DE102012109198B4 - Process for controlling the defrosting of a refrigerant evaporator - Google Patents

Abstract

Method for controlling the defrosting of an evaporator (4) of a refrigerant circuit, whereby it is made dependent on the evaporation pressure or the evaporation temperature, when a respective defrosting process is started, and wherein a respective defrosting process is started when the difference between a starting evaporating temperature and the current evaporation temperature, or the difference between a start evaporation pressure and the current evaporation pressure exceeds a predetermined threshold value, characterized in that it is made dependent on the evaporation pressure averaged over a certain preceding time period or on the evaporation temperature averaged over a certain previous time period defrosting is started.

Description

The present invention relates to a method according to the preamble of claims 1, 2, 9 and 11, i.e. a method for controlling the defrosting of an evaporator of a refrigerant circuit.

A refrigerant circuit is used, for example, but not exclusively in heat pump heating systems. Such heat pump heating systems can be used, for example, for heating heating water and / or process water, but also for any other media. The energy required to heat the medium to be heated can be taken from the air that is fed to the heat pump heating system. Such heat pump heating systems are referred to as air / water heat pump heating systems and are widely used for heating buildings and for heating water.

The basic structure of such a heat pump heating system is in 1 illustrated.

That in the 1 The heat pump heating system shown is essentially formed by a closed refrigerant circuit through which a refrigerant flows, which is a compressor 1 , a condenser 2nd , an expansion valve 3rd , and an evaporator 4th contains. They are also an evaporator 4th associated fan 5 which one the evaporator 4th passing air flow generated, and a control device controlling the above components 6 intended.

For the sake of completeness, it should already be pointed out here that only the components of the heat pump heating system that are of particular interest here are shown and described. Heat pump heating systems usually contain a whole range of other components such as various temperature and / or pressure sensors, pressure switches, a condensate pan, a condensate pan heater, etc.

That with the compressor 1 incoming refrigerant is in the gaseous state, more precisely it is a gas under low pressure. Through the compressor 1 the refrigerant is compressed, this compression resulting in an increase in pressure and, accordingly, in a correspondingly strong heating of the refrigerant. The refrigerant, also called hot gas in this state, comes from the compressor 1 to the condenser 2nd . The condenser 2nd is a heat exchanger through which the hot gas and the medium to be heated (heating water, process water, etc.) are heated. In this heat exchanger, the medium to be heated by the heat pump heating system is heated. As a result, the refrigerant cools down and gets into the liquid state. The refrigerant comes from the condenser 2nd to the expansion valve 3rd . Through the expansion valve 3rd the refrigerant, which is still under high pressure, is expanded. As a result, the refrigerant cools even further and becomes a liquid under low pressure. The expanded refrigerant comes from the expansion valve 3rd on to the evaporator 4th . The evaporator 4th is a heat exchanger through which the refrigerant flows and that from a fan 5 generated air flow is passed. The air is, for example, outside air drawn in from outside the building and / or warm air drawn in from inside the building, for example generated by a clothes dryer or a cooker. Because of the evaporator 4th passing airflow is warmer than that on the evaporator 4th incoming refrigerant, the refrigerant in the evaporator 4th heated by the air flowing past it and thereby becomes a gas under low pressure. The refrigerant comes from the evaporator 4th again to the compressor 1 , from which the steps explained above are repeated.

The control device 6 controls the heat pump heating system. Among other things, it monitors the temperature of the medium to be heated and / or the heated medium and switches the heat pump heating system, more precisely the compressor 1 and the fan 5 the same depending on this and on other parameters on and off. The control device 6 also has a number of other functions such as, but not limited to, compressor shutdown 1 and the fan 5 , if the pressure in the part of the refrigerant circuit carrying the hot gas becomes too high.

During the operation of the heat pump heating system forms on the evaporator 4th Ice. This is because that is the evaporator 4th refrigerant flowing through has a temperature below 0 ° C in certain operating conditions. This is what happens on the evaporator 4th for the formation of frost or for the formation of condensed water, which immediately freezes.

Which is on the evaporator 4th the ice layer that forms thereby hinders the air flow and the heat exchange between that on the evaporator 4th flowing air and the refrigerant. As the layer of ice thickens, the heat exchange can even come to a complete standstill.

Therefore, it must be on the evaporator 4th forming ice can be defrosted from time to time. This can be done using, for example so-called cycle reversal can be accomplished. The basic structure of a heat pump heating system in which this is possible is in 2A illustrated.

