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  • 1.
    Akander, Jan
    et al.
    Högskolan i Gävle, Institutionen för teknik och byggd miljö, Ämnesavdelningen för byggnadskvalitet.
    Stojanovic, Bojan
    Högskolan i Gävle, Institutionen för teknik och byggd miljö, Ämnesavdelningen för byggnadskvalitet.
    Hallberg, Daniel
    Högskolan i Gävle, Institutionen för teknik och byggd miljö, Ämnesavdelningen för byggnadskvalitet.
    Simulated Long-term Thermal Performance of a Building That Utilizes a Heat Pump System and Borehole2008Ingår i: Durability of Building Materials & Components 11: Globality and Locality in Durability / [ed] A. Nil Türkeri, Özkan Sengül, Istanbul, Turkey: Istanbul Technical University, 2008Konferensbidrag (Refereegranskat)
    Abstract [en]

    Over the last decades, installation and use of heat pumps has grown rapidly in Sweden, to the extent that these mainly or partly heat roughly 25 % of the heated floor space in single-family houses. A majority are ground coupled where the heat exchanger is a borehole of 60-220 m depth. As the heat pump system operates, heat extraction will in time reduce borehole temperatures, rendering lowered efficiency of the heat pump system thus directly affecting its economical and environmental aspects. Within the building sector, durability and life performance dynamics of energy systems is often not reflected upon. System performance and efficiency is assumed to be static over time, changing only due to different operation scenarios. This paper serves to quantify the long-term thermal performance degradation of a component, in this case the borehole, and how the degradation of this component affects performance-over-time of an entire system, in this case the heating system of the building. A dynamic thermal simulation model is used to assess the long-term thermal performance of the borehole. The building, which the heat pump serves, is assumed to be a typical Swedish house with normal energy consumption. Simulation results show that the depth of the borehole is of great importance to limit over-time temperature drops. The efficiency of the heat pump system is directly dependent of temperatures in the borehole. How the overall system performance is affected by component performance degradation, is highlighted.

  • 2.
    Hallberg, Daniel
    et al.
    Högskolan i Gävle, Institutionen för teknik och byggd miljö, Ämnesavdelningen för byggnadskvalitet.
    Akander, Jan
    Högskolan i Gävle, Institutionen för teknik och byggd miljö, Ämnesavdelningen för byggnadskvalitet.
    Stojanovic, Bojan
    Högskolan i Gävle, Institutionen för teknik och byggd miljö, Ämnesavdelningen för inomhusmiljö.
    Kedbäck, Mikael
    Life Cycle Management System: a planning tool supporting Long-term based design and maintenance planning2008Ingår i: Durability of Building Materials & Components 11: Globality and Locality in Durability / [ed] A. Nil Türkeri, Özkan Sengül, Istanbul: Istanbul Technical University , 2008, s. 1871-1878Konferensbidrag (Refereegranskat)
    Abstract [en]

    Construction projects include large amounts of information that has to be communicated to a number of actors, such as authorities, companies, clients and end users. Information exchange is complex, involving various players on different levels and phases of the construction process. For private clients, who generally have little experience and knowledge of this process, the on-going “Bygga Villa”-project has developed a web-portal, which offers them relevant information about the process and a number of services to facilitate realisation of their projects. One of the services provides a tool for supporting long-term strategy planning. The tool is based on the Life cycle Management System (LMS) that is a predictive and generic life cycle-based management system, aimed to support decision-making and planning of optimal design and maintenance of any construction works. The LMS-Bygga Villa tool estimates service life and maintenance intervals of different building parts and systems based on environmental-dependent degradation models. Simulated scenarios can give optimised solutions by applying life cycle cost analysis. This paper presents two case studies within LMS-Bygga Villa. The first case focuses on service life performance analysis of exterior parts of buildings. The second focuses on service life performance analysis of energy systems; here specifically a borehole assisted heat pump system used for heating a Swedish single-family residence.

