Liquid cooling system

Abstract

The invention relates to a photovoltaically powered system for cooling liquids, in particular water. The cooling system includes a photovoltaic system for generating direct current solar power. The solar-powered cooling system is particularly suitable for use in hot and dry regions where access to electricity and water is limited or expensive. In such regions, the demand for cooling is high, as the hot climate can also lead to various health problems and discomfort. The solar-powered cooling system provides a sustainable, environmentally friendly, and cost-effective solution to meet this demand while simultaneously reducing dependence on conventional energy and water sources.

Description

[0001] The invention relates to a system for cooling water and a method for cooling water using the system, in particular in combination with a photovoltaically powered reverse osmosis system for producing drinking water. Description

[0002] The invention provides a cooling system, in particular a water cooling system, that utilizes the abundant and renewable energy of the sun to cool lukewarm liquids such as water or milk for human consumption, especially in remote areas where access to electricity is limited. Furthermore, the cooled water is intended to serve as raw water for desalination plants in volcanic regions where the natural raw water has temperatures exceeding 30°C, which complicates desalination because the produced permeate has a higher salt content compared to plants with lower inlet water temperatures.

[0003] In the following, the invention is often described by way of example in connection with water as the liquid to be cooled. However, the invention is not limited to water, but can in principle also be used for other liquids.

[0004] The cooling system according to the invention reduces dependence on traditional power and cooling systems.

[0005] The goal of using (exclusively) solar energy to power the system initially conflicts with the goal of ensuring a continuous and reliable supply of chilled water. Environmental factors such as cloud cover and rain must be compensated for. The availability of chilled water must also be guaranteed at night, which is why the water must be cooled to an adaptively adjustable degree. To achieve this, the temperature is reduced before sunset so that the cooling temperature in a first water tank is as low as possible, ensuring continuous cooling of the water in a second tank. In case of cloud cover or rain, the motor is not switched off; instead, a solar-powered frequency converter reduces the motor's speed, allowing it to operate at a lower cooling capacity.

[0006] Furthermore, in certain embodiments, the invention prevents the oil from mixing with the cooling medium when the engine is switched off.

[0007] The invention relates to a system for cooling liquids such as water or milk, which is self-sufficient and comprises - a first tank containing a liquid to be cooled, - a second tank to cool the first tank, - a first heat exchanger and - a second heat exchanger where - the first tank is connected to the second heat exchanger in such a way that heat energy can be dissipated via the second heat exchanger and - the second water tank is connected to the second heat exchanger in such a way that heat energy can be dissipated from the liquid to be cooled in the first water tank via the second heat exchanger, further showing - a photovoltaic system for generating direct current solar power, - an AC-powered pressure pump with an asynchronous motor to generate the pressure required for pumping the liquid, a frequency converter is installed between the pressure pump and the photovoltaic system, which combines the properties of an inverter and a converter and converts the solar power in such a way that the asynchronous motor of the AC-operated pressure pump can be operated dynamically depending on the available solar voltage energy.

[0008] In one embodiment, the invention relates to a system for cooling water that can be operated autonomously, comprising - a first water tank containing water to be cooled, - a second water tank to cool the first water tank, - a first heat exchanger and - a second heat exchanger where - the first water tank is connected to the second heat exchanger in such a way that heat energy can be dissipated via the second heat exchanger and - the second water tank is connected to the second heat exchanger in such a way that heat energy can be dissipated from the water to be cooled in the first water tank via the second heat exchanger, further showing - a photovoltaic system for generating direct current solar power, - an AC-operated pressure pump with an asynchronous motor to generate the pressure required for pumping the water, wherein a frequency converter is installed between the pressure pump and the photovoltaic system, which combines the properties of an inverter and a converter and converts the solar power in such a way that the asynchronous motor of the AC-operated pressure pump can be operated dynamically depending on the available solar voltage energy.

[0009] In some embodiments, the water cooling system has an AC-operated compressor, wherein a frequency converter is installed between the compressor and the photovoltaic system, which combines the properties of an inverter and a converter and converts the solar power in such a way that the asynchronous motor of the AC-operated compressor can be operated dynamically depending on the available solar voltage energy.

[0010] The compressor has a cooling capacity of 22.2 kW and is operated by an asynchronous motor with a power capacity of 5.5 kW.

