DK201670152A1

DK201670152A1 - Heat pump

Info

Publication number: DK201670152A1
Application number: DKPA201670152A
Authority: DK
Inventors: Niels Hansen
Original assignee: Hsl Energy Holding Aps
Priority date: 2016-03-15
Filing date: 2016-03-15
Publication date: 2017-10-02
Also published as: DK179079B1

Abstract

Disclosed is a heat pump apparatus (1) for cooling a first heat exchange medium (2) in heat exchange with a working fluid (4) circulating in a closed circuit, and heating a second heat exchange medium (3) in heat ex-change with said working fluid (4). The heat pump which is efficient at extracting the energy build up in the working fluid during compression. Furthermore, the heat pump is capable of using alternative working fluids, which are not environmentally suspicious.

Description

Introduction

The present invention relates to a heat pump for cooling a first heat exchange medium in heat exchange with a working fluid circulating in a closed circuit, and heating a second heat exchange medium in heat exchange with said working fluid, and to the use of such a heat pump. The invention also relates to a process for cooling a first heat exchange medium in heat exchange with a working fluid circulating in a closed circuit, and heating a second heat exchange medium in heat exchange with said working fluid.

Background art

Heat pumps using vapor-compression refrigeration/heating are well known and are often used in smaller scale for heating, ventilation, and air conditioning (HVAC) purposes. Recently heat pumps have also proved useful for larger scale heating purposes such as district heating facilities using air or seawater to evaporate the working fluid.

However, known heat pump designs fail to fully extract the energy which is stored in the working fluid during the compression process of the working fluid, which in turn makes them more expensive to run in order to achieve the desired heating of the second heat exchange medium, and produces a higher carbon emission to provide power for the compressor.

Furthermore, current heat pump designs favour ammonia as a working fluid as it is both cheaper and more efficient than chlorofluorocarbons (CFC), while also being considerably safer on the environment. However, ammonia is corrosive and incompatible with several metals, e.g. copper, putting limitations on the materials used in the heat pump, and it is poisonous in high concentrations. US 3665724 A discloses a heat pump, wherein working fluid is passed from a stage other than the last stage of a multistage centrifugal compressor to a waste heat condenser for liquefying working fluid and returning it to an evaporator. A line is provided for passing gaseous working fluid from the last stage of the compressor to a second condenser, which serves as a heat exchanger for heating a second heat exchange medium for satisfying a heat- ing load demand. A working fluid line extends from the second condenser to the first condenser. A gaseous working fluid line including a flow control valve extends from the vapor area of the first condenser to the inlet of each stage of the compressor. In the waste heat condenser the latent heat of the working fluid, along with the heat of compression, is rejected to the atmosphere as by a cooling tower and interconnecting water circuit, This configuration favors a greater temperature rise in the second condenser, but the rejection of the latent heat in the waste heat condenser reduces the amount of energy which can be extracted from the working fluid, thereby giving the heat pump a lower coefficient of performance (COP). EP 2317251 A1 discloses a two-stage compression heat pump using ammonia heat as a heat carrier, wherein three kinds of heat carriers in a higher temperature range, a medium temperature range and a lower temperature range can be extracted at the same time while stabilizing extraction of the high-temperature heat-transfer medium. The following configuration is employed for the device. A first heat carrier line is provided in a condenser to generate the high-temperature heat-transfer medium through latent heat exchange of a first heat-transfer medium a with a gaseous heat-transfer medium in the condenser, while a second a heat carrier line is provided in an evaporator to generate the low-temperature heat transfer media through latent heat exchange of second heat-transfer medium with a liquid heat-transfer medium in the evaporator. Further, a first sub-cooling device is interposed between the condenser and an intermediate cooler, while a second sub-cooling device is interposed between the intermediate cooler and the evaporator, and a third heat carrier line is provided in series with the first sub-cooling device via the second sub-cooling device to generate the medium-temperature heat-transfer medium through sensible heat exchange of third heat-transfer medium with the liquid heat-transfer medium in the first and second sub-cooling devices. This heat pump however, have limited options for working fluids as the two-stage compressor cannot provide the compression required to bring working fluid such as propane or isobutene to an optimal temperature and pressure, without using compressors with an excessively large compression ratio. On this background, it is therefore an object of the invention to provide a heat pump which is more efficient at extracting the energy build up in the working fluid during compression.

It is a further object of the invention to provide a heat pump which is capable of using alternative working fluids which do not suffer from the above-mentioned drawbacks.

Summary of the invention

According to the invention, this is accomplished by a Heat pump apparatus (1) for cooling a first heat exchange medium (2) in heat exchange with a working fluid (4) circulating in a closed circuit, and heating a second heat exchange medium (3) in heat exchange with said working fluid (4), said apparatus (1) comprising: an evaporation portion (100) adapted for cooling the first heat exchange medium (2) in heat exchange with the working fluid (4), wherein the evaporation portion (100) comprises, a first evaporator stage unit comprising an evaporator (112) which uses energy from the first heat exchange medium (2) to evaporate the working fluid (4), and a first evaporation stage compressor (111) arranged downstream from the evaporator (112); and a condenser portion (200) adapted for heating the second heat exchange medium (3) in heat exchange with the working fluid (4), wherein the condenser portion (200) comprises, a) a final condenser stage unit comprising a final condenser (222) which transfers energy from condensation of the working fluid (4) to the second heat exchange medium (3), and a final condenser stage compressor (221) arranged upstream from the final condenser (222), and b) a non-final condenser stage unit arranged between the evaporation portion (100) and the final condenser unit, said first condenser unit comprising a non-final condenser (212) which transfers energy from condensation of the working fluid (4) to the second heat exchange medium (3), and a nonfinal condenser stage compressor (211) arranged upstream from the non-final condenser (212), wherein a part of the working fluid (4) exiting the non-final condenser stage compressor (211) is transferred to the non-final condenser (212) and a remaining part of the working fluid (4) is transferred to the final condenser stage compressor (221).

The advantage of using a first evaporation stage compressor, a nonfinal condenser stage compressor, and a final condenser stage compressor to compress the working fluid, is that the working fluid is compressed over several stages meaning that the compressors with a significantly smaller compression ratio can be used in the heat pump, making the initial manufacturing cost cheaper. The compression over several stages also allows the heat pump to use alternative working fluids such as propane or isobutane, which are more efficient working fluids than ammonia, and do not suffer from the before-mentioned drawbacks.

