Method for operating a hot water system, hot water system and computer program

Abstract

A method for operating a hot water system (1) is proposed, comprising a hot water storage tank (2) connected to a circulation line (3) via a flow line (5) and a return line (6), in which one or more hot water draw-off points (4) are arranged, wherein the circulation line (3) is traversed from the flow line (5) to the return line (6) in a flow direction (17), a circulation pump (8) circulates the hot water in the circulation line (3) in the flow direction (17), and a return temperature sensor (7) is arranged upstream of a heating device (9) in the return line (6) with respect to the flow direction (17), wherein a temperature detected by the return temperature sensor (7) is compared with a predetermined or determined target temperature, and the heating device (9) is activated depending on the comparison. A hot water system (2) and a computer program (21) are also proposed.

Description

[0001] The invention relates to a method for operating a hot water system, comprising a hot water storage tank and a circulation line, a hot water system and a computer program.

[0002] Hot water systems typically include a hot water storage tank to store the heated drinking or service water. Particularly when using renewable energy sources like solar thermal energy, favorable conditions for heat generation and hot water demand can occur at different times. To ensure that the required quantity and temperature of solar thermally heated water can be delivered simultaneously, hot water storage tanks are used to store the heated water until needed.

[0003] A temperature stratification typically develops in hot water storage tanks. This allows hot water to be drawn from the upper part of the tank. Hot water systems are often operated with a circulation line, which, connected to the supply and return lines of the storage tank, uses a circulation pump to circulate the hot water. This ensures that hot water at the desired temperature is available at the taps without any waiting or warm-up time. A particular disadvantage of this system is that the water returned to the storage tank from the return line is cooler than the water from the supply line, and this mixing disrupts the temperature stratification within the tank. This can cause the temperature of the stored hot water to drop below a certain threshold, triggering a charging cycle.Furthermore, forecasting the demand-driven supply of hot water is made more difficult, as the ambient conditions and thus the water temperature in the return line vary individually depending on the building. Therefore, influencing the temperature stratification of the hot water storage tank also leads to a reduction in its energy efficiency.

[0004] From DE 39 05 874 C2, a hot water storage tank with a charging and transfer device is known, consisting of a hot water supply pipe arranged vertically in the storage tank in the flow line of the heating circuit. The hot water supply pipe has an inlet at the bottom and opens freely into the storage space at its upper end. It has outlets arranged one above the other, each with its own independently acting flap valves, which open according to the temperature stratification and thus allow the supplied medium to flow into the water space at the most favorable level.

[0005] Furthermore, DE 44 17 138 A1 discloses a stratified hot water storage tank with a combination of a vertically arranged flow chamber and a return chamber. The flow water first passes from the flow chamber into a settling chamber at all heights and only then into the surrounding storage tank. The aforementioned solutions are complex in terms of manufacturing and maintenance. Moreover, they offer only limited flexibility and / or adaptability to usage requirements.

[0006] DE 10 233 138 C1 describes a hot water storage tank with a charging and switching device that enables the injection of heated water into corresponding temperature layers of the hot water storage tank.

[0007] DE 10 2022 112 758 A1 describes a method for operating a heating appliance with a hot water supply arrangement, wherein, in a water circuit for heating the hot water, a first heat exchanger utilizes condensation heat for the hot water, and a downstream second heat exchanger can transfer heat from a heating circuit to the hot water. The method cannot contribute to solving the aforementioned problem of the disruption of the temperature stratification in a hot water storage tank by recirculated water from the return line of a circulation loop.

[0008] German patent DE 20 2016 004 882 U1 describes a domestic hot water heater with a first and a second heat exchanger for hot water preparation, which are connected to a buffer storage tank. The domestic hot water system is intended to ensure a constant outlet temperature. However, this domestic hot water system also fails to address the problem of the disruption of the temperature stratification in a hot water storage tank caused by inflow from the return line of a circulation loop.

[0009] The described state of the art is therefore complex and requires specially designed hot water storage tanks.

[0010] Based on this, the object of the invention is to propose a method for operating a hot water system, a hot water system, and a computer program that at least partially overcome the problems of the prior art described above and enable particularly energy-efficient operation of a hot water system with a hot water storage tank connected to a circulation line. In particular, the method should be simple and automated, and the invention should be easily retrofittable to existing hot water systems.

[0011] These problems are solved by the features of the independent claims. Further advantageous embodiments of the solution proposed here are specified in the dependent claims. It should be noted that the features listed in the dependent claims can be combined with one another in any technologically meaningful way and define further embodiments of the invention. Furthermore, the features specified in the claims are further specified and explained in the description, which also presents further preferred embodiments of the invention.