[0011] Depending on the cooling capacity and the associated compressor motor, in some embodiments a modified solar-powered variable frequency drive (VFD) dynamically controls the speed of the compressor motor and / or the pressure pump motor depending on the available solar voltage energy.

[0012] "Dynamic operation" means that the asynchronous motor is operated depending on the intensity of solar radiation and thus depending on the temporarily available solar energy or solar voltage energy. The power generated by the asynchronous motor decreases or increases with the current energy production of the photovoltaic system.

[0013] The water cooling system always includes a condenser fan for ventilating the condenser. The size of the condenser fan is directly and appropriately proportional to the cooling capacity of the compressor.

[0014] In some embodiments of the water cooling system, the solar panel supplies power to the compressor, the condenser fan and / or the water pumps.

[0015] In some embodiments of the water cooling system, the cooled drinking water is decoupled from a cooling system comprising a second water tank and pipework by means of two heat exchangers.

[0016] In some embodiments of the water cooling system, the first heat exchanger is used to cool the water in the first water tank with the water to be cooled.

[0017] In some embodiments of the water cooling system, water from the cooling water tank flows through one side of the heat exchanger, and the refrigerant flows through the other. The refrigerant, connected to the cooling system, absorbs the thermal energy in the cooling water tank, thereby cooling it. In some embodiments, the refrigerant absorbs the thermal energy in the cooling water tank to such an extent that it cools down to a temperature of approximately 2 to 3 degrees Celsius.

[0018] In some embodiments of the water cooling system, the second heat exchanger is connected on one side to the cooling water tank and on the other side to the drinking water tank.

[0019] In some embodiments of the water cooling system, the water from both tanks flows continuously through the heat exchanger, thereby transferring heat from the drinking water to the cooling water and thus cooling the drinking water.

[0020] The solar-powered cooling system according to the invention (see also the exemplary embodiment of the Fig. 1) uses an efficient refrigeration cycle to achieve the desired cooling effect, which is described below.

[0021] A refrigeration cycle is a thermodynamic process that enables the transfer of energy from a lower energy level to a higher energy level, resulting in the cooling of the desired medium. This process, however, is the opposite of natural energy flow, where heat is transferred from a warmer environment to a cooler medium. To reverse this process, energy must be introduced into the refrigeration process. The refrigeration cycle consists of four main phases: compression, condensation, expansion, and evaporation. Each phase is essential for the overall cooling process.

[0022] The first phase of the cycle is the compression phase. Here, the refrigerant gas is compressed by the compressor, increasing its pressure and temperature. The compressed gas is then directed to the condenser, where it undergoes the second phase of the cycle – condensation. In this phase, the refrigerant gas is cooled and, by releasing its heat to the surroundings, is typically converted into a liquid via a heat exchanger.

[0023] The third phase of the cycle is the expansion phase, in which the liquid refrigerant expands through a throttle valve, reducing pressure and temperature. As a result, the refrigerant evaporates and absorbs heat from the surroundings, thus cooling them (evaporation phase). Finally, the refrigerant is returned to the compressor to complete the cycle.

[0024] In the solar-powered water cooling system, solar panels are used to supply the compressor, condenser fans, and water pumps with the necessary energy. This represents a significant innovation in the refrigeration industry, as it enables the direct use of renewable energy sources and eliminates reliance on grid electricity. The integration of solar panels into the cooling system is crucial to the technology's success, as it is a unique selling point and ensures that the system operates sustainably, cost-effectively, and largely autonomously.Although small solar water cooling units for water and dairy products currently exist on the market, they use direct current for the compressors, which makes their repair and control very expensive and severely limits the water cooling capacity, or inverters and battery banks for three-phase asynchronous motors are used, which is unaffordable for the intended application and therefore not economically competitive.

[0025] To optimize system performance, a variable frequency drive (VFD) is used to control the compressor motor's speed. This allows the compressor to operate at different speeds depending on cooling requirements, resulting not only in reduced energy consumption but also in an extended compressor lifespan. This approach is better suited to the use of solar modules, as the speed is simply adjusted to accommodate fluctuations in power output, rather than switching on or off at a fixed limit. Compared to conventional on / off control, this saves energy because the energy-intensive compressor start-up process is eliminated, resulting in fewer switching cycles, which—as mentioned above—increases the service life. Therefore, in the system according to the invention, water cooling can be achieved without batteries, significantly reducing investment and maintenance costs.