Additionally, by only condensing a part of the working fluid exiting the non-final condenser stage compressor and transferring the remaining part for further compression in the final condenser stage compressor, the remaining part can be compressed to a higher pressure and enthalpy, whereby a greater amount of energy can be extracted from the working fluid.

It should be understood that throughout the description and the claims, each compressor can be a single-stage compressor, a multi-stage compressor, or it can be one or more of the stages in a multi-stage compressor, wherein working fluid can be extracted between the stages.

In an embodiment of the invention the condenser portion (200) comprises two or more non-final condenser stage units arranged between the evaporation portion (100) and the final condenser stage unit, such that the remaining part of the working fluid (4) exiting a non-final condenser stage compressor (211) is transferred to the non-final condenser stage compressor (211) of a subsequent non-final condenser stage unit or the final condenser unit.

The advantage of adding additional non-final condenser stage units is that the working fluid remaining after each extraction may be compressed to an even higher pressure and enthalpy or it allows for compressors with a smaller compression ratio. This allows the heat pump to build up and extract more energy in the working fluid or reduces the manufacturing costs of the heat pump.

In an embodiment of the invention the condenser portion (200) further comprises one or more condenser stage flash tank(s) (203) arranged downstream from the final condenser unit, each of the one or more flash tanks(s) (203) being adapted for flashing the condensed working fluid (4) and transferring the flashed gaseous working fluid (4) to a non-final condenser stage compressor (211) and transferring the remaining liquid condensed working fluid (4) to a subsequent condenser stage flash tank (203) or to the evaporation portion (100).

The advantages of adding flash tanks downstream of the higher pressure steps of the condenser portion is that the enthalpy which is stored within the working fluid may be used to evaporate some of the liquid working fluid, when this is brought to a lower pressure. The flashed gaseous working fluid may then be returned to a non-final condenser stage compressor with a pressure that is substantially equal to that of the flashed gaseous working fluid. Thus, the energy which it would have otherwise cost to bring the flashed gaseous working fluid to that pressure is saved, thereby reducing the energy cost of running the heat pump.

In an embodiment of the invention the evaporation portion (100) further comprises one or more secondary evaporation stage unit(s) arranged between the first evaporation unit and the condenser portion (200), said one or more secondary evaporation stage unit(s) comprising a secondary evaporation stage compressor (121) arranged downstream from the first evaporation stage compressor (111) and upstream from the condenser portion (200), so that the gaseous working fluid (4) exiting a secondary evaporation stage compressor (121) is transferred to a subsequent secondary evaporation unit or to the condenser portion (200), and an evaporation stage flash tank (123) arranged downstream from the condenser portion (200), adapted for flashing the condensed working fluid (4) and transferring the flashed gaseous working fluid (4) to the secondary evaporation stage compressor (121) via a gas out let, and transferring the remaining condensed working fluid (4) to a subsequent evaporation stage flash tank (203) or to the first evaporation unit via a liquid outlet.

The advantages of adding one or more secondary evaporation stage unit(s) to the evaporation portion is firstly, that additional compressors stages are added to the heat pump, whereby the increase in pressure that each compressor have to provide to the working fluid may be decreased. This in turn allows the heat pump to use smaller compressors or to bring the working fluid to a higher final pressure. Secondly, the advantage of adding flash tanks downstream of the higher pressure of the condenser portion is that the pressure of the working fluid may be used to evaporate the working fluid. The flashed gaseous working fluid may then be returned to the secondary evaporation stage compressor with a pressure that is substantially equal to that of the evaporated gaseous working fluid. Thus, the energy which it would have otherwise cost to bring the flashed gaseous working fluid to that pressure is saved, thereby reducing the energy cost of running the heat pump.

In an embodiment of the invention at least one of the one or more secondary evaporation stage unit(s) comprises a secondary evaporator (122) arranged upstream from the secondary evaporation stage compressor (121) and downstream of the liquid outlet of the evaporation stage flash tank (123), so that a part of the liquid working fluid (4) exiting the evaporation stage flash tank (123) is transferred to said secondary evaporator (122), said secondary evaporator (122) using energy from the first heat exchange medium (2) to evaporate the working fluid (4).

The advantage of adding a secondary evaporator to one or more of the secondary evaporation units is that the secondary evaporator(s) may operate at a higher pressure than the evaporator of the evaporator of the first evaporation stage unit and transfer the gaseous working fluid directly to the secondary evaporation stage compressor. This in turn means that the heat pump does not have to provide the energy that would have otherwise been required to bring the working fluid from the pressure of the first evaporator stage unit to that of the secondary evaporator stage unit.

In an embodiment of the invention the condenser portion (200) further comprises one or more heat exchanger(s) (214, 224, 215, 225) for transferring energy from the working fluid (4) to the second heat exchange medium (3), arranged downstream and/or upstream from the condenser of the one or more non-final condenser stage unit(s) and/or of the final condenser unit.

The advantages of adding one or more heat exchanger(s) in thermal contact with the second heat exchange medium before and/or after condensing the working fluid is that not just the pressure, but also the temperature which is build up during compression of the working fluid may be used to heat the second heat exchange medium. Heat exchangers placed upstream of the condenser(s) of the non-final condenser stage unit(s) and/or of the final condenser unit may extract heat from the gaseous working fluid, which may be superheated by the compression process, while heat exchangers placed downstream may under-cool the liquid working fluid. This allows the heat pump to extract additional energy from the working fluid, thereby enhancing the efficiency of the apparatus.

In an embodiment of the invention two or more of the first evaporator stage compressor (111), the one or more secondary evaporator stage compressors) (121), the one or more non-final condenser stage compressor(s) (211), and/or the final condenser stage compressor (221) are driven co-axially by a driver (5).

The advantages of driving two or more of the compressors co-axially is that the heat pump may be driven by a single or few drivers, which reduce the maintenance cost of running the heat pump. This embodiment may be realized by integrating the compressors in a multi-stage compressor, wherein each impeller can be considered as one of the compressors.

In an embodiment of the invention the compressors are driven by an internal combustion engine, a gas turbine, a gas engine, a steam turbine and/or an electric motor.

The advantages of using the conventional combustion drivers is that the heat pump may be completely independent of existing infra structure as it can run on its own means as long as it is supplied with fuel. The advantage of using an electric motor as a driver is that the exhaust emission may be virtually zero, which may be desired in population areas. A further advantage of using electric motors is that electricity in certain areas may be abundant and cheap, making it favorable to use electricity to drive the heating process. Areas with abundant electricity will typically be areas with access to hydro, geo or nuclear electricity. In an embodiment the compressor may be driven by a combination of an electric motor and one of the other mentioned conventional motors, so that the electric motor can be operated as a back-up to the conventional motor.

