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  • 1.
    Fiedler, Frank
    et al.
    Dalarna University, School of Technology and Business Studies, Energy and Environmental Technology.
    Persson, Tomas
    Dalarna University, School of Technology and Business Studies, Energy and Environmental Technology.
    Carbon monoxide emissions of combined pellet and solar heating systems2009In: Applied Energy, ISSN 0306-2619, E-ISSN 1872-9118, Vol. 86, no 2, p. 135-143Article in journal (Refereed)
    Abstract [en]

    Emissions are an important aspect of a pellet heating system. Low harmful emissions, particularly carbon monoxide, are a measure of a well performing system. High carbon monoxide emissions are often caused by unnecessary cycling of the burner and when the average load is below the lowest possible combustion power of the burner. Combining pellet heaters with a solar heating system can significantly reduce cycling of the pellet heater and avoid the inefficient summer operation of the pellet heater. Five combined systems representing the range of typical solutions of this system type and one recently developed system have been studied, modelled and simulated. These systems are compared to a reference system, which is based on a pellet boiler and is not combined with a solar heating system. The aim was to study CO-emissions of the different types of systems and to analyse the potential of CO-emission reduction when the pellet heater is combined with a solar heating systems. Another aim was to compare the yearly CO-emissions obtained from simulations under realistic dynamic conditions with the yearly CO-emissions calculated based on the values that are obtained by the standard test methods. The study was performed with the simulation tool TRNSYS. The parameter used in the study have been identified from lab measurements on existing pellet boilers/stoves and solar heating systems. The results from the simulations show that it is possible to almost halve the CO-emission if the pellet heater is combined with a solar heating system. The results also show that the CO-emission of existing combined solar and pellet heating systems can be drastically reduced if the pellet heater is properly controlled and some basic design rules are observed. This can also be seen when analyzing the results for the new system concept where these rules have been taken into account. Comparing the yearly CO-emissions obtained from the simulations with the yearly CO-emissions calculated based on the standard test methods shows that using the latter give too low CO-values for the whole year. It is also shown that for the existing systems the average emissions under these realistic annual conditions were greater than the limit values of two Eco-labels.

  • 2.
    Gustafsson, Marcus
    et al.
    Dalarna University, School of Technology and Business Studies, Energy Technology.
    Swing Gustafsson, Moa
    Dalarna University, School of Technology and Business Studies, Energy Technology.
    Myhren, Jonn Are
    Dalarna University, School of Technology and Business Studies, Construction.
    Bales, Chris
    Dalarna University, School of Technology and Business Studies, Energy Technology.
    Holmberg, Sture
    Techno-economic analysis of energy renovation measures for a district heated multi-family house2016In: Applied Energy, ISSN 0306-2619, E-ISSN 1872-9118, Vol. 177, p. 108-116Article in journal (Refereed)
    Abstract [en]

    Renovation of existing buildings is important in the work toward increased energy efficiency and reduced environmental impact. The present paper treats energy renovation measures for a Swedish district heated multi-family house, evaluated through dynamic simulation. Insulation of roof and façade, better insulating windows and flow-reducing water taps, in combination with different HVAC systems for recovery of heat from exhaust air, were assessed in terms of life cycle cost, discounted payback period, primary energy consumption, CO2 emissions and non-renewable energy consumption. The HVAC systems were based on the existing district heating substation and included mechanical ventilation with heat recovery and different configurations of exhaust air heat pump.Compared to a renovation without energy saving measures, the combination of new windows, insulation, flow-reducing taps and an exhaust air a heat pump gave up to 24% lower life cycle cost. Adding insulation on roof and façade, the primary energy consumption was reduced by up to 58%, CO2 emissions up to 65% and non-renewable energy consumption up to 56%. Ventilation with heat recovery also reduced the environmental impact but was not economically profitable in the studied cases. With a margin perspective on electricity consumption, the environmental impact of installing heat pumps or air heat recovery in district heated houses is increased. Low-temperature heating improved the seasonal performance factor of the heat pump by up to 11% and reduced the environmental impact.

  • 3. He, Wei
    et al.
    Hong, Xiaoqiang
    Zhao, Xudong
    Zhang, Xingxing
    University of Hull.
    Shen, Jinchun
    Ji, Jie
    Operational performance of a novel heat pump assisted solar facade loop-heat-pipe water heating system2015In: Applied Energy, ISSN 0306-2619, E-ISSN 1872-9118, Vol. 146, p. 371-382Article in journal (Refereed)
    Abstract [en]

    This paper aims to present an investigation into the operational performance of a novel heat pump assisted solar façade loop-heat-pipe (LHP) water heating system using both theoretical and experimental methods. This involved (1) development of a computer numerical model; (2) simulation of the operational performance of the system by using the model; (3) test rig construction; and (4) dedicated experiment for verification of the model. It was found that the established model is able to predict the operational performance of the system at a reasonable accuracy. Analyses of the research results indicated that under the selected testing conditions, the average thermal efficiency of the LHP module was around 71%, much higher than that of the loop heat pipe without heat pump assistance. The thermal efficiency of the LHP module grew when the heat pump was turned-on and fell when the heat pump was turned-off. The water temperature remained a steadily growing trend throughout the heat pump turned-on period. Neglecting the heat loss of the water tank, the highest coefficient of the performance could reach up to 6.14 and its average value was around 4.93. In overall, the system is a new façade integrated, highly efficient and aesthetically appealing solar water heating configuration; wide deployment of the system will help reduce fossil fuel consumption in the building sector and carbon emission to the environment.

