EP2918923A1 - Method for venting the heat transfer medium of heating devices - Google Patents

Abstract

The invention relates to a method for venting the heat transfer medium of a heater (1). According to the invention, the pressure or the volume flow is determined in a venting program. If the current gradient or the gradient related to the beginning of the measurement exceeds a threshold value, the deaeration program is ended.

Description

The invention relates to a method for venting the heat transfer medium of heaters, in particular of heaters with helically coiled heat exchangers.

For a trouble-free operation of heaters, it is necessary that the heat transfer medium, usually water, is free of air or gas bubbles. For this purpose, a deaerator is provided in the closed heat transfer medium circulation usually at the locally or absolutely geodetically highest point at which collect the gas bubbles.

In cases where a helically coiled heat exchanger with horizontally oriented axis is used in the heater, the upper halves of the pipe bends from which the walls are formed represent a local geodetically highest point in which air bubbles can collect. This can lead to local overheating during operation. A heater with such a heat exchanger with a vent at the end of the heat exchanger is known from the patent EP 2 306 112 B1 known.

For heaters with such heat exchangers, it is necessary to activate during the device installation a venting program, which expels the air bubbles from the upper halves of the pipe bends and transported to a central quick exhaust valve to be deposited there. Typically, this quick exhaust is either below the heat exchanger in the vicinity of the heating water pump or above the heat exchanger at the highest point of the hydraulic circuit.

Known venting programs include a timed operation of the heating pump, in which the pump is operated at fixed intervals at a certain speed, in order to flush any air bubbles from the heat exchanger to the quick exhaust, where they are deposited. Depending on the amount and location of the existing air bubbles this process of deposition takes different lengths. Furthermore, the venting program is usually composed of temporally phases of different flow rate and cyclic repetition of these phases over a set total duration implemented. The total duration depends on the ventilation time required for the most unfavorable ventilation case of an assumed installation. It follows that in a vast number of installations a much shorter venting time would be sufficient and thus the time required for the commissioning of the heater is unnecessarily high.

It is therefore an object of the invention to provide a method which shortens the required duration of the venting program by adapting the venting period not to the worst case but to the actual case.

This is achieved by a method according to the independent claim 1. Advantageous developments are described in the dependent claims.

For this purpose, a characteristic value such as the pressure or the volume flow of the heat transfer medium is cyclically measured in a venting program, which is carried out after installation or as needed, and compared with a previously measured characteristic value. For this purpose, the difference of the characteristic values is formed and divided by the time interval of the measurements, so that a quotient is formed. This quotient provides a statement as to how far the process of the deaerator has progressed.

The characteristic value with which the respective measured characteristic value is compared can be either the characteristic value measured at the beginning of bleeding or a characteristic value which was previously measured at a fixed time interval. Since there are no old characteristic values at the beginning of the procedure, the quotient can not be determined at the beginning. Once the quotient is determined, it is compared to a threshold. If the quotient, which is usually negative, is greater than a threshold, the cyclic steps of the deaeration process are completed. The threshold depends on the heater and can be determined and determined by a person skilled in the art.

The invention makes use of the knowledge that in the course of venting the pressure or the volume flow decrease. This is the case in particular when the sensor is provided behind the air separator in the conveying direction of the heat transfer medium. If, however, the sensor is arranged in front of the air separator, a momentary increase in the volume flow is observed.

In order to preclude termination too early due to randomly fluctuating measured values, in a further development of the invention closure can be precluded before the expiration of a minimum venting time.

In a further development of the invention, the individual steps of the method according to the invention are repeated with different pump speed within the venting program. This development is particularly advantageous because the degree of air dispersion in the heat transfer medium has an influence on the effectiveness of the deposition. Large bubbles can be well separated at medium to high volume flows, while finely dispersed bubbles are no longer effectively separated from the liquid phase due to the short residence times. Therefore, it is advantageous to repeat the inventive method with different pump speeds.

The invention will now be explained in detail with reference to FIGS.

Figur 1:

Eine Vorrichtung zum Durchführen des erfindungsgemäßen Verfahrens,

Figur 2:

Den zeitlichen Verlauf des gemessenen Kennwertes während des Entlüftens.

They show:

FIG. 1:

An apparatus for carrying out the method according to the invention,

FIG. 2:

The time course of the measured characteristic value during venting.

