Heat of soil on depth to 20 m is saved-up solar heat which passes to soil thanks to direct heating by sunshine, heat transfer from air or the dropped-out atmospheric precipitation. Warmly deeper layers, is lower 20 m (so-called «a neutral zone»), are formed by the energy arriving from a subsoil of the earth, and practically does not depend on seasonal climate changes.
For selection of heat of soil thermal pumps of a configuration soil/water or soil/air are used. Such systems consist of the thermal pump and soil heat exchangers. The thermal pump have in a boiler room to which to be brought a contour of the soil heat exchanger. By an action principle soil thermal pumps divide on:
- systems of direct expansion – in soil the contour of the copper pipeline on which the coolant circulates is put. In the course of circulation it heats up and there is an evaporation process then it arrives directly in the compressor;
- systems with rassolny liquid – in soil the pipeline contour on which the nonfreezing heat-carrier circulates is put. Warmly selected in the course of circulation it is transferred to the thermal pump.
Thermal pumps with soil heat exchangers of direct expansion have higher efficiency in comparison with thermal pumps of soil type with brine use. This difference speaks that in systems to a rassolny contour there is a double heat exchange soil – a brine, a brine – a coolant, unlike heat exchange of systems of direct expansion «soil – a coolant». In systems with heat-carrier use as heat carrier, additional costs of ensuring operation of the circulating pump also are imposed. Soil rassolny a contour share on: vertical and horizontal.
- Horizontal soil contour:
Advantages: low price; Shortcomings: need of existence of the big area of the earth used for an arrangement of heat exchangers; influence of weather changes on soil temperature; restriction whenever possible vegetation growths in the territory with an earth contour; complexity of carrying out repair work in case of contour depressurization. The soil thermal pump with a horizontal contour
- Vertical soil contour (probes):
Advantages: the soil temperature, does not depend on ambient temperature; the arrangement on the small area of the earth is possible. Shortcomings: high price; complexity of carrying out repair work in case of contour depressurization. The thermal pump with a vertical contour (probe)
The useful quantity of heat and efficiency of the thermal pump, and thus the area of a necessary surface of heat exchange depend on heatphysical properties of soil and from climatic conditions of the region. Thermal properties of soil, such as a volume thermal capacity and heat conductivity, very strongly depend on granulometric structure and a condition. Heatheat-sink properties and heat conductivity of soil of subjects are higher, than more its humidity, a mineralization and than is less maintenance of a time in it with air. Therefore the soil thermal pumps identical on capacities and being in one climatic zone, can differ demanded quantity of soil contours and in their length.