That in the 2A shown heat pump heating system contains all components of the in the 1 shown heat pump heating system. Components identified by the same reference numerals are identical or corresponding components. This also includes in the 2A shown heat pump heating system a four-way valve 7 . The four-way valve 7 has four connections, as in the 2A shown with the compressor 1 , the condenser 2nd , and the evaporator 4th are connected. Of the four connections, two are connected to each other via internal connection paths. However, the internal connection paths can be changed. Ie, it is adjustable which connection of the four-way valve 7 with which other connection of the four-way valve 7 connected is. More specifically, by the control device 6 which connection of the four-way valve 7 with which other connection of the four-way valve 7 connected is.

There are two different setting options, the first time the internal connection paths of the four-way valve are set 7 resulting connections between the individual components of the heat pump heating system in 2 B are illustrated, and which are in the second setting of the internal connection paths of the four-way valve 7 resulting connections between the individual components of the heat pump heating system in 2C are illustrated.

The connections that occur when you first set the internal connection paths of the four-way valve 7 result (see 2 B) , are exactly the same connections as the one in the 1 shown heat pump heating system. Ie, in the first setting of the four-way valve 7 is that in the 2A shown heat pump heating system in heating mode.

The connections that occur during the second setting of the internal connection paths of the four-way valve 7 result (see 2C ) result in a reversal of the circulation. More specifically, it is the case here that the condenser 2nd leaving refrigerant through the compressor 1 is compressed, and the compressed and accordingly hot refrigerant (the hot gas) into the evaporator 4th reached. The high temperature of the evaporator 4th refrigerant flowing through has the consequence that on the evaporator 4th existing ice melts. That is, with the second setting of the internal connection paths of the four-way valve 7 is that in the 2A shown heat pump heating system in a defrost mode.

Such defrosting of the evaporator 4th has the disadvantage that it uses a relatively large amount of energy. First, electrical energy is used to operate the compressor 1 secondly, the refrigerant removes the medium to be heated in the condenser 2nd Heat that must be returned to the refrigerant in a heating phase following the defrost phase. The latter stems from the fact that the refrigerant is in the evaporator 2nd and in the expansion valve arranged behind (in relation to the direction of flow of the refrigerant) 3rd cools down a lot, and thus the condenser 2nd refrigerant flowing through is much colder than the medium to be heated by the heat pump heating system. This takes place in the condenser 2nd cooling of the medium to be heated (and heating of the refrigerant) instead. The reheating of the medium to be heated again after defrosting leads to a further consumption of electrical energy. This affects the efficiency of the heat pump heating system. In addition, no heating power is available during defrosting.

Another known method for defrosting the evaporator 4th is the so-called hot gas defrost. A heat pump heating system in which hot gas defrosting is possible is a heat pump heating system according to 1 which, however, between the outlet of the compressor 1 and the entrance of the evaporator 4th an additional connection is provided. Such a heat pump heating system works during the heating phases like that in the 1 heat pump heating system shown; the additional connection between the outlet of the compressor 1 and the entrance of the evaporator 4th is blocked during the heating phases. In the defrost phases, the refrigerant circuit is on one between the compressor 1 and the condenser 2nd lying point interrupted and the additional connection between the outlet of the compressor 1 and the entrance of the evaporator 4th open. This gets it from the compressor 1 generated hot gas as in the circuit reversal directly into the evaporator 4th and defrost it. Such defrosting of the evaporator 4th However, it has disadvantages similar to defrosting by reversing the circulation.

Another state of the art is from DE 100 43 169 A1 , the US 2011/013219 A1 , the US 5,319,943A , the JP S54-24344A , and the WO 2011/031 014 A2 known

Regardless of how the evaporator is defrosted, the average heating output and efficiency of the Heat pump heating system also because defrosting does not take place as required, i.e. it starts too early or too late and / or ends too early or too late.

The present invention is therefore based on the object of finding a way by which the average heating power and efficiency of the heat pump heating system can be improved.

This object is achieved according to the invention by the methods claimed in claims 1, 2, 9 and 11.

These processes enable defrosting that is precisely tailored to actual needs. More specifically, by using the claimed criteria for the beginning and the end of the respective defrosting processes, it is possible that a respective defrosting process is always started exactly when it is actually necessary due to the existing ice formation, and that a respective defrosting process always ends exactly then as soon as there is no more ice on the evaporator. This means that both the frequency and the duration of the defrosting process, i.e. the times during which the refrigeration cycle cannot be used for its actual purpose, can be reduced to a minimum. At the same time, there is never so much ice on the evaporator that the refrigerant circuit can no longer be operated efficiently. As a result, the average heating output and the efficiency of the system containing the refrigerant circuit increase.

The additional technical effort to be accepted for this is negligible in relation to the advantages that can be achieved thereby.

Advantageous developments of the invention can be found in the subclaims, the following description and the figures.

