Change search
Refine search result
12 1 - 50 of 57
CiteExportLink to result list
Permanent link
Cite
Citation style
  • apa
  • harvard1
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • Other style
More styles
Language
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Other locale
More languages
Output format
  • html
  • text
  • asciidoc
  • rtf
Rows per page
  • 5
  • 10
  • 20
  • 50
  • 100
  • 250
Sort
  • Standard (Relevance)
  • Author A-Ö
  • Author Ö-A
  • Title A-Ö
  • Title Ö-A
  • Publication type A-Ö
  • Publication type Ö-A
  • Issued (Oldest first)
  • Issued (Newest first)
  • Created (Oldest first)
  • Created (Newest first)
  • Last updated (Oldest first)
  • Last updated (Newest first)
  • Disputation date (earliest first)
  • Disputation date (latest first)
  • Standard (Relevance)
  • Author A-Ö
  • Author Ö-A
  • Title A-Ö
  • Title Ö-A
  • Publication type A-Ö
  • Publication type Ö-A
  • Issued (Oldest first)
  • Issued (Newest first)
  • Created (Oldest first)
  • Created (Newest first)
  • Last updated (Oldest first)
  • Last updated (Newest first)
  • Disputation date (earliest first)
  • Disputation date (latest first)
Select
The maximal number of hits you can export is 250. When you want to export more records please use the Create feeds function.
  • 1. Andersson, O.
    et al.
    Hellström, Göran
    Nordell, Bo
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Architecture and Water.
    Recent UTES development in Sweden2000In: Proceedings: TERRASTOCK 2000, 8th International Conference on Thermal Energy Storage : University of Stuttgart, Germany, August 28th until September 1st, 2000 / [ed] Martin Benner, Stuttgart: Universität Stuttgart , 2000, p. 75-80Conference paper (Refereed)
  • 2. Andersson, Olof
    et al.
    Hellström, Göran
    Nordell, Bo
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Architecture and Water.
    Heating and cooling with UTES in Sweden: current situation and potential market development2003In: Proceedings: Futurestock 2003, 9th International Conference on Thermal Energy Storage : Warsaw, Poland, September 1 - 4, 2003, Warszawa: PW Publishing House , 2003, p. 207-215Conference paper (Refereed)
    Abstract [en]

    Underground Thermal Energy Storage (UTES) applications have slowly gained acceptance on the Swedish energy market. Two UTES concepts are successfully implemented; the ATES (aquifer storage) and the BTES (borehole storage) systems. Also snow storage in pits or caverns has reached a commercial status. The number of ATES has steadily grown to 40 large-scale plants at the end of 2002. The systems are usually designed for cold storage in district cooling application, but industrial process cooling is also common. The economical potential in terms of straight payback time is usually very favourable. However, there is still a certain risk for operational problems that might jeopardize the calculated profit. Well clogging problems and system control remain as R&D issues to be solved. From a legislation point of view any ATES application needs a permit. The process of obtaining a permit has become complex and time-consuming since a new act on environmental assessment was put into effect in 1999.BTES systems are normally used in smaller applications. At the end of 2002 there were more than 200 installations comprising more than 10 boreholes. The majority of these are applied for space cooling of commercial or institutional buildings and for process cooling within the telecommunication sector. From a technical point of view, BTES are much simpler to construct and operate than ATES. Furthermore, they can be applied in almost any kind of geology. Another advantage compared to ATES is that the permitting procedure is much simpler. The major market obstacle is that the profitability is not always acceptable if calculated as a straight payback time. To increase the market potential, there is a need for further R&D on improvement of borehole heat exchangers and of more effective drilling methods.Snow storage is still a new technology though the Sundsvall snow storage plant has been operated successfully for several years. This good example has inspired several pre-studies of new snow storage plants. These have shown that snow storage is feasible in various sizes and in different applications.

  • 3.
    Chaesson, Johan
    et al.
    University of Lund.
    Hellström, Göran
    Conformal flow models for warm and cold storage in aquifers1992In: Proceedings of the Intersociety Energy Conversion Engineering Conference, ISSN 0146-955X, Vol. 4, p. 125-129Article in journal (Refereed)
    Abstract [en]