  • 4. He, Wei
    et al.
    Zhang, Gan
    Zhang, Xingxing
    University of Nottingham.
    Ji, Jie
    Li, Guiqiang
    Zhao, Xudong
    Recent development and application of thermoelectric generator and cooler2015In: Applied Energy, ISSN 0306-2619, E-ISSN 1872-9118, Vol. 143, p. 1-25Article in journal (Refereed)
    Abstract [en]

    Energy crisis and environment deterioration are two major problems for 21st century. Thermoelectric device is a promising solution for those two problems. This review begins with the basic concepts of the thermoelectric and discusses its recent material researches about the figure of merit. It also reports the recent applications of the thermoelectric generator, including the structure optimization which significantly affects the thermoelectric generator, the low temperature recovery, the heat resource and its application area. Then it reports the recent application of the thermoelectric cooler including the thermoelectric model and its application area. It ends with the discussion of the further research direction.

  • 5. Huang, P
    et al.
    Fan, C
    Zhang, Xingxing
    Dalarna University, School of Technology and Business Studies, Energy Technology.
    Wang, J
    A hierarchical coordinated demand response control for buildings with improved performances at building group2019In: Applied Energy, ISSN 0306-2619, E-ISSN 1872-9118, Vol. 242, p. 684-694Article in journal (Refereed)
    Abstract [en]

    Demand response control is one of the common means used for building peak demand limiting. Most of the existing demand response controls focused on single building’s performance optimization, and thus may cause new undesirable peak demands at building group, imposing stress on the grid power balance and limiting the economic savings. A few latest studies have demonstrated the potential benefits of demand response coordination, but the proposed methods cannot be applied in large scales. The main reason is that, for demand response coordination of multiple buildings, associated computational load and coordination complexity, increasing exponentially with building number, are challenges to be solved. This study, therefore, proposes a hierarchical demand response control to optimize operations of a large scale of buildings for group-level peak demand reduction. The hierarchical control first considers the building group as a ‘virtual’ building and searches the optimal performance that can be achieved at building group using genetic algorithm. To realize such optimal performance, it then coordinates each single building’s operation using non-linear programming. For validations, the proposed method has been applied on a case building group, and the study results show that the hierarchical control can overcome the challenges of excessive computational load and complexity. Moreover, in comparison with conventional independent control, it can achieve better performances in aspects of peak demand reduction and economic savings. This study provides a coordinated control for application in large scales, which can improve the effectiveness and efficiency in relieving the grid stress, and reduce the end-users’ electricity bills.

  • 6.
    Huang, Pei
    et al.
    Dalarna University, School of Technology and Business Studies, Energy Technology.
    Copertaro, Benedetta
    Dalarna University, School of Technology and Business Studies, Energy Technology.
    Zhang, Xingxing
    Dalarna University, School of Technology and Business Studies, Energy Technology.
    Shen, Jingchun
    Dalarna University, School of Technology and Business Studies, Construction.
    Löfgren, Isabelle
    Rönnelid, Mats
    Dalarna University, School of Technology and Business Studies, Energy Technology.
    Fahlen, Jan
    Andersson, Dan
    Svanfeldt, Mikael
    A review of data centers as prosumers in district energy systems: Renewable energy integration and waste heat reuse for district heating2019In: Applied Energy, ISSN 0306-2619, E-ISSN 1872-9118Article in journal (Refereed)
    Abstract [en]

    As large energy prosumers in district energy systems, on the one hand, data centers consume a large amount of electricity to ensure the Information Technologies (IT) facilities, ancillary power supply and cooling systems work properly; on the other hand, data centers produce a large quantity of waste heat due to the high heat dissipation rates of the IT facilities. To date, a systematic review of data centers from the perspective of energy prosumers, which considers both integration of the upstream green energy supply and downstream waste heat reuse, is still lacking. As a result, the potentials for improving data centers’ performances are limited due to a lack of global optimization of the upstream renewable energy integration and downstream waste heat utilization. This study is intended to fill in this gap and provides such a review. In this regard, the advancements in different cooling techniques, integration of renewable energy and advanced controls, waste heat utilization and connections for district heating, real projects, performance metrics and economic, energy and environmental analyses are reviewed. Based on the enormous amount of research on data centers in district energy systems, it has been found that: (1) global controls, which can manage the upstream renewable production, data centers’ operation and waste heat generation and downstream waste heat utilization are still lacking; (2) regional climate studies represent an effective way to find the optimal integration of renewable energy and waste heat recovery technologies for improving the data centers’ energy efficiency; (3) the development of global energy metrics will help to appropriately quantify the data center performances.

  • 7.
    Huang, Pei
    et al.
    Dalarna University, School of Technology and Business Studies, Energy Technology. City University of Hong Kong.
    Fan, Cheng
    Zhang, Xingxing
    Dalarna University, School of Technology and Business Studies, Energy Technology.
    Wang, Jiayuan
    A hierarchical coordinated demand response control for buildings with improved performances at building group2019In: Applied Energy, ISSN 0306-2619, E-ISSN 1872-9118, Vol. 242, p. 684-694Article in journal (Refereed)
    Abstract [en]

    Demand response control is one of the common means used for building peak demand limiting. Most of the existing demand response controls focused on single building’s performance optimization, and thus may cause new undesirable peak demands at building group, imposing stress on the grid power balance and limiting the economic savings. A few latest studies have demonstrated the potential benefits of demand response coordination, but the proposed methods cannot be applied in large scales. The main reason is that, for demand response coordination of multiple buildings, associated computational load and coordination complexity, increasing exponentially with building number, are challenges to be solved. This study, therefore, proposes a hierarchical demand response control to optimize operations of a large scale of buildings for group-level peak demand reduction. The hierarchical control first considers the building group as a ‘virtual’ building and searches the optimal performance that can be achieved at building group using genetic algorithm. To realize such optimal performance, it then coordinates each single building’s operation using non-linear programming. For validations, the proposed method has been applied on a case building group, and the study results show that the hierarchical control can overcome the challenges of excessive computational load and complexity. Moreover, in comparison with conventional independent control, it can achieve better performances in aspects of peak demand reduction and economic savings. This study provides a coordinated control for application in large scales, which can improve the effectiveness and efficiency in relieving the grid stress, and reduce the end-users’ electricity bills.

