This might seem like fantasy if it weren't true. It turns out that in harsh Siberian conditions, you can get heat directly from the ground. The first objects from geothermal systems heating appeared in the Tomsk region last year, and although they can reduce the cost of heat by about four times compared to traditional sources, there is still no mass circulation "under the ground". But the trend is noticeable and, most importantly, it is gaining momentum. In fact, this is the most affordable alternative energy source for Siberia, where solar panels or wind generators, for example, cannot always show their effectiveness. Geothermal energy, in fact, just lies under our feet.

“The depth of soil freezing is 2–2.5 meters. The ground temperature below this mark remains the same both in winter and in summer, ranging from plus one to plus five degrees Celsius. Job heat pump built on this property, - says the power engineer of the education department of the administration of the Tomsk region Roman Alekseenko. - Connecting pipes are buried in the earth contour to a depth of 2.5 meters, at a distance of about one and a half meters from each other. A coolant - ethylene glycol - circulates in the pipe system. The external horizontal earth circuit communicates with the refrigeration unit, in which the refrigerant - freon, a gas with a low boiling point, circulates. At plus three degrees Celsius, this gas begins to boil, and when the compressor sharply compresses the boiling gas, the temperature of the latter rises to plus 50 degrees Celsius. The heated gas is sent to a heat exchanger in which ordinary distilled water circulates. The liquid heats up and spreads heat throughout the heating system laid in the floor.

Pure physics and no miracles

A kindergarten equipped with a modern Danish geothermal heating system was opened in the village of Turuntaevo near Tomsk last summer. According to the director of the Tomsk company Ecoclimat George Granin, the energy-efficient system allowed several times to reduce the payment for heat supply. For eight years, this Tomsk enterprise has already equipped about two hundred objects in different regions of Russia with geothermal heating systems and continues to do so in the Tomsk region. So there is no doubt in the words of Granin. A year before the opening of a kindergarten in Turuntaevo, Ecoclimat equipped a geothermal heating system, which cost 13 million rubles, another kindergarten"Sunny Bunny" in the microdistrict of Tomsk "Green Hills". In fact, it was the first experience of its kind. And he was quite successful.

Back in 2012, during a visit to Denmark, organized under the program of the Euro Info Correspondence Center (EICC-Tomsk region), the company managed to agree on cooperation with the Danish company Danfoss. And today, Danish equipment helps to extract heat from the Tomsk bowels, and, as experts say without too much modesty, it turns out quite efficiently. The main indicator of efficiency is economy. “The heating system for a 250-square-meter kindergarten building in Turuntayevo cost 1.9 million rubles,” says Granin. “And the heating fee is 20-25 thousand rubles a year.” This amount is incomparable with the one that the kindergarten would pay for heat using traditional sources.

The system worked without problems in the conditions of the Siberian winter. A calculation was made of the compliance of thermal equipment with SanPiN standards, according to which it must maintain a temperature of at least + 19 ° C in the kindergarten building at an outdoor air temperature of -40 ° C. In total, about four million rubles were spent on redevelopment, repair and re-equipment of the building. Together with the heat pump, the amount was just under six million. Thanks to heat pumps today, kindergarten heating is a completely isolated and independent system. There are no traditional batteries in the building now, and the space is heated using the “warm floor” system.

Turuntayevsky kindergarten is insulated, as they say, “from” and “to” - additional thermal insulation is equipped in the building: a 10-cm layer of insulation equivalent to two or three bricks is installed on top of the existing wall (three bricks thick). Behind the insulation is an air gap, followed by metal siding. The roof is insulated in the same way. The main attention of the builders was focused on the "warm floor" - the heating system of the building. It turned out several layers: a concrete floor, a layer of foam plastic 50 mm thick, a system of pipes in which hot water circulates and linoleum. Although the temperature of the water in the heat exchanger can reach +50°C, the maximum heating of the actual floor covering does not exceed +30°C. The actual temperature of each room can be adjusted manually - automatic sensors allow you to set the floor temperature in such a way that the kindergarten room warms up to the required temperature. sanitary standards degrees.

The power of the pump in the Turuntayevsky garden is 40 kW of generated thermal energy, for the production of which the heat pump requires 10 kW of electrical power. Thus, out of 1 kW consumed electrical energy The heat pump produces 4 kW of heat. “We were a little afraid of winter - we did not know how heat pumps would behave. But even in very coldy it was consistently warm in the kindergarten - from plus 18 to 23 degrees Celsius, - says the director of the Turuntaevskaya high school Evgeny Belonogov. - Of course, here it is worth considering that the building itself was well insulated. The equipment is unpretentious in maintenance, and despite the fact that this is a Western development, it proved to be quite effective in our harsh Siberian conditions.”

A comprehensive project for the exchange of experience in the field of resource conservation was implemented by the EICC-Tomsk region of the Tomsk Chamber of Commerce and Industry. Its participants were small and medium-sized enterprises that develop and implement resource-saving technologies. In May last year, Danish experts visited Tomsk as part of a Russian-Danish project, and the result was, as they say, obvious.

Innovation comes to school

A new school in the village of Vershinino, Tomsk region, built by a farmer Mikhail Kolpakov, is the third facility in the region that uses the heat of the earth as a source of heat for heating and hot water supply. The school is also unique because it has the highest energy efficiency category - "A". The heating system was designed and launched by the same Ecoclimat company.

“When we were deciding what kind of heating to install in the school, we had several options - a coal-fired boiler house and heat pumps,” says Mikhail Kolpakov. - We studied the experience of an energy-efficient kindergarten in Zeleny Gorki and calculated that heating in the old fashioned way, on coal, will cost us more than 1.2 million rubles per winter, and we also need hot water. And with heat pumps, the cost will be about 170 thousand for the whole year, along with hot water.”

The system needs only electricity to produce heat. Consuming 1 kW of electricity, heat pumps in a school produce about 7 kW of thermal energy. In addition, unlike coal and gas, the heat of the earth is a self-renewable source of energy. Installation of a modern heating system The school cost about 10 million rubles. For this, 28 wells were drilled on the school grounds.

