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  • 1.
    Bales, Chris
    et al.
    Dalarna University, School of Technology and Business Studies, Environmental Engineering.
    Lindberg, Eva
    Dalarna University, School of Technology and Business Studies, Environmental Engineering.
    Fiedler, Frank
    Dalarna University, School of Technology and Business Studies, Environmental Engineering.
    Rönnelid, Mats
    Dalarna University, School of Technology and Business Studies, Environmental Engineering.
    European Solar Engineering School ESES: Past and Future2006In: Eurosun 2006, Glasgow, Scotland, 2006Conference paper (Other academic)
    Abstract [en]

    The European Solar Engineering School ESES is a one-year masters program that started in 1999 at the Solar Energy Research Center SERC, Dalarna University College. It has been growing in popularity over the years, with over 20 students in the current year. Approximately half the students come from Europe, the rest coming from all over the globe. This paper described the contents and experiences from seven years of running the programme and the plans for adapting the programme to the Bologna process. The majority of the students from ESES have found work in the solar industry, energy industry or taken up PhD positions. An alumni group has been started that actively gives support to past, present and potential future students.

  • 2.
    Bastholm, Caroline
    et al.
    Dalarna University, School of Technology and Business Studies, Energy Technology.
    Fiedler, Frank
    Dalarna University, School of Technology and Business Studies, Energy Technology.
    Techno-economic study of the impact of blackouts on the viability of connecting an off-grid PV-diesel hybrid system in Tanzania to the national power grid2018In: Energy Conversion and Management, ISSN 0196-8904, E-ISSN 1879-2227, Vol. 171, no 1, p. 647-658Article in journal (Refereed)
    Abstract [en]

    National electrification plans for many countries with a low level of electrification promote the implementation of centralized and decentralized electrification in parallel. This paper explores different ways of utilizing an established off-grid PV-diesel hybrid system when the national grid becomes available. This is a rather unique starting point within the otherwise well-explored area of rural electrification. With particular focus on the impact of blackouts in the national grid, we evaluate the economic viability of some alternatives: to continue to use the off-grid micro-grid, to connect the existing micro-grid with or without battery backup to the national grid, or to use the national grid only. Our simulation results in HOMER demonstrate that with a grid without blackouts, there are few benefits to maintain the existing system. Low grid-connection fees, low tariffs and low revenues from selling excess electricity to the grid contribute to this result despite the fact that the system does not carry any investment costs. With a grid with blackouts, it is beneficial to maintain the system. The extent of blackouts and the load on the system determine which system configuration is most feasible. The results make clear the importance of taking blackouts in the national grid into consideration when possible system configurations are being evaluated. This is rarely quantified in studies comparing different electrification alternatives, but deserves more attention.

  • 3.
    Fiedler, Frank
    Dalarna University, School of Technology and Business Studies, Energy and Environmental Technology.
    A testing and demonstration facility for PV systems and components2013In: Proceedings of 3rd Symposium Small PV Applications: Rural Electrification and commercial use / [ed] OTTI e.V., Regensburg, Germany, 2013, p. 111-116Conference paper (Other academic)
    Abstract [en]

    A test and demonstration facility for PV and PV hybrid systems and system components has been designed and installed at Dalarna University in Sweden. The facility allows studies of complete PV systems or single components in a range of 0.1-10 kW. The facility includes two grid-connected PV systems, a PV Hybrid off-grid system, three emulators and the necessary measurement and control equipment. Tests can be done manually or automatically through programmed test procedures controlled that will be implemented in Labview. The facility shall be used by researchers, professionals of the industry and engineering students.

  • 4.
    Fiedler, Frank
    Dalarna University, School of Technology and Business Studies, Environmental Engineering.
    Combined solar and pellet heating systems: Studies of energy use and CO-emissions2006Doctoral thesis, monograph (Other academic)
    Abstract [en]

    In this study 4 solar and pellet heating systems have been studied with the help of annual dynamic simulations. Two of the systems comprised a pellet stove and two systems were solar combisystems; one with a store integrated pellet burner, the other with a separate pellet boiler. The aim was to evaluate their thermal performance and their CO-emissions. The systems have been modelled based on lab measurements of the single system components. The used models allow a detailed study of the dynamic behaviour of the systems. The stove systems have the least primary energy consumption provided the auxiliary electricity is taken into account with a conversion factor of 100%. If the auxiliary electricity is taken into account with a conversion of 40% and/or the systems are placed in the heated area the combisystems need less or a similar amount of primary energy. Modulating combustion power reduces the number of starts and stops and for most pellet units this reduces the total CO emissions. The obtained annual CO emissions are higher than the values obtained from the standard test methods. It was shown that the average emissions under realistic annual conditions were greater than the limit values of two Eco-labels. The system performance can be significantly improved by a proper control of the pellet heater and by sizing the pellet heater according to the size of the peak space heating demand. Based on these findings from the simulations two prototypes of a combined solar and pellet heating system has been designed, built and tested; one for the lab and one that has been installed in a demonstration house. The system is very compact and is suitable for detached houses with no heating room or little space for a heating system.

