EP2649387B1

EP2649387B1 - Refrigeration circuit

Info

Publication number: EP2649387B1
Application number: EP10794942.2A
Authority: EP
Inventors: Oliver Finckh; Tobias Sienel; Christoph Kren; Alexander Tambovtsev
Original assignee: Carrier Corp
Current assignee: Carrier Corp
Priority date: 2010-12-08
Filing date: 2010-12-08
Publication date: 2018-08-15
Anticipated expiration: 2030-12-08
Also published as: DK2649387T3; CN103299141A; EP2649387A1; CN103299141B; WO2012076049A1

Description

Refrigeration circuits which are configured for circulating a refrigerant and which are comprising in flow direction of the refrigerant a heat rejecting heat exchanger, a receiver, an expansion device, an evaporator, and a compressor are widely known and used for refrigeration purposes. In those types of refrigeration circuits liquid refrigerant is stored within the receiver. However, when such a refrigeration circuit is switched off, the temperature of the refrigerant in the refrigeration lines and within the receiver increases due to heat impact from the environment. This results in the evaporation of refrigerant and an increase off pressure within the refrigeration circuit. In order to avoid damage of the system's components caused by said increasing pressure, common refrigeration circuits include at least one pressure relief valve, which opens when a predetermined pressure within the refrigeration circuit is exceeded in order to allow refrigerant to escape from the refrigeration circuit.
Removing refrigerant from the refrigeration circuit via pressure relief valves, however, results in loss of refrigerant, and at some point the removed refrigerant needs to be replaced which increases the costs for operating and maintaining the refrigeration circuit. Additionally the removed refrigerant pollutes the environment.
In order to avoid this problem it is known to use an auxiliary cooler, which uses e.g. HFC as refrigerant, in order to cool the refrigerant stored within the receiver when the refrigeration system is not operating.
It would be beneficial to provide means for avoiding the increase of pressure in a non-working refrigeration circuit without the need for an auxiliary cooler.
It furthermore would be beneficial to increase the performance of the refrigeration circuit when running at hot ambient temperatures.
DD 108 366 A1 discloses a refrigerating system according to the preamble of claim 1 and a method for operating a refrigerating system according to the preamble of claim 10. Exemplary embodiments of the invention include a refrigeration circuit configured for circulating a refrigerant and comprising in flow direction of the refrigerant a heat rejecting heat exchanger, a receiver, an expansion device, an evaporator, and a compressor. The refrigeration circuit further includes a coldness storage device which is configured to receive and store coldness in a first mode of operation during the operation of the refrigeration system, and to cool refrigerant which is stored within the receiver using the stored coldness in a second mode of operation, in particular when the refrigeration system is not operating.
Exemplary embodiments further include a refrigeration circuit, wherein the coldness storage device is configured to receive and store coldness during the operation of the refrigeration circuit, and to pre-cool refrigerant leaving the heat rejecting heat exchanger before entering the receiver.
Embodiments of the invention are described in greater detail below with reference to the attached figures, wherein:

Fig. 1 shows a schematic view of a first embodiment of a refrigeration circuit according to the invention;
Fig. 2 shows a schematic view of a second embodiment of a refrigeration circuit according to the invention;
Fig. 3 shows a schematic view of a third embodiment of a refrigeration circuit according to the invention;
Fig. 4 shows a schematic view of a fourth embodiment of a refrigeration circuit according to the invention.

