Method for discharging a gas from a heat pump, and heat pump

Abstract

The invention relates to a method for discharging a gas from a heat pump (1), with an inflow section (9), an outflow section (6), which is at an angle with respect to said inflow section (9), and a suction section (5) being formed in a tube line system, said suction section (5) being connected to the inflow section (9) and the outflow section (6), wherein in the method, a solvent (8) is guided, such that contraction turbulence is generated, from the inflow section (9) into the outflow section (6), the gas to be discharged is absorbed by the solvent (8) as a result of the contraction turbulence and, after flowing out through the outflow section (6), said gas is discharged from the tube line system. The invention also relates to a heat pump (1).

Description

The invention relates to a method for removing a gas from a heat pump and a heat pump.

PRIOR ART

A heat pump serves to exchange heat between a use area and a buffer medium. Examples for heat pumps are air conditioning systems and absorption cooling machines where heat is transferred from a use area, such as, for example, a living room or a refrigerator to a buffer medium.

Such heat pumps usually comprise a refrigerating agent, which is exposed to different states of aggregation and temperature ranges in a cycle process and which exchanges energy in the form of heat with a use area medium and a buffer medium due to the changing neighbourhood with such media, such as, for example, with the use of heat exchangers. Further to the heat pump agent an absorption heat pump usually also comprises an absorption medium which is adapted to have the heat pump medium dissolved therein in a section of the heat pump which is called an absorber. Afterwards heat is exchanged between the use area medium and the use area.

For different reasons, for example due to corrosion or leakage, unwanted gases, so called external gases, may occur in the heat pump. These gases generally have a negative effect on the thermodynamic performance of the heat pump process and cause a reduction of the efficiency of the heat pump. Furthermore, such gases can cause damaging of the heat pump due to chemical reactions with the heat pump medium and/or with different parts of the heat pump and/or due to a pressure increase. Therefore, it is particularly important that such gases are removed from the heat pump as completely and continuously as possible.

Various methods have been proposed to remove gases from heat pumps. An external vacuum pump was used for this purpose in known devices, which is operated at set intervals to extract the gases from the various sections of the heat pump. Such pumps, however, are very expensive and moisture sensitive, too.

An auxiliary absorber can be used operating according to the same principles as the absorber, but operating on a relatively low temperature level and, thereby generating a suction pressure. This generated relative underpressure is used to suck a gas and remove it from the heat pump. The backflow of the gas into the heat pump is avoided by means of a stagnating liquid column in a connection pipe. The auxiliary absorber operates parallely with the absorber of the heat pump. The suction effect, however, is in this case below a level achieved with an external vacuum pump. Furthermore, the operation of an auxiliary absorber requires a certain amount of energy causing a reduction of the efficiency and an increase of the irreversabilities of the heat pump.

Furthermore, there are devices known, where jet pumps are used to suck gases from a heat pump. Jet pumps use a driving jet from a liquid and generate a local under pressure according to the Bernoulli principle by means of a flow change in a suction space. A flow change is generally achieved by means of a flow through a pipe neck. The minimum suction pressure achievable with jet pumps is the steam pressure of the driving jet liquid.

The publication U.S. Pat. No. 3,367,134 describes an absorption cooling system where gas is removed by entering a pumped liquid into the jet from a pipe section through a chamber in an opposite pipe section to generate a suction in the chamber in order to extract gas through a lateral pipe section.

Additionally, a mechanical vacuum pump may be provided which is used for the exhaustion. Simple jet pump systems for sucking off gases could not be put into practice before. As the driving jet for the generation of a local under pressure must have a suitable pressure, i.e. in this case several hundreds of milibars (mbar), the use of a pump is necessary to pump the driving jet through the jet pump with the required pumping energy. Such additional pumps, however, cause an increase of the energy consumption and of the costs of the device.

THE INVENTION

It is an object of the invention to provide a method for removing gases from a heat pump and a heat pump where gas can be removed from the heat pump in an efficient and cheap manner.

According to the present invention this object is achieved with a method according to the independent claim 1 and with a heat pump according to the independent claim 10.