    The paper presents the thermohydraulic models for aquifer thermal energy storage developed by the Lund Group for Ground Heat. The basic assumption is that the aquifer is horizontally homogeneous and that the groundwater flow is two-dimensional without a vertical component. The groundwater flow field is then given by an analytical function, or conformal transformation, which is obtained from the positions of the well, the pumping rates, and the regional flow. The first set of PC models concerns the groundwater flow and the motion of thermal fronts for any set of wells and a regional flow. The flow field, with streamlines and stagnation points, is presented graphically on the screen. The motion of the thermal fronts is determined by particle tracking. These interactive models have proven to be very convenient and useful design tools. The complete three-dimensional thermal process is solved in the second set of PC models. The groundwater flow is again given by the explicit analytical formulas, while the thermal process is solved numerically. The coupled groundwater and the heat flow process in the aquifer is dealt with using a new entropy-conservation technique. The models are carefully documented and available on PC. They have been validated against a few field experiments and they are used extensively for design studies

  • 4. Claesson, Johan
    et al.
    Eftring, B.
    Eskilson, J.
    Hellström, Göran
    Markvärme: en handbok om termiska analyser1985Book (Other academic)
  • 5.
    Claesson, Johan
    et al.
    Lund University.
    Eftring, Bengt
    Hellström, Göran
    Ground heat storage: a handbook on thermal analysis1983In: Proceedings: International conference on subsurface heat storage in theory and practice, Stockholm, June 6-8, 1983, Statens råd för byggnadsforskning , 1983, Vol. 2, p. 494-499Conference paper (Refereed)
  • 6.
    Claesson, Johan
    et al.
    Department of Building Physics, Lund University.
    Follin, S.
    Department of Engineering Geology, Lund University.
    Hellström, Göran
    Wallin, N-O
    Department of Mathematics, Lund University.
    On the use of the diffusion equation in test case 6 of DECOVALEX1995In: International Journal of Rock Mechanics and Mining Sciences & Geomechanics Abstracts, ISSN 0148-9062, E-ISSN 1879-2073, Vol. 32, no 5, p. 525-528Article in journal (Refereed)
  • 7. Claesson, Johan
    et al.
    Hellström, Göran
    Analytical studies of the influence of regional groundwater flow on the performance of borehole heat exchangers2000In: Proceedings: TERRASTOCK 2000, 8th International Conference on Thermal Energy Storage : University of Stuttgart, Germany, August 28th until September 1st, 2000 / [ed] Martin Benner, Stuttgart: Universität Stuttgart , 2000Conference paper (Refereed)
  • 8.
    Claesson, Johan
    et al.
    Lund University.
    Hellström, Göran
    Forced convective-diffusive heat flow in insulations: a new analytical technique applied to air leakage through a slit1995In: Journal of Thermal Insulation and Building Envelopes, ISSN 1065-2744, Vol. 18, no Jan, p. 216-228Article in journal (Refereed)
    Abstract [en]

    Forced convective-diffusive heat flow in porous insulation materials is governed by an equation for the air pressure distribution with an ensuing air flow and a heat equation with convection and diffusion. The pressure equation for a homogeneous material may be solved analytically with simple geometries and boundary conditions. The new technique uses a transformed form of the convective-diffusive equation for which the awkward first-order derivatives of the temperature (the convective part) are removed. New explicit solutions for certain two-dimensional, steady-state cases may be derived. The considered example concerns air leakage through an insulation which is open on one side and airtight on the other except for an open slit. Air infiltrates through the slit and leaves through the open side. The solution gives the complete pressure and temperature fields. The extra heat loss due to air leakage is given by an explicit expression which contains only a single, dimensionless parameter.

  • 9. Claesson, Johan
    et al.
    Hellström, Göran
    Thermoelastic stress due to an instaneous finite line heat source in an infinite medium1996Report (Other (popular science, discussion, etc.))
  • 10. Claesson, Johan
    et al.
    Hellström, Göran
    Probert, Thomas
    Buoyancy flow in fractured rock with a salt gradient in the groundwater: a second study of coupled salt and thermal buoyancy1992Report (Other (popular science, discussion, etc.))
  • 11. Dahlenbäck, J-O
    et al.
    Hellström, Göran
    Lundin, S-E
    Nordell, Bo
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Architecture and Water.
    Solar heated borehole heat storage for space heating of the Anneberg residential area at Danderyd, Sweden2000In: Proceedings: TERRASTOCK 2000, 8th International Conference on Thermal Energy Storage : University of Stuttgart, Germany, August 28th until September 1st, 2000 / [ed] Martin Benner, Stuttgart: Universität Stuttgart , 2000, p. 201-206Conference paper (Refereed)
  • 12. Dalenbäck, J-O
    et al.
    Dahm, J
    Lundin, S-E
    Hellström, Göran
    Nordell, Bo
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Architecture and Water.
    Solar heated residential area Anneberg2000In: Proceedings Third ISES Europe Solar Congress: Eurosun 2000 / [ed] A.G. Elvang; S. Iversen, International Solar Energy Society, 2000Conference paper (Refereed)
    Abstract [en]

