RU75670U1 - SOIL VERTICAL PROBE - Google Patents

Abstract

The utility model relates to the field of technology for producing low-grade thermal energy from ground soil and can be used as a ground-type heat exchanger in instrumentation and technological schemes for producing low-potential thermal energy from ground through heat pumps.

The created design of the vertical soil probe is less dependent on the negative influence of the surface soil layer, which has a negative temperature in winter or in frozen conditions. The problem was solved by creating a soil probe design, consisting of two main elements: the main lower part, made of polyethylene pipes connected by a corner in the form of a U-sample, manufactured and lowered into place in the well; the upper part is made in the form of a polyethylene pipe of the same diameter with a thermo-hydroinsulating jacket to the depth of freezing of the soil, which is manufactured under production conditions and connected in place with the main part by electrothermal welding.

The practical value of the utility model is to increase the efficiency of the heat pump.

Description

The scope of the proposed utility model relates to techniques for producing low-grade thermal energy from soil through heat pumps. Soil vertical probe is a device used in hardware and technology circuits with heat pumps for heat extraction from the soil when the coolant circulates in them.

The main technical device of this scheme (Fig. 1) is a heat pump 1 that implements the process of transferring low-temperature thermal energy from heat soil to a higher temperature level. As a device for pumping heat from the earth, vertical soil probes (heat exchangers) 2 are used, through which a heat carrier circulates in a closed cycle, which is heated by the heat of the earth and which transfers heat to the heat pump for direct use. The coolant circulates through pipes (most often polyethylene or propylene) laid in vertical wells with a depth of 50 to 200 m. There are dozens of different probe designs that are sometimes very unusual (for example, in the form of pipes walled in the foundation piles of a house), but the most applicable are U-shaped and pipe in the pipe.

Usually two types of vertical soil heat exchangers are used (FIG. 1):

- U-shaped heat exchanger, which is 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 soil probes in Europe.

- coaxial (concentric) heat exchanger, which consists of two pipes of different diameters, one of which is located inside the other pipe due to the smaller diameter. Coaxial heat exchangers can be more complex configurations (figure 1).

An analysis of the current state of the technology of using soil probes made it possible to establish that the main attention in optimizing the heat transfer process from soil to

vertical soil probe [1, 2, 3] is given to the exclusion of air throughout the depth of the well. For this purpose, drilled wells with installed vertical soil probes are filled with clay solutions or their combination with concrete and cement to create homogeneity and reduce heat transfer resistance with equally close values of thermal conductivity. As studies in Germany and Switzerland showed [2], the task was achieved and the average value of the heat extracted by the soil probe was determined in the range of 30 ÷ 100 W per 1 m of the well depending on the soil structure (clay, sand, peat, humidity, etc. .).

Although at present in all developed countries the use of ground heat of the earth using vertical soil probes has become widespread, an analysis of the available data has allowed [2] to establish that the main volume of sales of heat pumps with soil probes is due to two circumstances:

1. the use of heat pumps with soil probes using the heat of the earth is typical for countries with a moderately mild climate, namely Spain, Greece, Italy, Germany and others, where it is concentrated up to 75 ° of the total volume.

2. In countries with a cold climate (Sweden, Norway, Russia, etc.), directions towards the use of heat using horizontal collectors (sea, sewage treated sewage) are predetermined.

It is clear that in both cases there is a sufficiently high efficiency due to a rather small difference in the user and initial temperatures, as well as minimal heat losses during the delivery of the heated coolant to the heat pump due to mild weather conditions.

In countries with a colder climate, accompanied by freezing of the surface layer of the earth to 1.5 ÷ 2 m, the use of vertical soil probes is complicated by the deterioration of heat transfer conditions from the bowels of the earth, namely, increased heat losses when the coolant passes through the frozen ground layer.

The studies and calculations show that in the soil zone with a minus temperature (of the order of -3 ° ÷ -5 ° C) adjacent to the earth's surface (up to 5 m), there are conditions for cooling the coolant that enters the soil probe through the surface layer from the heat pump and cooling the output heated coolant at 3-5 ° C as it passes through the same soil layer into the heat pump.

Reducing the temperature of the coolant supplied to the heat pump by 3-5 ° C determines, other things being equal, a decrease in the efficiency

heat pump, namely the increase in additional energy costs to achieve the same heat capacity or by reducing the power of the heat pump at the same operating costs.

