EP3786545A1

EP3786545A1 - Integrated cold storage system

Info

Publication number: EP3786545A1
Application number: EP19209171.8A
Authority: EP
Inventors: Sami Abdulrahman ALBAKRI
Original assignee: Sab Engineers GmbH
Current assignee: Sab Engineers GmbH
Priority date: 2019-08-30
Filing date: 2019-11-14
Publication date: 2021-03-03

Abstract

A Cold Storage System comprises: a compressor (12) for compressing and enabling a circulation of a heat transfer fluid (HTF); a condenser (13) with condenser unit (131) for cooling the compressed HTF and an expansion unit (132) for decreasing the pressure of the HTF, thereby further cooling the HTF; and a cold storage (14) with an integrated evaporator (145), the cold storage (14) is configure to store the coldness transferred by the HTF.

Description

The present invention relates to a Cold Storage System and a method for performing a cold storage and, in particular, to an integrated chiller-storage system in which the chiller is in part combined with the cold storage.

BACKGROUND

Cold Storage Systems find applications in industry as well as in commercial and private contexts. An example of such an application is temperature equalization over day and night cycles in buildings or in industrial plants like e.g. solar panel systems, in particular in countries where differences between daytime and nighttime temperatures are considerable. Furthermore, as scientific research confirms that human activities contribute significantly to global climate change, technical facilities in general are facing a challenge to reduce the emission of heat energy and greenhouse gases, and to operate in more energy efficient ways. This pertains in particular to devices providing refrigeration. Cold Storage Systems - rather than devices delivering refrigeration without comprising an integrated cold storage - can be an efficient, economic way to contribute to these objectives.
The term Cold Storage System refers to a system of heat energy transfer comprising a device designed to retain refrigerated material (the cold storage), which may further encompass means for achieving the refrigeration of this material (a chiller) and for absorbing heat energy (by a heat exchanger) from a particular part of the environment (the consumer) for the duration of predefined periods of time.
Fig. 9 depicts a conventional Cold Storage System, comprising a circuit of pipes holding an appropriate medium for the conduction of the heat energy (HTF, heat transfer fluid), moved by a pumping device (here a compressor 12) and passing in series through a chiller 16, a cold storage 14 - which due to the intended functionality of the system will be referred to as "charged" if it is capable of absorbing heat energy from the HTF - and a heat exchanger 15 to provide refrigeration to a consumer 31. In the following, a situation in which the Cold Storage System is operated to provide coldness to the consumer 31 via the heat exchanger 15 will be referred to as discharging mode, while a situation in which the Cold Storage System is operated to reduce the heat energy in the cold storage 14 (here by means of the chiller 16) will be referred to as charging mode.
In a conventional setup, like the one exemplified in Fig. 9, the chiller 16 includes of a vapor-compression refrigeration system, which effectively absorbs heat energy from the HTF and emits it into the environment via a separate refrigerant (RT) circuit. The RT (which can include e.g. carbon dioxide, ammonia, sulfur dioxide, or non-halogenated hydrocarbons) is set in motion by its own compressor 162, and passes through a condenser unit 163, an expansion unit 164 (e.g. a valve), and an evaporator 165 where it gets in thermal contact with the HTF, producing the cooling effect via a reverse-Rankine cycle. The HTF circuit and the RT circuit form two separate closed systems, and the heat transfer between HTF and RT takes place using a fluid-fluid-heat exchanger.
The requirement of two separate systems naturally increases the probability of malfunctions and/or failures, and can reduce overall system efficiency. In consequence there is a demand for reduction of complexity and increase of efficiency, without compromising the intended effects of individual parts and/or functions of the full system.