In an embodiment of the invention the first heat exchange medium (2) is air, water from a natural reservoir and/or process water from an industrial process and the second heat exchange medium (3) is water from a district or central heating system.

The inventors have found that a heat pump according the invention, depending on the temperature of the first heat exchange medium, may have a coefficient of performance (COP) more than 3.5, which means that 1 unit of electricity is combined with 2.5 units of heat from e.g. the seawater to provide 3.5 units of heat to the district or central heating circuit. This makes it cheaper and more environmentally friendly to run a heat pump according to the invention than a gas or electric boiler. A second aspect of the invention relates to A process for cooling a first heat exchange medium in heat exchange with a working fluid circulating in a closed circuit, and heating a second heat exchange medium in heat exchange with said working fluid, said process comprising the steps of: cooling the first heat exchange medium in an evaporation stage comprising the steps of: evaporating the working fluid by using energy from the first heat exchange medium, and compressing the evaporated gaseous working fluid to form a compressed evaporation stage working fluid; and heating the second heat exchange medium in a condenser stage comprising the steps of: compressing the compressed evaporation stage working fluid to form a first compressed condenser stage working fluid, condensing a first part of the compressed first condenser stage working fluid in heat exchange with the second heat exchange medium, thereby forming a first liquid condenser stage working fluid, compressing a second part of the compressed first condenser stage working fluid to form a final condenser stage working fluid, condensing the final condenser stage working fluid in heat exchange with the second heat exchange medium, thereby forming a final liquid condenser stage working fluid, and conveying the first liquid condenser stage working fluid and the final liquid condenser stage working fluid to the evaporation stage.

The advantage of compressing the gaseous working fluid over several stages is that the work done in compressing the air is reduced so that power is saved. Additionally, the compression ratio at each stage is lower than what would have been required if using a single stage of compression. Furthermore, by continuing to compress the second part of the working fluid after having extracted a first part for condensation, even more energy may be put into the second part and extracted when condensing the second part of the working fluid. Thus, the process can achieve a higher COP and operate using a type of working fluid that would have otherwise required a single-stage compressor with an unrealistic compression ratio. In addition, the passing of the second heat exchange medium through two or more condensers implies a gradual heating, which in each condenser is of a lower temperature range compared to a single condenser.

In an embodiment of the invention the first compressed condenser stage working fluid is conveyed to a second or further non-final condenser stage compressing steps (n) before compressing to the final condenser stage working fluid.

In an embodiment of the invention the number of non-final condenser stage compressing steps (n) is 1 to 15. Usually, the number of non-final condenser stage compressing steps (n) is at least 2, such as 3, 4, 5, 6, 7, 8, 9, or more. In some embodiments, the number of non-final condenser stage compressing steps (n) does not exceed 15, such as 14, 13, 12, 11, 10, 9, 8, 7, 6, 5, 4, 3, or 2.

The advantage of repeating the non-final compression step and extracting a part of the working fluid for condensing at each step is as mentioned above, that the amount of energy which can be put into and extracted from the part of the working fluid which is conveyed to further compression is increased. Using several compression steps is particularly advantageous, when using a working fluid which requires a large compression ratio, such as isobutane.

In an aspect of the invention, the pressure of the working fluid is increased by 1 to 10 bars in each of the n compressing steps. Generally, it is preferred with a relatively low pressure difference between each stage to optimize the enthalpy of the system. In a certain embodiment the pressure of the working fluid is increased by 9 bars or less, such as 8, 7, 6, 5, 4, 3, and 2 bar or less. For isobutane the pressure of the working fluid is preferably increased by 1 to 4 bar and for propane the pressure of the working fluid is preferably increased by 2 to 8 bar in each of the compressing steps.

The pressure of the final condenser stage working fluid depend on the chemical nature of the working fluid. In general, the pressure of the final condenser stage working fluid is between 10 and 40 bar. For isobutane the preferred pressure of the final condenser stage working fluid is 8 to 15 bar and for propane the preferred pressure of the final condenser stage working fluid is 25 to 35 bar.

In a certain aspect of the invention, the pressure of the first compressed condenser stage working fluid is between 1.5 and 20 bar. In an embodiment of the invention, the pressure of the first compressed condenser stage working fluid is at least 2 bars, such as 3, 4, 5, 6, 7, 8, 9,10,11,12,13, 14, 15, 16, 17, 18, or 19. In other embodiments the pressure of the first compressed condenser stage working fluid is less than 19 bars, such as less than 18, 17, 16, 15, 14, 13, 12, 11, 10, 9, 8, 7, 6, 5, 4, 3, 2, or less. For isobutane the preferred pressure of the first compressed condenser stage working fluid is 2 to 4 and for propane the pressure of the first compressed condenser stage working fluid is 10 to 20 bar.

According to a certain aspect of the invention the final liquid condenser stage working fluid is flashed, thereby forming a gaseous working fluid which is conveyed to the nth non-final compressing step, and a liquid working fluid, which is conveyed to the evaporation stage or to a (n-1)th non-final flash tank.

The advantages of adding flash tanks downstream of the higher pressure steps of the condenser portion is that the enthalpy which is stored within the working fluid may be used to evaporate some of the working fluid, when this is brought to a lower pressure. The flashed gaseous working fluid may then be returned to a non-final condenser stage compressor with a pressure that is substantially equal to that of the flashed gaseous working fluid. Thus, the energy which it would have otherwise cost to bring the flashed gaseous working fluid to that pressure is saved, thereby reducing the energy cost of running the heat pump.

In an aspect of the invention a heat exchanging step is performed before and/or after the condensing step, in which the working fluid is cooled and the second heat exchange medium is heated.

According to an aspect of the invention, the first compressed evaporator stage working fluid is conveyed to one or more secondary evaporation compressing steps (m) before compressing in the condenser stage. In a preferred aspect, the number of secondary evaporation compressing steps (m) is 0 to 15. Especially, the number of secondary evaporation compressing steps (m) is 1 or more, such as 2, 3, 4, 5, 6, 7, 8, 9,10, 11, 12,13, 14, or more.