As known solutions [4] that can eliminate the negative influence of the negative temperature of frozen soil on the temperature of the coolant, there may be:

- the device of wells made of reinforced concrete rings with a depth of 2 ÷ 3 m for thermal insulation of the output and input upper ends of soil probes (figure 2);

- creating a heat-insulating shell 4 on the upper part of the soil probes in the process of lowering the probes into the well (figure 3).

Practice shows that the costs in the construction, arrangement and operation of heat-insulating wells and trays (figure 2) are significant, which leads to additional capital and operating costs. In addition, when organizing heating of large-area (over 1000 m ² ) office-production premises with a small soil probe power (not more than 4-5 kW), the use of wells in order to reduce heat loss is problematic.

The option of installing a soil probe with the subsequent application of an insulating layer, which is used as a shell half-cylinder made of polyurethane foam, which are used, as a rule, for thermal insulation of pipelines, at the upper ends of the soil probe (Fig. 3), is closest to solving the task. Unfortunately, the manufacture of a heat-insulating shirt in place does not allow for high-quality insulation, which, as practice has shown, does not provide the required performance for thermal waterproofing due to poor-quality joining of the shirt with a polyethylene pipe and becomes unusable due to mechanical damage during the lowering of the probe. In addition, polyurethane shell half-cylinders, along with a low coefficient of thermal conductivity (not more than 0.028-0.045 W / ° C) are prone to partial absorption of moisture (up to 10% at the surface boundary), which in wet soil at a depth of up to 5.0 m Helps reduce heat transfer resistance.

The purpose of this utility model patent is to create a soil probe design that would be less dependent on the negative effects of the surface soil layer, especially in frozen ground and on technical decisions made on the spot during the installation of soil probes.

The problem is solved by creating conditions for maximum resistance to heat transfer in the system of the surface of the soil probe - soil (clay solution), which

It would make it possible to increase the temperatures of both the coolant at the probe outlet and at the entrance up to 5 m below the ground surface in the case of negative soil temperature by selecting (installing) a thermo-waterproofing jacket with higher thermal resistance coefficients and creating a unified design of a vertical soil probe.

To improve the quality of the heat-insulating shell and, accordingly, a more reliable design, an option is proposed when the soil probe is divided into 2 components, namely:

- the main (lower) part of the U-shaped probe from two high-pressure polyethylene pipes with a tip with a length depending on the depth of the well;

- a separate (upper) part of the same polyethylene pipes and a height of 3 to 5 m (exceeding the depth of freezing of the soil by 1.5 ÷ 2 m) and having bends for connection with the main part of the probe and the collector.

The joints of the heat-insulating jacket and the polyethylene pipe are sealed using heat-shrink sleeves. Quality is checked on site. The connection of the upper and lower (main) part of the probe is carried out on site using electric heat welding.

The subject of the application for a utility model is the creation of a soil probe design consisting of two components: the main one is the lower part made of polyethylene pipes connected by a corner in the form of a U-sample made and lowered in place; the upper part - made in the form of a thermo-waterproofing section (shirt) of a polyethylene pipe to a depth below the freezing of the soil, manufactured under industrial conditions, and which is connected in place with the main part by electric heat welding. In order to reduce heat loss and prevent swelling of thermal insulation, the use of thermal insulation materials is provided, which, in combination with the available indicators of the thermal conductivity (an order of magnitude less than the soil), have high rates of moisture penetration resistance coefficients. This can be tubular insulation based on foamed rubber (for example: Kaiflex ST) or thermal insulation made of polyurethane foam in a plastic film in a corrugated waterproof membrane. For such options for thermal insulation, the value of the thermal conductivity varies in the range of 0.02-0.03 W / ° C (at 10 ° C) and moisture penetration resistance from 3000 to 7000. In addition, the high quality of this thermal insulation is achieved by manufacturing it in production conditions and guaranteed by a remote control system

humidity. A flexible polyethylene double pipe with heat insulation made of polyurethane foam in a corrugated polyethylene sheath, the diameter of which is equal to the diameters of the pipes of the main part of the probe, can be used as the upper component. The design of the developed model of the soil probe is shown in (Figs. 4 and 5) and described in the application examples.