  • 5.
    Fiedler, Frank
    Dalarna University, School of Technology and Business Studies, Energy and Environmental Technology.
    Förstudie småskalig pelletanvändning i Chile2009Report (Other academic)
    Abstract [sv]

    Syftet med denna förstudie var att undersöka vilka förutsättningar finns för pelletvärmesystem och om marknaden i Chile kan vara intressant för svenska företag som tillverka den typ värmesystem. De viktigaste resultaten är: 1. Träpellets finns tillgängliga i Chile tillverkade av tre företag med en total tillverkningskapacitet av 100000 ton. En typ pellets finns på marknaden som har ungefär samma kvalitet som svensk tillverkade pellets. 2. Än så länge finns i Chile bara ett företag som tillverkar pelletskaminer. Det finns ytterligare företag som importerar pelletskaminer och pelletspannor från Europa. 3. På grund av det milda klimatet har bostadshus inga vattenburna värmedistributionssystem eller även inga värmesystem alls. 4. Mest vanliga är enkla vedkaminer. Det finns potential att ersätta dessa kaminer speciellt i storstadsområdet där deras användning har inskränkts på grund av de höga utsläppen de orsakar och där gas, el eller olja för uppvärmning kan ersättas. 5. Priser för svenska pelletkaminer är för höga för att kunna konkurrera på den chilenska marknaden. 6. På grund av det milda klimatet och de höga kostnaderna för vattenburna värmedistributionssystem kommer vattenburna värmesystem att ha även i framtiden bara en liten marknad.

  • 6.
    Fiedler, Frank
    Dalarna University, School of Technology and Business Studies, Environmental Engineering.
    The Application Of Renewable Energy For Prefab Houses In Germany2003Report (Other academic)
    Abstract [en]

    Within the framework of the REBUS project the German building industry has been investigated regarding their energy concepts. The intention was to evaluate the establishment of renewable energy sources on the German market for new built houses and prefab houses in particular. For this purpose the products of 85 manufacturers of prefab houses have been analyzed. Of special interest was the application of heating and hot water systems driven by solar energy and biomass. The results show that both techniques are well accepted and established. Almost 90% of the manufacturers offer solar systems on request and almost 70% heating systems based on Pellets. 24% offered solar and 7% as standard options in their range. From the achieved figures the potential of the Swedish market can be worked out. Strategies to introduce renewable energy to a greater extent to Swedish house manufacturers and builders might also be found.

  • 7.
    Fiedler, Frank
    Dalarna University, School of Technology and Business Studies, Environmental Engineering.
    The state of the art of small-scale pellet-based heating systems and relevant regulations in Sweden, Austria and Germany2004In: Renewable & sustainable energy reviews, ISSN 1364-0321, E-ISSN 1879-0690, Vol. 8, no 3, p. 201-221 Article in journal (Refereed)
    Abstract [en]

    The emphasis of this report is on the actual technology of small-scale pellet combustion units and important regulations concerning emissions and pellets. Wood as a heating source has a long tradition in Sweden, but the use of compressed wood pellets in domestic stoves and boilers is rather new. Based on a literature survey, information from manufacturers and test institutes, this report gives an overview about existing technology and investigates how mature it is already. Some comparisons were made to similar heating units in Austria, where this technique is also widely used. It could be seen that the Austrian boilers are more sophisticated including a high level of comfort for the user. On the other hand the simpler Swedish boilers are significantly less expensive, and it is questionable if Swedish costumers are willing to pay for the higher comfort. Relevant regulations concerning emissions and fuel quality are also reported and compared between Sweden, Germany and Austria. In addition some interesting non-official certificates and environmental labels are presented. These give an outlook to future, probably more stringent, regulations.

  • 8.
    Fiedler, Frank
    et al.
    Dalarna University, School of Technology and Business Studies, Energy Technology.
    Bales, Chris
    Dalarna University, School of Technology and Business Studies, Energy Technology.
    Persson, Jannika
    Dalarna University, School of Technology and Business Studies, Construction.
    Gustavsson, Marcus
    Dalarna University, School of Technology and Business Studies, Energy Technology.
    Kovacs, Peter
    RISE.
    Hemlin, Olleper
    RISE.
    Ollas, Patrik
    RISE.
    Thuvander, Liane
    Chalmers Tekniska Högskolan.
    Femenías, Paula
    Chalmers Tekniska Högskolan.
    Lundin, Michelle
    Chalmers Tekniska Högskolan.
    Larsson, David
    Solkompaniet.
    Miljontak Delprojekt 2: Sammanfattning av litteratursammanställning2018Report (Other academic)
  • 9.
    Fiedler, Frank
    et al.
    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.
    Persson, Tomas
    Dalarna University, School of Technology and Business Studies, Energy and Environmental Technology.
    Optimisation method for solar heating systems in combination with pellet boilers/stoves2007In: International Journal of Green Energy, ISSN 1543-5075, E-ISSN 1543-5083, Vol. 4, no 3, p. 325-337Article in journal (Refereed)
    Abstract [en]

    In this study an optimisation method for the design of combined solar and pellet heating systems is presented and evaluated. The paper describes the steps of the method by applying it for an example system. The objective of the optimisation was to find the design parameters that give the lowest auxiliary energy (pellet fuel + auxiliary electricity) and carbon monoxide (CO) emissions for a system with a typical load, a single family house in Sweden. Weighting factors have been used for the auxiliary energy use and CO emissions to give a combined objective function. Different weighting factors were tested. The results show that extreme weighting factors lead to their own minima. However, it was possible to find factors that ensure low values for both auxiliary energy and CO emissions, and suitable weighting factors are suggested.

