The present invention relates to a heat exchanger arrangement according to Patent Claim 1, and to a heat pump comprising same according to Claim 8.

CO2 heat pumps can provide heating up to or even at high temperatures for media to be heated. Typical parameters that can presently be reached and are realized in corresponding heat pumps are temperatures of up to 150°C and pressures of up to 130 bar.

In heat pumps of this type, CO2 releases heat in the transcritical phase, i.e. it is cooled without condensation. This makes it a good candidate for heating flows of water, air or other fluids with a large increase in temperature, starting at low temperatures.

At the same time, CO2 heat pumps can provide cold water at low temperatures (<5°C). In this context, CO2 heat pumps are quite unique, since they can provide high-temperature heating and low-temperature cooling at the same time with single-stage compression.

However, the specific heat capacity of CO2 in the transcritical phase varies considerably during the cooling.

CONFIRMATION COPY In order to produce a fluid (for example air or water) with a high temperature by means of transcritical CO2, it is therefore advantageous at least for certain fluids, i.e. fluids that have a different specific heat capacity profile to CO2, to perform the CO2 cooling in more than one stage for different temperature ranges, each cooling stage being assigned a separate heat exchanger. This is advantageous, since e.g. when heating water, which has an approximately constant heat capacity cp throughout a temperature range of 10-130°C, in a low-temperature stage, in which CO2 can release a greater quantity of energy than in a high-temperature stage, more water can be heated to the desired temperature in the low-temperature stage than in the high-temperature stage. Consequently, a mass flow of water determined by the high-temperature stage can be heated, with the result that good correspondence of the CO2 and water temperature profiles is obtained.

A paper for the Gustav Lorentzen conference 2018, OPTIMUM HIGH PRESSURE FOR TRANSCRITICAL C02 HEAT PUMPS CONSIDERING ISENTROPIC EFFICIENCY AND GLIDING HEAT EXTRACTION", Klaus Spindler, 13th HR Gustav Lorentzen Conference, Valencia, 2018, presents a setup of CO2 heat pumps in which 4 gas coolers, each with different water mass flows, are connected in series in order to optimize the efficiency of the heat pump.

The result of such split CO2 cooling is that the mass flow of heated fluid that is available in a CO2 heat pump at high temperature (>75°C) is smaller than the mass flow of heated fluid that is available at lower temperatures.

The result of this is that, in order to attain a desired mass flow of fluid with a high temperature, a heat exchanger arrangement or a heat pump must be dimensioned such that in the region of lower temperatures it functions ineffectively or exhibits an excess of heat, which adversely affects the efficiency.

Taking this as a starting point, the object of the present invention is to specify a heat exchanger arrangement and a corresponding heat pump which ensure that the heat energy released by CO2 is utilized as optimally as possible.

This object is achieved by a heat exchanger arrangement having the features of Patent Claim 1 and by a heat pump according to Claim 8. Accordingly, the object relating to the heat exchanger arrangement is achieved by a heat exchanger arrangement for a heat pump, comprising the following: at least two heat exchangers, specifically a first heat exchanger and a second heat exchanger, wherein each of the first heat exchanger and the second heat exchanger is designed to allow a transfer of heat from a flowing operating medium, in particular from a gaseous operating medium of a heat pump, which is in a transcritical state, furthermore in particular from R744 in a transcritical state, to a heat-absorbing medium (heat-receiving medium), wherein the first heat exchanger and the second heat exchanger are arranged one after the other in a flow direction of the operating medium and form a first heat transfer stage and a second heat transfer stage, each of which is designed to transfer heat to the heat-absorbing medium, and at least one additional heat source, which is arranged and designed to transfer heat to the heat-absorbing medium in parallel with the transfer of heat from the operating medium in the first heat transfer stage and/or the second heat transfer stage.