[0012] This involves a method for operating a hot water system. The hot water system comprises a hot water storage tank connected to a flow and return line via a circulation line. The flow direction of water runs from the flow to the return. A circulation pump circulates hot water in the circulation line in this direction. A return temperature sensor is located upstream of a heating element in the return line, relative to the flow direction of the circulation line. The proposed method involves comparing the temperature measured by the return temperature sensor with a predetermined or determined limit temperature and, depending on the comparison, activating (or preventing) the heating element.

[0013] A hot water storage tank is a storage unit for hot water supply, for example, to a building. The hot water storage tank can be designed as a stratified storage tank and has a container for holding heated or to-be-heated potable or process water. It can include a heat exchanger for transferring heat, for example, for heat exchange with a heating circuit or a heating system during the charging or heating process of the hot water storage tank. The heat exchanger can, for example, be designed as a coiled pipe, which (when installed) is usually located in a (geodesically) lower section of the hot water storage tank. The hot water storage tank can have a minimum or exactly one volume of water inside, and (if applicable)(separated from the adjacent water volume by means of a separating layer, preferably variably arranged and / or flexible) and comprising at least or exactly one gas volume. The water volume corresponds to a predefinable water capacity of the hot water storage tank. The hot water storage tank is designed to hold heated or to-be-heated drinking or process water.

[0014] The gaseous fluid in the gas volume can be, in particular, (ambient) air. Other gases, such as nitrogen, can also be used.

[0015] To replenish used hot water, hot water storage tanks typically have a cold water inlet, i.e., a supply of fresh water, often connected to a domestic water system or mains water supply. The cold water inlet is usually located in a lower section of the hot water storage tank to promote temperature stratification within the water volume.

[0016] The hot water storage tank can include thermal insulation that thermally isolates the tank from the environment. This thermal insulation can be a known, state-of-the-art insulation, such as foamed PUR (polyurethane) insulation.

[0017] The hot water storage tank is connected to a circulation line via a flow and return connection. One or more hot water outlets, such as showers or faucets, are located in the circulation line. A circulation pump is installed in the circulation line and is designed to circulate the hot water in a flow direction from the flow to the return. A return temperature sensor is also located in the return line of the circulation line, and a heating element is positioned downstream of this sensor, relative to the flow direction. The term "in the return line" here means that the return temperature sensor and the heating element are located downstream of the outlets in the circulation line, relative to the flow direction.The hot water storage tank can be designed to supply hot water to a single-family or multi-family house and can have a storage volume of 50 liters to 500 liters.

[0018] The heating device can be any type of heating device that heats the hot water flow in the return line of the circulation loop using the flow-through principle. In particular, the heating device can be an electric instantaneous water heater. The heating device can be configured to determine the required heating output based on an inlet temperature (e.g., measured by a return temperature sensor) and a measured or determined mass or volume flow rate of hot water. This heating output is then used to heat the hot water flow to a predetermined target temperature. Alternatively or additionally, the heating device can include an outlet temperature sensor that determines the outlet temperature of the heating device. A control device can be configured to regulate the outlet temperature of the heating device to a predetermined target temperature.The control device could, for example, be a control unit for the hot water system.

[0019] The target temperature can be predetermined or determined. In particular, the target temperature can be the temperature of the hot water in the tank of the hot water storage tank at the level or geodetic height of the return connection.

[0020] The process can also include demand-based activation of the circulation pump. This can incorporate recorded user data, such as periods of regular hot water withdrawal, withdrawal volume, etc. Furthermore, the process can include initiating the charging of the hot water storage tank. For this purpose, a recorded storage temperature can be compared with a predefined or determined target storage temperature, and charging is triggered if the temperature falls below the target. A tolerance can be included in the comparison if necessary. Charging can involve the activation of a heating appliance connected to the hot water system, whereby the heat exchanger of the hot water storage tank can be connected to a flow and return line of a heating circuit connected to the heating appliance, and heat is transferred from the heating circuit to the hot water storage tank.

[0021] According to one embodiment, at least one temperature of the hot water contained in the hot water storage tank can be measured. In particular, several temperatures at different geodetic heights within the tank can be measured to enable temperature stratification. Measuring the temperature of the water in the hot water storage tank allows for targeted heating of the hot water flow in the return line by the heating element to the measured temperature of the hot water in the temperature layer at the return connection of the circulation line. For this purpose, one or more storage tank temperature sensors can be used, which can be connected to a control unit of the hot water system for automated operation.