  • 3.
    Hallberg, Daniel
    et al.
    Högskolan i Gävle, Institutionen för teknik och byggd miljö, Ämnesavdelningen för byggnadskvalitet.
    Stojanovic, Bojan
    Högskolan i Gävle, Institutionen för teknik och byggd miljö, Ämnesavdelningen för byggnadskvalitet.
    Analytical and numerical thermal modelling & analysis of an building integrated unglazed solar collector: PhD course paper2007Ingår i: Mathematics for PhD-students in building science, Stockholm: Architecture and the Built Environment, Royal Institute of Technology , 2007Kapitel i bok, del av antologi (Övrig (populärvetenskap, debatt, mm))
    Abstract [en]

    The objective of this report is to derive an analytical and numerical USC model for thermal analysis. These models are meant to calculate USC temperature variation across the USC duct as well as the fluid temperature along the USC. The main purpose of the analytical model is to attain a detailed steady state tool for USC (as in this report) design and dimensioning. The numerical model is meant to calculate the time dependant USC thermal performance as well as being a benchmark for the analytical model.

  • 4.
    Hallberg, Daniel
    et al.
    Högskolan i Gävle, Institutionen för teknik och byggd miljö, Ämnesavdelningen för byggnadskvalitet.
    Stojanovic, Bojan
    Högskolan i Gävle, Institutionen för teknik och byggd miljö, Ämnesavdelningen för byggnadskvalitet.
    Akander, Jan
    Högskolan i Gävle, Institutionen för teknik och byggd miljö, Ämnesavdelningen för byggnadskvalitet.
    Långsiktig underhållsplanering av fjärrvärmenät: en förstudie av möjligheter till utveckling av LMS2007Rapport (Övrig (populärvetenskap, debatt, mm))
    Abstract [en]

    Samtidigt som fjärrvärme är ett effektivt sätt att leverera värme så leder en centraliserad värmeproduktion till att fler personer drabbas vid eventuella driftavbrott. Detta skapar ett behov av ökad leveranssäkerhet och kontroll av prestanda över hela fjärrvärmenätets livscykel. Genom en långsiktig planering av nätets utbyggnad och förvaltning erhålls effektivare resursanvändande och större säkerhetsmarginaler. Långsiktig planering bygger till stor del på analys av olika scenarier där såväl rådande förutsättningar som ”worst cases” kan beaktas utifrån olika aspekter (tekniska, ekonomiska, säkerhetsmässiga m.m.). Målet är att hitta optimerade åtgärder, vilket kräver systematisk hantering och bearbetning av en stor mängd information. Detta kan endast göras rationellt med hjälp av IT-verktyg. Life cycle Management System (LMS) är ett resultat av tre konsekutiva EU-finansierade forskningsprojekt där gruppen för byggnadsmaterialteknik – Högskolan i Gävle, har haft en ledande roll. Systemet innehåller utvecklade rutiner och metoder för hantering av information som ligger till grund för långsiktig planering och optimerad förvaltning av byggnadsverk. Systemmässigt är LMS uppbyggt av moduler som hanterar och analyserar data på olika sätt. Anledningen till systemets modulbaserade struktur är att det, helt eller i delar, kan anpassas mot de krav och önskemål som klienten ställer på systemet. På så sätt behöver klienten bara komplettera sitt befintliga system med de funktioner som önskas av LMS, samtidigt som denne undviker att ”kasta ut” det gamla systemet. Förstudien omfattar en litteraturstudie och analys av Gävle Energi AB:s (GEAB) drift- och underhållsdata. Förstudiens syfte är att identifiera och kartlägga de anpassnings- och utvecklingsbehov som föreligger en implementering av LMS som planeringsverktyg för GEAB:s fjärrvärmenät.

  • 5.
    Hallberg, Daniel
    et al.
    Högskolan i Gävle, Akademin för teknik och miljö, Avdelningen för bygg- energi- och miljöteknik, Byggvetenskap - byggnadsmateriallära.
    Stojanovic, Bojan
    Högskolan i Gävle, Akademin för teknik och miljö, Avdelningen för bygg- energi- och miljöteknik, Byggvetenskap - byggnadsmateriallära.
    Akander, Jan
    Högskolan i Gävle, Akademin för teknik och miljö, Avdelningen för bygg- energi- och miljöteknik, Byggnadsteknik.
    Status, needs and possibilities for service life prediction and estimation of district heating distribution networks2012Ingår i: Structure and Infrastructure Engineering, ISSN 1573-2479, E-ISSN 1744-8980, Vol. 8, nr 1, s. 41-54Artikel, forskningsöversikt (Refereegranskat)
    Abstract [en]