“The arithmetic here is simple. We calculated that the maintenance of the coal boiler, taking into account the salary of the stoker and the cost of fuel, will cost more than a million rubles a year, - notes the head of the education department Sergey Efimov. - When using heat pumps, you will have to pay for all resources about fifteen thousand rubles a month. The undoubted advantages of using heat pumps are their efficiency and environmental friendliness. The heat supply system allows you to regulate the heat supply depending on the weather outside, which eliminates the so-called "underheating" or "overheating" of the room.

According to preliminary calculations, expensive Danish equipment will pay for itself in four to five years. The service life of Danfoss heat pumps, with which Ecoclimat LLC works, is 50 years. Receiving information about the air temperature outside, the computer determines when to heat the school, and when it is possible not to do so. Therefore, the question of the date of switching on and off the heating disappears altogether. Regardless of the weather, climate control will always work outside the windows inside the school for children.

“When the Ambassador Extraordinary and Plenipotentiary of the Kingdom of Denmark came to the all-Russian meeting last year and visited our kindergarten in Zeleniye Gorki, he was pleasantly surprised that those technologies that are considered innovative even in Copenhagen are applied and work in the Tomsk region, - says the commercial director of Ecoclimat Alexander Granin.

In general, the use of local renewable energy sources in various sectors of the economy, in this case in social sphere, which includes schools and kindergartens, is one of the main areas implemented in the region as part of the program for energy saving and energy efficiency. The development of renewable energy is actively supported by the governor of the region Sergey Zhvachkin. And three budget institutions with a geothermal heating system - only the first steps towards the implementation of a large and promising project.

The kindergarten in Zelenye Gorki was recognized as the best energy-efficient facility in Russia at a competition in Skolkovo. Then came the Vershininskaya school with geothermal heating, also of the highest category of energy efficiency. The next object, no less significant for the Tomsk region, is a kindergarten in Turuntaevo. This year, the Gazhimstroyinvest and Stroygarant companies have already begun construction of kindergartens for 80 and 60 children in the villages of the Tomsk region, Kopylovo and Kandinka, respectively. Both new facilities will be heated by geothermal heating systems - from heat pumps. In total, this year the district administration intends to spend almost 205 million rubles on the construction of new kindergartens and the repair of existing ones. It is planned to reconstruct and re-equip the building for a kindergarten in the village of Takhtamyshevo. In this building, heating will also be implemented by means of heat pumps, since the system has proved itself well.

Kirill Degtyarev, Researcher, Moscow State University them. M. V. Lomonosov.

In our country, rich in hydrocarbons, geothermal energy is a kind of exotic resource that, in the current state of affairs, is unlikely to compete with oil and gas. Nevertheless, this alternative form of energy can be used almost everywhere and quite efficiently.

Photo by Igor Konstantinov.

Change in soil temperature with depth.

Temperature increase of thermal waters and dry rocks containing them with depth.

Change in temperature with depth in different regions.

The eruption of the Icelandic volcano Eyjafjallajökull is an illustration of violent volcanic processes occurring in active tectonic and volcanic zones with a powerful heat flow from the earth's interior.

Installed capacities of geothermal power plants by countries of the world, MW.

Distribution of geothermal resources on the territory of Russia. The reserves of geothermal energy, according to experts, are several times higher than the energy reserves of organic fossil fuels. According to the Geothermal Energy Society Association.

Geothermal energy is the heat of the earth's interior. It is produced in the depths and comes to the surface of the Earth in different forms and with different intensities.

The temperature of the upper layers of the soil depends mainly on external (exogenous) factors - sunlight and air temperature. In summer and during the day, the soil warms up to certain depths, and in winter and at night it cools down following the change in air temperature and with some delay, increasing with depth. The influence of daily fluctuations in air temperature ends at depths from a few to several tens of centimeters. Seasonal fluctuations capture deeper layers of soil - up to tens of meters.

At a certain depth - from tens to hundreds of meters - the temperature of the soil is kept constant, equal to the average annual air temperature near the Earth's surface. This is easy to verify by going down into a fairly deep cave.

When the average annual air temperature in a given area is below zero, this manifests itself as permafrost (more precisely, permafrost). In Eastern Siberia, the thickness, that is, the thickness, of year-round frozen soils reaches 200-300 m in places.

From a certain depth (its own for each point on the map), the effect of the Sun and the atmosphere weakens so much that endogenous (internal) factors come first and the earth's interior is heated from the inside, so that the temperature begins to rise with depth.

The heating of the deep layers of the Earth is associated mainly with the decay of the radioactive elements located there, although other sources of heat are also named, for example, physicochemical, tectonic processes in the deep layers of the earth's crust and mantle. But whatever the cause, the temperature of rocks and associated liquid and gaseous substances increases with depth. Miners face this phenomenon - it is always hot in deep mines. At a depth of 1 km, thirty-degree heat is normal, and deeper the temperature is even higher.

The heat flow of the earth's interior, reaching the surface of the Earth, is small - on average, its power is 0.03-0.05 W / m 2,
or about 350 Wh/m 2 per year. Against the background of the heat flux from the Sun and the air heated by it, this is an imperceptible value: the Sun gives each square meter earth's surface about 4,000 kWh annually, that is, 10,000 times more (of course, this is an average, with a huge spread between polar and equatorial latitudes and depending on other climatic and weather factors).

The insignificance of the heat flow from the depths to the surface in most of the planet is associated with the low thermal conductivity of rocks and the peculiarities of the geological structure. But there are exceptions - places where the heat flow is high. These are, first of all, zones of tectonic faults, increased seismic activity and volcanism, where the energy of the earth's interior finds a way out. Such zones are characterized by thermal anomalies of the lithosphere, here the heat flow reaching the Earth's surface can be many times and even orders of magnitude more powerful than the "usual" one. A huge amount of heat is brought to the surface in these zones by volcanic eruptions and hot springs of water.

It is these areas that are most favorable for the development of geothermal energy. On the territory of Russia, these are, first of all, Kamchatka, the Kuril Islands and the Caucasus.

