Cross-reference to Related Applications

This application claims the benefit of United States Provisional Patent Applications USSN 62/527,055 filed June 30, 2017 and USSN 62/544,583 filed August 1 1 , 2017, the contents of both of which are herein incorporated by reference.

Field

This application relates to a thermosyphon and methods of using the thermosyphon to freeze ground or maintain ground in a frozen state.

Background A thermosyphon is a heat transfer device, which extracts heat from the ground and disperses it into the air. In a permafrost environment, thermosyphons help maintain a below-zero ground temperature throughout the year thus preventing frozen ground from thawing. Thermosyphon technology is successfully used for the stabilization of building foundations, frozen core of dams or in the form of thermopiles along the pipelines. There are two types of thermosyphons, passive and hybrid. The passive thermosyphon is a pressurized vessel filled with liquid ammonia, propane or carbon dioxide with pressure varying from about 2100 to 4800 kPa. The hybrid thermosyphon combines a passive unit with a refrigerating system, which requires a substantial external power source. While passive thermosyphons do not require extensive maintenance, installation must be performed by specially trained personnel. Further, passive thermosyphons are not effective enough because heat is removed too slowly. Both of these thermosyphons are very expensive, which limits their use on a large scale under linear infrastructure such as pipelines, railroads, highways etc.

A comprehensive analysis of thermosyphons or heat pipe application for ground stabilization under prolonged linear infrastructure such as the Alaska Pipeline, was done by Heuer, 1979 for the U.S. Army Cold Regions Research and Engineering Laboratory. Another detailed study of building support provided by thermosyphon technology was conducted by Holubec, 2008 for the Government of the NT Asset Management Division Public Works and Services. Both studies described two-phase thermosyphons. In the Alaska Pipeline case, only passive thermosyphons were used, while projects in Northwest Territories employed passive as well as hybrid thermosyphon technology. While ground freezing with thermosyphons can be considered as a "last line of defense" when any other methods for foundation stabilization are not available or are not feasible due to geotechnical conditions or high costs, thermosyphon technology is nonetheless very expensive. According to the Government of the Northwest Territories, Department of Transportation, climate change may affect the quality of Highway 3, the main highway of the NT, which is already under extensive maintenance every summer. However, thermosyphon technology is not applied in this case because of associated costs, among other factors. The complex installation process of thermosyphons is another factor which limits their use. Heuer, 1979 noted that installation of heat pipes affected construction timing, due to the requirement for special knowledge and skills, which are often not available within general drilling contractor crews.

There remains a need for thermosyphon technology, which is more effective, simpler in design and/or lower cost than existing thermosyphon technologies.

Summary

A thermosyphon for cooling ground, in particular freezing ground, comprises just two pipes, a heat exchanger, a pump, a power supply for the pump and a switch to control power to the pump.

In one aspect, there is provided a thermosyphon for freezing ground, the thermosyphon comprising: a first pipe comprising a sealed bottom and a first internal volume, the first pipe configured to be at least partially inserted into the ground; a second pipe disposed within the first pipe, the second pipe comprising a second internal volume, the second internal volume in fluid communication with the first internal volume; a heat exchanger comprising a third internal volume, the third internal volume in fluid communication with the internal volumes of the first and second pipes, the first, second and third internal volumes defining a fluid flow space, the heat exchanger further comprising an external surface at least partially exposed to surrounding air above the ground; a heat exchange fluid in the fluid flow space; a pump configured to circulate the fluid through the internal volumes of the heat exchanger and first and second pipes; a power supply configured to power the pump; and, a switch configured to switch on the pump when the surrounding air is below freezing temperature of water. In another aspect, there is provided a method for maintaining ground in a frozen state by using the thermosyphon, the method comprising: creating a hole in the ground; inserting at least a bottom portion of the first pipe of the thermosyphon into the hole; and, back-filling the hole so that an external wall of the at least a bottom portion of the first pipe is in the direct contact with the ground, and the external surface of the heat exchanger is at least partially exposed to surrounding air above the ground.

The present thermosyphon is more effective, simpler in design and lower cost than existing thermosyphon technologies. The present thermosyphon does not require special training or licensing for its operation, although the need for some maintenance may limit use in remote, uninhabited regions with limited access. The present thermosyphon has low power demand, providing efficient cooling while only requiring the use of low power output power sources (e.g. solar panels).