Fig. 1 shows a schematic view of a refrigeration circuit 2 according to a first embodiment of the invention.
The refrigeration circuit 2 shown in Fig. 1 is a two-stage expansion refrigeration circuit 2 comprising in flow direction of the refrigerant a heat rejecting heat exchanger 4, a high pressure expansion device 8, which are configured for expanding the circulating refrigerant from high pressure to intermediate pressure, a receiver for receiving, collecting and storing the intermediate pressure refrigerant, two low pressure expansion devices 24a, 24b, which are configured for expanding the circulating refrigerant from intermediate pressure to low pressure and two evaporators 26a, 26b which are configured for evaporating the low-pressure refrigerant.
The heat rejecting heat exchanger 4 includes two fans 6 which are configured for blowing air by the refrigerant flowing through the heat rejecting heat exchanger 4 in order to improve the heat exchange between the refrigerant flowing though the heat rejecting heat exchanger 4 and the environment.
Each of the evaporators 26a, 26b includes a fan 28a, 28b, which is configured for blowing air by the refrigerant flowing through the evaporators 26a, 26b in order to improve the evaporation of the refrigerant. The refrigeration circuit 2 further includes a set 30 of compressors 30a, 30b, 30c, which are arranged in parallel to each other in order to receive gaseous refrigerant leaving the evaporators 26a, 26b and for compressing the gaseous refrigerant and delivering the refrigerant to the heat rejecting heat exchanger 4, completing the refrigeration cycle.
In the exemplary embodiment shown in Fig. 1 two serial arrangements of a low pressure expansion device 24a, 24b and an evaporator 26a, 26b are connected in parallel to each other. However, it is evident for the skilled person that any number of such combinations may be connected in parallel.
A pressure release line 12 including a pressure relief valve 14 is fluidly connected to the receiver 10. The pressure relief valve 14 is configured to open when the pressure within the receiver 10 exceeds a predetermined value in order to release a portion of the refrigerant from the receiver 10 and to reduce the pressure within the receiver in order to avoid damage of the components of the refrigeration circuit 2 caused by high refrigerant pressure within the refrigeration circuit 2.
A flash gas tap line 16 comprising a flash gas expansion device 18 fluidly connects the receiver 10 with the inlets of the compressors 30a, 30b, 30c in order to allow to tap flash gas generated within the receiver 10 from the receiver 10 and to convey the flash gas to the compressors 30a, 30b, 30c bypassing the low pressure expansion devices 24a, 24b and the evaporators 26a, 26b. Tapping flash gas from the receiver 10 allows to improve the efficiency of the refrigeration circuit 2.
In the embodiment shown in Figure 1 the flash gas tap line 16 extends through a coldness storage device 15 which is arranged downstream of the flash gas expansion device 18. Thus, after flash gas has been tapped from the receiver and expanded by the flash gas expansion device 18, the expanded flash gas flows through the coldness storage device 15 thereby cooling a coldness storage medium 13 arranged within the coldness storage device 15.
The refrigeration circuit 2 further includes a receiver cooling line 20 extending from the receiver through the coldness storage device 15 and back to the receiver 10. An on/off-valve 22 is arranged within the receiver cooling line 20 downstream of the coldness storage device 15. When the refrigeration circuit 2 is not operating, i.e. when the compressors 30a, 30b, 30c are stopped, the expansion devices 8, 24a, 24b, 18 are usually closed.
In order to avoid an increase of temperature and pressure of the refrigerant stored within the receiver 10 due to the impact of ambient heat, the on/off-valve 22 is opened allowing gaseous refrigerant from the receiver 10 to flow via the receiver cooling line 20 through the coldness storage device 15 by the coldness storage medium 13 and the opened on/off-valve back 22 to the receiver 10.
Before flowing back into the receiver 10 the refrigerant flowing through the receiver cooling line 20 is cooled by the coldness storage medium 13 arranged within the coldness storage device 15. The gaseous refrigerant may be cooled even so much that it is condensed and liquid refrigerant is flowing back from the receiver cooling line 20 into the receiver 10.
The cooled refrigerant flowing back into the receiver 10 reduces the temperature of the refrigerant stored within the receiver 10 and avoids an undesirable increase of pressure within the receiver 10 and the refrigeration circuit 2. Thus, there is no need for the pressure relief valve 14 to open in order to decrease the pressure within the receiver 10 by releasing refrigerant from the refrigeration circuit 2.
