Description

The present invention relates to heat pump applications and, in particular, to heat pump systems assembled from several heat pump stages.

Typical fields of application of heat pumps are cooling a region to be cooled and/or heating a region to be heated. A heat pump which typically includes an evaporator, a compressor and a condenser for this purpose includes an evaporator side on the one hand and a condenser side on the other hand, as is exemplarily illustrated in Fig. 5 for a heat pump 100. The heat pump is coupled to an evaporator- side heat exchanger 102 and a condenser- side heat exchanger 104. In particular, the heat pump 100 for this purpose includes an evaporator inlet 101a and an evaporator outlet 101b. Additionally, the heat pump 100 includes a condenser inlet 103a and a condenser outlet 103b. The working (or operating) liquid on the evaporator side is introduced into the evaporator of the heat pump 100 via the evaporator inlet 101a, cooled there and taken from the evaporator outlet 101b as a cooler working liquid. At the same time, the evaporator inlet 101a and the evaporator outlet 101b are, as is shown in Fig. 5, coupled to the heat exchanger 102 such that a hotter working liquid (at a temperature t) is fed into the heat exchanger, the working liquid being cooled in the heat exchanger and transported to the region to be cooled. Typical temperature conditions are indicated in Fig. 5, wherein a "heat exchanger loss" of 1° Celsius is assumed here. In particular, t exemplarily is the set temperature in the region to be cooled.

The heat exchangers 102 and 104 each comprise a primary side directed towards the heat pump, and a secondary side directed away from the heat pump, i.e. towards the region to be cooled and the region to be heated, respectively. The primary side of the heat exchanger 102 includes the hot connection (or terminal) 101a and the cold connection 101b, wherein "hot" and "cold" are to be understood as terms, and wherein the medium in the connection 101a is hotter than in the connection 101b. Correspondingly, connection 103b is the hot connection of the primary side of the heat exchanger 104, and connection 103a is the cold connection. On the secondary side of the heat exchangers 102 and 104, the hot connection is the respective upper connection and the cold connection is the respective lower connection in Fig. 5.

On the condenser side of the heat pump 100, the condenser outlet 103b is connected to the "hot" connection of the heat exchanger 104, and the condenser inlet is connected to the cooler end of the heat exchanger 104. In addition, the heat exchanger is, on the other side directed away from the heat pump 100, connected to the region to be heated where a set temperature T is to be found. When using the heat pump as a cooling unit, the region to be cooled in a way is the "useful side". The region to be cooled may exemplarily be indoors, such as, for example, a computer room or another room to be cooled or air-conditioned. In this case, the region to be heated would, for example, be the outside wall of a building or a roof top or another region where the waste heat is to be directed. When, however, using the heat pump 100 as a heater, the region to be heated in a way is the "useful side" and the region to be cooled would exemplarily be earth, ground water or the like.

Typically, there are requirements as to a set temperature in the region to be cooled and/or a set temperature in the region to be heated. The power of the heat pump 100 to be employed results from these set temperatures and the volumes of the regions to be cooled or the heat dissipation or heat supply required. The greater the power, the greater the heat pump 100 implemented has to be. This procedure is of disadvantage in several aspects, since in this case a special heat pump would actually have to be constructed for each application. However, this procedure is, on the one hand, problematic with regard to economy since a manufacturer of heat pumps would have to offer any number of heat pumps of different classes which would all be implemented differently with regard to condenser, compressor and evaporator. In addition, when not requiring full load, when exemplarily the region to be cooled or the region to be heated exhibits rather favorable temperatures, operating an over-sized heat pump which is really designed for worst-case operation, meaning that sufficient cooling is obtained in the middle of summer and sufficient heating is obtained in the middle of winter, will not always be efficient.

It is the object of the present invention to provide a more efficient heat pump concept. This object is achieved by a heat pump system in accordance with claim 1 , a method for pumping heat in accordance with claim 15 or a method for producing a heat pump system in accordance with claim 16.

The present invention is based on the finding that a special connection of individual heat pump stages results in a significant increase in efficiency. Particularly, a heat pump system includes at least two heat pump stages which are coupled to one another such that the evaporator outlet of a first heat pump stage is coupled fluidically to the evaporator inlet of a second heat pump stage and that additionally the condenser outlet of the second heat pump stage is coupled fluidically to the condenser inlet of the first heat pump stage. By means of this, in a way, "series connection", the temperature difference each heat pump stage has to be able to provide by itself becomes smaller compared to the case in which a single heat pump is used or compared to the situation where two individual heat pump stages are connected in parallel.