    An optimised and proactive maintenance strategy aims to maximise the economical profit, minimise environmental impacts and keep the risk of failure to a low level. Implementation of such strategy in the context of district heating requires efforts and abilities for predicting future performances and estimating service life of district heating components. A literature review on failures (damages and performance reductions) occurring on district heating pipes, reveals that failures in district heating pipes are mainly leaks due to corrosion or mechanical impacts and reduced thermal insulation performance: leaks being the more serious damage type. A feasible service life estimation method for this type of damage is the Factor Method. Since the application of this method within the context of DH pipes has not been found in other publications, this paper focuses on describing the method and discusses the possibilities on how to apply it in two specific cases with respect to leakage: service life estimation of repaired district heating pipe sections (i.e. maintenance of district heating network) and of district heating pipes in new or extended district heating networks. A particular attention is paid on which modifying factors to consider and how to quantify them.

  • 6.
    Mattsson, Magnus
    et al.
    Högskolan i Gävle, Institutionen för teknik och byggd miljö, Ämnesavdelningen för inomhusmiljö.
    Stojanovic, Bojan
    Högskolan i Gävle, Institutionen för teknik och byggd miljö, Ämnesavdelningen för byggnadskvalitet.
    Elfman, Lena
    Effect of Particulate Air Cleaners on the Content of airborne Dust and Cat Allergen in Classrooms2004Ingår i: Roomvent 2004: 9th international conference on air distribution in rooms, 2004Konferensbidrag (Refereegranskat)
    Abstract [en]

    Electrostatic air cleaners (precipitators) were tested in four classrooms during ordinary lessons for four weeks. Airborne dust in the classrooms was collected on filters using two different kinds of samplers: IOM-sampler and a new kind of ionizing sampler. The amount of collected dust was evaluated by visual inspection (“filter blackening”) and the content of cat allergen was measured using an amplified ELISA assay. It was found that the filter blackening was 64% lower when the air cleaners were active than when they where inactive (p<0.001). This suggests that the air cleaners were effective in reducing the content of airborne particulate matter. The reduction in cat allergen appeared however to be less substantial. The variance of the allergen data was unexpectedly large, presumably due to relatively few allergen-carrying particles in the sampled air. It is believed that larger sampling volumes are needed to get more reliable data of airborne cat allergen in spaces where the allergen is emitted indirectly.

  • 7.
    Stojanovic, Bojan
    Högskolan i Gävle, Institutionen för teknik och byggd miljö, Ämnesavdelningen för byggnadskvalitet.
    Energy performance and absorber coating degradation of a solar collector: PhD course paper, Byggnaders livslängd och karakterisering av nedbrytningsmiljö, KTH research school - University of Gävle, Gävle, Sweden2004Övrigt (Övrig (populärvetenskap, debatt, mm))
    Abstract [en]

    The use of solar collectors has grown in Sweden during the last 20 years. At the present the fastest growing collector applications are Domestic Hot Water (DHW) systems. The life performance of these systems is important due to their intended long use. This applies emphasis on the system durability and service life, which is in consent with the European Construction Products Directive (CPD). It states that the essential requirements on constructed work should be met during the intended working life of the building; this results in essence in a performance requirement on all building products. The life performance of building materials and products has to be assessed and declared. This paper presents a literature study of the degradation of flat plate solar collectors used in DHW systems. The scope of the paper is limited to the selective absorber coating of the collector and is focused on the research made in the IEA Task X programme. The objective is to investigate the potentials of computer simulations of collector system performance reduction, due to absorber coating degradation. The Task X study used an approach of accelerated testing to access the extent of absorber coating degradation. Mathematical models of the coating degradation were used to transform the accelerated test results to in-service conditions. A model of the microclimate in a flat plate solar collector was also developed. Results from the study shows that the accelerated testing procedure is in fairly good agreement, although it contains a number of simplifications, when compared with specimens from in-service collectors that have been working for 3 to 15 years. By using in-service microclimate data and accelerated test results, calculations of approximated real time degradation can be made. The developed microclimate model, which was intended for computer simulations, gave deviating result when compared with measurements, showing that further development is needed. The methodologies from the Task X study could also be useful when assessing the effects of absorber coating degradation on other types of collector systems, e.g. a solar-assisted heat pump system, if the system performance criterion, which is related to the spectral properties of the absorber coating, is declared.

