Heat-absorbing heat exchanger, refrigeration system and process

Abstract

A heat-absorbing heat exchanger for a refrigeration system, a refrigeration system, a method for controlling the power of a compressor of a refrigeration system, and a method for operating a refrigeration system are described, which are improved with respect to various parameters.

Description

[0001] The invention relates to a heat-absorbing heat exchanger for a refrigeration system, a refrigeration system, a method for controlling the power of a compressor of a refrigeration system, and a method for operating a refrigeration system.

[0002] A refrigeration system is used to cool a system to a desired temperature, such as a medium to be cooled, a freezer for food, storage or production halls, or server farms. A refrigerant circulating in a closed loop undergoes several changes of state: The gaseous refrigerant is first compressed by a compressor. In the subsequent heat-releasing heat exchanger, it condenses, releasing heat. The liquid refrigerant then expands due to the pressure change via a throttling device, such as an expansion valve or a capillary tube. In the downstream heat-absorbing heat exchanger (evaporator), the refrigerant evaporates at a low temperature, absorbing heat (evaporative cooling). The cycle can then begin again. The process must be maintained externally by supplying mechanical work (drive power) to the compressor.

[0003] For the efficient operation of such a refrigeration cycle, it is necessary to regulate the output of the compressor (or several parallel compressors) according to the required cooling load. On the one hand, the different operating states and environmental conditions must be taken into account; on the other hand, the process parameters must not be operated outside of their application limits, for example, to ensure the return transport of lubricants to the compressors.

[0004] It is therefore the object of the invention to improve a refrigeration system with regard to the aforementioned parameters.

[0005] This problem is solved by a heat-absorbing heat exchanger for a refrigeration system, comprising a plurality of pipe coils, each with an inlet and an outlet, wherein the respective inlets are connected via a distribution pipe and the outlets are connected via a collector pipe, wherein the collector pipe is at least partially geometrically arranged above the distribution pipe, so that the heat exchanger is designed for a flow from bottom to top, and wherein the collector pipe has an upper and a lower end, with a bypass line leading from the lower end of the collector pipe to a discharge downstream of the upper end.

[0006] Advantageously, the bypass line and collector pipe are arranged and dimensioned in such a way that the pressure difference between the inlet and outlet of the bypass line, generated by the flow velocity in the discharge, exerts such a high force on the medium in the bypass line that oil is conveyed via the bypass line.

[0007] A refrigeration system comprising at least the following components arranged successively in the direction of refrigerant flow: a compressor, a heat-emitting heat exchanger, a throttling device, advantageously includes a heat-absorbing heat exchanger as described above.

[0008] The problem is further solved by a method for controlling the power of a compressor of a refrigeration system, comprising an ejector whose pressure-side inlet is downstream of a heat-emitting heat exchanger and whose suction-side inlet is downstream of the heat-absorbing heat exchanger, wherein the power of the compressor is controlled on the basis of the pressure at the suction-side inlet of the ejector as a reference variable.

[0009] A refrigeration system comprising at least the following components arranged successively in the direction of refrigerant flow: a compressor, a heat-emitting heat exchanger, an ejector, and a heat-absorbing heat exchanger, advantageously further comprises a control unit designed to carry out the above-described process.

[0010] The problem is further solved by a refrigeration system comprising at least the following components arranged successively in the direction of refrigerant flow: a compressor, a heat-emitting heat exchanger, a throttling device, and a heat-absorbing heat exchanger, wherein the heat-absorbing heat exchanger is designed for heat exchange with air, further comprising a second heat-absorbing heat exchanger connected in parallel to the first heat-absorbing heat exchanger, which is designed for heat exchange with a liquid, in particular water.

[0011] Advantageously, each of the heat-absorbing heat exchangers is assigned a control valve designed to regulate the refrigerant flow of the respective heat-absorbing heat exchanger.

[0012] Advantageously, the refrigeration system also includes a control device designed to regulate the control valves based on the media temperatures of the respective heat-absorbing heat exchangers.

