EP2908059A1 - Method for the diagnosis of a heating installation with at least one heat exchanger - Google Patents

Abstract

The invention relates to a method for the diagnosis of a heating system with at least one heatable heat exchanger, which is flowed through by a fluid to be heated. It is proposed that a message be issued and / or stored when a heating of the fluid by a certain or determinable temperature longer than a predetermined or predeterminable time needed and / or if the heating by the heat exchanger of a certain or determinable mass flow of the fluid below a predetermined or predeterminable temperature difference remains.

Description

The invention relates to a method for the diagnosis of a heating system with at least one heatable heat exchanger, which is flowed through by a fluid to be heated. The invention also relates to a heating system in which the method for diagnosis runs.

State of the art

Heat exchangers are used wherever a cold medium, such as water, is to be heated by heat transfer. With increasing use and aging of the heat exchanger decreases its heat transfer performance, for example due to pollution. Therefore, a heat exchanger must be cleaned at regular intervals.

It is desirable to equip a heating system which has at least one heat exchanger, so that the causes of reduced efficiency of the heat exchanger, in particular by contamination, can be detected early, so that maintenance and possibly repair of the heat exchanger allows early and full Functioning of the heat exchanger can be quickly restored.

Disclosure of the invention

This object is solved by the inventive method for diagnosis in a heating system with at least one heatable heat exchanger, which is traversed by a fluid to be heated, according to the main claim. The method is characterized in that a message is issued and / or is stored when heating of the fluid by a certain or determinable temperature takes longer than a predetermined or predeterminable time and / or when the heating by the heat exchanger of a certain or determinable mass flow of the fluid remains below a predetermined or predeterminable temperature difference.

Here, a fluid is defined as a flowable substance which can absorb, store and release heat, such as a gas or a liquid. In principle, solid substances are also conceivable which can store and release heat. When the term fluid is used here, it is meant in general heat transfer media that can be used in a heating system.

A heat exchanger is understood to mean a device for transferring heat to a fluid. The term heat exchanger is also used synonymously.

The time for heating the fluid by a certain or determinable temperature is also abbreviated as the warm-up time.

The features listed in the dependent claims advantageous refinements of the method for diagnosing a heating system according to the main claim are possible.

In one step of the method, one or more parameters are determined and / or stored, such as the time for heating the fluid by a certain or determinable temperature, that is, the warm-up time, and / or a heat transfer coefficient of the heat exchanger and / or a temperature difference between a flow and return temperature of the heat exchanger, which has the advantage that this information can be used for diagnostic and / or prognostic purposes, for example, with respect to the state of the heat exchanger. It is advantageous if a message, in particular about a reduced functionality of the heat exchanger, in particular due to contamination, issued and / or stored as soon as the number of cases in which the parameter or reaches a certain or determinable threshold, a certain or determinable value exceeds. Such a hysteresis has the further advantage that a message is not issued immediately at the first occurrence of such a case, but that the accumulation of occurring cases can be regarded as a reliable indication.

In order to obtain an even more reliable statement about the power state of the heat exchanger, it is advantageous if, in addition to the temperature difference between flow temperature and return temperature of the heat exchanger, a power of a pump in a first Teilheizkreis can be used as an indicator. If, for example, a higher power of the pump is required in the course of time, with a constant or even decreasing temperature difference, this indicates a reduced functionality.

To determine the temperature difference, it is advantageous if in a method step, the flow temperature, in particular via a first sensor in the flow of the first Teilheizkreises, and the return temperature, in particular via a second sensor in the return of the first Teilheizkreises can be determined.

In one step of the method, at least one threshold value for the parameter or parameters is specified and / or calculated, if they have not yet been determined. Also, at least one value each is given as an upper bound for the number of cases in which the parameter (s) reach the associated threshold, if it has not yet been determined. This has the advantage that settings for the diagnosis of the heating system can be made flexibly and according to the needs and / or can be determined precisely by means of calculations. At the same time, the comfort for the user is increased, which makes it possible to enter values themselves or to use provided values.