[0026] In the solar-powered water cooling system, the chilled drinking water is decoupled from the cooling system by two heat exchangers to ensure that even in the event of a leak in the compression system, there is no contact between the drinking water and the refrigerant. The first heat exchanger is used to cool the water in the cooling water tank. This is achieved by the water from the cooling water tank flowing through one side of the heat exchanger and the refrigerant through the other. The refrigerant, which is connected to the cooling system, absorbs the thermal energy in the cooling water tank, thus cooling it to a temperature of approximately 2-3 degrees Celsius.

[0027] To ensure proper temperature regulation of the water tank, a thermometer is installed inside the tank, connected to the electronic control unit (ECU), which continuously monitors the temperature. This data is sent to the automated, AI-based control system, which adjusts the compressor motor speed via a variable frequency drive (VFD) as needed. The frequency converter allows the compressor to operate at different speeds by varying the voltage.

[0028] The second heat exchanger is connected to the cooling water tank on one side and the drinking water tank on the other. Water from both tanks flows continuously through the heat exchanger, transferring heat from the drinking water to the cooling water and thus cooling the drinking water. Using the cooling water tank as a buffer between the drinking water and the cooling system is primarily a safety measure. While this does result in some reduction in efficiency, it significantly increases safety and eliminates the risk of refrigerant contamination of the drinking water. Additionally, the cooling water tank serves as a temporary buffer to respond to problems and failures while maintaining cooling capacity.

[0029] In a second aspect, the invention relates to a method for cooling water, in particular using the system described herein.

[0030] In some embodiments of the method, an artificial intelligence (AI) receives weather data from the local installation site as part of the control system. Specifically, artificial neural networks for machine learning are integrated into the control system, and complex data flows are implemented to provide a basis for training the AI ​​tools. The AI ​​training and testing are carried out to ultimately obtain an easy-to-use, plug-and-play product. In particular, edge computing is used and does not require a continuous internet connection.

[0031] Depending on the weather forecast, the AI ​​can variably adjust the compressor motor speed. This lowers the water level in the tank if cloudy weather or rain is expected.

[0032] In some embodiments of the method, an alternating voltage can be connected to the frequency converter so that, if the frequency converter's speed falls below a predefined minimum (n2), power is drawn from a power grid to compensate for the missing power from the solar panels. The defined speed (n2) can vary, in particular, depending on the following specifications: A: If the goal is to save on grid power, n2 is set to 20 Hz. This ensures that the motor frequency n1, for example, from 50 Hz to 20 Hz, is powered by solar energy, and grid power is only used before n2 falls below this frequency. Between operating points n1 and n2, the motor is operated using the solar-powered MPPT (Maximum Power Point Tracking) of the frequency converter. B. If the goal is to ensure a consistent cooling temperature over a defined period, n2 will be close to n1, with a difference of 0.1 Hz. Therefore, underlining n2 indicates that the energy for the water cooling system is supplied by the mains electricity.

[0033] In some embodiments of the method, several frequency converters are interconnected via software, so that the power from the solar panels is distributed and prioritized among several motors, in particular three. For example, when solar power is low, pump 2 initially runs at speed n2. As soon as more solar power is available, pump 1 is also activated at speed n2, and finally, the compressor motor also starts at speed n2. With a further increase in solar power, the speed of the pumps and the motor increases to speed n1 according to the predefined prioritization.

[0034] In some embodiments of the method, the rotational speed, temperature and / or voltage of the frequency converters, as well as the amount of water and / or the water temperature, are remotely monitored.

[0035] The invention makes it possible to cool water quantities sufficient for a community supply cost-effectively and continuously using solar power.

[0036] In particular embodiments of the invention, the water cooling system is coupled with a desalination plant, which is described below in various embodiments.

[0037] The desalination plant, as part of the invention, makes it possible to desalinate seawater or brackish water. As described above and herein, the desalinated water can then be cooled and provided as treated drinking water. One possible technique for desalinating and treating such water is the use of reverse osmosis.

[0038] In reverse osmosis, the water to be treated is forced through a semipermeable membrane under high pressure (reverse osmosis pressure), which is higher than the osmotic pressure of the water being treated. Besides desalination, it is also possible to filter out bacteria and viruses, mineral compounds such as limescale, and even harmful or toxic substances.

