METHOD FOR REGULATING A HEATING UNIT, AND HEATING UNIT

Abstract

A method for regulating a heating unit, and heating unit, are provided. A method is provided for regulating a heating unit, and to a heating unit which includes a combustion chamber, combustion air being introduced into the combustion chamber via a controllable blower. A rotational speed of the blower wheel is detected. The purpose is to make it possible to ascertain an air volume flow with little complexity. The method is characterized in that a static pressure and/or a power consumption of the blower is/are ascertained, a volume flow of the combustion air being determined on the basis of the rotational speed in conjunction with the static pressure or the power consumption. For this purpose, the heating unit includes a rotational speed sensor and a pressure sensor and/or a power sensor.

Description

FIELD OF THE INVENTION

The present invention relates to a method for regulating a heating unit. The present invention also relates to a heating unit for carrying out the method.

BACKGROUND INFORMATION

Such heating units serve for heating a heating medium, heating water being generally used. The heating unit includes a combustion chamber in which a fuel, such as a gas for example, is burned. In the process, combustion air is supplied via a blower. The heat which is released is transferred to the heating medium in a heat exchanger.

A correct ratio of the supplied volume of combustion air to the supplied quantity of fuel is essential for clean combustion. If too little air is supplied, the fuel cannot burn completely. This results in high pollutant emissions, particularly carbon monoxide and hydrocarbon. If too much air is supplied, the combustion is cooled and this likewise results in increased pollutant emissions.

The quantity of supplied combustion air is usually controlled by the appropriate activation of the blower. The blower generally includes a blower wheel, the rotational speed of which influences a volume flow of the combustion air, i.e., the volume per unit of time. The volume flow may be monitored.

It is known to ascertain the volume flow by a differential pressure measurement. For this purpose, it is provided for example in German Published Patent Appln. No. 10 159 033 to detect a pressure at two different measuring points. Since a static pressure of the combustion air is partially converted into a dynamic pressure between the two measuring points due to a difference in speed, a differential pressure may be measured between the measuring points. The volume flow may be determined therefrom in a known manner. In addition, a rotational speed of a blower wheel is measured and thus the volume flow is determined, taking into account the design of the equipment. A redundant control system is thus obtained.

This method requires a specific air guide and multiple measuring points. It is therefore relatively complex and thus cost-intensive. The measuring results may be falsified, for example due to soiling or due to parameter changes. There is also the problem of drift and other aging phenomena.

German Published Patent Appln. No. 19 945 562 describes a method for monitoring and/or regulating a vehicle heating device, a rotational speed of a blower being regulated in order to control a volume flow of combustion air. In the process, a combustion in the combustion chamber is monitored by a pressure sensor or a sound pressure sensor.

German Published Patent Appln. No. 10 2005 011 021 describes a method for adapting the device heating power of a blower-assisted heating device to the individual pressure losses of a fresh air/exhaust gas pipeline system, a blower rotational speed and a blower power being detected. If the ratio of the blower rotational speed to the measured blower power does not lie within a predefinable range, a fault message is output.

It is also known to ascertain a mass flow via heating wire sensors. However, these are relatively expensive and sensitive. Drift phenomena often occur.

SUMMARY

An object of the present invention is to eliminate the disadvantages of the related art and in particular to make it possible to regulate the heating unit with little complexity.

According to the present invention, a static pressure and/or a power consumption of the blower is/are ascertained, a volume flow of the combustion air being determined on the basis of the rotational speed in conjunction with the static pressure and/or the power consumption. A rotational speed detection is generally provided in any case in variably activatable blowers. Therefore, only one sensor for detecting the static pressure and/or the power consumption of the blower has to be provided in addition. This may be achieved with very little effort. Such sensors are available as mass-produced articles at very little cost.

Preferably, reference values for a pressure coefficient and/or a power coefficient are ascertained as a function of a volume flow coefficient at a reference blower, the reference values being taken into account when determining the volume flow. Pressure coefficient H is dependent on gravity acceleration g, rotational speed N, diameter D of the blower wheel and static pressure h and is calculated according to the following formula:

$\begin{array}{cc}H=\frac{g\times h}{N^2\times D^2}& \left(1\right)\end{array}$

Since the gravity acceleration g is a constant variable and the diameter of the blower wheel is a known, unchangeable variable, the pressure coefficient may be determined after measuring the static pressure and the rotational speed.