With the inventive connection of the two heat pump stages, each heat pump stage has to manage the same flow-through. However, the temperature difference to be provided by each heat pump stage between the evaporator outlet of a heat pump stage and the condenser outlet of said heat pump stage is reduced. The temperature difference to be provided, however, enters the power required by the heat pump quadratically, whereas the flow-through quantity enters the power required linearly. In accordance with the invention, a significant increase in efficiency is achieved in accordance with the invention by reducing the temperature difference to be provided by the individual heat pump stage, since this also means a quadratic decrease in the power to be provided by said heat pump. In further embodiments of the present invention, the temperature difference may be reduced further when more than two stages are connected correspondingly, i.e. when connecting the evaporator inlets and evaporator outlets in series and at the same time also connecting in series the condenser inlets and the condenser outlets. The result is cascading of individual heat pumps, the first heat pump stage of a cascade being connected to the region to be cooled via the evaporator inlet and connected to the region to be heated via the condenser outlet, whereas the last stage of the cascade is connected to the region to be cooled with its evaporator outlet and the last heat pump stage of the cascade is connected to the region to be heated with its condenser inlet.

In embodiments of the present invention, each heat pump stage itself may in turn consist of a series, but also parallel connection of individual heat pump units, an individual heat pump unit consisting of a single evaporator, a compressor and a single condenser. A heat pump stage within the heat pump system may thus be implemented as a heat pump unit or a combination of heat pump units.

Preferred embodiments of the present invention will be detailed subsequently referring to the appended drawings, in which: Fig. 1 shows a block circuit diagram of a preferred implementation of a heat pump system;

Fig. 2 shows an alternative implementation of the heat pump system; Fig. 3 is an illustration of a heat pump unit;

Fig. 4 shows a parallel connection of two heat pump stages; and

Fig. 5 shows an arrangement of a heat pump between two heat exchangers.

Fig. 1 shows a heat pump system comprising a first heat pump stage 10 and a second heat pump stage 12. The first heat pump stage includes a first evaporator inlet 11a and a first evaporator outlet 1 lb. In addition, the first heat pump stage includes a first condenser inlet 13a and a first condenser outlet 13b. Furthermore, the heat pump system includes the second heat pump stage, again comprising a second evaporator inlet 15a and a second evaporator outlet 15b. Additionally, the second heat pump stage 12 includes a second condenser inlet 17a and a second condenser outlet 17b. As is shown in Fig. 1 , the first evaporator outlet l ib and the second evaporator inlet 15a are coupled fluidically. In addition, the second condenser outlet 17b and the first condenser inlet 13a are also coupled to each other fluidically. Fluidic coupling means that the two connecting points, i.e. inlets and outlets, are connected to each other such that the working liquid which, for example, exits the first evaporator outlet l ib, enters the second evaporator inlet 15a. Correspondingly, the second condenser outlet 17b is coupled to the first condenser inlet such that the working liquid exiting the outlet 17b enters the inlet 13a and thus the first heat pump stage, more precisely its condenser. Exemplarily, inlets or outlets are connected to one another by a pressure- and liquid-tight pipe, exemplarily made of plastic. The implementation shown in Fig. 1 additionally illustrates a region to be cooled. A region to be heated is also illustrated. The region to be cooled characterized by the reference numeral 18 may be cooled directly by the working liquid or may comprise a heat exchanger, as has been illustrated with regard to Fig. 5. Correspondingly, the working liquid may also flow directly through the region to be heated 19 or, alternatively, the region to be heated may also comprise a heat exchanger, as has been illustrated with regard to Fig. 5 using the heat exchanger 104 of Fig. 5. The region to be heated includes a "hot" connection 20a and a "cold" connection 20b. Correspondingly, the region to be cooled includes a "hot" connection 23a and a "cold" connection 23b. As is shown in Fig. 1, the first evaporator outlet of the first heat pump stage is connected to the "hot" connection 20a of the region to be heated or a corresponding heat exchanger, and the "cold" connection 20b is connected to the second evaporator inlet 17a of the second heat pump stage. Correspondingly, the "hot" connection of the region to be cooled 23a is connected to the first evaporator inlet 1 la of the first heat pump stage 10, and the "cold" connection 23b is connected to the second evaporator outlet 15b of the second heat pump stage. Temperature distributions for a typical scenario in which the region to be heated receives the working medium at a temperature of 46° Celsius via the "hot" connection 20a and outputs the medium at 40° Celsius at its "cold" connection 20b, are illustrated in Fig. 1. A typical application on the side of the region to be cooled would be a working medium at 21° Celsius flowing in the "hot" connection 23a and a working medium at 15° Celsius flowing in the "cold" connection 23b. Preferably, water is used as the working medium or, after the evaporator, water vapor (or steam), although different working liquids and vapors may also be employed, depending on the implementation. However, with regard to its characteristics, water is favorable for heat pump applications and is, of course, harmless to the environment. However, a negative pressure is required for water in order for evaporation to occur at corresponding temperatures. A corresponding heat pump operating using water as the working medium is, for example, disclosed in EP 2016349 Bl which is incorporated herein by reference.