For further diagnosis and for prognosis purposes, it is advantageous if the parameter (s), the respectively associated threshold value and / or the respectively associated value for the number of cases in which the respective threshold value is reached are recorded and / or output and / or can be read out.

In a further step of the method, a counter is initiated as soon as the threshold is reached for the first time, and the counter is incremented as the parameter (s) reach the respective threshold once more. Depending on the choice of parameter (s), the counter is also initiated or incremented if the threshold is undershot or exceeded. This is advantageous because such a counter can serve as a starting point for the diagnosis of the heating system. Another advantage lies in the prognosis of a possible malfunction of the heating system or the need for maintenance, so that it is possible to respond quickly to errors.

It is advantageous if the counter can be recorded and / or output and / or read out.

berechnet, wobei c die Wärmekapazität des Fluids, ΔT_Schwelle die Temperaturdifferenz, beispielsweise zwischen dem Wärmetauscher und dem Fluid oder die Temperaturdifferenz von Vorlauftemperatur zu Rücklauftemperatur, m der Massenstrom des Fluids, A die freie Wärmeübertragungsfläche und ΔT _Schwelle die zu ΔT_Schwelle gehörende, gemittelte logarithmische Temperaturdifferenz ist, welche berechnet wird aus den Eintrittstemperaturen in den Wärmetauscher und den Austrittstemperaturen aus dem Wärmetauscher.The threshold value for the heat transfer coefficient can be calculated, which has the advantage that an accurate, theoretical value can be used as the reference value. In this case, in one step of the method, the threshold k _threshold according to the formula $$k_{\mathit{threshold}}={}^{c\cdot \dot{m}\cdot \mathrm{\Delta }{T}_{\mathit{threshold}}}{/}_{A\cdot \widetilde{\mathrm{\Delta }{T}_{\mathit{threshold}}}}$$

where c is the heat capacity of the fluid, ΔT _{threshold is} the temperature difference, for example between the heat exchanger and the fluid or the temperature difference between flow temperature and return temperature, m is the mass flow of the fluid, A is the free heat transfer area and .DELTA.T _{Threshold is} the average logarithmic temperature difference associated with ΔT _Threshold , which is calculated from inlet temperatures into the heat exchanger and outlet temperatures from the heat exchanger.

The invention also relates to a heating system with at least one heatable heat exchanger through which a fluid to be heated flows, in which the above-described method for diagnosis runs. In this case, a message is issued and / or stored when a heating of the fluid by a certain or determinable temperature longer than a predetermined or predeterminable time needed and / or if the heating by the Heat exchanger of a certain or determinable mass flow of the fluid remains below a predetermined or predeterminable temperature difference.

drawing

• Figur 1 ein Ausführungsbeispiel einer erfindungsgemäßen Heizungsanlage,
• Figur 2 die prinzipiellen Schritte des Verfahrens zur Diagnose in der Heizungsanlage.

In the figures, a schematic representation of a heating system according to the invention is to be seen, as well as a method according to the invention for fault diagnosis, which will be explained in more detail in the following description. Show it

• FIG. 1 an embodiment of a heating system according to the invention,
• FIG. 2 the basic steps of the procedure for diagnosis in the heating system.

Description of the drawings

The embodiment in FIG. 1 shows a heating system 10 with a heat generator 12, which is provided with a heat exchanger 14. In a first Teilheizkreis 16, a fluid, such as heating water, is heated by the heat exchanger 14, and a second Teilheizkreis 18 is used to heat cold hot water by means of a heat exchanger 20, for example in the continuous flow principle. The first Teilheizkreis 16 has a pump 22 and a three-way valve 24 and a three-way valve 25 to ensure the circulation of the fluid. At least one heat consumer 25 is supplied with warm heating water. In the flow of the heat generator 12 is a sensor 26, in particular a temperature sensor, for measuring the flow temperature. Also located in the return, a sensor 28 for measuring the return temperature.