  • 10.
    Fiedler, Frank
    et al.
    Dalarna University, School of Technology and Business Studies, Environmental Engineering.
    Bales, Chris
    Dalarna University, School of Technology and Business Studies, Environmental Engineering.
    Persson, Tomas
    Dalarna University, School of Technology and Business Studies, Environmental Engineering.
    Nordlander, Svante
    Comparison of carbon monoxide emissions and electricity consumption of modulating and non-modulating pellet and solar heating systems2007In: International journal of energy research (Print), ISSN 0363-907X, E-ISSN 1099-114X, Vol. 31, no 10, p. 915-930Article in journal (Refereed)
    Abstract [en]

    Emission and electricity consumption are important aspects of a pellet heating system. Low noxious 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, poor adjustment of the combustion air and insufficient maintenance. The carbon monoxide output, the thermal performance and the electricity consumption for modulating and non-modulating operation mode have been investigated by simulations of four stoves/boilers as part of combined solar and pellet heating systems. The systems have been modelled with the simulation programme TRNSYS and simulated with the boundary conditions for space heating demand, hot water load and climate data as used in earlier research projects. The results from the simulations show that operating the pellet units with modulating combustion power reduces the number of starts and stops but does not necessarily reduce the carbon monoxide output. Whether the carbon monoxide output can be reduced or not depends very strongly on the reduction of starts and stops and how much the carbon monoxide emissions increase with decreased combustion power, which are in turn dependent on the particular settings of each pellet burner and how the heat is transferred to the building. However, for most systems the modulating operation mode has a positive impact on carbon monoxide emissions. Considering the total auxiliary energy demand, including the electricity demand of the pellet units, the modulating combustion control is advantageous for systems 1 and 4 for the used boundary conditions. The study also shows that an appropriate sizing of the stove or boiler has a huge potential for energy saving and carbon monoxide emission reduction.

  • 11.
    Fiedler, Frank
    et al.
    Dalarna University, School of Technology and Business Studies, Environmental Engineering.
    Bales, Chris
    Dalarna University, School of Technology and Business Studies, Environmental Engineering.
    Persson, Tomas
    Dalarna University, School of Technology and Business Studies, Environmental Engineering.
    Thür, Alexander
    Design method for solar heating systems in combination with pellet boilers/stoves2006In: EuroSun 2006, Glasgow, UK, 2006Conference paper (Other academic)
    Abstract [en]

    In this study an optimization method for the design of combined solar and pellet heating systems is presented and evaluated. The paper describes the steps of the method by applying it for an example of system. The objective of the optimization was to find the design parameters that give the lowest auxiliary energy (pellet fuel + auxiliary electricity) and carbon monoxide (CO) emissions for a system with a typical load, a single family house in Sweden. Weighting factors have been used for the auxiliary energy use and CO emissions to give a combined target function. Different weighting factors were tested. The results show that extreme weighting factors lead to their own minima. However, it was possible to find factors that ensure low values for both auxiliary energy and CO emissions.

  • 12.
    Fiedler, Frank
    et al.
    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.
    Vestlund, Johan
    Dalarna University, School of Technology and Business Studies, Energy and Environmental Technology.
    Erfahrungen mit einem neu entwickelten kombinierten Pellet- und Solarheizungssystems2008In: 18. Symposium Thermische Solarenergi, Kloster Banz, Bad Staffelstein, 2008Conference paper (Other academic)
  • 13.
    Fiedler, Frank
    et al.
    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.
    Vestlund, Johan
    Dalarna University, School of Technology and Business Studies, Energy and Environmental Technology.
    Monitoring results of combined pellet and solar heating system2007In: ISES Solar World Congress 2007, ISES 2007, 2007, Vol. 2, p. 867-871Conference paper (Other academic)
    Abstract [en]

    In this study the monitoring results of prototype installation of a recently developed solar combisystem have been evaluated. The system, that uses a water jacketed pellet stove as auxiliary heater, was installed in a single family house in Borlänge/Sweden. In order to allow an evaluation under realistic conditions the system has been monitored for a time period of one year. From the measurements of the system it could be seen that it is important that the pellet stove has a sufficient buffer store volume to minimize cycling. The measurements showed also that the stove gives a lower share of the produced heat to the water loop than measured under stationary conditions. The solar system works as expected and covers the heat demand during the summer and a part of the heat demand during spring and autumn. Potential for optimization exists for the parasitic electricity demand. The system consumes 680 kWh per year for pumps, valves and controllers which is more than 4% of the total primary heating energy demand.

  • 14.
    Fiedler, Frank
    et al.
    Dalarna University, School of Technology and Business Studies, Energy and Environmental Technology.
    Nielsen, Caroline
    Dalarna University, School of Technology and Business Studies, Energy and Environmental Technology.
    Design Study of a PV-Diesel Hybrid System for a Micro-Grid in Tanzania2012Conference paper (Other academic)
    Abstract [en]

    In 2008 a micro PV-Diesel Hybrid system has been installed at the Ihushi Development Center (IDC) near Mwanza in Tanzania. In April 2011 a monitoring system was installed at IDC to study the system performance and the usage of the system. Measured data from April to July 2011 have been used to model the system with the simulation software HOMER. One question was if HOMER allows accurate modelling and simulations of the actual system. In addition, it has been studied if the current system can be optimized and what system design solutions are most promising when the system need to be redesigned for a higher load.