    A solar heated area comprising 50 residential units is under construction. The system includes low-temperature space heating with seasonal ground storage of solar heat. Heating is supplied by 2 400 m{sup 2} of solar collectors and individual electrical heaters for supplementary heating. During the summer part of collected heat is stored in a borehole store with 100 boreholes drilled to 65 m depth. The groundwater-filled boreholes are fitted with double U-tubes. The average temperature of the seasonal store, about 60,000 m{sup 3} of crystalline rock, varies between 30 and 45 deg. C over the year. A floor heating system designed for a supply temperature of 32 deg. C provides space heating. The system is also equipped with buffer tanks for pre-heating of domestic hot water. The collectors will have favourable working conditions but the store is rather small and the estimated heat loss from the heat store is about 40% of collected solar heat. The average solar fraction is estimated to 70% and the resulting total heating cost is estimated to about 1 000 SEK/MWh ({approx}120{open_square}/MWh).

  • 13.
    Doughty, Christine
    et al.
    Lawrence Berkeley Laboratory.
    Hellström, Göran
    Tsang, Chin Fu
    Lawrence Berkeley Laboratory.
    Claesson, Johan
    Lunds tekniska högskola, LTH.
    A dimensionless parameter approach to the thermal behavior of an aquifer thermal energy storage system1982In: Water resources research, ISSN 0043-1397, E-ISSN 1944-7973, Vol. 18, no 3, p. 571-587Article in journal (Refereed)
    Abstract [en]

    To predict the performance of an aquifer thermal energy system, an understanding of the system`s hydrothermal behavior is needed.^ One possibility is to run a detailed numerical simulation of the system.^ However, for a single-well system in which fluid flow is limited to steady radial flow, a characterization scheme based on a set of four dimensionless parameter groups allows production temperatures and energy recovery factors to be read from graphs.^ The assumption of radial fluid flow is valid when buoyancy flow can be neglected and a well is fully screened in a horizontal aquifer which is confined above and below by impermeable layers.^ Criteria for little buoyancy flow include a low permeability or vertically stratified aquifer, a small temperature difference between injected and ambient water, and short cycle length.^ The basic energy transport equations for the aquifer-confining layer system with steady radial fluid flow in the aquifer are nondimensionalized to derive the key parameter groups.^ Next a numerical model which calculates the heat transfer in the aquifer and confining layers for an injection-storage-production cycle is run for a range of values of these groups.The calculated production temperatures and energy recovery factors are then presented graphically as a function of the parameter groups.^ Comparisons between results of field experiments and recovery factors read from the graphs show good agreement.

  • 14.
    Doughty, Christine
    et al.
    Lawrence Berkeley Laboratory.
    Hellström, Göran
    Tsang, Chin Fu
    Lawrence Berkeley Laboratory.
    Claesson, Johan
    Lunds tekniska högskola, LTH.
    Steady flow model user`s guide1984Report (Other academic)
    Abstract [en]

    Sophisticated numerical models that solve the coupled mass and energy transport equations for nonisothermal fluid flow in a porous medium have been successfully used to match analytical results as well as field data for aquifer thermal energy storage (ATES) systems.^Generally these models are expensive and time-consuming to use.^Typically an ATES study is concerned primarily with energy balances and heat flows.^Often the fluid flow field is simple and reaches steady-state rapidly.^As an alternative for this sort of ATES problem the Steady Flow Model (SFM), a simplified but fast numerical model, has been developed.^Rather than solving the mass transport equation to obtain a fluid flow field that varies with time, a steady purely radial flow field is prescribed in the aquifer, and incorporated into the heat transport equation which is then solved numerically.^While the radial flow assumption limits the range of ATES systems that can be studied using the SFM, it greatly simplifies use of this code.^The preparation of input is quite simple compared to that for a sophisticated coupled mass and energy model, and the cost of running the SFM is far cheaper as well.^Furthermore, the simple flow field allows use of a special calculational mesh that eliminates the numerical dispersion usually associated with the numerical solution of convection problems.^The present report defines the problem considered, briefly outlines the algorithm used to solve it, then describes the input and output for the SFM.