At the same time, the development of geothermal energy is possible almost everywhere, since the increase in temperature with depth is a ubiquitous phenomenon, and the task is to “extract” heat from the bowels, just as mineral raw materials are extracted from there.

On average, the temperature increases with depth by 2.5-3 o C for every 100 m. The ratio of the temperature difference between two points lying at different depths to the difference in depth between them is called the geothermal gradient.

The reciprocal is the geothermal step, or the depth interval at which the temperature rises by 1 o C.

The higher the gradient and, accordingly, the lower the step, the closer the heat of the Earth's depths approaches the surface and the more promising this area is for the development of geothermal energy.

In different areas, depending on the geological structure and other regional and local conditions, the rate of temperature increase with depth can vary dramatically. On the scale of the Earth, fluctuations in the values ​​of geothermal gradients and steps reach 25 times. For example, in the state of Oregon (USA) the gradient is 150 o C per 1 km, and in South Africa - 6 o C per 1 km.

The question is, what is the temperature at great depths - 5, 10 km or more? If the trend continues, the temperature at a depth of 10 km should average about 250-300 ° C. This is more or less confirmed by direct observations in ultra-deep wells, although the picture is much more complicated than a linear increase in temperature.

For example, in the Kola superdeep well drilled in the Baltic crystalline shield, the temperature changes at a rate of 10 o C / 1 km to a depth of 3 km, and then the geothermal gradient becomes 2-2.5 times greater. At a depth of 7 km, a temperature of 120 o C was already recorded, at 10 km - 180 o C, and at 12 km - 220 o C.

Another example is a well laid in the Northern Caspian, where at a depth of 500 m a temperature of 42 o C was recorded, at 1.5 km - 70 o C, at 2 km - 80 o C, at 3 km - 108 o C.

It is assumed that the geothermal gradient decreases starting from a depth of 20-30 km: at a depth of 100 km, the estimated temperatures are about 1300-1500 o C, at a depth of 400 km - 1600 o C, in the Earth's core (depths of more than 6000 km) - 4000-5000 o WITH.

At depths up to 10-12 km, the temperature is measured through drilled wells; where they do not exist, it is determined by indirect signs in the same way as at greater depths. Such indirect signs may be the nature of the passage of seismic waves or the temperature of the erupting lava.

However, for the purposes of geothermal energy, data on temperatures at depths of more than 10 km are not yet of practical interest.

There is a lot of heat at depths of several kilometers, but how to raise it? Sometimes nature itself solves this problem for us with the help of a natural coolant - heated thermal waters that come to the surface or lie at a depth accessible to us. In some cases, the water in the depths is heated to the state of steam.

There is no strict definition of the concept of "thermal waters". As a rule, they mean hot groundwater in a liquid state or in the form of steam, including those that come to the Earth's surface with a temperature above 20 ° C, that is, as a rule, higher than the air temperature.

Warm groundwater, steam, steam-water mixtures - this is hydrothermal energy. Accordingly, energy based on its use is called hydrothermal.

The situation is more complicated with the production of heat directly from dry rocks - petrothermal energy, especially since sufficiently high temperatures, as a rule, begin from depths of several kilometers.

On the territory of Russia, the potential of petrothermal energy is a hundred times higher than that of hydrothermal energy - 3,500 and 35 trillion tons of standard fuel, respectively. This is quite natural - the warmth of the Earth's depths is everywhere, and thermal waters are found locally. However, due to obvious technical difficulties, most of the thermal waters are currently used to generate heat and electricity.

Waters with temperatures from 20-30 to 100 o C are suitable for heating, temperatures from 150 o C and above - and for generating electricity at geothermal power plants.

In general, geothermal resources on the territory of Russia, in terms of tons of reference fuel or any other unit of energy measurement, are approximately 10 times higher than fossil fuel reserves.

Theoretically, only geothermal energy could fully meet the energy needs of the country. Practically on this moment in most of its territory, this is not feasible for technical and economic reasons.

In the world, the use of geothermal energy is most often associated with Iceland - a country located at the northern end of the Mid-Atlantic Ridge, in an extremely active tectonic and volcanic zone. Probably everyone remembers the powerful eruption of the Eyjafjallajökull volcano in 2010.

It is thanks to this geological specificity that Iceland has huge reserves of geothermal energy, including hot springs that come to the surface of the Earth and even gushing in the form of geysers.

In Iceland, more than 60% of all energy consumed is currently taken from the Earth. Including due to geothermal sources, 90% of heating and 30% of electricity generation are provided. We add that the rest of the electricity in the country is produced by hydroelectric power plants, that is, also using a renewable energy source, thanks to which Iceland looks like a kind of global environmental standard.

The "taming" of geothermal energy in the 20th century helped Iceland significantly in economic terms. Until the middle of the last century, it was a very poor country, now it ranks first in the world in terms of installed capacity and production of geothermal energy per capita, and is in the top ten in terms of absolute installed capacity of geothermal power plants. However, its population is only 300 thousand people, which simplifies the task of switching to environmentally friendly energy sources: the need for it is generally small.

In addition to Iceland, a high share of geothermal energy in the total balance of electricity generation is provided by New Zealand and the island states of Southeast Asia (Philippines and Indonesia), countries Central America and East Africa, whose territory is also characterized by high seismic and volcanic activity. For these countries, at their current level of development and needs, geothermal energy makes a significant contribution to socio-economic development.

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To model temperature fields and for other calculations, it is necessary to know the soil temperature at a given depth.

The temperature of the soil at depth is measured using exhaust soil-deep thermometers. These are planned studies that are carried out regularly. meteorological stations. Research data serve as the basis for climate atlases and regulatory documentation.

To obtain the soil temperature at a given depth, you can try, for example, two simple ways. Both methods are based on the use of reference literature:

1. For an approximate determination of temperature, you can use the document TsPI-22. "Transitions railways pipelines." Here, within the framework of the methodology for the heat engineering calculation of pipelines, Table 1 is given, where for certain climatic regions, soil temperatures are given depending on the depth of measurement. I present this table below.

