EP2463593A1 - Method of operating a heating system - Google Patents

Abstract

The method involves heating of a heating circuit medium circulating in a heating circuit (1) temporarily with a burner (2), and determining the circulation of the heating circuit medium with a unit (3) for detecting the volume flow. The burner is turned on and off by a controller (4). The switching on and off the burner below a predefined minimum volume flow of the heating circuit medium in the circuit is defined by the controller corresponding to the volume flow determined with the unit for detecting the volume flow.

Description

The invention relates to a method for operating a heating system according to the preamble of patent claim 1.

A heating system or a method for operating a heating system of the type mentioned is according to the DE 10 2008 003 315 A1 known. In this, a circulating in a heating circuit heating medium is at least temporarily heated with a burner, wherein the circulation or a circulation measure of the heating medium with a flow meter (a means for detecting the flow rate) determines and the burner is switched on and off via a control.

Furthermore, from the DE 196 46 314 C1 a heating system known, in which also a circulating in a heating circuit Heizkreismedium is at least temporarily heated with a burner. In this heating system between the flow and the return of the heating circuit an overflow is provided with an overflow valve, which ensures a flow of Heizkreismemediums by the heater or its heat exchanger even if, for example, all thermostatic valves are closed in the heating circuit. By this measure, the heater or its heat exchanger is protected from damage by boiling. At the same time, however, the efficiency of the heating system deteriorates due to this safety function.

The invention has for its object to improve a method for operating a heating system of the type mentioned. In particular, to be improved by a special operation, the efficiency of such a heating system, for example, even with closed thermostatic valves.

This object is achieved by a method for operating a heating system of the type mentioned by the features listed in the characterizing part of patent claim 1.

According to the invention, it is thus provided that the switching on and off of the burner below a predefined minimum volume flow of the heating medium in the heating circuit is determined in dependence on a volumetric flow determined by the volumetric flow meter with the control.

• Da bei der zum Stand der Technik gehörenden Heizungsanlage der tatsächliche Volumenstrom durch das Heizgerät wahlweise nicht bekannt ist bzw. diese Information für andere Zwecke verwendet wird, bestand bisher die einzige Möglichkeit, auf eine Unterschreitung des Mindestvolumenstroms zu reagieren, darin, den Heizkreis über das Überströmventil kurzzuschließen.

In other words, thanks to the inventively provided interconnection of the control and the volumetric flow meter (or a suitable means for detecting the volume flow or the circulation) and according to the invention to be defined minimum volume flow can be dispensed with the above-mentioned overflow valve, which is explained in more detail below:

• Since in the state of the art heating system, the actual volume flow through the heater is either not known or this information is used for other purposes, was previously the only way to respond to a shortfall of the minimum flow, in the heating circuit via the overflow short-circuit.

With the volumetric flow meter connected to the regulation according to the invention, it is now possible to detect the actual volumetric flow in a targeted manner, and to selectively influence the service life of the burner when the minimum volumetric flow is undershot. According to the invention, therefore, provision is made in particular for the burner to be actuated by the control above a predefined minimum volume flow in the usual way. However, if the said minimum volume flow is not reached, a function to be explained in more detail is used to determine the maximum Set the burner operating time as a function of the actual volume flow of the heating circuit.

Other advantageous developments of the method for operating a heating system according to the invention will become apparent from the dependent claims.

The inventive method for operating a heating system including its advantageous developments according to the dependent claims will be explained in more detail with reference to the drawing of a preferred embodiment.

Figur 1

eine Heizungsanlage gemäß dem Stand der Technik mit Überströmventil zwischen Vor- und Rücklauf;

Figur 2

die erfindungsgemäße Heizungsanlage mit einem Volumenstromsensor;

Figur 3

ein Diagramm der Brennerleistung und der Vorlauftemperatur aufgetragen über der Zeit;

Figur 4

ein Diagramm der zulässigen Brennerlaufzeit aufgetragen über dem Volumenstrom.

