CASCADE HEAT PUMP AND METHOD FOR HEATING OR COOLING A COOLANT BY MEANS OF A CASCADE HEAT PUMP

Abstract

In order to provide a cascade heat pump with which a large temperature lift can be provided with high efficiency, a cascade heat pump comprising n stages where n≥2 is proposed. Each of the n stages has a heat pump with a coolant inlet, a first coolant outlet, and a second coolant outlet. Each heat pump has a hot side and a cold side and a flow divider to divide a coolant flow entering the coolant inlet between the hot side and the cold side. The first coolant outlet of the heat pump of each stage i, where i=1 . . . n−1, is connected to the coolant inlet of the heat pump of a subsequent stage i+1. The second coolant outlet of the heat pump of at least one subsequent stage i+1 is connected by a recirculation line to the coolant inlet of the heat pump of a preceding stage.

Claims

1. A cascade heat pump comprising n stages where each of the n stages comprising: a heat pump with a coolant inlet; a first coolant outlet; and a second coolant outlet, wherein the heat pump has a hot side and a cold side and a flow divider, wherein the flow divider divides a coolant flow entering the coolant inlet between the hot side and the cold side, wherein the first coolant outlet of the heat pump of each stage i, where i=1 . . . n−1, is connected to the coolant inlet of the heat pump of a subsequent stage i+1, wherein the second coolant outlet of the heat pump of at least one subsequent stage i+1, where i=1 . . . n−1, is connected via a recirculation line to the coolant inlet of the heat pump of a preceding stage 1 . . . i.

2. The cascade heat pump according to claim 1, wherein the second coolant outlet of the heat pump of each subsequent stage i+1, where i=2 . . . n−1, is connected via a recirculation line to the coolant inlet of the heat pump of a preceding stage 1 . . . i.

3. The cascade heat pump according to claim 2, wherein the second coolant outlet of the heat pump of each subsequent stage i+1, where i=2 . . . n−1, is connected via a recirculation line to the coolant inlet of the heat pump of the preceding stage i.

4. The cascade heat pump according to claim 1, wherein the heat pump is a caloric heat pump, an electrocaloric heat pumps, a magnetocaloric heat pump, or elastocaloric heat pump, and/or wherein the heat pump is equipped to achieve a temperature spread of the coolant between the hot side and the cold side of at least 5° C., or of at least 10°, further preferably of at least 20° C.

5. The cascade heat pump according to claim 1, wherein at least the first coolant outlet of the heat pump of the last stage i=n is connected to a first coolant branch, wherein the first coolant branch is connected to the coolant inlet of the heat pump of the first stage i=1, and wherein the first coolant branch includes a heat exchanger.

6. The cascade heat pump according to claim 1, wherein at least the second coolant outlet of the heat pump of the first stage i=1 is connected to a second coolant branch, wherein the second coolant branch is connected to the coolant inlet of the heat pump of the first stage i=1, wherein the second coolant outlet of each of the heat pumps of the first j stages, j=1 . . . n−1, or of the first two stages, is connected to the second coolant branch, and wherein the second coolant branch includes a heat exchanger or a cooler.

7. The cascade heat pump according to claim 1, wherein the first coolant outlet of every heat pump is associated with the hot side, and wherein the second coolant outlet of every heat pump is associated with the cold side, or wherein the first coolant outlet of every heat pump is associated with the cold side, and wherein the second coolant outlet of every heat pump is associated with the hot side, and/or wherein each heat pump has a switchover device, wherein the switchover device is designed to selectably associate the hot side with the first coolant outlet and the cold side with the second coolant outlet or associate the cold side with the first coolant outlet and the hot side with the second coolant outlet.

8. The cascade heat pump according to claim 1, wherein at least five, at least seven, or at least ten stages are provided.

9. A method for heating or cooling a coolant, carried out with a cascade heat pump comprising n stages where n≥2 according to claim 1, the method comprising: providing a coolant flow to a coolant inlet of the heat pump of the first stage i=1, wherein, in each of the stages i, where i=1 . . . n−1, providing a first partial flow of the coolant to the coolant inlet of the heat pump of the subsequent stage i+1 through the first coolant outlet of the respective heat pump, wherein, in at least one of the subsequent stages i+1, where i=1 . . . n−1, a second partial flow of the coolant is fed to the coolant inlet of the heat pump of a preceding stage 1 . . . i through the second coolant outlet of the respective heat pump.

10. The method according to claim 9, wherein, in each of the subsequent stages i+1, where i=2 . . . n−1, the second partial flow of the coolant is fed to the coolant inlet of the heat pump of a preceding stage 1 . . . i through the second coolant outlet of the respective heat pump, wherein, in each of the subsequent stages i+1, where i=2 . . . n−1, the second partial flow of the coolant preferably is fed to the coolant inlet of the heat pump of the preceding stage i through the second coolant outlet of the respective heat pump.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0060] The present invention will become more fully understood from the detailed description given hereinbelow and the accompanying drawings which are given by way of illustration only, and thus, are not limitive of the present invention, and wherein:

[0061] FIG. 1 shows an example of a cascade heat pump;

[0062] FIG. 2 shows an example of a cascade heat pump; and

[0063] FIG. 3 shows an example of a cascade heat pump.

