DE20203713U1 - Device in a building for obtaining thermal energy for a heat pump - Google Patents

Description

DE 8303 Patent Attorney

Graduate Physicist

Reinfried Frhr. v. Schorlemer

Karthäuserstr. 5A 34117 Kassel Allemagne

Telephone/Telephone (0561) 15335

(0561)780031 Fax/Telecopier (0561)780032

Martina Orth, 34308 Bad Emstal
Günter Hinrichs, 22149 Hamburg

Device in a building for generating thermal energy using a heat pump

The invention relates to a device of the type specified in the preamble of claim 1.

Buildings often have devices that work with heat pumps to generate additional heat energy in order to use this energy to at least partially heat the water used to operate heating systems, washing machines, dishwashers and other household appliances, but also for showering, bathing, etc. The heat sources for the heat pumps can be water, air or geothermal energy. In this context, it is particularly useful to use the latent heat of water or the heat of conversion that occurs in a water tank when water changes to ice, known as latent heat, since the resulting storage density of 84.4 kWh/m ³ is considerably greater than the storage density of water. Alternatively or additionally, such buildings are often equipped with air/liquid heat exchangers in the form of solar collectors or solar absorbers, which also serve as heat sources for the heat pumps (e.g. DE 26 37 784 C2, DE 27 17 075 Al, DE 198 39 867 Al, US-PS 5 207 075). It is also known to use the heat energy contained in the exhaust air from kitchens, bathrooms, toilets or the like as a heat source by feeding the exhaust air either to the cold side of a

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preparation or a supply air/exhaust air heat exchanger (e.g. DE 299 22 865 Ul), which preheats the supply air that must be supplied to a building by recovering the thermal energy contained in the exhaust air. However, heat pumps or heat exchangers operated with exhaust air usually have a comparatively low efficiency and require considerable investment.

In contrast, the present invention is based on the technical problem of making the thermal energy stored in the exhaust air usable in a device of the type described at the beginning without large investment costs and yet with a high degree of efficiency.

The characterizing features of claim 1 serve to solve this problem.

The invention is based on the surprising discovery that a liquid heat exchange medium flowing through a conventional air/liquid heat exchanger, particularly in the form of a solar absorber, can be heated considerably, even in the absence of sunlight and/or in colder seasons, simply by flushing the underside of the heat exchanger with exhaust air from the building. Apparently, many solar absorbers are also good air/liquid heat exchangers, or vice versa, which make it possible to recover the thermal energy contained in the air and thus also in the exhaust air. In addition, since the coefficient of performance of a conventional heat pump does not only depend on the temperature difference between the flow and return lines, but above all increases largely linearly with the level of the return temperature, used but still warm air, which would otherwise be released unused into the atmosphere as exhaust air, can serve to noticeably increase the efficiency of the heat pump, even if it only heats the heat exchange medium by a few degrees. The collecting line according to the invention also fulfils its purpose completely maintenance-free and can be routed to the air/liquid heat exchanger in buildings with several floors, for example via the usual exhaust air shaft.

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Advantageous features of the invention emerge from the subclaims.

The invention is explained in more detail below in conjunction with the accompanying drawings using an exemplary embodiment. They show:
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Fig. 1 is a schematic circuit and functional diagram of a device according to the invention;

™ Fig. 2 is a plan view of a heat exchanger according to the invention for the pre-

direction according to Fig. 1;

Fig. 3 is a schematic section along the line ΛΠ-ΛΠ of Fig. 1;

Fig. 4 is an enlarged detail of Fig. 3;
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Fig. 5 is a schematic side view of an exhaust air duct according to the invention for additional use of the thermal energy contained in the exhaust air;

Fig. 6 is a schematic front view of the exhaust air duct according to Fig. 5; and ■■ 20

Fig. 7 shows a schematic example of the connection of a heat pump in a building.