[0039] The invention is also designed as an island system in the embodiment with a desalination plant and is therefore independent of the local power grid and the use of batteries, and can thus be operated autonomously.

[0040] In another aspect, the invention relates to a water cooling system with a photovoltaically powered reverse osmosis system for producing drinking water. The photovoltaically powered reverse osmosis system for producing drinking water is described below.

[0041] The reverse osmosis system includes a photovoltaic system for generating direct current solar power, a reverse osmosis unit, and an alternating current-operated pressure pump with an asynchronous motor to generate the pressure required for reverse osmosis.

[0042] The reverse osmosis system is characterized by the fact that a modified frequency converter is installed between the pressure pump and the photovoltaic system, which combines the properties of an inverter and a converter and converts the solar power in such a way that the pressure pump, which can be operated with alternating current, and in particular its asynchronous motor, can be operated dynamically depending on the available solar voltage energy.

[0043] "Dynamic operation" means that the asynchronous motor is operated depending on the intensity of solar radiation and thus depending on the temporarily available solar energy or solar voltage energy. The power generated by the asynchronous motor decreases or increases with the current energy production of the photovoltaic system.

[0044] For the desalination and purification of seawater or brackish water, which are characterized by high osmotic pressures, the pressure pump is in particular a high-pressure pump with which a reverse osmosis pressure of 3 bar to 90 bar, especially from 15 bar to 60 bar, can be generated.

[0045] In one embodiment of the reverse osmosis system according to the invention, the frequency of the asynchronous motor of the system's internal pressure pump is adjusted by the modified frequency converter as a function of the solar energy provided by the photovoltaic system, the available quantity of which depends directly on the intensity of the solar radiation, so that the reverse osmosis system according to the invention does without batteries and the use of DC motors.

[0046] In a further embodiment, the modified frequency converter has the technical feature of simultaneously • to convert the single-phase direct current from the photovoltaic system into three-phase alternating current as well as • to convert the generated three-phase alternating voltage into an alternating voltage with different frequencies and amplitudes.

[0047] The modified frequency converter differs from standard frequency converters primarily in its technical features listed below. The following modifications may be present individually or in combination: • The solar voltage generated by the photovoltaic system is connected to the intermediate circuit of the modified frequency converter in such a way that the diode voltage of the modified frequency converter, which generates direct current from alternating current, is bridged, and / or • The voltage conversion achievable by the modified frequency converter is for a defined frequency range Hz min ≤ Hz x ≤ Hz max determined (with Hz) min = minimum frequency; Hz x = variable actual frequency; Hz max (= maximum frequency).

[0048] In one embodiment, the photovoltaically operated reverse osmosis system is designed such that if the Hz threshold is not reached, the system shuts down. min The pumps will be switched off and only switched back on when sufficient voltage is available again.

[0049] Alternatively, a commercially available frequency converter can be used to provide a modified frequency converter, which is modified according to the technical characteristics described here.

[0050] In order to be able to provide the population with treated drinking water even during periods of low solar intensity, the reverse osmosis system according to the invention includes in particular a water tank for storing the drinking water produced by the reverse osmosis system.

[0051] In advantageous embodiments of the reverse osmosis system according to the invention, all hydraulic connections of the reverse osmosis system are designed to be screwed together, so that, for example, only screwdrivers and / or open-end wrenches are required for assembling and disassembling the reverse osmosis system. The requirement of only simple tools offers advantages in that the reverse osmosis system can be easily and inexpensively repaired in the event of a defect, or relocated quickly if necessary. In particular, welding can then be avoided.

[0052] For high weather resistance, the metallic components of the reverse osmosis system are preferably made of a suitable stainless steel.

[0053] In one embodiment, the photovoltaically powered reverse osmosis system has at least two pumps: a high-pressure pump and a water-feed pump. In another embodiment, the photovoltaically powered reverse osmosis system is designed such that the intensity of the sun is distributed between the pumps in such a way that the high-pressure pump is the controller (so-called "master") and the water-feed pump is the peripheral (so-called "slave").