DETAILED DESCRIPTION

[0064] FIG. 1 shows a cascade heat pump 100 in accordance with the invention, on the basis of which a method 200 for heating or cooling a coolant shall be explained in detail. The cascade heat pump 100 comprises five stages i=1 . . . 5. Each of the stages i includes a heat pump 10 with a coolant inlet 11, a first coolant outlet 12, and a second coolant outlet 13. Each heat pump 10 of each stage i further includes a hot side 14 and a cold side 15. In the cascade heat pump 100 shown in FIG. 1, in each stage i the cold side 15 is associated with the first coolant outlet 12 and the hot side 14 with the second coolant outlet 13. The heat pumps 10 additionally have flow dividers 24, wherein the flow dividers 24 are equipped to divide a coolant flow entering the coolant inlet 11 of the respective heat pump 10 between the hot side 14 and the cold side 15. The first coolant outlet 12 of each heat pump 10 of the first four stages i=1 . . . 4 is connected to the coolant inlet 11 of the heat pump 10 of a subsequent stage i+1. The first coolant outlet 12 of the heat pump 10 of the last stage i=5 is connected to a first coolant branch 16. Furthermore, the second coolant outlets 13 of the heat pump 10 of the first stage i=1 and of the heat pump 10 of the second stage i=2 are connected to a second coolant branch 17.

[0065] Located in the first coolant branch 16 is a heat exchanger 18 for a passenger compartment of a motor vehicle that is not shown, and another heat exchanger 19 in the form of a cooler 20 of the motor vehicle (not shown in detail) is located in the second coolant branch 17. The second coolant outlets 13 of the third through fifth stages i+1=3 . . . 5 are each connected to the coolant inlet 11 of the preceding stage i by a respective recirculation line 21, so that a coolant passing out of the second coolant outlet 13 of the heat pump 10 of the third stage i=3 is fed to the coolant inlet 11 of the heat pump 10 of the second stage i=2, a coolant passing out of the second coolant outlet 13 of the heat pump 10 of the fourth stage i=4 is fed to the coolant inlet 11 of the heat pump 10 of the third stage i=3, and a coolant passing out of the second coolant outlet 13 of the heat pump 10 of the fifth stage i=5 is fed to the coolant inlet 11 of the heat pump 10 of the fourth stage i=4.

[0066] The heat pumps 10 are designed as elastocaloric heat pumps 22. Each of the heat pumps 10 is equipped to achieve a temperature spread of the coolant between the hot side 14 and the cold side 15 of 10° C. For the purpose of explanation, it is further assumed by way of example that the coolant conducted into the coolant inlet 11 of the heat pump 10 of the first stage i=1 has a temperature of 20° C. In the heat pump 10 of the first stage i=1, the coolant is divided into two partial flows to the hot side 14 and the cold side 15, and heat is transferred from the cold side 15 to the hot side 14. The coolant passing out of the first coolant outlet 12 of the heat pump 10 of the first stage i=1 then has a temperature of 15° C. and is fed to the coolant inlet 11 of the heat pump 10 of the second stage i=2. The coolant passing out of the second coolant outlet 13 of the heat pump 10 of the first stage i=1 has a temperature of 25° C. and is fed to the second coolant branch 17. The coolant passing out of the first coolant outlet 12 of the heat pump 10 of the second stage i=2 has a temperature of 10° C. and is fed to the coolant inlet 11 of the heat pump 10 of the third stage i=3. The coolant passing out of the second coolant outlet 13 of the heat pump 10 of the second stage i=2 has a temperature of 20° C. and is likewise fed to the second coolant branch 17. The coolant passing out of the first coolant outlet 12 of the heat pump 10 of the third stage i=3 has a temperature of 5° C., and the coolant passing out of the second coolant outlet 13 of the heat pump 10 of the third stage i=3 has a temperature of 15° C. The temperature relationships of the fourth and fifth stages i=4 and i=5 apply correspondingly.

[0067] The coolant passing out of the second coolant outlet 13 of the heat pump 10 of the third stage i=3 with a temperature of 15° C. is fed to the coolant inlet 11 of the heat pump 10 of the second stage through the corresponding recirculation line 21, where it mixes with the coolant having the same temperature of 15° C. passing out of the first coolant outlet 12 of the heat pump 10 of the first stage i=1. The same applies for the coolant passing out of the second coolant outlets 13 of the heat pumps 10 of the fourth and fifth stages i=4 and i=5.

[0068] As a result of this recirculation of the coolant, the flow volume of the coolant that passes out of the first coolant outlet 12 of the heat pump 10 of the last stage i=5 that can be used for cooling decreases only by a factor ½n= 1/10 as compared with a reduction by the factor ½.sup.n= 1/32 that would exist if no coolant recirculation were provided. A larger quantity of coolant is thus available for cooling.