In the second Teilheizkreis 18 cold service water is transported to the heat exchanger 20, where it is heated, then the hot water is passed to the end user. A sensor 30 measures the temperature of the cold water Entry through the heat exchanger 20, a sensor 32 measures the temperature of the heated cold water after leaving.

The heat generator 12 may be a variety of heaters that operate on fossil or renewable resources. In the exemplary embodiment, there are a gas burner 33 and the heat exchanger 14 in the heat generator 12. Here, the heat generator 12 with the aid of a blower 34 via a line 36, a gas-air mixture is supplied. In this line 36 is still a valve 38. Exhaust products are passed through an exhaust pipe 40 to the outside. By a flame generated by the gas burner 33, the fluid which circulates through the heat exchanger 14 is heated.

In the embodiment in FIG. 1 The heating system 10 further includes a display 42 and a control and / or regulating unit 44, wherein it is located outside of the heat generator 12. The display 42 is attached to the heat generator 12. The heat generator 12, the control and / or regulating unit 44 and the display 42 are connected to each other and can communicate with each other. Often, the heat generator 12 via the control and / or regulating unit 44 is still connected to the heat consumer 25 and other control or regulating elements, such as the pump 22, the valves 23, 24, the blower 34, the valve 38 and / or with a room thermostat to ensure an even more optimized and flawless process. Conceivable in this case is a wired or a wireless connection, as well as a mixture of these types of connections.

Alternatively, the control and / or regulating unit 44 may also be located within the heat generator 12. Other embodiments are also conceivable. The same applies to the display 42.

For the diagnosis of the heating system 10 runs from a method which is based on the FIG. 2 is described.

The time for heating the fluid through the heat exchanger 14, 20, called warm-up time briefly, its heat transfer coefficient and the temperature difference between flow and return temperature of the heat exchanger 14, 20 are system inherent parameters and are used according to the invention as indicators of reduced efficiency of the heat exchanger 14, 20, especially due to pollution, used. Thus, the heat transfer coefficient decreases with increasing resistance of the heat exchanger 14, 20, which is the case, for example, precisely when the surface of the heat exchanger 14, 20 is increasingly polluted. In this case, the performance of the heat exchanger 14, 20, which leads to a higher warm-up time, on the other hand, if one specifies a fixed duration, to a lower temperature difference after this time has expired.

While the heat transfer coefficient and the temperature difference are determined during the operation of the gas burner 33, the determination of the warm-up time is dependent on the burner start. The time measurement starts at burner start and ends as soon as a setpoint temperature for the fluid, for example for the service water or heating water, has been reached.

The core of the method is the output of a message when a heating of the fluid by a certain or determinable temperature longer than a predetermined or predeterminable time needed or if the heating by the heat exchanger 14, 20 of a certain or determinable mass flow of the fluid below a predetermined or predeterminable Temperature difference remains. Both cases can occur. The message is saved for later purposes, such as for a prognosis or diagnosis, so that it is retrievable at any time.

The method is applicable in principle to any heat exchanger. In the following, it will be explained with reference to the heat exchanger 14.

At the beginning of the procedure, at step 50, the user enters the parameter (s) to be diagnosed. He can make a diagnosis based on the warm-up time, the heat transfer coefficient or select the temperature difference between flow and return temperatures. It is also possible to select several modes at the same time, which are then executed in parallel or serially. In the following, the case is considered that all modes are selected and executed in parallel.

In step 52, the flow temperature via the sensor 26 and the return temperature via the sensor 28 are measured. Further, a target value for a temperature of the fluid, such as a target value for the temperature of the heating water and the service water, set.

In steps 53, 54 and 55, the values necessary for the method are specified or calculated, if they are not yet present. The values can be specified for the same systems. For example, they can be set as defaults that are used automatically or chosen by the user. They can also be entered by the user. For new or maintained systems, the values can be reset or recalculated.