Table 1

1. Table of soil temperatures at various depths from a source "to help a gas industry worker" from the times of the USSR

Normative freezing depths for some cities:

The depth of soil freezing depends on the type of soil:

I think the easiest option is to use the reference data above and then interpolate.

The most reliable option for accurate calculations using ground temperatures is to use data from the meteorological services. On the basis of meteorological services, some online directories work. For example, http://www.atlas-yakutia.ru/.

Here it is enough to choose locality, type of soil and you can get a temperature map of the soil or its data in tabular form. In principle, it is convenient, but it seems that this resource is paid.

If you know more ways to determine the soil temperature at a given depth, then please write comments.

You may be interested in the following material:

temperature inside the earth. The determination of the temperature in the Earth's shells is based on various, often indirect, data. The most reliable temperature data refer to the uppermost part of the earth's crust, which is exposed by mines and boreholes to a maximum depth of 12 km (Kola well).

The increase in temperature in degrees Celsius per unit of depth is called geothermal gradient, and the depth in meters, during which the temperature increases by 1 0 C - geothermal step. The geothermal gradient and, accordingly, the geothermal step vary from place to place depending on the geological conditions, endogenous activity in different areas, as well as the heterogeneous thermal conductivity of rocks. At the same time, according to B. Gutenberg, the limits of fluctuations differ by more than 25 times. An example of this are two sharply different gradients: 1) 150 o per 1 km in Oregon (USA), 2) 6 o per 1 km registered in South Africa. According to these geothermal gradients, the geothermal step also changes from 6.67 m in the first case to 167 m in the second. The most common fluctuations in the gradient are within 20-50 o , and the geothermal step is 15-45 m. The average geothermal gradient has long been taken at 30 o C per 1 km.

According to VN Zharkov, the geothermal gradient near the Earth's surface is estimated at 20 o C per 1 km. Based on these two values ​​of the geothermal gradient and its invariance deep into the Earth, then at a depth of 100 km there should have been a temperature of 3000 or 2000 o C. However, this is at odds with the actual data. It is at these depths that magma chambers periodically originate, from which lava is poured onto the surface, having maximum temperature 1200-1250 o. Considering this kind of "thermometer", a number of authors (V. A. Lyubimov, V. A. Magnitsky) believe that at a depth of 100 km the temperature cannot exceed 1300-1500 o C.

At higher temperatures, the mantle rocks would be completely melted, which contradicts the free passage of transverse seismic waves. Thus, the average geothermal gradient can be traced only to some relatively small depth from the surface (20-30 km), and then it should decrease. But even in this case, in the same place, the change in temperature with depth is not uniform. This can be seen in the example of temperature change with depth along the Kola well located within the stable crystalline shield of the platform. When laying this well, a geothermal gradient of 10 o per 1 km was expected and, therefore, at the design depth (15 km) a temperature of the order of 150 o C was expected. However, such a gradient was only up to a depth of 3 km, and then it began to increase by 1.5 -2.0 times. At a depth of 7 km the temperature was 120 o C, at 10 km -180 o C, at 12 km -220 o C. It is assumed that at the design depth the temperature will be close to 280 o C. Caspian region, in the area of ​​more active endogenous regime. In it, at a depth of 500 m, the temperature turned out to be 42.2 o C, at 1500 m - 69.9 o C, at 2000 m - 80.4 o C, at 3000 m - 108.3 o C.

What is the temperature in the deeper zones of the mantle and core of the Earth? More or less reliable data have been obtained on the temperature of the base of the B layer in the upper mantle (see Fig. 1.6). According to V. N. Zharkov, "detailed studies of the phase diagram of Mg 2 SiO 4 - Fe 2 Si0 4 made it possible to determine the reference temperature at a depth corresponding to the first zone of phase transitions (400 km)" (i.e., the transition of olivine to spinel). The temperature here as a result of these studies is about 1600 50 o C.

The question of the distribution of temperatures in the mantle below layer B and in the Earth's core has not yet been resolved, and therefore various views are expressed. It can only be assumed that the temperature increases with depth with a significant decrease in the geothermal gradient and an increase in the geothermal step. It is assumed that the temperature in the Earth's core is in the range of 4000-5000 o C.

Average chemical composition Earth. To judge the chemical composition of the Earth, data on meteorites are used, which are the most probable samples of protoplanetary material from which the terrestrial planets and asteroids were formed. To date, many meteorites that have fallen to Earth at different times and in different places have been well studied. According to the composition, three types of meteorites are distinguished: 1) iron, consisting mainly of nickel iron (90-91% Fe), with a small admixture of phosphorus and cobalt; 2) iron-stone(siderolites), consisting of iron and silicate minerals; 3) stone, or aerolites, consisting mainly of ferruginous-magnesian silicates and inclusions of nickel iron.

The most common are stone meteorites - about 92.7% of all finds, stony iron 1.3% and iron 5.6%. Stone meteorites are divided into two groups: a) chondrites with small rounded grains - chondrules (90%); b) achondrites that do not contain chondrules. The composition of stony meteorites is close to that of ultramafic igneous rocks. According to M. Bott, they contain about 12% iron-nickel phase.

Based on the analysis of the composition of various meteorites, as well as the obtained experimental geochemical and geophysical data, a number of researchers give a modern estimate of the gross elemental composition of the Earth, presented in Table. 1.3.

As can be seen from the data in the table, the increased distribution refers to the four most important elements - O, Fe, Si, Mg, constituting over 91%. The group of less common elements includes Ni, S, Ca, A1. Other elements periodic system Mendeleev on a global scale in terms of general distribution are of secondary importance. If we compare the given data with the composition of the earth's crust, we can clearly see a significant difference consisting in a sharp decrease in O, Al, Si and a significant increase in Fe, Mg and the appearance of S and Ni in noticeable amounts.

The shape of the earth is called the geoid. The deep structure of the Earth is judged by longitudinal and transverse seismic waves, which, propagating inside the Earth, experience refraction, reflection and attenuation, which indicates the stratification of the Earth. There are three main areas:

Earth's crust;

mantle: upper to a depth of 900 km, lower to a depth of 2900 km;

the core of the Earth is outer to a depth of 5120 km, inner to a depth of 6371 km.