The advantages of adding one or more secondary evaporation stage unit(s) to the evaporation portion is firstly, that additional compressors stages are added to the heat pump, whereby the increase in pressure that each compressor have to provide to the working fluid may be decreased. This in turn allows the heat pump to use smaller compressors or to bring the working fluid to a higher final pressure. Secondly, the secondary evaporator(s) may operate at a higher pressure than the evaporator of the evaporator of the first evaporation stage unit and transfer the gaseous working fluid directly to the secondary evaporation stage compressor. This in turn means that the heat pump does not have to provide the energy that would have otherwise been required to bring the working fluid from the pressure of the first evaporator stage unit to that of the secondary evaporator stage unit.

The present apparatus and process may be used for a variety of purposes. According to a certain aspect the apparatus and the process may be used 9 for district heating, wherein the second heat exchange medium is part of the heating circuit. According to this use the return heat exchange medium, which typically is water, is heated in the apparatus and the heat of the water is subsequently delivered to households or industries. The now cooled water is then returned to the apparatus for renewed heating.

In other embodiments of the invention the apparatus and the process is used 9 for heating purposes in horticulture, abattoirs or industry.

In a certain aspect of the invention the first heat exchange medium is air, water from a natural reservoir and/or process water from an industrial process. The first heat exchange medium may be a closed circuit or and open circuit depending on the circumstances. Furthermore, the cooled first heat exchange medium may be discarded to the environment or may be used for cooling purposes, such as cooling electronics, air condition, refrigerated storage, etc.

Summary of the drawings

The present invention will now be described in greater detail based on preferred embodiments with reference to the drawings on which:

Figure 1 shows a diagram of the simplest embodiment of a heat pump according to the invention,

Figure 2 shows a diagram of the heat pump shown in figure 1, wherein heat exchangers have been added,

Figure 3 shows a diagram of the heat pump shown in figure 1, wherein a flash tank have been added,

Figure 4 shows a diagram of the heat pump shown in figure 1, with both heat exchangers and a flash tank added,

Figure 5 shows a diagram of a heat pump according to the invention, wherein additional evaporation and condenser stages have been added,

Figure 6 shows a diagram of a heat pump according to the invention, wherein heat exchangers have been added upstream of the condensers,

Figure 7 shows a diagram of a heat pump according to the invention, wherein heat exchangers have been added downstream of the condensers, Figure 8 shows a diagram of a heat pump according to the invention, wherein heat exchangers have been added both upstream and downstream of the condensers, and

Figure 9 shows a diagram of a heat pump according to the invention, wherein the number of secondary evaporation units is zero and the number of non-final condenser units is 4.

Detailed description

Turning first to figure 1 which shows the simplest embodiment of a heat pump according to the invention. The heat pump comprises a closed circuit, wherein a working fluid 4 is transferred between an evaporation portion 100 and a condenser portion 200. The working fluid 4 is brought into gaseous form under heat exchange with a first heat exchange medium 2 in the evaporation portion 100, and then passed from an outlet of the evaporation portion 100 to an inlet of the condenser portion 200. In the condenser portion 200 the working fluid is then brought into liquid form under heat exchange with a second heat transfer medium 3. The liquid working fluid 4 is then returned from one or more outlet(s) of the evaporation portion 100 to an inlet of the evaporation portion 100 to be recycled.

The working fluid 4 can be any chemical suitable for vapor-compression refrigeration/heating. However, in the preferred embodiments of the invention the working fluid is either propane or isobutane, which are less corrosive and toxic than alternatives such as ammonia, and less damaging to the environment than alternatives such as CFC.

Isobutane has been shown to be more efficient than propane as a working fluid 4. However, the disadvantage of isobutane is that it requires a greater compression ratio of the compressors, making the initial cost of manufacturing the heat pump larger. As shown later, this disadvantage can be overcome by adding additional compressor stages, rather than increasing the size of the compressors.

The evaporation portion 100 comprises a first evaporator stage unit, which in the shown embodiment contains an evaporator 112, which uses energy from the first heat exchange medium 2 to evaporate the working fluid 4 while cooling the first heat exchange medium 2. The evaporator 112 will in most cases have heat fins in contact with the first heat exchange medium 2 to ensure effective transfer of heat.

The first heat exchange medium 2 can be any liquid or gaseous substance with a temperature higher than the boiling point of the working fluid at the pressure in the evaporator 112. The first heat exchange medium 2 is preferably atmospheric air, water from a natural reservoir, process water from industry, or a combination of these. Natural reservoirs are meant to cover sea and fresh water from surface sources such as oceans, rivers, lakes, etc. and subsurface sources. Alternatively the first heat exchange medium 2 may be the ground, if enough geothermal energy is present to fuel the evaporation of the working fluid 4.

When using liquids as a first heat exchange medium 2 the temperature at the evaporator 112 should be higher than the freezing point of the first heat exchange medium 2.

The first evaporator stage unit further comprises a first evaporation stage compressor 111, to which the working fluid 4 is conveyed after being brought into gaseous form. As noted earlier, the first evaporation stage compressor 111 may be a multi-stage compressor, wherein the working fluid 4 is compressed over several stages. In the embodiment shown in fig. 1, the compressed gaseous working fluid 4 is conveyed from the first evaporation stage compressor 111 to the outlet of the evaporation portion 100, from where it is conveyed to the condenser portion 200.

The condenser portion 200 comprises a non-final condenser stage unit and a final condenser stage unit. The non-final condenser stage unit comprises a non-final condenser stage compressor 211, to which the gaseous working fluid 4 is conveyed after entering the condenser portion 200. The gaseous working fluid 4 is then compressed further to a pressure where it can be condensed.

The compressed gaseous working fluid 4 exiting the non-final condenser stage compressor 211 is split into two parts, wherein the first part is transferred to a non-final condenser 212 of the non-final condenser unit. The non-final condenser 212 is adapted for condensing the gaseous working fluid 4, whereby heat is generated. The heat is deposited in the second heat exchange medium 3 which is brought into thermal contact with the non-final condenser 212.

The second part of the gaseous working fluid 4 is transferred to the final condenser stage unit. The final condenser stage unit comprises a final condenser stage compressor 221 to which the gaseous working fluid 4 is conveyed. The gaseous working fluid 4 is then compressed even further to a final pressure and temperature. From the final condenser stage compressor 221 the gaseous working fluid 4 is conveyed to a final condenser 222, where the energy realised by condensation of the working fluid 4 is transferred to the second heat exchange medium 3 which has already been heated by the nonfinal condenser 212. By letting the second heat exchange medium 3 pass through the various stages of heat exchange with the working fluid 4 in series, the temperature may rise gradually as the second heat exchange medium 3 is passed from the heat exchange step with the lowest temperature, which in the embodiment shown in fig. 1 is the non-final condenser 212, to the heat exchange step with the higher temperature, which in the embodiment shown in fig. 1 is the final condenser 222.