[0013] The problem is further solved by a refrigeration system comprising at least the following components arranged successively in the direction of refrigerant flow: a compressor, a heat-emitting heat exchanger, a throttling device, and a heat-absorbing heat exchanger, wherein the heat-emitting heat exchanger is designed for heat exchange with air, further comprising a second heat-emitting heat exchanger upstream of the throttling device, which is designed for heat exchange with a liquid, in particular water, and which has an externally connectable inlet and outlet with respect to the liquid.

[0014] Advantageously, the second heat-emitting heat exchanger is connected downstream of the first heat-emitting heat exchanger.

[0015] The problem is further solved by a refrigeration system comprising at least the following components arranged successively in the direction of refrigerant flow: a compressor, a heat-emitting heat exchanger, a throttling device, and a heat-absorbing heat exchanger, wherein the refrigeration system has a support frame designed for roof mounting and a housing arranged on the support frame, wherein the heat-absorbing heat exchanger is arranged below the support frame and the support frame and the bottom of the housing have a recess designed for connecting the heat-absorbing heat exchanger.

[0016] Advantageously, the heat-emitting heat exchanger is arranged on the housing, and the compressor and throttling device are arranged inside the housing.

[0017] Advantageously, the refrigeration system also features a refrigerant collection tank located inside the housing.

[0018] The problem is further solved by a refrigeration system comprising at least the following components arranged successively in the direction of refrigerant flow: a compressor, a heat-discharging heat exchanger, an ejector, a refrigerant receiver, and a heat-absorbing heat exchanger, wherein the heat-absorbing heat exchanger is connected downstream of the refrigerant receiver on the liquid side and upstream of the ejector on the suction side, and wherein the compressor is connected downstream of the refrigerant receiver on the gas side, further comprising a pump connected downstream of the refrigerant receiver on the liquid side, a switching valve connected downstream of the heat-absorbing heat exchanger, which is designed to divert the refrigerant to the heat-discharging heat exchanger instead of the suction side of the ejector, and a bypass valve associated with the compressor.

[0019] Advantageously, the pump is located upstream of the heat-absorbing heat exchanger.

[0020] Advantageously, the pump is designed for use as a generator.

[0021] Advantageously, the refrigeration system is operated using a method in which the refrigeration system is switched from a normal operating mode to a winter operating mode by switching off the compressor and opening the bypass valve, starting the pump, and the changeover valve directing the refrigerant from the heat-absorbing heat exchanger to the heat-discharging heat exchanger, reversing the refrigerant flow direction in the heat-discharging heat exchanger.

[0022] Advantageously, every refrigeration system described above is designed to operate with carbon dioxide as a refrigerant.

[0023] All of the independent embodiments described above can be combined with each other in any way.

[0024] The advantages achieved with the invention consist in particular in the fact that the described heat-absorbing heat exchangers for a refrigeration system, refrigeration systems, methods for controlling the power of a compressor of a refrigeration system, and methods for operating a refrigeration system provide a refrigeration system that has a particularly efficient control quality, adapts to the ambient conditions in an energy-efficient manner, includes possibilities for subsequent performance increase, and thereby extends the application limits for maintaining the cooling circuit by means of measures for improved oil recirculation.

[0025] Exemplary embodiments of the invention are explained in more detail with reference to the drawings. These show: Fig. 1 a heat-emitting heat exchanger according to the state of the art, Fig. 2 a heat-emitting heat exchanger with flow direction from bottom to top, Fig. 3 a compact refrigeration unit for roof installation, and Fig. 4 a refrigeration system with on-demand compressor shutdown.

[0026] Identical parts are only found in the Fig. 1 and Fig. 2 with the same reference numerals. Fig. 3 and Fig. 4 each use new reference symbols, as indicated at the end of the description.

