Soil regeneration (recovery) system and seasonal accumulation of thermal energy by means of a solar concentrator for efficient operation of geothermal heat pumps.

         Recently geothermal heat pumps have been gaining popularity in Ukraine. This is the most efficient type of heat pump. In Europe, the popularity of heat pumps is declining as there is a problem of soil cooling around the probe. Although the earth’s warmth is a renewable energy source, thermal regeneration (recovery) is not as fast as we consume soil heat.

         Therefore, all data are given in the light of 1800 hours of heat pump operation per year. According to studies in the first 3 years, the soil temperature around the heat exchangers decreases, but every year the temperature decrease decreases. All this leads to a decrease in the efficiency of the heat pump. However, if a heat pump is used for more than 1800 hours per year, there is a risk of a significant decrease in the temperature around the well or even freezing of some areas.

           This can cause some layers of soil to settle and destroy the heat exchanger pipes or cause more dangerous consequences for the soil microclimate and structures near the well. For better soil regeneration, it is recommended to supply additional heat to the heat exchanger during the summer, for example from solar collectors or to use a heat pump. But these tools are not effective because they have low efficiency and high cost.

              We propose to use a solar concentrator with high efficiency, low cost compared to solar collectors and a small installation area (no collector fields needed) for soil regeneration. Without additional equipment, it easily adapts to the geothermal heat pump and is able not only to restore the soil heat balance during the summer, but also to accumulate enough energy to heat the house in winter.  

            The heat removal from the vertical heat exchanger is higher than that of the horizontal heat exchanger and is accepted on average 50 W / m. However, the real value may vary greatly and depends on the humidity of the rock and the availability of groundwater.

Type of breed          Removal of heat,

                                               W / m

Dry sedimentary rocks           20

Dry sand, gravel                       25

Wet sand                                 35-40

Rocky soil, saturated

 with water, moist clay         40-50

Limestone                              50-60

Granite                                    60-80

Groundwater                         80-100

           It should be noted that pipes of geothermal heat pumps are ground heat exchangers that can operate in reverse mode without alterations, that is, geothermal heat pump can not only remove thermal energy from the bowels of the earth, but also pump heat from the sun.

         As can be seen from the table, subsoil consists of many types of rocks, which have their own heat capacity and their coefficient of thermal conductivity. For example, compare the heat and heat conductivity characteristics of dry sand and granite: Sand heat capacity of 800-900 J / kg deg. C, heat capacity of granite up to 2800 J / kg deg C, coefficient of thermal conductivity of sand 0,35 W / m cubic grade C, coefficient of thermal conductivity of granite 2.8 W / m cubic C.

         We see that when thermal energy is stored, granite will act as a heat accumulator, and sand as a natural insulator. It is clear that these are ideal conditions and practically not observed in nature, but the physical properties of the species of rocks in the bowels differ (as seen in the example). Therefore, nature has created a heat accumulator, which at depths of 20 -100 m will work very effectively, that is, one type of rock will work as a heat energy storage, the other as a thermal insulator.

           Using a solar concentrator paired with a geothermal heat pump, we get an efficient system that will not create environmental pressure at work, and in times will increase the efficiency of the geothermal heat pumps.

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