• 1 den prinzipiellen Aufbau eines herkömmlichen Wärmepumpenheizsystems,
• 2A den prinzipiellen Aufbau eines herkömmlichen Wärmepumpenheizsystems, bei welchem bei Bedarf eine Kreislaufumkehr erfolgen kann,
• 2B die sich zwischen den Komponenten des in der 2A gezeigten Wärmepumpenheizsystems einstellenden Verbindungen, wenn sich das Wärmepumpenheizsystem in der Heiz-Betriebsart befindet,
• 2C die sich zwischen den Komponenten des in der 2A gezeigten Wärmepumpenheizsystems einstellenden Verbindungen, wenn sich das Wärmepumpenheizsystem in der Abtau-Betriebsart befindet, und
• 3 den prinzipiellen Aufbau eines Wärmepumpenheizsystems, bei welchen die im Folgenden näher beschriebenen Abtauverfahren durchgeführt werden können.

The invention is explained in more detail below using exemplary embodiments with reference to the figures. Show it

• 1 the basic structure of a conventional heat pump heating system,
• 2A the basic structure of a conventional heat pump heating system, in which a cycle reversal can be carried out if necessary,
• 2 B which is between the components of the in the 2A connections shown in the heat pump heating system when the heat pump heating system is in the heating mode,
• 2C which is between the components of the in the 2A shown heat pump heating system setting connections when the heat pump heating system is in the defrost mode, and
• 3rd the basic structure of a heat pump heating system, in which the defrosting process described in more detail below can be carried out.

The methods presented here are used in the example considered in the refrigerant circuit of a heat pump heating system, more precisely an air / water heat pump heating system. At this point, however, it should be pointed out that there is no restriction. The methods presented here can be used in any refrigerant circuits in which a more or less frequent defrosting of the evaporator is necessary or advantageous.

The basic structure of a heat pump heating system, in which the methods presented here can be used, is in 3rd illustrated.

That in the 3rd The heat pump heating system shown largely corresponds to that in the 2A shown and already described heat pump heating system. Components identified by the same reference numerals are identical or corresponding components. That in the 3rd However, the heat pump heating system shown also contains between the four-way valve 7 and the inlet port of the compressor 1 a pressure sensor 8th and between the compressor output port 1 and the four-way valve 7 a pressure sensor 9 .

The pressure sensor 8th is a low pressure sensor and is used to record the evaporation pressure, i.e. the pressure at which the refrigerant evaporates.

The pressure sensor 9 is a high pressure sensor and is used to record the condensation pressure, i.e. the pressure at which the refrigerant condenses (liquefies).

For the sake of completeness it should be noted that in the 3rd only the components of the heat pump heating system and the refrigerant circuit contained therein that are of particular interest are shown. The heat pump heating system can contain additional components such as further temperature and / or pressure sensors, pressure switches, a condensate pan, a condensate pan heater, etc.

Irrespective of this, the components contained in the refrigerant circuit shown can be at least partially implemented differently in practice. For example, the expansion valve 3rd can be formed either by a thermostatic expansion valve or by an electronic expansion valve.

If the outside air temperature drops below a certain value, it forms during normal operation, i.e. during the use of the refrigerant circuit for heating on the evaporator 4th a layer of ice that must be removed by cyclical defrosting for the reasons mentioned at the beginning. The outside air temperature at which ice forms depends on other parameters.

The present invention relates to the criteria that must be met in order for a respective defrosting process to be started or ended.

Defrosting the evaporator 4th takes place in the example considered by the circuit reversal already described at the beginning. The four-way valve 7 is controlled so that during the defrosting of the evaporator 4th the in the 2C Set connections shown, and that at all other times, but at least in the phases in which the heat pump heating system is in the heating mode, that in the 2 B set the connections shown.

Defrosting the evaporator 4th can, however, also take place in any other way, for example, but not exclusively, by means of the hot gas defrost, which was also described at the beginning. It should be obvious and requires no further explanation that the structure of the 3rd shown heat pump heating system depending on the defrosting process used. The criteria described below, which have to be fulfilled for each defrost to start, can be used with all types of defrost.

It is first described which conditions must be fulfilled for the start of a particular defrosting process.

In the method presented here, it is made dependent on the evaporation pressure or the evaporation temperature when a respective defrosting process is started.

In the example described below, the procedure is such that the sensor 8th the evaporation pressure is recorded, then the recorded evaporation pressure is converted into the evaporation temperature using a previously created and stored steam pressure curve, and it is then made dependent on the evaporation temperature when a respective defrosting process is started.

At this point it should already be pointed out that the conversion of the evaporation pressure into the evaporation temperature is not absolutely necessary. It could also be the same through the sensor 8th detected evaporation pressure can be made dependent on when a respective defrosting process is started. However, it could also be provided that the evaporation temperature is immediately detected by a temperature sensor and that it depends on the evaporation temperature thus obtained when a respective defrosting process is started.