Each heat pump stage has to provide for a temperature difference of only 28° Celsius, as is illustrated in Fig. 1. If, however, only a single stage was employed, said heat pump stage would have to provide for a temperature difference of 31° Celsius. Since the power for operating a heat pump, however, increases quadratically with an increasing temperature difference, using a single heat pump stage is inefficient due to the higher temperature difference. In accordance with the invention, the efficiency is increased by connecting several heat pump stages, as is shown in Fig. 1, such that the temperature difference is partitioned, i.e. such that the temperature difference for each individual heat pump stage becomes smaller than when using only a single heat pump. This advantage increased with an increasing number of heat pump stages connected to one another, as is exemplarily illustrated in Fig. 2. When, for example, N=3, which corresponds to the example shown in Fig. 2, the temperature difference to be provided by a single heat pump stage decreases from 28° Celsius in the implementation in Fig. 1 to only 27° Celsius. The higher the number of stages N, the smaller the temperature difference and the more efficient the heat pump system will be with regard to the energy required for operating the heat pump system and, in particular, for operating the compressors. In particular, Fig. 2 shows a heat pump system in which, except for the two heat pump stages 10, 12 of Fig. 1, there is another heat pump stage 26, this other heat pump stage 26 in turn comprising an evaporator inlet 27a and an evaporator outlet 27b and a condenser inlet 28a and a condenser outlet 28b. When implementing three heat pump stages, i.e. when N=3, the condenser inlet 28a is connected to the second evaporator outlet 15b of the second heat pump stage. Correspondingly, the condenser outlet 28b of the third heat pump stage 26 is connected to the second condenser inlet 17a of the second heat pump stage. When, as is shown in Fig. 2, only three heat pump stages are connected, the condenser inlet 28a is coupled to the "cold" connection 20b of the region to be heated, whereas the evaporator outlet 27b of the third heat pump stage is coupled to the "cold" connection 23b (Fig. 1) of the region to be cooled. As has been illustrated with regard to Fig. 5, depending on the implementation, the result is a set temperature in the region to be cooled and a set temperature in the region to be heated. Depending on the implementation of the heat exchanger and the temperature difference required at the heat exchanger inputs/outputs, what results, together with the number of heat pump stages, is a corresponding temperature difference to be provided by each individual heat pump stage. In the embodiment shown in Fig. 2, the temperature difference is only 27° Celsius. If, however, a number of six heat pump stages were employed instead of the, for example, three heat pump stages, only a temperature difference of 26° Celsius would be required, i.e. the heat pump system would become even more efficient as regards power consumption, at the expense of additional expenditure for heat pump stages.

