US20070137236A1

US20070137236A1 - Ground heat exchanger

Info

Publication number: US20070137236A1
Application number: US11/638,967
Authority: US
Inventors: Krzysztof Cwik
Original assignee: Individual
Current assignee: Individual
Priority date: 2005-12-14
Filing date: 2006-12-13
Publication date: 2007-06-21
Also published as: LT1798509T; EP1798509A3; EP1798509A2; EP1798509B1

Abstract

The invention relates to a ground heat exchanger utilizing the geothermal energy of the ground, comprising pipe conduits and channels mounted within a support structure. According to the invention, a layer of air-permeable materials is formed on the virgin soil (1), horizontally and/or at a small inclination angle relative to the horizontal direction, creating a circulation channel (9) of the exchanger, the channel being confined by a support slab (14) with spacer elements (11) coupled with a construction net (8) seated onto a stabilizing net (7), the whole structure being covered by an insulating layer (19). Furthermore, the heat exchanger is equipped with a collector of the process air having an appropriate shape.

Description

The invention relates to a ground heat exchanger utilizing the geothermal energy of the ground in which the heat exchanger is seated at a certain depth. The heat exchanger may constitute an element of a ventilation system of an apartment or office/factory building, in which a collector directs the process air to the ventilation system of the building.
From Polish patent application No. 119749 one knows a cooling/heating device employing the heat energy of the ground for cooling or heating the air. The device comprises vertical air intakes made in the ground, preferably in the form of wells. Lower ends of the wells are connected to a collecting chamber via conduits seated in a layer of the ground, or via a layer of the ground having small flow resistance and good thermal conductivity. The collector of the exchanger is composed from conduits with circular cross-section, laid in a layer of the ground and also connected to the collecting chamber. The collecting chamber is connected to a technological device, such as an air-cooled liquefier, cooler of water, an air-conditioning or ventilation device.
The cited invention allows for significant energy savings, particularly during periods of maximum or minimum temperature of the atmospheric air.
Another embodiment of a system for heating and ventilation of a building is known from PCT/SE95/00569. According to that invention, a building has a peripheral foundation wall or has peripheral foundation beams, on which external wall and the floor of the building rest, the floor defining the residential floor areas in the building. A room is situated below the floor within the contour of the foundations. Openings or apertures—circulation conduits are made in the floor, through which air of desired parameters is circulated from the room below the floor to dwellings of the building. An air chamber is located below the floor slab, the air chamber being connected to the conduit directing the air. The chamber is closed with a membrane in a form of a tight barrier made from a plastic material. The membrane is seated on a porous layer, which is air-permeable, the layer having a form of a gravel prime coat and being situated at least on the portion of the support area of the ground below the foundation wall.
The invention relates to a ground heat exchanger, in which a stabilizing layer of a material with good thermal conductivity is formed in the virgin soil, the layer being located horizontally or at a small angle relative to the horizontal direction. The layer of the material has a form of a gravel prime coat and/or a square stone prime coat, which is filled with sand to increase the contact area with the air. The layer creates a circulation channel of the exchanger with the support slab. The slab has spacer elements, which are coupled with the construction net seated onto the stabilizing net, which covers the layer of the air-permeable material. The air intake and the exhaust channel have encased temperature, humidity, flow rate sensors and other necessary measuring devices. The whole structure, except to the contour of the intake and the exhaust channel, is covered with an insulating layer, preferably made from foamed polystyrene.
The collector of the heat exchanger according to the invention, directing the process air, comprises generally a plane of the flow of the process air and an air-distributing element. The cross-section of the element has a form of a sector confined by any curve, preferably it is a circular sector or any other geometric figure. The element is confined by a support point on the side of the process air inlet, while its opposite point is a bear point. The element is made from a metal or another material, preferably from polypropylene and/or a thermoplastic material. The longitudinal section of the element has any shape, however its modular length depends on acceptable technological parameters of the following air. The foundation slab with openwork apertures and/or the stabilizing net seated onto the gravel prime coat defines the airflow plane.