It should be noted that the working fluid 4 when exiting the final condenser stage compressor 221 has the largest amount of enthalpy and pressure and therefore defines the maximum temperature which the outgoing heat exchange medium 3 can achieve. The final pressure and temperature of the gaseous working fluid 4 exiting the final condenser stage compressor 221 may therefore be selected according to the temperature of the incoming second heat exchange medium 3 and the desired temperature of the outgoing second heat exchange medium 3.

The final pressure and temperature of the gaseous working fluid 4 exiting the final condenser stage compressor 221 may further vary depending on which working fluid 4 is used by the heat pump. If propane is used as a working fluid 4, it should in a preferred embodiment be brought to a final pressure of around 31 bar and a temperature 115 degrees Celsius. If isobutane is used as a working fluid 4, the final pressure in a preferred embodiment should be around 12 bar and the temperature should be around 115 degrees Celsius.

The liquid working fluid 4 returning from the non-final condenser 212 and the final condenser 222 is then conveyed to the evaporation portion 100, where it can once again be evaporated by extracting energy from the first heat exchange medium 2. Because most suitable working fluids 4 have a boiling point below 0 degrees Celsius the temperature of the first heat exchange medium 2 need not be particularly high, e.g. a heat pump according to the invention may use seawater with a temperature of 3 degrees Celsius to supply the energy for evaporating the working fluid 4, whereby the heat pump despite the low temperature of the first heat exchange medium 3 can still achieve a COP of at least 2,9.

Figure 2 shows a diagram of the heat pump described above, where the non-final compressor stage unit and the final compressor stage unit further comprise a heat exchanger 214, 224. In the shown embodiment the heat exchangers are arranged downstream of the non-final condenser 212 and the final condenser 222, such that they are in thermal contact with the liquid working fluid 4 exiting the condensers 212, 222. The heat exchangers 214, 224 are also in thermal contact with the second heat exchange medium 3 which when entering the heat pump is cooler than the liquid working fluid 4 exiting the condensers 212, 222. Energy is thereby transferred from the liquid working fluid 4 to the second heat exchange medium 3 which is heated in the process. Through this process the liquid working fluid 4 is under-cooled before being conveyed to the evaporation portion 100.

In an alternative embodiment the non-final compressor stage unit and the final compressor stage unit further comprise a heat exchanger 215, 225 arranged upstream of the non-final condenser 212 and the final condenser 222, such that they are in thermal contact with the gaseous working fluid 4 entering the condensers 212, 222. This configuration allows the heat pump to transfer energy from the superheated gaseous working fluid 4 exiting the non-final condenser stage compressor 211 or the final condenser stage compressor 221 to the second heat exchange medium 3.

It should be noted that such heat exchangers 215, 225 would have the highest temperature in the heat pump, and the second heat medium 3 should therefore, if transferred through the heat pump in a single supply line, be brought into thermal contact with these heat exchangers 215, 225 after being heated at the upstream heat exchangers 214, 224 and/or non-final condenser 212 and final condenser 222.

In another embodiment the heat pump may comprise a combination of the aforementioned heat exchangers 214, 224, 215, 225 so that the working fluid 4 is brought into thermal contact with the second heat exchange medium both before entering and after exiting the non-final condenser 212 and the final condenser 222. It should be noted, that each of the heat exchangers 214, 224, 215, 225 are independent of the others and a heat pump could therefore have any configuration of heat exchangers, e.g. a single heat exchanger 215 arranged upstream of the non-final condenser 212 and a single heat exchanger 224 arranged upstream of the final condenser 222, and still fall within the scope of the invention.

Figure 3 shows a diagram of the heat pump described above, where the condenser portion 200 further comprises a condenser stage flash tank 203 arranged downstream of the final condenser 222. The condenser stage flash tank 203 is connected to a non-final condenser stage compressor 221 via a gas outlet and to the evaporation portion 100 via a liquid outlet.

The pressure inside the condenser stage flash flash tank 203 of the condenser portion 200 is substantially the same as the pressure at the exit of the non-final condenser stage compressor 211, so that the liquid working fluid 4 when entering the flash tank 203 from the higher pressure of the final condenser stage unit is flashed, whereby a flashed gaseous working fluid 4 is formed.

The flashed gaseous working fluid 4 is conveyed from the condenser stage flash tank 203 to the exit of the non-final condenser stage compressor 211 via the gas outlet, where it is mixed with the working fluid 4 that is being transferred to the non-final condenser 212 and/or the working fluid 4 that is being transferred to the final condenser stage unit. The flashed gaseous working fluid 4 is thereby reusable for condensation without having been returned to the evaporation portion 100. This allows the heat pump to extract more of the energy put into the working fluid and increases the COP. The remaining liquid working fluid 4 is transferred from the condenser stage flash tank 203 to the evaporation portion 100 via the liquid outlet

The flash tank 203 itself may be provided with a heat sink on the outside to create a larger contact area with the ambient air so that it can better absorb heat to counter the cooling effect of flashing. The liquid working fluid 4 remaining after flashing is conveyed to the evaporation portion 100 for recycling.

Figure 4 shows a diagram of a heat pump according to the invention which comprises both a flash tank 203 and heat exchangers 214, 224 arranged downstream of the non-final condenser 212 and the final condenser 222. This combination combines the advantages described above by extracting the latent heat stored in the liquid working fluid 4 and by using the pressure build up in the working fluid 4 to flash the working fluid 4 so that the flashed gaseous working fluid 4 may be returned directly to the compressors without passing the evaporation portion 100.

Figure 5 shows a diagram of a heat pump according to the invention, depicting how the heat pump may be expanded with an additional number (m) of secondary evaporation stage units and an additional number (n) of non-final condenser stage units.