[0027] The Fig. Figure 1 shows a heat-absorbing heat exchanger for a state-of-the-art refrigeration system, while Fig. Figure 2 shows a heat-absorbing heat exchanger according to an embodiment of the invention. The latter is advantageously integrated into the Fig. 3 and Fig. 4 described refrigeration systems for application. Fig. 1 and Fig. Figure 2 shows the respective heat exchangers in their geometric orientation during operation, i.e., "bottom" and "top" in the Fig. 1 and Fig. Figure 2 corresponds to the actual setup situation in relation to gravity. The heat-absorbing heat exchangers are designed for the exchange of thermal energy between the refrigerant and the air to be cooled.

[0028] The heat exchanger after Fig. The unit 1 is designed for downward flow. It has a distribution pipe 1 on the inlet side, from which the refrigerant flow is distributed to, in this embodiment, two coiled pipes 2 with fins 3. The coiled pipes 2 are arranged one above the other, so that the inlet and outlet of one coiled pipe 2 are located above the inlet and outlet of the other coiled pipe 2. On the outlet side, the coiled pipes terminate in a vertical manifold 4, the outlet of which points downwards.

[0029] The heat-absorbing heat exchanger according to the embodiment of the invention described here in Fig. Section 2 now includes a modified flow direction and a bypass line 5 running parallel to the manifold 4, which ensures the oil return from the evaporator. The bypass line 5 is connected to the underside of the manifold 4 and leads upwards via a U-shaped fitting, parallel to the manifold 4, and then via another U-shaped fitting from above into the manifold.

[0030] The advantages of the altered flow direction (from bottom to top) are that the density difference between the liquid and gas during evaporation provides additional flow impetus. This allows for the introduction of more refrigerant. However, a potential problem is that oil can accumulate in the manifold 4, which, due to its weight, is not drawn upwards. Therefore, in the exemplary embodiment, a bypass line 4 is provided, and suitable dimensioning and operation ensure that the pressure differential in the manifold 4 is high enough to draw sufficient oil through the bypass line 5. This is ultimately achieved through the pressure drop in the pipe and the Bernoulli effect at the inlet of the bypass line 5 to the drain.

[0031] In the Fig. 3 and Fig. Figure 4 shows refrigeration systems 1 according to exemplary embodiments of the invention. These are each designed for operation with carbon dioxide as a refrigerant. In such refrigeration circuits designed for operation with carbon dioxide, the described heat exchanger offers particular advantages, since the temperatures at the compressor can be especially high in this case. The described refrigeration circuits are designed in the exemplary embodiments for stationary cooling of production or storage halls as well as for server cooling.

[0032] First, the refrigeration system 1 is operated according to the Fig. 3 described. It has two parallel compressors 2 which are connected on the outlet side to heat-emitting heat exchangers 3. There are two heat-emitting heat exchangers 3 which exchange heat with the outside air via fins and a fan and form a gas cooler unit.

[0033] On the outlet side, a further heat exchanger 14 is connected downstream of the heat-discharging heat exchangers 3. This heat exchanger is designed for heat exchange with a liquid and has external connections for this purpose, allowing a second liquid circuit to be connected as needed. This second heat-discharging heat exchanger 14 offers the possibility of further increasing the efficiency of the refrigeration system by connecting cooling medium from, for example, a cooling tower to the heat exchanger 14. This function is intended to compensate for performance losses due to fouling (especially on the first heat-discharging heat exchangers 3) or a subsequent increase in the required cooling capacity, for example, due to increased ambient temperatures or an increase in heat input.

[0034] A changeover valve 11 connects the refrigerant-side outlet of the heat exchanger 14 to the pressure-side inlets of two parallel ejectors 4, which act as throttling devices and expand the refrigerant. On the outlet side, the ejectors are connected to a refrigerant receiver 5, which has a gas-side outlet at the top and a liquid-side outlet at the bottom. The gas-side outlet is connected via the previously described heat exchanger 10 to the inlet side of the compressors 2, where a pressure sensor 12 is also located. The changeover valve 12 allows refrigerant from the heat-discharging heat exchangers 3 and 14 to be directed into the heat exchanger 10 as needed. This can improve the system's efficiency under certain operating conditions.