FIG. 1 shows an apparatus for carrying out the method according to the invention. A heater 1 comprises a heat source 4, which cooperates with the helically coiled heat exchanger 2, that the heat is transferred to a heat transfer medium. This heat transfer medium is circulated by a pump 5 in a heating circuit 6 in the form of a pipe system so that the heat is transferred from the heat source 4 to a heat sink 9. The heat sink 9 can be, for example, one or more radiators or hot water to be heated. As the heat transfer medium usually a liquid, preferably water is used. In order to deposit air or gas bubbles contained in the heat transfer medium, a vent valve 3 is provided. This vent valve is arranged so that the bubbles can collect in the area of the vent valve 3, which then escape via the vent valve 3. Advantageously, the vent valve 3 should be arranged at the highest point of the heating circuit 6. Because of the helically wound structure of the heat exchanger 2, the upper halves of the coils each form regions which are geodetically higher than the adjacent regions, so that air bubbles can collect here, too, which are difficult to convey out of the heat exchanger 2 during normal operation.

To carry out the method according to the invention, the device has a pressure sensor 7 or volume flow sensor 8 connected to the heating circuit 6.

In FIG. 2 For explaining the method according to the invention, the time profile of the characteristic value measured by the pressure sensor 7 or volume flow sensor 8 is shown. In the course shown here starts the process with stationary pump 5. The in FIG. 2 illustrated course of the characteristic before switching on the pump corresponds to a pressure curve. The characteristic value 16 measured for the first time is the static pressure, which increases by a known offset 15 when the pump is switched on. For the variant that the volumetric flow is used as a parameter, a different course would be available quantitatively before switching on the pump. Due to the stationary pump 5, the volume flow before switching on the pump would be 0.

After the start of the method according to the invention for venting, the pressure measured by the pressure sensor 7 or the characteristic value measured by the volume flow sensor 8 initially decreases rapidly and progressively more slowly as the vent progresses. In the method according to the invention, the gradient 13 between the currently measured characteristic value 12 and the first measured characteristic value 10, which was either measured directly or was determined by adding the characteristic value 16 with the offset 15, is formed in a variant. In another variant of the method, the gradient 14 between the currently measured characteristic value 12 and a previously measured characteristic value 11 is determined. As the characteristic decreases continuously, the gradients are negative. They are determined continuously in the method according to the invention and compared with a predetermined threshold value. As soon as the gradients 13 or 14 exceed the threshold value, this is an indication that no further venting progress has been recorded and thus the heat transfer medium has been successfully vented.

According to the invention, the steps of the deaeration process can be repeated with a changed pump speed.

LIST OF REFERENCE NUMBERS

1

heater

2

heat exchangers

3

vent valve

4

heat source

5

pump

6

heating circuit

7

pressure sensor

8th

Flow Sensor

9

heat sink

10

first measured characteristic value while the pump is running

11

previously measured characteristic value

12

current measured characteristic value

13

gradient

14

gradient

15

offset

16

first measured characteristic value with stationary pump

Claims (10)

A method for venting the heat transfer medium of a heating device (1), comprising a heat exchanger (2), a pump (5) for conveying the heat transfer medium and a sensor (7, 8) for detecting a characteristic value of the heat transfer medium, characterized by the cyclically performed process steps when turned on Pump: (a) Measuring the instantaneous characteristic value (12) measured with the sensor (7, 8) (b) forming the difference between the instantaneous characteristic value (12) and a previously measured characteristic value (10, 11, 16), if this is already present (c) Forming the quotient of the difference and the time interval of the measurements underlying the difference. (d) terminate the venting process as soon as the quotient exceeds a threshold. The method of claim 1, wherein in step (b), the previously measured characteristic value is the characteristic value that was previously measured at a fixed time interval. The method of claim 1, wherein in step (b) the previously measured characteristic value is the characteristic value (10, 16) which was measured when the method steps were cyclically performed for the first time. The method of claim 3, wherein the first-time cyclical performing the method steps when the pump is switched off (5). Method according to claim 4, wherein an offset (15) which takes into account the known change of the characteristic value by the running pump is added to the characteristic value (16) measured during the first cyclical carrying out of the method steps. Method according to one of claims 1 to 5, wherein in the method step (d) the method is not terminated until a minimum time has elapsed since the first cyclic performing the method steps. Method according to one of claims 1 to 6, wherein the characteristic value is the pressure of the heat transfer medium and the sensor is a pressure sensor (7). Method according to one of claims 1 to 6, wherein the characteristic value of the volume flow of the heat transfer medium and the sensor is a volume flow sensor (8). Method according to one of claims 1 to 8, wherein after completion of steps (a) to (d) after a waiting time, the steps (a ') to (d') are performed cyclically, wherein the steps (a ') to (d' ) correspond to steps (a) to (d) with changed pump speed. Method according to one of the preceding claims, wherein the heat exchanger (2) is a helically coiled heat exchanger with horizontally arranged axis.

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