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  • 251. Wang, Xinru
    et al.
    Xia, Liang
    Bales, Chris
    Dalarna University, School of Technology and Business Studies, Energy Technology.
    Zhang, Xingxing
    Dalarna University, School of Technology and Business Studies, Energy Technology.
    Copertaro, Benedetta
    Dalarna University, School of Technology and Business Studies, Energy Technology.
    Pan, Song
    Wu, Jinshun
    A systematic review of recent air source heat pump (ASHP) systems assisted by solar thermal, photovoltaic and photovoltaic/thermal sources2020In: Renewable energy, ISSN 0960-1481, E-ISSN 1879-0682, Vol. 146, p. 2472-2487Article in journal (Refereed)
  • 252. Wei, Yixuan
    et al.
    Xia, Liang
    Pan, Song
    Wu, Jinshun
    Zhang, Xingxing
    Dalarna University, School of Technology and Business Studies, Energy Technology.
    Han, Mengjie
    Dalarna University, School of Technology and Business Studies, Statistics.
    Zhang, Weiya
    Xie, Jingchao
    Li, Qingping
    Prediction of occupancy level and energy consumption in office building using blind system identification and neural networks2019In: Applied Energy, ISSN 0306-2619, E-ISSN 1872-9118, Vol. 240, p. 276-294Article in journal (Refereed)
    Abstract [en]

    Occupancy behaviour plays an important role in energy consumption in buildings. Currently, the shallow understanding of occupancy has led to a considerable performance gap between predicted and measured energy use. This paper presents an approach to estimate the occupancy based on blind system identification (BSI), and a prediction model of electricity consumption by an air-conditioning system is developed and reported based on an artificial neural network with the BSI estimation of the number of occupants as an input. This starts from the identification of indoor CO2 dynamics derived from the mass-conservation law and venting levels. The unknown parameters, including the occupancy and model parameters, are estimated by using a frequentist maximum-likelihood algorithm and Bayesian estimation. The second phase is to establish the prediction model of the electricity consumption of the air-conditioning system by using a feed-forward neural network (FFNN) and extreme learning machine (ELM), as well as ensemble models. To analyse some aspects of the benchmark test for identifying the effect of structure parameters and input-selection alternatives, three studies are conducted on (1) the effect of predictor selection based on principal component analysis, (2) the effect of the estimated occupancy as the supplementary input, and (3) the effect of the neural network ensemble. The result shows that the occupancy number, as the input, is able to improve the accuracy in predicting energy consumption using a neural network model.

  • 253. Wei, Yixuan
    et al.
    Zhang, Xingxing
    Dalarna University, School of Technology and Business Studies, Energy Technology.
    Shi, Yong
    Xia, Liang
    Pan, Song
    Wu, Jinshun
    Han, Mengjie
    Dalarna University, School of Technology and Business Studies, Microdata Analysis.
    Zhao, Xiaoyun
    Dalarna University, School of Technology and Business Studies, Microdata Analysis.
    A review of data-driven approaches for prediction and classification of building energy consumption2018In: Renewable & sustainable energy reviews, ISSN 1364-0321, E-ISSN 1879-0690, Vol. 82, no 1, p. 1027-1047Article in journal (Refereed)
    Abstract [en]

    A recent surge of interest in building energy consumption has generated a tremendous amount of energy data, which boosts the data-driven algorithms for broad application throughout the building industry. This article reviews the prevailing data-driven approaches used in building energy analysis under different archetypes and granularities, including those methods for prediction (artificial neural networks, support vector machines, statistical regression, decision tree and genetic algorithm) and those methods for classification (K-mean clustering, self-organizing map and hierarchy clustering). The review results demonstrate that the data-driven approaches have well addressed a large variety of building energy related applications, such as load forecasting and prediction, energy pattern profiling, regional energy-consumption mapping, benchmarking for building stocks, global retrofit strategies and guideline making etc. Significantly, this review refines a few key tasks for modification of the data-driven approaches in the context of application to building energy analysis. The conclusions drawn in this review could facilitate future micro-scale changes of energy use for a particular building through the appropriate retrofit and the inclusion of renewable energy technologies. It also paves an avenue to explore potential in macro-scale energy-reduction with consideration of customer demands. All these will be useful to establish a better long-term strategy for urban sustainability.