For the warm-up time, a threshold 56 is set or calculated in step 53. Further, a value or a maximum number 58 may be determined, which represents an upper bound for the number of cases in which the warm-up time reaches or exceeds the threshold 56. If the maximum number 58 is 20, for example, a message is issued when the 21st case of an increased warm-up time occurs. Threshold 56 is present in the system as a default or can be changed or specified by the user.

berechnet. Hierbei ist ΔT_Schwelle eine feste, vorgegebene Temperaturdifferenz zwischen einem idealen, beispielsweise unverschmutzten, Wärmetauscher, welcher von der vom Gasbrenner 33 erzeugten heißen Luft erwärmt wird, und dem Heizwasser, an welches die Wärme abgegeben wird, A die freie Wärmeübertragungsfläche, m der Massen- bzw. Volumenstrom und c die Wärmekapazität des Fluids. Die Temperatur und der Massenstrom können über entsprechende Sensoren gemessen werden. Die Wärmekapazität des Fluids kann Tabellen entnommen werden. Weiter ist ΔT _Schwelle die zu ΔT_Schwelle gehörende, feste gemittelte logarithmische Temperaturdifferenz, welche bestimmt wird aus den fest vorgegebenen Temperaturen der anwesenden Eintritte und Austritte des idealen Wärmetauschers. Durch den Wärmetauscher 14 strömt das heiße Abgas des Gasbrenners 33, das sich abkühlt und seine Wärmeenergie auf das Heizwasser überträgt.For the heat transfer coefficient as an indicator for a reduced functionality of the heat exchanger 14, a threshold value 60 k _{threshold is} set or calculated in step 54. For the calculation, ideal heat transfer conditions of the heat exchanger 14 are assumed. The threshold 60 is above the expression $$k_{\mathit{threshold}}={}^{c\cdot \dot{m}\cdot \mathrm{\Delta }{T}_{\mathit{threshold}}}{/}_{A\cdot \widetilde{\mathrm{\Delta }{T}_{\mathit{threshold}}}}$$

calculated. Here ΔT _{threshold is} a fixed, predetermined temperature difference between an ideal, for example, unpolluted, heat exchanger, which is heated by the hot air generated by the gas burner 33, and the heating water to which the heat is released, A the free heat transfer surface, m the mass or volume flow and c the heat capacity of the fluid. The temperature and the mass flow can be measured via corresponding sensors. The heat capacity of the fluid can be found in tables. Next is .DELTA.T _threshold the fixed averaged logarithmic temperature difference associated with the ΔT _threshold which is determined from the fixed preset temperatures of the inlet and outlet of the ideal heat exchanger. Through the heat exchanger 14, the hot exhaust gas of the gas burner 33 flows, which cools and transfers its heat energy to the heating water.

At step 54 is also the specification of a maximum number 62 for the heat transfer coefficient, from which a message about the reduced functionality of the heat exchanger 14 is to be output. The maximum number 62 gives an upper limit to the number of cases where the heat transfer coefficient falls below the threshold value 60.

If the temperature difference between the flow and return of the heat exchanger 14 is used as an indicator, a threshold value 64 and a maximum number 66 for the temperature difference is set or calculated in step 55, analogous to the steps 53 and 54. The maximum number 66 is an upper bound for the Number of cases in which the temperature difference falls below the threshold 64. If the flow and return temperatures have not yet been measured, for example because step 52 has been skipped, then this is done in step 55.

If the power of the pump 22 together with the temperature difference is used as an indicator for a reduced functionality of the heat exchanger 14, a threshold value 65 for the power of the pump 22 is additionally set in step 55. Alternatively it can be calculated. The maximum number 66 is then an upper bound for the number of Cases in which the temperature difference reaches or falls below threshold 64 and the power of pump 22 reaches or exceeds threshold 67.