In so encased space, the spatial position of the element, with mutual position of the points relative to the airflow plane, is of fundamental importance for obtained technological and strength properties.
According to the invention, the support point is situated above the airflow plane or in the airflow plane, while the bear point is seated above the airflow plane, and another bear point is seated in the said airflow plane, and also, as the third possibility, the bear point is positioned below the airflow plane.
The optimal position of the element is if the support point is positioned in the airflow plane. An appropriate number of open and/or closed channels, having appropriate shapes, are made in the side wall of the element on the side of the air inflow. The inner surface of the element is lined with a coat of an antistatic and/or antibacterial material. The technological parameters are controlled by temperature, pressure, humidity and flow rate sensors. An air moistener is located within the inventive element, axially and longitudinally, and a UV light source and iodine micronutrients dispensers are located along the air moistener.
Preferably, the element has a shape of circular sector, and the support point is positioned above the airflow plane, while the bear point is positioned in this plane, the footing of the element being seated in a tray in a form of a channel guide with strut-seal elements. The guide is seated indirectly on a spacer bracket, preferably in a form of a T-bar and/or on another bearing structure.
According to the invention, the air introduced into dwellings flows peripherally around the floor, this creating the appropriate air circulation. By directing the exhaust through the foundations of the building and heating up its lower portions, one can avoid detrimental moistening of the building and the foundations.
The structure of the ground heat exchanger according the invention guarantees the contact of the whole volume of the circulating air directly with the ground. As a result of employing the heat exchanger equipped with a collector according to the invention, one obtains significant savings of heating, investment and operation costs, preserving a preferable microclimate of the ventilated building.
A very good and recommended supplemental for the ventilation system for private house building is mounting a ground heat exchanger outside the ventilated building. The heat exchanger employs the phenomena of the constancy of the year-round ground temperature (at a level of about 10° C.) at a depth of 6 to 10 m below the ground surface.
The invention will be better appreciated by reading the following description of preferred embodiment in conjunction with accompanying drawings of which:
FIG. 1 shows a segment of a ground heat exchanger according to the invention in a cross-sectional view.
FIG. 2 shows a joint of a collector with a slab of a ground heat exchanger in a cross-sectional view.
FIG. 3 shows a cross-sectional view of an air-distributing element.
FIG. 4 shows a cross-sectional view of a collector in the case of the element having a form of a circular sector and the airflow plane being the foundation slab.
FIG. 5 shows an air-distributing element in an axonometric projection.
FIG. 6 shows a mounting of the element footing in a guide.
FIG. 7 shows a cross-sectional view of the encased element
FIG. 8 shows a cross-sectional view of the encased element mounted in the airflow plane.
According to the invention, a ground heat exchanger is located in an excavation at an optimal, technological depth, necessarily above the ground water level. As it results from FIG. 1, properly compacted virgin soil 1 defines a surface 2 of a prime coat creating a foundation of a heat exchanger. The surface 2 is positioned horizontally or is slightly inclined relative to the horizontal direction in the appropriate direction. The direction of the inclination of the surface 2 relative to the surface of the virgin soil 1 depends on the mutual position and the whole` configuration of the exchanger.
A gravel prime coat 4, poured loosely without compaction, is laid onto the surface 2. Dimensions of the gravel grains in the prime coat 4 increase from the surface 2 and range from 5 to 20 mm. Square stone prime coat 5 or grit prime coat may be employed instead of the gravel prime coat 4. Thickness of the gravel prime coat 4 as well as the square stone prime coat 5 is about 20 to 60 cm, this resulting from calculation of the efficiency of the heat exchanger according the invention. Free spaces in the gravel prime coat 4 as well as in the square stone prime coat 5 should be filled with rinsed sand 6. The sand 6 fills free spaces between the gravel grains or stones increasing the thermal conductivity of the prime coat. So formed prime coat layer exhibits good thermal conductivity and a small airflow resistance.
