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  • 1.
    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)
  • 2.
    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.

  • 3.
    Vestlund, Johan
    Dalarna University, School of Technology and Business Studies, Energy and Environmental Technology.
    Ett bad när som helst: Dimensioneringsråd för varmvatten2011Report (Other academic)
    Abstract [sv]

    Rapporten Ett bad när som helst - Dimensioneringsråd för varmvatten är framtagen av Johan Vestlund inom delprojekt Sol- och biovärme. Syftet med studien är att utreda vilka kriterier som gäller i en ackumulatortank med dubbla varmvattenslingor för att i alla situationer kunna leverera tillräckligt med varmvatten för en badkarsuppfyllning. Enkla underlag för att beräkna erforderlig slinglängd har tidigare saknats och tidsödande provning har behövt genomföras för att optimera varmvattenkapaciteten i ackumulatortankar. I denna rapport presenteras ett nomogram (figur 4, sida 13) som visar sambandet mellan be-redskapsvolym, temperaturnivå och slinglängd för att uppfylla Boverkets byggregler för ett småhus. Att tillräcklig varmvattenkomfort erhålls är viktigt, också för att kunden ska bli nöjd med ett solvärmesystem. Att detta kan ske vid rimliga tanktemperaturer på 60-65 °C är viktigt för att solvärmetillskottet ska bli högt. Ökad varmvattenkomfort ökar energibehovet och minskar solvärmebidraget varför det är viktigt att dimensionera korrekt. Utgångspunkten för att bygga ett effektivt solvärmesystem är därför att först utgå från en korrekt dimensionerad varmvattenkapacitet. Mängd varmvatten som det går att få ut från en ackumulatortank bestäms av volymen på det uppvärmda vattnet i tankens topp, temperaturen i tanken, och slingornas längd och placering.

  • 4.
    Vestlund, Johan
    Dalarna University, School of Technology and Business Studies, Energy and Environmental Technology.
    Gas-filled, flat plate solar collectors2012Doctoral thesis, monograph (Other academic)
    Abstract [en]

    This work treats the thermal and mechanical performances of gas-filled, flat plate solar collectors in order to achieve a better performance than that of air filled collectors. The gases examined are argon, krypton and xenon which all have lower thermal conductivity than air. The absorber is formed as a tray connected to the glass. The pressure of the gas inside is near to the ambient and since the gas volume will vary as the temperature changes, there are potential risks for fatigue in the material. One heat transfer model and one mechanical model were built. The mechanical model gave stresses and information on the movements. The factors of safety were calculated from the stresses, and the movements were used as input for the heat transfer model where the thermal performance was calculated. It is shown that gas-filled, flat plate solar collectors can be designed to achieve good thermal performance at a competitive cost. The best yield is achieved with a xenon gas filling together with a normal thick absorber, where normal thick means a 0.25 mm copper absorber. However, a great deal of energy is needed to produce the xenon gas, and if this aspect is taken into account, the krypton filling is better. Good thermal performance can also be achieved using less material; a collector with a 0.1 mm thick copper absorber and the third best gas, which is argon, still gives a better operating performance than a common, commercially produced, air filled collector with a 0.25 mm absorber. When manufacturing gas-filled flat plate solar collectors, one way of decreasing the total material costs significantly, is by changing absorber material from copper to aluminium. Best yield per monetary outlay is given by a thin (0.3 mm) alu-minium absorber with an argon filling. A high factor of safety is achieved with thin absorbers, large absorber areas, rectangular constructions with long tubes and short distances between glass and absorber. The latter will also give a thin layer of gas which gives good thermal performance. The only doubtii ful construction is an argon filled collector with a normal thick (> 0.50 mm) aluminium absorber. In general, an assessment of the stresses for the proposed construction together with appropriate tests are recommended before manufacturing, since it is hard to predict the factor of safety; if one part is reinforced, some other parts can experience more stress and the factor of safety actually drops.

  • 5.
    Vestlund, Johan
    et al.
    Dalarna University, School of Technology and Business Studies, Energy and Environmental Technology.
    Dalenbäck, Jan-Olof
    Rönnelid, Mats
    Dalarna University, School of Technology and Business Studies, Energy and Environmental Technology.
    Design of gas filled solar collectors2010In: Eurosun 2010 / [ed] Vestlund, Johan, Graz, 2010Conference paper (Other academic)
    Abstract [en]

    With a suitable gas filling used between cover glass and absorber in a flat plate solar collector, it is possible achieving better thermal performance at the same time as the distance between absorber and glass can be reduced. Though, even if there is no vacuum inside the box, there will be potential risks for exhaustion due to stresses depending on the gas volume varies as the temperature varies. This study found out that it is possible build such a collector with less material in the absorber and the tubes and still getting better performance, without risks for exhaustion.

  • 6.
    Vestlund, Johan
    et al.
    Dalarna University, School of Technology and Business Studies, Energy and Environmental Technology.
    Dalenbäck, Jan-Olof
    Rönnelid, Mats
    Dalarna University, School of Technology and Business Studies, Energy and Environmental Technology.
    Movement and mechanical stresses in sealed, flat plate solar collectors2012In: Solar Energy, ISSN 0038-092X, E-ISSN 1471-1257, Vol. 86, no 1, p. 339-350Article in journal (Refereed)
    Abstract [en]

    This article describes movements and mechanical stresses in sealed, gas-filled, flat plate solar collectors. The advantage of a sealed space between a collector absorber and glass cover is that it (i) eliminates the influence of humidity condensation and dust and (ii) it lowers the heat losses when the enclosed space is filled with a suitable gas at normal pressure. However as the solar collector temperature varies, volume and pressure changes cause movement and mechanical stresses. In this study, the finite element method was used to determine movements and mechanical stresses. Several geometries were analyzed and it was found that the stresses in the investigated collectors are a factor 2–4 below the critical stress levels. Furthermore, it was found to be possible to reduce the stresses and improve the factor of safety by (i) using a larger area and/or reducing the distance between the glass and the absorber and/or (ii) changing the length and width so the tubes are longer.

