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  • 301.
    Zhang, Fan
    et al.
    Dalarna University, School of Technology and Business Studies, Energy Technology.
    Fleyeh, Hasan
    Dalarna University, School of Technology and Business Studies, Computer Engineering.
    Hybrid Artificial Neural Networks Based Models for Electricity Spot Price Forecasting - A Review2019In: 2019 16th European Energy Market Conference (EEM 19), 2019, article id 8916245Conference paper (Refereed)
    Abstract [en]

    Electricity price forecasting plays a crucial role in aliberalized electricity market. In terms of forecasting approaches,artificial neural networks are the most popular amongresearchers due to their flexibility and efficiency in handlingcomplexity and non-linearity. On the other hand, a single neuralnetwork presents certain limitations. Therefore, in recent years,hybrid models that combine multiple algorithms to balance outthe advantages of a single model have become a trend. However,a review of recent applications of hybrid neural networks basedmodels with respect to electricity price forecasting is not found inthe literature and hence, the motivation of this paper is to fill thisresearch gap. In this study, methodologies of existing forecastingapproaches are briefly summarized, followed by reviews of neuralnetwork based hybrid models concerning electricity forecastingfrom year 2015 onwards. Major contributions of each study,datasets adopted in experiments as well as the correspondingexperiment results are analyzed. Apart from the review ofexisting studies, the novelty and advantages of each type of hybridmodel are discussed in detail. Scope of the review is theapplication of hybrid neural network models. It is found that theforecast horizon of the reviewed literature is either hour ahead orday ahead. Medium and long term forecasting are notcomprehensively studied. In addition, though hybrid modelsrequire relatively large computational time, time measurementsare not reported in any of the reviewed literature.

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  • 302.
    Zhang, Fan
    et al.
    Dalarna University, School of Technology and Business Studies, Energy Technology.
    Fleyeh, Hasan
    Dalarna University, School of Technology and Business Studies, Computer Engineering.
    Short Term Electricity Spot Price Forecasting Using CatBoost and Bidirectional Long Short Term Memory Neural Network2019In: 19th European Energy Market Conference (EEM 19), 2019Conference paper (Refereed)
    Abstract [en]

    Electricity price forecasting plays a crucial role in liberalized electricity markets. Generally speaking, short term electricity price forecasting is essential for electricity providers to adjust the schedule of production in order to balance consumers’ demands and electricity generation. Short term forecasting results are also utilized by market players to decide the timing of purchasing or selling to gain maximized profit. Among existing forecasting approaches, neural networks are regarded as the state of art method. However, deep neural networks are not studied comprehensively in this field, thus the motivation of this study is to fill this research gap. In this paper, a novel hybrid approach is proposed for short term electricity price forecasting. To be more specific, categorical boosting (Catboost) algorithm is used for feature selection and a bidirectional long short term memory neural network (BDLSTM) serves as the main forecasting engine. To evaluate the effectiveness of the proposed approach, two datasets from the Nord Pool market are employed in the experiment. Moreover, the performance of multi-layer perception (MLP) neural network, support vector regression (SVR) and ensemble tree models are evaluated and compared with the proposed model. Results show that the proposed approach outperforms the rest models in terms of mean absolute percentage error (MAPE).

  • 303.
    Zhang, Fan
    et al.
    Dalarna University, School of Technology and Business Studies, Energy Technology.
    Fleyeh, Hasan
    Dalarna University, School of Technology and Business Studies, Computer Engineering.
    Wang, X.
    Lu, M.
    Construction site accident analysis using text mining and natural language processing techniques2019In: Automation in Construction, ISSN 0926-5805, E-ISSN 1872-7891, Vol. 99, p. 238-248Article in journal (Refereed)
    Abstract [en]

    Workplace safety is a major concern in many countries. Among various industries, construction sector is identified as the most hazardous work place. Construction accidents not only cause human sufferings but also result in huge financial loss. To prevent reoccurrence of similar accidents in the future and make scientific risk control plans, analysis of accidents is essential. In construction industry, fatality and catastrophe investigation summary reports are available for the past accidents. In this study, text mining and natural language process (NLP) techniques are applied to analyze the construction accident reports. To be more specific, five baseline models, support vector machine (SVM), linear regression (LR), K-nearest neighbor (KNN), decision tree (DT), Naive Bayes (NB) and an ensemble model are proposed to classify the causes of the accidents. Besides, Sequential Quadratic Programming (SQP) algorithm is utilized to optimize weight of each classifier involved in the ensemble model. Experiment results show that the optimized ensemble model outperforms rest models considered in this study in terms of average weighted F1 score. The result also shows that the proposed approach is more robust to cases of low support. Moreover, an unsupervised chunking approach is proposed to extract common objects which cause the accidents based on grammar rules identified in the reports. As harmful objects are one of the major factors leading to construction accidents, identifying such objects is extremely helpful to mitigate potential risks. Certain limitations of the proposed methods are discussed and suggestions and future improvements are provided.