  • 8.
    Huang, Pei
    et al.
    City University of Hong Kong.
    Huang, Gongsheng
    Sun, Yongjun
    Uncertainty-based life-cycle analysis of near-zero energy buildings for performance improvements2018In: Applied Energy, ISSN 0306-2619, E-ISSN 1872-9118, Vol. 213, p. 486-498Article in journal (Refereed)
    Abstract [en]

    Near-zero energy buildings (nZEBs) are considered as an effective solution to mitigating CO2 emissions and reducing the energy usage in the building sector. A proper sizing of the nZEB systems (e.g. HVAC systems, energy supply systems, energy storage systems, etc.) is essential for achieving the desired annual energy balance, thermal comfort, and grid independence. Two significant factors affecting the sizing of nZEB systems are the uncertainties confronted by the building usage condition and weather condition, and the degradation effects in nZEB system components. The former factor has been studied by many researchers; however, the impact of degradation is still neglected in most studies. Degradation is prevalent in energy components of nZEB and inevitably leads to the deterioration of nZEB life-cycle performance. As a result, neglecting the degradation effects may lead to a system design which can only achieve the desired performance at the beginning several years. This paper, therefore, proposes a life-cycle performance analysis (LCPA) method for investigating the impact of degradation on the longitudinal performance of the nZEBs. The method not only integrates the uncertainties in predicting building thermal load and weather condition, but also considers the degradation in the nZEB systems. Based on the proposed LCPA method, a two-stage method is proposed to improve the sizing of the nZEB systems. The study can improve the designers’ understanding of the components’ degradation impacts and the proposed method is effective in the life-cycle performance analysis and improvements of nZEBs. It is the first time that the impacts of degradation and uncertainties on nZEB LCP are analysed. Case studies show that an nZEB might not fulfil its definition at all after some years due to component degradation, while the proposed two-stage design method can effectively alleviate this problem.

  • 9.
    Huang, Pei
    et al.
    Dalarna University, School of Technology and Business Studies, Energy Technology.
    Lovati, Marco
    EURAC Research, Bolzano, Italy; University of Trento, Trento, Italy.
    Zhang, Xingxing
    Dalarna University, School of Technology and Business Studies, Energy Technology.
    Bales, Chris
    Dalarna University, School of Technology and Business Studies, Energy Technology.
    Hallbeck, Sven
    NIBE Climate Solutions, Sweden.
    Becker, Anders
    Ferroamp Elektronik AB, Spånga, Sweden.
    Bergqvist, Henrik
    LudvikaHem AB Bobutiken, Ludvika, Sweden.
    Hedberg, Jan
    LudvikaHem AB Bobutiken, Ludvika, Sweden.
    Maturi, Laura
    EURAC Research, Bolzano, Italy.
    Transforming a residential building cluster into electricity prosumers in Sweden: Optimal design of a coupled PV-heat pump-thermal storage-electric vehicle system2019In: Applied Energy, ISSN 0306-2619, E-ISSN 1872-9118, Vol. 255, article id 113864Article in journal (Refereed)
    Abstract [en]

    Smart grid is triggering the transformation of traditional electricity consumers into electricity prosumers. This paper reports a case study of transforming an existing residential cluster in Sweden into electricity prosumers. The main energy concepts include (1) click-and-go photovoltaics (PV) panels for building integration, (2) centralized exhaust air heat pump, (3) thermal energy storage for storing excess PV electricity by using heat pump, and (4) PV electricity sharing within the building cluster for thermal/electrical demand (including electric vehicles load) on a direct-current micro grid. For the coupled PV-heat pump-thermal storage-electric vehicle system, a fitness function based on genetic algorithm is established to optimize the capacity and positions of PV modules at cluster level, with the purpose of maximizing the self-consumed electricity under a non-negative net present value during the economic lifetime. Different techno-economic key performance indicators, including the optimal PV capacity, self-sufficiency, self-consumption and levelized cost of electricity, are analysed under impacts of thermal storage integration, electric vehicle penetration and electricity sharing possibility. Results indicate that the coupled system can effectively improve the district-level PV electricity self-consumption rate to about 77% in the baseline case. The research results reveal how electric vehicle penetrations, thermal storage, and energy sharing affect PV system sizing/positions and the performance indicators, and thus help promote the PV deployment. This study also demonstrates the feasibility for transferring the existing Swedish building clusters into smart electricity prosumers with higher self-consumption and energy efficiency and more intelligence, which benefits achieving the ‘32% share of renewable energy source’ target in EU by 2030.

  • 10.
    Huang, Pei
    et al.
    Dalarna University, School of Technology and Business Studies, Energy Technology. City University of Hong Kong.
    Ma, Z.
    Xiao, L.
    Sun, Y.
    Geographic Information System-assisted optimal design of renewable powered electric vehicle charging stations in high-density cities2019In: Applied Energy, ISSN 0306-2619, E-ISSN 1872-9118, Vol. 255, article id 113855Article in journal (Refereed)
  • 11.
    Huang, Pei
    et al.
    City University of Hong Kong.
    Sun, Yongjun
    A clustering based grouping method of nearly zero energy buildings for performance improvements2019In: Applied Energy, ISSN 0306-2619, E-ISSN 1872-9118, Vol. 235, p. 43-55Article in journal (Refereed)
    Abstract [en]

    Collaborations among nearly zero energy buildings (nZEBs) (e.g. renewable energy sharing) can improve nZEBs’ performance at the community level. To enable such collaborations, the nZEBs need to be properly grouped. Grouping nZEBs with similar energy characteristics merely brings limited benefits due to limited collaboration existed, while grouping nZEBs with diverse energy characteristics can bring more benefits. In the planning of nZEB communities, due to the large diversity of energy characteristics and computation complexity, proper grouping that maximizes the collaboration benefits is difficult, and such a grouping method is still lacking. Therefore, this paper proposes a clustering based grouping method to improve nZEB performance. Using the field data, the grouping method first identifies the representative energy characteristics by advanced clustering algorithms. Then, it searches the optimal grouping alternative of these representative profiles that has the optimal performance. For validation, the proposed grouping method is compared with two cases (the nZEBs are either not grouped or randomly grouped) in aspects of economic costs and grid interaction. The study results demonstrate that the proposed method can effectively improve nZEBs’ performances at the community level. The propose method can provide the decision makers a means to group nZEBs, which maximize the collaboration benefits and thus assists the planning of nZEB communities.