According to Fig. 1, a device for obtaining thermal energy using, for example, the latent heat of water mainly contains a heat pump 1 and a heat source in the form of a water tank 2. The heat pump 1 can be any conventional heat pump, e.g. provided with a compressor and a circulation pump 3, each of which has an evaporator (cold side) and a condenser (warm side) (not shown). The heat pump 1 has a flow line 4 and a return line 5 on the cold side. The flow line 4 is connected to the inlet of a heat exchange section 6 of a heat exchanger 7, which is arranged at the bottom of the water tank 2, while the outlet of the heat exchange section 6 is connected to the return line 5.

is closed. A suitable heat exchange medium, e.g. water, flows through the circuit mentioned. The heat exchanger 7 extracts heat energy from the water supply in the water tank 2 and therefore supplies the return line 5 with warmer water than flows into it from the flow line 4, whereby the necessary heat of evaporation for the working or cooling medium of the heat pump 1 is generated. In addition, the warm side of the heat pump 1 has a flow and a return line 8 and 9, respectively, both of which are connected to a hot water tank 10 and heat the water supply therein, which can be used in a building as hot water or as heating water for a wall or underfloor heating system 11.

The water reservoir 2 can be designed in a known manner as a cistern with a capacity of several cubic metres, e.g. made of concrete, which is arranged at a sufficient depth in a building or in the ground, so that the water supply in it is always kept at a sufficiently high temperature, which is above 0 ⁰ C and is usually higher than the temperature of the water flowing in from the flow line 4, by heat exchange with the surrounding earth, as indicated by arrows 12.

The water coming from the flow line 4, which is mixed with a sufficient amount of antifreeze or anti-freeze agent such as glycol and can reach a temperature of -10 ^° C, for example, causes ice to form on those surfaces of the heat exchanger 7 that are in contact with the water supply in the water tank 2. The thicker this layer of ice becomes, the poorer the heat transfer from the water tank 2 to the water flowing in the heat exchange section 6, since the layer of ice acts as an insulator. It is therefore necessary to avoid the formation of ice, as is generally known to those skilled in the art and does not need to be explained in more detail (e.g. DE 30 11 840 Al, DE 44 05 991 Cl, DE 198 39 867 Al).

According to the invention, the measures explained below are provided to prevent ice formation or to remove layers of ice that have already formed. 30

First, the heat exchanger 7 is prepared according to Fig. 2 and 3

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formed. The heat exchange section 6 then contains a first section 6a, which is preferably designed as a hollow cylindrical tube with a straight axis 14 and has a circular cross-section. The lower end of the section 6a is fastened in a liquid-tight manner to a base 15, which consists, for example, of a plane-parallel plate arranged perpendicular to the axis 14. A plurality of heat conducting elements 16 are fastened to the section 6a, which are provided with smooth heat exchange surfaces 16a arranged essentially radially to the axis 14 and opposite one another. The individual heat conducting elements 16 preferably consist of plane-parallel plates which surround the axis 14 in a star shape according to Fig. 2. The heat conducting elements 16 are preferably arranged partly on the outside and partly on the inside of the casing of the section 6a, so that they partly protrude radially outwards from it and partly protrude inwards into the section 6a. The heat exchanger 7 can therefore be manufactured from a material with good heat conduction, such as aluminum, for example, by inserting the plate-shaped heat conducting elements 16 into slots in the tubular section 6a that run parallel to the axis 14 and then connecting them to it by soldering or welding. Alternatively, the entire unit can also be obtained from an aluminum profile produced by extrusion by cutting it to length. The heat exchange surfaces 16a are each formed by the opposing broad sides of the plate-shaped heat conducting elements 16, which creates outer and inner chambers 17a and 17b (Fig. 2).

At the lower end associated with the base 15, the section 6a has an inlet opening 18 in its outer surface, to which a second section 6b of the heat exchange section 6 is connected in a watertight manner from the outside. The section 6b preferably consists of a hollow cylindrical tube which is correspondingly curved at its lower end and is inserted into the inlet opening 18. This tube is also expediently arranged in one of the chambers 17a between two of the heat conducting elements 16 and parallel to the axis 14, so that the entire heat exchanger 7 forms a compact structural unit.