The coldness storage medium 13 included within the coldness storage device 15 may be a phase change material storing and releasing heat and/or coldness, respectively, by undergoing a phase transition process. A phase transition process provides a very efficient means for storing and releasing heat and/or coldness, respectively. The coldness storage medium 13 may include freezing and melting water. The melting point of the water may be adjusted by adding suitable additives.
The refrigeration circuit 2 according to the first embodiment shown in Fig. 1 allows to efficiently avoid an increase of pressure of the refrigerant stored in the receiver 10 due to increasing the temperature by using flash gas, which is tapped from the receiver 10 during normal operation of the refrigeration circuit 2 and storing the coldness generated by expanding the flash gas in a suitable coldness storage device 15. The coldness storage device 15 includes a coldness storage medium 13 which undergoes a phase transition for storing and releasing coldness.
In a refrigeration circuit 2 according to the first embodiment no auxiliary cooler is necessary in order to cool the refrigerant stored within the receiver 10. The pressure relief valve 14 needs to open only in cases of emergency but not under normal operating conditions when the refrigeration circuit 2 is switched off and the release of valuable and potentially dangerous refrigerant to the environment is avoided.
Since flash gas tapped from the receiver 10 is used for producing the coldness needed for cooling the receiver 10, no additional energy is needed in order to generate the coldness stored within the coldness storage device 15. Thus, an refrigeration circuit according to the first embodiment may be operated with high efficiency.
Fig. 2 shows aschematic view of arefrigeration circuit 32 according to a second embodiment.
The components of the refrigeration circuit 32 which correspond to the components of the refrigeration circuit 2 according to the first embodiment shown in Fig. 1 are labelled with the same reference signs and will not be discussed in detail again.
In the refrigeration circuit 32 according to the second embodiment the coldness storage medium 13 arranged in the coldness storage device 15 is not cooled by flash gas tapped from the receiver 10. Instead, there is provided a further refrigerant line 36 extending from the bottom of the receiver 10 through the coldness storage device 15 to the inlets of the compressors 30a, 30b, 30c. Upstream of the coldness storage device 15, i. e. between the receiver 10 and the coldness storage device 15, a coldness storage expansion device 34 is arranged within the refrigerant line 36, which is configured for expanding the refrigerant flowing from the receiver 10 to the coldness storage device 15.
In a refrigeration circuit 32 according to the second embodiment shown in Figure 2 during normal operation a portion of the refrigerant stored within the receiver 10 is flowing through the refrigerant line 36, expanded by the coldness storage expansion device 34 and cooling the coldness storage medium 13 arranged in the coldness storage device 15.
When the refrigeration circuit 32 is not operating and the compressors 30a, 30b, 30c are stopped, in order to cool the refrigerant stored within the receiver 10, flash gas is tapped from the top of the receiver 10 by a flash gas tapping line 20 and flown by the coldness storage medium 13 within the coldness storage device 15 and back into the receiver as described above with respect to the refrigeration circuit 2 according to the first embodiment.
The refrigeration circuit 32 according to the second embodiment allows efficient cooling of the coldness storage medium 13 within the coldness storage device 15 independently of any flash gas generated within the receiver 10.
In a further embodiment, which is not shown in the figures, a flash gas line 16 comprising a flash gas expansion device 18 as shown in Figure 1 may be additionally added to the refrigeration circuit 32 according to the second embodiment shown in Figure 2 in order to allow cooling of the coldness storage medium 13 stored within the coldness storage device 15 selectively by flash gas tapped from the top of the receiver 10 and/or by liquid refrigerant taken from the bottom of the receiver according to the second embodiment shown in Figure 2.
This allows a very efficient and energy-saving cooling of the coldness storage medium 13.
A refrigeration circuit 42 according to a third embodiment of the is shown in Fig. 3. The components which are equivalent to the components of the refrigeration circuits 2, 32 according to the first and second embodiment shown in Figs. 1 and 2 are labelled with the same reference signs and will not be described in detail again.