All values are stored and can be recalled or changed by the user.

In step 68, a warm-up time counter 70, a heat transfer coefficient counter 72, and a temperature difference counter 74 are initiated. For example, they are set to 0.

As soon as the heat generator 12 starts, a time measurement for determining the warm-up time of the fluid through the heat exchanger 14 starts in step 76. If the heating water reaches the predetermined setpoint temperature, the time measurement is ended. The elapsed time is saved as the warm-up time.

zugrunde gelegt. Hier ist nun ΔT die (variable) Temperaturdifferenz zwischen dem Wärmetauscher 14 und dem Heizwasser und ΔT die (variable) mittlere logarithmische Temperaturdifferenz zwischen Wärmetauscher 14 und Heizwasser, gegeben durch $$\overline{\mathrm{\Delta }T}=\frac{\mathrm{\Delta }{\mathrm{T}}_{\mathrm{2}}-\mathrm{\Delta }{\mathrm{T}}_{\mathrm{1}}}{\ln \left[\frac{\mathrm{\Delta }{\mathrm{T}}_{\mathrm{2}}}{\mathrm{\Delta }{\mathrm{T}}_{\mathrm{1}}}\right]}\mathrm{.}$$

In step 77, the heat transfer coefficient is calculated. For this the formula becomes $$k={}^{c\cdot \dot{m}\cdot \mathrm{\Delta }T}{/}_{A\cdot \widetilde{\mathrm{\Delta }T}}$$

based on. Here now Δ T is the (variable) temperature difference between the heat exchanger 14 and the heating water and Δ T the (variable) average logarithmic temperature difference between the heat exchanger 14 and heating water, given by $$\widetilde{\mathrm{\Delta }T}=\frac{\mathrm{\Delta }{\mathrm{T}}_{\mathrm{2}}-\mathrm{\Delta }{\mathrm{T}}_{\mathrm{1}}}{\ln \left[\frac{\mathrm{\Delta }{\mathrm{T}}_{\mathrm{2}}}{\mathrm{\Delta }{\mathrm{T}}_{\mathrm{1}}}\right]}\mathrm{,}$$

Here, Δ T ₂ ≥ Δ T ₁ was adopted, so that the log mean temperature difference is positive. ΔT ₂ and ΔT ₁ are defined as follows: At the first inlet of the heat exchanger 14, the temperature T _{inlet 1 of} the hot air or the temperature of the heat exchanger 14 is measured. At the first outlet, the temperature T _{outlet 1 of} the cooled air prevails in the exhaust gas line. At the second inlet, the entry of Rücklaufheizwassers in the heat exchanger 14, was in step 52, the return temperature measured by the sensor 28 _Eintritt2 T, and the second outlet from the heat exchanger, the flow temperature T _Austritt2 by the sensor 26. It then calculates the difference .DELTA.T _1: = | T _entry1 - T _Austritt2 | and ΔT ₂ : = | T _{exit 1} -T _{entry 2} |, if ΔT ₁ ≥ ΔT ₂ . Otherwise _{.DELTA.T.sub.2:} = | T _entry1 - T _Austritt2 | and ΔT ₁ : = | T _Outlet1 - T _Inlet2 |.

In step 78, the calculation of the temperature difference between the flow and return temperatures is performed. If the flow and return temperatures have not yet been measured, for example because step 52 has been skipped, then the measurement is carried out before the temperature difference is calculated.

In step 80, the query takes place as to whether the respective parameters reach their associated threshold: it is queried whether the warm-up time is greater than the threshold 56, whether the heat transfer coefficient is less than the threshold 60, and if the temperature difference is less than the threshold 64 ,

If this is not true (step 82), the counters 70, 72, 74 remain unchanged. The process continues at steps 76, 77, and / or 78, depending on whether the warm-up time, the heat transfer coefficient, and / or the temperature difference have been selected (step 50).