The secondary evaporation stage units each comprise a secondary evaporation stage compressor 121 which is arranged downstream of the first evaporation stage compressor 111 so that the pressure of the gaseous working fluid 4 can be raised in stages before it is conveyed to the condenser portion 200. The secondary evaporation stage units further comprise an evaporation stage flash tank 123 arranged downstream of the condenser portion 200 so that the liquid working fluid 4 returning for evaporation passes through the evaporation stage flash tank 123. The pressure inside the flash tanks of each secondary evaporation stage unit corresponds to that at the entrance of the secondary evaporation stage compressor 121 of that secondary evaporation stage unit. Thus, liquid working fluid 4 entering the evaporation stage flash tank 123 from a higher pressure level will to some extent be flashed, and the flashed gaseous working fluid 4 can be conveyed to the compressor stage with the appropriate pressure. The remaining liquid working fluid (4) can be conveyed to the evaporation stage flash tank 123 of a subsequent secondary evaporation stage unit or to the first evaporation stage unit.

In the shown embodiment the evaporation stage flash tanks 123 of the evaporation portion are all arranged in series such that liquid working fluid (4) is consecutively transferred from the flash tank 123 of the secondary evaporation stage unit with the highest pressure the subsequent evaporation stage flash tank 123 of the secondary evaporation stage unit with the lower pressure, before the liquid working fluid 4 which remains after the flashing stages is finally transferred to the first evaporator 112.

As seen in figs. 6-8, each secondary evaporation stage unit can further comprise a secondary evaporator 122 configured to evaporate the liquid working fluid 4 returning from the condenser portion 200 at substantially the same pressure as the entrance of the secondary evaporation stage compressor 121 of that secondary evaporation stage unit.

In the shown embodiments, the first heat exchange medium 2 is passed through the various evaporators 112, 122 in series. Similarly to the previously mentioned flow of the second heat exchange medium 3, the flow of the first heat exchange medium 2 may be configured such, that the first heat exchange medium will brought into heat exchange with evaporator 122 with the highest temperature, before being conveyed to a subsequent evaporator 112, 122 with a lower temperature. Alternatively, the evaporators 112, 122 may have individual supply lines for the first heat exchange medium, i.e. the first heat exchange medium 2 will be conveyed in parallel to the evaporators. In the embodiment where the heat pump uses the ground as a first heat exchange medium 2, i.e. a geothermal heat pump, the first heat exchange medium 2 will of course be non-flowing (static).

In the shown embodiment of the invention the m secondary evaporation stage units and the n non-final condenser stage units are arranged in series between the first evaporation stage unit and the final condenser stage unit, so that gaseous working fluid 4 is transferred successively from one compressor to the subsequent on its path towards the final condenser stage compressor 221, and so that that liquid working fluid 4 is transferred successively from one flash tank to the subsequent on its path towards first evaporator 112. An alternative embodiment could be conceived, wherein the m secondary evaporation stage units and the n non-final condenser stage units would be arranged in parallel, so that the gaseous working fluid 4 from the first evaporation unit would be split to secondary evaporation stage compressors 121 of the m secondary evaporation stage units, from where it could be conveyed to the non-final condenser stage compressors 211 of the n non final condenser stage units, before being conveyed to the final condenser stage unit.

Figure 6, 7, and 8 show embodiments of the invention, wherein the number m of secondary evaporation stage units is 1 and the number n of non-final condenser stage units is 1. In the shown embodiments, the m secondary evaporation stage units and the n non-final condenser stage units further comprise heat exchangers 214, 224, 215, 225 and flash tanks 123, 223 so that the heat pump may have the above-mentioned advantages. As previously mentioned, the heat exchangers 214, 224, 215, 225 and flash tanks 123, 223 are independent of each other and need not be present in all or any of the m secondary evaporation stage units and the n non-final condenser stage units.

Figure 9 shows an example of a heat pump of the invention, wherein the number m of secondary evaporation stage units is zero, and the number n of non-final condenser stage units is four. The heat pump may be designed with m and n secondary evaporation stage units and non-final condenser stage units according to the requirements of the output effect which has to be transferred to the second heat exchange medium 3 and the amount of energy provided by the first heat exchange medium 2. Furthermore, the heat pump may be designed with a number m and n of secondary evaporation stage units and non-final condenser stage units, respectively, so that the compressors with the optimal compression ratio may be used. This allows the manufacturing cost of the heat pump to be minimized.

In the embodiment shown in fig. 9 the condenser portion 200 comprises 3 condenser stage flash tanks 203 connected to the 2nd, 3rd, and 4th non-final condenser stage units. This means that the pressure inside the condenser stage flash tanks 203 is substantially the same as the pressure as the exit of the non-final condenser stage compressor 221 to which they are coupled.

In the embodiment shown in fig. 9 the condenser portion 200 has heat exchangers arranged downstream of the final condenser 222 and downstream of the non-final condenser 212 of the 3rd and 4th non-final condenser stage units. The heat exchangers can in some cases be omitted at the nonfinal condenser stage units with lower pressure because the temperature of the condensed working fluid (4) exiting the non-final condenser 212 of these non-final condenser stage units is insufficient to heat the second heat exchange medium 3.

Although the figures all show the first and second heat exchange mediums 2, 3 running in single lines through the evaporation portion 100 and the condenser portion 200, respectively, it should be understood that each component of the heat pump, which transfers energy between the working fluid 4 and one of the heating mediums 2, 3, could have an individual supply of heating medium, such that the heat exchange would occur in parallel rather than in series.

In such embodiments it could be conceived, that the first and/or second heat exchange medium 2, 3 could comprise several different substances being brought into heat exchange with different. For example, the evaporation portion 100 could use air as a first heat exchange medium 2 for some of the evaporators and water as a first heat exchange medium 2 for others.

The supply lines leading the second heat exchange medium 3 into thermal contact with the condensers 212, 222 and heat exchangers 214, 224, 215, 225 of the condenser portion 200 may in some embodiments of the invention be redirectable, such that the flow of the of the second heat exchange medium 3 is optimized according to the temperature at the various heat exchanging stages, the desired outlet temperature of the second heat exchange medium 3, and the inlet temperature of the second heat exchange medium 3.

It should be noted, that although the figures shows that the liquid working fluid 4 exiting the non-final condenser 212 and the final condenser 222 being returned to the evaporation portion 100 through a single line, it is possible to couple the non-final condenser 212 and the final condenser 222 to separate inlets of the evaporation portion 100, this could be done to convey liquid working fluid 4 directly from the final condenser stage unit to secondary evaporation stage units and liquid working fluid 4 from the non-final condenser stage unit to first evaporation stage unit.

The heat exchangers 214, 224, 215, 225 and the flash tanks 123, 203 are all optional components which can be added to the heat pump independently of each other.

