DK2918923T3

DK2918923T3 - Method for ventilating the heat transfer medium of heating devices

Info

Publication number: DK2918923T3
Application number: DK15157316.9T
Authority: DK
Inventors: Jochen Wriske; Matthias Wodtke
Original assignee: Vaillant Gmbh
Priority date: 2014-03-13
Filing date: 2015-03-03
Publication date: 2017-08-21
Also published as: PT2918923T; EP2918923B1; EP2918923A1; AT515127A4; HRP20171131T1; AT515127B1; ES2634814T3

Description

Method for venting the heat transfer medium of heating devices

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

For undisrupted operation of heating devices, it is necessary for the heat transfer medium, generally water, to be free from air or gas bubbles. To this end, in the closed heat transfer circuit a ventilator is generally provided at the locally or absolutely geodetically highest location at which the gas bubbles accumulate.

In cases in which a helically coiled heat exchanger with a horizontally orientated axis is used in the heating device, the upper halves of the pipe bends from which the walls are formed constitute a local geodetically highest location in which air bubbles can accumulate. This can lead to local overheating during operation. A heating device having a heat exchanger which is constructed in this manner and which has a ventilator at the end of the heat exchanger is known from the patent specification EP 2 306 112 Bl.

With heating devices having such heat exchangers it is necessary when the device is installed to activate a ventilation program which drives the air bubbles out of the upper halves of the pipe bends and transports them to a central rapid vent valve in order to be separated at that location. Generally, this rapid ventilator is either below the heat exchanger close to the heating water pump or above the heat exchanger at the highest location of the hydraulic circuit.

Known ventilation programs have a time-controlled operation of the heating pump, in which the pump is operated at fixed intervals at a specific speed in order in this manner to flush any air bubbles out of the heat exchanger to the rapid ventilator, where they are separated. Depending on the quantity and accumulation location of the air bubbles which are present, this process of separation lasts for differing lengths of time. Furthermore, the ventilation program is generally composed of phases with a different flow speed in terms of time and a cyclical repetition of these phases is implemented over a fixed overall duration. The overall duration is in this instance based on the necessary ventilation time according to experience for the most unfavourable ventilation case of an installation to be assumed. Consequently, in the majority of installations, a significantly shorter ventilation time would be sufficient and consequently the time required for starting up the heating device is unnecessarily high. EP 0 924 472 A2 discloses a method for controlling the venting of a heating installation. It is proposed during venting, depending on the pressure path determined over time, that different degassing processes be selected and activated. To this end, a control device detects the time pressure path in a pressure build-up phase or pressure reduction phase and controls valves and the pressure pump. DE 10 2009 022 765 A1 discloses a solar installation in which, in order to vent during operation periodically or after emptying or refilling over a relatively long period of time, an excess pressure is built up. As a result of the pressure drop at a resiliently loaded valve, released gas is degassed.

An object of the invention is to provide a method which shortens the required duration of the ventilation program in that it adapts the venting duration not to the most unfavourable case, but instead to the actual case.

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

To this end, according to the invention in a ventilation program which is carried out after the installation or as required, a characteristic value such as the pressure or the volume flow of the heat transfer medium is measured cyclically and compared with a previously measured characteristic value. To this end, 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 information relating to how far the process of the ventilator has progressed.

The characteristic value with which the measured characteristic value is compared can either be the characteristic value measured at the beginning of the venting or a characteristic value which was previously measured at a fixed time interval. Since at the beginning of the method there are no old characteristic values available, the establishment of the quotient cannot yet be carried out at the beginning. As soon as the quotient has been established, this is compared with a threshold value. If the quotient which is generally negative is greater than a threshold value, the steps of the venting method which are carried out in a cyclical manner are terminated. The threshold value is based on the heating device and can be established and determined by a person skilled in the art.

The invention makes use of the knowledge that during the venting the pressure or the volume flow decrease. This is particularly the case when the sensor is provided in the conveying direction of the heat transfer medium downstream of the air separator. If, in contrast, the sensor is arranged upstream of the air separator, a momentary increase of the volume flow can be determined.

In order to eliminate premature termination as a result of randomly fluctuating measurement values, in a development of the invention a termination before a minimum venting time has elapsed can be eliminated.

In a development of the invention, within the ventilation program the individual steps of the method according to the invention are repeated at a different pump speed. This development is particularly advantageous since the degree of air dispersion in the heat transfer medium has an influence on the effectiveness of the separation. Large bubbles in medium to high volume flows can be readily separated, whilst finely dispersed bubbles as a result of the short dwell times can no longer effectively be separated from the liquid phase. It is therefore advantageous to repeat the method according to the invention at different pump speeds.