  • 254.
    Weldemariam, Ashenafi
    Dalarna University, School of Technology and Business Studies, Energy Technology.
    Analyzing the Effect of Soiling on the Performance of a Photovoltaic System of Different Module Technologies in Kalkbult, South Africa2016Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    The fact that most of the large scale solar PV plants are built in arid and semi-arid areas

    where land availability and solar radiation is high, it is expected the performance of the PV

    plants in such locations will be affected significantly due to high cell temperature as well as

    due to soiling. Therefore, it is essential to study how the different PV module technologies

    will perform in such geographical locations to ensure a consistent and reliable power

    delivery over the lifetime of the PV power plants.

    As soiling is strongly dependent on the climatic conditions of a particular location a test

    station, consisted of about 24 PV modules and a well-equipped weather station, was built

    within the fences of Scatec’s 75 MW Kalkbult solar PV plant in South Africa.

    This study was performed to a better understand the effect of soiling by comparing the

    relative power generation by the cleaned modules to the un-cleaned modules. Such

    knowledge can enable more quantitative evaluations of the cleaning strategies that are

    going to be implemented in bigger solar PV power plants.

    The data collected and recorded from the test station has been analyzed at IFE, Norway

    using a MatLab script written for this thesis project. This thesis work has been done at

    IFE, Norway in collaboration with Stellenbosch University in South Africa and Scatec

    Solar a Norwegian independent power producer company.

    Generally for the polycrystalline modules it is found that the average temperature

    corrected efficiency during the period of the experiment has been 15.00±0.08 % and for

    the thin film-CdTe with ARC is 11.52% and for the thin film without ARC is about

    11.13% with standard uncertainty of ±0.01 %.

    Besides, by comparing the initial relative average efficiency of the polycrystalline-Si

    modules when all the modules have been cleaned for the first time and the final relative

    efficiency; after the last cleaning schedule which is when all the reference modules E, F, G,

    and H have been cleaned for the last time it is found that poly3 performs 2 % and 3 %

    better than poly1 and poly16 respectively, poly13 performs 1 % better than poly15 as well

    as poly5 and poly12 performs 1 % and 2 % better than poly10 respectively. Besides, poly5

    and poly12 performs a 9 % and 11 % better than poly7. Furthermore, there is no change

    in performance between poly6 and poly9 as well as poly4 and poly15. However, the

    increase in performance of poly3 to poly1, poly13 to poly15 as well as poly5 and poly12 to

    poly10 is insignificant.

    In addition, it is found that TF22 perform 7% better than the reference un-cleaned module

    TF24 and similarly; TF21 performs 7% higher than TF23. Furthermore, modules with

    ARC glass (TF17, TF18, TF19, and TF20) shows that cleaning the modules with only

    distilled water (TF19) or dry-cleaned after cleaned with distilled water(TF20) decreases the

    performance of the modules by 5 % and 4 % comparing to its respective reference uncleanedmodules TF17 and TF18 respectively.

  • 255.
    Wilson, Jason Clifford
    Dalarna University, School of Technology and Business Studies, Energy Technology.
    A techno-economic environmental approach to improving the performance of PV, battery, grid-connected, diesel hybrid energy systems: A case study in Kenya2018Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    Backup diesel generator (DG) systems continue to be a heavily polluting and costly solution for institutions with unreliable grid connections. These systems slow economic growth and accelerate climate change. Photovoltaic (PV), energy storage (ES), grid connected, DG – Hybrid Energy Systems (HESs) or, PV-HESs, can alleviate overwhelming costs and harmful emissions incurred from traditional back-up DG systems and improve the reliability of power supply. However, from project conception to end of lifetime, PV-HESs face significant barriers of uncertainty and variable operating conditions. The fit-and-forget solution previously applied to backup DG systems should not be adopted for PV-HESs.

    To maximize cost and emission reductions, PV-HESs must be adapted to their boundary conditions for example, irradiance, temperature, and demand. These conditions can be defined and monitored using measurement equipment. From this, an opportunity for performance optimization can be established. The method demonstrated in this study is a techno-economic and environmental approach to improving the performance of PV-HESs. The method has been applied to a case study of an existing PV-HES in Kenya. A combination of both analytical and numerical analyses has been conducted. The analytical analysis has been carried out in Microsoft Excel with the intent of being easily repeatable and practical in a business environment. Simulation analysis has been conducted in improved Hybrid Optimization by Genetic Algorithms (iHOGA), which is a commercially available software for simulating HESs.