The specific configuration in terms of the additional heat source, in particular the configuration as regards whether heat is transferred to the heat-absorbing medium only in one heat transfer stage or in the two heat transfer stages, depends on the specifications for the heat pump; in most cases, the additional heat source is used for the additional transfer of heat in a high-temperature stage of the heat pump.

The arrangement may comprise a further heat exchanger which forms a further heat transfer stage, or may comprise multiple further heat exchangers which are arranged one after the other in the flow direction of the operating medium and form further heat transfer stages, wherein each of the further heat exchangers or the further heat exchanger is arranged upstream or downstream of the first and the second heat exchanger in the flow direction of the operating medium. The additional stages ensure a finer distribution of the heating process for the heat-absorbing medium. It is also conceivable for one or more additional stages to be assigned an additional heat source, in order to make the heating of the heat-absorbing medium as optimal as possible in energy terms. For this purpose, the arrangement may comprise one or more further heat sources, which is/are arranged and designed to transfer heat to the heat-absorbing medium in parallel with the transfer of heat from the operating medium in the first heat transfer stage and/or the second heat transfer stage and/or an (the) additional heat transfer stage or one or more of (the) additional heat transfer stages.

The heat exchangers are optionally gas coolers, this allowing an optimum transfer of heat from the transcritical phase in the case of the refrigerant R744 (C0 ₂ ). In the wording of the present application, gas coolers are heat exchangers which the operating medium enters in a gaseous state and leaves again also in a gaseous state.

The heat source and/or (the) one or more further heat sources may each be a heat pump or a steam heater or a gas burner or an electric heater, this not being an exclusive list; all known heat sources or energy sources would be conceivable.

In one possible embodiment, the first heat transfer stage is a medium-temperature stage and the second heat transfer stage is a high-temperature stage.

In addition or as an alternative to this, the arrangement may comprise a cooling-stage heat exchanger, which is arranged and designed to transfer heat from a medium to be cooled to the operating medium. This makes it possible, in addition to the heating of the heat-absorbing medium, also to cool a medium to be cooled, with the result that the refrigerating power of the installation can be utilized as a cooling function in parallel with the heating function.

The aspect of the object relating to the specification of a heat pump is achieved by a heat pump or heat pump apparatus according to Claim 8, i.e. by a heat pump apparatus comprising an arrangement according to the description above.

In one possible embodiment, the operating medium is R744 in a transcritical state and the heatabsorbing medium may be air or water. This list is also not exclusive; in particular, any other desired fluids come into consideration as heat-absorbing media. Other refrigerants likewise come into consideration as operating medium, in particular refrigerants with a similar specific heat capacity profile to R744.

Further optional features of the invention are specified in the following description of the figures. The respective features described may be realized individually or in any desired combinations. Accordingly, the invention will be described below with regard to the appended drawings and with reference to exemplary embodiments. In the drawings:

Figure 1 shows a schematic view of a first embodiment of a heat exchanger arrangement according to the invention; Figure 2 shows a schematic view of a second embodiment of a heat exchanger arrangement according to the invention, which shows a modification of the first embodiment;

Figure 3 shows a schematic view of a third embodiment of a heat exchanger arrangement according to the invention;

Figure 4 shows a schematic view of a fourth embodiment of a heat exchanger arrangement according to the invention, which shows a modification of the third embodiment;

Figure 5 shows a temperature-enthalpy diagram for elucidating the function or action (effect) of the heat exchanger arrangement according to the invention.

Figure 1 illustrates a first embodiment of a heat exchanger arrangement 10 according to the invention. The arrangement 10 comprises a first heat exchanger 12 and a second heat exchanger 14. Each of the heat exchangers 12, 14 is arranged to bring about a transfer of heat from a flowing operating medium - in the embodiment described in the present instance, this is R744 (C0 ₂ ) in a transcritical state - to a heat-absorbing medium or heat-receiving medium - in the embodiment described in the present instance, this is water. For this purpose, the operating medium flows through the first heat exchanger 12 and the second heat exchanger 14 on a primary side, and the heat-absorbing medium flows through said heat exchangers on a secondary side.