According to the invention, a method is provided for removing gases from a heat pump where an inlet section is defined in a pipe installation, an outlet section forming an angle thereto and a sucking section connected to the inlet section and the outlet section wherein with this method a solvent is flowed from the inlet section to the outlet section thereby forming contraction turbulence, and wherein the gas to be removed is absorbed by the solvent due to the contraction turbulence and is removed after flowing out through the outlet section from the pipe installation.

Contrary to known methods for removing a gas from a heat pump, the invention has the advantage that there are no parts of the device moved thereby avoiding wear and tear. The contraction turbulence causes the absorption of the gas in the solvent. The gas can, for example, be dissolved in the solvent or it can form bubbles in the solvent. Due to the removing of the gas an under pressure is formed in the suction section whereby further gas is sucked from the pipe installation into the suction section.

In a preferred modification of the present invention it is provided that the solvent in the outlet section where it is present in the form of a gas-/solvent mixture flow is moved by means of gravity forces. This is advantageous, as no additional pumping power is required for the sucking of the solvent. Therefore, there are no additional costs or material expenses involved which are necessary with an additional pump. In an advantageous embodiment of the present invention the solvent is moved in the inlet section by means of gravity.

In an advantageous embodiment of the invention, the solvent is pumped out of the outlet section.

In a further preferred modification of the invention, a flow velocity in the inlet section is controlled and thereby the removal rate for the removal of the gas from the heat pump is controlled. This is advantageous because the removal rate can be adapted to the operating conditions of the heat pump. The removal of the gas can be effected, for example, only when there is a leakage. However, the removal may also be effected in intervals.

In a preferred embodiment of the invention, water is used as a solvent. This causes the use of an environmentally friendly solvent which can be disposed of in an easy way without polluting the environment.

In an advantageous modification of the invention, the solvent is removed together with the gas to be removed from the pipe installation. This is advantageous because the gas can be removed from the heat pump without detours. Therefore, no additional method steps are necessary, for example, to remove the gas absorbed by the solvent from the solvent.

Advantageously a working fluid of the heat pump is used as a solvent in an embodiment of the invention. For this purpose, for example, a portion of the working fluid flowing in the pipe installation of the heat pump can be taken by means of a branching-off element and flowed to the inlet section. It is then not necessary to provide additional liquids for the heat pump. Therefore, various requirements regarding storage and disposal of such additional liquids are avoided.

According to an advantageous modification of the present invention the gas absorbed by the solvent is removed from the solvent by means of a precipitator. This is advantageous because after this treatment the solvent is present in an essentially pure form and can be re-used.

In a preferred modification of the present invention the gas removed from the solvent is collected in a collection container. Thereby the possibility is provided to dispose of the gas at a later stage without environmental pollution.

Preferred embodiments of the invention according to the depending claims in combination with the corresponding method claims show the above mentioned advantages accordingly.

DESCRIPTION OF THE PREFERRED EMBODIMENT

Embodiments of the invention are described below in greater detail with reference to the accompanying figures in the drawings. They show:

FIG. 1 a heat pump in the form of an absorption cooling machine;

FIG. 2 a vapor pressure diagram for water-lithium bromide solutions;

FIG. 3 a suction device with a suction section, an inlet section and an outlet section;

FIG. 4 a section of a heat pump with an absorber, a suction device and a precipitator;

FIG. 5 a section of a further heat pump with an absorber, a suction device and a precipitator;

FIG. 6 a section of a different heat pump with a condenser and a suction device; and

FIG. 7 a diagram where the effect of a method for removing gases from a heat pump is shown.

FIG. 1 shows an embodiment of a heat pump 1 which is called an absorption cooling machine. The heat pump 1 comprises the following components: An evaporator 10, an absorber 11, a generator 12, which is also called a desorber, and a condenser 13. Furthermore, further components are shown, such as pumps 14, 15, a dissolving heat exchanger 18, and reducing means 16 and 17, such as U-pipes. A heat pump medium 2, such as, for example, water is evaporated with low pressure in the evaporator 10. The pressure in the evaporator 10 corresponds in this case to the vapor pressure of the heat pump medium 2 at a temperature of about 5° C. to 15° C. The heat pump medium 2 draws energy in the form of heat from a use area medium, for example water. This is effected, for example, in that the evaporator 10 comprises a heat exchanger and in that water from a cold water circle in an air conditioner of a building flows through the heat exchanger and is cooled therein.