Further features will be described or will become apparent in the course of the following detailed description. It should be understood that each feature described herein may be utilized in any combination with any one or more of the other described features, and that each feature does not necessarily rely on the presence of another feature except where evident to one of skill in the art.

Brief Description of the Drawings For clearer understanding, preferred embodiments will now be described in detail by way of example, with reference to the accompanying drawings, in which:

Fig. 1 depicts a schematic diagram of a first embodiment of a thermosyphon of the present invention;

Fig. 2 depicts a schematic diagram of a second embodiment of a thermosyphon of the present invention;

Fig. 3 depicts locations of thermistors associated with an installed thermosyphon of the present invention;

Fig. 4 is a graph depicting timed temperature distribution in ground around the thermosyphon of Fig. 2 when the thermosyphon was installed in the ground; Fig. 5 is a graph depicting timed temperature distribution in ground around the thermosyphon of Fig. 1 when the thermosyphon was installed in the ground;

Fig. 6 depicts locations of thermistor arrays associated with a cluster of installed thermosyphons; Fig. 7 depicts graphs comparing timed temperature distribution in ground around the cluster of thermosyphons of Fig. 6 during the winters of 2015-2016 and 2016-2017 (left panel) to the winter of 2017-2018 (right panel); and,

Fig. 8 depicts a graph comparing timed temperature distribution in ground during the years 2015-2018 using different thermosyphon arrangements.

Detailed Description

The thermosyphon is very simple and may comprise just two pipes, a heat exchanger, a pump, a power supply for the pump and a switch to control power to the pump. The two pipes may comprise a first pipe and a second pipe disposed within the first pipe. Thus, the first pipe may be an external pipe and the second pipe may be an internal pipe situated inside the external pipe, i.e. a pipe-in-pipe arrangement. The two pipes may be of any suitable cross-section, for example circular, oval or polygonal (e.g. triangular, square, rectangular, pentagonal, hexagonal, etc.) provided the first pipe is able to contain the second pipe while permitting fluid flow between an inner surface of the first pipe and an outer surface of the second pipe. Preferably, both pipes have circular cross- sections. Preferably, the two pipes are longitudinally coaxial, although the second pipe does not need to have the same longitudinal axis as the first pipe. The longitudinal axes of the two pipes may be offset. When the two longitudinal axes are offset, the axes are preferably substantially parallel.

The first pipe has a first internal volume. The second pipe has a second internal volume. The first and second internal volumes may be in fluid communication to facilitate circulation of fluid in and out of the pipes. The first pipe has a bottom and a top. The second pipe has a bottom and a top. The bottom of the first pipe may be closed. The top of the first pipe may be open. The bottom of the second pipe may be open. The top of the second pipe may be open. The open bottom of the second pipe may be in fluid communication with the first internal volume proximate the bottom of the first pipe.

The heat exchanger may comprise a wall or walls that define a third internal volume. The wall or walls may have an external surface that is at least partially exposed to surrounding air above the ground when the thermosyphon is in use. The heat exchanger may comprise structures to increase surface area of the external surface that is in contact with the surrounding air, for example coiled or serpentine tubes, or raised channels, dimples or other surface irregularities, which increase surface area of the external surface exposed to the air while not making the heat exchanger unduly large. The third internal volume is in fluid communication with the internal volumes of the first and second pipes, the first, second and third internal volumes defining a fluid flow space in which the heat exchange fluid may be circulated. To facilitate fluid circulation in the thermosyphon, the tops of the first and second pipes may be in fluid communication with the third internal volume. In one embodiment, the heat exchanger may be disposed at the top of the first pipe. In one embodiment, the heat exchanger may be attached to the top of the first pipe so that the open top of the first pipe directly opens into the third volume. In one embodiment, the second pipe may extend into the third volume so that the open top of the second pipe is situated above the open top of the first pipe.