    Using six months of measurement data, the method presented identifies performance inefficiencies and explores corrective interventions. The proposed interventions are evaluated, by simulation analyses, using a set of techno-economic and environment key performance indicators, namely: Net Present Cost (NPC), generator runtime, fuel consumption, total system emissions, and renewable fraction. Five corrective interventions are proposed, and predictions indicate that if these are implemented fuel consumption can be reduced by 70 % and battery lifetime can be extended by 28 %, net present cost can be reduced by 30 % and emissions fall by 42 %. This method has only been applied to a single PV-HES; however, the impact this method could have on sub-Saharan Africa as well as similar regions with unreliable grid connections is found to be significant. In the future, in sub-Saharan Africa alone, over $500 million dollars (USD) and 1.7 billion kgCO2 emissions could be saved annually if only 25 % of the fuel savings identified in this study were realized. The method proposed here could be improved with additional measurement data and refined simulation models. Furthermore, this method could potentially be fully automated, which could allow it to be implemented more frequently and at lower cost.

  • 256.
    Win, Kaung Myat
    Dalarna University, School of Technology and Business Studies, Energy Technology. Mälardalens högskola.
    Emissions from realistic operation of residential wood pellets heating systems2015Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Emissions from residential combustion appliances vary significantly depending on the firing behaviours and combustion conditions, in addition to combustion technologies and fuel quality. Although wood pellet combustion in residential heating boilers is efficient, the combustion conditions during start-up and stop phases are not optimal and produce significantly high emissions such as carbon monoxide and hydrocarbon from incomplete combustion. The emissions from the start-up and stop phases of the pellet boilers are not fully taken into account in test methods for ecolabels which primarily focus on emissions during operation on full load and part load.

    The objective of the thesis is to investigate the emission characteristics during realistic operation of residential wood pellet boilers in order to identify when the major part of the annual emissions occur. Emissions from four residential wood pellet boilers were measured and characterized for three operating phases (start-up, steady and stop). Emissions from realistic operation of combined solar and wood pellet heating systems was continuously measured to investigate the influence of start-up and stop phases on total annual emissions. Measured emission data from the pellet devices were used to build an emission model to predict the annual emission factors from the dynamic operation of the heating system using the simulation software TRNSYS.

    Start-up emissions are found to vary with ignition type, supply of air and fuel, and time to complete the phase. Stop emissions are influenced by fan operation characteristics and the cleaning routine. Start-up and stop phases under realistic operation conditions contribute 80 – 95% of annual carbon monoxide (CO) emission, 60 – 90% total hydrocarbon (TOC), 10 – 20% of nitrogen oxides (NO), and 30 – 40% particles emissions. Annual emission factors from realistic operation of tested residential heating system with a top fed wood pelt boiler can be between 190 and 400 mg/MJ for the CO emissions, between 60 and 95 mg/MJ for the NO, between 6 and 25 mg/MJ for the TOC, between 30 and 116 mg/MJ for the particulate matter and between 2x10-13 /MJ and 4x10-13 /MJ for the number of particles. If the boiler has the cleaning sequence with compressed air such as in boiler B2, annual CO emission factor can be up to 550 mg/MJ. Average CO, TOC and particles emissions under realistic annual condition were greater than the limits values of two eco labels. These results highlight the importance of start-up and stop phases in annual emission factors (especially CO and TOC). Since a large or dominating part of the annual emissions in real operation arise from the start-up and stop sequences, test methods required by the ecolabels should take these emissions into account. In this way it will encourage the boiler manufacturers to minimize annual emissions.

    The annual emissions of residential pellet heating system can be reduced by optimizing the number of start-ups of the pellet boiler. It is possible to reduce up to 85% of the number of start-ups by optimizing the system design and its controller such as switching of the boiler pump after it stops, using two temperature sensors for boiler ON/OFF control, optimizing of the positions of the connections to the storage tank, increasing the mixing valve temperature in the boiler circuit and decreasing the pump flow rate. For 85 % reduction of start-ups, 75 % of CO and TOC emission factors were reduced while 13% increase in NO and 15 % increase in particle emissions was observed.