The first heat exchanger 12 and the second heat exchanger 14 are arranged one after the other in a flow direction of the operating medium, which is indicated by an arrow 16, and are a constituent part of or form a first heat transfer stage 18 and a second heat transfer stage 20, in each case to transfer heat, more specifically heat energy, from the operating medium to the heat-absorbing medium.

The first heat transfer stage 18 serves to heat the heat-absorbing medium to a medium temperature. In the embodiment described here, the medium temperature is a temperature of approximately 70°C to 80°C, preferably approximately 75°C. The second heat transfer stage 20 serves to heat the heat-absorbing medium to a high temperature. In the embodiment described here, the high temperature is a temperature of approximately 140°C to 160°C, preferably approximately 150°C. The first heat transfer stage 18 is therefore also referred to as medium- temperature stage, and the second heat transfer stage 20 is therefore also referred to as high- temperature stage. Similarly, the first heat exchanger 12 is also referred to as medium- temperature exchanger and the second heat exchanger 14 is referred to as high-temperature exchanger.

The arrangement 10 furthermore comprises an additional heat source 22, which is arranged to transfer heat to the heat-absorbing medium in parallel with the transfer of heat from the operating medium in the second heat transfer stage 20. This is indicated by an arrow 24, which illustrates that a quantity of heat AQ is transferred from the additional heat source 22 to the heat-absorbing medium. In the present embodiment, the quantity of heat AQ is fed from the additional heat source 22 to the heat-absorbing medium in parallel by way of the and/or in the second heat exchanger 14. In other words, the quantity of heat AQ is transferred from the additional heat source 22 in parallel with the feed of heat energy from the operating medium to the heat absorbing medium. In the first embodiment described here, in this respect the quantity of heat AQ from the additional heat source 22 and the heat from the operating medium act on the total flow of the heat-absorbing medium. In other words, this means that the quantity of heat AQ from the additional heat source 22 and the heat from the operating medium are both transferred to the total flow of the heat-absorbing medium.

The additional heat source 22 may be assigned to the second heat transfer stage 20 or be a constituent part of the second heat transfer stage 20, as is indicated in Figure 1. However, the additional heat source 22 may also be a heat source which is not a constituent part of the second heat transfer stage 20 or cannot be assigned to it or can be assigned to it at least non-exclusively. For example, in alternative embodiments comprising further heat transfer stages, the additional heat source 22 may also supply (additional) heat to one or more further heat transfer stages.

As an alternative to the design described above, however, any other type of parallel feed of a (additional) quantity of heat AQ is also conceivable. An alternative example to this will be elucidated below with reference to Figure 2.

In the described first embodiment of an arrangement 10 according to the invention, the additional heat source 22 is a heat pump, in this instance a heat pump providing heat at a high temperature, which preferably functions with much higher temperatures on the cold side than CO2 heat pumps. This type of heat source can consequently also be referred to as booster. As an alternative to this, other heat pumps and also any desired other heat sources are also conceivable (a person skilled in the art will select the additional heat source taking into account the respective area of use of the arrangement 10), in particular for example also fluid flows or liquid flows from conventional heating devices. Conventional examples are steam heaters. They function at steam pressures of over 20 bar. The condensate leaves this heater at high pressure and high temperatures and should be cooled down below 90°C before being returned to the steam boiler. Therefore, it is a heat source functioning in an ideal temperature range. Furthermore, gas burners are also conceivable. Depending on the type of the burner, flue gases from the combustion process are discharged at temperatures of higher than 250°C, which can be cooled down to less than 80°C. Furthermore, electric heaters are also suitable and conceivable for this type of use.

Figure 5 illustrates a temperature-enthalpy diagram for elucidating the function or action of the heat exchanger arrangement 10 according to the invention. From this, it is possible to see the contributions of the operating medium CO2 and of the additional heat source to the total enthalpy of the heat-absorbing medium.