  • 8.
    Stojanovic, Bojan
    Högskolan i Gävle, Institutionen för teknik och byggd miljö, Ämnesavdelningen för byggnadskvalitet.
    Life performance assessment methodologies for combined solar energy technologies: a case study on system parts in Nordic climates2007Licentiatavhandling, sammanläggning (Övrigt vetenskapligt)
    Abstract [en]

    The main questions concerning energy technologies today are their economical and environmental impacts. These entities are (at the present) assessed on the basis that operations proceed as newly installed/designed systems, during an assumed working life period. While this is the common way of perceiving energy systems, performance-over-time will change as an effect of (e.g. material) degradation and not solely of different operation scenarios. How and to what extent, is the question that needs assessing in order to evaluate if these changes will jeopardise the intended system performance requirement. In turn, this pro-active assessment and analysis is in line with today’s performance based directives, laws, regulations and concepts; of which the working life is an essential part. The main context of the thesis, is a contribution to the R&D topic on life performance of energy technologies, with papers on a literature review and case study on two system parts: solar collector and ground heat exchanger (borehole); within the energy technology area of combined solar energy technologies/systems utilised in buildings. The thesis specifically presents a general description of requirements on constructed works and their material, components and systems. It also gives an insight to the energy technology R&D and engineering sector, regarding durability and service life assessment methodologies; and also to the durability of constructed works sector, regarding the needs for assessing material degradation in relation to system performance. The case studies presented in the thesis, show how durability of energy technologies may be sought-after, as well as specific knowledge and useful tools, methodologies and test setups for assessing long-term performance of combined solar energy technologies (in this case a solar-assisted heat pump system utilising a building integrated Unglazed Solar Collector and energy storage). The utilisation of solar collectors and heat pumps (primarily for space and domestic tap water heating) has rapidly increased in Sweden during the last decades. Sweden has today the largest heat pump market in Europe. During recent years, there has also been an increased interest in heating systems that combine heat pumps with solar collectors (glazed and unglazed) and energy storages; with the aim of attaining a system that provides higher energy and greater economical performances than individual solar collector or heat pump systems. If these systems are to be successful they must be economically feasible; placing emphasis on the cost, durability and performance of the system. The main issue on life performance of energy technologies is how and to what extent, performance reduction in individual materials and components influences the overall system performance; as the essence of energy system sustainability is system performance.

  • 9.
    Stojanovic, Bojan
    Högskolan i Gävle, Institutionen för teknik och byggd miljö, Ämnesavdelningen för inomhusmiljö.
    Lifetime performance assessment of thermal systems: studies on building, solar and district heating applications2009Doktorsavhandling, sammanläggning (Övrigt vetenskapligt)
  • 10.
    Stojanovic, Bojan
    Högskolan i Gävle, Institutionen för teknik och byggd miljö, Ämnesavdelningen för byggnadskvalitet.
    On Reduced Energy Performance of a Solar-Assisted Heat Pump System due to Absorber Coating Degradation2005Ingår i: 10th DBMC International Conference on durability of building materials and components, 2005, s. 876-883Konferensbidrag (Refereegranskat)
    Abstract [en]