The internal heat of the Earth is associated with the decay of radioactive elements - uranium, thorium, potassium, rubidium, etc. The average value of the heat flux is 1.4-1.5 μkal / cm 2. s.

1. What is the shape and size of the Earth?

2. What are the methods for studying the internal structure of the Earth?

3. What is the internal structure of the Earth?

4. What seismic sections of the first order are clearly distinguished when analyzing the structure of the Earth?

5. What are the boundaries of the sections of Mohorovic and Gutenberg?

6. What is the average density of the Earth and how does it change at the boundary between the mantle and the core?

7. How does the heat flow change in different zones? How is the change in geothermal gradient and geothermal step understood?

8. What data is used to determine the average chemical composition of the Earth?

Literature

• Voytkevich G.V. Fundamentals of the theory of the origin of the Earth. M., 1988.

• Zharkov V.N. Internal structure of the Earth and planets. M., 1978.

• Magnitsky V.A. Internal structure and physics of the Earth. M., 1965.

• Essays comparative planetology. M., 1981.

• Ringwood A.E. Composition and origin of the Earth. M., 1981.

"Use of low-potential thermal energy of the earth in heat pump systems"

Vasiliev G.P., Scientific director OJSC INSOLAR-INVEST, Doctor of Technical Sciences, Chairman of the Board of Directors of OJSC INSOLAR-INVEST
N. V. Shilkin, engineer, NIISF (Moscow)

Rational use of fuel and energy resources today is one of the global world problems, the successful solution of which, apparently, will be of decisive importance not only for the further development of the world community, but also for the conservation of its habitat. One of the promising ways to solve this problem is application of new energy-saving technologies using non-traditional renewable energy sources (NRES) The depletion of traditional fossil fuels and the environmental consequences of burning them have led to a significant increase in interest in these technologies in almost all countries in recent decades. developed countries peace.

The advantages of heat supply technologies that use in comparison with their traditional counterparts are associated not only with significant reductions in energy costs in the life support systems of buildings and structures, but also with their environmental friendliness, as well as new opportunities in the field of increasing the degree of autonomy of life support systems. Apparently, in the near future, it is these qualities that will be of decisive importance in shaping a competitive situation in the heat generating equipment market.

Analysis of possible areas of application in the Russian economy of energy saving technologies using non-traditional energy sources, shows that in Russia the most promising area for their implementation is the life support systems of buildings. At the same time, the widespread use of heat pump heat supply systems (TST), using the soil of the surface layers of the Earth as a ubiquitously available low-potential heat source.

Using Earth's heat There are two types of thermal energy - high-potential and low-potential. The source of high-potential thermal energy is hydrothermal resources - thermal waters heated to a high temperature as a result of geological processes, which allows them to be used for heat supply to buildings. However, the use of high-potential heat of the Earth is limited to areas with certain geological parameters. In Russia, this is, for example, Kamchatka, the region of the Caucasian mineral waters; in Europe, there are sources of high-potential heat in Hungary, Iceland and France.

In contrast to the "direct" use of high-potential heat (hydrothermal resources), use of low-grade heat of the Earth through heat pumps is possible almost everywhere. It is currently one of the fastest growing areas of use non-traditional renewable energy sources.

Low-potential heat of the Earth can be used in various types of buildings and structures in many ways: for heating, hot water supply, air conditioning (cooling), heating paths in the winter season, for preventing icing, heating fields in outdoor stadiums, etc. In the English-language technical literature, such systems are designated as "GHP" - "geothermal heat pumps", geothermal heat pumps.

The climatic characteristics of the countries of Central and Northern Europe, which, together with the United States and Canada, are the main areas for the use of low-grade heat of the Earth, determine mainly the need for heating; cooling of the air, even in summer, is relatively rarely required. Therefore, unlike the United States, heat pumps in European countries they operate mainly in heating mode. IN THE USA heat pumps are more often used in air heating systems combined with ventilation, which allows both heating and cooling the outside air. In European countries heat pumps commonly used in water heating systems. Because the heat pump efficiency increases with a decrease in the temperature difference between the evaporator and condenser, floor heating systems are often used for heating buildings, in which a coolant of a relatively low temperature (35–40 °C) circulates.

Majority heat pumps in Europe, designed to use the low-grade heat of the Earth, are equipped with electrically driven compressors.

Over the past ten years, the number of systems that use the low-grade heat of the Earth for heat and cold supply of buildings through heat pumps, increased significantly. The largest number of such systems is used in the USA. A large number of such systems operate in Canada and the countries of central and northern Europe: Austria, Germany, Sweden and Switzerland. Switzerland leads in the use of low-grade thermal energy of the Earth per capita. In Russia, over the past ten years, using technology and with the participation of INSOLAR-INVEST OJSC, which specializes in this area, only a few objects have been built, the most interesting of which are presented in.

In Moscow, in the Nikulino-2 microdistrict, in fact, for the first time, a hot water heat pump system multi-storey residential building. This project was implemented in 1998–2002 by the Ministry of Defense of the Russian Federation jointly with the Government of Moscow, the Ministry of Industry and Science of Russia, the NP ABOK Association and within the framework of "Long-term energy saving program in Moscow".

As a low-potential source of thermal energy for the evaporators of heat pumps, the heat of the soil of the surface layers of the Earth, as well as the heat of the removed ventilation air, is used. The hot water preparation plant is located in the basement of the building. It includes the following main elements:

• vapor compression heat pump installations (HPU);
• hot water storage tanks;
• systems for collecting low-grade thermal energy of the soil and low-grade heat of removed ventilation air;
• circulation pumps, instrumentation

The main heat-exchange element of the system for collecting low-grade ground heat is vertical coaxial ground heat exchangers located outside along the perimeter of the building. These heat exchangers are 8 wells with a depth of 32 to 35 m each, arranged near the house. Since the operating mode of heat pumps using the warmth of the earth and the heat of the removed air is constant, while the consumption of hot water is variable, the hot water supply system is equipped with storage tanks.

Data estimating the world level of use of low-potential thermal energy of the Earth by means of heat pumps are given in the table.