A second embodiment of an arrangement 10' according to the invention is illustrated in Figure 2. The second embodiment in turn comprises a first heat transfer stage 18' and a second heat transfer stage 20'.

The first heat transfer stage 18' of the arrangement 10' according to the second embodiment has a similar form to that of the first embodiment and comprises a heat exchanger 12', which has a similar form to the heat exchanger 12.

The second heat transfer stage 20' comprises a second heat exchanger 14' and a first additional heat exchanger 14z. The second heat exchanger 14' differs from the second heat exchanger 14 of the first embodiment in that the second heat exchanger 14' serves to heat a first partial flow or partial mass flow of the heat-absorbing medium exclusively by transfer of heat from the operating medium, whereas the first additional heat exchanger 14z serves to heat a second partial flow or partial mass flow of the heat-absorbing medium exclusively by transfer of the quantity of heat AQ from an additional heat source 22', which corresponds to the additional heat source 22 in the embodiment described. In this case, it holds true that the sum of the first partial flow of the heat-absorbing medium and the second partial flow of the heat-absorbing medium gives the total flow of the heat-absorbing medium. In other words, the total flow or total mass flow of the heat-absorbing medium is subdivided prior to being heated by the second heat transfer stage 20' and then the resulting two partial flows are heated in parallel in separate heat exchangers (first heat exchanger 14' for transferring heat from the operating medium to the first partial flow and first additional heat exchanger 14z for transferring heat from the additional heat source 22') and recombined after being heated.

The first heat exchanger 12' and the second heat exchanger 14' are in the form of gas coolers. In the wording of the present application, gas coolers are heat exchangers which the operating medium enters in a gaseous state and leaves again also in a gaseous state, this being the case for R744 in the transcritical phase.

A third embodiment of an arrangement 10" according to the invention is illustrated in Figure 3.

This arrangement comprises a first heat exchanger 12" and a second heat exchanger 14", and additionally a zeroth heat exchanger 40 and a third heat exchanger 42. The first heat exchanger 12" and the second heat exchanger 14" have a similar form to the first heat exchanger 12 and to the second heat exchanger 14, respectively. The zeroth heat exchanger 40 has a similar form to the first heat exchanger 12" (and therefore also to the first heat exchanger 12); the third heat exchanger 42 has a similar form to the second heat exchanger 14" (and therefore also to the second heat exchanger 14).

Each of the heat exchangers 40, 12", 14" and 42 is arranged to bring about a transfer of heat from the flowing operating medium - in the embodiment described in the present instance, this is in turn R744 in a transcritical state - to the heat-absorbing medium - in the embodiment described in the present instance, this is air. For this purpose, the operating medium flows through the zeroth heat exchanger 40, the first heat exchanger 12", the second heat exchanger 14" and the third heat exchanger 42 on a primary side, and the heat-absorbing medium flows through said heat exchangers on a secondary side.

The zeroth heat exchanger 40, the first heat exchanger 12", the second heat exchanger 14" and the third heat exchanger 42 are arranged one after the other in a flow direction of the operating medium, which is in turn indicated by the arrow 16, and are a constituent part of or form a zeroth heat transfer stage 44, a first heat transfer stage 18", a second heat transfer stage 20" and a third heat transfer stage 46, respectively, in each case serving to transfer heat from the operating medium to the heat-absorbing medium.

The zeroth heat transfer stage 44 serves to heat the heat-absorbing medium to a first temperature, the first heat transfer stage 18" serves to heat the heat-absorbing medium to a second temperature greater than the first temperature, the second heat transfer stage 20" serves to heat the heat-absorbing medium to a third temperature greater than the second temperature, and the third heat transfer stage 46 serves to heat the heat-absorbing medium to a fourth temperature, which is the final temperature of the arrangement 10" and is greater than the third temperature.