The heat conducting elements 16 are in their lower and in the section 6a projecting

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Areas are preferably provided with recesses 19 so that they are opposite the base 15 at a certain axial distance which is greater than the axial distance of the inlet opening 18 from the base 15. This creates a distribution space by means of which water flowing in through the section 6b is distributed to the inner chambers 17b without any significant pressure loss.

A coaxial, circular cover plate 20 is fastened in a watertight manner to the upper end of the parts of the heat conducting elements 16 that protrude into the section 6a, which covers a cylindrical space 21 in which the inner edges of the heat conducting elements 16 are radially opposite one another. The outer cross section of the cover plate 20 is smaller than the inner cross section of the section 6a, so that gaps 6c remain between the outer edge of the cover plate 20 and the inner casing of the section 6a. The upper end of the section 6a is covered at a point above the cover plate 21 with a further cover plate 22, which has an outlet opening to which a connection piece 23 is connected in a watertight manner. In addition, an end of the section 6b of the heat exchange section 6 that protrudes from the heat exchanger 7 is designed as a connection piece 24.

Furthermore, the heat exchanger 7 described with reference to Figs. 2 and 3 is arranged according to Fig. 1 with its base 15 on the bottom of the water tank 2, so that the axis 14 and the heat exchange surfaces 16a are arranged vertically. The heat exchange surfaces 16a thus come into intimate heat-conducting contact with the water supply in the water tank 2, which reaches up to a schematically indicated water level 2a. The connecting pieces 23, 24 are connected to the return line 5 and the flow line 4 via watertight lines.

According to a further advantageous feature of the invention, the flow line is connected to a second circuit which serves to heat the water flowing through the heat exchange section 6. This second circuit contains a first flow line 25 which begins at the outlet of a heat exchanger 26 and ends at a branch 27 which is in the line leading from the flow line 4 to the connection piece 24.

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line, and a second flow line 28, which starts from a branch 29, which is arranged in the line leading from the connection piece 23 to the return line 5 and ends at the inlet of the heat exchanger 26. The heat exchanger 26 is an air/liquid heat exchanger which interacts with the surrounding atmosphere and preferably consists of a solar absorber or collector mounted on the roof of a building or the like, which, in particular when exposed to sunlight, heats the water flowing in the flow lines 25, 28, which, like the water coming from the heat pump 1, is enriched with an antifreeze. A circulation pump 30 is also connected to the flow line 28. In order to prevent

In order for the water circulating in the flow lines 25, 28 to reach the heat pump 1 through the flow line 4, a check valve 31 is provided between the flow line 4 and the branch 27.

For additional heating of the water in the water tank 2, 15! rainwater can be used, which is fed via an inlet channel 32 into the container of the water tank 2 which is open at the top.

According to the invention, it is further provided to arrange a further heat exchanger 33 for heat recovery in the line between the connection piece 23 and the return line 5, to which warm waste water from showers, dishwashers or the like from a building or the like is fed by means of a line 34 in order to additionally heat the water fed to the heat pump 1.

Finally, it is possible to provide at least one three-way valve 35, 36 in the flow line 25 in order to supply the water heated in the air/air or solar circuit directly to a heat exchanger 37 which serves to prepare hot water and/or heating purposes and is arranged in the hot water tank 10.

The device described works essentially as follows: 30

During normal operation of the device in winter, heat pump 1 is always

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switched on when there is a need for heat energy for the hot water tank 10. At the outlet of the cold side, ie at the flow 4, water of e.g. -10 ⁰ C is released, which enters section 6b at the connection piece 24, then passes through the inlet opening 18 into section 6a, leaves this through the openings 6c and the connection piece 23 and finally flows through the return line 5 back to the evaporator side of the heat pump 1. The water in the water tank 2 is heated so that it has a temperature of e.g. 0 ⁰ C in the return line.