A stabilizing net 7 made from a thermoplastic material is laid on so formed layer of the aggregate. The shapes and dimensions of the meshes of the net 7 depend on the employed aggregate, preferably the dimensions should be smaller than dimensions of the grains of the aggregate the net rests on, the mesh dimension being 10 mm, for example. A construction net 8 with ca. 20-70mm meshes is freely laid on the net 7, to transfer the load of the remaining structure of the heat exchanger and soil layers 18 onto the virgin soil 1.
The basic element of the heat exchanger is a circulation channel 9, the height of which is constant and dimensioned by the module size—the efficiency of the exchanger. The channel 9 is confined by the net 8 via a spacer element 11. The spacer element 11 is joined to the net 8, for example by welding of plastic elements. The support slab 14 has the appropriate length, and for preserving the modularity of the heat exchanger the support slabs 14 may mutually overlap 14.1. For example, the channel 9 has a height from 20 to 40 mm for given size of the module and technological parameters of the exchanger, for example for the air flow rate of 1.0-3.0 ms
The support slab 14 is a basic and a repeatable module of the exchanger. Exemplary size of the slab 14 is 1.9×1.9 m and for the air flow rate of the order of 400 m³/h nine such slabs 14 should be mounted in the exchanger. The cross-sections of the spacer elements 11 have shape of any geometrical figure. Most preferably, the shape is a trapezoid, the lower base of which, i.e. the shorter side 12, is joined inseparably to the net 8, creating a supporting, stiff, spatial structure with the slab 14. The number of the elements 11 and the positions of on the slab 14 as well as their dimensions depend on the load transferred by the exchanger. Channel trays 15 are mounted at the ends of the slab 14 and on the net 7, in which the endings of the air-distributing elements 13 are located, while a pipe 16 delivering the air to the channel 9 is placed within the element 13.
An appropriate soil layer 18 is laid onto so formed exchanger, and, still above, a technological insulating layer 19 to uplift the isotherms of 8-12° C. Most preferably, the layer 19 is made from foamed polystyrene, and a film 20 made from a plastic material is placed on the layer 19. The layer 19 and the film 20 play a role of an insulator eliminating the temperature difference.
The air intake 21 is formed above the ground level and equipped with a filter 23, most preferably a non-woven filter, for removing dust and allergens. The air intake 21 and the exhaust channel 22 are equipped with temperature sensors 24, flow rate sensors 25 and humidity sensors 26.
The external air is taken, for example, by a metal air intake 21 equipped with a nonwoven air filter, at least of a class EU3. Next, the air is flowing into the element 13, having a semicircle shape in this embodiment, being the ceiling for the flowing air. From below, the air has a direct contact with the layer of the gravel prime coat 4 or square stone prime coat 5 covered with sand 6. In the channel 9 the essential exchange of heat and humidity between the flowing air and the gravel and/or stones 5 covered with sand 6 occurs. Then, the air is collected to the collecting channel 17 and further to the ventilation system of the building. The flow rate of the air flowing through the air exchanger segment is of the order of 1.0-3.0 m/s. The number of segments for an individual air exchanger is selected basing on the planned efficiency of the exchanger. The amount of the flowing air should be divided by 20-40 m³per one segment for 24 hours per day of operation of the exchanger. For example, for the flow rate of 400 m³/h nine segments should be employed.
Research and tests confirmed the extraordinary efficiency of the inventive heat exchanger. For example, for an exchanger seated at a depth of 6-7 m, the air is heated by 2-6° C. and is humidified by the humidity coming from the ground to 80-92% at an ambient temperature of −20° C. The humidity of the air, after heating up in the building to about 20° C., is in the range of 30-35%. On the other hand, during the summer heatwaves, the air is cooled down, for example from 34° C. to a temperature of 15-17° C. and the air humidity is increased from 55% to 98-100%. The humidity of the air introduced to a building is of the order of 55% for 26° C. The condensate produced during the cooling process enters directly the ground or is drained from the surface 2 of the prime coat and the layer 19 via drainage pipes 3. As research and tests showed, the maximum amount of the condensate is 0.8 l/m²of the segment area, this giving an amount of 6 to 10 liters per 24 hours of operation.
The collector of the process air, as shown in FIG. 2, comprises generally two portions, mutually dependent and coupled technologically, these being a foundation slab 10 and an upper, exchangeable encasing element in a form of the air-distributing element 13.