[0054] In one embodiment of the invention, dynamic synchronization between a feed pump (P2) and a high-pressure pump (P3) is implemented, controlled according to a Function Block Diagram (FBD) known in the prior art. This control is independent of Maximum Power Point Tracking (MPPT) techniques and enables real-time adjustment of the operating frequency based on system requirements such as pressure and flow rate. In one embodiment, the control dynamically adjusts the pump frequency in real time, depending on the specific operating requirements and not just on a linear frequency characteristic. This adjustment can be achieved via logic in the FBD that enables bidirectional communication between the pumps to ensure that the high-pressure pump (P3) is operated only when the feed pump (P2) provides a sufficient flow rate at the required frequency (in particular, F ≥ 30 Hz).

[0055] In one embodiment, the photovoltaically powered reverse osmosis system is configured such that the pump speed is regulated by the maximum permissible membrane pressure and the conductivity of the incoming and outgoing water. If the maximum permissible membrane pressures are exceeded, the speed of the pressure-generating pump decreases, for example by 2.0 Hz to 5 Hz, and in particular by 3.5 Hz.

[0056] In one embodiment, the photovoltaically powered reverse osmosis system is designed such that the frequency of the pumps describes a straight line, the slope of which is given by the quotient of Hz max and Hz min The rotational speed of the pumps graphically corresponds to a straight line. The slope m of the line depends on the f. min and f max , where delta m = f max / f min .

[0057] In one embodiment, the photovoltaically powered reverse osmosis system is operated "hybrid," i.e., with alternating current and direct current. For this purpose, a load disconnect switch is provided, which is supplied with both voltage types, whereby the diode bridge is not bridged in the alternating current mode.

[0058] In one embodiment, protection against exceeding the maximum pressure in the reverse osmosis system is implemented. This can be achieved using integrated logic in the FBD to automatically switch off the pumps when frequencies or pressure values ​​fall below or exceed the defined limits. This ensures that the system's operating conditions are constantly monitored and adjusted, extending the service life of the components and maximizing efficiency.

[0059] In various configurations, several parameters of the photovoltaic-powered reverse osmosis system can be read using a smartphone. These parameters are recorded by the system's control software. Such parameters can include: the water pressure in the membrane, the conductivity of the water at the inlet and outlet of the reverse osmosis unit, the pump speed, the amount of water produced, the amount of water inlet, the current DC link voltage, and the temperature of the frequency converter. These parameters can represent current readings and / or parameters stored during system operation.

[0060] In various embodiments, a multitude of frequency converters are interconnected via software, so that the power from the solar panels is distributed and prioritized across multiple motors, particularly three. For example, when solar power is low, pump 2 initially runs at speed n2. As soon as more solar power becomes available, pump 1 is also activated at speed n2, and finally, the compressor motor also starts at speed n2. With a further increase in solar power, the speed of the pumps and the motor increases to speed n1 according to the predefined prioritization.

[0061] In another aspect, the invention relates to a method for providing drinking water, in particular using the photovoltaically operated reverse osmosis system described here.

[0062] In a further aspect, the invention relates to a kit for manufacturing the water cooling system and / or the photovoltaically powered reverse osmosis system described herein. The kit particularly includes a modified frequency converter of the type described herein. Figures Figure 1 shows a schematic view of an embodiment of the solar-powered cooling system. Exemplary parameters for operating the system are given below.

[0063] The system shown for cooling liquids, especially water, comprises - a first tank containing a liquid to be cooled, in particular water (drinking water tank), a second tank for cooling the first tank (drinking water tank), a first heat exchanger and a second heat exchanger, wherein the first tank is connected to the second heat exchanger in such a way that heat energy can be dissipated via the second heat exchanger and the second tank is connected to the second heat exchanger in such a way that heat energy can be dissipated from the liquid (water) to be cooled in the first tank via the second heat exchanger. First heat exchanger, heat exchanger 1 (evaporator) • Cooling capacity: 16 kW • Cold side medium: R134a • Mass flow rate: 396 kg / h • Evaporation temperature: 1 °C • Suction gas temperature: 8 °C Warm side, medium: cooling water • Flow rate: 2600 l / h • Inlet temperature: 17 °C • Outlet temperature: 6 °C Second heat exchanger, heat exchanger 2 • Plate heat exchanger • Cooling capacity: 16 kW • Cold side medium: Cooling water • Flow rate: 2600 l / h • Inlet temperature: 6 °C • Outlet temperature: 11 °C Second page, medium: drinking water • Flow rate: 1300 l / h • Inlet temperature: 25 °C

Images