  • 304. Zhang, Nan
    et al.
    Chen, Xiangjie
    Su, Yuehong
    Zheng, Hongfei
    Ramandan, Omar
    Zhang, Xingxing
    Dalarna University, School of Technology and Business Studies, Energy Technology.
    Chen, Hongbin
    Riffat, Saffa
    Numerical investigations and performance comparisons of a novel cross-flow hollow fiber integrated liquid desiccant dehumidification system2019In: Energy, ISSN 0360-5442, E-ISSN 1873-6785, Vol. 182, p. 1115-1131Article in journal (Refereed)
    Abstract [en]

    The heat and mass transfer process of a novel cross-flow hollow fiber integrated liquid desiccant dehumidification system is analysed numerically. Compared with other porous media or packing towers in dehumidification applications, hollow fibre membranes have significant advantages including low weight, corrosion resistant and no liquid droplet carryover. A novel air-KCOOH cross-flow dehumidification system was designed and manufactured, with 5500 hollow fibres formed into a circular module. The variations of the dehumidification effectiveness and moisture removal rates were studied numerically and validated against experimental results under the incoming air mass flow rates of 0.08-0.26kg/s and relative humidity from 55% to 75%. The dehumidification performance comparisons for the proposed system using CaCl2, LiCl and KCOOH as the desiccants have been conducted as well. The results demonstrated that under the same m*(ratio between solution mass flow rate to the air mass flow rate), the proposed system using 62% KCOOH could achieve approximately the same latent effectiveness compared with 40% CaCl2 and 32% LiCl, with the at least 3.1% sensible effectiveness increased by. Therefore, it could be concluded that the proposed system using KCOOH as desiccant could be more applicable for dehumidification purpose compared with other systems using conventional liquid desiccants.

  • 305.
    Zhang, Xingxing
    et al.
    Dalarna University, School of Technology and Business Studies, Energy Technology.
    Lovati, Marco
    Vigna, Ilaria
    Widén, Joakim
    Han, Mengjie
    Dalarna University, School of Technology and Business Studies, Microdata Analysis.
    Gál, Csilla V
    Dalarna University, School of Technology and Business Studies, Energy Technology.
    Feng, Tao
    A review of urban energy systems at building cluster level incorporating renewable-energy-source (RES) envelope solutions2018In: Applied Energy, ISSN 0306-2619, E-ISSN 1872-9118, Vol. 230, p. 1034-1056Article in journal (Refereed)
    Abstract [en]

    The emergence of renewable-energy-source (RES) envelope solutions, building retrofit requirements and advanced energy technologies brought about challenges to the existing paradigm of urban energy systems. It is envisioned that the building cluster approach—that can maximize the synergies of RES harvesting, building performance, and distributed energy management—will deliver the breakthrough to these challenges. Thus, this paper aims to critically review urban energy systems at the cluster level that incorporate building integrated RES solutions. We begin with defining cluster approach and the associated boundaries. Several factors influencing energy planning at cluster scale are identified, while the most important ones are discussed in detail. The closely reviewed factors include RES envelope solutions, solar energy potential, density of buildings, energy demand, integrated cluster-scale energy systems and energy hub. The examined categories of RES envelope solutions are (i) the solar power, (ii) the solar thermal and (iii) the energy-efficient ones, out of which solar energy is the most prevalent RES. As a result, methods assessing the solar energy potentials of building envelopes are reviewed in detail. Building density and the associated energy use are also identified as key factors since they affect the type and the energy harvesting potentials of RES envelopes. Modelling techniques for building energy demand at cluster level and their coupling with complex integrated energy systems or an energy hub are reviewed in a comprehensive way. In addition, the paper discusses control and operational methods as well as related optimization algorithms for the energy hub concept. Based on the findings of the review, we put forward a matrix of recommendations for cluster-level energy system simulations aiming to maximize the direct and indirect benefits of RES envelope solutions. By reviewing key factors and modelling approaches for characterizing RES-envelope-solutions-based urban energy systems at cluster level, this paper hopes to foster the transition towards more sustainable urban energy systems.

