Natural circulation evaporator for water supply pipes for distributed geothermal collection

Abstract

The main claims include two structural types of natural circulation evaporators for water supply pipelines, both of which enable expanded functionality, thereby allowing for the decentralized harvesting of near-surface geothermal energy contained in the water supply in a renewable manner. This includes both applications on existing pipelines and new applications using composite pipelines. Thus, low-temperature geothermal energy can be provided to heat pumps in heat-consuming buildings adjacent to the pipelines, from which the heat pumps then generate high-temperature effective heat.

Description

Technical Field

[0001] This invention relates to two structural types of natural circulation evaporators for water supply pipelines, both of which expand functionality and enable decentralized harvesting of near-surface geothermal energy contained in the water supply in a renewable manner. This includes applications on existing pipelines as well as new applications using composite pipelines. Thus, low-temperature geothermal energy can be provided to heat pumps in heat-consuming buildings adjacent to the pipelines, from which the heat pumps then generate high-temperature effective heat. Background Technology

[0002] The prior art is documented in the following patent documents:

[0003] It is known from DE 10 2007 054472 A1 that heat can be collected from a water supply pipe using a heat exchanger inside the pipe. In contrast, in this invention, such a heat exchanger, in the form of an evaporator-heat transferor, is arranged outside the water supply pipe.

[0004] DE 10 2013 000213 A1 describes a heat exchanger for electronic components, which is constructed as an open-pore metal body through which a single-phase liquid or gaseous temperature-controlled fluid flows, wherein the single-phase circulating volume flow rate is regulated by means of a pump or valve as forced convection. In contrast, in this invention, spontaneous two-phase liquid / gas natural circulation is generated in an evaporator-heat transferor made of a porous, permeable solid. Furthermore, the heat transfer process from turbulent liquid flow (water supply) to a two-phase single-component heat transfer fluid is fundamentally different from the heat transfer process from a solid (electronic device) to a single-phase heat transfer fluid.

[0005] According to DE 20 2008 017 571 U1, a tubular hollow profile is spirally wrapped along its outer surface through hollow profile channels, wherein the hollow profile channels are configured as heat exchangers through which heat transfer fluid flows. In contrast, in this invention, hollow profile channels are not used within the evaporator-heat transfer body; instead, a porous, permeable solid is used.

[0006] As can be seen from DE 27 47 356 A1, heat is extracted from stagnant surface water and groundwater surrounding a packed bed thermal storage tank (sump) via heat exchanger coils located in an open casing. In contrast, in this invention, heat transfer is achieved using a porous, permeable solid inside the evaporator-heat transfer body.

[0007] DE 10 2006 001 169 A1 describes a method for improving heat harvesting from near-surface geothermal energy based on water infiltration. For this purpose, a geothermal exchange device in the form of a known horizontal coil collector is used, which is installed in the soil beneath a sewage pipe. In contrast, in this invention, heat harvesting is achieved using a porous, permeable evaporator-heat transferor on a water supply pipe.

[0008] According to EP 2 223 020 B1, a method for harvesting geothermal energy from a water supply network is known, in which a portion of the water volumetric flow rate is diverted via a bypass pipe parallel to the main pipe and flows through a heat exchanger tank connected thereto. Metal pipes are installed in the tank, through which liquid refrigerant flows downwards and evaporates according to the heat pipe principle, while refrigerant gas rises in the same pipe, thereby enabling natural refrigerant circulation between the evaporator and the heat pump via a single connecting pipe. However, due to space limitations of the bypass pipes and the limited amount of heat energy that can be harvested from the portion of the flow rate, some practical problems still exist. Summary of the Invention

[0009] The object of this invention is to solve the corresponding problem by providing a particularly advantageous, technically feasible, functionally suitable, and quality-safe implementation scheme for drinking water supply.

[0010] This objective is achieved through the features of the two independent main claims.

[0011] A natural circulation evaporator for use in existing pipelines of a water supply network, as a functional extension of decentralized geothermal energy harvesting, is characterized by:

[0012] • The evaporator-free compartment is located inside the water supply pipe.

[0013] • The existing water supply pipeline, buried in the soil, is segmented and enclosed by two similar evaporator-type semi-shell heat transfer bodies. These two semi-shell heat transfer bodies are interconnected via their vertically arranged boundary surfaces and are thermally coupled to the existing pipeline.