The arrangement 10" furthermore comprises a first additional heat source 22", which in the embodiment described is a constituent part of the second heat transfer stage 20" and is arranged to transfer heat to the heat-absorbing medium in parallel with the transfer of heat from the operating medium in the second heat transfer stage 20". The heat transferred by the first additional heat source 22" is heat that does not originate from the operating medium, but rather is additional heat, i.e. heat originating from the first additional heat source 22". This is indicated by an arrow 24", which illustrates that a quantity of heat AQl is transferred from the first additional heat source 22" to the heat-absorbing medium. In the present embodiment, the quantity of heat AQl is fed to the heat-absorbing medium by way of the second heat exchanger 14", in a manner in parallel with the feed of heat energy from the operating medium to the heat-absorbing medium. As an alternative to this, however, any other type of parallel feed of a (additional) quantity of heat AQ is also conceivable.

The arrangement 10" furthermore comprises a second additional heat source 48, which in the embodiment described is a constituent part of the third heat transfer stage 46 and is arranged to transfer heat to the heat-absorbing medium in the third heat transfer stage 46. The heat transferred by the second additional heat source 48 is in turn heat that does not originate from the operating medium, but rather is additional heat, i.e. heat originating from the second additional heat source 48. This is indicated by an arrow 50, which illustrates that a quantity of heat AQ2 is transferred from the second additional heat source 48 to the heat-absorbing medium in parallel with the transfer of heat from the operating medium. In the present embodiment, the quantity of heat AQ2 is fed to the heat-absorbing medium by way of the third heat exchanger 42, in a manner in parallel with the feed of heat energy from the operating medium to the heat-absorbing medium. As an alternative to this, however, any other type of parallel feed of a (additional) quantity of heat AQ is also conceivable.

In the described third embodiment of an arrangement 10" according to the invention, the first additional heat source 22" is a heat pump and the second additional heat source 48 is a gas burner.

As an alternative to this, for any additional heat source other heat pumps and also any desired other heat sources are also conceivable (a person skilled in the art will select the additional heat source taking into account the respective area of use of the arrangement 10"), in particular for example also fluid flows or liquid flows from conventional heating devices. Conventional examples are steam heaters. They function at steam pressures of over 20 bar. The condensate leaves this heater at high pressure and high temperatures and should be cooled down below 90°C before being returned to the steam boiler. Therefore, it is a heat source functioning in an ideal temperature range. Furthermore, gas burners are also conceivable. Depending on the type of the burner, flue gases from the combustion process are discharged at temperatures of higher than 250°C, which can be cooled down to less than 80°C. Furthermore, electric heaters are also suitable and conceivable for this type of use.

In an alternative embodiment, it is also conceivable that the first additional heat source 22" and the second additional heat source 48 are fed from a common source or are a common additional heat source, for example a steam heater, which can transfer, among other things, heat of condensation in the form of energy, for example.

The arrangement 10" additionally comprises a cooling-stage heat exchanger 52, which transfers heat from a medium to be cooled to the operating medium, as a result of which the arrangement 10" can operate both a heating circuit and a refrigerating circuit or cooling circuit. This ensures energy-efficient use of the arrangement 10".

A fourth embodiment of an arrangement 10"' according to the invention is illustrated in Figure 4. The fourth embodiment deviates from the third embodiment and differs from the third embodiment in a similar way to how the first and second embodiments differ. Like the third embodiment, the arrangement 10"' comprises four heat transfer stages, specifically a zeroth heat transfer stage 44', a first heat transfer stage 18"', a second heat transfer stage 20'" and a third heat transfer stage 46'. The zeroth heat transfer stage 44' and the first heat transfer stage 18'" have similar forms or structures to the zeroth heat transfer stage 44 and the first heat transfer stage 18" of the third embodiment, and comprise a zeroth heat exchanger 40' and a first heat exchanger 12'", which in turn have similar structures to the zeroth heat exchanger 40 and the first heat exchanger 12" of the third embodiment.

The second heat transfer stage 20'" and the third heat transfer stage 46' have similar structures to the second heat transfer stage 20' of the second embodiment.