Fig. 3 shows an implementation of a heat pump stage, in particular the setup of a heat pump unit of which there may be one or several in a heat pump stage. A heat pump unit includes an evaporator 31, a compressor 32 and a condenser 33. The evaporator 31 includes an evaporator inlet for introducing the ("hot") working medium to be evaporated and additionally includes an evaporator outlet for leading out the ("cold") evaporation medium. Correspondingly, the condenser 33 includes a condenser inlet for introducing the "cold" working medium and for leading out the "hot" working medium, the media in the evaporators 31 and 33 being liquids. Additionally, "cold" vapor from the evaporator 31 is compressed by the compressor 32 using the heat pump process and heated up by this, the "hot" vapor then being fed to the condenser 33 in order for the "hot" vapor to condense and the liquid in the condenser 33 which is then led out by the condenser outlet to be heated by the "hot" vapor by the condensing process. When a heat pump stage comprises only one heat pump unit shown in Fig. 3, the inlets and outlets illustrated in Figs. 1 and 2 correspond to the inlets and outlets of Fig. 3. However, each heat pump stage may also comprise a connection of individual heat pump units, such as, for example, the two heat pump units 41, 42 of Fig. 4. With regard to the designations of the inflows for the evaporator and condenser and outflows for the evaporator and condenser, it has been assumed that the first heat pump stage 10 in Fig. 1 includes a parallel connection of two heat pump units 41 , 42 of Fig. 4.

In a preferred embodiment of the present invention, the heat pump stages are spatially arranged to one another such that, as is particularly to be seen schematically from Fig. 2, the working liquid which exits from the evaporator of the first heat pump stage will enter the condenser of the second heat pump stage already caused by gravity. It is necessary here for the evaporator of the second heat pump stage or, when the stage comprises several heat pump units, the evaporator inflow to be arranged to be lower than the evaporator outlet of the first heat pump stage. Correspondingly, such an arrangement of the condensers relative to one another may also contribute to the fact that the transport from the condenser outlet of one heat pump stage to the condenser inlet of the other heat pump stage takes place due to gravity or is supported by gravity such that no pumping or only little pumping and, thus, little power output for an additional pump are required.

As has been explained, it is preferable to use water as the working liquid and to use water vapor as the working vapor. This is of advantage in that there will not be any environmental issues. On the other hand, due to its constitution, water has to be put under a certain negative pressure in order for it to evaporate at the exemplary temperature indicated in Fig. 1.

Furthermore, it is to be pointed out that the temperatures shown in Fig. 1 are merely exemplary. However, the temperature differences, as have been illustrated with regard to Fig. 5, may also be utilized for different set temperatures in the region to be cooled and set temperatures in the region to be heated, wherein, however, the differences shown depend on the implementation of the corresponding heat exchanger. Other temperatures which may be higher or lower may also be used, exemplarily in cooling in industrial processes or the like, where the temperature conditions may be highly different compared to the temperature conditions which may arise when cooling buildings or computer centers or computer racks.

An inventive method for pumping heat using a heat pump system comprising a first heat pump stage 10 comprises a first evaporator inlet 1 1a and a first evaporator outlet l ib, a first condenser inlet 13a and a first condenser outlet 13b; and a second heat pump stage 12 comprising a second evaporator inlet 15a and a second evaporator outlet 15b, a second condenser inlet 17a and a second condenser outlet 17b comprises the steps of: leading out a working liquid from the first evaporator outlet 1 lb and then introducing the working liquid into the second evaporator inlet 15a; and leading out a working liquid from the second condenser outlet 17b and then introducing the working liquid into the first condenser inlet.

An inventive method for producing a heat pump system includes the following steps: providing a first heat pump stage 10 comprising a first evaporator inlet 1 1a and a first evaporator outlet l ib, a first condenser inlet 13a and a first condenser outlet 13b, and a second heat pump stage 12 comprising a second evaporator inlet 15a and a second evaporator outlet 15b, a second condenser inlet 17a and a second condenser outlet 17b; fiuidically coupling the first evaporator outlet l ib to the second evaporator inlet 15a; and fluidically coupling the second condenser outlet 17b to the first condenser inlet 13 a.

Although certain elements have been described as elements of devices, it is to be pointed out that the description is equally to be understood as a description of steps of a method and vice versa. Exemplarily, the block circuit diagram shown in Fig. 2 equally represents a flowchart of a corresponding inventive method, which correspondingly also applies for the block circuit diagrams of Figs. 4, 5.

Depending on the circumstances, the inventive method may be implemented in either hardware or software. The implementation may be on a non-volatile storage medium, a digital or other storage medium, in particular on a disc or CD comprising control signals which may be read out electronically, which are able to cooperate with a programmable computer system such that the method will be executed. In general, the invention thus also consists in a computer program product comprising program code stored on a machine- readable carrier for performing the method when the computer program product runs on a computer. In other words, the invention may also be realized as a computer program comprising program code for performing the method when the computer program runs on a computer.