During operation of the heat pump 1, a layer of ice forms on the heat exchange surfaces 16a (Fig. 2), the thickness of which depends on how often the heat pump 1 is switched on. The ice layer that forms is indicated in Fig. 2 by rod-shaped ice blocks 38 that form between the heat conducting elements 16 or in the outer chambers 17a. The formation of ice is used on the one hand to utilize the latent heat of 84 kWh/m ³ released during the transition from water to ice and to be able to use comparatively small water reservoirs. On the other hand, however, the ice armor surrounding the heat exchanger 7 hinders the transfer of heat from external water layers into the heat exchange section 6. Normally, the heat pump 1 would therefore switch off automatically as soon as the temperature difference between the flow and return 4.5 is no longer sufficiently large. According to the invention, this is avoided by providing a circuit through the heat exchanger 26 parallel to the heat pump circuit.

In sunny, cold weather, even in winter, the temperature in the circuit of the heat exchanger 26 is sufficiently high, at least during the day, to heat the water coming from the flow 4 to a temperature above 0 ⁰ C by mixing in the area of the branch 27 before it enters the heat exchange section 6 when the circulation pump 30 is switched on. This ensures that the section 6a of the heat exchange section 6 gives off heat to the wall of the pipe forming it and thus also to the heat conducting elements 16 from the inside. As a result, a thin film of water is formed between the heat exchange surfaces 16a and the ice blocks 38, which causes the ice to be detached or broken off from the heat exchange surfaces 16.

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and immediately rises due to buoyancy up to the water level 2a of the water reservoir 1, as indicated in Fig. 1 with the reference number 39. For this purpose, the height of the storage tank 2, which is expediently open at the top, is preferably chosen to be at least so much greater than the height of the heat exchanger 7 that the heat exchange surfaces 16a remain largely ice-free when the water reservoir 2 is full of water, or are automatically made ice-free, even if the ice pieces 39 that have formed are not immediately converted back into water by the earth's heat or otherwise. In other words, a water supply is provided above the heat exchanger 7 that is large enough to allow all the ice that has formed to float above the heat exchanger 7.

In the breaks between successive operating cycles of the heat pump 1, the temperature of the water flowing through the heat exchanger 26 and the heat exchange section 6 is normally sufficient to completely remove any layers of ice that have formed, so that they rise upwards and the heat pump 1 can operate with optimum efficiency again when it is switched on again. In contrast, the pieces of ice 39 are generally gradually thawed again by the thermal energy introduced into the water tank 2 by means of the geothermal energy. It would also be possible, however, to allow the layer of pieces of ice 39 to grow ever larger on cold days, e.g. during the winter, and then gradually remove them again in the summer with the help of the geothermal energy or the heat exchanger 26. In this way, the thawing of the layer of ice can be postponed to a later time and the heat required for this can be obtained from energy that would otherwise be wasted.

Regardless of when the ice layer 39 is thawed, the heat exchange surfaces 16a are largely automatically kept free of ice, so that the heat transfer from the water reservoir 2 to the section 6a of the heat exchange section 6 is always sufficiently good. It is not necessary to apply the full conversion energy of 84 kWh/m ³ . Rather, a very small part of it is sufficient to form thin water films and thereby detach the ice blocks 38 where they adhere to the heat exchange surfaces 16a in the chambers 17a.

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No complex regulation or control mechanisms are required for the described automation. This means that the entire device can be manufactured inexpensively and operated without being prone to failure. In addition, the heat generated by the heat exchanger 26 can be used directly for hot water preparation via the three-way valves 35, 36 whenever it is not needed to remove the ice blocks 38. This is especially true for the warmer seasons, when the heat pump 1 is practically not needed if the entire device is dimensioned accordingly.

The automatic detachment of the ice blocks 38 is mainly achieved by the fact that they are essentially only thawed in thin zones which are arranged between them and the vertically arranged, as smooth as possible heat exchange surfaces 16a. In the lower area of the heat exchanger 7, where the water in the water reservoir 2 is consistently above 0 ⁰ C, no or only short-term ice formation takes place. The formation of a thin film of water is therefore sufficient to completely separate the ice blocks 38 and allow them to rise upwards. Due to the special design of the heat exchanger 7, the ice blocks 38 also have no areas surrounding the heat conducting elements 16 in a ring shape, and there are also no components or the like which prevent the ice blocks 38 from rising. This applies even if ice formation should also take place in the inner chambers 17b (Fig. 2). Finally, since the heat conducting elements 16 are arranged radially from the inside to the outside, the ice blocks 38 also grow from the inside to the outside with the result that, if appropriately dimensioned, they never reach the radially outer ends of the heat conducting elements 16.

