EP0807790A2 - Method and system for prepairing sanitary hot water - Google Patents

Abstract

The device comprises a primary circuit (10) which has a heater (1) producing warm or hot fluid and a conveyor (14) with a regulator for the fluid. A secondary circuit (20) is for the service water to be heated up. A heat exchanger (5) transfers heat from the fluid in the primary circuit to the service water in the secondary circuit. The primary circuit in the heat exchanger or the output side pipe (13) has a first temperature sensor (17). The secondary circuit in the heat exchanger or the output side pipe (23) has a second temperature sensor (27). The regulator has a circuit which switches on the conveyor when the temperature drops below a nominal value and or exceeds a nominal value on the second temperature sensor, and switches off the conveyor when the temperature exceeds a nominal value and or exceeds an amount on the first temperature sensor.

Description

The invention relates to an arrangement and a method for providing hot domestic water with a primary circuit with a fluid, a device providing hot or hot fluid and a conveying device for the fluid, a secondary circuit for the domestic water to be heated, a heat exchanger for heat transfer from the fluid of the primary circuit on the process water in the secondary circuit, a control device for the conveyor and a temperature sensor in the primary or secondary circuit.

The hot domestic water is conventionally provided by means of a heating source in a domestic water storage tank, a so-called boiler, which also takes on the task of temporarily storing energy.

In many cases it makes sense and is also proven to separate the process water on the one hand and the actually heated fluid on the other. This fluid is usually also water, but for example the water of a heating system, which is not intended for normal consumption or use.

DE 295 19 473 U1 proposes a flow water heater. In this case, a process water queue runs through a heating water storage tank, during which process hot water is to be reheated via an assigned heating device. In order to recognize that hot water is being drawn off, a temperature sensor is arranged in the thermally conductive contact with the hot water coil in the area where the hot water coil flows into the heating water tank. After the start of the tap, cool fresh water flows through exactly this junction area, and the resulting small temperature drop is transferred to the temperature sensor, which can thus be used to control the heating device.

In other cases, the process water is heated with the help of an external heat exchanger as a water heater. The fluid or heating water is pumped in a primary circuit through the heat exchanger, which heats the process water in the secondary circuit. Cold water is thus fed to the heat exchanger in the secondary circuit and brought there to the desired useful temperature by transferring the heat from the heating water from the heat generator through the heat exchanger to the process water. After passing through the heat exchanger, the hot water is available in a heated form.

So-called stratified superchargers, as are known, for example, from EP 0 384 423 B1, are particularly suitable as sources or stores for the hot fluid or heating water. The hotter amounts of water or fluid are layered on top of one another in a storage vessel. The primary circuit removes hot fluid from the top of the storage vessel, it flows through the heat exchanger mentioned and is then cooled again and is then stratified in a region of the storage vessel corresponding to the temperature between the amounts of water or fluid located there.

In order to be able to provide a reasonably constant water temperature for the process water, a control device can be provided.

Such a control device is known for example from CH-PS 285 708; a temperature sensor is provided there, which is provided either in the primary circuit or also in the secondary circuit and acts on a three-way valve and thus regulates the primary-side temperature in the heat exchanger by changing the mixing ratio of the heating water in the primary circuit.

With the rest of the same mode of operation, for example in DE 40 35 115 C2 a speed control of the pump controlled by a flow switch is used in the primary circuit. However, this has the disadvantage Proven use of a flow switch in the hot water pipe. Flow monitors require considerable acquisition and installation costs and are extremely prone to errors. As such, the flow monitors should recognize, based on a flow, whether water is flowing, and therefore process water is being drawn, and, depending on this, switch on or off the circulation pumps.

The object of the invention is to propose an arrangement and a method for providing hot industrial water which does not require such flow monitors and at the same time creates an inexpensive control option.

This object is achieved in an arrangement in that a first temperature sensor is arranged both in the primary circuit in the heat exchanger or in the line on the outlet side with respect to the heat exchanger and in the secondary circuit in the heat exchanger or in the second line temperature sensor in the outlet side with respect to the heat exchanger, and in that the control device has a circuit which switches on the conveying device when the temperature drops below a desired value and / or a temperature gradient amount exceeding a desired value at the second temperature sensor and switches off the conveying device at the first temperature sensor when the temperature increases above a desired value and / or when the temperature gradient exceeds a desired value.

In a method, the object is achieved in that the temperature is measured both in the primary circuit in the heat exchanger or in the line on the outlet side with respect to the heat exchanger and in the secondary circuit in the heat exchanger or in the line on the outlet side with respect to the heat exchanger, and in that the temperature drops below a setpoint and / or via a setpoint increasing temperature gradient in the heat exchanger or in the line leading away from the heat exchanger in the secondary circuit, the conveying device begins to convey the fluid in the primary circuit, and that when the setpoint temperature rises and / or the setpoint temperature gradient increases in the heat exchanger or in the line away from the heat exchanger in the primary circuit, the delivery of the fluid in the primary circuit is ended.