  • 15.
    Fiedler, Frank
    et al.
    Dalarna University, School of Technology and Business Studies, Environmental Engineering.
    Nordlander, Svante
    Dalarna University, School of Technology and Business Studies, Environmental Engineering.
    Persson, Tomas
    Dalarna University, School of Technology and Business Studies, Environmental Engineering.
    Bales, Chris
    Dalarna University, School of Technology and Business Studies, Environmental Engineering.
    Thermal performance of combined solar and pellet heating systems2006In: Renewable energy, ISSN 0960-1481, E-ISSN 1879-0682, Vol. 31, no 1, p. 73-88Article in journal (Refereed)
    Abstract [en]

    Various pellet heating systems are marketed in Sweden, some of them in combination with a solar heating system. Several types of pellet heating units are available and can be used for a combined system. This article compares four typical combined solar and pellet heating systems: System 1 and 2 with a pellet stove, system 3 with a store integrated pellet burner and system 4 with a pellet boiler. The often lower efficiency of pellet heaters compared to oil or gas heaters increases the final energy demand. Consequently heat losses of the various systems have been studied. The systems have been modeled in TRNSYS and simulated with parameters identified from measurements. For almost all systems the flue gas losses are the main heat losses except for system 3 where store heat losses prevail. Relevant are also the heat losses of the burner and the boiler to the ambient. Significant leakage losses are noticed for system 3 and 4. For buildings with an open internal design system 1 is the most efficient solution. Other buildings should preferably apply system 2 or 3. The right choice of the system depends also on whether the heater is placed inside or outside of the heated area. Unlike the expectations and results from other studies, the operation of the pellet heaters with modulating combustion power is not necessarily improving the performance. A large potential for system optimization exists for all studied systems, which when applied could alter the relative merits of the different system types.

  • 16.
    Fiedler, Frank
    et al.
    Dalarna University, School of Technology and Business Studies, Energy and Environmental Technology.
    Pazmino, Victor
    Berruezo, Irati
    PV-Wind Hybrid Systems for Swedish Locations2008In: 4th European PV-Hybrid and Mini-Grid Conference, Glyfada, Greece, 2008Conference paper (Other academic)
    Abstract [en]

    PV-Wind-Hybrid systems for stand-alone applications have the potential to be more cost efficient compared to PV-alone systems. The two energy sources can, to some extent, compensate each others minima. The combination of solar and wind should be especially favorable for locations at high latitudes such as Sweden with a very uneven distribution of solar radiation during the year. In this article PV-Wind-Hybrid systems have been studied for 11 locations in Sweden. These systems supply the household electricity for single family houses. The aim was to evaluate the system costs, the cost of energy generated by the PV-Wind-Hybrid systems, the effect of the load size and to what extent the combination of these two energy sources can reduce the costs compared to a PV-alone system. The study has been performed with the simulation tool HOMER developed by the National Renewable Energy Laboratory (NREL) for techno-economical feasibility studies of hybrid systems. The results from HOMER show that the net present costs (NPC) for a hybrid system designed for an annual load of 6000 kWh with a capacity shortage of 10% will vary between $48,000 and $87,000. Sizing the system for a load of 1800 kWh/year will give a NPC of $17,000 for the best and $33,000 for the worst location. PV-Wind-Hybrid systems are for all locations more cost effective compared to PV-alone systems. Using a Hybrid system is reducing the NPC for Borlänge by 36% and for Lund by 64%. The cost per kWh electricity varies between $1.4 for the worst location and $0.9 for the best location if a PV-Wind-Hybrid system is used.

  • 17.
    Fiedler, Frank
    et al.
    Dalarna University, School of Technology and Business Studies, Energy and Environmental Technology.
    Pazmino, Victor
    Berruezo, Irati
    Techno-economic feasibility analysis of PV-wind hybrid systems for Sweden2008In: Eurosun 2008, Lisbon, 2008Conference paper (Other academic)
    Abstract [en]

    PV-Wind-Hybrid systems for stand-alone applications have the potential to be more cost efficient compared to PV-alone systems. The two energy sources can, to some extent, compensate each others minima. The combination of solar and wind should be especially favorable for locations at high latitudes such as Sweden with a very uneven distribution of solar radiation during the year. In this article PV-Wind-Hybrid systems have been studied for 11 locations in Sweden. These systems supply the household electricity for single family houses. The aim was to evaluate the system costs, the cost of energy generated by the PV-Wind-Hybrid systems, the effect of the load size and to what extent the combination of these two energy sources can reduce the costs compared to a PV-alone system. The study has been performed with the simulation tool HOMER developed by the National Renewable Energy Laboratory (NREL) for techno-economical feasibility studies of hybrid systems. The results from HOMER show that the net present costs (NPC) for a hybrid system designed for an annual load of 6000 kWh with a capacity shortage of 10% will vary between $48,000 and $87,000. Sizing the system for a load of 1800 kWh/year will give a NPC of $17,000 for the best and $33,000 for the worst location. PV-Wind-Hybrid systems are for all locations more cost effective compared to PV-alone systems. Using a Hybrid system is reducing the NPC for Borlänge by 36% and for Lund by 64%. The cost per kWh electricity varies between $1.4 for the worst location and $0.9 for the best location if a PV-Wind-Hybrid system is used.

  • 18.
    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.
    Annual CO-emissions of combined pellet and solar heating systems2007In: ISES Solar World Congress 2007, ISES 2007, 2007, Vol. 4, p. 2468-2472Conference paper (Other academic)
    Abstract [en]

    Emissions are an important aspect of a pellet heating system. High carbon monoxide emissions are often caused by unnecessary cycling of the burner when the burner is operated below the lowest combustion power. Combining pellet heating systems with a solar heating system can significantly reduce cycling of the pellet heater and avoid the inefficient summer operation of the pellet heater. The aim of this paper was to study CO-emissions of the different types of systems and to compare the yearly CO-emissions obtained from simulations with the yearly CO-emissions calculated based on the values that are obtained by the standard test methods. The results showed that the yearly CO-emissions obtained from the simulations are significant higher than the yearly CO-emissions calculated based on the standard test methods. It is also shown that for the studied systems the average emissions under these realistic annual conditions were greater than the limit values of two Eco-labels. Furthermore it could be seen that is possible to almost halve the CO-emission if the pellet heater is combined with a solar heating system.