  • 12.
    Joudi, Ali
    et al.
    Dalarna University, School of Technology and Business Studies, Energy and Environmental Technology.
    Svedung, Harald
    Dalarna University, School of Technology and Business Studies, Energy and Environmental Technology.
    Bales, Chris
    Dalarna University, School of Technology and Business Studies, Energy and Environmental Technology.
    Rönnelid, Mats
    Dalarna University, School of Technology and Business Studies, Energy and Environmental Technology.
    Highly reflective coatings for interior and exterior steel cladding and the energy efficiency of buildings2011In: Applied Energy, ISSN 0306-2619, E-ISSN 1872-9118, Vol. 88, no 12, p. 4655-4666Article in journal (Refereed)
    Abstract [en]

    The effect of surface heat-radiation properties of coil-coated steel cladding material on the energy efficiency of buildings in Nordic climate is addressed by parallel temperature and energy usage measurements in a series of test cabins with different exterior solar reflectivity and interior thermal reflectivity. During one year, a number of one- or two-week experiments with air conditioner cooling and electrical floor heating were made while logging air-, radiation- and surface temperatures, energy consumption and weather conditions. Measurements show significant energy savings in the test cabins by the use of high thermal reflectivity interior surfaces both during heating and cooling and a strongly reduced cooling demand by the use of high solar reflectivity exterior surfaces. Results are interpreted within the context of a steady-state energy flux model, to illuminate the importance of surface resistance properties (radiation and convective heat dissipation).

  • 13.
    Joudi, Ali
    et al.
    Dalarna University, School of Technology and Business Studies, Energy and Environmental Technology.
    Svedung, Harald
    Dalarna University, School of Technology and Business Studies, Energy and Environmental Technology. SSAB EMEA.
    Cehlin, Mathias
    Building, Energy and Environmental Engineering, University of Gävle.
    Rönnelid, Mats
    Dalarna University, School of Technology and Business Studies, Energy and Environmental Technology.
    Reflective coatings for interior and exterior of buildings and improving thermal performance2013In: Applied Energy, ISSN 0306-2619, E-ISSN 1872-9118, Vol. 103, p. 562-570Article in journal (Refereed)
    Abstract [en]

    The importance of reducing building energy usage and thriving for more energy efficient architectures, has nurtured creative solutions and smart choices of materials in the last few decades. Among those are optimizing surface optical properties for both interior and exterior claddings of the building. Development in the coil-coating steel industries has now made it possible to allocate correct optical properties for steel clad buildings with improved thermal performance. Although the importance of the exterior coating and solar gain are thoroughly studied in many literatures, the effect of interior cladding are less tackled, especially when considering a combination of both interior and exterior reflective coatings. This paper contemplates the thermal behavior of small cabins with reflective coatings on both interior and exterior cladding, under different conditions and climates with the aim to clarify and point out to the potential energy saving by smart choices of clad coatings.

  • 14.
    Lidberg, Tina
    et al.
    Dalarna University, School of Technology and Business Studies, Energy Technology.
    Gustafsson, Marcus
    Dalarna University, School of Technology and Business Studies, Energy Technology. KTH.
    Myhren, Jonn Are
    Dalarna University, School of Technology and Business Studies, Construction.
    Olofsson, Thomas
    Dalarna University, School of Technology and Business Studies, Construction. Umeå universitet.
    Ödlund, L
    Environmental impact of energy refurbishment of buildings within different district heating systems2018In: Applied Energy, ISSN 0306-2619, E-ISSN 1872-9118, Vol. 227, no SI, p. 231-238Article in journal (Refereed)
    Abstract [en]

    The refurbishment of existing buildings is often considered a way to reduce energy use and CO2 emissions in the building stock. This study analyses the primary energy and CO2 impact of refurbishing a multi-family house with different refurbishment packages, given various district heating systems. Four models of typical district heating systems were defined to represent the Swedish district heating sector. The refurbishment packages were chosen to represent typical, yet innovative ways to improve the energy efficiency and indoor climate of a multi-family house. The study was made from a system perspective, including the valuation of changes in electricity use on the margin. The results show a significant difference in primary energy use for the different refurbishment packages, depending on both the package itself as well as the type of district heating system. While the packages with heat pumps had the lowest final energy use per m2 of floor area, air heat recovery proved to reduce primary energy use and emissions of CO2-equivalents more, independent of the type of district heating system, as it leads to a smaller increase in electricity use.

  • 15. Liu, Shengchun
    et al.
    Hao, Ling
    Rao, Zhiming
    Zhang, Xingxing
    University of Nottingham.
    Experimental study on crystallization process and prediction for the latent heat of ice slurry generation based sodium chloride solution2017In: Applied Energy, ISSN 0306-2619, E-ISSN 1872-9118, Vol. 185, p. 1948-1953Article in journal (Refereed)
    Abstract [en]

    The research on the crystallization process is a fundamental task for the investigation of freezing properties of ice slurry. This paper presents an experimental study on the influence of concentration on essential parameters of the crystallization process for the ice slurry produced from sodium chloride solution using a scraped surface heat exchanger. It was found that the liquid temperature experiences four different segments during the whole crystallization process. This trend keeps accordance with the result from literature and it was used to verify the accuracy of the experiment test. It was also observed that the concentrations of sodium chloride solution have significant effects on several freezing properties of the ice slurry generation. The curves obtained in this paper are useful to predict the freezing point and the solidification time in practice. Additionally, a mathematical correlation between the latent heat and concentration was developed eventually by polynomial fitting the curve gained from experiments. The error between the fitting curves and original experimental data was no more than 5%. Totally, during the ice generation process, it is of great significance that the concentration of brine solution can be adjusted to meet the cooling capacity requirement according to the fitting curves and mathematical correlations obtained in this paper.