Through this consistent use of temperature sensors and the determination of temperatures and / or temperature gradients, all flow monitors can be completely dispensed with.

Nevertheless, it is possible to always provide the desired hot water temperature (hot water temperature).

If you first consider the switch-on criterion for the fluid delivery device, this is essentially determined by the temperature sensor in the process water circuit. This temperature sensor is particularly preferably arranged directly at the outlet of the heat exchanger in the secondary circuit. If the tap in the hot water pipe is opened after a previous standstill and hot water is requested, the hot water begins to flow in the secondary circuit. The temperature, which is initially at the level of the heat exchanger, i.e. at a relatively high level, begins to drop quite spontaneously when the water from the cold water supply of the process water runs through the heat exchanger, whose heat reserve naturally decreases.

This falling temperature is immediately recognized by the temperature sensor. In one variant, this can be done in that this temperature falls below a desired value; in a preferred variant, this is simply determined by the temperature gradient. The latter also has the advantage that when the control system is started up with a cold store (initial start-up), the conveyor device is not switched on, even though a setpoint is undershot.

One of these two criteria now leads immediately to the activation of the conveyor in the primary circuit, which now supplies hot fluid from the primary circuit to the heat exchanger and thus enables heat transfer within the heat exchanger from this fluid to the process water.

The conveyor does not switch off yet, as process water continues to be withdrawn and there is therefore still a need for heat supply. Although the temperature gradient on this second temperature sensor in the secondary circuit is now very low or fluctuates around a zero value and the temperature is therefore constant and also above the setpoint, this is not a switch-on criterion: the conveyor is still running.

However, if the process water withdrawal is now stopped, the thermal energy of the hot fluid is no longer released to the process water in the primary circuit, since the process water is already at the appropriate temperature and requires no additional supply. As a result, the fluid in the primary circuit flows through the heat exchanger without having completely lost its heat, which leads to a very rapid temperature rise in the region of the first temperature sensor on the output side of the heat exchanger in the primary circuit. This rising temperature can be used as a switch-off criterion either by exceeding a setpoint or also by recognizing a temperature gradient, and thus stops the conveyor.

A particularly quick response is ensured if the respective temperature sensors are provided on the heat exchanger on the output side. In certain applications, it may even make sense to provide the temperature sensors inside the heat exchanger. The closer the temperature sensors are to the heat exchanger, the faster they can detect any changes in temperature and thus prevent the creation of undesired cold water areas in the hot water supply.

The conveying device, in particular a pump, in the primary circuit should, if possible, be arranged in the line leading away from the heat exchanger, that is to say in its line on the outlet side. As a result, colder primary fluid flows through the conveying device, particularly when it is at a standstill, which is more favorable for its durability and ease of maintenance. It is special useful if the first temperature sensor is arranged between the heat exchanger and the conveyor.

The arrangement and the method can be used particularly well if the warm or hot fluid is provided by a buffer store, but the flow of a boiler, a district heating network or the like are also suitable.

When used in conjunction with a buffer store, it is preferred if a third temperature sensor is also provided, which is located either in the buffer store or in the line from the buffer store to the heat exchanger. The control device has a further circuit with which the temperature determined by the third temperature sensor is used when determining the setpoint value of the temperature at the second temperature sensor. In this way, the case can be taken into account that there may not be enough warm or hot fluid in the buffer storage, for example when the system is started up for the first time or simply after considerable consumption has already taken place. It can then be prevented by lowering the setpoint values of the temperatures at the second temperature sensor that the buffer memory continuously releases further contents without it being possible at all to achieve the setpoint values otherwise desired by the control device.

Furthermore, the invention makes it possible, by observing the storage tank temperature in relation to the desired water temperature, to prevent the storage tank from mixing due to an excessive flow rate of the primary circuit and to maintain standby operation. For this purpose, a diagram of the temperature curve at various measuring points on the heat exchanger and storage tank is considered in relation to a typical user behavior, ie different amounts of water taken off and the turning on and off of the tap were simulated. If the heat storage tank does not have the temperature required for the hot water setpoint temperature, the hot water setpoint temperature is reduced from the storage tank temperature adjustable difference is calculated. The hot water target temperature is therefore not an absolute value, but - if the storage tank temperature is too low - also dependent on this.