SUMMARY OF THE INVENTION

At least to some extent, the problems mentioned in the preceding section are solved by a system according to claim 1 and a corresponding method according to claim 12.
The present invention relates to a Cold Storage System comprising a compressor (or some other sort of pumping device) for compressing and enabling a circulation of a heat transfer fluid (HTF, as e.g. carbon dioxide, ammonia, or non-halogenated hydrocarbons), a condenser with a condenser unit for cooling the compressed HTF (e.g. by ambient air) and an expansion unit (as e.g. an expansion valve) for decreasing the pressure of the HTF, thereby further cooling the HTF, and a cold storage with an integrated evaporator, where the cold storage is configured to store the coldness transferred by the HTF.
The devices are positioned on an HTF circuit, such that the system can operate in a charging mode in which the cold storage is refrigerated (charged), e.g. by the HTF undergoing a reverse-Rankine cycle: The compressor will compress the HTF to a higher pressure (of e.g. 50 bar), thereby also increasing the HTF temperature. The HTF then enters the condenser unit, where it effectively emits heat energy into the environment (e.g. into the ambient air). After the condenser unit, the HTF enters the expansion valve, where its pressure decreases (e.g. to 10 bar), combined with a (sharp) reduction of its temperature. The cold HTF flows into the cold storage, which it refrigerates by passing through the integrated evaporator. After leaving the packed bed system, the HTF (which may now be entirely in a gaseous state) will eventually enter the compressor again, and the cycle is repeated.
Optionally, the Cold Storage System further comprises a heat exchanger for delivering of coldness to a consumer, wherein the heat exchanger is arranged between the compressor and the cold storage. The Cold Storage System is operable in a charging mode during which the heat energy stored in the cold storage decreases, or in a discharging mode during which the heat exchanger delivers coldness to the consumer.
The heat exchanger can e.g. include a coil through which the HTF streams, exchanging heat with ambient air passed over the coil (e.g. by means of a fan). Furthermore, the heat transfer may be achieved by a single circuit by only using the HTF without using a heat transfer between the HTF and a refrigerant (RT).
According to embodiments, the cold storage includes an integrated evaporator.
This is in particular realised if the cold storage includes a multi-packed bed system. A packed bed is a vertical vessel including a packing material (a bulk of monodisperse and/or polydisperse solid particles made of e.g. aluminium oxide, steel or ceramic and/or phase change material (PCM)), through which a stream of gas or liquid (here the HTF) passes in order to either deposit or extract heat energy from the packing material, depending on the mode of operation. Originally designed to facilitate specific chemical processing applications (such as, e.g., adsorption, distillation, separation processes or catalytic reactions), packed beds may be combined into multi-packed bed systems including a plurality (one or more) of such packed beds, and provide efficient, durable, simple to construct, and scalable thermal energy storage devices.
Optionally, the cold storage therefore includes a multi-packed bed system comprising a plurality of packed beds, which are employed as an evaporator for the HTF in charging mode.
Optionally, the multi-packed bed system further comprises a plurality of packed bed valves, such that the amount of heat transfer fluid flowing through each packed bed is controlled by at least one respective packed bed valve.
Depending on intended applications of particular embodiments, managing one or more correspondingly adapted charging and discharging processes for the multi-packed bed system is important for an efficient application of the system. Different charging and discharging processes can have different effects on temperature profiles, longevity, and/or timescales of the operation of the multi-packed bed system.
Optionally, the Cold Storage System is chiller-free, by which it is understood that the system does not include any further device adapted to reduce the temperature of the heat transfer fluid and/or the amount of heat energy stored in the cold storage other than the aforementioned condenser unit and expansion unit.
This optional feature in particular instantiates the reduction of complexity of the system mentioned in the introduction.
Optionally, the Cold Storage System further comprises a heat exchanger bypass with a heat exchanger bypass valve, where the heat exchanger bypass is adapted to bypass the heat exchanger and to channel heat transfer fluid from the outlet of the cold storage to the inlet of the compressor, and the heat exchanger bypass valve is adapted to control a flow of heat transfer fluid through the heat exchanger bypass to keep a temperature at the inlet of the compressor at a predefined range of temperature (e.g. between 20 °C and 30 °C) or around a setpoint temperature (e.g. 25 °C).
The compressor operates efficiently only within a specific range of conditions for the HTF. In particular, the HTF temperature is related to the volumetric flow rate of the HTF, and larger volumetric flow rates lead to higher power consumption for the compressor. At the outlet of the heat exchanger, the HTF is generally at a high temperature (which may be related to an ambient temperature, and can be e.g. 50 °C). The heat exchanger bypass reduces this temperature and thereby the volumetric flow rate of the HTF before the HTF enters the compressor, and therefore has a positive effect on the efficiency of the compressor.
The efficiency of the cold storage to absorb heat energy from the HTF in discharging mode can vary over time, which can lead to a varying HTF temperature at the exit of the cold storage, and therefore also at the inlet of the heat exchanger. This, in turn, can mean that the heat exchanger does not absorb heat energy from the environment and thus not deliver coldness to the consumer in a constant way.
Optionally, the Cold Storage System therefore further comprises a cold storage bypass with a cold storage bypass valve, wherein the cold storage bypass is adapted to bypass the cold storage and to channel heat transfer fluid from the inlet of the cold storage to the inlet of the heat exchanger, and the cold storage bypass valve is adapted to control a flow of heat transfer fluid through the cold storage bypass line to keep a temperature at the inlet of the heat exchanger at a predefined range of temperature or around a setpoint temperature.
Depending on the application, the setpoint temperature may be selectable by the consumer, and should lie above the low or ultra-low temperature at which the HTF exits the cold storage, but below the ambient air temperature (examples for the setpoint temperature could be 8 °C, 14 °C, or 16 °C). According to embodiments, the operation of the cold storage bypass does not interfere with the operation of the aforementioned heat exchanger bypass.
Optionally, the Cold Storage System includes only a single compressor, and no further pumping device.
The system can be in charging mode, during which the HTF is refrigerated over time, and the heat energy in the cold storage decreases. This can have the effect that the compressor is required to work under varying HTF temperature conditions over the course of the charging process. In particular, such varying conditions can again have a negative effect on the efficiency of the compressor.
Optionally, the Cold Storage System therefore further comprises a chiller/cold storage bypass with a chiller/cold storage bypass valve, wherein the chiller/cold storage bypass is adapted to bypass the condenser and the cold storage and to channel heat transfer fluid from a position between the compressor and the condenser unit and from a position after the expansion valve to the inlet of the compressor when the Cold Storage System is operated in a charging mode, and wherein the chiller/cold storage bypass valve is adapted to control a flow of heat transfer fluid through the chiller bypass to keep a temperature at the inlet of the compressor at a predefined range of temperature or around a setpoint temperature.
Optionally, the Cold Storage System further comprises a control unit configured to control one or more of the following:

periods of time where the Cold Storage System is in a charging mode and in a discharging mode, respectively,
the heat exchanger bypass valve, in order to keep, in discharging mode, the temperature of the heat exchange fluid at the inlet of the compressor in a predefined temperature range or around a setpoint temperature (e.g. 25 °C),
the cold storage bypass valve, in order to keep, in discharging mode, the temperature of the heat exchange fluid at the inlet of the heat exchanger in a predefined temperature range or around a setpoint temperature (which could be selectable by the consumer),
the chiller/cold storage bypass valve, in order to keep, in charging mode, the temperature of the heat exchange fluid at the inlet of the compressor in a predefined temperature range or around a setpoint temperature (e.g. 10 °C),
the plurality of packed bed valves, such that in discharging mode, individual packed beds can be discharged selectively, and in charging mode, individual packed beds can be charged selectively.