  • 15. Erlandsson, Bitte
    et al.
    Hellström, Göran
    Behandlingsutrustningar för försurat brunnsvatten: effekter på vattenkvaliteten vid användning i enskilt hushåll1994Report (Other academic)
  • 16. Erlandsson, Bitte
    et al.
    Hellström, Göran
    Installation av filter mot surt brunnsvatten: en bra åtgärd?1993In: Grundvatten, ISSN 0282-0102, no 1, p. 14-16Article in journal (Other academic)
    Abstract [sv]

    Avsyrningsfilter tar i allmänhet bort de problem som orsakas av surt brunnsvatten. Detta trots att pH-värdet ofta inte höjs tillräckligt enligt de gränsvärden som finns. Det visar en undersökning som SGU genomfört på ett sjuttiotal filter som är installerade i hushåll med egna brunnar.

  • 17.
    Gehlin, Signhild
    et al.
    Luleå tekniska universitet.
    Hellström, Göran
    Comparison of four models for thermal response test evaluation2003In: ASHRAE Transactions, ISSN 0001-2505, Vol. 109, p. 135-146Article in journal (Refereed)
    Abstract [en]

    Four two-variable parameter estimation models for evaluation of thermal response test data are compared when applied on the same temperature response data. Two models are based on line-source theory, the third model is a cylinder-source-based solution, and the fourth is a numerical one-dimensional finite difference model. The data sets contain measured temperature response, heat load, and undisturbed ground temperature from three thermal response tests, together with physical data of the tested borehole heat exchangers (BHE). The models estimate ground thermal conductivity and thermal resistance of the BHE and are compared regarding test length and data interval used. For the three defined data sets, the line source approximation model shows the closest agreement with the measured temperature response. The cylinder source and numerical models show sensitivity to the inclusion of early data. A recommended minimum response test duration of 50 hours is concluded from the model comparison

  • 18.
    Gehlin, Signhild
    et al.
    Luleå tekniska universitet.
    Hellström, Göran
    Termisk responstest - att ta reda på energibrunnens effektivitet: teknik och forskning2002In: Energi och miljö, ISSN 1101-0568, no 3, p. 75-76Article in journal (Other academic)
  • 19.
    Gehlin, Signhild
    et al.
    Luleå tekniska universitet.
    Hellström, Göran
    Nordell, Bo
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Architecture and Water.
    The influence of the thermosiphon effect on the thermal response test2003In: Renewable energy, ISSN 0960-1481, E-ISSN 1879-0682, Vol. 28, no 14, p. 2239-2254Article in journal (Refereed)
    Abstract [en]

    The issue of natural and forced groundwater movements, and its effect on the performance of ground heat exchangers is of great importance for the design and sizing of borehole thermal energy systems (BTESs). In Scandinavia groundwater filled boreholes in hard rock are commonly used. In such boreholes one or more intersecting fractures provide a path for groundwater flow between the borehole and the surrounding rock. An enhanced heat transport then occurs due to the induced convective water flow, driven by the volumetric expansion of heated water. Warm groundwater leaves through fractures in the upper part of the borehole while groundwater of ambient temperature enters the borehole through fractures at larger depths. This temperature driven flow is referred to as thermosiphon, and may cause considerable increase in the heat transport from groundwater filled boreholes. The thermosiphon effect is connected to thermal response tests, where the effective ground thermal conductivity is enhanced by this convective transport. Strong thermosiphon effects have frequently been observed in field measurements. The character of this effect is similar to that of artesian flow through boreholes.

  • 20. Gehlin, Signild
    et al.
    Hellström, Göran
    Influence on thermal response test by groundwater flow in vertical fractures in hard rock2003In: Renewable energy, ISSN 0960-1481, E-ISSN 1879-0682, Vol. 28, no 14, p. 2221-2238Article in journal (Refereed)
    Abstract [en]

    In this paper different approaches to groundwater flow and its effect in the vicinity of a borehole ground heat exchanger are discussed. The common assumption that groundwater flow in hard rock may be modelled as a homogeneous flow in a medium with an effective porosity is confronted and models for heat transfer due to groundwater flow in fractures and fracture zones are presented especially from a thermal response test point of view. The results indicate that groundwater flow in fractures even at relatively low specific flow rates may cause significantly enhanced heat transfer, although a continuum approach with the same basic assumptions would suggest otherwise.