  • 257.
    Win, Kaung Myat
    et al.
    Dalarna University, School of Technology and Business Studies, Energy Technology.
    Persson, Tomas
    Dalarna University, School of Technology and Business Studies, Energy Technology.
    Emissions from residential wood pellet boilers and stove characterized into start-up, steady operation and stop emissions2014In: Energy & Fuels, ISSN 0887-0624, E-ISSN 1520-5029, Vol. 28, no 4, p. 2496-2505Article in journal (Refereed)
    Abstract [en]

    Gaseous and particulate emissions from three residential wood pellet boilers and a stove were characterized and quantified at start-up, steady (full, medium and low combustion power), and stop phases. The aim was to characterize the emissions during the different phases of boiler operation and to identify when the major part of the emissions occur to enable actions for emission reduction where the savings can be highest. The investigated emissions comprised carbon monoxide (CO), nitrogen oxide (NO), total organic carbon (TOC), and particulate matter (PM 2.5). In this study, particle emissions were characterized by both number and mass concentration. The emission characteristics at high combustion power were relatively similar for all tested devices while significant differences in CO and TOC were observed at lower combustion power. Highest CO and TOC emissions are produced by the bottom fed boiler at low combustion power. The accumulated start-up emissions of the tested devices varied in the ranges of 0.5−12 g CO, 0.1−0.7 g NO, 0.1−2 g TOC, 0.12−2.9 g PM2.5, and 2.4 × 1013 to 3.1 × 1014 particles PM2.5. The accumulated stop emissions varied in the ranges 4−15.5 g CO, 0.01−0.11 g NO, 0.02−1.6 g TOC, 0.1−1.3 g PM2.5, and 3.3 × 1013 to 1.4 × 1014 particles PM2.5. The bottom fed boiler B1 had higher start-up and stop emissions than the tested top fed boilers and more particle emissions were accumulated in start-up phase than in stop phases of boiler B1, B3, and stove S1. Number of particles emitted from residential wood pellet combustion is dominated by fine particles smaller than 1 μm and similar particle distribution both in number and mass were observed for the tested devices. The start-up phase generated higher accumulated particle mass than the stop phase.

  • 258. Wu, J.
    et al.
    Zhang, Xingxing
    Dalarna University, School of Technology and Business Studies, Energy Technology.
    Shen, Jingchun
    University of Nottingham, Ningbo.
    Wu, Y.
    Connelly, K.
    Yang, T.
    Tang, L.
    Xiao, M.
    Xu, P.
    Wang, H.
    A review of thermal absorbers and their integration methods for the combined solar photovoltaic/thermal (PV/T) modules2017In: Renewable & sustainable energy reviews, ISSN 1364-0321, E-ISSN 1879-0690, Vol. 75, p. 839-854Article in journal (Refereed)
    Abstract [en]

    Thermal absorbers and their integration methods are critical to solar photovoltaic/thermal (PV/T) modules. These two elements directly influence the cooling effort of PV layers and as a result, the related electrical/thermal/overall efficiency. This paper conducts a critical review on the essential thermal absorbers and their integration methods for the currently-available PV modules for the purpose of producing the combined PV/T modules. A brief overview of different PV/T technologies is initially summarized, including aspects of their structure, efficiencies, thermal governing expressions and their applications. Seven different types of thermal absorbers and four corresponding integration methods are subsequently discussed and summarized in terms of their advantages/disadvantages and the associated application for various PV/T modules. Compared to traditional thermal absorbers, such as sheet-and-tube structure, rectangular tunnel with or without fins/grooves and flat-plate tube, these four types, i.e. micro-channel heat pipe array/heat mat, extruded heat exchanger, roll-bond heat exchanger and cotton wick structure, are promising due to the significant enhancement in terms of efficiency, structure, weight, and cost etc. The appropriate or suitable integration method varies in different cases, i.e. the ethylene-vinyl acetate (EVA) based lamination method seems the best option for integration of PV layer with thermal absorber when compared with other conventional methods, such as direct contact, thermal adhesive and mechanical fixing. Finally, suggestions for further research topics are proposed from five aspects. The overall research results would provide useful information for the assistance of further development of solar PV/T modules with high feasibility for widespread application in energy supply even at district or city-level in the near future. © 2016 Elsevier Ltd.

