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horizontal loop

Heat pumps on a horizontal loop

The ground stocks solar energy throughout the year. This constantly replenished source of energy is thus available and recoverable by a WATER-TO-WATER heat pump.

Heat pumps on a horizontal loop

The theory is simple

circulate a fluid through buried pipes which absorb heat contained in the ground and carry it to the heat pump.

  • the fluid used is a glycol-water solution (brine -15°C).
  • the heat from the ground is essentially restored during the summer, but can also be renewed during sunny periods throughout the rest of the year.
  • rain also contributes to the loop's energy renewal.
  • 95% of the recovered heat comes from the sun's heat; the calories that rise by convection from deep layers only represent a negligible 0.2 to 0.5 W/m2.

Dimensions of the loop

Firstly, the surface area of land available for the loop should be 1.5 to 2 times the surface area to be heated. For example: to heat a 130 m2 house, 200 to 260 m2 of loop is necessary.

Different types of horizontal loops

3 types of loop are generally used:

  • The traditional horizontal loop
    Stripping off of top level of soil.
    Depth 0.8 m, below the frost line
    Minimum 0.4 m pitch, 25 mm diameter pipes
    Laid on a bed of sand and delimited by boundary markers
  • The 2-pipe trench loop.
  • The 4-pipe trench loop
    Dig to a depth of 0.6 to 1.20 m
    Maximum length of trench 50 m
    Distance between 2 trenches 0.5 m
Average recovered capacity according to loop type (watt/m)
Configuration Per metre of trench (W/m) Per metre of piping (W/m)
Per m2 of land (W/m)
Stripping* / 15* 37*
2-pipe loop30 15*
4-pipe loop 44 11 37

(*) For regions in which the outdoor temperature can drop to -10°C, the values are 12W /m and 30W/m2
These values are indicative; they depend on the nature of the land.

Table of minimum distances to be respected between the loop and other elements on the land

ObstaclesMinimum distance in metres
Trees 2
Non-hydraulic sunken networks 1.5
Foundations, wells, septic tanks, etc. 3

Geothermal energyHeat pumpsGroundwater heat pumpsHorizontal loop