  • 21.
    Gustafsson, Anna-Maria
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Architecture and Water.
    Westerlund, Lars
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    Hellström, Göran
    CFD-modelling of natural convection in a groundwater-filled borehole heat exchanger2010In: Applied Thermal Engineering, ISSN 1359-4311, E-ISSN 1873-5606, Vol. 30, no 6-7, p. 683-691Article in journal (Refereed)
    Abstract [en]

    In design of ground-source energy systems the thermal erformance of the borehole heat exchangers is important. In Scandinavia, boreholes are usually not grouted but left with groundwater to fill the space between heat exchanger pipes and borehole wall. The common U-pipe arrangement in a groundwater-filled BHE has been studied by a three-dimensional, steady-state CFD model. The model consists of a three meter long borehole containing a single U-pipe with surrounding bedrock. A constant temperature is imposed on the U-pipe wall and the outer bedrock wall is held at a lower constant temperature. The occurring temperature gradient induces a velocity flow in the groundwater-filled borehole due to density differences. This increases the heat transfer compared to stagnant water. The numerical model agrees well with theoretical studies and laboratory experiments. The result shows that the induced natural convective heat flow significantly decreases the thermal resistance in the borehole. The density gradient in the borehole is a result of the heat transfer rate and the mean temperature level in the borehole water. Therefore in calculations of the thermal resistance in groundwater filled boreholes convective heat flow should be included and the actual injection heat transfer rate and mean borehole temperature should be considered.

  • 22. Hellström, Göran
    Avsyrningsutrustningar: fältuppföljning av funktion och effekt1998In: Grundvatten, ISSN 0282-0102, no 2, p. 12-13Article in journal (Other academic)
  • 23. Hellström, Göran
    Bedrock heat store in Luleå: numerical simulation for 1983-19881991In: Proceedings: Thermastock '91, International Conference on Thermal Energy Storage, Scheveningen, 13 - 16 May 1991, Utrecht: Novem , 1991Conference paper (Refereed)
  • 24. Hellström, Göran
    Bedrock heat store in Luleå: numerical smulation for 1983-19881991Report (Other academic)
  • 25. Hellström, Göran
    Borehole heat exchangers: state of the art 20012002In: Implementing Agreement on Energy Conservation through Energy Storage: Annex 13 - Design, Construction and Maintenance of UTES Wells and Boreholes. Subtask 2, Final Report, International Energy Agency (IEA), 2002Chapter in book (Other academic)
  • 26. Hellström, Göran
    Comparison between theoretical models and field experiments for ground heat systems1983In: Proceedings: International conference on subsurface heat storage in theory and practice, Stockholm, June 6-8, 1983, Statens råd för byggnadsforskning , 1983, Vol. 1, p. 102-115Conference paper (Refereed)
  • 27. Hellström, Göran
    Dimensionering1984In: Borrhålsvärmelager: temadag vid Högskolan i Luleå 21 november 1984 / [ed] Bo Nordell, Högskolan i Luleå , 1984, p. 126-132Conference paper (Other academic)
  • 28. Hellström, Göran
    Filter mot surt vatten: test av elva avsyrningsfilter1992In: Grundvatten, ISSN 0282-0102, no 1, p. 10-13Article in journal (Other academic)
  • 29. Hellström, Göran
    Simulering av markvärmesystem1997In: Byggforskning : Byggforskningsrådets tidning för en bättre byggd miljö, ISSN 1102-3686, no 3, p. 28-30Article in journal (Other (popular science, discussion, etc.))
  • 30. Hellström, Göran
    Statsbidraget till sura brunnar: utvärdering och förslag till fortsatt verksamhet1988In: Grundvatten, ISSN 0282-0102, no 2, p. 9-10Article in journal (Other academic)
  • 31. Hellström, Göran
    Testning av små vattenbehandlingsutrustningar för surt grundvatten1989In: Grundvatten, ISSN 0282-0102, no 1, p. 3-5Article in journal (Other academic)
  • 32. Hellström, Göran
    Thermal performance of borehold heat exchangers1998Conference paper (Refereed)
    Abstract [en]

    An important issue in the design of systems using borehole heat exchangers is to find costeffective methods to construct the borehole heat exchanger so that heat can be injected or extracted from the ground without excessive temperature differences between the heat carrier fluid and the surrounding ground. This paper presents an overview of experiences and current activities in this field.