Table 1. World level of use of low-potential thermal energy of the Earth through heat pumps

Soil as a source of low-potential thermal energy

As a source of low-potential thermal energy, groundwater with a relatively low temperature or soil of the surface (up to 400 m deep) layers of the Earth can be used.. The heat content of the soil mass is generally higher. The thermal regime of the soil of the surface layers of the Earth is formed under the influence of two main factors - the solar radiation incident on the surface and the flow of radiogenic heat from the earth's interior. Seasonal and daily changes in the intensity of solar radiation and outdoor temperature cause fluctuations in the temperature of the upper layers of the soil. The depth of penetration of daily fluctuations in the temperature of the outside air and the intensity of the incident solar radiation, depending on the specific soil and climatic conditions, ranges from several tens of centimeters to one and a half meters. The depth of penetration of seasonal fluctuations in the temperature of the outside air and the intensity of the incident solar radiation does not, as a rule, exceed 15–20 m.

The temperature regime of soil layers located below this depth (“neutral zone”) is formed under the influence of thermal energy coming from the bowels of the Earth and practically does not depend on seasonal, and even more so daily changes in outdoor climate parameters (Fig. 1).

Rice. 1. Graph of changes in soil temperature depending on depth

With increasing depth, the temperature of the soil increases in accordance with the geothermal gradient (approximately 3 degrees C for every 100 m). The magnitude of the flux of radiogenic heat coming from the bowels of the earth varies for different localities. For Central Europe this value is 0.05–0.12 W/m2.

During the operational period, the soil mass located within the zone of thermal influence of the register of pipes of the soil heat exchanger of the system for collecting low-grade ground heat (heat collection system), due to seasonal changes in the parameters of the outdoor climate, as well as under the influence of operational loads on the heat collection system, as a rule, is subjected to repeated freezing and defrosting. At the same time, naturally, there is a change state of aggregation moisture contained in the pores of the soil and located in the general case both in the liquid, and in the solid and gaseous phases at the same time. In other words, the soil massif of the heat collection system, regardless of what state it is in (frozen or thawed), is a complex three-phase polydisperse heterogeneous system, the skeleton of which is formed by a huge number of solid particles of various shapes and sizes and can be both rigid and and mobile, depending on whether the particles are firmly bound together or whether they are separated from each other by a substance in the mobile phase. Interstices between solid particles can be filled with mineralized moisture, gas, steam and ice, or both. Modeling the processes of heat and mass transfer that form the thermal regime of such a multicomponent system is an extremely difficult task, since it requires taking into account and mathematical description of various mechanisms for their implementation: heat conduction in an individual particle, heat transfer from one particle to another upon their contact, molecular heat conduction in a medium filling gaps between particles, convection of steam and moisture contained in the pore space, and many others.

Special attention should be paid to the influence of soil mass moisture and moisture migration in its pore space on thermal processes that determine soil characteristics as a source of low-potential thermal energy.

In capillary-porous systems, which is the soil mass of the heat collection system, the presence of moisture in the pore space has a significant effect on the process of heat distribution. Correct accounting of this influence today is associated with significant difficulties, which are primarily associated with the lack of clear ideas about the nature of the distribution of solid, liquid and gaseous phases of moisture in a particular structure of the system. The nature of the forces of moisture bonding with skeletal particles, the dependence of the forms of moisture bonding with the material at various stages of moistening, and the mechanism of moisture movement in the pore space have not yet been elucidated.

If there is a temperature gradient in the thickness of the soil mass, the vapor molecules move to places with a lower temperature potential, but at the same time, under the action of gravitational forces, an oppositely directed flow of moisture in the liquid phase occurs. In addition, moisture affects the temperature regime of the upper layers of the soil. precipitation as well as groundwater.

The main factors under the influence of which are formed temperature regime soil mass collection systems for low-potential soil heat are shown in fig. 2.

Rice. 2. Factors under the influence of which the temperature regime of the soil is formed

Types of systems for the use of low-potential thermal energy of the Earth

Ground heat exchangers connect heat pump equipment with soil mass. In addition to "extracting" the heat of the Earth, ground heat exchangers can also be used to accumulate heat (or cold) in the ground massif.

In the general case, two types of systems for the use of low-potential thermal energy of the Earth can be distinguished:

• open systems: as a source of low-potential thermal energy, groundwater is used, which is supplied directly to heat pumps;
• closed systems: heat exchangers are located in the soil massif; when a coolant circulates through them with a temperature lowered relative to the ground, thermal energy is “selected” from the ground and transferred to the evaporator heat pump(or, when using a coolant with an elevated temperature relative to the ground, its cooling).

The main part of open systems is wells, which allow extracting groundwater from aquifers of the soil and returning water back to the same aquifers. Usually paired wells are arranged for this. A diagram of such a system is shown in fig. 3.

Rice. 3. Scheme of an open system for the use of low-potential thermal energy of groundwater

The advantage of open systems is the possibility of obtaining a large amount of thermal energy at relatively low cost. However, wells require maintenance. In addition, the use of such systems is not possible in all areas. The main requirements for soil and groundwater are as follows:

• sufficient permeability of the soil, allowing replenishment of water reserves;
• good groundwater chemistry (e.g. low iron content) to avoid pipe scale and corrosion problems.

Open systems are more often used for heating or cooling large buildings. The world's largest geothermal heat pump system uses groundwater as a source of low-potential thermal energy. This system is located in the USA in Louisville, Kentucky. The system is used for heat and cold supply of a hotel-office complex; its power is about 10 MW.

Sometimes systems that use the heat of the Earth include systems for using low-grade heat from open water bodies, natural and artificial. This approach is adopted, in particular, in the United States. Systems using low-grade heat from reservoirs are classified as open, as are systems using low-grade heat from groundwater.

Closed systems, in turn, are divided into horizontal and vertical.

Horizontal ground heat exchanger(in English literature, the terms “ground heat collector” and “horizontal loop” are also used) is usually arranged near the house at a shallow depth (but below the level of soil freezing in winter). The use of horizontal ground heat exchangers is limited by the size of the available site.