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  • 306.
    Zhang, Xingxing
    et al.
    Dalarna University, School of Technology and Business Studies, Energy Technology.
    Pan, Song
    Wu, Jinshun
    Xia, Liang
    China leans balance to distributed solar-power projects: challenge and opportunities2017Conference paper (Refereed)
  • 307.
    Zhang, Xingxing
    et al.
    Dalarna University, School of Technology and Business Studies, Energy Technology.
    Pan, Song
    Wu, Jinshun
    Xia, Liang
    Recycling discarded shipping containers for reliable building envelopes: a design case for senior citizens in Solar Decathlon China 20172017Conference paper (Refereed)
  • 308.
    Zhang, Xingxing
    et al.
    Dalarna University, School of Technology and Business Studies, Energy Technology.
    Wang, X.
    Zhao, Xiaoyun
    Dalarna University, School of Technology and Business Studies, Microdata Analysis.
    Solar System Design and Energy Performance Assessment Approaches2019In: Advanced Energy Efficiency Technologies for Solar Heating, Cooling and Power Generation, Springer, 2019, p. 417-451Chapter in book (Refereed)
    Abstract [en]

    Recently, solar system has gained a rapid development in many countries because it is clean and sustainable. Many solar systems including the solar photovoltaic/loop-heat-pipe (PV/LHP), solar loop-heat-pipe (LHP), solar photovoltaic/micro-channel heat pipe (PV/MCHP) system, and solar thermal facade system (STF) have been designed for energy saving. To assess these systems’ performance, there are many approaches such as energy and exergy assessment which is used in this chapter to analyze their performance. Besides the system design, the authors set up dedicated experimental models in combination with computer models to test the systems’ performance. Furthermore, some systems are compared with the conventional system, and the performance of these solar systems is better than the conventional system. In addition, these solar systems are applied in many real buildings and their performance is examined, the results show that the solar systems have more potential to boost the building energy efficiency and create the possibility of solar development in buildings. © 2019, Springer Nature Switzerland AG.

  • 309.
    Zhang, Xingxing
    et al.
    Dalarna University, School of Technology and Business Studies, Energy Technology.
    Wei, Y.
    He, W.
    Qiu, Z.
    Zhao, Xiaoyun
    Dalarna University, School of Technology and Business Studies, Microdata Analysis.
    Solar Systems’ Economic and Environmental Performance Assessment2019In: Advanced Energy Efficiency Technologies for Solar Heating, Cooling and Power Generation / [ed] Xudong Zhao, Xiaoli Ma, Springer, 2019, p. 453-486Chapter in book (Refereed)
    Abstract [en]

    The economic and environmental performance assessment of the solar system plays a critical role in building design, operation and retrofit. A dedicated economic model is necessary to assess the investment feasibility on a new technology, which allows investors to decide on a profitable investment, compare investment projects and know about the benefits of the best investment. An environmental model is adopted to predict carbon emission reduction in the solar system relative to the traditional heating and electronic systems. This chapter introduced three up-to-date solar system models and corresponding assessments related to their applications, including solar photovoltaic/loop heat pipe (PV/LHP) heat pump water heating system, loop heat pipe-based solar thermal facade (LHP-STF), heat pump water heating system as well as solar thermal facade (STF). The research results will be able to assist in decision-making in implementation of the proposed PV/T technology and analyses of the associated economic and environmental benefits, thus contributing to realization of regional and global targets on fossil fuel energy saving and environmental sustainability.

  • 310.
    Zhang, Xingxing
    et al.
    Dalarna University, School of Technology and Business Studies, Energy Technology.
    Wu, J.
    Pan, S.
    Han, Mengjie
    Dalarna University, School of Technology and Business Studies, Microdata Analysis.
    An economic analysis of the solar photovoltaic/thermal (PV/T) technologies in Sweden: A case study2019In: IOP Conference Series: Materials Science and Engineering, 2019, Vol. 556, no 1, article id 012002Conference paper (Refereed)
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  • 311.
    Zhang, Xingxing
    et al.
    Dalarna University, School of Technology and Business Studies, Energy Technology.
    Wu, J
    Zhang, Y
    Pan, S
    Wei, Y
    Xia, L
    Zhang, W
    Numerical study on thermal performance of a gravity assisted loop heat pipe2017Conference paper (Refereed)
    Abstract [en]