Optionally, the control unit controls the periods of time where the Cold Storage System is in charging and in discharging mode following readings of an external temperature and/or following the day and night cycle.
The present invention also pertains to a method for performing a cold storage, comprising:

compressing and enabling a circulation of a heat transfer fluid;
cooling the compressed heat transfer fluid (e.g. by ambient air) in a condenser unit;
expanding the heat transfer fluid in an expansion unit, thereby further cooling the heat transfer fluid; and
storing coldness delivered by the heat transfer fluid by evaporating the heat transfer fluid in a cold storage,

According to embodiments of the present invention, the function of an evaporator included in a conventional chiller of a Cold Storage System comprising a multi-packed bed system as cold storage is taken over by the multi-packed bed system, while the condenser unit and the expansion unit are included directly in the HTF circuit. A conventional chiller, including a separate RT circuit, and in particular an RT compressor and an RT evaporator, is therefore no longer required in the Integrated Cold Storage System. An RT compressor and the HTF compressor will be replaced with a single compressor, while the multi-packed bed system will be used as an evaporator. In charging mode, the cold HTF flows into the cold storage, where it transfers the coldness to the packing material. In the multi-packed bed system, the HTF fluid will be evaporated, given its latent heat of evaporation to the packing material. The heat transfer is achieved by a single circuit only using the HTF, without using a heat transfer between the HTF and an RT. This new concept has positive impacts on the system efficiency, investment and operation costs.

SHORT DESCRIPTION OF FIGURES

Fig. 1: shows an embodiment of an Integrated Cold Storage System.
Fig. 2: exhibits a comparison between a conventional Cold Storage System with two fluid circuits and an Integrated Cold Storage System with a combined circuit.
Fig. 3A: shows a process layout for an embodiment of an Integrated Cold Storage System in charging mode.
Fig. 3B: displays HTF temperature against time across the condenser for an embodiment as displayed in Fig. 3A.
Fig. 4A: shows a process layout for an embodiment of an Integrated Cold Storage System comprising a chiller/cold storage bypass, in charging mode.
Fig. 4B: displays HTF temperature against time across the condenser for an embodiment as displayed in Fig. 4A.
Fig. 5: shows from top to bottom three consecutive steps (a), (b), (c) for charging an embodiment of an Integrated Cold Storage System comprising a chiller/cold storage bypass, for a case where the cold storage is a multi-packed bed system and the plurality of packed beds is charged selectively.
Fig. 6: shows settings for charging an embodiment of an Integrated Cold Storage System comprising a chiller/cold storage bypass, for a case where the cold storage is a multi-packed bed system and the plurality of packed beds is charged in parallel.
Fig. 7A: shows a process layout for an Integrated Cold Storage System comprising a heat exchanger bypass and a cold storage bypass, in discharging mode.
Fig. 7B: displays HTF temperature against time at a position X3 in the HTF circuit for a system as shown in Fig. 7A, for a case where the system comprises the cold storage bypass as well as for a case where the system does not comprise the cold storage bypass.
Fig. 7C: displays HTF temperature against time at a position X5 in the HTF circuit for a system as shown in Fig. 7A, for a case where the system comprises the heat exchanger bypass as well as for a case where the system does not comprise the heat exchanger bypass.
Fig. 8: shows from top to bottom three consecutive steps (a), (b), (c) for discharging an embodiment of an Integrated Cold Storage System comprising a heat exchanger bypass and a cold storage bypass, for a case where the cold storage is a multi-packed bed system and the plurality of packed beds is discharged selectively.
Fig. 9: shows a conventional Cold Storage System including a chiller.