The evaporated heat pump medium 2 is flowed into the absorber 11 afterwards which is indicated by an arrow A in FIG. 1. The evaporated heat pump medium 2 is absorbed in the absorber 11 by the absorption medium, for example, a concentrated lithium bromide solution (LiBr-solution), in an absorption process. The absorber 11 comprises a heat exchanger with a buffer medium 21 flowing therethrough, having a medium temperature level. Afterwards the heat pump medium 2 is dissolved in the absorption medium in a rich solution 22. The pressure level in the absorber 11 is essentially the same as the pressure level in the evaporator 10. The rich solution 22 is pumped by means of a pump 15 to a higher pressure level into a generator 12. The generator 12 comprises a further heat exchanger where hot water or water steam, for example, flow through. The heat pump medium 2 from the rich solution 22 is evaporated in the generator 12 absorbing energy thereby. The poor solution 23 remains in the generator 12. The poor solution 23 has a lower concentration of dissolved heat pump medium 2 than the rich solution 22. The poor solution 23 with the higher concentration of lithium bromide is available for the absorption process again.

The evaporated heat pump medium 2 is flowed to a condenser 13 as it is indicated by an arrow B in FIG. 2. In the condenser 13, evaporated heat pump medium 2 is condensed and brought to a lower pressure level by means of a throttle means 16 and flowed to the evaporator 10. Gas break through in the heat pump 1 is avoided by the throttle means 16 and 17 by bringing flowing fluids from a high to a low pressure level. The condenser 13 comprises a heat exchanger with a buffer medium 21 on a medium temperature, for example environmental temperature, flowing therethrough. The pressure level in the condenser 13 and in the generator 12 is set by the equilibrium pressure of the heat pump medium 2 upon condensation. Usually temperatures are between 25° C. and about 40° C.

Absorption cooling systems can be operated with different material pairings. Depending on the thermodynamic properties of these material pairings, absorption cooling systems can be operated with over pressure, such as with the material pairing ammonia-water, or with under pressure, such as with the material pairing water-lithium bromide. In researching cooling and for the air conditioning of buildings, heat pumps 1 where water is used as a heat pump medium 2 and lithium bromide is used as an absorption medium play a superior role.

FIG. 2 shows a vapor pressure diagram for the material pairing water-lithium bromide. Graphs 31 are shown in the vapor pressure diagram, which each represent the pressure depending on the temperature for a certain mixing ratio of a water-lithium bromide solution. For example, it can be seen in the vapor pressure diagram, that water, i.e. a water-lithium bromide-solution with a mixing ratio 1,0 can be evaporated in the evaporator 11 at a temperature of about 10° and a pressure of 12 mbar. The condensation can be effected in the condenser 13 at, for example, 36° C. and, therefore, at a pressure of 59 mbar. 12 mbar and 59 mbar are the absolute pressure levels during the operation of such a heat pump 1. A process of a heat pump 1 according to FIG. 1 is schematically shown in the vapor pressure diagram 30 by means of a so called installation characteristic curve 32. Thermodynamic states, where the water-lithium bromide solution is present in the evaporator 10, in the absorber 11, in the generator 12, or in the condenser 13 are marked with letters V, A, G, K in the installation characteristic curve 32. Connecting lines between the states represent the state changes in the heat pump 1.