[0022] According to a further aspect of the invention, a hot water system is proposed. This system comprises a hot water storage tank connected to a flow and return line of a circulation line via a flow connection and a return connection. A circulation pump arranged in the circulation line is configured to pump hot water in the circulation line in a flow direction. A heating device is arranged in the return line of the circulation line, and, with respect to the flow direction, a return temperature sensor is arranged upstream of this heating device. The hot water system includes a control unit, for example, of a heating device connected to the hot water storage tank, which can be configured to carry out a method proposed herein. The control unit can, for example, include and / or have a processor.In this context, the processor can, for example, execute the procedure stored in a memory (of the control unit). Advantageously, operating data and reference values ​​for carrying out a procedure presented here can also be stored in the memory of the control unit. The control unit can, in particular, have an electrical connection to devices for acquiring parameters for carrying out a procedure proposed here, and thus execute the procedure fully automatically. For example, an electrical connection can exist to the circulation pump, the return temperature sensor, the heating device, and / or storage temperature sensors for acquiring one or more of the temperatures of the hot water in the hot water storage tank. An electrical connection here refers to a wired or wireless connection for data transmission or control.

[0023] According to one embodiment, a return flow heating device can be provided, which is arranged in the return line of the circulation loop and comprises the circulation pump, the return temperature sensor, and the heating element. The return flow heating device can have (exactly) one housing in which the circulation pump, the return temperature sensor, and the heating element are arranged. The housing or the return flow heating device can include an interface for data communication with a process-executing device, for example, a control unit of the hot water system. A power supply for the return flow heating device can be provided, either integrated into the interface or as a separate unit.

[0024] According to one embodiment, the hot water system can be connected to a heating appliance designed to heat the hot water storage tank. For this purpose, a heat exchanger in the hot water storage tank can be connected to a flow and return line of a heating circuit coupled to the heating appliance. The heating appliance can be any type of heating device, such as a gas boiler, a heat pump, a solar thermal system, an electric heater, etc.

[0025] Another aspect is the proposal for a computer program designed to (at least partially) execute the procedure presented here. In other words, this specifically concerns a computer program (product) comprising commands that, when executed by a computer, cause it to carry out the proposed procedure. The computer could, for example, be the control unit of a hot water system.

[0026] Another aspect that is proposed is a machine-readable storage medium on which the computer program is stored. This machine-readable storage medium is typically a computer-readable data carrier.

[0027] The details, features, and advantageous configurations discussed in connection with the process may also occur in the computer program and / or hot water system presented here, and vice versa. In this respect, full reference is made to the explanations provided therein for a more detailed characterization of the features.

[0028] This document presents a method for operating a hot water system, a hot water system itself, and a computer program that at least partially solve the problems described with reference to the prior art. In particular, the method, the hot water system, and the computer program contribute to enabling particularly energy-efficient operation of the hot water system. This is achieved by largely maintaining temperature stratification in the hot water storage tank of the hot water system, even during operation of the circulation pump. Furthermore, and particularly advantageously, the invention can be easily retrofitted to existing hot water systems.

[0029] The invention and its technical context are explained in more detail below with reference to the accompanying figure. It should be noted that the invention is not limited by the exemplary embodiments shown. In particular, unless explicitly stated otherwise, it is also possible to extract partial aspects of the facts illustrated in the figure and combine them with other components and findings from the present description. It should be emphasized that the figure, and especially the depicted dimensions, are only schematic. It shows: Fig. 1: a hot water system proposed here.

[0030] Fig. 1Figure 1 shows an exemplary and schematic representation of a proposed hot water system 1. This system comprises a hot water storage tank 2 with a storage container for hot water, i.e., heated or to-be-heated drinking or service water. The storage container can have a heat exchanger 12 in a lower geodetic section, which can be connected to a heating circuit 15 of a heating appliance 11. This allows the hot water storage tank 2 to be charged with heat, which can be transferred to the hot water storage tank 2 by means of the heat transfer medium circulated in the heating circuit 15. The heating circuit 15 can also be connected to consumers (not shown here) such as radiators or underfloor heating systems for the building's heat supply.

[0031] The hot water storage tank 2 is connected to a flow line 5 and a return line 6 of a circulation line 3. At least one hot water outlet 4, for example a shower faucet, can also be connected to the circulation line 3. A return heating device 10 can be arranged in the return line 6. This device includes a circulation pump 8, which pumps or circulates the potable or service water in the circulation line 3 in a flow direction 17. The return heating device 10 also has a return temperature sensor 7 and a heating element 9. The heating element 9 is located downstream of the return temperature sensor 7 with respect to the flow direction 17, so that the temperature of the water in the circulation line 3 can be determined before it is heated by the heating element 9.The heating device 9 is an electric heating device with a heating coil 22 that is in contact with the water flow circulating in the circulation line 3 and, when an electric current flows through it, heats the water by resistance. The return flow heating device 10 comprises exactly one housing 19 in which the return temperature sensor 7, the circulation pump 8, and the heating device 9 are arranged. Furthermore, the housing 19, or the return flow heating device 10, has an interface 20 that enables a simple electrical connection to a control unit 13. The interface 20 can establish an electrical or data connection from the control unit 13 to the return temperature sensor 7, the heating device 9, and the circulation pump 8.