DETAILED DESCRIPTION OF FIGURES

Various examples will now be described more fully with reference to the accompanying drawings, in which some examples are illustrated.
Accordingly, while examples are capable of various modifications and alternative forms, the illustrative examples in the figures will herein be described in detail. It should be understood, however, that there is no intent to limit examples to the particular forms disclosed, but on the contrary, examples are to cover all modifications, equivalents, and alternatives falling within the scope of the disclosure. Like numbers refer to like or similar elements throughout the description of the figures.
The terminology used herein is for the purpose of describing illustrative examples only and is not intended to be limiting. As used throughout in this document, the singular forms "a," "an" and "the" are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms "comprises," "comprising," "includes" and/or "including," when used herein as well as everywhere else in this document, specify the presence of stated features, steps, operations, elements and/or components, but do not preclude the presence or addition of one or more other features, steps, operations, elements, components and/or groups thereof.
Fig. 1 shows an embodiment of a Cold Storage System according to the present invention. The system comprises a compressor 12, a condenser unit 131, an expansion unit 132, a cold storage 14, and a heat exchanger 15, placed in this order along a heat transfer fluid (HTF) circuit 11. The condenser unit 131 and the expansion unit 132 are grouped together in a dashed box, which will be referred to collectively as condenser 13.
When the system is in charging mode, the HTF cools (charges) the cold storage 14, e.g. by undergoing a reverse Rankine cycle. The HTF is set in motion by the compressor 12 and enters, e.g. in a state of superheated vapor, into the condenser unit 131. During condensation, the HTF emits heat energy into the ambient air 32. Now e.g. in a state of saturated liquid, the HTF enters the expansion unit 132 where it experiences a rapid pressure decrease, thereby reducing its temperature. Next, the HTF, which may now e.g. be in a mixture of a vapor state and a liquid state, enters the cold storage, where it passes through an integrated evaporator 145, absorbing heat energy from and thereby cooling (charging) the cold storage 14. After leaving the cold storage 14, the HTF enters the compressor 12 again, which closes the circuit.
When the system is in discharging mode, the heat exchanger 15 is in operation and delivers coldness to the consumer 31. The heat exchanger 15 may e.g. comprise a coil, over which ambient air 32 is passed by a fan 151. Depending on application and/or design of the embodiment, the condenser unit 131 and the expansion unit 132 may or may not be switched on. The HTF is at low (e.g. below -10 °C) or ultra-low (e.g. -50 °C) temperature at the exit of the cold storage 14. In contrast, the HTF temperature at the outlet of the heat exchanger 15 is high; this temperature can e.g. be related to the ambient temperature and may be at about 50 °C. The temperature of the HTF is furthermore increased when the HTF passes through the compressor 12.
Fig. 2 illustrates schematically the difference between a conventional Cold Storage System on the left, and the present Integrated Cold Storage system on the right. In both cases, a process layout for a respective charging mode is depicted.
In the left part of the figure, a solid outer circle represents an HTF circuit 11 (marked as "outer circuit" in the figure), along which the HTF is set in motion by a compressor 12 in counterclockwise direction. The HTF passes through a refrigerant (RT) evaporator 165, and through a cold storage 14. A dotted inner circle (marked as "inner circuit" in the figure) represents an RT circuit 161, along which as key components of a vapor-compression refrigeration system are placed: an RT compressor 162, an RT condenser unit 163, an RT expansion unit 164 and an RT evaporator 165. The RT, which may e.g. comprise carbon dioxide, ammonia, sulfur dioxide, or non-halogenated hydrocarbons, circulates between the RT condenser unit 163 and the RT evaporator 165, producing the cooling effect via a reverse-Rankine cycle. The HTF circuit and the RT circuit are separate closed systems which are in thermal contact within the RT evaporator 165, where the heat transfer between HTF and RT takes place using a fluid-fluid-heat exchanger. In charging mode, the HTF is moved by means of the compressor 12, refrigerated by passing heat energy to the RT in the RT evaporator 165, and in turn refrigerates (charges) the cold storage 14.
In the right part of the figure, a compressor 12, a condenser unit 131, an expansion unit 132 and a cold storage 14 are positioned in this order along an HTF circuit 11 (marked as "combined circuit" in the figure). The cold storage system 14 comprises an evaporator 145, in which the HTF can absorb heat energy, thereby refrigerating (charging) the cold storage 14. In charging mode, the HTF undergoes a cycle analogous to that of the RT in the left part of the figure: Compression by the compressor 12, condensation and release of heat energy into the ambient air 32 in the condenser unit 131, temperature reduction in the expansion unit 132, and absorption of heat energy in the evaporator 145 included in the cold storage 14.
A particular instance where an evaporator 145 is naturally included in the cold storage 14 occurs if the cold storage 14 is a multiple-packed bed system. In this case, evaporation of the HTF occurs within the packed beds upon passing through particles of a packing material.
Thus, embodiments integrate both inner and outer circuits into a combined circuit. This can be achieved by replacing the evaporator with the multi-packed bed system. A single compressor enables the HTF circulation between the condenser 13 and the cold storage (multi-packed bed system) 14.
The advantages of the concept displayed in the right part of the figure over the concept displayed in the left part include:

On the right, a single HTF circuit 11 is employed, and therefore the complexity of the system is reduced significantly. As a result, the investment and operation costs are much lower than in the concept displayed on the left.
On the right, a single compressor 12 is used, instead of two separated compressors for HTF (compressor 12) and RT (RT compressor 162) on the left.
On the right, a single fluid (refrigerant) is used instead of separated fluids (HTF and RT) on the left.
On the right, an evaporator 145 is integrated in the cold storage 14. This is in particular realised if the cold storage comprises a multi-packed bed system. In consequence there is no need for heat energy exchange between the HTF and the RT in an RT evaporator 165. Furthermore, the heat transfer between the HTF and the particles of the packing material in the multi-packed bed system can be very high if said heat transfer is based on the latent heat of HTF evaporation.
A system according to the right part of the figure has a better scalability compared with a system according to the left part of the figure.