It shows

FIG. 1

a heating system according to the prior art with overflow valve between flow and return;

FIG. 2

the heating system according to the invention with a volume flow sensor;

FIG. 3

a graph of burner performance and flow temperature versus time;

FIG. 4

a diagram of the permissible burner runtime plotted against the volume flow.

In the currently available and preferably used for the invention wall-mounted condensing boilers with small water content of the heat exchanger is often, as explained above, an overflow valve (bypass) integrated to operate the heater properly. This overflow valve is installed between the supply and return of the heating system (see FIG. 1 ).

With high heat gain (solar radiation, lighting, electronic devices) or by closing the thermostatic valves by the user of the heating system, the volume flow through the radiator or 5, 6 decreases. FIG. 1 represents the example case that the thermostatic valve on the radiator 5 is closed by the user intervention, so that the volume flow through this radiator 5 is practically close to zero. The return temperature of this radiator is thus very low (approximately room temperature). The thermostatic valve from the radiator 6 is almost closed in this example due to high solar radiation. Through the radiator 6 so that only flows a small volume flow of, for example, 30 l / h (liters per hour). The return temperature of the radiator 6 is higher than that of the radiator 5. The total volume flow through the heating system is for the case mentioned far below 50 l / h.

However, the boiler with low water content mentioned above requires a minimum volume flow that is well above 100 l / h. If this minimum volume flow is not reached, boiling occurs within the heat exchanger. The frequent repetition of this operating condition caused by the boiling material breaks, corrosion and limescale. As a result, damage to the heat exchanger and, ultimately, this shortens the life of the boiler. In summary, the reliability of the heater in the illustrated example is not guaranteed.

To some extent as a compromise solution for the above-mentioned problem case, the heating system, as explained above, equip with an overflow valve that connects the flow line with the return line. If the thermostatic valves of radiator 5 and 6 are almost closed, the hydraulic resistance of the heating system and the available delivery pressure increase. If this delivery pressure exceeds the spring force of the overflow valve, it opens, ie, the heating water (heating medium) flows via the overflow valve from the flow line to the return line. Thus, the overflow valve ensures the minimum volume flow in the boiler circuit. The volume flow that flows through the boiler consists of two partial volume flows: the one flowing through the overflow valve and the one flowing through the heating circuit with the two radiators 5 and 6. Since the temperature after the overflow valve (but before mixing with the return from the heating system) is almost identical to the flow temperature, the return temperature at the boiler inlet increases the more heating medium flows through the overflow valve. This effect is called the increase in the boiler return temperature, which reduces the efficiency of condensing boilers.

Most overflow valves are equipped with springs. The spring force can be adjusted. If the spring force is set too low, the overflow valve will open too often. Thus, the boiler efficiency or the calorific value utilization is not exhausted. In addition, the pump must be driven at high speed in order to transport the heat from the boiler to the individual rooms. Although this ensures user comfort, but increases the electrical energy for pump operation. On the other hand, if the pump speed is low, the heating medium flows exclusively through the heating circuit. In this case, the overflow valve does not open, d. H. the minimum circulation through the boiler is not guaranteed.

In cases where the spring force is set too high, the pump must always ensure a certain available delivery pressure, which is higher than the spring force of the spill valve, with a correspondingly high pump speed to ensure that at a very low total volume flow, the spill valve opens.

If the delivery pressure of the pump is high, strong noises will be generated on the thermostatic valves if they are in the "almost closed" position. In addition, the pump runs unnecessarily at high speed and consumes a corresponding amount of electrical energy.

Intermediate result: The overflow valve guarantees the minimum volume flow. However, this results in a reduction of the boiler efficiency and a greater consumption of electrical energy for pump operation. Incorrect setting of the pump speed and / or the spring force of the overflow valve, which unfortunately often occurs in practice, moreover, noise, loss of comfort and a reduction in the boiler efficiency.