[0014] • The evaporator's semi-shell heat transfer elements are integrally molded from a porous, permeable solid with good thermal conductivity (preferably open-cell metal foam). Each element is hydraulically sealed and pressure-resistant through its surrounding walls.

[0015] • The surrounding wall is made of a solid material (preferably solid metal) with good thermal conductivity, which completely and firmly fills the pore structure of the porous, permeable solid in its edge regions, thereby forming a high degree of thermal coupling through a large contact inner surface.

[0016] • In the permeable pore space of the evaporator semi-shell heat transfer body, a single-component heat transfer fluid, preferably carbon dioxide (R744), is formed due to numerous nucleation sites and bubble dynamics. This fluid flows spontaneously in a two-phase natural circulation, where simultaneously, the liquid phase flows in from below under gravity and transforms into vapor, while the gas phase rises due to density-buoyancy and flows out from the top as gas.

[0017] • Due to the convective water flow, heat conduction through the pipe walls, surrounding walls, and the solid matrix of the evaporator-heat transfer body, and the resulting temperature gradient, the geothermal energy stored in the supply water is transferred to a cooler heat-carrying fluid circulating in the pore spaces of a porous, permeable solid.

[0018] • Convection heat transfer is achieved through building connection pipes (consisting of gas riser and liquid return pipes) for the heat-carrying fluid, utilizing natural circulation, between the lower evaporator shell heat transfer body and the decentralized heat pump in the heat-consuming building located above and adjacent to the water supply pipes.

[0019] Specifically, the natural circulation evaporator is constructed in such a way that no heat exchanger is located inside the existing piping, but rather the evaporator's semi-shell heat transfer body (which can be constructed as described above) is always located outside the existing piping. This means that there is no need to structurally alter these pipes. In particular, there are no compartments (also called chambers, cavities, or zones) for heat transfer inside the existing piping.

[0020] A natural circulation evaporator integrated into a composite pipeline designed as a new pipeline for water supply and decentralized geothermal extraction, characterized in that...

[0021] • Evaporator-free compartments are located inside the water supply compartments, and vice versa.

[0022] • The composite pipeline laid in the soil consists of an external pipeline for water supply and transportation and an internal heat transfer element in an evaporator for the circulation of heat-carrying fluid.

[0023] • The external piping consists of an outer wall with good thermal conductivity, an inner wall with good thermal conductivity (equivalent to an enclosing wall), and spacers.

[0024] • The heat transfer medium inside the evaporator is composed of a porous, permeable solid (preferably open-cell metal foam), which is tightly sealed by surrounding walls and divided into equidistant longitudinal internal sections by vertical partition walls with good thermal conductivity and hydraulic sealing.

[0025] • The surrounding wall is made of a solid material (preferably solid metal) with good thermal conductivity, which completely and firmly fills the pore structure of the porous, permeable solid in its edge regions, thereby forming a high degree of thermal coupling through a large contact inner surface.

[0026] • Within the permeable pore space of the heat transfer medium inside the evaporator, a single-component heat transfer fluid, preferably carbon dioxide (R744), is formed due to numerous nucleation sites and bubble dynamics. This fluid flows spontaneously in a two-phase natural circulation, where simultaneously, the liquid phase flows in from below under gravity and transforms into vapor, while the gas phase rises due to density-buoyancy and flows out from the top as gas.

[0027] • Due to the convective water flow, thermal conduction through the surrounding walls and the solid matrix of the evaporator-heat transfer medium, and the resulting temperature gradient, the geothermal energy stored in the water supply is transferred to a cooler heat transfer fluid circulating in the pore spaces of the porous, permeable solid.

[0028] • Convection heat transfer is achieved through building connection piping (consisting of a gas riser and a liquid return pipe) for the heat transfer fluid, utilizing natural circulation, between the heat transfer medium inside the evaporator and a decentralized heat pump in the heat-consuming building adjacent to the water supply piping.

[0029] • Connect the building's water-consuming pipes to the external connections of the composite pipe system.

[0030] The ecological and economic advantages achieved through this invention are relevant to energy and climate transition. There is significant market potential for upgrading to a combined water supply and geothermal harvesting network. This can be achieved directly at the heat-consuming building site by adding to existing piping or by new construction / segmental replacement. Therefore, the composite piping forms the basis of an innovative mesh-like network that simultaneously enables the transport, distribution, development, transfer, extraction, and sustainable regeneration of low-temperature geothermal energy. This, in turn, makes the production of emission-free, decentralized, and independent high-temperature usable heat possible when using climate-neutral heat pump electricity.