  • 16.
    Persson, Tomas
    et al.
    Dalarna University, School of Technology and Business Studies, Energy and Environmental Technology.
    Fiedler, Frank
    Dalarna University, School of Technology and Business Studies, Energy and Environmental Technology.
    Nordlander, Svante
    Bales, Chris
    Dalarna University, School of Technology and Business Studies, Energy and Environmental Technology.
    Paavilainen, Janne
    Dalarna University, School of Technology and Business Studies, Energy and Environmental Technology.
    Validation of a dynamic model for wood pellet boilers and stoves2009In: Applied Energy, ISSN 0306-2619, E-ISSN 1872-9118, no 86Article in journal (Refereed)
    Abstract [en]

    Optimising systems with wood pellet boilers or stoves using simulations requires realistic computer models. The objective of this work was to develop and verify a mathematical model for wood pellet boilers and stoves for use in system simulations with the dynamic simulation programme TRNSYS, calculating both the energy balance and the CO-emissions (carbon monoxide emissions). Laboratory measurements have been carried out and a mathematical two-node model was developed and implemented as a TRNSYS component. Parameters were identified and the model has been compared with measurements. The model shows in general good agreement with measured data, however there are details that could be improved. This involves improved modelling of the dynamic response for boilers with large water volumes and improved modelling of the air factor and the CO-emissions, especially during start and stop conditions. Further improved methodology and accuracy for measuring and parameter identification is recommended.

  • 17. Petrovic, Bojana
    et al.
    Myhren, Jonn Are
    Dalarna University, School of Technology and Business Studies, Construction.
    Zhang, Xingxing
    Dalarna University, School of Technology and Business Studies, Energy Technology.
    Wallhagen, Marita
    Eriksson, Ola
    Life cycle assessment of a wooden single-family house in Sweden2019In: Applied Energy, ISSN 0306-2619, E-ISSN 1872-9118, Vol. 251, p. 113-253, article id 113253Article in journal (Refereed)
    Abstract [en]

    To understand the reasons behind the large environmental impact from buildings the whole life cycle needs to be considered. Therefore, this study evaluates the carbon dioxide emissions in all stages of a single-family house in Sweden from the production of building materials, followed by construction and user stages until the end-of-life of the building in a life cycle assessment (LCA). The methodology applied is attributional life cycle assessment (LCA) based on ‘One Click LCA’ tool and a calculated life span of 100 years. Global warming potential (GWP) and primary energy (PE) are calculated by using specific data from the case study, furthermore the data regarding building materials are based on Environmental Product Declarations (EPDs). The results show that the selection of wood-based materials has a significantly lower impact on the carbon dioxide emissions in comparison with non-wood based materials. The total emissions for this single-family house in Sweden are 6 kg CO 2 e/m 2 /year. The production stage of building materials, including building systems and installations represent 30% of the total carbon dioxide equivalent emissions, while the maintenance and replacement part represents 37%. However, energy use during the in-use stage of the house recorded lower environmental impact (21%) due to the Swedish electricity mix that is mostly based on energy sources with low carbon dioxide emissions. The water consumption, construction and the end-of-life stages have shown minor contribution to the buildings total greenhouse gas (GHG) emissions (12%). The primary energy indicator shows the largest share in the operational phase of the house.

  • 18.
    Poppi, Stefano
    et al.
    Dalarna University, School of Technology and Business Studies, Energy Technology. KTH.
    Bales, Chris
    Dalarna University, School of Technology and Business Studies, Energy Technology.
    Haller, Michel Y.
    University of Applied Sciences HSR, Switzerland.
    Heinz, Andreas
    Institute of Thermal Engineering, Graz University of Technology.
    Influence of boundary conditions and component size on electricity demand in solar thermal and heat pump combisystems2016In: Applied Energy, ISSN 0306-2619, E-ISSN 1872-9118, Vol. 162, p. 1062-1073Article in journal (Refereed)
    Abstract [en]

    Solar thermal and heat pump combisystems are used to produce domestic hot water (DHW) and space heating (SH) in dwellings. Many systems are available on the market. For an impartial comparison, a definite level of thermal comfort should be defined and ensured in all systems. This work studied the influence of component size on electricity demand for a state of the art solar thermal and heat pump system. A systematic series of parametric studies was carried out by using TRNSYS to show the impact of climate, load and size of main components as well as heat source for the heat pump. Penalty functions were used to ensure that all variations provided the same comfort requirements. Two reference systems were defined and modelled based on products on the market, one with ambient air and the other with borehole as heat source for the heat pump. The results show that changes in collector area from 5 to 15 m2 result in a decrease in system electricity of between 305 and 552 kW h/year. Changes in heat exchanger size for DHW preparation were shown to give nearly as large changes in electricity use due to the fact that the set temperature in the store was changed to give the same thermal comfort in all cases. Decrease in heat pump size was shown to give a decrease in electricity use for the ASHP in the building with larger heat demand while it increased or had only a small change for other boundary conditions. Heat pump losses were shown to be an important factor highlighting the importance of modelling this factor explicitly