Fig. 3A shows a process layout for an embodiment of a Cold Storage System comprising a compressor 12, a condenser unit 131, an expansion unit 132 and a cold storage 14, placed in this order along a heat transfer fluid (HTF) circuit 11, in charging mode.
The HTF is compressed, heated and set in motion by the compressor 12. The HTF pressure at position X6 after the compressor 12 may be e.g. 50 bar. The HTF then enters the condenser unit 131, where it emits heat energy into e.g. the ambient air 32. After condensation, the HTF enters the expansion unit 132 (e.g. an expansion valve), where it undergoes depressurization and temperature reduction, such that HTF pressure and temperature at position X7 after the expansion unit 132 are e.g. 10 bar and -50 °C, respectively. The HTF enters the cold storage 14, where it passes through an integrated evaporator 145 and absorbs heat energy from (i.e., charges) the cold storage 14.
Fig. 3B shows, for a Cold Storage System as displayed in Fig. 5A, a qualitative plot of the HTF temperature against time at the positions X5 before the compressor 12 and X6 after the compressor 12. As the cold storage 14 is charged over time, the HTF temperature at the outlet of the cold storage 14 goes down, and the compressor 12 operates under HTF temperature conditions varying over time.
Fig. 4A shows a process layout for an embodiment of a Cold Storage System comprising a compressor 12, a condenser unit 131, an expansion unit 132 and a cold storage 14, placed in this order along a heat transfer fluid (HTF) circuit 11, in charging mode. The Cold Storage System further comprises a chiller/cold storage bypass 23, which connects a position X6 before the condenser unit 131 and a position X7 after the expansion unit 132 with a position X2 before the compressor 12.
The HTF is compressed, heated and set in motion by the compressor 12. The HTF pressure at position X6 after the compressor 12 may be e.g. 50 bar. The HTF then enters the condenser unit 131, where it emits heat energy into e.g. the ambient air 32. After condensation, the HTF enters the expansion unit 132 (e.g. an expansion valve), where it undergoes depressurization and temperature reduction, such that HTF pressure and temperature at the position X7 are e.g. 10 bar and -50 °C, respectively. At this stage, a part of the HTF enters the chiller/cold storage bypass 23. Controlling the mass flow of HTF through the chiller/cold storage bypass 23 by the chiller/cold storage bypass valve 231, the HTF temperature at position X5 before the compressor 12 and at position X6 after the compressor 12 can be regulated. As higher HTF temperatures can lead to higher power consumption for the operation of the compressor 12, a system according to the present figure, compared to a system according to Fig. 3B, has the advantage that the compressor 12 can be operated at higher efficiency.
The chiller/cold storage bypass valve 231 may, for example, be a three-way valve so that it can control the bypass of the condenser 13 and/or the cold storage 14.
The part of the HTF which exits the expansion unit 132 but does not enter the chiller/cold storage bypass 23 continues on the HTF circuit and enters the cold storage 14, where it passes through an integrated evaporator 145 and absorbs heat energy from (i.e., charges) the cold storage 14.
Fig. 4B shows, for a Cold Storage System as displayed in Fig. 6A, a qualitative plot of the HTF temperature against time at the positions X5 before the compressor 12 and X6 after the compressor 12. As the cold storage 14 is charged over time, the HTF temperature at position X2 after the outlet of the cold storage 14 is kept constant at a setpoint temperature (e.g. 10 °C), by means of controlling the mass flow of HTF through the chiller/cold storage bypass 23 via the chiller/cold storage bypass valve 231. In consequence, the compressor 12 operates under constant HTF temperature conditions.
Fig. 5 shows, from top to bottom, three consecutive steps (a), (b), (c) for charging a Cold Storage System comprising a compressor 12, condenser 13, and a cold storage 14, placed in this order along a circuit of heat transfer fluid (HTF). The condenser 13 includes a condenser unit 131 and an expansion unit 132, which are not displayed in the figure. The Cold Storage System further comprises a chiller/cold storage bypass 23, and a cold storage bypass 22. In this embodiment, the cold storage 14 is a multi-packed bed system of three packed beds 141, 142, 143 connected together in parallel. Throughout the process, the chiller/cold storage bypass valve 231 is operated to control the temperature at the inlet of the compressor 12. The cold storage bypass valve 221 is closed. The three consecutive steps comprise, in turn,

(a) charging the first packed bed 141. This is achieved if the control valve 1407 between the entries of the first and second packed bed and the control valve 1406 between the entries of the second and third packed bed are closed. The control valves between the exits of the first and second packed bed 1409 and between the exit of the second and third packed bed 1408 are opened. Therefore, the HTF flows via the point X7 through the first packed bed 141, and from there through the packed bed valves 1409 and 1408 to the point X0.
(b) When the HTF temperature at the exit of first packed bed 141 reaches a setpoint temperature (e.g. -5 °C) predefined for the HTF at the exit X0 of the multi-packed bed system, the second packed bed 142 starts charging, while the first packed bed 141 continues the charging process. At this stage, the packed bed valve 1406 between the entries of the second and third packed bed is still closed. The packed bed valve 1407 between the entries of the first and the second packed bed, along with the packed bed valve 1409 between the exits of the first and the second packed bed and the packed bed valve 1408 between the exits of the second and the third packed bed are opened. Therefore, the HTF flows through both the first packed bed 141 and the second packed bed 142.
(c) When the HTF temperature at the exit of the second packed bed 142 reaches the setpoint temperature predefined for the HTF at the exit X0 of the multi-packed bed system, the third packed bed 143 starts charging. The second packed bed 142 continues the charging process. To this end, the packed bed valve 1409 between the exits of the first and second packed bed is closed. The packed bed valves between the entries of the first and second packed beds 1407, between the entries of the second and third packed beds 1406, and between the exits of the second and third packed beds 1408 are opened. Therefore, the HTF flows via both the packed bed 142 and the packed bed 143.