The practical value of the proposed utility model is confirmed by experiments on the installation of such soil probes in a heat station using a DS - 5017 heat pump in comparison with soil probes not protected by thermal insulation. An increase in the temperature of the coolant entering the heat pump was achieved by 3-4 ° C. The temperature of the heat carrier removed from the heat pump to the soil probe was correspondingly also higher by 3-4 ° С.

The advantages of the proposed utility model of a vertical soil probe is the following:

- unification of geothermal probes, as a result of which the quality and reliability of the product increases, the time for installing geothermal probes is reduced;

- the use of more waterproof materials that increase along with increased thermal insulation and resistance to moisture penetration;

- expansion of the geography of introducing heat pumps, in particular in the northern regions of the Russian Federation.

Example 1. In a drilled well ⌀ 140 mm and a depth of 70 m, a soil probe (Fig. 4) is lowered, consisting of the main part - a U-shaped pipe made of polyethylene ⌀ 40 mm (5) with a tip and a total height of 66 m, pre-filled with 30% solution of ethylene glycol in water. Upon reaching a depth of 65 m, a second element is welded to the upper ends of the lowered U-gage, which is similar polyethylene pipes with a diameter of 40 mm and a length of 4 m. Covered with a thermo-waterproof jacket made of polyurethane foam or foamed rubber (6) 20 mm thick and 3.5 m high protected on top by a plastic sheath. Shrink sleeves (7) are installed in the upper and lower parts of the thermal insulation jacket at the point of its contact with the pipe in order to prevent moisture from entering the thermal insulation layer of the jacket. A similar element is installed at both ends of the probe. The upper part of the probe is connected to the main (lower) part of the probe using electric heat welding, after which the soil probe is lowered to the required depth, and ethylene glycol solution is added to it. On the output sections of the probe

soft inserts are installed for the purpose of thermal condensation, which are flexible (corrugated) insulating sections of polyethylene pipes that reduce heat loss and take into account the change in probe height due to temperature changes (40 ÷ 50 cm) (figure 4).

The temperature of the heat carrier removed from the probe was + 3 ° С, instead of + -1 ° С, and that entering the earth (after the heat pump) was -1 ° С, instead of -4 ° С. The outdoor temperature is -15 ° С, the heat pump DS 5107. The calculation shows that the pump performance increased by 0.8 kW.

Example 2. Conditions similar to Example 1, except that the heat-insulating element is made in the form of a heat-insulating shirt with two polyethylene pipes (Fig. 5) of the same diameter as the main pipe of the soil probe. After lowering the main element of the soil probe, the heat-insulating element is connected immediately to both ends of the main element of the soil probe. Similarly, docking joints are protected. The difference is that the thermal insulation and thermal compensation is provided by a corrugated 2-pipe thermal insulation from polyurethane foam.

It was found that during the operation of the DS 5107.3 heat pump at an external air temperature of -15 ° С, the temperature of the heat carrier introduced into the heat pump was +3, 4 ° C instead of -1 ° C, and after the heat pump the heat carrier entering the soil probe had a temperature of 0 , 2 ° C, instead of -3.6 ° C. At the same time, the pump capacity for thermal energy increased by 1.0 kW.

Bibliography:

1. "More on the principles of operation of heat pumps" Renewable Energy Center. www.energy-center.ru

2. The use of low-potential thermal energy of the earth in heat pump systems. G.P. Vasiliev, N.V. Shilkin. AVOK Magazine No. 2, 2003.

3. Guidance on the use of heat pumps using secondary energy resources and alternative renewable energy sources. Lusk. Architecture. State Unitary Enterprise "NIAC", 2001.

4. Heat pumps. Comfort technology Stiebel Eltron, TCP / Haqer, Deutschland, 37601 Holzminden. Page 59-66.

Claims (1)

A vertical soil probe lowered into the well to extract low potential heat from the ground, made in the form of a U-shaped polyethylene pipe, which circulates the coolant from the ground to the heat pump and vice versa, characterized in that it consists of two components joined together by electrothermal welding : the lower main part is made in the form of a U-shaped pipe, and the upper part is in the form of a section of pipes coated to the depth of freezing of the soil with a thermo-waterproofing jacket made of polyurethane foam or foam rubber, protected from above with a polyethylene sheath, the upper and lower edges of which are sealed with a polyethylene pipe by heat-shrink cuffs.