The pressure in the evaporator has a value where the heat pump medium 2 already evaporates at a temperature of, for example, −15° C. The evaporated heat pump medium 2 is dissolved in the absorption medium of the absorber 11 where the heat generated thereby is removed by the buffer medium 21. The rich solution 22 produced by dissolving the heat pump medium 2 in the absorption medium is pumped to a higher pressure level by the pump 15. By heating with a temperature of, for example, 110° C. the evaporated heat pump medium 2 is evaporated in the generator 12 from the rich solution 22 in such a way that the absorption means is present in the generator in the form of a poor solution 23. The evaporated heat pump medium 2 is flowed to the condenser 13 and cooled down to a temperature of about 30° to 40° C. by means of the buffer medium 21, causing liquidizing of the heat pump medium 2. After throttling the heat pump medium 2, it is ready to be evaporated again in the evaporator 10. The poor solution 23 generated in the generator 12 is flowed through the dissolving heat exchanger 18 and then to the absorber 11.

The rich solution 22 coming from the absorber 11 is preheated in the dissolving heat exchanger 18 by means of the poor solution 23 coming from the generator 12 and having a higher temperature.

Similarly to compression cooling systems in an absorption cooling system it is made use of the fact that the heat pump medium 2 has pressure dependent melting- and evaporating points. In the case of a compression cooling system an electrically operated compressor is used for increasing the pressure of a cooling medium vapor to a pressure level of a condenser.

Contrary to this, a second absorption medium cycle is used in a sorption cooling system, where the refrigerating medium is condensed. As the refrigerating medium is present in a solution and has, therefore, a smaller specific volume, it can be brought to a higher pressure with much less electrical energy consumption.

The components, evaporator 10, absorber 11, generator 12, and condenser 13 comprised in the heat pump 1 each comprise heat exchangers where heat is transferred between external media, i.e. media flowing outside of the respective component, and internal media, i.e. media flowing within each component. The efficiency of the heat exchange is reduced in desired condensation and absorption processes as they occur in the condenser 13 and in the absorber 11 by the presence of undesired gases which are also called external gases. A loss of energy of 50% can be expected at an external gas portion of as little as 3-5 vol.-%. Furthermore, if oxygen is a component of the external gases it can cause corrosion of the heat pump 1 when it combines with the water-lithium bromide solution, thereby causing the damaging of the thermodynamic process and also the operating lifetime of the system.

FIG. 3 shows a suction device 3 with a suction section 5, an outlet section 6, and an inlet section 9. Arrows 8, 8′, 8″ in FIG. 3 indicate the flow direction. The suction section 5 serves to guide gas which shall be removed from the heat pump to the suction device 3. A solvent 8 is flowed through the inlet section 9 in the range 7 of the suction device 3. In the range 7 contraction turbulences are formed which cause the absorption of the gas in the solvent 8 in the range 7. The gas may form bubbles in the solvent 8. However, the gas may be, at least partially, dissolved in the solvent 8. The contraction turbulences are formed, for example, by the solvent freely falling through the outlet section 6. The formation of turbulences can be supported by providing baffle plates or lateral flows.

The inlet section 9 is arranged perpendicular to the outlet section 6 as it is shown in FIG. 3. Thereby the formation of a contraction turbulence is supported. The inlet section 9 can, however, also form any other angle with the outlet section 6. For example, the suction device 3 may be Y-shaped. Furthermore the suction section 5 can comprise a pipe section (not shown) projecting into the suction device 3. In FIG. 3 the suction section 5, the inlet section 9 and the outlet section 6 have the same even cross sections. The cross sections, however, can be different for each individual section. Furthermore, it may be provided that the cross section changes along a section. In particular, a narrowing cross section in the range 7 may be provided to support the formation of contraction turbulences.

After flowing through the range 7 the solvent 8 flows out through the outlet section 6 together with the gas absorbed in the range 7. Therefore, an under pressure is generated in the emptied range with respect to the suction section 5 which is responsible for a suction effect in the suction section 5 in the range 7. Further gas flows from the suction section 5 to the range 7 due to this suction effect.

A liquid column of solvent 8 is formed in the outlet section 6 due to the solvent 8 flowing thereto from the inlet section 9, the liquid column being upwardly limited by a liquid state in the outlet section. The outlet section 6 operates as a down pipe. In this case the strength of the suction effect at the suction section 5 depends on the length of the liquid column extending below the liquid state in the outlet section 6. The length of the liquid column can be determined by means of the choice of the length of the outlet section 6 and the installation height of the suction device 3.