If, during operation, the storage tank temperature falls below the temperature level required for the hot water setpoint control, the pump would run fully in order to get as close as possible to the set hot water setpoint with the maximum available energy. Due to the maximum primary flow, the primary return temperature rises unnecessarily high. This can lead to rapid disintegration or temperature stratification in the storage tank, which results in a further drop in the storage tank temperature. The actual hot water setpoint can therefore be calculated again from the storage tank temperature minus the set difference. This prevents the primary flow from being exceeded above a desired limit value and the storage stratification is retained under all operating conditions.

A pump runtime element is useful in order to bridge temperature fluctuations after switching on, which could be regarded as a switch-off criterion. Furthermore, it is normally chosen so that enough thermal energy is pumped into the system to bring the heat exchanger and thus the hot water outlet to the required temperature.

It is also particularly preferred if the conveying device is a speed-controlled pump and the regulating device has a circuit which, depending on the temperature gradient at the second temperature sensor, also regulates the conveying speed of the conveying device, that is to say, for example, the speed.

It is also particularly preferred if one or both temperature sensors, preferably together with the heat exchanger, are arranged within the insulation of the buffer store. This allows the heat exchanger to reach the target temperature are kept, simply by heat conduction automatically from the buffer storage.

The control device can also use a special combination of different process stages. For example, a start-up control program can be run for a limited period of time, for example 30 seconds, which provides for a constantly predetermined pump speed, or a special P-I-D setting that can react very quickly to changes in temperature. In this way, the target temperature can be maintained and cold water holes avoided at the start of hot water tapping.

The use of the temperature gradient amount as a switch-on criterion has also proven to be useful for the following reason: After opening the hot water tap, the hot water in the heat exchanger is at a slightly higher level than the thermal sensor on the output side of the heat exchanger can detect a short distance away. One of the effects of this is that, due to convection currents on the primary side in the heat exchanger, a very slightly higher temperature is set there than can be the case with a non-running secondary circuit in the process water. This effect is usually hardly measurable. However, it does have the consequence that after turning the tap on for a brief moment, the temperature at the second thermocouple in the secondary circuit rises very slightly, since the somewhat hotter amount of hot water from the heat exchanger now flows past the thermocouple. This determines a temperature gradient; the fact that this is positive is irrelevant for the magnitude of the temperature gradient and thus leads in the control device to the fact that the conveyor device is switched on. This happens at a time when the risk of a cold water hole has not yet arisen, so that the conveyor is already running much faster than when the temperature falls below the setpoint (the second switch-on criterion) and brings hot fluid in the primary circuit into the heat exchanger.

If this effect does not occur, for example because a slightly higher temperature level has not yet arisen in the heat exchanger due to the influence of convection, the control device also determines the amount of the temperature gradient due to its falling and can react accordingly.

• Figur 1 eine Schema-Darstellung der Erfindung.

In the following an embodiment of the invention will be described with reference to the drawing. It shows:

• Figure 1 is a schematic representation of the invention.

The purely schematic illustration, which shows only the most essential parts of the entire arrangement, shows a primary circuit 10 in the left half and a secondary circuit 20 in the right half.

The primary circuit 10 begins on the left with a device that provides warm or hot fluid, here a buffer store 11. From this buffer store 11, a line 12 leads to a heat exchanger 5. After passing through the heat exchanger 5 and giving off the thermal energy in it, the fluid leads in the primary circuit 10 back via an outlet-side line 13 to the buffer store 11. In the outlet-side line 13 a conveying device, here a pump 14, is provided, between the heat exchanger 5 and the pump 14 a first temperature sensor 17 is arranged.

The hot fluid is usually removed from the upper region of the buffer store 11, fed to the heat exchanger 5 and returned by the pump 14 to the lower region of the buffer store 11.

To layer the cooled fluid into the buffer store 11, a fluid single-layer device 18, which is only indicated schematically here, can be provided, for example a stratified charger according to EP 0 384 423 B1. In the buffer storage 11, hot fluid remains undisturbed in the upper region, where the line 12 also draws it off. Additional hot fluid or thermal energy for heating existing fluids can be provided by layering fluids heated by solar collectors and / or by installing burners (not shown in each case) or in another way.

The secondary circuit 20 on the right side begins with a cold water supply line 22, with which cold process water (drinking water, wash water, etc.) is fed to the heat exchanger 5. The heat energy of the primary circuit 10 running in countercurrent is received in the heat exchanger 5. After passing through the heat exchanger 5, the process water leaves it again and flows through an outlet-side line 23 to the hot water withdrawal point. The promotion in the secondary circuit can take place, for example, in that the cold water supply takes place under pressure and the hot water withdrawal point by a tap may block this pressure.

There is a temperature sensor 27 in the line 23 for the hot water or actual service water. The temperature sensor 27 thus detects the hot water temperature as close as possible to the heat exchanger 5.