Furthermore, it can be provided to assign temperature sensors to the heat exchanger 26 and the water tank 2 and to provide a control such that the heat exchanger 26 is only switched on when the water flowing through the lines 25, 28 is, for example, at least 5 ^° C warmer than the water in the water tank 2.

A further advantage of the device according to the invention is that the heat

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pump 1 can usually be operated in a very favorable performance range, since the temperature in the return line 5 is comparatively high. This is especially true if additional waste heat (heat exchanger 33) or rainwater (inlet channel 32) is used to preheat the water supplied to the heat pump 1. But even when a heat exchanger 26 in the form of a solar absorber is used exclusively, the heating of the water flowing in the lines 25, 28 is sufficiently high even in the absence of solar radiation due to the use of diffuse radiation, rain or wind.

In order to increase the efficiency of the heat exchanger 26, the invention provides for the exhaust air that inevitably arises in the building to be used for additional heating of the heat exchange medium flowing through the heat exchanger 26. For this purpose, the heat exchanger 26 is constructed, for example, according to Fig. 5 to 7, from plate elements 41 arranged parallel to one another, which are mounted on the roof or on a house wall and have flow channels 42 that are connected in a manner not shown in detail to the flow lines 25, 28 according to Fig. 1. Each plate element 41 is constructed, for example, from two flexible plates 41a, 41b arranged parallel to one another and a flexible grid network (not shown in detail) arranged between them, which acts as a spacer and between the plates 41a, 41b the

20' leaves flow channels 42 free. At least one plate 41a, 41b is provided with connecting flanges or the like for connecting the flow channels 25, 28, as is schematically indicated in Fig. 5 and 6 by two connecting channels 43, 44 attached to the ends of the flow channels 42, which each extend over the entire width of the plate elements 41.

The plates 41a, 41b are particularly advantageously made of a soft polyvinyl chloride (soft PVC), polyurethane, a copolymer or a synthetic rubber with a high heat exchange efficiency against solar energy, air or wind. So-called spacer fabrics made of polyester or nylon can be used as a grid network.

3Ci can be used, so that the entire heat exchanger 26 can be composed of large-area mats. Plate elements 41 of this type are generally known,

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(e.g. DE 30 33 451 Al, DE 36 11 916 Al) and therefore do not need to be explained in more detail to the person skilled in the art.

According to the invention, it is further provided that the plate elements 41 are arranged at a small distance from the roof surface, the house wall or the like in order to thereby create a hollow space 45 (Fig. 5) between the undersides of the plate elements 41 and the respective roof tile or plaster layer or the like. The thickness or depth of the space 45 can be, for example, 20 mm to 200 mm and is preferably approximately 60 mm to 100 mm. The components that can be used to assemble the plate elements 41 are known per se and are therefore not shown individually. Furthermore, the space 45 thus formed is expediently open on all sides.

To use the exhaust air, the building is provided with at least one collecting line 46, which takes in exhaust air generated in the building at an inlet side and releases it into the intermediate space 45 at an outlet side. Such a collecting line 46 is shown schematically in Fig. 5 and 6. Its outlet end 48 projects through a roof and/or wall construction 47 of the building and ends in the intermediate space 45. In this embodiment, the heat exchanger 26 is mounted on a sloping roof, e.g. a gable roof, with the plate elements 41 extending from the lower eaves to the higher ridge 50. In this case, the collecting line 46 preferably ends in the eaves area so that the exhaust air is extracted like a carbon dioxide extractor and flows along the underside of the plate elements 41 in the direction of the arrows shown until it reaches the free atmosphere in the ridge area. The exhaust air enters into intensive, heat-exchanging interaction with the heat exchange medium flowing in the plate elements 41.