Considered objectively, the invention is in particular that instead of the overflow valve, a means for detecting the volume flow 3 or a volume flow meter is arranged on the heating circuit or particularly preferably on the central return line of the heating circuit (see FIG. 2 ). The volume flow sensor preferably has a measuring range of 10 to 2000 l / h with an accuracy of less than 2% of the measured value or an absolute deviation of +/- 10 l / h. In addition, the pressure drop at the volume flow sensor at a flow rate of 2000 l / h is preferably less than 70 mbar.

In the control, the function "duration of the burner runtime" depending on the "volume flow" is stored in case it is smaller than a predefined minimum volume flow. This minimum volume flow is either permanently stored in the control or can be entered individually. If, for example, the volumetric flow sensor detects the current volume flow of 30 l / h, which is far below the predefined minimum volumetric flow of, for example, 120 l / h, the above-mentioned function is activated. This function passes the Control then the maximum allowable burner runtime of, for example, 50 seconds. At the same time, the controller checks whether the current boiler return temperature falls below a temperature setpoint. If this is the case, the burner is started for the previously determined permissible burner runtime. As soon as the permitted burner run time has expired, the burner is switched off. This is done regardless of the actual boiler flow temperature, as this allows no statement about the actual temperature within the heat exchanger due to the low flow rate and the low flow velocity of the heating medium in the heating circuit. - Or again in other words: It is particularly preferred that a return temperature at return 7 of the heating circuit 1 is determined and the burner 2 is turned on at a below the predefined minimum volume flow volume flow in the heating circuit 1 only when the return temperature falls below a predetermined temperature setpoint. In this case, it is furthermore preferably provided that a function is stored in the control 4, with which a maximum permissible burner running time is assigned to each actually determined volume flow lying below the predefined minimum volume flow.

FIG. 3 illustrates this connection: After the expiry of the specified burner runtime (from - as in this example - 60 seconds), the temperature at the flow is still below 40 ° C. Although the burner 1 is switched off, the flow temperature continues to rise and reaches the maximum value of about 60 ° C. Thus, vice versa is preferably provided that the burner 2 is switched off at a below the predefined minimum volume flow volume flow after the burner run time even if a flow temperature at the flow 8 of the heating circuit 1 does not yet correspond to a predetermined temperature setpoint.

FIG. 4 finally shows an example of the above-mentioned function of the permissible burner running time as a function of the volume flow.

With the method according to the invention, as shown, the ease of use and at the same time the technical safety of the device can be increased. The mentioned effect of the "return lift" does not occur due to the elimination of the overflow valve. As a result, the boiler efficiency increases. The pump is no longer unnecessarily driven at high speed and thus saves electrical energy. Furthermore, no noise is generated at the thermostatic valves.

LIST OF REFERENCE NUMBERS

1

heating circuit

2

burner

3

Means for detecting the volume flow

4

regulation

5

radiator

6

radiator

7

returns

8th

leader

Claims (4)

Method for operating a heating system, wherein in a heating circuit (1) circulating Heizkreismedium is at least temporarily heated with a burner (2), wherein the circulation of the heating medium with a means for detecting the volume flow (3) determines and the burner (2) via a control (4) is switched on and off, characterized
that the switching on and off of the burner (2) is below a predefined minimum volume flow of the Heizkreismediums in the heating circuit (1) as a function of one with the means for detecting the volume flow (3) determined volume flow with the control (4) is fixed. Method according to claim 1,
characterized,
that a return temperature at the return (7) of the heating circuit (1) is determined and the burner (2) at a below the predefined minimum volume flow volume flow in the heating circuit (1) is only turned on when the return temperature falls below a predetermined temperature setpoint. Method according to claim 1 or 2,
characterized,
that in the control (4) a function is stored with which each actually determined, lying below the predefined minimum volume flow volume flow is assigned a maximum allowable burner runtime. Method according to claim 3,
characterized,
that the burner (2) at a below the predefined minimum volume flow volume flow is also switched off after the burner running time when a flow temperature at the flow (8) of the heating circuit (1) yet does not correspond to a predetermined temperature setpoint.

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