  • 33. Hellström, Göran
    Vattenbehandling i hushåll: ett sätt att lösa problem med vattenkvaliteten?1990In: Grundvatten, ISSN 0282-0102, no 2, p. 5-6Article in journal (Other (popular science, discussion, etc.))
  • 34. Hellström, Göran
    et al.
    Gehlin, Signhild
    Luleå tekniska universitet.
    Bergvärmesystem med fler än en energibrunn: universitets- och högskoleforskning2000In: Energi och miljö, ISSN 1101-0568, no 2, p. 53-55Article in journal (Other academic)
  • 35.
    Hellström, Göran
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Architecture and Water.
    Gehlin, Signhild
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Architecture and Water.
    Borrhålet och dess funktion: universitets- och högskoleforskning2008In: Energi och miljö, ISSN 1101-0568, no 1, p. 55-56Article in journal (Other academic)
  • 36. Hellström, Göran
    et al.
    Kjellsson, E.
    Laboratory study of the heat transfer in a water-filled borehole with a single U-pipe1997In: Proceedings of Megastock '97: 7th International Conference on Thermal Energy Storage, Sapporo, Japan, June 18-21 1997 / [ed] Kiyoshi Ochifuji, Sapporo, 1997Conference paper (Refereed)
  • 37. Hellström, Göran
    et al.
    Larson, Sven
    Department of Geology, Earth Sciences Centre, Göteborg.
    Seasonal thermal energy storage: the HYDROCK concept2001In: Bulletin of Engineering Geology and the Environment, ISSN 1435-9529, E-ISSN 1435-9537, Vol. 60, no 2, p. 145-156Article in journal (Refereed)
    Abstract [en]

    A method for seasonal storage of heat or cold in the bedrock (the HYDROCK concept) is presented and its thermal performance discussed. It involves the use of a fractured bedrock at shallow depths (ca. 50-250 m), where existing fractures are stimulated or new fractures artificially created and used as flow-paths for a heat/cold carrier (usually water). The fracture surfaces are used as heat exchangers and the bedrock is loaded and unloaded to suit the energy needs. Propants are injected into the fractures to keep them open and reduce the energy needed for pumping water through the system. Field tests confirm that stacked parallel fractures can be produced by hydraulic fracturing. The thermal performance of the store is modelled and compared with a ducted ground heat store. It is shown that the HYDROCK store may yield 10-20% more energy during extraction than a ducted ground heat store for similar amounts of injected energy. This indicates that the HYDROCK concept is competitive as a seasonal energy store and may be of particular importance as an alternative energy source where existing methods cannot be economically justified.

  • 38. Hellström, Göran
    et al.
    Nordell, Bo
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Architecture and Water.
    Ökat intresse - lagring och uttag av värme och kyla med borrhål i berg1997In: Byggforskning : Byggforskningsrådets tidning för en bättre byggd miljö, ISSN 1102-3686, no 3, p. 26-27Article in journal (Other academic)
  • 39. Hellström, Göran
    et al.
    Tsang, Chin-Fu
    Lawrence Berkeley Laboratory, University of California.
    Claesson, Johan
    University of Lund.
    Buoyancy flow and thermal stratification in aquifer hot-water storage1980In: LBL, ISSN 0195-721X, no No. 10686, p. 132-133Article in journal (Refereed)
  • 40. Hellström, Göran
    et al.
    Tsang, Chin-Fu
    Earth Sciences Division, Lawrence Berkeley Laboratory, University of California.
    Claesson, Johan
    Lund University.
    Buoyancy flow at a two-fluid interface in a porous medium: analytical studies1988In: Water resources research, ISSN 0043-1397, E-ISSN 1944-7973, Vol. 24, no 4, p. 493-506Article in journal (Refereed)
    Abstract [en]

    Analytical solutions for the pressure distribution and the flow field are derived for several idealized situations involving an injection well and a vertical plane or cylindrical interface between two fluids of different density and viscosity in an infinite anisotropic aquifer bounded by two horizontal planes. The interface, or transition zone, between the two fluids may be either sharp or of finite width. The buoyancy flow induced by the density difference will cause the two-fluid interface to tilt. A characteristic time scale for the buoyancy tilting rate is deduced. The conditions at the well are found to have only a small influence on the buoyancy flow except very close to the well. The buoyancy flow decreases with increasing width of the transition zone.

  • 41. Hellström, Göran
    et al.
    Tsang, Chin-Fu
    Earth Sciences Division, Lawrence Berkeley Laboratory, University of California.
    Claesson, Johan
    Department of Building Technology, Lund Institute of Technology.
    Combined forced-convection and buoyancy flow at a two-fluid interface in a porous medium: analytical studies1988In: Water resources research, ISSN 0043-1397, E-ISSN 1944-7973, Vol. 24, no 4, p. 507-515Article in journal (Refereed)
    Abstract [en]

    The motion of a two-fluid interface in an aquifer is a combination of buoyancy flow and forced convection. The buoyancy flow, which is due to density variations of the fluid, and the forced convection, which acts on the viscosity variations, will cause the two-fluid interface to tilt. The basic case of a plane interface between two immiscible fluids of different density and viscosity in an infinite anisotropic aquifer bounded by two horizontal planes is analyzed in detail. The groundwater flow in the aquifer is treated as a superposition of buoyancy flow and forced convection. The buoyancy flow and the forced-convection components are shown by analytical methods to be related to each other. The tilting angle of the two-fluid interface is given by a simple formula containing only two parameters. There exists a certain stationary tilting angle, the stability of which depends on the two viscosities.