    This paper presents a literature study of the degradation of flat plate solar collectors used in Domestic Hot Water (DHW) systems. The scope of the paper is limited to the selective absorber coating of the collector and is focused on the research made in the IEA Task X study. The objective is to investigate the potentials of computer simulations of performance reduction of a solar-assisted heat pump system, due to absorber coating degradation. The Task X study used an approach of accelerated testing to access the extent of absorber coating degradation. Mathematical models describing the coating degradation were used to transform the accelerated results into in-service conditions. A mathematical model of the microclimate in a flat plate collector was also developed. Results showed that the accelerated test procedure is in fairly good agreement, although it contains a number of simplifications, when compared with specimens from in-service collectors that have been working for 3 to 15 years. By using in-service microclimate data and accelerated test results, calculations into approximated real time degradation can be made. The microclimate model that was intended for simulations gave deviating results when compared with measurements, showing that further development is needed. The methodologies from the Task X study could also be useful when assessing the effects of absorber coating degradation on other types of collector systems, e.g. a solar-assisted heat pump system. Such a system is under evaluation in the ongoing EU project named: Endothermic Technology for Energy Efficient Housing in the EU (ENDOHOUSING). The project uses solar-assisted heat pumps to provide the thermal energy to meet space heating, cooling and hot water requirements for domestic houses in different regions of the EU throughout the year. Six demonstration houses (endohouses) will be established and equipped accordingly across the EU and evaluated during the project. If these systems are to be commercially installed and used they must be economically feasible. This places emphasis on the cost, durability and performance of the system. A solar collector is exposed to various strains that will contribute to a degradation of the collector materials, which will decrease its energy performance. These changes will in turn be transposed throughout the system lowering its degree of efficiency that directly relates to the economical aspect of the system. As a result of these changes a performance over time assessment is needed for this type of system, which in turn is in line with the European Construction Products Directive (CPD).

  • 11.
    Stojanovic, Bojan
    et al.
    Högskolan i Gävle, Akademin för teknik och miljö, Avdelningen för bygg- energi- och miljöteknik, Byggvetenskap - byggnadsmateriallära.
    Akander, Jan
    Högskolan i Gävle, Akademin för teknik och miljö, Avdelningen för bygg- energi- och miljöteknik, Byggnadsteknik.
    Build-up and long-term performance test of a full-scale solar-assisted heat pump system for residential heating in Nordic climatic conditions2010Ingår i: Applied Thermal Engineering, ISSN 1359-4311, E-ISSN 1873-5606, Vol. 30, nr 2-3, s. 188-195Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    This paper presents the build-up and long-term performance test of a full-scale Solar-Assisted Heat Pump System (SAHPS) for residential heating in Nordic climatic conditions. This particular SAHPS was developed within the EU project ENDCHOUSING, by predominantly using components and techniques that are available on the market. The analysis primarily focuses on system performance, with emphasis on Heat Pump (HP) and total system Seasonal Performance Factor (SPF), based on long-term and full-scale operation. Analysis shows that despite unfavourable building conditions, for low energy use and utilisation of a SAHPS, the system was successfully in full operation (for about 2 years) fulfilling heating requirements. Data processing of the series representing the full year period of 2007(February)-2008(February), presented a HP and total SAHPS performance of. SPF(HP) = 2.85 and SPF(SAHPS) = 2.09. The authors argue that with an optimised SAHPS control and operation strategy, additional use of circulation pumps and energy (electricity) could be vastly reduced, hence attaining a SPF(SAHPS) value that is in parity with the SPF(HP). As the Nordic (Swedish) Endohousing SAHPS has not yet been properly optimised/designed and installed in an appropriate house, the SPFHP = 2.85 is considered satisfactory.

  • 12.
    Stojanovic, Bojan
    et al.
    Högskolan i Gävle, Institutionen för teknik och byggd miljö, Ämnesavdelningen för byggnadskvalitet.
    Akander, Jan
    Högskolan i Gävle, Institutionen för teknik och byggd miljö, Ämnesavdelningen för byggnadskvalitet.
    Long-Term Thermal Performance Modelling and Simulations of a Borehole2005Konferensbidrag (Refereegranskat)
    Abstract [en]