[0035] The liquid-side outlet of the refrigerant receiver 5 is connected to the heat-absorbing heat exchangers 7, 8. The first two heat-absorbing heat exchangers 7 can be configured, for example, as shown in Fig. The two heat exchangers are shown in Figure 2 and form an evaporator unit 19. They exchange heat with the air via fins and a fan. The second heat exchanger 8 is connected in parallel to the first two heat exchangers 7. It is designed for heat exchange with water and can be used, for example, to cool coolant for servers. The water circuit of the heat exchanger 8 has a corresponding pump 9 for this purpose.

[0036] The supply lines to the air heat exchangers 7 and the water heat exchanger 8 each have a control valve 6 to regulate the flow rate. The refrigeration system can therefore be operated with liquid and air simultaneously or sequentially as the cooling medium. A control unit (not shown) determines which medium is prioritized. This unit uses the medium temperatures (air and water) and the current operating behavior of the system to control the distribution between the two media via the control valves 6. For example, one of the two temperatures (air or water) can be prioritized as needed.

[0037] Alternatively or additionally, for the efficient operation of refrigeration system 1, a special control system can influence the opening degree of the control valves 6 to the evaporator unit 19 and the heat exchanger 8, respectively, so that the distribution leads to the best possible operating conditions at the compressors 2. For example, if the fluid temperature of the heat-absorbing heat exchanger 8 is higher, it can be advantageous for system efficiency to automatically limit the output of the air cooler (evaporator unit 19) using the control valves 6 in order to achieve a higher and therefore more efficient compressor suction pressure. If the fluid temperature subsequently drops again, the output of the air cooler can be increased again. This prevents the entire refrigeration system 1 from having to operate at a less energy-efficient level if only one heat exchanger 7 or 8 is operating under less than ideal conditions.

[0038] From the outlets of the evaporator unit 19 and the heat exchanger 8, the refrigerant is then supplied to the suction side of the ejectors 4, where a further pressure sensor 13 is located. In the exemplary embodiment, a control unit (not shown) is used to regulate the output of the compressors 2, deviating from the known prior art, where typically the pressure at the compressor inlet (pressure sensor 12) is used as the primary control variable. In the exemplary embodiment shown here, the pressure at the pressure sensor 13, i.e., the pressure at the suction-side inlet of the ejectors, is used as the primary control variable. The advantage here is more energy-efficient operation of the refrigeration system 1. In other words, the output adjustment of the compressors 2 is not regulated here, as is otherwise known, by means of the pressure on the inlet side upstream of the compressors 2 as the reference variable, but rather via the pressure at the suction-side inlet of the ejector 4.

[0039] Finally, the in Fig. Figure 3 shows a refrigeration unit 1 designed for installation on a roof 16. The refrigeration unit 1 is arranged as a connected unit on a support frame 15 on the roof 16. The support frame 15 serves as a device for sealing and weight distribution and can be designed as a steel tube frame with appropriate flanges and sealing material. The support frame has a recess on its underside through which the evaporator unit projects downwards and through a corresponding opening in the roof 16 into the area to be cooled, e.g., a production or storage hall.

[0040] A surrounding housing 17 is arranged on the support frame 15. The gas cooler unit 17, which exchanges heat with the environment, is located on the upper side of this housing. All other components of the refrigeration system 1 necessary for operation are integrated within the housing 17. The housing 17 also has a suitable recess on its underside for the evaporator unit 19.

[0041] Fig. Figure 4 shows another refrigeration system, which is depicted in a simpler way, but essentially has the same structure as refrigeration system 1. Fig. 3 features. Its special feature is a free cooling operation function using a pump circuit, which can also be combined with the Fig. The 3 described features can be combined or integrated into the refrigeration system 1. Fig. 3 can be integrated.