In the countries of Western and Central Europe, horizontal ground heat exchangers are usually separate pipes laid relatively tightly and connected to each other in series or in parallel (Fig. 4a, 4b). To save site area, improved types of heat exchangers have been developed, for example, heat exchangers in the form of a spiral, located horizontally or vertically (Fig. 4e, 4f). This form of heat exchangers is common in the USA.

Rice. 4. Types of horizontal ground heat exchangers
a - a heat exchanger of series-connected pipes;
b - heat exchanger from parallel pipes;
c - a horizontal collector laid in a trench;
d - heat exchanger in the form of a loop;
e - a heat exchanger in the form of a spiral located horizontally (the so-called "slinky" collector;
e - a heat exchanger in the form of a spiral located vertically

If a system with horizontal heat exchangers is used only to generate heat, its normal operation is possible only if there is sufficient heat input from the earth's surface due to solar radiation. For this reason, the surface above the heat exchangers must be exposed to sunlight.

Vertical ground heat exchangers(in English literature, the designation "BHE" - "borehole heat exchanger" is accepted) allow the use of low-potential thermal energy of the soil mass lying below the "neutral zone" (10–20 m from ground level). Systems with vertical ground heat exchangers do not require large areas and do not depend on the intensity of solar radiation falling on the surface. Vertical ground heat exchangers work effectively in almost all types of geological environments, with the exception of soils with low thermal conductivity, such as dry sand or dry gravel. Systems with vertical ground heat exchangers are very widespread.

The scheme of heating and hot water supply of a single-apartment residential building by means of a heat pump unit with a vertical ground heat exchanger is shown in fig. 5.

Rice. 5. Scheme of heating and hot water supply of a single-apartment residential building by means of a heat pump unit with a vertical ground heat exchanger

The coolant circulates through pipes (most often polyethylene or polypropylene) laid in vertical wells from 50 to 200 m deep. Two types of vertical ground heat exchangers are usually used (Fig. 6):

• U-shaped heat exchanger, which are two parallel pipes connected at the bottom. One or two (rarely three) pairs of such pipes are located in one well. The advantage of such a scheme is the relatively low manufacturing cost. Double U-shaped heat exchangers are the most widely used type of vertical ground heat exchangers in Europe.
• Coaxial (concentric) heat exchanger. The simplest coaxial heat exchanger consists of two pipes of different diameters. A smaller diameter pipe is placed inside another pipe. Coaxial heat exchangers can be of more complex configurations.

Rice. 6. Section various types vertical ground heat exchangers

To increase the efficiency of heat exchangers, the space between the walls of the well and the pipes is filled with special heat-conducting materials.

Systems with vertical ground heat exchangers can be used to heat and cool buildings of various sizes. For a small building, one heat exchanger is enough; for large buildings, a whole group of wells with vertical heat exchangers may be required. The largest number of wells in the world is used in the heating and cooling system of Richard Stockton College in the US state of New Jersey. The vertical ground heat exchangers of this college are located in 400 wells 130 m deep. In Europe, the largest number of wells (154 wells 70 m deep) are used in the heating and cooling system of the central office of the German Air Traffic Control Service (“Deutsche Flug-sicherung”).

A special case of vertical closed systems is the use of building structures as soil heat exchangers, for example, foundation piles with embedded pipelines. The section of such a pile with three contours of a soil heat exchanger is shown in fig. 7.

Rice. 7. Scheme of ground heat exchangers embedded in the foundation piles of the building and the cross section of such a pile

The ground mass (in the case of vertical ground heat exchangers) and building structures with ground heat exchangers can be used not only as a source, but also as a natural accumulator of thermal energy or "cold", for example, solar radiation heat.

There are systems that cannot be clearly classified as open or closed. For example, the same deep (from 100 to 450 m deep) well filled with water can be both production and injection. The diameter of the well is usually 15 cm. A pump is placed in the lower part of the well, through which water from the well is supplied to the evaporators of the heat pump. Return water returns to the top of the water column in the same well. There is a constant recharge of the well with groundwater, and the open system works like a closed one. Systems of this type in the English literature are called "standing column well system" (Fig. 8).

Rice. 8. Scheme of the well type "standing column well"

Typically, wells of this type are also used to supply the building with drinking water.. However, such a system can only work effectively in soils that provide a constant supply of water to the well, which prevents it from freezing. If the aquifer is too deep, a powerful pump will be required for the normal functioning of the system, requiring increased energy costs. The large depth of the well causes a rather high cost of such systems, so they are not used for heat and cold supply of small buildings. Now there are several such systems in the world in the USA, Germany and Europe.

One of the promising areas is the use of water from mines and tunnels as a source of low-grade thermal energy. The temperature of this water is constant throughout the year. Water from mines and tunnels is readily available.

"Sustainability" of systems for the use of low-grade heat of the Earth

During the operation of the soil heat exchanger, a situation may arise when during the heating season the temperature of the soil near the soil heat exchanger decreases, and in the summer the soil does not have time to warm up to the initial temperature - its temperature potential decreases. Energy consumption during the next heating season causes an even greater decrease in the temperature of the soil, and its temperature potential is further reduced. This forces system design use of low-grade heat of the Earth consider the problem of "stability" (sustainability) of such systems. Often, energy resources are used very intensively to reduce the payback period of equipment, which can lead to their rapid depletion. Therefore, it is necessary to maintain such a level of energy production that would allow exploiting the source of energy resources. long time. This ability of systems to maintain the required level of heat production for a long time is called “sustainability”. For systems using low-potential Earth's heat the following definition of stability is given: “For each system of using the low-potential heat of the Earth and for each mode of operation of this system, there is some maximum level energy production; energy production below this level can be maintained for a long time (100–300 years).”