  • 7.
    Vestlund, Johan
    et al.
    Dalarna University, School of Technology and Business Studies, Energy and Environmental Technology.
    Dalenbäck, Jan-Olof
    Rönnelid, Mats
    Dalarna University, School of Technology and Business Studies, Energy and Environmental Technology.
    Movements and mechanical stresses in gas-filled flat plate solar collectors2008In: Eurosun 2008, Lissabon, 2008Conference paper (Other academic)
    Abstract [en]

    Sealed gas filled flat plate solar collectors will have stresses in the material since volume and pressure varies in the gas when the temperature changes. Several geometries were analyzed and it could be seen that it is possible reducing the stresses and improve the safety factor of the weakest point in the construction by using larger area and/or reducing the distance between glass and absorber and/or change width and height relationship so the tubes are getting longer. Further it could be shown that the safety factor won't always get improved with reinforcements. It is so because when an already strong part of the collector gets reinforced it will expose weaker parts for higher stresses. The finite element method was used for finding out the stresses.

  • 8.
    Vestlund, Johan
    et al.
    Dalarna University, School of Technology and Business Studies, Energy and Environmental Technology.
    Dalenbäck, Jan-Olof
    Rönnelid, Mats
    Dalarna University, School of Technology and Business Studies, Energy and Environmental Technology.
    Thermal and mechanical performance of sealed, gas-filled, flat plate solar collectors2012In: Solar Energy, ISSN 0038-092X, E-ISSN 1471-1257, Vol. 86, no 1, p. 13-25Article in journal (Refereed)
    Abstract [en]

    The study includes calculations for both the thermal performance and the mechanical behaviour of a gas-filled, flat plate solar collector without external gas expansion, i.e., a collector with varying gas volume and gas pressure and movement in both cover glass and absorber. Classical theories for the thermal performance are combined with a finite-element method to investigate which factors have an impact from the mechanical stress point of view. This article describes major results for collectors with copper and aluminium absorbers combined with different inert gases. It is shown that a collector may be designed which uses less material than a standard collector but achieves at least the same thermal performance, by using a thinner collector and a thinner absorber and a suitable gas filling other than air. If copper is used in absorber and tubes, a 0.15 mm thick absorber together with a tube-to-tube distance of 103 mm results in the same performance as a 0.3 mm absorber with a 144 mm tube-to-tube distance, but the former will use 25% less material. The use of copper can be further reduced if the absorber is made of aluminium and the tubes are made of copper. The factor of safety for thick (>0.5 mm) aluminium absorbers is, however, not as large as it is for copper absorbers.

  • 9.
    Vestlund, Johan
    et al.
    Dalarna University, School of Technology and Business Studies, Energy and Environmental Technology.
    Dalenbäck, Jan-Olof
    Rönnelid, Mats
    Dalarna University, School of Technology and Business Studies, Energy and Environmental Technology.
    Thermal losses in sealed, gas-filled flat plate solar collectors2007In: Solar World Congress, Peking, 2007, Vol. 1, p. 651-655Conference paper (Other academic)
    Abstract [en]

    A sealed space between absorber and cover glass makes it possible reducing the influence of humidity condensate and dust at the same time as the enclosed space can be filled with a suitable gas for lowering the losses. This paper is about the size of the losses in these collectors. A calculating model of a gas-filled flat plate solar collector was built in Matlab with standard heat transfer formulas. It showed that the total loss can be reduced up to 20% when changing to an inert gas. It is also possible using a much shorter distance and still achieve low losses at the same time as the mechanical stresses in the material is reduce.

  • 10.
    Vestlund, Johan
    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.
    Win, Kaung Myat
    Dalarna University, School of Technology and Business Studies, Energy and Environmental Technology.
    Effektiviseringspotential för värmesystem med sol och pellets: Parameterstudier, emissionsfaktorer och simuleringsresultat2012Report (Other academic)
    Abstract [sv]

    Syftet med denna studie är att hitta driftsbetingelser som sänker pelletsförbrukning och utsläpp och därmed även de totala kostnaderna för ett värmesystem. Värmesystemet har två huvudsakliga energikällor; sol och pellets. En elpatron används också, för att täcka upp med värme när solen lyser med sin frånvaro och pelletsystemet inte har hunnit börja leverera värme, till exempel i samband med start av brännaren. Lasten utgör värme till ett småhus av dagens standard och tappvarmvattenbehov.

  • 11.
    Vestlund, Johan
    et al.
    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.
    Dalenbäck, Jan-Olof
    Thermal performance of gas-filled flat plate solar collectors2009In: Solar Energy, ISSN 0038-092X, E-ISSN 1471-1257, Vol. 83, no 6, p. 896-904Article in journal (Refereed)
    Abstract [en]

    A sealed space between absorber and cover glass in a flat plate solar collector makes it possible to reduce the influence of humidity condensate and dust at the same time as the enclosed space can be filled with a suitable gas for lowering the heat losses. This article describes the influence of different gases on the heat losses in a typical flat plate solar collector. A model of a gas-filled flat plate solar collector was built in Matlab with standard heat transfer formulas. The results show that the overall heat loss can be reduced by up to 20% when changing from air to an inert gas. It is further possible to reduce the distance between absorber and cover in order to reduce the mechanical stresses in the material with similar heat losses.

1 - 11 of 11
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