  • 19.
    Poppi, Stefano
    et al.
    Dalarna University, School of Technology and Business Studies, Energy Technology. KTH.
    Bales, Chris
    Dalarna University, School of Technology and Business Studies, Energy Technology.
    Heinz, Andreas
    Hengel, Franz
    Cheze, David
    Mojic, Igor
    Cialani, Catia
    Dalarna University, School of Technology and Business Studies, Economics.
    Analysis of system improvements in solar thermal and air source heat pump combisystems2016In: Applied Energy, ISSN 0306-2619, E-ISSN 1872-9118, Vol. 173, p. 606-623Article in journal (Refereed)
    Abstract [en]

    A solar thermal and heat pump combisystem is one of many system alternatives on the market for supplying domestic hot water (DHW) and space heating (SH) in dwellings. In this study a reference solar thermal and air source heat pump combisystem was defined and modelled based on products available on the market. Based on the results of an extensive literature survey, several system variations were investigated to show the influence of heat pump cycle, thermal storage and system integration on the use of electricity for two houses in the climates of Zurich and Carcassonne. A singular economic cash flow analysis was carried out and the “additional investment limit” of each system variation was determined for a range of economic boundary conditions. This is the maximum extra investment cost for the system variant compared to the reference system that will give a break even result for a 10 year period. The results show that variations in electricity price affects the additional investment limit far more than the other economic parameters. Several of the variants show potential for achieving a cost benefit, but the potential varies a lot depending on load and climate boundary conditions. For all variants, the biggest difference in electricity savings was found for Zurich rather than in Carcassonne, which is explained by the larger heating load. However, in three cases the largest savings were for the SFH45 house despite the fact that the annual electricity use of the system is much lower than that for the SFH100 house, 3581 kW h/year compared to 8340 kW h/year. This was attributed to the fact that, in these cases, the operating level of the space heating circuit played a significant role, the SFH45 house being supplied with a 35/30 °C heating system while the SFH100 was supplied with a 55/45 °C heating system.

  • 20.
    Psimopoulos, Emmanouil
    et al.
    Dalarna University, School of Technology and Business Studies, Energy Technology. Uppsala University.
    Bee, Elena
    Widén, Joakim
    Bales, Chris
    Dalarna University, School of Technology and Business Studies, Energy Technology.
    Techno-economic analysis of control algorithms for an exhaust air heat pump system for detached houses coupled to a photovoltaic system2019In: Applied Energy, ISSN 0306-2619, E-ISSN 1872-9118, Vol. 249, p. 355-367Article in journal (Refereed)
    Abstract [en]

    Operational control strategies for the heating system and “smart” utilization of energy storage were developed and analyzed in a simulation based case study of a single-family house with exhaust air heat pump and photovoltaic system. Rule based control algorithms that can easily be implemented into modern heat pump controllers were developed with the aim to minimize final energy and maximize self-consumption by the use of the thermal storage of the building, the hot water tank and electrical storage. Short-term weather and electricity price forecasts are used in some of the algorithms. Heat supply from an exhaust air heat pump is limited by the ventilation flow rate fixed by building codes, and compact systems employ an electric heater as backup for both space heating and hot water. This heater plays an important role in the energy balance of the system. A typical system designed for new detached houses in Sweden was chosen for the study. This system, together with an independent photovoltaic system, was used as a base case and all results are compared to those for this base case system. TRNSYS 17 was used to model the building and system as well as the control algorithms, and special care was taken to model the use of the backup electric heater as this impacts significantly on final energy use. Results show that the developed algorithms can reduce final energy by 5–31% and the annual net cost for the end user by 3–26%, with the larger values being for systems with a battery storage. Moreover, the annual use of the backup electric heater can be decreased by 13–30% using the carefully designed algorithms.

  • 21.
    Psimopoulos, Emmanouil
    et al.
    Dalarna University, School of Technology and Business Studies, Energy Technology. Uppsala University.
    Johari, Fatemeh
    Uppsala University.
    Widén, Joakim
    Uppsala University.
    Bales, Chris
    Dalarna University, School of Technology and Business Studies, Energy Technology.
    Impact of boundary conditions on the performance enhancement of advanced control strategies for a residential building with a heat pump and PV system with energy storage2019In: Applied Energy, ISSN 0306-2619, E-ISSN 1872-9118Article in journal (Refereed)
  • 22. Shen, Jingchun
    et al.
    Zhang, Xingxing
    University of Nottingham.
    Yang, Tong
    Tang, Llewellyn
    Cheshmehzangi, Ali
    Wu, Yupeng
    Huang, Guiqin
    Zhong, Dan
    Xu, Peng
    Liu, Shengchun
    Characteristic study of a novel compact Solar Thermal Facade (STF) with internally extruded pin-fin flow channel for building integration2016In: Applied Energy, ISSN 0306-2619, E-ISSN 1872-9118, Vol. 168, p. 48-64Article in journal (Refereed)
    Abstract [en]

    The fully building integrated Solar Thermal Facade (STF) systems can become potential solutions for aesthetics architectural design, as well as for the enhancement of energy efficiency and reduction of operational cost in the contemporary built environment. As a result, this article introduces a novel compact STF with internally extruded pin–fin flow channel that is particularly suitable for the building integration. A dedicated simulation model was developed on basis of the heat transfer and the flow mechanics. A prototype of this STF was fabricated and then it was tested under a series of controlled environmental conditions. The experimental validation illustrated a good agreement with the simulation results, indicating the established model was able to predict the STF’s thermal performance at a reasonable accuracy (i.e. mean deviation of less than 5.46%). The impacts of several operational parameters, i.e. equivalent solar radiation, air temperature, air velocity, water mass flow rate and inlet water temperature, on the STF thermal performance were then discussed respectively. Given the baseline testing condition, the collector efficiency factor F′ is almost 0.9930, leading to a relatively high nominal thermal efficiency at about 63.21%, which demonstrates such STF, with simpler structure, lower cost and higher feasibility in architectural design, can achieve an equivalent or better thermal performance than recent bionic STF or the conventional ones. It is also concluded that the thermal efficiency varies proportionally with solar radiation, air temperature, and mass flow rate of water, but oppositely to air velocity and inlet water temperature. A sharp decreasing trend of this STF’s thermal efficiency against the (Tin − Ta)/I was observed under the given operational conditions, which indicates current STF design is only suitable for pool heating, domestic hot water and radiant space heating in areas/climates with warm ambient air temperature and sufficient solar radiation. The overall research results are beneficial for further design, optimization and application of such STF in various solar driven systems, including the provision of hot water, space heating/cooling, increased ventilation, or even electricity in buildings. Such STF technology has the potential to boost the building energy efficiency and literally turn the envelope into an independent energy plant, creating the possibility of solar-thermal technologies deployment in high-rise buildings.