Patent items 1. Heat pump apparatus (1) for cooling a first heat exchange medium (2) in heat exchange with a working fluid (4) circulating in a closed circuit, and heating a second heat exchange medium (3) in heat exchange with said working fluid (4), said apparatus (1) comprising: an evaporation portion (100) adapted for cooling the first heat exchange medium (2) in heat exchange with the working fluid (4), wherein the evaporation portion (100) comprises, a first evaporator stage unit comprising an evaporator (112) which uses energy from the first heat exchange medium (2) to evaporate the working fluid (4), and a first evaporation stage compressor (111) arranged downstream from the evaporator (112); and a condenser portion (200) adapted for heating the second heat exchange medium (3) in heat exchange with the working fluid (4), wherein the condenser portion (200) comprises, a) a final condenser stage unit comprising a final condenser (222) which transfers energy from condensation of the working fluid (4) to the second heat exchange medium (3), and a final condenser stage compressor (221) arranged upstream from the final condenser (222), and b) a non-final condenser stage unit arranged between the evaporation portion (100) and the final condenser unit, said first condenser unit comprising a non-final condenser (212) which transfers energy from condensation of the working fluid (4) to the second heat exchange medium (3), and a non-final condenser stage compressor (211) arranged upstream from the non-final condenser (212), wherein a part of the working fluid (4) exiting the non-final condenser stage compressor (211) is transferred to the non-final condenser (212) and a remaining part of the working fluid (4) is transferred to the final condenser stage compressor (221). 2. The heat pump apparatus (1) of item 1, wherein the condenser portion (200) comprises two or more non-final condenser stage units arranged between the evaporation portion (100) and the final condenser stage unit, such that the remaining part of the working fluid (4) exiting a nonfinal condenser stage compressor (211) is transferred to the non-final condenser stage compressor (211) of a subsequent non-final condenser stage unit or the final condenser unit. 3. The heat pump apparatus (1) of any one of the previous items, wherein the condenser portion (200) further comprises one or more condenser stage flash tank(s) (203) arranged downstream from the final condenser unit, each of the one or more flash tanks(s) (203) being adapted for flashing the condensed working fluid (4) and transferring the flashed gaseous working fluid (4) to a non-final condenser stage compressor (211) and transferring the remaining liquid condensed working fluid (4) to a subsequent condenser stage flash tank (203) or to the evaporation portion (100). 4. The heat pump apparatus (1) of any one of the previous items, wherein the evaporation portion (100) further comprises one or more secondary evaporation stage unit(s) arranged between the first evaporation unit and the condenser portion (200), said one or more secondary evaporation stage unit(s) comprising a secondary evaporation stage compressor (121) arranged downstream from the first evaporation stage compressor (111) and upstream from the condenser portion (200), so that the gaseous working fluid (4) exiting a secondary evaporation stage compressor (121) is transferred to a subsequent secondary evaporation unit or to the condenser portion (200), and an evaporation stage flash tank (123) arranged downstream from the condenser portion (200), adapted for flashing the condensed working fluid (4) and transferring the flashed gaseous working fluid (4) to the secondary evaporation stage compressor (121) via a gas outlet, and transferring the remaining condensed working fluid (4) to a subsequent evaporation stage flash tank (203) or to the first evaporation unit via a liquid outlet. 5. The heat pump apparatus (1) of item 4, wherein at least one of the one or more secondary evaporation stage unit(s) comprises a secondary evaporator (122) arranged upstream from the secondary evaporation stage compressor (121) and downstream of the liquid outlet of the evaporation stage flash tank (123), so that a part of the liquid working fluid (4) exiting the evaporation stage flash tank (123) is transferred to said secondary evaporator (122), said secondary evaporator (122) using energy from the first heat exchange medium (2) to evaporate the working fluid (4). 6. The heat pump apparatus (1) of any one of the previous items, wherein the condenser portion (200) further comprises one or more heat exchangers) (214, 224, 215, 225) for transferring energy from the working fluid (4) to the second heat exchange medium (3), arranged downstream and/or upstream from the condenser of the one or more nonfinal condenser stage unit(s) and/or of the final condenser unit. 7. The heat pump apparatus (1) of any one of the previous items, wherein two or more of the first evaporator stage compressor (111), the one or more secondary evaporator stage compressor(s) (121), the one or more non-final condenser stage compressor(s) (211), and/or the final condenser stage compressor (221) are driven co-axially by a driver (5). 8. The heat pump apparatus (1) of any one of the previous, wherein the compressors are driven by an internal combustion engine, a gas turbine, a gas engine, a steam turbine and/or an electric motor. 9. The heat pump apparatus (1) of any one of the previous, wherein the first heat exchange medium (2) is air, water from a natural reservoir and/or process water from an industrial process and the second heat exchange medium (3) is water from a district or central heating system. 10. A process for cooling a first heat exchange medium in heat exchange with a working fluid circulating in a closed circuit, and heating a second heat exchange medium in heat exchange with said working fluid, said process comprising the steps of: cooling the first heat exchange medium in an evaporation stage comprising the steps of: evaporating the working fluid by using energy from the first heat exchange medium, and compressing the evaporated gaseous working fluid to form a compressed evaporation stage working fluid; and heating the second heat exchange medium in a condenser stage comprising the steps of: compressing the compressed evaporation stage working fluid to form a first compressed condenser stage working fluid, condensing a first part of the compressed first condenser stage working fluid in heat exchange with the second heat exchange medium, thereby forming a first liquid condenser stage working fluid, compressing a second part of the compressed first condenser stage working fluid to form a final condenser stage working fluid, condensing the final condenser stage working fluid in heat exchange with the second heat exchange medium, thereby forming a final liquid condenser stage working fluid, and conveying the first liquid condenser stage working fluid and the final liquid condenser stage working fluid to the evaporation stage. 11 .The process of item 10, wherein the first compressed condenser stage working fluid is conveyed to a second or further non-final condenser stage compressing steps (n) before compressing to the final condenser stage working fluid. 12.The process of items 10 or 11 wherein the number of non-final condenser stage compressing steps (n) is 1 to 15. 13. The process of any one of items 11 and 12, wherein the pressure of the working fluid is increased by 1 to 10 bars in each of the n compressing steps. 14. The process of any one of items 10 to 13, wherein the pressure of the final condenser stage working fluid is between 10 and 40 bar. 15. The process of any one of items 10 to 14, wherein the pressure of the first compressed condenser stage working fluid is between 1.5 and 20 bar. 16. The process of any one of items 10 to 15, wherein the final liquid condenser stage working fluid is flashed, thereby forming a gaseous working fluid which is conveyed to the nth non-final compressing step, and a liquid working fluid, which is conveyed to the evaporation stage or to a (n-1 )th non-final flash tank. 17. The process of any one of items 10 to 16, wherein a heat exchanging step is performed before and/or after the condensing step, in which the working fluid is cooled and the second heat exchange medium is heated. 18. The process according to any one of the items 10 to 17, wherein the first compressed evaporator stage working fluid is conveyed to one or more secondary evaporation compressing steps (m) before compressing in the condenser stage. 19. The process according to any one of the items 10 to 18, wherein the number of secondary evaporation compressing steps (m) is 0 to 15. 20. Use of the apparatus according to any one of the items 1 to 9 for district heating, wherein the second heat exchange medium is part of the heating circuit. 21. Use of the apparatus according to any one of the items 1 to 9 for heating purposes in horticulture, abattoirs or industry. 22. Use of the apparatus according to any of the items 20 or 21, wherein the first heat exchange medium is air, water from a natural reservoir and/or process water from an industrial process.