    This paper presents the long-term thermal performance modelling and simulation of a single heat extraction borehole with a U-shaped pipe, by applying the Macro Element Modelling (MEM) method, developed by Schmidt (2004). The dynamic thermal performance of the ground around the borehole is analysed in the frequency domain. Thereafter, the ground properties are transformed into a network of discrete resistances and capacitances (RC’s) that together with the pipe, models the thermal performance of the borehole. The method allows the parameters of the RC-network components to be estimated and optimised for time domain simulations. The advantage of this modelling method is that it establishes a simplified yet accurate thermal borehole model, which requires less computing time and power compared to a traditional finite difference/element model. This makes it easier to perform several decades of long-term thermal performance simulations. In this paper the U-pipe was modelled by applying a star resistance network that calculates the weighted heat fluxes between the solid borehole and the U-pipe. The presented work shows that at small temperature increases and at relative large fluid velocities the U-pipe fluid temperature can be seen as rising linearly. This provides the borehole modelling with the possibility to model the entire borehole construction by using only one macro element. To compensate for any errors when using the linearly increasing fluid temperature for calculating the energy extraction from the borehole, the total U-pipe star resistance network is compensated. The U-pipe star network was also compared with a FEM (Finite Element Method) simulation, showing that the correspondence between the two models is good. The half 5-node network that was used by Schmidt (2004) for modelling the solid construction of the borehole was modified in this paper, with an additional resistance to ensure the stability of the network when simulation long-term heat extraction periods. The borehole RC-network was optimised for a time period of 100 years. The results from the long-term performance simulation made with the derived borehole model, were also compared to other presented borehole simulations. The model proved to have, at a first stage of comparison, a good correspondence with the other presented results.

  • 13.
    Stojanovic, Bojan
    et al.
    Högskolan i Gävle, Institutionen för teknik och byggd miljö, Ämnesavdelningen för inomhusmiljö.
    Akander, Jan
    Högskolan i Gävle, Institutionen för teknik och byggd miljö, Ämnesavdelningen för byggnadskvalitet.
    Oglasade takintegrerade solfångare: Ett energitekniskt aktivt byggnadsskal2008Ingår i: Bygg & Teknik, ISSN 0281-658X, nr 4Artikel i tidskrift (Övrig (populärvetenskap, debatt, mm))
  • 14.
    Stojanovic, Bojan
    et al.
    Högskolan i Gävle, Institutionen för teknik och byggd miljö, Ämnesavdelningen för byggnadskvalitet.
    Akander, Jan
    Högskolan i Gävle, Institutionen för teknik och byggd miljö, Ämnesavdelningen för byggnadskvalitet.
    Use of a Peltier Element to Increase Time of Wetness of Unglazed Solar Collector Specimens in a Natural Field Exposure Test2008Ingår i: Durability of Building Materials & Components 11 (11DBMC), Istanbul, Turkey, 11-14 May 2008, 2008, s. 1169-1175Konferensbidrag (Refereegranskat)
    Abstract [en]

    In accelerated testing, material specimens are exposed to completely artificial environments, where exposure to individual degradation agents is enhanced. In contrast, field-testing exposes specimens to multiple degradation agents. When performing a semi-natural test, the influence of a selected degradation agent may be increased while the specimen is still situated in its natural environment. Moisture is such an agent. In an experimental set-up for evaluating long-term optical performance of an building integrated Unglazed Solar Collector, a sub-task was to increase Time of Wetness (TOW) for several collector specimens for two reasons: to “simulate” an active cooling of the component as is the case for solar collectors; and to assess the role of TOW on optical degradation of the solar collector. Specimen cooling and increase in TOW was achieved by utilisation of a Direct-Air Peltier Element. TOW was estimated through measurements with WETCORR sensors (monitoring surface temperatures and moisture) and climate parameters (temperature and relative humidity) at site. At this particular test site in Gävle, Sweden, TOW was more than doubled in comparison to non-cooled surfaces. The Peltier Element proved to be inexpensive and flexible for this purpose.