Power coefficient P is dependent on power consumption W, the density of combustion air p, rotational speed N, and diameter D and is calculated according to the following formula:

$\begin{array}{cc}P=\frac{W}{p\times N^3\times D^5}& \left(2\right)\end{array}$

The density of the combustion air may be regarded approximately as constant. In order to increase the accuracy, however, the density may also be detected in addition. The diameter of the blower wheel is constant. By detecting the rotational speed and the power consumption, the power coefficient may thus be calculated easily.

Volume flow coefficient F, which is a square function of the pressure coefficient and of the power coefficient, is dependent on volume flow V, rotational speed N and diameter D and is calculated according to the following formula:

$\begin{array}{cc}F=\frac{\stackrel{.}{V}}{N\times D^3}& \left(3\right)\end{array}$

For the pressure coefficients or power coefficients calculated in each case on the basis of the measured rotational speed and the measured power consumption or the ascertained static pressure, the volume flow coefficient may be determined on the basis of reference values which have been obtained using a geometrically similar blower and which are stored for example in the form of characteristic curves. The volume flow may then be determined relatively easily therefrom based on the above formula (3). The volume flow may thus be ascertained with relatively little effort. In order to increase the operational reliability, the volume flow may optionally also be ascertained on two routes in parallel, i.e., on the one hand by measuring the power consumption and on the other hand by detecting the static pressure. In order to be able to determine the volume flow with sufficient accuracy, the Reynolds number should be sufficiently high and influences of the viscosity should be low. However, this is generally the case.

Preferably, the power consumption of the blower is ascertained from the electrical power consumed by an electric blower motor, a degree of efficiency being taken into account. Detecting the electrical power consumption takes less effort than determining a mechanical power of the blower wheel. The mechanical power is dependent on the electrical power and the degree of efficiency, which depends on a load and a motor speed. This degree of efficiency may be ascertained, for example, via tests and may then be stored in a control unit. The relationship between electrical power consumption and mechanical power is as follows, where η_e indicates the degree of efficiency, which is dependent for example on the load and on a motor speed:

P_mechanical=η_e×P_electrical

η_e=ƒ_(N;Lead)   (4)

Preferably, the static pressure is ascertained downstream from the blower in the flow direction. With the blower switched off, the instantaneous air pressure may then be ascertained, whereas the static pressure of the combustion air may be determined relatively accurately during operation.

The object is also achieved by the heating unit for carrying out a method having the features of the present invention.

This heating unit serves for heating a heating medium, in particular heating water, and has a combustion chamber into which combustion air may be fed via a blower and fuel may be fed via a feed line. The heating unit includes a rotational speed sensor and a pressure sensor and/or a power sensor. By determining the volume flow of the combustion air, the combustion may then be well-regulated. In particular, the supplied volume of combustion air may be adapted as a function of the quantity of supplied fuel. An optimal combustion is thus ensured.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 schematically shows a heating unit of a first specific embodiment.

FIG. 2 schematically shows a heating unit of a second specific embodiment.

FIG. 3 schematically shows a diagram including a power coefficient characteristic curve and a pressure coefficient characteristic curve.

DETAILED DESCRIPTION

FIG. 1 schematically shows a heating unit which includes a blower 1, a burner, a heat exchanger 3, an exhaust duct 4 and an exhaust pipe 5. Via blower 1, combustion air is conveyed into a combustion chamber of the heating unit. Burner 2 and heat exchanger 3 are also situated in the combustion chamber. Fuel, such as a gas for example, is conveyed to burner 2. However, this is not shown. Blower 1 has a supply interface 1.2 for its power supply.

In heat exchanger 3, the heat released in the burner is transferred to a heating medium, such as heating water, for example.

For clean and low-emission combustion, it is necessary to adjust the supplied volume of combustion air to the supplied quantity of fuel. A volume flow is substantially influenced by a rotational speed of blower 1. The rotational speed of a blower wheel is therefore detected with the aid of a rotational speed sensor 1.1, which is configured, for example, as a Hall-effect sensor. Via a pressure sensor 1.3, a static pressure of the combustion air is ascertained between blower 1 and burner 2.