In this way, particularly in cold seasons when the building is heated more and the exhaust air reaches temperatures of 20 ⁰ C and more, the heat exchange medium is well preheated before it enters the heat exchanger. At the same time, this increases the return temperature of heat pump 1 and thus significantly increases its coefficient of performance.

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Fig. 6 and 7 show that different exhaust air flows can be supplied to different plate elements 41. For example, in Fig. 6, four collecting lines 51 to 54 are provided that are arranged next to one another and lead to the intermediate space 45. These lines are used, for example, to collect and convey the exhaust air from a living room, from any household appliance such as an extractor hood or a tumble dryer, or from the usual duct ventilation. In a similar way, Fig. 7 shows how these lines 51 to 54 are laid in a building, for example, and can also open into the intermediate space 45 at places other than the eaves area. An exhaust air fan 55 can be connected to one or more of the lines as required.

The invention is not limited to the embodiment described, which could be modified in many ways. This applies in particular to the special design of the heat exchanger 7. It is only necessary to ensure that the heat conducting elements 16 are constructed in such a way that they themselves or their heat exchange surfaces 16a do not form any obstacles that prevent the ice blocks 38 that are formed from rising. It is especially important to prevent the ice blocks 38 from enclosing the heat conducting elements 16 in a ring shape and in such a way that they have to be practically completely dissolved before the heat conducting elements 16 are free of ice again. Furthermore, it is in principle irrelevant whether

2Cl the material from which the heat exchanger 7 is made, provided that it is a material that conducts heat sufficiently well. Therefore, the heat exchanger 7 can also be made of plastic and by extrusion instead of metal, in particular aluminum. The cross-sections of the sections 6a, 6b can also be other than circular, in particular square, rectangular or oval. The sections 6a, 6b can also take up a different position in the heat exchanger 7. In particular, the section 6b could be arranged radially inside instead of outside the section 6a, in which case the inlet opening 18 would be omitted. Apart from that, the heat exchanger 7 can be replaced by another heat exchanger, since the effect of the heat exchanger 26 is independent of the heat source with which the heat pump 1 is operated. If necessary, additional air could also be supplied to the intermediate space 45, which is preheated, for example, by geothermal energy by

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through a pipe laid in the ground at a sufficient length and sufficiently deep (ground heat exchanger). It is also clear that the heat exchanger 26 has been described only as an example and can be manufactured and used in numerous other suitable embodiments. Finally, it is understood that the various features can also be used in combinations other than those shown and described.

Claims (7)

1. Device in a building for obtaining thermal energy with a heat pump ( 1 ) which is provided with a flow line ( 4 ) and a return line ( 6 ) on the cold side through which a heat exchange medium flows and which has an air/liquid heat exchanger ( 26 ) connected between the flow line ( 4 ) and the return line ( 6 ) and mounted on a wall or on the roof of the building, characterized in that the heat exchanger ( 26 ) is arranged a short distance from the wall or roof to form an intermediate space ( 45 ) and the intermediate space ( 45 ) is connected to at least one collecting line ( 46 , 51 to 54 ) laid in the building for exhaust air generated in the building. 2. Device according to claim 1, characterized in that the collecting line ( 46 ) is connected to a plurality of rooms of the building. 3. Device according to one of claims 1 or 2, characterized in that the collecting line ( 46 ) is connected to the exhaust air outlet of at least one household appliance. 4. Device according to one of claims 1 to 3, characterized in that the collecting line ( 46 ) is connected to the duct ventilation of the building. 5. Device according to one of claims 1 to 4, characterized in that the intermediate space ( 45 ) is connected to several collecting lines ( 51 to 54 ) connected to different exhaust air sources. 6. Device according to one of claims 1 to 5, characterized in that at least one collecting line ( 46 , 51 to 54 ) is provided with an exhaust air fan ( 55 ). 7. Device according to one of claims 1 to 6, characterized in that the collecting line ( 46 ) opens into the intermediate space ( 45 ) in the eaves region ( 49 ) of a heat exchanger ( 26 ) installed on a pitched roof.