The suction effect in the suction section 5 is based on the suction pressure which is at least as large as the vapor pressure of the solvent 8. The vapor pressure of the solvent 8 is, however, smaller than the pressure in the absorber 11 or in the condenser 12 in any case. The reason for this is the cooling occurring upon condensation or absorption of the heat pump medium 2. The method can be carried out without applying a pre-pressure and only with the pressure formed by the difference in height between the inlet for the solvent 8 and the liquid state in the outlet section 6.

FIG. 4 shows a portion of the heat pump 1 in an embodiment. In this embodiment, gas present in the absorber 11 is removed. This embodiment is advantageous because the absolute pressure level in the absorber 11 is lower than in the condenser 12 and the gas, therefore, preferably accumulates in the absorber. The shown portion comprises the absorber 11, the suction device 3, the pump 15, the precipitator 40, a collection container 41, and a connecting pipe 42 for the connection with the dissolving heat exchanger 18. The solvent 8, which is in this case the poor solvent 23 from the absorber 11, is conveyed to the inlet section 9 of the suction device 3 instead of to the pump 15 of the dissolving heat exchanger 18 as it is shown in FIG. 1. The suction section 5 of the suction device 3 is connected to the absorber 11 to remove gas present in the absorber 11. The solvent 8 absorbs the gas and is flowed through the outlet section 6 to the precipitator 40. In the precipitator 40 the gas is taken from the solvent 8 and the thus cleaned solvent 8 is flowed to the generator 12 as an absorption medium through the dissolving heat exchanger 18. The removed gas is collected in a collection container 41 if it may not be released to the environment, because it is, for example, poisonous or explosive.

In this embodiment, a counterpressure occurs in the outlet section 6 described by the following formula: p_G=Δp_{Pipe loss}+Δp_LWÜ+Δp_hydrostat+p_Generator. p_G denotes the pressure in the absorber 11, p_Generator denotes the pressure in the Generator 12, Δp_{Pipe loss} is a pressure loss due to pipe losses, Δp_LWÜ is a pressure required to drive the absorption medium through the dissolving heat exchanger 18, and Δp_hydrostat is a pressure due to the liquid column due to the hydrostatic inlet height corresponding to the height between the suction device 3 and the inlet into the generator 12.

The pressure at the suction section 5 corresponds to the pressure in the absorber 11. Therefore, the suction device 3 must be installed sufficiently high so that the liquid column in the outlet section 6 can generate a sufficiently high hydrostatic pressure to convey the absorption medium through the dissolving heat exchanger 18 through the pipe connections against the hydrostatic inlet height in the generator 12 and against the pressure in the generator 11. Depending on the kind of heat pump this can be easily achieved.

Alternatively, only a portion of the flow from the solvent flowing to the generator 12 can be used as it is shown in another embodiment in FIG. 5 and flowed in the form of the solvent 8 to the inlet section 9. For this purpose, the solvent 8 is released from the gas in the precipitator 40 after removing the gas and it is flowed to the absorber though a connecting pipe 43. This is advantageous because the counter pressure is kept small. The counter pressure below the intermediate section 7 is calculated according to the following formula: p_G=Δp_{Pipe loss}+Δp_hydrostat+p_Generator. This counter pressure is essentially less than the one in the embodiment according to FIG. 4. In addition to the connection of the suction section 5 to the absorber 11a, connection to the condenser 12 can be provided to suck off both components simultaneously by means of the suction section 3.

If gases shall be removed from the condenser 12 the embodiment according to FIG. 6 is chosen. The rich solution 23 from the condenser 12 is used as a solvent 8 for removing the gases by means of the suction device 3 therein. Similar to FIG. 4 and FIG. 5, a precipitator 40 and a collection container 41 is provided in this embodiment.

It is also possible to provide several suction devices 3 at different sections of the heat pump 1 in order to increase the efficiency. These suction devices 3 can be operated with a solvent 8 from one single source or from several sources.