  • 15.
    Stojanovic, Bojan
    et al.
    Högskolan i Gävle, Institutionen för teknik och byggd miljö, Ämnesavdelningen för inomhusmiljö.
    Akander, Jan
    Högskolan i Gävle, Institutionen för teknik och byggd miljö, Ämnesavdelningen för byggnadskvalitet.
    Eriksson, Bengt
    Högskolan i Gävle, Institutionen för teknik och byggd miljö, Ämnesavdelningen för byggnadskvalitet.
    Natural and semi-natural field exposure testing and analysis, on optical degradation of a building integrated unglazed solar collector surface2008Ingår i: Materials and Structures, ISSN 1359-5997, E-ISSN 1871-6873, Vol. 41, nr 6, s. 1057-1071Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Durability is of great importance when considering sustainable energy systems. In turn it lays emphasis on assessing performance over time of energy systems and components. This paper presents a study on optical degradation of a building-integrated Unglazed Solar Collector (USC) surface, by exposing USC specimens to a natural and semi-natural field exposure test. Particular interest is devoted to the semi-natural field exposure test method evaluation, and the degradation of optical properties. The study showed that about 11 months of field exposure testing did not cause any significant optical (total solar absorptance and IR emittance) or material (surface coating) degradation; although measurements revealed a decrease in specular reflectance as diffuse increased. It was likely due to surface pollution that predominantly consisted of quartz. The study also showed that it is possible to achieve a considerable increased moisture exposure on test surfaces (seminatural field exposure test), through a relatively simple cooling device (Direct-Air Peltier-Element) and rough control strategy.

  • 16.
    Stojanovic, Bojan
    et al.
    Högskolan i Gävle, Institutionen för teknik och byggd miljö, Ämnesavdelningen för byggnadskvalitet.
    Akander, Jan
    Högskolan i Gävle, Institutionen för teknik och byggd miljö, Ämnesavdelningen för byggnadskvalitet.
    Oostendrop, Peter
    TNO.
    Kronström, Urban
    IVT.
    Improvements in Heat Pumps for Endothermic Systems: ENDOHOUSING deliverable D7b2006Rapport (Övrigt vetenskapligt)
  • 17.
    Stojanovic, Bojan
    et al.
    Högskolan i Gävle, Akademin för teknik och miljö, Avdelningen för bygg- energi- och miljöteknik, Byggvetenskap - byggnadsmateriallära.
    Hallberg, Daniel
    Högskolan i Gävle, Akademin för teknik och miljö, Avdelningen för bygg- energi- och miljöteknik, Byggvetenskap - byggnadsmateriallära.
    Akander, Jan
    Högskolan i Gävle, Akademin för teknik och miljö, Avdelningen för bygg- energi- och miljöteknik, Byggnadsteknik.
    A steady state thermal duct model derived by fin-theory approach and applied on an unglazed solar collector2010Ingår i: Solar Energy, ISSN 0038-092X, E-ISSN 1471-1257, Vol. 84, nr 10, s. 1838-1851Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    This paper presents the thermal modelling of an unglazed solar collector (USC) flat panel, with the aim of producing a detailed yet swift thermal steady-state model. The model is analytical, one-dimensional (ID) and derived by a fin-theory approach. It represents the thermal performance of an arbitrary duct with applied boundary conditions equal to those of a flat panel collector. The derived model is meant to be used for efficient optimisation and design of USC flat panels (or similar applications), as well as detailed thermal analysis of temperature fields and heat transfer distributions/variations at steady-state conditions; without requiring a large amount of computational power and time. Detailed surface temperatures are necessary features for durability studies of the surface coating, hence the effect of coating degradation on USC and system performance. The model accuracy and proficiency has been benchmarked against a detailed three-dimensional Finite Difference Model (3D FDM) and two simpler ID analytical models. Results from the benchmarking test show that the fin-theory model has excellent capabilities of calculating energy performances and fluid temperature profiles, as well as detailed material temperature fields and heat transfer distributions/variations (at steady-state conditions), while still being suitable for component analysis in junction to system simulations as the model is analytical. The accuracy of the model is high in comparison to the 3D FDM (the prime benchmark), as long as the fin-theory assumption prevails (no 'or negligible' temperature gradient in the fin perpendicularly to the fin length). Comparison with the other models also shows that when the USC duct material has a high thermal conductivity, the cross-sectional material temperature adopts an isothermal state (for the assessed USC duct geometry), which makes the ID isothermal model valid. When the USC duct material has a low thermal conductivity, the heat transfer course of events adopts a 1D heat flow that reassembles the conditions of the 1D simple model (for the assessed USC duct geometry); ID heat flow through the top and bottom fins/sheets as the duct wall reassembles a state of adiabatic condition.

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