The chiller/cold storage bypass valve 231 may, for example, be a three-way valve so that it can control the bypass of the condenser 13 and/or the cold storage 14.
Fig. 6 shows the settings for charging an embodiment of a Cold Storage System a compressor 12, condenser 13, and a cold storage 14, placed in this order along a circuit of heat transfer fluid (HTF). The condenser 13 includes a condenser unit 131 and an expansion unit 132, which are not displayed in the figure. The Cold Storage System further comprises a chiller/cold storage bypass 23, and a cold storage bypass 22. In this embodiment, the cold storage 14 is a multi-packed bed system of three packed beds 141, 142, 143 connected together in parallel. Throughout the process, the chiller/cold storage bypass valve 231 is operated to control the temperature at the inlet of the compressor 12. The cold storage bypass valve 221 is closed. In this setting, the packed bed valves 1406, 1407, 1408 and 1409 are open, and the three packed beds 141, 142, 143 are charged at the same time.
The chiller/cold storage bypass valve 231 may again be a three-way valve so that it can control the bypass of the condenser 13 and/or the cold storage 14.
Fig. 7A shows an embodiment of a Cold Storage System comprising a compressor 12, a cold storage 14, and a heat exchanger 15, placed in this order along an HTF circuit 11. The system further comprises the heat exchanger bypass 21 and a cold storage bypass 22. The heat exchanger bypass 21 starts on the HTF circuit 11 at position X1 after the cold storage 14, bypasses the heat exchanger 15, and ends on the HTF circuit 11 at position X5 after the heat exchanger 15. The cold storage bypass 22 starts on the HTF circuit at position X6 after the compressor 12, bypasses the cold storage 14, and ends on the HTF circuit at position X3 before the heat exchanger 15. The Cold Storage System is displayed in discharging mode, where the heat exchanger 15 is in operation and delivers coldness to (i.e., absorbs heat energy from) a consumer 31.
During the discharging process, the temperature of the HTF at the outlet of the cold storage 14 is initially at a low (e.g. below -10 °C) or ultra-low (e.g. -50 °C) temperature. Depending on the type of cold storage employed, this temperature rises over time, e.g. due to the deposit of heat energy through the HTF in the cold storage 14. The heat exchanger 15 can be realized e.g. as a coil, through which cooling is delivered to the consumer 31 by a flow of ambient air 32 passing over the coil by means of a fan 151. In this setup, the amount of cooling delivered to the consumer 31 depends on the HTF temperature at the inlet of the heat exchanger 15. In order to cancel the time variation in HTF temperature arriving from the cold storage 14, the cold storage bypass 22 delivers HTF of higher temperature from the position X6 after the compressor 12 to the inlet of the heat exchanger 15. Controlling the flow rate of HTF through the cold storage bypass 22 by means of the cold storage bypass valve 221, a constant setpoint temperature at the inlet of the heat exchanger 15 can be achieved. Therefore, by means of the cold storage bypass 22, the heat exchanger 15 can deliver coldness to the consumer 31 in a way which is controlled and constant over time. In addition, by means of the cold storage bypass 22 the amount of heat energy entering the Cold Storage System through the heat exchanger 15 is controlled, which can be utilized for a controlled discharging process of the cold storage 14.
The HTF temperature at the outlet X4 of the heat exchanger 15 is high; it may depend on the ambient temperature, and can be e.g. 50 °C. Compression of the HTF at the correspondingly high volumetric flow rate would lead to a high power consumption for the compressor 12. At the position X5 before the compressor 12, the hot HTF which has passed through the heat exchanger 15 is mixed with the cold HTF that has passed through the heat exchanger bypass 21, such that the temperature of the HTF at the inlet of the compressor 12 is reduced (e.g. to 25 °C) relative to the temperature of the HTF at the outlet X4 of the heat exchanger 15. When the HTF passes through the compressor, the HTF temperature slightly increases (to e.g. +35 °C at position X6 after the compressor 12). Finally, the HTF enters the cold storage 14, where it deposits the heat energy and is cooled down. This completes the HTF circuit.
The reduction of HTF temperature by means of the heat exchanger bypass 21 at a position X5 before the compressor 12 decreases the HTF volumetric flow rate in the compressor 12, and allows an operation of the compressor 12 at a lower power consumption. In addition, the reduction of HTF temperature before the compressor 12 decreases the HTF temperature at the inlet of the cold storage 14, which depending on the type of cold storage employed can be further utilized for a controlled discharging process of the cold storage 14.
Fig. 7B shows, for a system as displayed in Fig. 7A, the effect of the cold storage bypass 22 on the temperature of the HTF at position X3 on the HTF circuit, before the HTF enters the heat exchanger 15. Without the cold storage bypass 22, the HTF temperature at position X3, and thus at the inlet of the heat exchanger 15, rises over time. With the cold storage bypass 22 in place, the temperature can be stabilized at a fixed setpoint. Since the intention is that this setpoint can be selected by the consumer 31, three different cases of such setpoints (8 °C, 14 °C, 16 °C) are displayed.
Fig. 7C shows, for a system as displayed in Fig. 7A, the temperature against time of the HTF at position X5 before the inlet of the compressor 12, for a case where the system does not comprise versus a case where the system does comprise the heat exchanger bypass 21. In both cases, the temperature at position X5 in the displayed example is constant in time. However, without the heat exchanger bypass 21 the temperature of the HTF at the position X5 before the inlet of the compressor 12 is high (e.g. 50 °C), whereas with the heat exchanger bypass 21, the temperature of the HTF at the position X5 before the inlet of the compressor 12 is reduced to a lower temperature (e.g. 25 °C) due to the cold HTF passing through the heat exchanger bypass 21.
Fig. 8 shows, from top to bottom, three consecutive steps (a), (b), (c) for discharging an embodiment of a Cold Storage System comprising a compressor 12, a cold storage 14, and a heat exchanger 15, placed in this order along an HTF circuit 11, further comprising a heat exchanger bypass 21 and a cold storage bypass 22, for the exemplary case where the cold storage 14 is a multi-packed bed system of three packed beds 141, 142, 143 connected together in parallel.
Throughout the process, the cold storage bypass valve 221 is operated to control the temperature at the inlet of the heat exchanger 15 to be at a setpoint temperature. Furthermore, throughout the process the heat exchanger bypass 21 is used to control, via the heat exchanger bypass valve 211, the temperature of the HTF at point X5 before the compressor 12. The heat exchanger bypass 21 is not explicitly drawn in the figure. The three consecutive steps comprise, in turn,