The first pipe is configured to be at least partially inserted into the ground, while the external surface of the heat exchanger is at least partially exposed to surrounding air above the ground. In one embodiment, an upper portion of the first pipe may also act as a heat exchanger. Preferably, the bottom of the first pipe is configured to be inserted within or proximate to permafrost in the ground. The first pipe has a sealed bottom to prevent fluid from escaping out of the first pipe into the ground. The fluid flow space may be completely sealed from an outside of the thermosyphon to prevent fluid from leaking out of the thermosyphon, and to prevent water and other contaminants from entering the thermosyphon. The heat exchange fluid may comprise a liquid or a gas having a freezing temperature below the freezing temperature of water. Preferably, the fluid is an antifreeze liquid. Liquids with high heat capacities are particularly useful. Useable liquids may include, for example, coolants, refrigerants or mixtures thereof. Some examples of useful heat exchange liquids include ethylene glycol, methanol and mixtures thereof. The pump is employed to circulate the heat exchange fluid in the fluid flow space of the thermosyphon. The pump is preferably a submersible pump mounted within the fluid flow space. In one embodiment, the pump may be disposed at the top of the second pipe. Preferably, the pump disposed at the top of the second pipe is attached to the top of the second pipe where it operates to pump fluid out of the third internal volume into the second internal volume. In another embodiment, the pump may be disposed at the bottom of the second pipe. Preferably, the pump disposed at the bottom of the second pipe is attached to the bottom of the second pipe where it operates to pump fluid out of the first internal volume into the second internal volume. Thus, the top or bottom of the second pipe may be connected to the pump, while the other remains open. The pump creates circulation throughout the fluid flow space to facilitate heat exchange between below-ground and above-ground environments.

Any suitable power supply may be used to operate the pump. However, it is an advantage of the present invention that a low power output power source is sufficient to operate the pump while providing efficient cooling of the ground. Consequently, the present invention is well suited for renewable energy sources, for example solar panels, wind turbine generators and the like. However, other energy sources such as diesel- powered generators, hydroelectric dams, batteries and the like may be used, if desired. The thermosyphon may be provided with a back-up power supply, for example a battery, if desired.

The switch is configured to switch on the pump when the surrounding air is below freezing temperature of water. When the temperature of the surrounding air is higher than the freezing temperature of water, effective cooling of the ground by the thermosyphon is either difficult or impossible. Operation of the thermosyphon when the temperature of the surrounding air is higher than the freezing temperature of water may cause the ground to heat, which could cause permafrost to melt instead of staying frozen. Thus, it is desirable to include a thermally actuated switch that switches off the pump when the temperature of the surrounding air is higher than the freezing temperature of water. At normal atmospheric pressure, the freezing temperature of water is 0°C. The thermosyphon may be used to maintain ground in a frozen state or to freeze unfrozen ground by inserting at least a bottom portion of the first pipe into a hole in the ground, while at least a portion of the external surface of the heat exchanger is exposed to surrounding air above the ground. The hole may be created by digging, drilling or the like. The hole is preferably vertical, although the thermosyphon may be installed at any angle to the ground provided that at least a portion of the heat exchanger remains exposed to surrounding air above the ground and above a maximum anticipated snow depth when the thermosyphon is in use. The hole is back-filled so that an outer surface of the wall of at least a bottom portion of the first pipe is in the direct contact with the ground, and the external surface of the heat exchanger is at least partially exposed to surrounding air above the ground and above the maximum anticipated snow depth. Preferably, the entire heat exchanger remains above the ground and above the maximum anticipated snow depth.

When the air temperature drops below the freezing temperature of water, the switch closes electrically connecting the pump to the power supply to permit the pump to circulate the heat exchange fluid inside the thermosyphon. Exposed to the freezing temperatures above ground through the external surface of the heat exchanger, the fluid in the third internal volume cools as heat escapes out of the heat exchanger. The cooled fluid in the third internal volume is pumped through the pipes, and cold fluid in the first internal volume of the first pipe absorbs heat from the ground, which is in contact with the outer surface of the wall of the first pipe. The warmer fluid in the first pipe is pumped into the heat exchanger where the fluid is once again cooled. In this manner, the ground around the first pipe can be cooled, and frozen or kept frozen.

By inverting the thermosyphon, the thermosyphon can be used in summertime to pump cold from permafrost at the bottom of the thermosyphon up to the top layer of the ground to keep the top layer of soil frozen in the summertime.

The thermosyphon is particularly useful for cooling the ground in permafrost environments, for example frigid areas of Earth such as the high Arctic and the Antarctica, where permafrost is present in the ground. Such ground generally comprises an underlying layer of permafrost, a perennially unfrozen layer (i.e. talik) above the permafrost and an active layer that is seasonally frozen above the perennially unfrozen layer. In particular, the thermosyphon is useful on a large scale under linear infrastructure, such as pipelines, railroads, highways, etc.

In one embodiment, the thermosyphon is particularly suitable for installation near roads in frigid areas of the Earth. The first and second pipes may be provided with a 90- degree knee that allows a lower part of the thermosyphon to be extended under the road.

