Soil/Ground Conditions

soil temperature

Photo supplied by Next Energy.

The heat pump system will be designed to suit your local soil/ground conditions.

The thermal behaviour of soils is controlled by soil composition, soil moisture, vegetation and local climate.

  • Favourable ground conditions: Sandy loams, sandy clay loam and loam; moist soils with high solar radiation
  • Normal ground conditions: Humid, silty-sandy ground with average solar radiation exposure
  • Poor ground conditions: Dry, coarse-grained soils (e.g. pumice, stony ground) and areas shaded from solar radiation
soil temperature map niwa

Image from

Three important measures

  1. Soil temperature at between 1 – 1.5m depths, the ground in New Zealand can be expected to have a year-round average temperature of 12 – 15°C.
  2. Heat capacity is a measure of the ability of a substance to store heat. For soils, this varies with moisture level.
  3. Thermal conductivity is a measure of the rate of heat transfer between the soils and ground loop. This will determine the length of piping required.

You can find out the soil temperature at your location using the NIWA ground temperature mapping tool.