The invention is now explained in detail with reference to the Figures.

In the drawings:

Figure 1: shows a device for carrying out the method according to the invention,

Figure 2: shows the time path of the measured characteristic value during the venting.

Figure 1 shows a device for carrying out the method according to the invention. A heating device 1 comprises a heat source 4 which cooperates with the helically coiled heat exchanger 2 in such a manner 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 in such a manner that the heat from the heat source 4 is transferred to a heat sink 9. The heat sink 9 may, for example, be one or more heating members or service water which is intended to be heated. A liquid, preferably water, is generally used as a heat transfer medium. In order to separate air or gas bubbles contained in the heat transfer medium, a vent valve 3 is provided. This vent valve is arranged in such a manner that the bubbles can accumulate in the region of the vent valve 3 and then escape via the vent valve 3. Advantageously, the vent valve 3 is intended to be arranged at the highest location of the heating circuit 6. As a result of the helically coiled 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 which during normal operation can only be driven out of the heat exchanger 2 with difficulty can also accumulate at that location.

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

In Figure 2, in order to explain the method according to the invention, the time path of the characteristic value measured by the pressure sensor 7 or volume flow sensor 8 is illustrated. In the path shown in this instance, the method begins with a stationary pump 5. The path of the characteristic value illustrated in Figure 2 before the pump is switched on corresponds to a pressure path. The characteristic value 16 measured first is the rest pressure which increases by the pump being switched on by a known offset 15. For the variant which is used as a characteristic value of the volume flow, there would quantitatively be a different path before the pump is switched on. As a result of the stationary pump 5, the volume flow before the pump is switched on would be 0.

After the beginning 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 falls rapidly and as the venting continues falls increasingly slowly. In the method according to the invention, in a variant the gradient 13 between the currently measured characteristic value 12 and the first measured characteristic value 10 which was either measured directly or established by addition of the characteristic value 16 with the offset 15 is formed. In another variant of the method, the gradient 14 between the currently measured characteristic value 12 and a previously measured characteristic value 11 is established. Since the characteristic value continuously decreases, the gradients are negative. They are in the method according to the invention established continuously 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 progression of venting can be recorded and consequently the heat transfer medium has been successfully vented.

According to the invention, the steps of the venting method can be repeated at a changed pump speed.

List of reference numerals 1 Heating device 2 Heat exchanger 3 Vent valve 4 Heat source 5 Pump 6 Heating circuit 7 Pressure sensor 8 Volume flow sensor 9 Heatsink 10 First measured characteristic value with pump running 11 Previously measured characteristic value 12 Current measured characteristic value 13 Gradient 14 Gradient 15 Offset 16 First measured characteristic value with pump stationary

Claims

A method of ventilating a heat transfer medium of a heat device (1), comprising a heat exchanger (2), a pump (5) for feeding the heat transfer medium and a sensor (7, 8) for detecting a characteristic value of the heat transfer medium, characterized by cyclically performing when the pump is on, the steps of: (a) measuring the current characteristic value (12) measured by the sensor (7, 8) (b) calculating the difference between the current characteristic value (12) and a previously measured characteristic value (10, 11, 16) if it is already available (c) to calculate the quotient of the difference and the time interval of the measurements which form the basis for the difference (d) to complete the venting process as soon as the quotient exceeds the threshold.

The method of claim 1, wherein in step (b), the previously measured characteristic value is the characteristic value measured at a fixed time interval previously.

The method of claim 1, wherein in step (b), the previously measured characteristic value is the characteristic value (10, 16) measured when the process steps were cyclically performed for the first time.

The method of claim 3, wherein cyclically performing the process steps is performed for the first time when the pump (5) is turned off.

The method of claim 4, wherein an offset (15) is added to the characteristic value (16) measured during cyclic performing the first steps, taking into account the known change of the characteristic value caused by the running pump.

A method according to any one of claims 1 to 5, wherein in the process step (d) the process is not terminated until a minimum time interval since cyclically performing the process steps has been completed for the first time.

The method of any 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).

The method of any one of claims 1 to 6, wherein the characteristic value is the volume velocity of the heat transfer medium and the sensor is a volume flow sensor (8).

A method according to any one of claims 1 to 8, wherein, after completion of steps (a) to (d), steps (a ') to (d') are performed cyclically after a waiting period, wherein steps (a1) to (d1) ) corresponds to steps (a) to (d) with modified pump speed.

A method according to any one of the preceding claims, wherein the heat exchanger (2) is a coiled coil heat exchanger with a horizontally disposed axis.