The second heat transfer stage 20'" comprises a second heat exchanger 14'" and a first additional heat exchanger 14z'. The second heat exchanger 14'" differs from the second heat exchanger 14" of the third embodiment in that the second heat exchanger 14'" serves to heat a first partial flow or partial mass flow of the heat-absorbing medium exclusively by transfer of heat from the operating medium, whereas the first additional heat exchanger 14z' serves to heat a second partial flow or partial mass flow of the heat-absorbing medium exclusively by transfer of the quantity of heat AQl from an additional heat source 22'".

In this case, it holds true that the sum of the first partial flow of the heat-absorbing medium and the second partial flow of the heat-absorbing medium gives the total flow of the heat-absorbing medium. In other words, the total flow or total mass flow of the heat-absorbing medium prior to being heated by the second heat transfer stage 20'" is subdivided and then the resulting two partial flows are heated in parallel in separate heat exchangers (second heat exchanger 14'" for transferring heat from the operating medium to the first partial flow and first additional heat exchanger 14z' for transferring heat from the additional heat source 22') and recombined after being heated.

The third heat transfer stage 46' comprises a third heat exchanger 42' and a second additional heat exchanger 42z'. The third heat exchanger 42’ differs from the third heat exchanger 42 of the third embodiment in that the third heat exchanger 42' serves to heat a third partial flow or partial mass flow of the heat-absorbing medium exclusively by transfer of heat from the operating medium, whereas the second additional heat exchanger 42z' serves to heat a fourth partial flow or partial mass flow of the heat-absorbing medium exclusively by transfer of the quantity of heat AQ2 from a second additional heat source 48'.

In this case, it holds true that the sum of the third partial flow of the heat-absorbing medium and the fourth partial flow of the heat-absorbing medium gives the total flow of the heat-absorbing medium. In other words, the total flow or total mass flow of the heat-absorbing medium prior to being heated by the third heat transfer stage 46' is subdivided in turn and then the resulting two partial flows are heated in parallel in separate heat exchangers (third heat exchanger 42' for transferring heat from the operating medium to the first partial flow and second additional heat exchanger 42z' for transferring heat from the additional heat source 48') and recombined after being heated.

All of the heat exchangers 40', 12'", 14'" and 42' are in the form of gas coolers.

In summary, the concept underlying the present invention can be described as adding one or more additional heat source(s) for providing a release of heat to the process in parallel with a CO2 heat pump to a high temperature and/or to a medium temperature, depending on the process requirements.

From its perspective, in this respect the process advantageously sees a single heat source (consisting of a CO2 heat pump and additional heat source or additional heat sources, for example boosters), with the result that it is possible to heat equalized mass flows to high and medium temperatures or, depending on the process requirements, to modify their ratio.

For example, the use of condensate from a steam heater as heat source in parallel with the C0 ₂ heat pump in a spray-drying installation is conceivable, since, in the case of most spray dryers under medium-temperature loading, an excess of heat would be produced if the CO2 heat pump is dimensioned such that it covers the high-temperature loading. Therefore, the cooling of the steam condensate in parallel with the high-temperature gas cooler would enable an increase the COP of the system and at the same time would reduce the number of installed compressors and therefore the investment costs. This is a possible way of maximizing energy savings.

In the case for example of spray-drying installations in cold climatic zones, which require air to be heated at subzero outside temperatures, a CO2 heat pump dimensioned for average conditions could supply an inadequate medium-temperature load during cold winter conditions and excessive medium-temperature load during summerlike conditions. The system can be optimized (better annual COP and still fewer installed compressors) by introducing parallel heating to both temperature levels.

Although the invention is described with reference to embodiments comprising fixed combinations of features, it also comprises the conceivable further advantageous combinations as are specified in particular, but not exhaustively, by the dependent claims. All of the features disclosed in the application documents are claimed as essential to the invention, provided that individual features or combinations of features are novel over the prior art.