Examples:

Two embodiments of thermosyphons were constructed in accordance with the present invention and then tested for performance. Fig. 1 depicts a first embodiment of a thermosyphon 1 , called Case A. Fig. 2 depicts a second embodiment of a thermosyphon 100, called Case B.

As depicted in Fig. 1 , the thermosyphon 1 (Case A) comprises a heat exchanger 10, a submersible pump 20, an external pipe 30, an internal pipe 40, a solar panel 50, a thermal switch 60 and a back-up battery 70. The heat exchanger 10 comprises a fluid chamber 11 enclosed by walls 12. External surfaces of the walls 12 are exposed to atmosphere above the ground 2 to permit heat transfer through the walls 12 between an antifreeze mixture in the chamber 11 and air outside the heat exchanger 10. The heat exchanger could comprise coiled tubing or other structures known in the art to increase surface area in contact with the atmosphere. The external pipe 30 has an open top 32, the open top 32 in fluid communication with the chamber 11 of the heat exchanger 10. The external pipe 30 is sealingly connected at the open top 32 of the external pipe 30 to a bottom 13 of the heat exchanger 10 such that the external pipe 30 extends vertically downward from the heat exchanger 10. The external pipe 30 has a closed and sealed bottom 31 , and a lower portion of the external pipe 30 extends into the ground 2.

The internal pipe 40 is disposed within and coaxial with the external pipe 30. The internal pipe 40 is open at both a bottom end 41 and a top end 42. The internal pipe 40 extends through the external pipe 30 so that the bottom end 41 of the internal pipe 40 is proximate the closed and sealed bottom 31 of the external pipe 30 while leaving sufficient space between the bottom end 41 of the internal pipe 40 and the bottom 31 of the external pipe 30 to permit fluid to flow between the two pipes 30, 40 at the respective bottoms 31 , 41. The internal pipe 40, extends into the chamber 11 of the heat exchanger 10 so that the top end 42 of the internal pipe 40 is disposed above the open top 32 of the external tube 30. The antifreeze mixture fills the fluid chamber 11 , the external pipe 30 and the internal pipe 40. The fluid chamber 11 , the external pipe 30 and the internal pipe 40 are in fluid communication, but are sealed from the outside to prevent leakage of antifreeze mixture and to prevent ingress of air, water or other contaminants from the atmosphere of the ground. The submersible pump 20 is connected to the top end 42 of the internal pipe 40 and is configured to pump the antifreeze mixture out of the chamber 11 of the heat exchanger 10 into the internal pipe 40, as shown by fluid flow 21. The submersible pump 20 is powered by the solar panel 50, or by the back-up battery 70 if the solar panel 50 fails. An electrical circuit 61 between the solar panel 50 (or the battery 70) and the submersible pump 20 comprises the thermal switch 60, which operates the submersible pump 20. The thermal switch 60 comprises a thermal sensor configured to measure air temperature around the switch 60. When the air temperature is above 0°C, the switch 60 is open and the pump 20 remains off. When the air temperature drops below 0°C, the switch 60 is closed thereby switching on the pump 20. The pump 20 is a low energy consumption unit, which can operate solely on renewable energy sources, such as the solar panel 50 or back-up battery 70.

As indicated above, a lower portion of the external pipe 30 extends into the ground 2. In frigid areas of the Earth, the ground 2 comprises three layers in descending order: an active layer 3, which is seasonally frozen; a perennially unfrozen layer (talik) 4, which is always unfrozen; and, a permafrost layer 5, which is always frozen. When installing the thermosyphon 1 in the ground 2, the external pipe 30 may be inserted into the ground 2 so that the bottom 31 is in the permafrost layer 5, or in the perennially unfrozen layer 4 just above the permafrost layer 5. The heat exchanger 10 is preferably above the ground 2 in a position higher than the maximum anticipated snow depth around the thermosyphon 1 .

