Energy storage in unsaturated soil using pore air flow

Ahti Eerikäinen, Matti Ettala, Markku Kangas, Terhi Kling, Peter Lund, Auli Niemi, Kaj Winqvist

Research output: Book/ReportReportProfessional

Abstract

Mineral grains in soil are surrounded by pores, the porosity of sandy soil being typically 25-35 % of its volume. Above the water table, such pores are filled with air. The heat stored in the mineral grains is transferred to the surrounding air in the pores. Field experiments on energy storage in unsaturated soil using pore air flow were carried out during 1990 - 1991 in Southern Finland. High volumes of pore air, for example 3 900 m3/h in this study, can be produced from a well installed to a depth of 5-7 m, where natural temperatures remain at 5-6°C throughout the year in Finland. The influence of the pumping can be detected far from the surroundings of the well; a 20 Pa pressure difference was measured in the soil 50 meters from the well in this study. For numerical simulation the multiphase, multicomponent model TOUGH was used, simulating the coupled transport of water, air and heat in gas and liquid phases. Heat transfer due to convection within air was found to be considerable in comparison to conduction. The injection flow rate mainly affects the radius of influence and the temperature of the injection air the temperature distribution near the well. Comparison of the results with a hypothetical situation where air is extracted from the soil under natural conditions shows that the benefit due to air injection reduces in 3 months to about 1 °C. Further studies are needed to take into account the subzero temperatures during the winter period. The possibility of using the model THETA to simulate the flow of air in a porous medium was also studied. The model is microcomputer based and simulates the coupled flow of fluid, heat and solute in saturated porous media. The simulations show that the compatibility of those two models seems to be fairly good. The actual suitability of microcomputer simulations by THETA depends on degree accuracy desired. A markedly better fit with experimental data was observed when more accurate ambient temperature data were used in THETA simulations. Most of the energy flux into the soil was caused by solar energy conduction. From the technical point of view heat can be stored in summer and cold in winter by pumping ambient air into the soil through a well. From the economical point of view this is however not viable. Heat derived from industry could be used with better efficiency. Natural heat storage in the unsaturated zone maintains the produced pore air at temperatures of at least 3-5 °C throughout the winter. From the technical point of view the method can be applied to keep lawns and sports grounds free of snow and unfrozen when occasional snow cover is acceptable. Sufficient data concerning the availability and temperature of pore air for calculations of the use of pore air flow directly into houses as indoor air, to heat greenhouses or to cool air-raid shelters were obtained in the study.
Original languageEnglish
Place of PublicationEspoo
PublisherVTT Technical Research Centre of Finland
Number of pages77
ISBN (Print)951-38-4202-9
Publication statusPublished - 1992
MoE publication typeNot Eligible

Publication series

NameVTT Tiedotteita - Meddelanden - Research Notes
PublisherVTT
No.1389
ISSN (Print)1235-0605
ISSN (Electronic)1455-0865

Fingerprint

airflow
air
soil
temperature
simulation
porous medium
energy storage
pumping
winter
mineral
indoor air
energy flux
vadose zone
sport
snow cover
shelter
sandy soil
ambient air
heat transfer
water table

Keywords

  • energy storage
  • soils
  • soil properties
  • porosity
  • heat transfer
  • heat storage
  • air flow
  • field tests
  • temperature
  • numerical analysis
  • simulation
  • estimating
  • moisture content
  • seasons
  • calculations
  • models
  • THETA
  • TOUGH
  • Finland

Cite this

Eerikäinen, A., Ettala, M., Kangas, M., Kling, T., Lund, P., Niemi, A., & Winqvist, K. (1992). Energy storage in unsaturated soil using pore air flow. Espoo: VTT Technical Research Centre of Finland. VTT Tiedotteita - Meddelanden - Research Notes, No. 1389
Eerikäinen, Ahti ; Ettala, Matti ; Kangas, Markku ; Kling, Terhi ; Lund, Peter ; Niemi, Auli ; Winqvist, Kaj. / Energy storage in unsaturated soil using pore air flow. Espoo : VTT Technical Research Centre of Finland, 1992. 77 p. (VTT Tiedotteita - Meddelanden - Research Notes; No. 1389).
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Eerikäinen, A, Ettala, M, Kangas, M, Kling, T, Lund, P, Niemi, A & Winqvist, K 1992, Energy storage in unsaturated soil using pore air flow. VTT Tiedotteita - Meddelanden - Research Notes, no. 1389, VTT Technical Research Centre of Finland, Espoo.

Energy storage in unsaturated soil using pore air flow. / Eerikäinen, Ahti; Ettala, Matti; Kangas, Markku; Kling, Terhi; Lund, Peter; Niemi, Auli; Winqvist, Kaj.

Espoo : VTT Technical Research Centre of Finland, 1992. 77 p. (VTT Tiedotteita - Meddelanden - Research Notes; No. 1389).