  • 19.
    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 systems2007In: International Green Energy Conference III, Västerås, 2007Conference paper (Other academic)
  • 20.
    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.

  • 21.
    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.
    CO-Emissionen solarer Kombisysteme mit Holzpelletkesseln2008In: 18. Symposium Thermische Solarenergie, Kloster Banz, Bad Staffelstein, 2008Conference paper (Other academic)
  • 22.
    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.
    Bales, Chris
    Dalarna University, School of Technology and Business Studies, Energy and Environmental Technology.
    Reduction of co-emissions by combining pellet and solar heating systems2008In: Eurosun 2008, Lisbon, 2008Conference paper (Other academic)
    Abstract [en]

    Emissions are an important aspect of a pellet heating system. High carbon monoxide emissions are often caused by unnecessary cycling of the burner when the burner is operated below the lowest combustion power. Combining pellet heating systems with a solar heating system can significantly reduce cycling of the pellet heater and avoid the inefficient summer operation of the pellet heater. The aim of this paper was to study CO-emissions of the different types of systems and to compare the yearly CO-emissions obtained from simulations with the yearly CO-emissions calculated based on the values that are obtained by the standard test methods. The results showed that the yearly CO-emissions obtained from the simulations are significant higher than the yearly CO-emissions calculated based on the standard test methods. It is also shown that for the studied systems the average emissions under these realistic annual conditions were greater than the limit values of two Eco-labels. Furthermore it could be seen that is possible to almost halve the CO-emission if the pellet heater is combined with a solar heating system.

  • 23.
    Fiedler, Frank
    et al.
    Dalarna University, School of Technology and Business Studies, Energy and Environmental Technology.
    Scherr, Tino
    Evaluation and simulation of a PV-Wind Hybrid System2009In: Symposium Small PV-Applications, Ulm, 2009Conference paper (Other academic)
    Abstract [en]

    This work is evaluating a PV-Wind Hybrid system that has been installed in 2006 on the roof of Dalarna University in Borlänge/Sweden. Complementing the measurements, simulations with HOMER have been performed for the same system type. The measurements results showed that the PV array of the PV-Hybrid system was providing the major part of the energy even it has only the half of the wind turbine’s nominal rated power. However, the energy production of wind turbine especially during December and January allowed providing an almost constant load of 35W throughout the year. The combination of PV and wind increases the reliability of power supply and allows a significant smaller PV array compared to a PV alone system. The simulation results with HOMER showed good accordance with the measured data. The maximal difference was 3%. Furthermore, HOMER proved to be an easy to use and powerful tool for the sizing of this system type for locations where weather data for solar radiations and wind speed are available.

  • 24.
    Fiedler, Frank
    et al.
    Dalarna University, School of Technology and Business Studies, Environmental Engineering.
    Thür, Alexander
    Bales, Chris
    Dalarna University, School of Technology and Business Studies, Environmental Engineering.
    Furbo, Simon
    The actual status of the development of a Danish/Swedish system concept of a solar combisystem2005In: Northsun, Vilnius, 2005Conference paper (Other academic)
    Abstract [en]

    At the beginning of 2003 the four year long research project REBUS on education, research, development and demonstration of competitive solar combisystems was launched. Research groups in Norway, Denmark, Sweden and Latvia are working together with partners from industry on innovative solutions for solar heating in the Nordic countries. Existing system concepts have been analyzed and based on the results new system designs have been developed. The proposed solutions have to fulfill country specific technical, sociological and cost requirements. Due to the similar demands on the systems in Denmark and Sweden it has been decided to develop a common system concept for both countries, which increases the market potential for the manufacturer. The focus of the development is on systems for the large number of rather well insulated existing single family houses. In close collaboration with the industrial partners a system concept has been developed that is characterized by its high compactness and flexibility. It allows the use of different types of boilers, heating distribution systems and a variable store and collector size. Two prototypes have been built, one for the Danish market with a gas boiler, and one for the Swedish market with a pellet boiler as auxiliary heater. After intensive testing and eventual further improvements at least two systems will be installed and monitored in demonstration houses. The systems have been modeled in TRNSYS and the simulation results will be used to further improve the system and evaluate the system performance.

  • 25.
    Fiedler, Frank
    et al.
    Dalarna University, School of Technology and Business Studies, Energy and Environmental Technology.
    Zapata, Angel
    Evaluation of a micro PV-Wind hybrid system in Nordic climate conditions2010In: 5th European Conference PV-Hybrid and Mini-Grid, Tarragona/Spain, 2010Conference paper (Refereed)
    Abstract [en]

    A one year data analysis for a micro PV-Wind hybrid system (0.52 kW + 1 kW), installed in Borlänge/Sweden is presented in this paper. The system performance was evaluated according the guidelines of the IEC 61724 standard. The parameters obtained allow a comparison with similar systems. The measurement data are also used to evaluate the sizing and operation of the hybrid system. In addition, the system was modelled in HOMER to study sizing options.

  • 26. Furbo, Simon
    et al.
    Thür, Alexander
    Bales, Chris
    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.
    Rekstad, John
    Meir, Michaela
    Blumberga, Dagnija
    Rochas, Claudio
    Solar thermal components adapted to common building standards (SCAS)2006Report (Other academic)
    Abstract [en]

    Pilot versions of a solar heating/natural gas burner system, of a solar heating/pellet burner system and of a façade/roof integrated polymeric collector have been installed in the summer of 2006 in a number of demonstration houses in Denmark, Sweden and Norway. These three new products have been evaluated by means of measurements of the thermal performance and energy savings of the pilot systems in practice and by means of a commercial evaluation. The conclusion of the evaluations is that the products are attractive for the industry partners METRO THERM A/S, Solentek and SOLARNOR. It is expected that the companies will bring the products into the market in 2007. Further, the results of the project have been presented atinternational and national congresses and seminars for the solar heating branch. The congresses and seminars attracted a lot of interested participants. Furthermore, the project results have been published in international congress papers as well as in national journals in the energy field. Consequently, the Nordic solar heating industry will benefit from the project.