[0031] Compared to district heating networks, central fossil-free heat sources and pipeline laying can significantly save on investment and operating costs, as well as planning and construction time.

[0032] Other advantages include high efficiency and the resulting energy savings, as well as high inlet water temperatures in the heating circuit, which are essential for applications in older, unrenovated buildings (i.e., using existing radiators without insulation) and for domestic hot water preparation (at least 60°C) generally required for hygiene reasons (Legionella). Here, the annual duty cycle (JAZ) is significant, as it is used in conjunction with the heat source to evaluate the heat pump. Even in the colder winter months, due to the constant high soil temperature of approximately 10°C to 14°C, this coefficient is significantly higher when using the geothermal source according to the invention (JAZ approximately 4-5) than when using ambient air (-3°C to 3°C) as the heat source (JAZ approximately 2-2.5). Furthermore, the one- to two-month time lag between the negative peak of the air temperature (maximum heat consumption) and the temporally delayed negative peak of the geothermal temperature has a positive impact, ensuring that the supply water temperature remains relatively high in the coldest winter months, and its slight decrease at the end of winter is no longer significant because the air temperature has already risen. Air source heat pumps are at a disadvantage due to low temperature levels, as technological optimization is limited from a physico-thermodynamic perspective. Therefore, using this equipment in older, unmodified buildings during cold winter weather is uneconomical due to its high power consumption. Furthermore, especially in urban areas, the placement of outdoor units presents challenges related to space requirements, aesthetics, and noise pollution.

[0033] Geothermal sources are also superior to using open water bodies as central heat sources, such as seawater, river water, and lake water, as well as raw water and stored water. These require integration with a central high-temperature large-scale heat pump and a high-temperature district heating network with inlet and outlet pipes. The extremely low water temperatures during the cold winter months (approximately -3°C to 3°C, similar to air temperature), the additional energy consumption for operating the district heating network pumps (other than those driven by heat pumps), heat losses during district heating distribution, and the limited amount of heat extraction power result in an inefficient annual duty cycle of approximately 2.5-3. Attached Figure Description

[0034] The present invention will now be explained in more detail with reference to the embodiments and the accompanying drawings.

[0035] in:

[0036] Figure 1 A schematic structure of a natural circulation evaporator for existing piping is shown in cross-sectional view; and

[0037] Figure 2 A schematic structure of a natural circulation evaporator integrated into a composite pipeline designed as a new pipeline is shown in cross-section. Detailed Implementation

[0038] according to Figure 1The existing water supply pipe 1, buried in the soil and transporting water (e.g., composed of cast iron pipe walls 5), is enclosed and thermally coupled by two identical, integrated, prefabricated evaporator semi-shell heat transfer bodies 2. The interiors of these semi-shells are each composed of a porous, permeable solid 3 (e.g., metal foam), which is completely sealed by an enclosure wall 4 (e.g., solid metal). As geothermal energy is transferred from the hotter water supply to the heat transfer bodies, the cooler heat transfer fluid (e.g., carbon dioxide) contained in the porous, permeable metal foam evaporates, thus forming a spontaneous convective two-phase natural circulation. Here, starting from the heat pump located above in the heated building, the heat transfer fluid in liquid phase 6a is simultaneously fed into the evaporator via the return pipe 7b under gravity through two lower ports, where it is converted into steam 6b, and returns to the heat pump in gas phase 6c due to density-buoyancy through the two upper ports and riser pipe 7a.

[0039] according to Figure 2 Inside the coaxial composite pipe system, hotter water is transported in the annular outer pipe 8, while colder heat transfer fluid is transported in the heat transfer medium 10 inside the central evaporator within a two-phase natural circulation system (e.g., Figure 1 The external conduit includes an outer wall 9 and an inner wall (equivalent to the surrounding wall 4) and a single spacer 11 between the two walls. A building connection pipe 12 for consuming water is implemented via a connection to the external conduit.