The temperature sensors 17 and 27 report their values to a control device, not shown.

The same is done by a third temperature sensor 37, which records the temperature of the hot fluid in the upper region of the buffer store 11.

The control device then controls the pump 14, on the one hand the switching on and off and on the other hand also the speed or conveying speed, if applicable.

Reference list

5

Heat exchanger

10th

Primary circuit

11

Buffer storage

12th

management

13

management

14

pump

17th

Temperature sensor

18th

Fluid single layer device

20th

Secondary circuit

22

Cold water supply

23

Pipe to the hot water withdrawal point

27

Temperature sensor

37

Temperature sensor

Claims (12)

Arrangement for providing hot water with a primary circuit (10) with a fluid, a device (11) providing warm or hot fluid and a conveying device (14) for the fluid, - a secondary circuit (20) for the domestic water to be heated, - a heat exchanger (5) for heat transfer from the fluid of the primary circuit (10) to the process water in the secondary circuit (20), - A control device for the conveyor (14) and - a temperature sensor (17, 27) in the primary (10) or secondary circuit (20),
characterized, that both in the primary circuit (10) in the heat exchanger (5) or in the line (13) on the outlet side with respect to the heat exchanger (5), a first temperature sensor (17) and also in the secondary circuit (20) in the heat exchanger (5) or in the one with respect to the heat exchanger (5) a second temperature sensor (27) is arranged on the outlet-side line (23), and that the control device has a circuit which switches on the conveying device (14) when the temperature drops below a setpoint and / or when the temperature gradient exceeds a setpoint, and when the temperature rises above a setpoint and / or when the temperature gradient exceeds a setpoint on the first temperature sensor (17) switches off the conveyor (14). Arrangement according to claim 1,
characterized, that the conveyor (14) is arranged in the primary circuit (10) in the line (13) leading away from the heat exchanger (5), the first temperature sensor (17) being arranged between the heat exchanger (5) and the conveyor (14). Arrangement according to claim 1 or 2,
characterized, that the first and second temperature sensors (17, 27) are arranged closely adjacent to the respective outputs of the heat exchanger (5). Arrangement according to one of the preceding claims,
characterized, that the warm or hot fluid supply device (11) has a buffer store, that a third temperature sensor (37) is provided in the buffer store (11) or in the line from the buffer store (11) to the heat exchanger (5), and that the control device has a further circuit with which the temperature determined by the third temperature sensor (37) is used in determining the setpoint value of the temperature on the second temperature sensor (27). Arrangement according to one of the preceding claims,
characterized, that the control device has delay elements which bridges fluctuating determined temperature values at the temperature sensors. Arrangement according to one of the preceding claims,
characterized, that the control device has a circuit which controls the conveying speed of the conveying device (14) for the fluid as a function of the speed of the temperature value decrease or of the temperature gradient at the second temperature sensor (27). Arrangement according to claim 6,
characterized, that the regulation of the conveying speed of the conveying device (14) is carried out by changing the pump speed in a speed-controlled pump. Arrangement according to one of the preceding claims 4 to 7,
characterized, that the first and / or the second temperature sensor (17, 27), preferably both, are preferably arranged with the heat exchanger (5) within the insulation of the buffer store (11). Method for providing hot service water, a fluid running in a primary circuit, a device (11) providing hot or hot fluid and a conveying device (14) conveying the fluid, - the service water to be heated running in a secondary circuit, - The heat from the fluid of the primary circuit (10) is transferred to the process water in the secondary circuit (20) in a heat exchanger (5), - The conveyor (14) is regulated, and - a temperature sensor (17, 27) is provided in the primary or secondary circuit,
characterized, that both in the primary circuit (10) in the heat exchanger (5) or in the line (13) on the outlet side with respect to the heat exchanger (5), and in the secondary circuit (20) in the heat exchanger (5) or in the line on the outlet side with respect to the heat exchanger (5) 23) the temperature is measured, and that when the temperature falls below a setpoint and / or increases above a setpoint temperature gradient in the heat exchanger (5) or in the line (23) leading away from the heat exchanger in the secondary circuit (20), the conveying device (14) begins to convey the fluid in the primary circuit (10) , and that when the temperature increases above a setpoint and / or increases the temperature gradient in the heat exchanger or in the line from the heat exchanger (5) in the primary circuit (10), the delivery of the fluid in the primary circuit is ended. Method according to claim 9,
characterized, that the temperature of the warm or hot fluid in the primary circuit (10) is used in determining one or more of the target values. A method according to claim 9 or 10,
characterized, that the amount of the temperature gradient is used to regulate the conveying speed of the conveying device. Method according to one of claims 9 to 11,
characterized, that the temperature gradient amount is used independently of the sign of the temperature gradient even in the control.

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