If the query in step 80 is yes, the warm-up time is greater than the threshold value 56 or the heat transfer coefficient is less than the threshold value 60 or the temperature difference is less than the threshold value 64, the counters 70, 72, 74 are increased in step 84, for example at 1.

Of course, hybrids are conceivable, for example, the warm-up time is greater than threshold 56 and the heat transfer coefficient is less than threshold 60. Then, counter 70 and counter 72 are incremented. Or the temperature difference is less than the threshold 64 and the Warm-up time greater than the threshold value 56. Then, the counter 74 and the counter 72 are increased, etc. Which and how many counters have been increased, can also give an indication of a reduced functionality of the heat exchanger 14. Therefore, the current state of the counters 70, 72, 76 is stored and can be read out at any time.

In step 86, it is queried whether at least one of the counters 70, 72, 76 has reached or exceeded the associated maximum number 64, 66, 68.

If not, the method begins again at step 76, step 77 and step 78 if all three modes have been selected in parallel, as assumed in this embodiment. The heat generator 14 continues to run and it is checked again whether a reduced function or malfunction exists.

If not all modes have been selected, for example only one, then the method continues after step 82 in step 76, step 77, or step 78, whichever mode has been selected. Accordingly, mixed forms are possible. Also a serial processing of steps 76, 77, 78 is possible, which is not shown.

The process may be interrupted in the meantime or prematurely ended to resume in a step of choice, for example in one of steps 50, 52, 53, 54, 55, etc.

For example, if the method is interrupted in step 80 or another step and the user selects step 50, this corresponds to a kind of restart. Already measured or calculated parameters, such as the warm-up time, or messages have been saved and can be read out. You can enter new values that will be used as the basis for the diagnosis, or you will use preset default values or previously entered values.

For example, jumping from step 84, or another step, to step 68 corresponds to a kind of reset. In step 68, the Counter 70, 72, 74 initiated, for example, set to 0. For example, if at least one of the counters 70, 72, 74 was greater than this initial value, it is reset to this initial value. Thus, the procedure begins again with the count of injury cases, but uses the values and measurements already entered.

The method may also be programmed to automatically switch to another selectable step after a selected step. It can also be turned off completely.

If, in step 86, the query indicates that at least one of the maximum numbers 58, 62, 66 has been reached or exceeded, a corresponding message is output and stored in step 88. The date and time of the message are saved with. For example, the message may include text stating that the efficiency of the heat exchanger 14 is reduced, particularly due to contamination. The text may additionally state that the heat exchanger 14 requires maintenance or cleaning or the like. The message may additionally or solely consist of a flashing of a light source, such as a light-emitting diode, or of a sound, such as a one-time or multiple beep. Other types of messages are also conceivable. The message can persist until the user actively terminates it. Also conceivable is a one-time issue that does not have to be actively terminated. The message will be recorded for retrieval at a later time.

For example, in step 88, a beep sounds for a few seconds, parallel to this, a red light is lit or flashing until the user acknowledges that he has acknowledged the message, for example, by pressing a button or a spoken command.

The heat generator 12 continues to operate after notification, even if no maintenance or cleaning or the like has been performed, and even if the message persists.

In step 90, it is determined whether maintenance or cleaning or the like has been performed.

If not, the method continues at step 76, step 77 and step 78 if all three modes have been selected. The message continues to be output. For example, the flashing of a light-emitting diode continues.

After maintenance or cleaning, that is, the query in step 90 has been answered in the affirmative, in step 92 the parameter values such as the warm-up time, the heat transfer coefficient, the temperature difference, the flow and return temperatures, the counters 70, 72, 74 are reset. The process starts again at step 50 and the diagnostics of the heat generator 14 begin again.