Claims

1. Heat pump apparatus (1) for cooling a first heat exchange medium (2) in heat exchange with a working fluid (4) circulating in a closed circuit, and heating a second heat exchange medium (3) in heat exchange with said working fluid (4), said apparatus (1) comprising: an evaporation portion (100) adapted for cooling the first heat exchange medium (2) in heat exchange with the working fluid (4), wherein the evaporation portion (100) comprises, a first evaporator stage unit comprising an evaporator (112) which uses energy from the first heat exchange medium (2) to evaporate the working fluid (4), and a first evaporation stage compressor (111) arranged downstream from the evaporator (112); and a condenser portion (200) adapted for heating the second heat exchange medium (3) in heat exchange with the working fluid (4), wherein the condenser portion (200) comprises, a) a final condenser stage unit comprising a final condenser (222) which transfers energy from condensation of the working fluid (4) to the second heat exchange medium (3), and a final condenser stage compressor (221) arranged upstream from the final condenser (222), and b) a non-final condenser stage unit arranged between the evaporation portion (100) and the final condenser unit, said first condenser unit comprising a non-final condenser (212) which transfers energy from condensation of the working fluid (4) to the second heat exchange medium (3), and a non-final condenser stage compressor (211) arranged upstream from the non-final condenser (212), wherein a part of the working fluid (4) exiting the non-final condenser stage compressor (211) is transferred to the non-final con denser (212) and a remaining part of the working fluid (4) is transferred to the final condenser stage compressor (221).

2. The heat pump apparatus (1) of claim 1, wherein the condenser portion (200) comprises two or more non-final condenser stage units arranged between the evaporation portion (100) and the final condenser stage unit, such that the remaining part of the working fluid (4) exiting a non-final condenser stage compressor (211) is transferred to the nonfinal condenser stage compressor (211) of a subsequent non-final condenser stage unit or the final condenser unit.

3. The heat pump apparatus (1) of any one of the previous claims, wherein the condenser portion (200) further comprises one or more condenser stage flash tank(s) (203) arranged downstream from the final condenser unit, each of the one or more flash tanks(s) (203) being adapted for flashing the condensed working fluid (4) and transferring the flashed gaseous working fluid (4) to a non-final condenser stage compressor (211) and transferring the remaining liquid condensed working fluid (4) to a subsequent condenser stage flash tank (203) or to the evaporation portion (100).

4. The heat pump apparatus (1) of any one of the previous claims, wherein the evaporation portion (100) further comprises one or more secondary evaporation stage unit(s) arranged between the first evaporation unit and the condenser portion (200), said one or more secondary evaporation stage unit(s) comprising a secondary evaporation stage compressor (121) arranged downstream from the first evaporation stage compressor (111) and upstream from the condenser portion (200), so that the gaseous working fluid (4) exiting a secondary evaporation stage compressor (121) is transferred to a subsequent secondary evaporation unit or to the condenser portion (200), and an evaporation stage flash tank (123) arranged downstream from the condenser portion (200), adapted for flashing the condensed working fluid (4) and transferring the flashed gaseous working fluid (4) to the secondary evaporation stage compressor (121) via a gas outlet, and transferring the remaining condensed working fluid (4) to a subsequent evaporation stage flash tank (203) or to the first evaporation unit via a liquid outlet.

5. The heat pump apparatus (1) of any one of the previous claims, wherein the condenser portion (200) further comprises one or more heat exchangers) (214, 224, 215, 225) for transferring energy from the working fluid (4) to the second heat exchange medium (3), arranged downstream and/or upstream from the condenser of the one or more nonfinal condenser stage unit(s) and/or of the final condenser unit.

6. A process for cooling a first heat exchange medium in heat exchange with a working fluid circulating in a closed circuit, and heating a second heat exchange medium in heat exchange with said working fluid, said process comprising the steps of: cooling the first heat exchange medium in an evaporation stage comprising the steps of: evaporating the working fluid by using energy from the first heat exchange medium, and compressing the evaporated gaseous working fluid to form a compressed evaporation stage working fluid; and heating the second heat exchange medium in a condenser stage comprising the steps of: compressing the compressed evaporation stage working fluid to form a first compressed condenser stage working fluid, condensing a first part of the compressed first condenser stage working fluid in heat exchange with the second heat exchange medium, thereby forming a first liquid condenser stage working fluid, compressing a second part of the compressed first condenser stage working fluid to form a final condenser stage working fluid, condensing the final condenser stage working fluid in heat exchange with the second heat exchange medium, thereby forming a final liquid condenser stage working fluid, and conveying the first liquid condenser stage working fluid and the final liquid condenser stage working fluid to the evaporation stage.

7. The process of claim 6, wherein the first compressed condenser stage working fluid is conveyed to a second or further non-final condenser stage compressing steps (n) before compressing to the final condenser stage working fluid.

8. The process of claims 6 or 7 wherein the number of non-final condenser stage compressing steps (n) is 1 to 15.

9. The process of any one of claims 6 and 8, wherein the pressure of the working fluid is increased by 1 to 10 bars in each of the n compressing steps.

10. The process of any one of claims 6 to 9, wherein the pressure of the final condenser stage working fluid is between 10 and 40 bar.