The refrigeration circuit 42 according to the third embodiment includes a coldness storage device 15 comprising a coldness storage medium 13 which may be cooled by refrigerant flowing through the coldness storage device 15 via the refrigerant line 36 and an coldness storage expansion device 34 which is arranged in said refrigerant line 36 upstream of said coldness storage device 15.
A first switchable valve 48 is arranged in the refrigeration circuit 42 in the refrigerant line 9 between the heat rejecting heat exchanger 4 and the high pressure expansion device 8. A pre-cooling line 45 branches off the refrigerant line 9 downstream of the heat rejecting heat exchanger 4 and upstream of the first switchable valve 48 extending through the coldness storage device 15 by the coldness storage medium 13 and rejoining the refrigeration line 9 at a position between the first switchable valve 48 and the high pressure expansion device 8, thereby bypassing the first switchable valve 48. The pre-cooling line 45 comprises second and third switchable valves 44, 50 arranged upstream and downstream of the coldness storage device 15, respectively. In the embodiment shown in Fig. 3 the second and third switchable valves 44, 50 are arranged near the first switchable valve 48 and the refrigeration line 9.
During low or medium load operation of the refrigeration circuit 42 the first switchable valve 48 is open and the second and third switchable valves 44, 50 are closed. Refrigerant leaving the heat rejecting heat exchanger 6 is flowing via the refrigerant line 9 and the open first switchable valve 48 to the high pressure expansion device 8 as described before with reference to the first and second embodiments.
A portion of the fluid refrigerant from the bottom of the receiver 10 is flowing via the expansion device 34 and the refrigerant line 36 through the coldness storage device 15 in order to cool the coldness storage medium 13 arranged in the coldness storage device 15 (Mode 1).
At high loads, i.e. due to high ambient temperatures, the first switchable valve 48 and the coldness storage expansion device 34 are closed and the second and third switchable valves 44, 50 are opened. Refrigerant leaving the heat rejecting heat exchanger 6 flows via the opened second switchable valve 44 and the subcooling line 45 through the coldness storage device 15 by the coldness storage medium 13 arranged in the coldness storage device 15 and via the third switchable valve 50 to the high pressure expansion device 8.
Since the coldness storage medium 13 arranged within the coldness storage device 15 has been cooled before, as described above, it now receives heat from the refrigerant flowing by through the subcooling line 45, thereby cooling the refrigerant before it reaches the high pressure expansion device 8.
This subcooling of the refrigerant before it is expanded by the high pressure expansion device 8 increases the efficiency of the refrigeration circuit 42 in particular if it is running at high load, i.e. due to high ambient temperatures.
In particular, superfluous cooling capacity during low load operation of the refrigeration circuit (i. e. during night time and/or low ambient temperatures) may be used for cooling the coldness storage medium 13 arranged in the coldness storage device 15. As a result, the excessive coldness produced during low load periods is saved to be used later in high load periods. This increases the efficiency of the refrigeration circuit 42 considerably and reduces the costs for running the refrigeration circuit 42 in particular during high load periods.
Fig. 4 shows a schematic view of a refrigeration circuit 52 according to a fourth embodiment. The refrigeration circuit 52 according to the fourth embodiment is similar to the refrigeration circuit according to the third embodiment shown in Fig. 3 and corresponding components of the refrigeration circuit 42 are labelled with the same reference signs and will not be described in detail again.
In the refrigeration circuit 52 according to the fourth embodiment, however, the coldness storage medium 13 arranged in the coldness storage device 15 is not cooled by expanding liquid refrigerant extracted from the bottom of the receiver 10, but by flash gas which is tapped from the top of the receiver as described with respect to the first embodiment shown in Fig. 1.
The refrigeration circuit 52 according to the fourth embodiment includes a flash gas tap line 16 extending from the top of the receiver 10 through the coldness storage device 15 to the inlets of the compressors 30a, 30b, 30c. A flash gas expansion device 18 is arranged in the flash gas tap line 16 between the receiver 10 and the coldness storage device 15.