    This article carried out a parametric study of the thermal performance of a novel gravity assisted loop heat pipe (GALHP)with composite mesh-screen wick structure. A refined three-way structure with interior liquid-vapour separator wasdeveloped on top of the evaporator to enable a gravity-assisted operation, which not only simplified the correspondingwick structure but also eliminated the ‘dry-out’ potential in conventional GALHPs. A dedicated simulation model wasdeveloped on basis of the heat transfer and the flow characteristics derived from the governing equations of mass, energyand momentum. The essential impact parameters to the GALHP thermal performance were further discussed. It was foundthat the GALHP thermal performance, represented by the reciprocal of overall thermal resistance, varies directly withapplied heat load, evaporator diameter, and vapour-liquid separator diameter. The research results would be useful fordesign, optimisation and application of such GALHP in the gravity-assisted circumstance for thermal management.

  • 312.
    Zhang, Xingxing
    et al.
    Dalarna University, School of Technology and Business Studies, Energy Technology.
    Xiao, M.
    He, W.
    Qiu, Z.
    Zhao, Xiaoyun
    Dalarna University, School of Technology and Business Studies, Microdata Analysis.
    Heat Pump Technologies and Their Applications in Solar Systems2019In: Advanced Energy Efficiency Technologies for Solar Heating, Cooling and Power Generation / [ed] Xudong Zhao, Xiaoli Ma, Springer, 2019, p. 311-339Chapter in book (Refereed)
    Abstract [en]

    As the well known that global energy demand is on a trend of continuous growth, reducing energy demand and making good use of renewable energy are thought to be the major routes toward low carbon and sustainable future, in particular for the building sector. Compared to traditional gas-fired heating systems, heat pumps have been proved to be an energy-efficient heating technology which can save fossil fuel energy and consequently reduce CO2 emission. However, the most outstanding challenges for the application of heat pumps lie in their high demand for electrical power, and the insufficient heat transfer between the heat source and the refrigerant. To overcome these difficulties, a solar-assisted heat pump has been proposed to tackle these challenges. A solar-assisted heat pump combines a heat pump with a solar collector, enabling the use of solar energy to provide space heating and hot water for buildings. This chapter introduces heat pump technologies and their applications in solar systems. Two types of solar-assisted heat pump, direct and indirect expansion, are illustrated in details. This work has provided the fundamental research and experience for developing a solar heat pump system and contributing to a significant fossil fuel saving and carbon reduction in the global extent.

  • 313. Zhu, Chaoyi
    et al.
    Gluesenkamp, Kyle R
    Yang, Zhiyao
    Blackman, Corey
    Dalarna University, School of Technology and Business Studies, Energy Technology. SaltX Technology; Mälardalens högskola.
    Unified thermodynamic model to calculate COP of diverse sorption heat pump cycles: Adsorption, absorption, resorption, and multistep crystalline reactions2019In: International journal of refrigeration, ISSN 0140-7007, E-ISSN 1879-2081, Vol. 99, p. 382-392Article in journal (Refereed)
    Abstract [en]

    A straightforward thermodynamic model is developed in this work to analyze the efficiency limit of diverse sorption systems. A method is presented to quantify the dead thermal mass of heat exchangers Solid and liquid sorbents based on chemisorption or physical adsorption are accommodated. Four possible single-effect configurations are considered: basic absorption or adsorption (separate desorber, absorber, condenser, and evaporator); separate condenser/evaporator (two identical sorbent-containing reactors with a condenser and a separate direct expansion evaporator); combined condenser/evaporator (one salt-containing reactor with a combined condenser/evaporator module); and resorption (two sorbent-containing reactors, each with a different sorbent). The analytical model was verified against an empirical heat and mass transfer model derived from component experimental results. It was then used to evaluate and determine the optimal design for an ammoniate salt-based solid/gas sorption heat pump for a space heating application. The effects on system performance were evaluated with respect to different working pairs, dead thermal mass factors, and system operating temperatures. The effect of reactor dead mass as well as heat recovery on system performance was also studied for each configuration. Based on the analysis in this work, an ammonia resorption cycle using LiCl/NaBr as the working pair was found to be the most suitable single-effect cycle for space heating applications. The maximum cycle heating coefficient of performance for the design conditions was 1.50 with 50% heat recovery and 1.34 without heat recovery.

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