[0042] The refrigeration system according to the Fig. Assembly 4 has a compressor 1, which is connected on its outlet side to a heat-discharging heat exchanger 2. On its outlet side, the heat-discharging heat exchanger is connected to the pressure-side inlet of an ejector 3, which acts as a throttling device and expands the refrigerant. On its outlet side, the ejector 3 is connected to a refrigerant receiver 4, which has a gas outlet on the top and a liquid outlet on the bottom. The gas outlet is connected to the inlet side of the compressor 1.

[0043] The liquid-side outlet of the refrigerant receiver 4 is connected to the heat-absorbing heat exchanger 6 via a control valve 5. From the outlet of the heat exchanger 6, the refrigerant is then fed to the suction side of the ejector 3.

[0044] The one in Fig. The refrigeration system shown in section 4 is designed for on-demand free cooling operation, i.e., without compressor operation, in which case cooling can only reach the outside temperature. For this purpose, the refrigeration circuit includes the following additional components: - Compressor 1 is assigned a bypass valve 8, which opens a bypass line via compressor 1 as required, i.e. the refrigerant can flow past compressor 1 when the bypass valve 8 is opened. - A pump 9 is integrated into the refrigerant flow between the liquid-side outlet of the refrigerant collection tank 4 and the control valve 5 to the heat-absorbing heat exchanger 6. - A switching valve 7 is arranged between the outlet of the heat-absorbing heat exchanger 6 and the suction-side inlet of the ejector 3, which can, if necessary, connect the outlet of the heat-absorbing heat exchanger 6 to the outlet of the heat-emitting heat exchanger 2 instead of to the suction-side inlet of the ejector 3.

[0045] If free cooling operation is activated by a control unit not shown in detail, the bypass valve 8 is opened and the compressor 1 is deactivated, while the pump 9 is activated and the switching valve 7 connects the outlet of the heat-absorbing heat exchanger 6 to the outlet of the heat-emitting heat exchanger 2 instead of the suction-side inlet of the ejector 3, as described.

[0046] The pump 9 keeps the circuit moving. The flow direction through the heat-absorbing heat exchanger 6 remains unchanged, but the flow direction through the heat-discharging heat exchanger 2 changes, bypassing the ejector 3 and the compressor 1. This alternative flow path is activated in colder outdoor conditions (winter operation, although the term "winter operation" is not to be taken literally, as switching can also occur outside of winter at correspondingly low outdoor temperatures or with low cooling demand) and switches off the compressor 1 to save energy. The liquid refrigerant is pumped from the refrigerant reservoir 4 by pump 9 through the open control valve 5 into the heat-absorbing heat exchanger 6 (evaporator).The switching valve 7 for adjusting the flow direction then directs the refrigerant towards the heat-emitting heat exchanger 2 (gas cooler), where it condenses and then flows back into the refrigerant collection tank 4.

[0047] It is also conceivable that, during normal operation, pump 9 is used as a generator that can recover energy from the flow energy. The pipes are designed accordingly for reversing the flow direction; in particular, they must not overcome excessive height. This can be especially problematic with a compact, roof-integrated system like the one described above. Fig. 3 shown, that would be the case.

[0048] In the alternative operation shown with pump 9, the refrigerant is circulated at a single pressure stage. It is possible that the refrigerant may undergo phase changes through evaporation or condensation. Reference symbol list Fig. 1 + Fig. 2: 1 distribution pipe 2 pipe coils 3 slats 4 Collector pipe 5 Bypass line Fig. 3 1 refrigeration system 2 compressors 3 heat-emitting heat exchangers 4 Throttle body, ejector 5 refrigerant collection containers 6 control valve 7, 8 heat-absorbing heat exchanger 9 pump 10 heat exchangers 11 Diverter valve 12, 13 Pressure sensor 14 heat-emitting heat exchanger 15 support frames 17 cases 18 Gas cooler unit 19 Evaporator unit Fig. 4 1 compressor 2 heat-emitting heat exchangers 3 Throttle body, ejector 4 refrigerant collection containers 5 control valve 6 heat-absorbing heat exchanger 7 Diverter valve 8 Control valve, bypass valve 9 pump

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