  • 23. Udomsri, Seksan
    et al.
    Bales, Chris
    Dalarna University, School of Technology and Business Studies, Energy and Environmental Technology.
    Martin, Andrew R.
    Martin, Viktoria
    Decentralized cooling in district heating network: system simulation and parametric study2012In: Applied Energy, ISSN 0306-2619, E-ISSN 1872-9118, Vol. 92, p. 175-184Article in journal (Refereed)
    Abstract [en]

    This paper presents system simulation and parametric study of the demonstration system of decentralized cooling in district heating network. The monitoring results obtained from the demonstration were calibrated and used for parametric studies in order to find improved system design and control. This study concentrates on system simulation studies that aim to: reduce the electricity consumption, to improve the thermal COP's and capacity if possible; and to study how the system would perform with different boundary conditions such as climate and load. The internal pumps inside the thermally driven chiller (TDC) have been removed in the new version TDC and implemented in this study to increase the electrical COP. Results show that replacement of the fourth with the fifth generation TDC increases the system electrical COP from 2.64 to 5.27. The results obtained from parametric studies show that the electrical and thermal COP's, with new realistic boundary conditions, increased from 2.74 to 5.53 and 0.48 to 0.52, respectively for the 4th generation TDC and from 5.01 to 7.46 and 0.33 to 0.43, respectively for the 5th generation TDC. Additionally the delivered cold increased from 2320 to 8670 and 2080 to 7740 kWh for the 4th and 5th generation TDC's, respectively. (C) 2011 Elsevier Ltd. All rights reserved.

  • 24. 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.

  • 25. Zhang, Sheng
    et al.
    Sun, Yongjun
    Cheng, Yong
    Huang, Pei
    City University of Hong Kong.
    Oladokun, Majeed Olaide
    Lin, Zhang
    Response-surface-model-based system sizing for Nearly/Net zero energy buildings under uncertainty2018In: Applied Energy, ISSN 0306-2619, E-ISSN 1872-9118, Vol. 228, p. 1020-1031Article in journal (Refereed)
    Abstract [en]

    Properly treating uncertainty is critical for robust system sizing of nearly/net zero energy buildings (ZEBs). To treat uncertainty, the conventional method conducts Monte Carlo simulations for thousands of possible design options, which inevitably leads to computation load that is heavy or even impossible to handle. In order to reduce the number of Monte Carlo simulations, this study proposes a response-surface-model-based system sizing method. The response surface models of design criteria (i.e., the annual energy match ratio, self-consumption ratio and initial investment) are established based on Monte Carlo simulations for 29 specific design points which are determined by Box-Behnken design. With the response surface models, the overall performances (i.e., the weighted performance of the design criteria) of all design options (i.e., sizing combinations of photovoltaic, wind turbine and electric storage) are evaluated, and the design option with the maximal overall performance is finally selected. Cases studies with 1331 design options have validated the proposed method for 10,000 randomly produced decision scenarios (i.e., users’ preferences to the design criteria). The results show that the established response surface models reasonably predict the design criteria with errors no greater than 3.5% at a cumulative probability of 95%. The proposed method reduces the number of Monte Carlos simulations by 97.8%, and robustly sorts out top 1.1% design options in expectation. With the largely reduced Monte Carlo simulations and high overall performance of the selected design option, the proposed method provides a practical and efficient means for system sizing of nearly/net ZEBs under uncertainty.

  • 26.
    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.

  • 27.
    Zhang, Xingxing
    et al.
    University of Hull.
    Shen, Jingchun
    Xu, Peng
    Zhao, Xudong
    Xu, Ying
    Socio-economic performance of a novel solar photovoltaic/loop-heat-pipe heat pump water heating system in three different climatic regions2014In: Applied Energy, ISSN 0306-2619, E-ISSN 1872-9118, Vol. 135, p. 20-34Article in journal (Refereed)
    Abstract [en]

    This paper aimed to study the socio-economic performance of a novel solar photovoltaic/loop-heat-pipe (PV/LHP) heat pump water heating system for application in three different climatic regions, namely, cold area represented by London, warm area represented by Shanghai, and hot (subtropical) area represented by Hong Kong. This study involved prediction of the annual fossil-fuel energy saving, investment return period and carbon emission reduction of the new system against the traditional gas-fired and electrical boilers based water heating systems. An established dynamic model developed by the authors was utilised to predict the system’s energy performance throughout a year in the three climatic regions. A life-cycle analytical model was further developed to analyse the economic and environmental benefits of the new system relative to the traditional systems. Analyses of the modelling results drew out several conclusive remarks: (1) the system could achieve the highest energy efficiency when operating at the hot (subtropical) climatic region (represented by Hong Kong), enabling the heat output of as high as 922 kW h/m2 yr and water temperature of above 45 °C, while the grid power input is only 59 kW h/m2 yr; (2) the system is worth for investment when operating at the high energy charging tariff area (represented by London), with the cost payback periods of 8 and 5 years relative to the traditional gas-fired and electrical boilers based systems, respectively; (3) the system could obtain the most promising environmental benefits when operating in Shanghai where the energy quality (embodied carbon volume of per kW h energy) is relatively poor, enabling reduction in life-cycle carbon emissions of around 4.08 tons/m2 and 17.87 tons/m2 respectively, relative to the gas-fired and electrical boilers. Answer to such a question on which area is most suitable for the system application is highly dependent upon the priority order among the three dominating factors: (1) energy efficiency, (2) economic revenue, and (3) environmental benefit, which may vary with the users, local concerns and policy influence, etc. The research results will be able to assist in decision making in implementation of the new PV/thermal technology and analyses of the associated economic and environmental benefits, thus contributing to realisation of the regional and global targets on fossil fuel energy saving and environmental sustainability.