Held in OJSC INSOLAR-INVEST studies have shown that the consumption of thermal energy from the soil mass by the end of the heating season causes a decrease in soil temperature near the register of pipes of the heat collection system, which, under the soil and climatic conditions of most of the territory of Russia, does not have time to compensate in the summer season, and by the beginning of the next heating season, the soil comes out with low temperature potential. The consumption of thermal energy during the next heating season causes a further decrease in the temperature of the soil, and by the beginning of the third heating season, its temperature potential differs even more from the natural one. And so on. However, the envelopes of the thermal influence of long-term operation of the heat collection system on the natural temperature regime of the soil have a pronounced exponential character, and by the fifth year of operation, the soil enters a new regime close to periodic, that is, starting from the fifth year of operation, long-term consumption of thermal energy from the soil mass the heat collection system is accompanied by periodic changes in its temperature. Thus, when designing heat pump heating systems it seems necessary to take into account the drop in temperatures of the soil massif, caused by the long-term operation of the heat collection system, and use the temperatures of the soil massif expected for the 5th year of operation of the TST as design parameters.

In combined systems, used for both heat and cold supply, the heat balance is set “automatically”: in winter (heat supply is required), the soil mass is cooled, in summer (cold supply is required), the soil mass is heated. In systems using low-grade groundwater heat, there is a constant replenishment of water reserves due to water seeping from the surface and water coming from deeper layers of the soil. Thus, the heat content of groundwater increases both "from above" (due to the heat of atmospheric air) and "from below" (due to the heat of the Earth); the value of heat gain "from above" and "from below" depends on the thickness and depth of the aquifer. Due to these heat transfers, the groundwater temperature remains constant throughout the season and changes little during operation.

In systems with vertical ground heat exchangers, the situation is different. When heat is removed, the temperature of the soil around the soil heat exchanger decreases. The decrease in temperature is affected by both the design features of the heat exchanger and the mode of its operation. For example, in systems with high heat dissipation values ​​(several tens of watts per meter of heat exchanger length) or in systems with a ground heat exchanger located in soil with low thermal conductivity (for example, in dry sand or dry gravel), the temperature decrease will be especially noticeable and can lead to to freezing of the soil mass around the soil heat exchanger.

German experts measured the temperature of the soil massif, in which a vertical soil heat exchanger with a depth of 50 m, located near Frankfurt am Main, is arranged. For this, 9 wells of the same depth were drilled around the main well at a distance of 2.5, 5 and 10 m. In all ten wells, temperature sensors were installed every 2 m - a total of 240 sensors. On fig. Figure 9 shows diagrams showing the temperature distribution in the soil mass around the vertical soil heat exchanger at the beginning and at the end of the first heating season. At the end of the heating season, a decrease in the temperature of the soil mass around the heat exchanger is clearly visible. There is a heat flow directed to the heat exchanger from the surrounding soil mass, which partially compensates for the decrease in soil temperature caused by the "selection" of heat. The magnitude of this flux compared with the magnitude of the heat flux from the earth's interior in a given area (80–100 mW/sq.m) is estimated quite high (several watts per square meter).

Rice. Fig. 9. Schemes of temperature distribution in the soil mass around the vertical soil heat exchanger at the beginning and at the end of the first heating season

Since vertical heat exchangers began to become relatively widespread approximately 15–20 years ago, there is a lack of experimental data all over the world obtained during long-term (several tens of years) operation periods of systems with heat exchangers of this type. The question arises about the stability of these systems, about their reliability for long periods of operation. Is the low-potential heat of the Earth a renewable energy source? What is the period of "renewal" of this source?

When operating a rural school in Yaroslavl region equipped heat pump system, using a vertical ground heat exchanger, the average values ​​of specific heat removal were at the level of 120–190 W/rm. m length of the heat exchanger.

Since 1986, research has been carried out in Switzerland near Zurich on a system with vertical ground heat exchangers. A vertical ground heat exchanger of a coaxial type with a depth of 105 m was arranged in the soil massif. This heat exchanger was used as a source of low-grade thermal energy for a heat pump system installed in a single-family residential building. The vertical ground heat exchanger provided a peak power of approximately 70 watts per meter of length, which created a significant thermal load on the surrounding ground mass. The annual production of thermal energy is about 13 MWh

At a distance of 0.5 and 1 m from the main well, two additional wells were drilled, in which temperature sensors were installed at a depth of 1, 2, 5, 10, 20, 35, 50, 65, 85 and 105 m, after which the wells were filled clay-cement mixture. The temperature was measured every thirty minutes. In addition to the ground temperature, other parameters were recorded: the speed of the coolant, the energy consumption of the heat pump compressor drive, the air temperature, etc.

The first observation period lasted from 1986 to 1991. The measurements showed that the influence of the heat of the outside air and solar radiation is noted in the surface layer of the soil at a depth of up to 15 m. Below this level, the thermal regime of the soil is formed mainly due to the heat of the earth's interior. During the first 2-3 years of operation ground mass temperature, surrounding the vertical heat exchanger, dropped sharply, but every year the decrease in temperature decreased, and after a few years the system reached a regime close to constant, when the temperature of the soil mass around the heat exchanger became lower than the initial one by 1–2 °C.

In the fall of 1996, ten years after the start of operation of the system, the measurements were resumed. These measurements showed that the ground temperature did not change significantly. In subsequent years, slight fluctuations in ground temperature were recorded within 0.5 degrees C, depending on the annual heating load. Thus, the system entered a quasi-stationary regime after the first few years of operation.

Based on the experimental data, mathematical models of the processes taking place in the soil massif were built, which made it possible to make a long-term forecast of changes in the temperature of the soil massif.

Mathematical modeling has shown that the annual temperature decrease will gradually decrease, and the volume of the soil mass around the heat exchanger, subject to temperature decrease, will increase every year. At the end of the operating period, the regeneration process begins: the temperature of the soil begins to rise. The nature of the regeneration process is similar to the nature of the process of "selection" of heat: in the first years of operation, a sharp increase in soil temperature occurs, and in subsequent years, the rate of temperature increase decreases. The length of the “regeneration” period depends on the length of the operating period. These two periods are about the same. In this case, the period of operation of the ground heat exchanger was thirty years, and the period of "regeneration" is also estimated at thirty years.

Thus, the heating and cooling systems of buildings, using the low-grade heat of the Earth, are a reliable source of energy that can be used everywhere. This source can be used for quite a long time, and can be renewed at the end of the operating period.

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