During low or medium load operation of the refrigeration circuit 52, when the first switchable valve 48 is open and the second and third switchable valves 44, 50 are closed, as described above with respect to the third embodiment, flash gas is tapped from the receiver 10 via a flash gas tap line 16 and expanded by the flash gas expansion device 18. The expanded flash gas is flown through the coldness storage device 15 in order to cool the coldness storage medium 13 arranged in the coldness storage device 15.
During high load operation the refrigeration circuit 52 according to the fourth embodiment the refrigeration circuit 52 is operated like the refrigeration circuit 42 according to the third embodiment shown in Fig. 3 described before, i. e. the first switchable valve 48 is closed and the second and third switchable valves 44, 50 are opened in order to flow the refrigerant leaving the heat rejecting heat exchanger 4 through the coldness storage device 15, where it is subcooled by transferring heat to the coldness storage medium 13 arranged in the coldness storage device 15, before the refrigerant is expanded by the high pressure expansion device 8.
It is evident to the skilled person that the third and fourth embodiments 42, 52 may be combined with each other in an embodiment, where in addition to the refrigerant line 36 comprising the refrigerant expansion device 34 a flash gas tap line 16 comprising a flash gas expansion device 18 extends through the coldness storage device 15 in order to cool the refrigerant medium 13 arranged in the refrigerant storage device 15 selectively by flash gas flowing through the flash gas tapping line 16 and/or the expanded refrigerant flowing the refrigerant line 36.
Such a combination of the embodiments shown in Figs. 3 and 4 allows a very efficient operation of the refrigeration circuit under all possible ambient conditions.
Although not shown in the figures it is also evident to the skilled person that the embodiments shown in Figs. 3 and 4 may be combined with the embodiments shown in Figs. 1 and 2, respectively, in order to aggregate the advantages of subcooling the refrigerant under high load conditions with the advantages of cooling the refrigerant comprised within the receiver 10 when the refrigeration circuit 2, 32, 42, 52 is not working and the compressors 30a, 30b, 30c are stopped.
While the invention has been described before with respect to a two-stage expansion, which is in particular efficient when a refrigerant including CO₂ is used, the skilled person will easily understand that the invention is also applicable to a one-stage expansion refrigeration circuit, which does not include a high-pressure expansion device 8.
By the exemplary embodiments of the invention, as described herein, pressure increase during stand still can reliably be avoided, and peak load shaving can be allowed by increasing load during high coefficient of performance operations while increasing the coefficient of performance during low load durations.
The coldness storage device may include a phase change material, which changes its phase when storing or delivering coldness. A phase change material is very efficient in storing and releasing heat and coldness, respectively.
The refrigerating may include a flash gas line extending from the receiver through the coldness storage device to the compressor and configured for tapping flash gas from the receiver.
The flash gas line may include a flash gas expansion device, which is located upstream of the coldness storage device and configured for expanding the flash gas. Expanded flash gas allows to cool the coldness medium within the coldness storage device very efficiently.
The refrigerating system may further include a cooling-storage-device-refrigerant line extending from the receiver through the coldness storage device to the compressor and configured to deliver liquid refrigerant from the receiver to the coldness storage device. This allows to efficiently cool the coldness storage medium arranged within the coldness storage device.
A coldness storage expansion device may be arranged in the storage-device-refrigerant line upstream of the coldness storage device. Expanding the refrigerant from the receiver improves the efficiency of cooling the coldness storage medium arranged within the coldness storage device.
The storage-device-refrigerant line may be formed as a heat-exchanger within the coldness storage device in order to improve the heat exchange between the refrigerant flowing through the storage-device-refrigerant line and the coldness storage medium arranged within the coldness storage device.
The may by atwo-stage expansion refrigerating system comprising a high pressure expansion device arranged between the heat rejecting heat exchanger and the receiver. Two-stage expansion increases the efficiency of the refrigeration circuit.
The refrigerant may include CO₂. CO₂ provides a very efficient refrigerant.