The element 13, due to the employed construction material, i.e., a metal as well as due to the size of the collector, takes various shapes, shown in a cross-sectional view in FIG. 3. Preferably, the element 13 is made from a plastic material, particularly polypropylene and/or a thermoplastic material. So, its cross-section is a sector of any curve 13.1 or any figure 13.2 and is confined from the side of the air inlet D by a support point A and an opposite bear point B. Exemplary curves 13.1 are circular sector 13.1.1 or ellipse sector 13.1.2, and geometrical figure sectors are rectangular sector 13.2.2 or triangle sector 13.2.2. The plane of the flow of the process air D is denoted by the letter C. The plane C is created indirectly by the stabilizing net 7 mounted on the construction net 8. In the case of different technologies of the air processing, the same plane C is created y the foundation slab 10, as a ferroconcrete or concrete slab with openwork openings 10.1. The structure of the slab C depends on the operation mode of the collector and technological demands imposed on the parameters of the process air D. In exemplary, optimal embodiment, if the element 13 has cross-section shaped as a circular sector 13.1, the mutual position of the points A and B may be diversified, as shown in FIG. 7. As is apparent from the figure, the point A may be situated above the plane C, the point A1 may be situated in the plane C, the point B1 is situated above the plane C, the point B2 in the plane C, while the point B3 may be situated on an appropriate structure mounted below the plane C. FIG 6 shows an embodiment of the invention, in which the point A1 is situated in the plane C, this requiring to have closed channels 27 and/or open channels for desired amount of the air D made in the element 13 on the side of the air D inlet. FIG. 5 shows the encasement of the inner surface 29 of the element 13, which is lined with an antistatic agent 30 and/or antibacterial agent 31.
The technological demands imposed by standards for the process air D require to have a proper number and a proper configuration of technological temperature sensors 24, as well as pressure, humidity and flow rate sensors mounted in the element 13. Also, FIG. 8 shows a moistener 32 placed within the element 13, axially and longitudinally in the plane C, and a UV light source 33 and an iodine micronutrients dispenser are located along the air moistener 34.
The load of the soil layer 18 is transferred by the element 13, and therefore one of a plurality of possible solutions of mounting two footings 35 of the element 13 in a channel tray 15 has been elaborated. The channel tray 15, as shown in FIG. 4, comprises strut-seal elements 15.1 which allow for controlled movement of the footing 35 under the loads, preserving watertightness and stable stiffness of the element 13. Depending on the position of the points A and B, the tray 15 may be mounted indirectly on a spacer bracket 36, e.g. a ferroconcrete footing for points B.
As already mentioned above, FIG. 2 shows a cross-section of a sector of the ground heat exchanger, from which the process air is flowing out, to a user via the collector for the process air according to the invention. A layer of a height 3-10 cm is properly laid on the virgin soil 1 and a gravel prime coat 4 of a height 3-10 cm, on which rest the construction net 8 and the stabilizing net 7, which defines the plane C. The support slab 14 is supported by the bracket—spacer element 11, the space, as already explained in reference to FIG. 1, defining the circulation channel 9 for the process air D, of a height in the range 2-5 cm. The slab 14, preferably made from polypropylene, transfers the load of the channel tray 15, playing a role of a guide via the space bracket 36, to the virgin soil 1. Preferably, the spacer bracket 36 has T-bar cross-section; however, due to strength considerations it may take different shapes, such as close sections, for example. Here, in the described structure of the collector, the element 13 has a shape of a circular sector 13.1. with a diameter of 30-80 cm, and its modular length is preferably 100 cm. A layer of soil 18 of a thickness more than 15 cm is located above the element 13, “encased” below the insulating layer 19 made from foamed polystyrene as the insulation for the ground isotherm.
The application of the ground heat exchanger according to the invention in the Polish climatic zone and similar zones gives benefits both in the summer and the winter. It allows for the utilization of the coolness of the ground to lower the air temperature during summer heatwaves to temperatures allowing for effective dehumidification of the air delivered to the building.
During the season of heating, the fresh air is initially heated in the heat exchanger and is humidified by direct contact with the ground. The plastic material used to build the heat exchanger makes the stream of the air to be properly formed. The material for slabs and the nets is a thermoplastic material with an addition of an antibacterial agent based on silver and/or gold oxides. Besides lowering the heating costs, the heat exchanger according to the invention improves the microclimate inside the ventilated building, because it prevents from excessive drying of the air in the winter.