  • 27. Furbo, Simon
    et al.
    Thür, Alexander
    Bales, Chris
    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.
    Rekstad, John
    Meir, Michaela
    Blumberga, Dagnija
    Rochas, Claudio
    Schifter-Holm, Torbjörn
    Lorenz, Klaus
    Competitive Solar Heating Systems for Residential Buildings (REBUS)2006Report (Other academic)
    Abstract [en]

    Research on solar combisystems for the Nordic and Baltic countries have been carried out. The aim was to develop competitive solar combisystems which are attractive to buyers and to educate experts in the solar heating field. The participants of the projects were the universities: Technical University of Denmark, Dalarna University, University of Oslo, Riga Technical University and Lund Institute of Technology, as well as the companies: Metro Therm A/S (Denmark), Velux A/S (Denmark), Solentek AB (Sweden), SolarNor (Norway) and SIA Grandeg (Latvia). The project included education, research, development and demonstration. The activities started in 2003 and were finished by the end of 2006. A number of Ph.D. studies in Denmark, Sweden and Latvia, and a post-doc. study in Norway were carried out. Close cooperation between the researchers and the industry partners ensured that the results of the projects can be utilized. The industry partners will soon be able to bring the developed systems into the market. In Denmark and Norway the research and development focused on solar heating/natural gas systems, and in Sweden and Latvia the focus was on solar heating/pellet systems. Additionally, Lund Institute of Technology and University of Oslo studied solar collectors of various types being integrated into the building.

  • 28. Furbo, Simon
    et al.
    Thür, Alexander
    Fiedler, Frank
    Dalarna University, School of Technology and Business Studies, Environmental Engineering.
    Bales, Chris
    Dalarna University, School of Technology and Business Studies, Environmental Engineering.
    Competitive solar heating systems for residential buildings2005In: Northsun, Vilnius, 2005Conference paper (Other academic)
  • 29. Furbo, Simon
    et al.
    Thür, Alexander
    Fiedler, Frank
    Dalarna University, School of Technology and Business Studies, Environmental Engineering.
    Bales, Chris
    Dalarna University, School of Technology and Business Studies, Environmental Engineering.
    Rekstad, John
    Meir, Michaela
    Blumberga, Dagnija
    Rochas, Claudio
    Karlsson, Björn
    Nordic Energy Research Cooperation on Solar Combisystems2006In: Eurosun 2006, Glasgow, UK, 2006Conference paper (Other academic)
    Abstract [en]

    This paper describes ongoing research on solar combisystems for the Nordic and Baltic countries carried out within the projects "Competitive solar heating systems for residential buildings" and "Solar thermal components adapted to common building standards". The aim of the projects is to develop competitive solar combisystems which are attractive to buyers and to educate experts in the solar heating field.

  • 30.
    Hernandez Velasco, Marco
    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.
    Timm, Dirk
    juwi Solar GmbH.
    COMPARISON OF PARTIAL SHADING LOSSES IN FREE FIELD PV-PLANTS WITH DIFFERENT ARRAY CONFIGURATIONS2013In: EU PVSEC Proceedings, 2013, p. 4171-4175Conference paper (Other academic)
    Abstract [en]

    A common problem when planning large free field PV-plants is optimizing the ground occupation ratio while maintaining low shading losses. Due to the complexity of this task, several PV-plants have been built using various configurations. In order to compare the shading losses of different PV technologies and array designs, empirical performance data of five free field PV-plants operating in Germany was analyzed. The data collected comprised 140 winter days from October 2011 until March 2012. The relative shading losses were estimated by comparing the energy output of selected arrays in the front rows (shading-free) against that of shaded arrays in the back rows of the same plant. The results showed that landscape mounting with mc-Si PV-modules yielded significantly better results than portrait one. With CIGS modules, making cross-table strings using the lower modules was not beneficial as expected and had more losses than a one-string-per-table layout. Parallel substrings with CdTe showed relatively low losses. Among the two CdTe products analyzed, none showed a significantly better performance.

  • 31.
    Hernandez Velasco, Marco
    et al.
    Dalarna University, School of Technology and Business Studies, Energy Technology.
    Fiedler, Frank
    Dalarna University, School of Technology and Business Studies, Energy Technology.
    Timm, Dirk
    juwi Solar GmbH.
    Weak light performance efficiency in installed pv-arrays of different module technologies2014In: 29th European Photovoltaic Solar Energy Conference and Exhibition Proceedings, 2014, p. 2515-2522Conference paper (Other academic)
    Abstract [en]

    This work analyses the weak light performance efficiency of six different free field and grid-connected PVarrays of various module technologies (mc-Si, CIGS, CdTe). The installed capacities per array range from 1,8kWp to 2,2kWp. The studied systems are located at the same site in Germany and are mounted on a ventilated and shaded-free structure. The irradiance was measured with both a pyranometer and a c-Si reference cell oriented at the plane of the array. Besides the weather conditions, the arrays share a similar system configuration (same inverter model, rack type and orientation, temperature sensors, etc.) making their results highly comparable. The data collected comprised 312 days from September 2011 until July 2012. When analyzing the data points at moments of low irradiance (< 800W/m2), a high dispersion was found which is most likely due to optical effects, different spectral distributions and changing module temperatures. To reduce the optical and spectral effects, a series of data filters were applied to limit the points used (Air Mass ≤4 and Angle of Incidence ≤50°). To compensate for the temperature effects and translate the values to STC (25°C), five different methods were assessed. The Procedure 2 of the IEC 60891 was considered the most suitable due to its relative simplicity, availability of parameters in the datasheets, good accuracy even with missing values, and the potential to improve the results when the complete set of inputs is available. The final analysis of the weak light performance showed no clear superiority of any particular PV-technology. From the results of this study, an overall advantage of thin-film over crystalline modules cannot be anymore concluded.