  • 42. Hellström, Göran
    et al.
    Tsang, Chin-Fu
    Lund Institute of Technology.
    Claesson, Johan
    Lund Institute of Technology.
    Heat storage in aquifers: buoyancy flow and thermal stratification problems1979Report (Other academic)
    Abstract [en]

    Heat Storage in aquifers involves injecting warm water into a confined aquifer and recovering the heat later by pumping out the warm water.^Heat loss in the aquifers is roughly proportional to the area of the warm storage region which may be increased to unacceptable levels by buoyancy effects.^Thermohydraulic problems in heat storage aquifers, methods for predicting the buoyancy flow, and changes in the thermal front within different aquifer types are discussed.^Some general observations are made.^Results of some analytical solutions are presented.^The superposition of forced and natural convection is dealt with.^Formulas for the tilting of the thermal front as a function of time are given.^These are tested against numerical simulations and applied to laboratory and field experiments.^The different results, formulas, and tilting criteria are summarized.

  • 43. Karlsson, Leif
    et al.
    Karlsson, K.G.
    Hellström, Göran
    Hällstrand, K.E.
    Försöksverksamhet med statsbidrag till åtgärder mot surt grundvatten: administrativ utvärdering1988Report (Other academic)
  • 44.
    Kjellsson, Elisabeth
    et al.
    Building Physics, Lund University.
    Hellström, Göran
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Architecture and Water.
    Perers, B.
    Department of Civil Engineering, Technical University of Denmark.
    Analyses of ground-source heat pumps combined with solarcollectors in dwellings2009In: Abstract book and proceeding : Effstock 2009: 11th International conference on Thermal Energy Storage for Energy Efficiency and Sustainability / [ed] Signhild Gehlin, Stockholm: Energi- och Miljötekniska Föreningen / EMTF Förlag , 2009Conference paper (Refereed)
  • 45.
    Kjellsson, Elisabeth
    et al.
    Lund University.
    Hellström, Göran
    Perers, B.
    Technical University of Denmark.
    Optimization of systems with the combination of ground-source heat pump and solar collectors in dwellings2009In: Energy, ISSN 0360-5442, E-ISSN 1873-6785Article in journal (Refereed)
    Abstract [en]

    The use of ground-source heat pumps for heating and domestic hot water in dwellings is common in Sweden. The combination with solar collectors has been introduced to reduce the electricity demand in the system. In order to analyze different systems with combinations of solar collectors and ground-source heat pumps, computer simulations have been carried out with the simulation program TRNSYS. Large differences were found between the system alternatives. The optimal design is when solar heat produces domestic hot water during summertime and recharges the borehole during wintertime. The advantage is related to the rate of heat extraction from the borehole as well as the overall design of the system. The demand of electricity may increase with solar recharging, because of the increased operating time of the circulation pumps. Another advantage with solar heat in combination with heat pumps is when the boreholes or neighbouring installations are drilled so close that they thermally influence each other. This may lead to decreasing temperatures in the ground, which gives decreased performance of the heat pump and increased use of electricity. The net annual heat extraction from the ground is reduced by recharge from solar heat. © 2009 Elsevier Ltd. All rights reserved.

  • 46. Lund, J.
    et al.
    Sanner, B.
    Rybach, L.
    Curtis, R.
    Hellström, Göran
    Geothermal (ground-source) heat pumps: a world overview2004In: Geo-Heat Center Quarterly Bulletin, ISSN 0276-1084, Vol. 25, no 3Article in journal (Other academic)
  • 47.
    Lundin, S.E.
    et al.
    Bjerking Ingenjörsbyrå AB, Uppsala.
    Nordell, Bo
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Architecture and Water.
    Dalenbäck, JO
    Chalmers University of Technology.
    Hellström, Göran
    Sjöstedt, S.
    VVs-Teknik AB, Trollhättan.
    Brinck, B.
    Geo-Konsult B. Brinck AB.
    Solvärme och säsongslagring med borrhål i berg och llågtemperatur för bostadsområdet Anneberg, Danderyd: Förprojektering1998Report (Other academic)
    Abstract [en]