  • 259.
    Wäckelgård, Ewa
    et al.
    Dalarna University, School of Technology and Business Studies, Energy Technology.
    Svedung, Harald
    Dalarna University, School of Technology and Business Studies, Energy Technology.
    Optical characterization and modelling of paint top-coatings for low-emittance applications2016In: Infrared physics & technology, ISSN 1350-4495, E-ISSN 1879-0275, Vol. 78, p. 275-281Article in journal (Refereed)
    Abstract [en]

    The study reports on characterization of low-infrared-emittance paint top-coatings for interior building applications in which the thermal radiation becomes important in comparison with thermal conductance. The top-coating that consist of a binder with aluminium flakes has been optically characterized in the infrared wavelength range in order to determine single flake and binder emittance from reflectance measurements. The single flake emittance was found to be 0.12 for non-leafing cornflake. The absorption coefficient that determines the binder emittance as a function of binder thickness was 0.060 [μm]−2 and 0.085 [μm]−2 for Lumiflon and polyester respectively. These results were used as parameters in a simple model of the flake-binder top-coating to investigate how the emittance of the top-coating was influence by the two components and compared with a state-of-art low-emittance commercial paint. It was found from the modelling that replacing the polyester binder with Lumiflon reduces the infrared emittance (at room temperature) from 0.36 to 0.30. Increasing flake reflectance from 0.88 to 0.96 and at the same time reduce flake thickness from 2 to 1 μm gives an emittance of 0.20. However, the real samples prepared with Lumiflon showed a severe degradation caused by the flakes floating up closer to the surface which indicates a viscosity problem that needs to be solved for practical use. Thinner flakes with higher reflectance can be found if vacuum metallised pigments are used instead of ball-milled.

  • 260. Xiao, M
    et al.
    Tang, L
    Zhang, Xingxing
    Dalarna University, School of Technology and Business Studies, Energy Technology.
    Yu-Fat-Lun, I
    Li, G
    Analysis on cooling technologies of concentrated solar power system: a review2017Conference paper (Refereed)
    Abstract [en]

    The application of the Concentrated Solar Power (CSP) system has attracted an ever-increasing attention with the deepening worldwide energy crisis. Operating temperature is one of the most important factors for CSP system that affects the solar photoelectric conversion efficiency. Reasonable cooling method cannot only decrease the operative temperature, balance flare inhomogeneity, also should display the characteristics of convenient installation, low power consumption and high reliability. Based on a comprehensive literature review, this work conducted a thorough compilation on different cooling techniques of CSP system. It includes the commonly used air cooling and water cooling, also illustrates the promising ground coupled cooling, impinging jet cooling, liquid immersion cooling, microchannel cooling, heat pipe cooling and Phase Change Material systems etc. Besides, the advantages and disadvantages of different cooling technologies are briefly analysed. It is expected that this paper could provide guidance for development and optimization of cooling technologies in CSP system.

  • 261. Xiao, Manxuan
    et al.
    Tang, Llewelly
    Zhang, Xingxing
    Dalarna University, School of Technology and Business Studies, Energy Technology.
    Lun, Isaac Yu Fat
    Yuan, Yanping
    A Review on Recent Development of Cooling Technologies for Concentrated Photovoltaics (CPV) Systems2018In: Energies, ISSN 1996-1073, E-ISSN 1996-1073, Vol. 11, no 12, article id 3416Article in journal (Refereed)
    Abstract [en]

    Concentrated Photovoltaics (CPV) technology, as an energy saving method which can directly generate electricity from the Sun, has attracted an ever-increasing attention with the deepening worldwide energy crisis. However, operating temperature is one of the main concerns that affect the CPV system. Excess cell temperature causes electrical conversion efficiency loss and cell lifespan decrease. Thus, reasonable cooling methods should decrease the operating temperature and balance the flare inhomogeneity. They also need to display high reliability, low power consumption, and convenient installation. This paper presented the architectural, commercial, and industrial usage of CPV system, reviewed the recent research developments of different cooling techniques of CPV systems during last few years, including the spectral beam splitting technology, cogeneration power technology, commonly used and promising cooling techniques, active and passive cooling methods. It also analysed the design considerations of the cooling methods in CPV systems, introduced the classification and basic working principles and provided a thorough compilation of different cooling techniques with their advantages, current research limitations, challenges, and possible further research directions. The aim of this work is to find the research gap and recommend feasible research direction of cooling technologies for CPV systems. 