  • 32. Ju, Zhenhe
    et al.
    Li, Shi
    Fiedler, Frank
    Dalarna University, School of Technology and Business Studies, Energy and Environmental Technology.
    Financial and technical Evaluation of Solar Streetlight System2009In: Symposium Small PV-Applications, Ulm, 2009Conference paper (Other academic)
    Abstract [en]

    According to the financial evaluation principle of technology, the authors analyze the investment of solar streetlight systems, calculate the net present value in life time and dynamic payback period of investment of solar streetlight system by the method of energy substitute which compares the solar streetlight with common electric power streetlight. The study provides a feasible financial evaluation way for application of solar streetlights.

  • 33. Jähnig, D.
    et al.
    Thür, A.
    Breidler, J.
    Kuhness, G.
    Letz, T.
    Papillon, P.
    Bales, Chris
    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.
    D5.1b : Standard Procedure describing how to evaluate solar combisystems2009Report (Other academic)
  • 34.
    Lindberg, Eva
    et al.
    Dalarna University, School of Technology and Business Studies, Energy Technology.
    Fiedler, Frank
    Dalarna University, School of Technology and Business Studies, Energy Technology.
    Bales, Chris
    Dalarna University, School of Technology and Business Studies, Energy Technology.
    Past and future of European Solar Energy School2007In: Proceedings of ISES Solar World Congress 2007: Solar energy and human settlement, vols I-V, 2007, Vol. 4, p. 3014-3018Conference paper (Refereed)
    Abstract [en]

    The European Solar Engineering School ESES is a one-year master program that started in 1999 at the Solar Energy Research Center SERC, Dalarna University College. It has been growing in popularity over the years, with over 20 students in the current year. Approximately half the students come from Europe, the rest coming from all over the globe. This paper describes the contents and experiences from eight years of running the programme an the adapting the programme to the Bologna process. The majority of the students from ESES have found work in the solar industry, energy industry or taken up PhD positions. An alumni group has been started that actively gives support to past, present and potential future students.

  • 35.
    Lindberg, Eva
    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.
    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.
    Review of an International Master Programme in Solar Energy Engineering2008In: Eurosun 2008, Lisbon, 2008Conference paper (Other academic)
    Abstract [en]

    The European Solar Engineering School ESES is a one-year master programme that started in 1999 at the Solar Energy Research Center, SERC, Dalarna University College. The programme, run in English, consists of courses which cover passive and active solar thermal, solar energy for tropical climates, PV and PV/Hybrid system design, and have sections on topics such as economy and social aspects as well as other renewable energy sources. ESES is then finished with a research project as thesis work. Over the years the contents have been evolved and improved, and new experimental work has been introduced. The programme has been growing in popularity over the years, with over 20 students each year. Approximately half of the students come from Europe, the rest coming from all over the globe. This paper describes the contents and experiences from eight years of running the programme. The majority of the students from ESES have found work in the solar industry, energy industry or taken up PhD positions. An alumni group has been started that actively gives support to past, present and potential future students.

  • 36. Meir, Michaela
    et al.
    Mathisen, Oyvind
    Rekstad, John
    Schakenda, Janet
    Fiedler, Frank
    Dalarna University, School of Technology and Business Studies, Environmental Engineering.
    Facade integration of polymeric solar collectors2005In: Northsun, Vilnius, 2005Conference paper (Other academic)
    Abstract [en]

    The present paper examines building integrated solar collectors with absorbers of polymeric materials. Efficiency measurements of façade-integrated collectors with non-selective black and spectrally selective coloured absorbers are carried out. The performance of the polymeric absorber was compared with solar glass and polycarbonate twin-wall sheets as collector cover. Simulations demonstrate a high solar fraction for a solar combisystem with façade collectors for a well-insulated house in a Nordic climate. Two examples of house concepts with façade collectors are presented which address a new type of customer than the solar enthusiasts with special interest in renewable energy

  • 37.
    Nielsen, Caroline
    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.
    Evaluation of a Micro PV-Diesel Hybrid System in Tanzania2012Conference paper (Refereed)
    Abstract [en]

    In April 2011 a monitoring system was installed to enable studies of the performance and the usage of a micro PV-Diesel Hybrid system at the Ihushi Development Center (IDC) near Mwanza in Tanzania. Estimations of the load have been obtained by a survey of installed appliances and interviews with users of installed equipment. The load profile obtained by measurements has been analyzed and compared to estimations of the energy use. Further, the system size and performance were studied.