FIG. 7 graphically illustrates the effect of the removal of the gases on the power of the heat pump 1. In this case the rich solvent 22 flowing from the absorber 11 to the dissolving heat exchanger, 18 was used as a solvent 8. The rich solution 22 exiting the absorber 11 is in a thermodynamic equilibrium state with the pressure present in the absorber 11 or it is slightly colder. A hermetic pump serves as a pump 15 to convey the rich solvent 22 to the generator 12. In the present case the power of a freshly evacuated heat pump 1 can be achieved.

FIG. 7 shows four heat exchanging powers of an absorption cooling system and the efficiency, denoted COP. It is shown for two flow rates of the solvent through the suction device 3 how the efficiency is decreased after the controlled addition of external gases in the absorption cooling system, at 14:40 o'clock and 16:54 o'clock and how they return to its optimal efficiency after successfully evacuating by means of the suction device 3.

The embodiment of the heat pump 1 described in the diagram 70 has a free falling height of 20 cm. This means that the solvent 8 can fall free for a distance of 20 cm in the outlet section 6, i.e. only by means of gravity. A falling height of at least 5 cm has been found to be advantageous. Furthermore the solvent 8 has a flow rate between 260 and 330 litres per hour (1/h) in the inlet section 9. Such a flow rate corresponds to flow rates which are applied by common heat pumps 1. The suction device 3 has a pipe diameter of 16 mm. In experiments it was found that with flow velocities of 20 to 40 cm/s an effective removal of gases could be achieved if water is used as a solvent 8. This is also the case with a water-lithium bromide-solvent.

The features of the invention disclosed in the above description, in the claims, and in the drawings can be important by themselves or in any combination for the realization of the invention in various embodiments.

Claims

1. (canceled)

2. A method according to claim 17, wherein the solvent is driven in the outlet section by means of gravity.

3. A method according to claim 17, wherein the solvent is pumped from the outlet section.

4. A method according to claim 17, wherein a flow rate in the inlet section is controlled and thereby a removal rate for removing of the gas from the heat pump is controlled.

5. A method according to claim 17, wherein water is used as a solvent.

6. A method according to claim 17, wherein the solvent is removed together with the gas from the pipe installation.

7. A method according to claim 17, wherein a working fluid is used in the heat pump and the working fluid of the heat pump is used as a solvent.

8. A method according to claim 17, wherein the gas absorbed by the solvent is removed from the solvent by means of a precipitator.

9. A method according to claim 8, wherein the gas removed from the solvent is collected in a collection container.

10. A heat pump with a pipe installation having a suction device for removing unwanted gases, from the heat pump, wherein the suction device is provided with an inlet section, an outlet section forming an angle thereto and a sucking section connected to the inlet section and the outlet section in such a way that a solvent flowed from the inlet section to the outlet section forms contraction turbulences which are adapted to absorb the gas to be removed from the solvent and be removed after flowing out through the outlet section.

11. A heat pump according to claim 10, wherein the inlet section forms an essentially rectangular angle with the outlet section.

12. A heat pump according to claim 10, wherein a pump for pumping off the solvent is connected to the outlet section.

13. A heat pump according to claim 10, further comprising a connecting piece connected to the inlet section to make use of a working fluid of the heat pump as solvent.

14. A heat pump according to claim 10, further comprising a precipitator for separating the gas from the solvent.

15. A heat pump according to claim 14, further comprising a connecting pipe for returning working fluid which has been used as a solvent to the heat pump.

16. A heat pump according to claim 14, further comprising a collection container for collecting the gases removed from the solvent.

17. A method for removing unwanted gas from a heat pump, said heat pump having a pipe installation, an inlet section provided at said pipe installation, an outlet section forming an angle with said inlet section and a sucking section connected to said inlet section and said outlet section, the method comprising the steps of: flowing a solvent from said inlet section to said outlet section thereby forming contraction turbulences,absorbing said gas by said solvent due to said contraction turbulence, andremoving said solvent with said gas after flowing out of said pipe installation through said outlet section.