(a) Discharging the third packed bed 143, which is achieved by closing the packed bed valve 1404 at the exit of first packed bed 141, the packed bed valve 1403 at the exit of second packed bed 142, as well as the packed bed valve 1401 between the inlets of the first and second packed bed and the packed bed valve 1400 between the inlets of the second and third packed bed. The packed bed valve 1402 at the exit of the third packed bed 143 and the packed bed valve 1405 between the exits of the packed beds 142 and 143 and the heat exchanger 15 are opened. Therefore, the HTF flows from the compressor 12 to the heat exchanger 15 via the third packed bed 143 and the cold storage bypass 22. The entry X1 of the heat exchanger bypass 21 is located after the third packed bed 143.
(b) When the HTF temperature at the outlet of the third packed bed 143 reaches the setpoint temperature defined for the HTF at the inlet of the heat exchanger 15, the discharging process of the third packed bed 143 is terminated, and the discharging of the second packed bed 142 commences. In order to discharge the second packed bed 142, the packed bed valves at the exit of first packed bed 1404, at the exit of third packed bed 1402, and between the inlets of the first and second packed bed 1401 are closed. The packed bed valves at the exit of the second packed bed 1403, between the inlets of the second and third packed bed 1400, and the packed bed valve 1405 between the exits of the packed beds 142 and 143 and the heat exchanger 15 are opened. Therefore, the HTF flows from the compressor 12 to the heat exchanger 15 via the second packed bed 142 and the cold storage bypass 22. The entry X1 of the heat exchanger bypass 21 is located after the second packed bed 142.
(c) When the HTF temperature at the outlet of the second packed bed 142 reaches the setpoint temperature for the HTF at the inlet of the heat exchanger 15, the discharging process of the second packed bed 142 is terminated, and the discharging of the first packed bed 141 commences. In order to discharge the first packed bed 141, the packed bed valves at the exit of the first packed bed 1404, at the exit of second packed bed 1403 and at the exit of third packed bed 1402 are closed. The discharge control valves between the inlets of the first and second packed bed 1401, between the inlets of second and third packed beds 1400 and the packed bed valve 1405 between the exits of packed beds 142 and 143 and the heat exchanger 15 are opened. Therefore, the HTF flows from the compressor 12 to the heat exchanger 15 via the first packed bed 141 and the cold storage bypass 22. The entry X1 of the heat exchanger bypass 21 is located after the first packed bed 141.

It is understood in all figures that temperatures, where indicated, are presented merely for illustrative purposes and can be adapted to the desired application and/or to the employed HTF in concrete embodiments.
Although the invention has been illustrated and described in detail by way of preferred embodiments, the invention is not limited by the examples disclosed, and other variations can be derived from these by the person skilled in the art without leaving the scope of the invention. It is therefore clear that there is a plurality of possible variations. It is also clear that embodiments stated by way of example are only really examples that are not to be seen as limiting the scope, application possibilities or configuration of the invention in any way. In fact, the preceding description and the description of the figures enable the person skilled in the art to implement the exemplary embodiments in concrete manner, wherein, with the knowledge of the disclosed inventive concept, the person skilled in the art is able to undertake various changes, for example, with regard to the functioning or arrangement of individual elements stated in an exemplary embodiment without leaving the scope of the invention, which is defined by the claims and their legal equivalents, such as further explanations in the description.
While each embodiment may stand on its own as a separate example, it is to be noted that in other embodiments the defined features can be combined differently, i.e. a particular feature described in one embodiment may also be realised in other embodiments. Such combinations are covered by the disclosure herein unless it is stated that a specific combination is not intended.