Research output: Book/ReportReportProfessional

TY - BOOK

T1 - Energy storage in unsaturated soil using pore air flow

AU - Eerikäinen, Ahti

AU - Ettala, Matti

AU - Kangas, Markku

AU - Kling, Terhi

AU - Lund, Peter

AU - Niemi, Auli

AU - Winqvist, Kaj

PY - 1992

Y1 - 1992

N2 - Mineral grains in soil are surrounded by pores, the porosity of sandy soil being typically 25-35 % of its volume. Above the water table, such pores are filled with air. The heat stored in the mineral grains is transferred to the surrounding air in the pores. Field experiments on energy storage in unsaturated soil using pore air flow were carried out during 1990 - 1991 in Southern Finland. High volumes of pore air, for example 3 900 m3/h in this study, can be produced from a well installed to a depth of 5-7 m, where natural temperatures remain at 5-6°C throughout the year in Finland. The influence of the pumping can be detected far from the surroundings of the well; a 20 Pa pressure difference was measured in the soil 50 meters from the well in this study. For numerical simulation the multiphase, multicomponent model TOUGH was used, simulating the coupled transport of water, air and heat in gas and liquid phases. Heat transfer due to convection within air was found to be considerable in comparison to conduction. The injection flow rate mainly affects the radius of influence and the temperature of the injection air the temperature distribution near the well. Comparison of the results with a hypothetical situation where air is extracted from the soil under natural conditions shows that the benefit due to air injection reduces in 3 months to about 1 °C. Further studies are needed to take into account the subzero temperatures during the winter period. The possibility of using the model THETA to simulate the flow of air in a porous medium was also studied. The model is microcomputer based and simulates the coupled flow of fluid, heat and solute in saturated porous media. The simulations show that the compatibility of those two models seems to be fairly good. The actual suitability of microcomputer simulations by THETA depends on degree accuracy desired. A markedly better fit with experimental data was observed when more accurate ambient temperature data were used in THETA simulations. Most of the energy flux into the soil was caused by solar energy conduction. From the technical point of view heat can be stored in summer and cold in winter by pumping ambient air into the soil through a well. From the economical point of view this is however not viable. Heat derived from industry could be used with better efficiency. Natural heat storage in the unsaturated zone maintains the produced pore air at temperatures of at least 3-5 °C throughout the winter. From the technical point of view the method can be applied to keep lawns and sports grounds free of snow and unfrozen when occasional snow cover is acceptable. Sufficient data concerning the availability and temperature of pore air for calculations of the use of pore air flow directly into houses as indoor air, to heat greenhouses or to cool air-raid shelters were obtained in the study.

AB - Mineral grains in soil are surrounded by pores, the porosity of sandy soil being typically 25-35 % of its volume. Above the water table, such pores are filled with air. The heat stored in the mineral grains is transferred to the surrounding air in the pores. Field experiments on energy storage in unsaturated soil using pore air flow were carried out during 1990 - 1991 in Southern Finland. High volumes of pore air, for example 3 900 m3/h in this study, can be produced from a well installed to a depth of 5-7 m, where natural temperatures remain at 5-6°C throughout the year in Finland. The influence of the pumping can be detected far from the surroundings of the well; a 20 Pa pressure difference was measured in the soil 50 meters from the well in this study. For numerical simulation the multiphase, multicomponent model TOUGH was used, simulating the coupled transport of water, air and heat in gas and liquid phases. Heat transfer due to convection within air was found to be considerable in comparison to conduction. The injection flow rate mainly affects the radius of influence and the temperature of the injection air the temperature distribution near the well. Comparison of the results with a hypothetical situation where air is extracted from the soil under natural conditions shows that the benefit due to air injection reduces in 3 months to about 1 °C. Further studies are needed to take into account the subzero temperatures during the winter period. The possibility of using the model THETA to simulate the flow of air in a porous medium was also studied. The model is microcomputer based and simulates the coupled flow of fluid, heat and solute in saturated porous media. The simulations show that the compatibility of those two models seems to be fairly good. The actual suitability of microcomputer simulations by THETA depends on degree accuracy desired. A markedly better fit with experimental data was observed when more accurate ambient temperature data were used in THETA simulations. Most of the energy flux into the soil was caused by solar energy conduction. From the technical point of view heat can be stored in summer and cold in winter by pumping ambient air into the soil through a well. From the economical point of view this is however not viable. Heat derived from industry could be used with better efficiency. Natural heat storage in the unsaturated zone maintains the produced pore air at temperatures of at least 3-5 °C throughout the winter. From the technical point of view the method can be applied to keep lawns and sports grounds free of snow and unfrozen when occasional snow cover is acceptable. Sufficient data concerning the availability and temperature of pore air for calculations of the use of pore air flow directly into houses as indoor air, to heat greenhouses or to cool air-raid shelters were obtained in the study.

KW - energy storage

KW - soils

KW - soil properties

KW - porosity

KW - heat transfer

KW - heat storage

KW - air flow

KW - field tests

KW - temperature

KW - numerical analysis

KW - simulation

KW - estimating

KW - moisture content

KW - seasons

KW - calculations

KW - models

KW - THETA

KW - TOUGH

KW - Finland

M3 - Report

SN - 951-38-4202-9

T3 - VTT Tiedotteita - Meddelanden - Research Notes

BT - Energy storage in unsaturated soil using pore air flow

PB - VTT Technical Research Centre of Finland

CY - Espoo

ER -

Eerikäinen A, Ettala M, Kangas M, Kling T, Lund P, Niemi A et al. Energy storage in unsaturated soil using pore air flow. Espoo: VTT Technical Research Centre of Finland, 1992. 77 p. (VTT Tiedotteita - Meddelanden - Research Notes; No. 1389).