  • 28.
    Zhang, Xingxing
    et al.
    University of Hull.
    Zhao, Xudong
    Shen, Jingchun
    Xu, Jihuan
    Yu, Xiaotong
    Dynamic performance of a novel solar photovoltaic/loop-heat-pipe heat pump system2014In: Applied Energy, ISSN 0306-2619, E-ISSN 1872-9118, Vol. 114, p. 335-352Article in journal (Refereed)
    Abstract [en]

    Objective of the paper is to present an investigation into the dynamic performance of a novel solar photovoltaic/loop-heat-pipe (PV/LHP) heat pump system for potential use in space heating or hot water generation. The methods used include theoretical computer simulation, experimental verification, analysis and comparison. The fundamental equations governing the transient processes of solar transmission, heat transfer, fluid flow and photovoltaic (PV) power generation were appropriately integrated to address the energy balances occurring in different parts of the system, e.g., glazing cover, PV cells, fin sheet, loop heat pipe, heat pump cycle and water tank. A dedicated computer model was developed to resolve the above grouping equations and consequently predict the system’s dynamic performance. An experimental rig was constructed and operated under the real weather conditions for over one week in Shanghai to evaluate the system living performance, which was undertaken by measurement of various operational parameters, e.g., solar radiation, photovoltaic power generation, temperatures and heat pump compressor consumption. On the basis of the first- (energetic) and second- (exergetic) thermodynamic laws, an overall evaluation approach was proposed and applied to conduct both quantitative and qualitative analysis of the PV/LHP module’s efficiency, which involved use of the basic thermal performance coefficient (COPth) and the advanced performance coefficient (COPPV/T) of such a system. Moreover, a simple comparison between the PV/LHP heat-pump system and conventional solar/air energy systems was conducted. The research results indicated that under the testing outdoor conditions, the mean daily electrical, thermal and overall energetic and exergetic efficiencies of the PV/LHP module were 9.13%, 39.25%, 48.37% and 15.02% respectively, and the average values of COPth and COPPV/T were 5.51 and 8.71. The PV/LHP module was found to achieve 3–5% higher solar exergetic efficiency than standard PV systems and about 7% higher overall solar energetic efficiency than the independent solar collector. Compared to the conventional solar/air heat pump systems, the PV/LHP heat pump system could achieve a COP figure that is around 1.5–4 times that for the conventional systems. It is concluded that the computer model is able to achieve a reasonable accuracy in predicting the system’s dynamic performance. The PV/LHP heat pump system is able to harvest significant amount of solar heat and electricity, thus enabling achieving enhanced solar thermal and electrical efficiencies. All these indicate a positive implication that the proposed system has potential to be developed into a high performance PV/T technology that can contribute to significant fossil fuel energy saving and carbon emission.

  • 29.
    Zhang, Xingxing
    et al.
    De Montfort University.
    Zhao, Xudong
    Xu, Jihuan
    Yu, Xiaotong
    Characterization of a solar photovoltaic/loop-heat-pipe heat pump water heating system2013In: Applied Energy, ISSN 0306-2619, E-ISSN 1872-9118, Vol. 102, p. 1229-1245Article in journal (Refereed)
    Abstract [en]

    This paper introduced the concept, potential application and benefits relating to a novel solar photovoltaic/loop-heat-pipe (PV/LHP) heat pump system for hot water generation. On this basis, the paper reported the process and results of characterizing the performance of such a system, which was undertaken through dedicated thermo-fluid and energy balance analyses, computer model development and operation, and experimental verification and modification. The fundamental heat transfer, fluid flow and photovoltaic governing equations were applied to characterize the energy conversion and transfer processes occurring in each part and whole system layout; while the energy balance approach was utilized to enable inter-connection and resolution of the grouped equations. As a result, a dedicated computer model was developed and used to calculate the operational parameters, optimise the geometrical configurations and sizes, and recommend the appropriate operational condition relating to the system. Further, an experimental rig was constructed and utilized to acquire the relevant measurement data that thus enabled the parallel comparison between the simulation and experiment. It is concluded that the testing and modelling results are in good agreement, indicating that the model has the reasonable accuracy in predicting the system’s performance. Under the given experimental conditions, the electrical, thermal and overall efficiency of the PV/LHP module were around 10%, 40% and 50% respectively; whilst the system’s overall performance coefficient (COPPV/T) was 8.7. Impact of the operational parameters (i.e. solar radiation, air temperature, air velocity, heat-pump’s evaporation temperature, glazing covers, and number of the absorbing heat pipes) to the performance of the system (in terms of efficiencies of the PV/LHP module and the system’s overall performance coefficient COPPV/T) was investigated individually. The results indicated that lower solar radiation, lower air temperature, higher air velocity and smaller cover number led to enhanced electrical efficiency but reduced thermal efficiency of the module; whereas lower heat-pump’s evaporation temperature and larger number of heat absorbing pipes gave rise to both thermal and electrical efficiencies of the module. The research results would assist in developing a high efficient solar (space or hot water) heating system and thus contribute to realisation of the energy saving and associated carbon emission targets set for buildings globally.

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