In operation, when the air temperature drops below 0°C, the thermal switch 60 closes and the submersible pump 20 circulates the antifreeze mixture inside the thermosyphon 1 . Exposed to freezing temperatures above the ground 2 through the walls 12 of the heat exchanger 10, the antifreeze mixture in the chamber 11 cools, losing heat through the processes of heat conduction through the walls 12 followed by heat radiation therefrom into the air around the thermosyphon 1. Cold antifreeze flows from the chamber 11 into the open top end 42 of the internal pipe 40, as shown by fluid flow 21. The cold fluid descends through the internal pipe 40 exiting through the open bottom end 41 thereof, displacing warmer fluid at the bottom 31 of the external pipe 30. The warmer fluid at the bottom 31 of the external pipe 30 ascends in the external pipe 30, as shown by fluid flow 22, the warmer fluid in the external pipe 30 being subsequently replaced by colder fluid. The warmer fluid in the external pipe 30 is forced into the chamber 11 of the heat exchanger 10, as shown by fluid flow 23, where the warmer fluid is cooled as described above. As depicted in Fig. 2, the thermosyphon 100 (Case B) also comprises a heat exchanger 110, a submersible pump 120, an external pipe 130, an internal pipe 140, a solar panel 150, a thermal switch 160 and a back-up battery 170. The thermosyphon 100 differs from the thermosyphon 1 in the positioning of the submersible pump 120, and the direction of fluid low. In the thermosyphon 100, the submersible pump 120 is connected to the open bottom end 141 of the internal pipe 140. The submersible pump 120 is configured to pump fluid from a close and sealed bottom 131 of the external pipe 130 into the open bottom end 141 of the internal pipe 140, as shown by fluid flow 122. A flow 123 of warmer fluid from below ground ascends into a fluid chamber 111 of the heat exchanger 110 through the internal pipe 140, displacing colder fluid in the fluid chamber 111 , the colder fluid being forced to descend, as shown by fluid flow 121. Colder fluid descends from the heat exchanger 110 above the ground 2 into the external pipe 130 where the colder fluid descends below the ground 2 to absorb heat from the ground 2 through walls of the external pipe 130 thereby cooling the ground 2.

For both the thermosyphon 1 and the thermosyphon 100, circulation of antifreeze mixture through the coaxial pipes create a heat pump effect, which cools the subsurface (below ground) environment, thereby preventing further thaw and promoting permafrost regeneration.

The thermosyphons 1 and 100 were installed in the Scotty Creek basin, which is located approximately 50 km SE of Fort Simpson, Northwest Territories, Canada. The average annual temperature in the region is -3.2°C. (1964-2013). The average temperatures for July and January are 17.1 °C and -25.9°C, respectively. The Scotty Creek basin belongs to the continental climate zone and is situated in a region of discontinuous permafrost. Installation was done in a highly disturbed area of the 1985 seismic line. Removal of vegetation and soil compaction at this seismic line led to the loss of about 2.5 m of permafrost during last 30 years. The active layer, the seasonally frozen layer, at the experimental site varies from 50 to 60 cm. Thickness of talik, the perennially unfrozen layer, is about 2 m. The soil layer of interest is 100% saturated peat with a porosity of about 80%. Testing of performance was done during the winter of 2016-2017. The test site was equipped with temperature monitoring stations in August 2014. Both Case A (Fig. 1 , thermosyphon 1) and Case B (Fig. 2, thermosyphon 100) were tested. Case A was tested with just a 20 W solar panel. Case B was tested with a 20 W solar panel backed up with a 12V car battery. The pumps operated even under a cloudy sky without direct sunlight. The diurnal cycle is reflected in a slight increase in nightly temperatures, with a general trend of temperature decrease. The aluminum external pipe had a length of 3 m and a diameter of 75 mm. The maximum snow thickness for the experiment was about 50 cm. Thus, only 50 cm of the thermosyphon was exposed to open air. The thermosyphon was equipped with a low power consumption (0.8 W) submersible pump to circulate coolant. The outflow from the submersible pump was directed through a 12.5 mm diameter internal pipe to the bottom (case A) or the top (case B) of the thermosyphon. The operational rate of the pump was between 40 and 120 liters/hour, depending on the performance of the solar panel. As part of the heat exchanger, a 0.25-inch copper coil was installed in the upper part of thermosyphon to reinforce the cooling process (Case B). In Case A, the top of the aluminum external pipe acted as the heat exchanger. The power line was equipped with a mechanical thermal switch, which connected the power supply to the pump when air temperatures dropped below 0°C. Four thermistors T4, T5, T7, T8 were placed around the thermosyphon at various distances and depths, as illustrated in Fig. 3 and Table 1 . An additional thermistor TS5 was placed close to the bottom of the thermosyphon at a depth of 199 cm. Table 1

Fig. 4 demonstrates test results for Case B. As can be seen in Fig. 4, the soil in close proximity of the thermosyphon was frozen to an average temperature of about -3°C. Radius of freezing reached about 25 cm with an average temperature of about -0.5°C. It should be noted that only one thermosyphon was tested in this experiment. A cluster of thermosyphons can be expected to yield much better results.