[0069] The cooled coolant passing out of the first coolant outlet 12 of the heat pump 10 of the last stage i=5 is fed to the heat exchanger 18 through the first coolant branch 16, and can be used to cool the passenger compartment of the motor vehicle. In this process, the coolant located in the first coolant branch 16 absorbs the heat from the passenger compartment and is heated up again to a temperature of, for example, 20° C. The coolant passing out of the second coolant outlets 13 of the heat pumps 10 of the first and second stages i=1 and i=2 is fed to the heat exchanger 19 or the cooler 20 through the second coolant branch 17 and dissipates the heat to the outside environment through the same. Alternatively, the heat of the coolant in the second coolant branch 17 can also be used for heating a battery or other systems of the motor vehicle. As a result of the fact that the coolant in the second coolant branch 17 dissipates the heat again through the heat exchanger 19, this coolant is again cooled to, for example, 20° C., and is likewise fed to the coolant inlet 11 of the heat pump 10 of the first stage i=1 at this temperature. Here, it mixes with the heated coolant from the first coolant branch 16, and the coolant circuit is closed.

[0070] In the case of air as coolant, it is also possible to dispense with the first coolant branch 16 and the second coolant branch 17 as well as the first heat exchanger 18 and the second heat exchanger 19 or the cooler 20. In this case, the cooled air from the first coolant outlet 12 of the heat pump 10 of the last stage i=5 can be used directly for cooling of, e.g., the vehicle passenger compartment, and the heated air from the second coolant outlets 13 of the heat pumps 10 of the first and second stages i=1 and i=2 is blown into the outside air.

[0071] FIG. 2 shows an alternative embodiment of the cascade heat pump 100, which can be used to heat a passenger compartment of a motor vehicle. As compared with the cascade heat pump 100 from FIG. 1, the roles of hot side 14 and cold side 15 are reversed in each of the heat pumps 10 in the cascade heat pump 100 of FIG. 2. Consequently, the hot side 14 is associated with the first coolant outlet 12, and the cold side 15 with the second coolant outlet 13, in every heat pump 10. The coolant flows through the cascade heat pump 100 in the previously described manner, although in this case a heated coolant with a temperature of 45° C. passes out of the first coolant outlet 12 of the heat pump of the last stage i=5. In contrast, the temperatures of the coolant passing out of the second coolant outlets 13 of the heat pumps 10 of the first and second stages i=1 and i=2 are 15° C. and 20° C., respectively. The heated coolant passing out of the first coolant outlet 12 of the heat pump 10 of the last stage i=5 is used to heat the passenger compartment through the heat exchanger 18 of the first coolant branch 16. As a result, the coolant cools down, and is again fed to the coolant inlet 11 of the heat pump 10 of the first stage i=1 through the first coolant branch 16. The cooled coolant passing out of the second coolant outlets 13 of the heat pumps 10 of the first and second stages i=1 and i=2 is fed to the heat exchanger 19 through the second coolant branch 17 and is heated up again to, e.g., 20° C. through the absorption of heat. The reheated coolant in the second coolant branch 17 is mixed with the cooled coolant from the first coolant branch 16, and is fed again to the coolant inlet 11 of the heat pump 10 of the first stage i=1.

[0072] As was already true with the embodiment from FIG. 1, in the case of air as coolant it is possible to dispense with the first coolant branch 16 and the second coolant branch 17 as well as the first heat exchanger 18 and the second heat exchanger 19. In this case, the heated air from the first coolant outlet 12 of the heat pump 10 of the last stage i=5 can be used directly for heating of, e.g., the vehicle passenger compartment, and the cooled air from the second coolant outlets 13 of the heat pumps 10 of the first and second stages i=1 and i=2 is blown into the outside air.

[0073] FIG. 3 shows another embodiment of the cascade heat pump 100. The function of the cascade heat pump 100 according to FIG. 3 corresponds to that of the cascade heat pumps 100 from FIG. 1 and FIG. 2. In this design, a switchover device 23 is provided in each of the five stages i=1 . . . 5 that is designed to selectably associate the hot side 14 with the first coolant outlet 12 and the cold side 15 with the second coolant outlet 13 or associate the hot side 14 with the second coolant outlet 13 and the cold side 15 with the first coolant outlet 12 in every heat pump 10. By simultaneous switching of the switchover devices 23, the cascade heat pump 100 from FIG. 3 can therefore be changed between the embodiments of FIGS. 1 and 2 and be used both for heating and for cooling of a motor vehicle passenger compartment.

[0074] In FIGS. 1 to 3, the cascade heat pumps 100 comprise five stages i=1 . . . 5. It is of course also possible, however, to expand the cascade heat pump 100 to seven, ten, or more stages.

[0075] The invention being thus described, it will be obvious that the same may be varied in many ways. Such variations are not to be regarded as a departure from the spirit and scope of the invention, and all such modifications as would be obvious to one skilled in the art are to be included within the scope of the following claims.