[0040] List of reference numerals

[0041] 1. Existing water supply pipelines

[0042] 2. Evaporator semi-shell heat transfer element

[0043] 3 Porous permeable solids

[0044] 4. Evaporator - Surrounding wall of heat transfer element

[0045] 5 Existing pipe wall

[0046] 6a Liquid phase of heat transfer fluid

[0047] 6b Steam of heat transfer fluid

[0048] 6c heat transfer fluid gas phase

[0049] 7a Gas riser pipe for heat transfer fluid building interface

[0050] 7b Liquid return pipe for heat transfer fluid building interface

[0051] 8 External pipes for water supply

[0052] 9. The outer wall of the external pipe

[0053] 10 Evaporator Internal Heat Transfer Element

[0054] 11 Spacers in external pipes

[0055] 12 Building connection pipes for water consumption

Claims

1. A natural circulation evaporator for use in existing pipelines of a water supply network, serving as a functional extension of decentralized geothermal energy harvesting, characterized in that: a) The evaporator compartment is located outside the water supply pipe. b) An existing water supply pipeline (1) buried in the soil is segmented and enclosed by two similar evaporator semi-shell heat transfer bodies (2), which are interconnected via a boundary surface and thermally coupled to the existing pipeline. c) The evaporator semi-shell heat transfer element (2) is integrally formed from a porous, permeable solid (3) with good thermal conductivity. Each of the evaporator semi-shell heat transfer elements achieves hydraulic sealing and pressure-resistant sealing through an enclosing wall (4). d) The surrounding wall (4) is made of a solid material with good thermal conductivity, which completely and firmly fills the pore structure of the porous permeable solid (3) in its edge region, thereby forming a high degree of thermal coupling through a large contact inner surface. e) In the permeable pore space of the evaporator semi-shell heat transfer body (2), a single-component heat transfer fluid is formed due to a large number of nucleation points and bubble dynamics, which flows spontaneously as a two-phase natural circulation. At the same time, the liquid phase (6a) flows in from below under the action of gravity and is converted into steam (6b), while the gas phase rises due to density-buoyancy and flows out from the top as gas (6c). f) Due to the convective water flow, the heat conduction of the solid matrix of the pipe wall (5), the surrounding wall (4), and the evaporator-heat transfer body, and the resulting temperature gradient, the geothermal energy stored in the water supply is transferred to a cooler heat-carrying fluid circulating in the pore space of the porous permeable solid, and g) Convection heat transfer is formed between the lower evaporator shell heat transfer body (2) and the distributed heat pump in the heat-using building located above and adjacent to the water supply pipe via a building connection pipe consisting of a gas riser pipe (7a) and a liquid return pipe (7b) for the heat-carrying fluid, by means of natural circulation.

2. A natural circulation evaporator integrated into a composite pipeline designed as a new pipeline for water supply and decentralized geothermal extraction, characterized in that, a) The evaporator compartment is located outside the water supply compartment, and vice versa. b) The composite pipeline buried in the soil consists of an external pipeline (8) for water supply and transportation and an internal heat transfer element (11) for heat transfer fluid circulation. c) The external pipe is composed of an outer wall (9) with good thermal conductivity, an inner wall equivalent to the surrounding wall (4) with good thermal conductivity, and a spacer (11). d) The heat transfer medium (10) inside the evaporator is composed of a porous, permeable solid (3) with good thermal conductivity. The solid is tightly sealed by the surrounding wall (4) and divided into equidistant longitudinal internal sections by hydraulically sealed vertical partition walls. e) The surrounding wall (4) is made of a solid material with good thermal conductivity, which completely and firmly fills the pore structure of the porous permeable solid in its edge region, thereby forming a high degree of thermal coupling through a large contact inner surface. f) A single-component heat transfer fluid is formed in the permeable pore space of the heat transfer medium inside the evaporator due to a large number of nucleation sites and bubble dynamics. It flows spontaneously as a two-phase natural circulation, wherein simultaneously, the liquid phase (6a) flows in from below under the action of gravity and is converted into steam (6b), and the gas phase rises due to density-buoyancy and flows out from the top as gas (6c). g) Due to the convective water flow, the thermal conduction of the solid matrix of the surrounding wall (4) and the evaporator-heat transfer body, and the resulting temperature gradient, the geothermal energy stored in the water supply is transferred to a cooler heat-carrying fluid circulating in the pore space of the porous permeable solid, and h) Through the building connection pipe for the heat-carrying fluid, consisting of the gas riser pipe (7a) and the liquid return pipe (7b), convective heat transfer is formed between the heat transfer medium inside the evaporator and the decentralized heat pump in the heat-consuming building adjacent to the water supply pipe by means of natural circulation, and i) Connect the building connection pipes used for consuming water (12) to the external connection of the composite pipes.

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