Claims

A refrigerating system (2; 32; 42; 52) configured for circulating a refrigerant and comprising in flow direction of the refrigerant:
a heat rejecting heat exchanger (4), a receiver (10), an expansion device (24a, 24b), an evaporator (26a, 26b) and a compressor (30a, 30b, 30c),

characterized in that the refrigerating system (2; 32; 42; 52) further comprises a coldness storage device (15) which is configured
a) to receive and store coldness during the operation of the refrigerating system (2; 32; 42; 52), and

b) to cool refrigerant stored within the receiver (10) or to cool refrigerant leaving the heat rejecting heat exchanger (4) before entering the receiver (10).
The refrigerating system (2; 32; 42; 52) of claim 1, wherein the coldness storage device (15) includes a phase change material (13), which changes its phase when storing or delivering coldness.
The refrigerating system (42; 52) of any of the preceding claims, comprising a coldness-storage-device-refrigerant-line (36) extending from the receiver (10) through the coldness storage device (15) to the compressor (30a, 30b, 30c) and configured to deliver liquid refrigerant from the receiver (10) to the coldness storage device (15).
The refrigerating system (42; 52) of claim 3, the coldness-storage-device-refrigerant-line (36) includes a further expansion device (34) upstream of the coldness storage device (15).
The refrigerating system (42; 52) of claim 3 or 4, wherein the coldness-storage-device-refrigerant-line (36) includes a heat-exchanger arranged within the coldness storage device (15), wherein the coldness-storage-device-refrigerant-line (36) is in particular formed as a heat-exchanger within the coldness storage device (15).
The refrigerating system (2; 32; 42; 52) of any of the preceding claims, wherein the refrigerating system (2; 32; 42; 52) is a two-stage expansion refrigerating system comprising a high pressure expansion device (8) arranged between the heat rejecting heat exchanger (4) and the receiver (10).
The refrigerating system (2; 32; 42; 52) of any of the preceding claims, wherein the refrigerant includes CO₂.
The refrigerating system (2; 32) of any of the preceding claims, comprising a flash gas line (16) extending from the receiver (10) through the coldness storage device (15) to the compressor (30a, 30b, 30c) and configured for tapping flash gas from the receiver (10).
The refrigerating system (2; 32) of claim 8, wherein the flash gas line (16) includes a flash gas expansion device (18), which is located upstream of the coldness storage device (15) and configured for expanding the flash gas.
A method of operating a refrigerating system (2; 32; 42; 52) comprising in flow direction of a refrigerant a heat rejecting heat exchanger (4), a receiver (10), an expansion device (24a, 24b), an evaporator (26a, 26b) and a compressor (30a, 30b, 30c),
characterized in that the method comprises the step of cooling refrigerant stored in the receiver (10) by tapping flash gas from the receiver (10), flowing the flash gas through a coolness storage device (15), which is configured to receive and store coldness during the operation of the refrigerating system (2; 32; 42; 52), and returning the cooled flash gas to the receiver (10) or the step of cooling refrigerant leaving the heat rejecting heat exchanger (4) before entering the receiver (10) by flowing the refrigerant through a coldness storage device (15), which is configured to receive and store coldness during the operation of the refrigerating system (2; 32; 42; 52).
The method of claim 10, wherein the coldness storage device (15) includes a coldness storage medium (13), which changes its phase when storing or delivering coldness.
The method of claim 11, wherein the coldness storage medium (13) is cooled by expanded flash gas tapped from the receiver (10) during normal operation of the cooling system (2; 32) and/or, wherein the coldness storage medium (13) is cooled by liquid refrigerant taken from the receiver (10).
The method of any of claims 10 to 12, wherein the refrigerant is expanded before entering the coldness storage device (15).
The method of any of claims 10 to 13 comprising the step of partially expanding the refrigerant from high pressure to medium pressure before entering the receiver (10).
The method of any of claims 10 to 14, wherein the refrigerant comprises CO₂.