[0032] The hot water storage tank 2 also has a cold water inlet 18, through which cold water, for example from a supply network, can be supplied to the hot water storage tank 2. In addition, the hot water system 1 has a storage temperature sensor 16, which detects the temperature of the hot water contained in the hot water storage tank 2, as well as a flow temperature sensor 14 for detecting the temperature of the water exiting the flow 5 of the hot water storage tank 2.

[0033] The control unit 13 can be configured to execute a procedure proposed here. For this purpose, it can be connected to the interface 20 or the device 10 for return flow heating, the heating unit 11, the flow temperature sensor 14, and the storage tank temperature sensor 16. A computer program 21 can be stored in the memory of the control unit 13, which causes the control unit 13 or the hot water system 1 to execute a procedure proposed here. The control unit 13 can be configured to compare the temperature detected by the return flow temperature sensor 7 with a target temperature, which may correspond to the temperature detected by the storage tank temperature sensor 16, and, if necessary, to activate the heating device 9 and thereby heat the hot water to the target temperature.For this purpose, the required heating output of the heating device 9 can be determined and set based on knowledge of the mass flow of water circulating in the circulation line 3 and its temperature upon entry into the heating device 9. Alternatively or cumulatively, the device 10 for return flow heating can also include an outlet temperature sensor (not shown here) that can detect the temperature of the water exiting the heating device 9, and the outlet temperature can be regulated to the target temperature. The control of the outlet temperature can also be carried out by the control unit 13. Reference symbol list

[0034] 1 Domestic hot water system 2 Domestic hot water storage tank 3 Circulation line 4 Draw-off point 5 Flow 6 Return 7 Return temperature sensor 8 Circulation pump 9 Heating system 10 Return flow heating device 11 Heating unit 12 Heat exchanger 13 Control unit 14 Flow temperature sensor 15 Heating circuit 16 Storage tank temperature sensor 17 Flow direction 18 Cold water inlet 19 Housing 20 Interface 21 Computer program product 22 Heating coil

Claims

1. Method for operating a hot water system (1), comprising a hot water storage tank (2) connected to a flow (5) and a return (6) of a circulation line (3) in which one or more hot water draw-off points (4) are arranged, wherein the circulation line (3) is traversed from the flow (5) to the return (6) in a flow direction (17), further comprising a circulation pump (8) which pumps hot water in the circulation line (3) in the flow direction (17), and a return temperature sensor (7) which is arranged upstream of a heating device (9) in the return line (6) with respect to the flow direction (17), wherein a temperature detected by the return temperature sensor (7) is compared with a predetermined or determined target temperature and the heating device (9) is put into operation depending on the comparison.

2. Method according to claim 1, wherein a target temperature of the hot water storage tank (2) is detected or predetermined, and the heating device (9) heats the hot water to an outlet temperature depending on the target temperature.

3. Method according to claim 2, wherein a heating output of the heating device (9) is determined and set on the basis of the temperature detected by the return temperature sensor (7), the target temperature and a detected or known volume flow of hot water in the circulation line (3).

4. Method according to one of claims 2 or 3, wherein the target temperature corresponds to the temperature at an inlet height of the return flow (6) into the hot water storage tank (2).

5. Hot water system (1) comprising a hot water storage tank (2), a circulation line (3) connected to the hot water storage tank (2) via a flow line (5) and a return line (6), a heating device (9) and a return temperature sensor (7) arranged upstream of the heating device (9) with respect to a flow direction (17) of the circulation line (3), a circulation pump (8) and a control unit (13) configured to carry out a method according to one of the preceding claims.

6. Hot water system (1) according to claim 5, wherein the hot water storage tank (2) has one or more storage temperature sensors (16) which detect a temperature of the hot water contained in the hot water storage tank (2).

7. Hot water system (2) according to one of claims 5 or 6, wherein the heating device (9) is an electric instantaneous water heater.

8. Hot water system (2) according to one of claims 5 to 7, wherein the circulation pump (8), the heating device (9) and the return temperature sensor (7) are arranged in a common housing (19).

9. Hot water system (2) according to claim 8, wherein the housing (19) comprises an interface (20) for connection to the control unit (13) and / or a connection for a power supply.

10. Computer program product (21) comprising commands that cause a hot water system (2) according to one of claims 5 to 9 to execute a method according to one of claims 1 to 4.

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