All values, whether entered, calculated or determined in the course of the procedure, are stored and recorded. The time of their creation is also stored. For example, it can be learned how quickly the warm-up time, the heat transfer coefficient or the temperature difference did not meet their respective thresholds 56, 60, 64, when the respective counters 70, 72, 74 were increased and when the maximum number 58, 62, 66 was achieved. Further, the timing and type of the message is stored in step 88. After maintenance, the memory can be reset to avoid a memory overflow. The time of maintenance is retained. The memory can also be reset manually. The user has access to all data for diagnostic and forecast purposes.

Claims (10)

A method for diagnosing a heating system (10) with at least one heatable heat exchanger (14, 20) through which a fluid to be heated flows, characterized in that a message is output and / or stored when a heating of the fluid by a certain or determine determinable temperature longer than a predetermined or predeterminable time and / or if the heating by the heat exchanger (14, 20) of a certain or determinable mass flow of the fluid remains below a predetermined or predeterminable temperature difference. A method according to claim 1, characterized in that one or more parameters, such as the time for heating the fluid by a certain or determinable temperature and / or a heat transfer coefficient of the heat exchanger (14, 20) and / or a temperature difference between a flow and return temperature the heat exchanger (14, 20), determined and / or stored, and that a message, in particular on a reduced functionality of the heat exchanger (14, 20), in particular due to contamination, issued and / or stored as soon as the number of cases in which the parameter (s) reaches a certain or determinable threshold exceeds a certain or determinable value (58, 62, 66). Method according to one of claims 1 to 2, characterized in that the temperature difference between flow temperature and return temperature of the heat exchanger (14, 20) and a power of a pump (22) as an indicator of reduced functionality of the heat exchanger (14, 20), in particular due to a Pollution, to be used. Method according to one of claims 1 to 3, characterized in that a flow temperature, in particular via a first sensor (57) in the flow of a first Teilheizkreises (54), and a return temperature, in particular via a second sensor (58) in the return of the first Teilheizkreises (54), are determined. Method according to one of Claims 1 to 4, characterized in that at least one respective threshold value (56, 60, 64) for the parameter (s) and at least one value (58, 62, 66) for the number of cases in which the parameter (s) (56, 60, 64) reach, be predefined and / or calculated, unless they have already been determined. Method according to one of the preceding claims, characterized in that the one or more parameters, the respectively associated threshold value (56, 60, 64) and / or the respectively associated value (58, 62, 66) are recorded and / or output and / or read out become. Method according to one of claims 1 to 6, characterized in that a counter is initiated as soon as the threshold value (56, 60, 64) is reached for the first time, and that the counter is incremented when the threshold value (56, 60, 64 ) is reached again. Method according to one of the preceding claims, characterized in that the counter is recorded and / or output and / or readable. Method according to one of claims 5 to 8, characterized in that the threshold value (58) for the heat transfer coefficient, k _threshold , according to the formula $$k_{\mathit{threshold}}={}^{c\cdot \dot{m}\cdot \mathrm{\Delta }{T}_{\mathit{threshold}}}{/}_{A\cdot \widetilde{\mathrm{\Delta }{T}_{\mathit{threshold}}}}$$

where c is the heat capacity of the fluid, ΔT _{threshold is} the temperature difference, for example between the heat exchanger (14, 20) and the fluid, or the temperature difference between flow temperature and return temperature, m the mass flow of the fluid, A the free flow Heat transfer surface and .DELTA.T _{Threshold is} the average logarithmic temperature difference associated with the ΔT _threshold , which is calculated from the inlet temperatures into the heat exchanger (14, 20) and the outlet temperatures from the heat exchanger (14, 20). Heating system with at least one heatable heat exchanger (14, 20), which is traversed by a fluid to be heated and in which a method for diagnosis runs in particular according to one of the preceding claims, characterized in that a message is output and / or stored, if a Heating the fluid by a certain or determinable temperature longer than a predetermined or predeterminable time needed and / or if the heating by the heat exchanger (14, 20) of a certain or determinable mass flow of the fluid remains below a predetermined or predeterminable temperature difference.

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