    In the planning of a new housing area for 100 dwellings, a pre-design has been made for a solar heating plant. The aim of designing a layout, is to compare the solar system with more conventional heating systems. Developers and contractors are invited for turn-key tenders of the different systems. The single family houses, apartments and service premises in two storey, will have a total floor area of 9000 m{sup 2}. The heating demand is estimated to 1100 MWh/year (120 kWh/m{sup 2}) and the power to 450 kW. A new concept system is designed with low temperatures in all essential parts, but heat pumps are not needed. (1) Flat plate solar collectors, mean temperature 60 deg C; (2) Seasonal bore hole heat store in rock, temperature level 30-45 deg C; (3) Heat distribution network, working temperature 20-80 deg C; (4) Floor heating coils, temperature 25-32 deg C; (5) Peak electrical heaters in houses; (6) Solar DHW and auxiliary individual electrical final heaters. The system has only one general heat fluid with a mixture of water and glycol flowing through solar collectors, store, culverts and the floor heating coils. In all operation modes the heat carrier has the same flow direction and even act as a`buffer volume`. The bedrock consist of outcrops of granite and the GWL is at a depth of 4 m below the ground. In a 120 m investigation bore hole, a so called`Response test` is made in situ of the rock and the duct system. The obtained thermal results are: Conductivity{lambda}= 4.1 W/m,K, Capacity C 0.6 kWh/K, m{sup 3}, Resistance total of PEM-tubes and rock mass R= 0.02 K/(W/m). The investment cost have been calculated to 5.4 mil SEK ({approx} 0.7 mil USD) excl. culvert, floor heating system, DHW tanks/heaters. The annual capital and running costs are 0.73 mil SEK (0.1 mil USD), calculated with an interest rate of 6% over 25 years (0.078). The total system heating cost will be 0.68 SEK/kWh (0.1 USD/kWh). With received EU- and -governmental subsides up to 2.0 mil SEK the heating costs drop to 0.54 SEK/kWh (0.07 USD/kWh). Solar energy is by that means cost-effective to conventional alternatives as district heating, bio-fuel block centrals, ground heat pumps or 100% electrical heating. The solar heating project seems in all respects possible to carry through - but the final decision is taken of the market response

  • 48.
    Margen, P.
    et al.
    Margen-Consult.
    Hellström, Göran
    Nordell, Bo
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Architecture and Water.
    Åberg, B.
    Åbyhammar, Tomas
    Hydrock: värmelager i spräckt berg1984Report (Other (popular science, discussion, etc.))
  • 49.
    Nordell, Bo
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Architecture and Water.
    Hellström, Göran
    Bergvärme - den nya folkrörelsen2004In: Miljöforskning : Formas tidning : för ett uthålligt samhälle, ISSN 1650-4925, no 5-6, p. 27-28Article in journal (Other (popular science, discussion, etc.))
  • 50.
    Nordell, Bo
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Architecture and Water.
    Hellström, Göran
    High temperature solar heated seasonal storage system for low temperature heating of buildings2000In: Solar Energy, ISSN 0038-092X, E-ISSN 1471-1257, Vol. 69, no 6, p. 511-523Article in journal (Refereed)
    Abstract [en]

    A preliminary study of a solar-heated low-temperature space-heating system with seasonal storage in the ground has been performed. The system performance has been evaluated using the simulation models TRNSYS and MINSUN together with the ground storage module DST. The study implies an economically feasible design for a total annual heat demand of about 2500 MWh. The main objective was to perform a study on Anneberg, a planned residential area of 90 single-family houses with 1080 MWh total heat demand. The suggested heating system with a solar fraction of 60% includes 3000 m2 of solar collectors but electrical heaters to produce peak heating. The floor heating system was designed for 30°C supply temperature. The temperature of the seasonal storage unit, a borehole array in crystalline rock of 60,000 m3, varies between 30 and 45°C over the year. The total annual heating costs, which include all costs (including capital, energy, maintenance etc.) associated with the heating system, were investigated for three different systems: solar heating (1000 SEK MWh−1), small-scale district heating (1100 SEK MWh−1) and individual ground-coupled heat pumps (920 SEK MWh−1). The heat loss from the Anneberg storage system was 42% of the collected solar energy. This heat loss would be reduced in a larger storage system, so a case where the size of the proposed solar heating system was enlarged by a factor of three was also investigated. The total annual cost of the solar heating system was reduced by about 20% to about 800 SEK MWh−1, which is lower than the best conventional alternative.

12 1 - 50 of 57
CiteExportLink to result list
Permanent link
Cite
Citation style
  • apa
  • harvard1
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • Other style
More styles
Language
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Other locale
More languages
Output format
  • html
  • text
  • asciidoc
  • rtf