Claims

1. A ground heat exchanger utilizing the thermal energy of the ground, comprising pipe conduits and channels mounted within a support structure, characterized in that a layer of air-permeable materials is formed on the virgin soil, horizontally and/or at a small inclination angle relative to the horizontal direction, creating a circulation channel of the exchanger, the channel being confined by a support slab with spacer elements coupled with a construction net seated onto a stabilizing net, the whole structure being covered by an insulating layer.

2. A heat exchanger according to claim 1, characterized in that the layer of air-permeable materials has a form of a gravel prime coat and/or a square stone prime coat and is filled with sand, and its length just bigger than the length of the support slab or its portion.

3. A heat exchanger according to claim 1, characterized in that a temperature sensor, a humidity sensor, and a flow rate sensor are all encased at an air intake and an exhaust channel.

4. A heat exchanger according to claim 1, characterized in that it comprises a collector of process air, coupled with the circulation channel, which consists of a plane of the flow of the process air and an air-distributing element, the cross-section of the element having a shape of any curve or any geometric figure, and the element being confined by a support point on a side of the process air inlet and by an opposite bear point, the element being made from a metal or non-metallic material, having arbitrary shape of the longitudinal cross-section, and its length being conditioned by technological parameter of the air flowing therethrough.

5. The heat exchanger according to claim 4, in that the cross-section of the element is a circular sector, and the support point is situated above the plane, a first in-plane point is situated in the plane, and an upper point is situated above the plane, a second in-plane point is situated in the plane, and a lower point is situated below the plane, and, moreover, channels having an appropriate shape are made in the element on a side of the air intake.

6. The heat exchanger according to claim 4, characterized in that the plane is defined by a foundation slab having a form of a ferroconcrete and/or concrete slab with openwork openings and/or with a stabilizing net and with a gravel prime coat, and the element is made, from polypropylene and/or thermoplastic material.

7. The heat exchanger according to claim 4, characterized in that an inner surface of the element is lined with a coat of an antistatic agent and/or a coat of an antibacterial agent, and sensors of temperature, pressure, and flow rate of the air are mounted in the element, and an air moistener is mounted within the element, axially and longitudinally, in the plane and a UV light source iodine micronutrients dispensers are located along the air moistener.

8. The heat exchanger according to claim 4, characterized in that the element has a shape of a circular section, positioned according to the support points and the second in-plane point, footings of which are seated in a channel tray with strut-seal elements the channel tray being seated indirectly on a spacer bracket in a form of a T-bar and/or another bearing structure, and at the support point the element has channels.

9. The heat exchanger according to claim 5, characterized in that the element has a shape of a circular section, positioned according to the support point and the second in-plane point, footings of which are seated in a channel tray with strut-seal elements, the channel tray being seated indirectly on a spacer bracket, in a form of a T-bar and/or another bearing structure, and at the support point the element has channels.

10. The heat exchanger according to claim 5, in which the channels are closed channels.

11. The heat exchanger according to claim 5, in which the channels are open channels.