Pressure sensor 1.3 and rotational speed sensor 1.1 are connected to a control unit 6 which calculates a volume flow on the basis of the values ascertained for a rotational speed of the blower wheel and the static pressure. For this purpose, control unit 6 has a memory in which reference values for a pressure coefficient, a power coefficient and a volume flow coefficient are stored in the form of characteristic curves. These reference values have been ascertained at a reference blower and are transferrable to blowers having similar geometric dimensions. The volume flow may therefore be determined relatively easily by detecting the rotational speed and the static pressure.

FIG. 2 shows a specific embodiment which has been modified slightly in comparison to FIG. 1. Identical and corresponding elements are provided with the same reference numerals.

In addition to detecting the rotational speed of the blower wheel via rotational speed sensor 1.1, in this specific embodiment a power consumption is measured via a power sensor and is provided to control unit 6. In the process, the electrical power supplied to a motor of blower 1 is measured. Based on this power and the rotational speed, the control unit then calculates the volume flow conducted by blower 1 to burner 2 or into the combustion chamber.

FIG. 3 is a diagram in which a pressure coefficient H is plotted in a first characteristic curve and a power coefficient P is plotted in a second characteristic curve, in each case over a volume flow coefficient F. These are characteristic curves which have been ascertained from reference values.

By detecting the rotational speed and the static pressure, it is possible to determine the pressure coefficient using formula (1) specified above. The volume flow coefficient may then be read from the characteristic curve shown in FIG. 3, and the volume flow may be calculated therefrom based on above formula (3).

In a corresponding manner, by detecting the rotational speed and the consumed power, the power coefficient may be ascertained using above formula (2) and the associated volume flow coefficient may be determined on the basis of the characteristic curve in FIG. 3. Hence, the volume flow may be calculated using above formula (3).

The method according to the present invention and the heating unit according to the present invention thus make it possible to ascertain the volume flow with little complexity. Only two sensors are required, namely a rotational speed sensor and a pressure sensor or a rotational speed sensor and a power sensor. Moreover, the calculation takes place on the basis of permanently stored values and dependencies. The determination of the volume flow is therefore subject to only a minor error rate. A clean, low-emission combustion may thus be ensured.

Claims

1.-6. (canceled)

7. A method for regulating a heating unit that includes a combustion chamber into which combustion air is introduced via a controllable blower having a blower wheel, comprising:

detecting a rotational speed of the blower wheel;

ascertaining at least one of a static pressure and a power consumption of the blower; and

determining a volume flow of the combustion air on the basis of the rotational speed in conjunction with at least one of the static pressure and the power consumption.

8. The method as recited in claim 7, further comprising ascertaining at least one reference value for at least one of a pressure coefficient and a power coefficient as a function of a volume flow coefficient, wherein the at least one reference value is taken into account when determining the volume flow.

9. The method as recited in claim 8, wherein the at least one reference value includes a plurality of reference values, the method further comprising storing the reference values as at least one of a pressure coefficient characteristic curve and a power coefficient characteristic curve.

10. The method as recited in claim 7, wherein the power consumption of the blower is ascertained from an electrical power consumed by an electric blower motor, a degree of efficiency being taken into account.

11. The method as recited in claim 7, wherein the static pressure is ascertained downstream from the blower in a flow direction.

12. A heating unit for carrying out a method for regulating a heating unit that includes a combustion chamber into which combustion air is introduced via a controllable blower having a blower wheel, the method including detecting a rotational speed of the blower wheel;

ascertaining at least one of a static pressure and a power consumption of the blower; determining a volume flow of the combustion air on the basis of the rotational speed in conjunction with at least one of the static pressure and the power consumption, the heating unit being for a heating medium and comprising:

the combustion chamber into which combustion air may be fed via the blower and fuel may be fed via a feed line;

a rotational speed sensor; and

at least one of a pressure sensor and a power sensor.

13. The device as recited in claim 12, wherein the heating medium includes water.