Fig. 5 demonstrates the limited data that was available for Case A.

The experimental study demonstrated that a liquid-filled thermosyphon with forced circulation can be a cost-effective alternative to the traditional, two-phase passive thermosyphon. According to data obtained from the field experiment, the proposed thermosyphon can transfer sufficient thermal energy to freeze the saturated peat layer within a diameter of at least 50 cm around, even with a relatively short above-ground section. The low power consumption submersible pump can maintain a below 0°C temperature in the frozen layer throughout the cold season, while operating exclusively on a renewable energy source, such as a solar panel or a small wind turbine generator.

Fig. 6 depicts a cluster of six thermosyphons 1a, 1 b, 1c. 1d, 1e, 1f that were installed in 2015 in the illustrated pattern at the Scotty Creek basin, the Scotty Creek basin being the location as described above. The thermosyphons 1a, 1 b, 1c were positioned about 1 m away from an edge of the seismic line 90. Center-to-center separation of each thermosyphon 1a, 1 b, 1c. 1d, 1e, 1f with respect to their nearest neighbors was about 1 .0 m. Thus, the center-to-center separation of thermosyphon 1a from thermosyphon 1c and of thermosyphon 1c from thermosyphon 1e was about 2 m. The thermosyphons 1a, 1 b, 1c. 1d, 1e, 1f were equipped with thermistors TS10, TS11 , TS12, TS13, TS14, TS15, respectively, located close to the bottom of the corresponding thermosyphon at a depth of about 2 m. Eleven thermistor arrays T10, T11 , T12, T13, T14, T15, T16, T17, T18, T19, T20 were placed around the thermosyphons as illustrated in Fig. 6 at distances of about 0.75 m from the centers of nearest neighbor thermosyphons. Each of the thermistor arrays T10, T11 , T12, T13, T14, T15, T16, T17, T18, T19, T20 comprised three thermistors installed at approximate depths of 2.0 m, 1 .5 m and 1 .0 m below ground.

Initially in 2015, all six of the thermosyphons were simple air-filled tubes. However, as illustrated in Fig. 7 (left panel) and Fig. 8, the use of such air-filled tubes in the winter of 2015-2016 failed to freeze the ground (talik). In August 2016, the thermosyphon 1d was modified to be a thermosyphon constructed like the thermosyphon of Case B (Fig. 2, thermosyphon 100) powered with a 20 W solar panel backed up with a 12V car battery. As seen in Fig. 7 (left panel) and in Fig. 8, in the winter of 2016-2017 the cluster of thermosyphons now comprising one thermosyphon 1d constructed in accordance with the thermosyphon 100 of the present invention was capable of reducing the talik temperature immediately around the thermosyphon 1d below the freezing point of water, thereby successfully freezing the talik immediately around the thermosyphon 1d.

In 2017, the battery backup was removed from thermosyphon 1d and three of the other thermosyphons were modified into thermosyphons constructed in accordance with the thermosyphon of Case A (Fig. 1 , thermosyphon 1). The four modified thermosyphons were operated only with solar power. As seen in Fig. 7 (right panel) and in Fig. 8, in the winter of 2017-2018 the cluster of thermosyphons now comprising four thermosyphons, one constructed in accordance with the thermosyphon 100 and three constructed in accordance with the thermosyphon 1 , was capable of reducing the talik temperature around the thermosyphon cluster even lower than was accomplished with only one thermosyphon of the present invention.

It is further evident from Fig. 8, that without the use of a thermosyphon of the present invention (winter 2015-2016), the talik temperature could not be significantly lowered below 0°C. With the use of one thermosyphon of the present invention (winter 2016-2017), the talik temperature within a radius of 0.25 m around the thermosyphon 1d could be lowered to about -1 °C. With the use of four thermosyphons of the present invention (winter 2017-2018), the talik temperature within a radius of 0.25 m around the thermosyphon and around the thermistors interspersed between the thermosyphons could be lowered to about -2.5°C. The novel features will become apparent to those of skill in the art upon examination of the description. It should be understood, however, that the scope of the claims should not be limited by the embodiments, but should be given the broadest interpretation consistent with the wording of the claims and the specification as a whole.