LIST OF REFERENCE LABELS

11: heat transfer fluid (HTF) circuit
12: compressor
13: condenser
131: condenser unit
132: expansion unit
14: cold storage
145: evaporator
15: heat exchanger
151: fan
16: chiller
161: refrigerant (RT) circuit
162: RT compressor
163: RT condenser unit
164: RT expansion unit
165: RT evaporator
21: heat exchanger bypass
211: heat exchanger bypass valve
22: cold storage bypass
221: cold storage bypass valve
23: chiller/cold storage bypass
231: chiller/cold storage bypass valve
31: consumer
32: ambient air
Q: heat energy

Claims

A Cold Storage System comprising:
a compressor (12) for compressing and enabling a circulation of a heat transfer fluid;

a condenser (13) with
- a condenser unit (131) for cooling the compressed heat transfer fluid,

- an expansion unit (132) for decreasing the pressure of the heat transfer fluid, thereby further cooling the heat transfer fluid;

and a cold storage (14) with an integrated evaporator (145), where the cold storage (14) is configured to store the coldness transferred by the heat transfer fluid.
The Cold Storage System of claim 1, further comprising a heat exchanger (15) for delivering of coldness to a consumer (31), wherein the heat exchanger (15) is arranged between the compressor (12) and the cold storage (14), and wherein the Cold Storage System is operable in a charging mode during which the heat energy stored in the cold storage decreases, or in a discharging mode during which the heat exchanger (15) delivers coldness to the consumer (31).
The Cold Storage System of claim 1 or claim 2, wherein the cold storage (14) includes a multi-packed bed system comprising a plurality of packed beds (141, 142, 143), which are employed as an evaporator (145) for the heat transfer fluid in charging mode.
The Cold Storage System of claim 3, wherein the multi-packed bed system further comprises a plurality of packed bed valves (1400, 1401, ...) such that the amount of heat transfer fluid flowing through each packed bed (141, 142, 143) is controlled by at least one respective packed bed valve (1400, 1401, ...).
The Cold Storage System of one of the preceding claims, which is chiller-free.
The Cold Storage System according to one of claims 2 to 5, further comprising a heat exchanger bypass (21) with a heat exchanger bypass valve (211),
wherein the heat exchanger bypass (21) is adapted to bypass the heat exchanger (15) and to channel heat transfer fluid from the outlet of the cold storage (14) to the inlet of the compressor (12), and the heat exchanger bypass valve (211) is adapted to control a flow of heat transfer fluid through the heat exchanger bypass (21) to keep a temperature at the inlet of the compressor (12) at a predefined range of temperature or around a setpoint temperature.
The Cold Storage System according to one of claims 2 to 6, further comprising a cold storage bypass (22) with a cold storage bypass valve (221), wherein the cold storage bypass (22) is adapted to bypass the cold storage (14) and to channel heat transfer fluid from the inlet of the cold storage (14) to the inlet of the heat exchanger (15), and the cold storage bypass valve (221) is adapted to control a flow of heat transfer fluid through the cold storage bypass (22) to keep a temperature at the inlet of the heat exchanger at a predefined range of temperature or around a setpoint temperature.
The Cold Storage System of one of the preceding claims, which includes only a single compressor (12), and no further pumping device.
The Cold Storage System of any of the preceding claims, further comprising a chiller/cold storage bypass (23) with a chiller/cold storage bypass valve (231),
wherein the chiller/cold storage bypass (23) is adapted to bypass the condenser (13) and/or the cold storage (14) and to channel heat transfer fluid from a position (X6) between the compressor (12) and the condenser (13) and from a position (X7) between the condenser (13) and the cold storage (14) to the inlet of the compressor (12), when the Cold Storage System is operated in a charging mode,
and wherein the chiller/cold storage bypass valve (231) is adapted to control a flow of heat transfer fluid through the chiller/cold storage bypass (23) to keep a temperature at the inlet of the compressor (12) at a predefined range of temperature or around a setpoint temperature.
The Cold Storage System according to one of the preceding claims, further comprising a control unit configured to control one or more of the following:
- periods of time where the Cold Storage System is in the charging mode and in the discharging mode, respectively,

- the heat exchanger bypass valve (211), in order to keep, in discharging mode, the temperature of the heat exchange fluid at the inlet of the compressor (12) in a predefined temperature range or around a setpoint temperature,

- the cold storage bypass valve (221), in order to keep, in discharging mode, the temperature of the heat exchange fluid at the inlet of the heat exchanger (15) in a predefined temperature range or around a setpoint temperature,

- the chiller/cold storage bypass valve (231), in order to keep, in charging mode, the temperature of the heat exchange fluid at the inlet of the compressor (12) in a predefined temperature range or around a setpoint temperature,

- the plurality of packed bed valves (1400, 1401, ...), such that in discharging mode, individual packed beds (141, 142, 143) can be discharged selectively, and
in charging mode, individual packed beds (141, 142, 143) can be charged selectively.
A Cold Storage System according to claim 10, wherein the control unit is configured to control the periods of time where the Cold Storage System is in charging and in discharging mode following readings of an external temperature and/or following the day and night cycle.
A method for performing a cold storage, comprising:
compressing and enabling a circulation of a heat transfer fluid;

cooling the compressed heat transfer fluid in a condenser unit (131);

expanding the heat transfer fluid in an expansion unit (132), thereby further cooling the heat transfer fluid; and

storing coldness delivered through the heat transfer fluid by evaporating the heat transfer fluid in a cold storage (14),

wherein the heat transfer fluid is cooled only by means of the condenser unit (131) and the expansion unit (132).