  • 38. Nordlander, Svante
    et al.
    Persson, Tomas
    Dalarna University, School of Technology and Business Studies, Environmental Engineering.
    Fiedler, Frank
    Dalarna University, School of Technology and Business Studies, Environmental Engineering.
    Rönnelid, Mats
    Dalarna University, School of Technology and Business Studies, Environmental Engineering.
    Bales, Chris
    Dalarna University, School of Technology and Business Studies, Environmental Engineering.
    Computer modelling of wood pellet stoves and boilers connected to solar heating systems2006In: Proc on USB of Pellets 2006, 30 May - 1 June, Jönköping, Sweden, Jönköping, Sweden, 2006Conference paper (Other academic)
    Abstract [en]

    When optimizing systems for wood pellet and solar heating, there is a need for realistic computer models of stoves and boilers in order to perform simulation studies. The objective of this work was to develop and verify a mathematical model for wood pellet stoves and boilers for use in system simulations with TRNSYS calculating both the energy balance and CO-emissions (carbon monoxide). Laboratory measurements have been carried out on three pellet stoves, one traditional and two with gas-liquid heat exchangers, and four pellet boilers. A mathematical two-node model of a stove was developed and implemented as a TRNSYS component. Parameters were identified for two stoves and three boilers. This new model makes it possible to perform detailed simulations with time steps less than a minute of complete wood pellet heating systems and to derive long term values, such as annual values, of efficiency and emissions for the boiler or stove in a system context under realistic conditions. In addition, parametric studies can be used in order to investigate how different operation principles and system design affect these values. The simulated energy balance of a water jacketed stove investigated in this work agreed well with measured data during both stationary and dynamic conditions.

  • 39.
    Persson, Tomas
    et al.
    Dalarna University, School of Technology and Business Studies, Environmental Engineering.
    Fiedler, Frank
    Dalarna University, School of Technology and Business Studies, Environmental Engineering.
    Methodology for identifying parameters for the TRNSYS model Type 210 -wood pellet stoves and boilers2006Report (Other academic)
    Abstract [en]

    This report describes a method how to perform measurements on boilers and stoves and how to identify parameters from the measurements for the boiler/stove-model TRNSYS Type 210. The model can be used for detailed annual system simulations using TRNSYS. Experience from measurements on three different pellet stoves and four boilers were used to develop this methodology. Recommendations for the set up of measurements are given and the re-quired combustion theory for the data evaluation and data preparation are given. The data evalua-tion showed that the uncertainties are quite large for the measured flue gas flow rate and for boilers and stoves with high fraction of energy going to the water jacket also the calculated heat rate to the room may have large uncertainties. A methodology for the parameter identification process and identified parameters for two different stoves and three boilers are given. Finally the identified models are compared with measured data showing that the model generally agreed well with meas-ured data during both stationary and dynamic conditions.

  • 40.
    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.
    Sol och pellets i kombination, ett sätt att minska utsläppen2008In: VVS-forum, Värme och energi, ISSN 0346-4644, p. 118-119Article in journal (Other academic)
  • 41.
    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.

  • 42.
    Persson, Tomas
    et al.
    Dalarna University, School of Technology and Business Studies, Environmental Engineering.
    Fiedler, Frank
    Dalarna University, School of Technology and Business Studies, Environmental Engineering.
    Rönnelid, Mats
    Dalarna University, School of Technology and Business Studies, Environmental Engineering.
    Bales, Chris
    Dalarna University, School of Technology and Business Studies, Environmental Engineering.
    Increasing efficiency and decreasing CO-emissions for a combined solar and wood pellet heating system for single-family houses2006In: Proc. on USB of Pellets 2006, 30 May - 1 June, Jönköping, Sweden, Jönköping, Sweden, 2006Conference paper (Other academic)
    Abstract [en]

    This study focus on how wood pellets and solar heating systems for single-family houses should be designed and controlled to reach high efficiency and to reduce the CO-emissions. A recently developed TRNSYS model was used to simulate the wood pellet boiler. Parameters for the model were identified from laboratory measurements on a boiler. A detailed simulation model of a complete solar combisystem was created and annual simulations were performed. Assuming that all heat losses to the room are waist heat, the results show that the most important factors to achieve high system efficiency are that the boiler and the buffer store should be well insulated. The sensor controlling the boiler should be placed in the store; the pump between the boiler and the store should only be in operation together with the burner and for some time after the burner have stopped to take care of the after burning heat. For boilers with relatively large start and stop CO-emissions modulating power may be an efficient measure to reduce CO-emissions. Especially for boilers using an ON-OFF control, the dominating contribution of CO-emissions may be during the start and stop phases, thus reducing emissions during operation may have little influence on the annual CO-emissions.

  • 43.
    Rönnelid, Mats
    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.
    Reserapport Plataforma SolarAlmeria, 5-8/6 20112012Report (Other academic)
    Abstract [sv]

    Reserapporten beskriver verksamheten vid Plataforma Solar Almeria (PSA) i Spanien och diskuterar tänkta samarbetsmöjligheter mellan PSA och Högskolan Dalarna

  • 44. Thür, Alexander
    et al.
    Furbo, Simon
    Fiedler, Frank
    Dalarna University, School of Technology and Business Studies, Environmental Engineering.
    Bales, Chris
    Dalarna University, School of Technology and Business Studies, Environmental Engineering.
    Development of a Compact Solar Combisystem2006In: Eurosun 2006, Glasgow, UK, 2006Conference paper (Other academic)
    Abstract [en]

    Within the frame of the project REBUS, "Competitive solar heating systems for residential buildings", which is financed by Nordic Energy Research, a new type of compact solar combisystem with high degree of prefabrication was developed. A hydraulic and control concept was designed with the goal to get highest system efficiency for use with either a condensing natural gas boiler or a pellet boiler. Especially when using the potential of high peak power of modern condensing natural gas boilers, a new operation strategy of a natural gas boiler/solar combisystem can increase the energy savings of a small solar combisystem by about 80% compared to conventional operation strategies.

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