its dependence on the energy storage capacity and the repetition value. We show that in certain scenarios, the energy availability remains unchanged despite randomness in the energy harvesting. We also derive the exact expression for the RACH success probability of a randomly chosen IoT device under the derived energy availability, which is validated under different repetition values via simulations. We show that the repetition scheme can efficiently improve the RACH success probability in a light traffic scenario, but only slightly improves that performance with very inefficient channel resource utilization in a heavy traffic scenario.

Defining Criteria for the Selection of Measures to Increase Energy Efficiency in Public Buildings

Buildings, although one of the largest energy consumers in the world, also represent big potential to reduce energy consumption, dependence on fossil fuels and carbon dioxide emissions, through the implementation of energy efficiency measures. Improvement of energy efficiency of existing buildings requires a dedicated, serious and detailed approach. Investors are often guided by economic criteria, which greatly influence on investments and interventions, potentially causing some negative side effects (comfort reduction, use of energy-intensive materials, etc.). Therefore, it is very important to rely on methods that provide detailed and affordable cost, technical and environmental analysis. Energy efficiency methods are often based on simple methods such as research, estimation of energy consumption, preliminary design, estimation of energy savings and financial cost-effectiveness. For example, in energy audits of buildings, annual energy consumption and cost-effectiveness are considered for analysis. For a more detailed assessment, a calculation tool based on the calculation of energy consumption of particular facility and the estimation of energy savings after the proposed energy efficiency measures is being used. The proposed measures generally represent a classic scenario of energy efficiency measures. In this paper, factors such as comparison of the share of fossil fuels and renewable energy sources (RES), the estimation of cost-effectiveness of the use of renewable energy technologies, aspect of embodied energy in materials and life cycle assessment in buildings are being considered. This paper defines the criteria for the evaluation of scenarios (functional groups of measures) for increasing energy efficiency of the building, which include, in addition to energy and economic aspects, environmental aspect. The six criteria have been defined for evaluation of energy efficiency scenarios related to: annual energy consumption, total annual primary energy, share of RES in primary energy, direct and indirect carbon emissions, embodied energy in applied materials and investment per scenario. For each criteria an expression for its calculation is given. Defined criteria are calculated for six scenarios of increasing the energy efficiency of Mechanical Engineering Faculty, University of Sarajevo. Based on the calculated different values of criteria of considered aspects, it is possible to identify in more detail way critical points, advantages and disadvantages of different combinations of energy efficiency measures, which can further serve to identify the best strategy necessary for evaluation of energy performance of the building before and after the intervention.

Opportunities and Limitations of Building Energy Performance Simulation Tools in the Early Stages of Building Design in the UK

This research investigates the use of Building Energy Performance Simulation (BEPS) tools in the early stages of building design in UK architectural practices with a particular focus on the barriers and opportunities to their effective application and further uptake. Two primary methods of investigation were undertaken; the first was a wide survey among UK architects and architectural practices, where the responses of 418 participants were electronically gathered and analysed. A deeper understanding of the issues was developed through an analysis of the process of low-energy building design using semi-structured interviews with six representatives of well-established architectural practices in the UK. The findings reveal that while there is an increasing understanding of the importance of BEPS involvement at the early design stages, there was limited evidence of actual early implementation of BEPS tools other than a few well known but specialised tools such as Passive House Planning Package (PHPP) which were used mainly for domestic energy performance evaluation. However, many practices surveyed showed interest in achieving higher standards than the “basic” regulatory backstops, which has resulted in Passive House and BREEAM seeing increasing use in domestic and non-domestic projects respectively. Although there has been a significant increase in the development and availability of tools and methodologies for assessing building energy performance our study shows that the focus for future research needs to be shifted from the “tool development” to looking at methods of implementing and using such tools in practice at the early design stages.

An assessment of biomass torrefaction severity indexes

Previous studies have quantified the efficiency of biomass torrefaction processes by proposing severity indexes to discuss the variability of thermally modified biomass properties. However, comparisons of the accuracy and applicability of those indexes are few in the literature. To fill that gap, this study sought to assess five indexes usually applied in some torrefaction studies: weight loss, index of torrefaction, torrefaction severity index, severity factor, and torrefaction severity factor. These indexes were compared to characterize torrefaction under different conditions, and their accuracy in evaluating, correlating and predicting the physical, chemical and energetical properties of torrefied eucalyptus. As a result, the five evaluated indexes presented R2 > 0.84 andp-values ≤ 0.05 when evaluating basic properties. For all five indexes, there was a statistical significance when evaluating energy performance and R2 > 0.81. The three yield property-based indexes were more effective in predicting torrefied product properties and energy performance parameters. The two operating condition-based indexes were more effective in analyzing solid product properties than devolatilization. This work provided insight into which index is more appropriate for research and industrial applications.

Experimental evaluation of energy and exergy performance of a nanofluid-based photovoltaic/thermal system equipped with a sheet-and-sinusoidal serpentine tube collector

The chief goal of this survey is about comprehensively examine a photovoltaic-thermal (PVT) system with a sheet-and-sinusoidal serpentine tube collector (PVT-S) experimentally from the perspective of energy, exergy and entropy generation. The results are compared with those of the PV module deprived of cooling and the PVT unit accompanied by a sheet-and-plain serpentine pipe collector (PVT-P). A water based nanofluid (NF) containing magnetite nanoadditives is considered as a coolant. The effects of volume concentration of nanoadditives (ϕ), NF mass flow rate (m˙nf), amplitude of the sinusoidal serpentine tube (a), and wavelength of the sinusoidal serpentine tube (w) on the performance metrics of the PVT unit are considered. The outcomes declared that the combined use of sinusoidal serpentine tube and NF leads to augmentation of energetic and exergetic performances of the PVT unit. According to the results, the first-law thermal, electrical and overall efficiencies of the PVT-S unit are 20.67–30.63%, 1.94–2.32% and 8.83–18.28% bigger than those of the PVT-P unit, respectively. In addition, the second-law thermal, electrical and overall efficiencies of the PVT-S unit are 10.56–26.68%, 1.94–2.32% and 2.44–4.57% greater than those of the PVT-P unit, respectively. Moreover, it was demonstrated that the increase of ϕ and m˙nf and the decrease of w result in an increment of performance features of the studied PVT units. Furthermore, it was found that among the entire the items considered in the survey, the best energetic and exergetic performances and the lowest entropy generation rate belongs to the NF-based PVT-S unit at ϕ=2%, m˙nf=80 kg/h, a=5 mm and w=60 mm.

Energy performance evaluation of two-phase injection heat pump employing low-GWP refrigerant R32 under various outdoor conditions

The refrigerant R32 has been receiving significant attention as an alternative to R410A used in heat pumps, owing to its lower global warming potential. The two-phase injection (TPI) technique is introduced to achieve improved energy performance along with high system reliability in R32 heat pumps, owing to their high discharge temperature. The objectives of this study are to compare the performances as well as reliabilities of the R32 and R410A TPI heat pumps and provide the design guidelines for achieving the best performance with safe operation. The performances of the R32 and R410A TPI heat pumps are measured by varying compressor frequency and outdoor temperature. The TPI technique enables the R32 heat pump to operate at a higher compressor frequency under severe weather conditions. At low outdoor temperatures of −10 °C and −15 °C, the R32 TPI heat pump demonstrates a superior heating capacity and coefficient of performance (COP) compared with the R410A TPI heat pump. In addition, the injection parameters in the R32 TPI heat pump are optimized under various operating conditions.