  • 262. Xiong, Y
    et al.
    Bo, L
    Qiang, M
    Wu, Y
    Zhang, Xingxing
    Dalarna University, School of Technology and Business Studies, Energy Technology. University of Nottingham.
    Xu, P
    Ma, C
    A characteristic study on the start-up performance of molten-salt heat pipes: Experimental investigation2017In: Experimental Thermal and Fluid Science, ISSN 0894-1777, E-ISSN 1879-2286, Vol. 82, p. 433-438Article in journal (Refereed)
    Abstract [en]

    This paper reports a fundamental experimental investigation of the start-up characteristics of heat pipes using a dedicated molten-salt mixture as the working fluid. Based on four single salt, i.e. NaNO3(AR), KNO3(AR), LiNO3(AR) and Ca(NO3)2(AR), a quaternary molten-salt working fluid was developed and charged at different masses into four heat pipes with the same dimensions of 980 mm in length and 22 mm in diameter. A parallel comparison on the start-up performance of these heat pipes was then conducted to observe the influence of the charging mass and the inclination angle under the consistent lab-controlled conditions. The experimental results showed the heat pipe with molten-salt charge of 40 g responded much quicker than those with molten salt charge of 60 g, 70 g and 80 g respectively; meanwhile, the molten-salt heat pipe achieved the maximum condensation temperature at inclination angle of 50°. Comparing to the conventional naphthalene heat pipe, the dedicated molten-salt heat pipe had a much shorter start-up time when they were charged with the same amount of 40 g. The overall research result is expected to provide certain guidance for further design and operation of molten-salt heat pipe in high-and-medium-temperature heat transfer and storage scenarios. 

  • 263.
    Yeneneh, Getu Temasgen
    Dalarna University, School of Technology and Business Studies, Energy Technology.
    Testing of Apis System Platform in Grid-Connected Photovoltaic System and Comparison with Metrum for Fault Detection and Diagnosis2016Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    A real time data management web-based software-platform for PV plant monitoring called Apis was tested for fault detection and diagnosis of large scale grid-connected photovoltaic systems. This method was compared with Metrum system which is also another web based monitoring system used in grid connected PV systems. The objective of testing and comparisons were to observe the Apis system performance in large scale PV systems particularly for fault detection, and to identify which of the two systems could give more information to easily identify type of fault and point out the fault location in PV plants.

    The experiment were carried out in the selected two different arrays that have a capacity of 18.4kW and 17.6 kW with four string inverters each, to test three cases at Glava energy center solar park, Sweden. The first demonstrates the response of the systems when the wiring loose or cable disconnection fault occurs in the plant. The second demonstrates the output of the inverters when partial shading is gradually increased and the third demonstrates the output when the fault at components (i.e. at inverter, fuse and circuit breaker) is applied. Both systems collect data from inverters. However, in Apis system, data from individual inverters of the plant could be collected separately in both AC and DC sides while Metrum system was measuring the total output of the whole inverters in the plant.

    During the string disconnection, the Apis monitoring system showed a power drop to zero from the defected strings making it possible to identify them. In the same way during the inverters’ fault the power output of the failed inverter was dropped to zero. However, the normal strings and inverters were still working properly. Meanwhile the Metrum system only displayed a reduced power output which doesn’t directly identify the problem and requires manual inspection. In the case of partial shading there was a persistent difference occurred between the defected string and normal one but it did not dropped to zero at all.

    Apis system is able to differentiate and locate the faults by comparing input and output results of different inverters within the plant, unlike Metrum system which measures the total output of the plant. Nevertheless, Apis system still has less possibility to determine the type of fault further than estimation.

  • 264. Yuan, Y
    et al.
    Ouyang, L
    Sun, L
    Cao, X
    Xiang, B
    Zhang, Xingxing
    Dalarna University, School of Technology and Business Studies, Energy Technology.
    Effect of connection mode and mass flux on the energy output of a PVT hot water system2017In: Solar Energy, ISSN 0038-092X, E-ISSN 1471-1257, Vol. 158, p. 285-294Article in journal (Refereed)
  • 265. 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.

  • 266.
    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.

  • 267.
    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)
  • 268.
    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)
  • 269.
    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.

  • 270.
    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.

  • 271.
    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.

  • 272.
    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.

  • 273. 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.

    The full text will be freely available from 2020-06-30 23:36
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