Since the evaporation pressure and the evaporation temperature can be converted into one another using the vapor pressure curve or the like, these are mutually corresponding variables which are mutually replaceable. This means that the evaporation pressure and the evaporation temperature are to be regarded as equivalents.

It is preferably not only dependent on the current evaporation temperature whether a respective defrosting process is started, but rather on the size of the difference Diff between a start value t0 Start and the current value t0 cycle of the evaporation temperature, the following being true: $$\text{Diff}=\text{t0 start}-\text{t0 cycle}$$

More specifically, a respective defrosting process is started when the difference Diff is greater than a predetermined threshold value.

The start temperature t0 Start is the evaporation temperature that arises as soon as after the start of a heating cycle in the evaporator 4th stable overheating has been reached, that is if the evaporator 4th leaving gas has a temperature which is stable by a certain value, for example by 3 Kelvin, above the evaporation temperature. A heating cycle is to be understood as the time during which the refrigerant circuit can be used for heating, i.e. the time between two defrosts, each heating cycle beginning with the end of the last defrosting process and ending with the beginning of the next defrosting process, and after a new heating cycle begins at the end of the next defrosting process.

The start evaporation temperature t0 Start is determined again in each heating cycle, but is only determined once per heating cycle.

In the example considered, it is assumed that the stable overheating has been reached after a predetermined time after the start of a heating cycle. More specifically, the start evaporation temperature t0 Start is determined 8 minutes after the start of the heating cycle in the example considered. The 8 minutes mentioned are only an example. The time it takes to reach stable overheating can vary for different refrigerant circuits.

In order not to be dependent on short-term fluctuations, temperatures averaged over a certain period of time are preferably used for t0 start and / or t0 cycle.

In the example under consideration, the averaged temperature t0 Start is determined by starting the measurement 8 minutes after the start of the heating cycle, as already mentioned, and then averaging the measurement result over a period of 8 minutes, so that the averaged start evaporation temperature t0 Start 16 minutes after the heat pump heating system is switched on.

The average temperature t0 cycle is averaged over 2 minutes in the example considered. More precisely, it is the case that the averaged temperature t0 cycle is determined continuously or repeatedly at short time intervals and the determined values for t0 cycle each represent the mean value of the preceding 2 minutes.

As already mentioned above, the evaporation temperatures t0 start and t0 cycle are determined by determining the evaporation pressures (using the sensor 8th ) and subsequent conversion using a vapor pressure curve stored in the system.

Although the use of averaged evaporation temperatures or averaged evaporation pressures proves to be advantageous in many cases, there is no imperative to use averaged values. If averaged values are used for t0 start and t0 cycle, the times over which the values are averaged are not limited to the times mentioned above. The times can be of any length independently of one another.

It proves to be advantageous if the threshold value, which the difference Diff must exceed, so that a defrosting process is started, is not a constant value, but is a statically or dynamically adaptable value. This option is also used in the example considered. More precisely, a threshold value is used in the example under consideration, the size of which changes as a function of the time that has elapsed since the start of the current heating cycle. The threshold value decreases as the duration of the current heating cycle progresses, the decrease following a hyperbolic function.

wobei „Heizzykluszeit“ die seit dem Beginn des aktuellen Heizzyklus vergangene Zeit ist.The threshold used in the example considered is calculated as follows: $$\begin{array}{l}\text{Threshold}\left[\text{Kelvin}\right]=\\ 30.901*{\left(\text{Heating cycle time}\left[\text{Minutes}\right]\right)}^{-0.6158}\end{array}$$

where “heating cycle time” is the time elapsed since the start of the current heating cycle.

The result of this threshold adjustment is that the sensitivity of the defrost initiation increases.

It should be obvious and requires no further explanation that the equation given for calculating the current threshold value is only to be regarded as an example and that different refrigerant circuits and / or different uses and / or different operating conditions may require corresponding adjustments.

Although it is advantageous to adapt the threshold value dynamically to the given conditions as described or in another way, the use of a constant threshold value which is not dynamically adapted to the given conditions as described or a threshold value which is “only” statically adapted to the given conditions also provides a suitable one Criterion for the start of a defrost process.

The threshold value is preferably additionally subjected to a correction by means of which working point shifts occurring during the heating cycle are taken into account. In the example considered, this is done by correcting the threshold value depending on parameters that change during operation of the heat pump heating system, in such a way that the correction eliminates the changes in the evaporation pressure or the evaporation temperature that are caused by the changing parameters. The changing parameters, taking into account which correction of the threshold value takes place, are on the one hand the temperature of the air with which the evaporator 4th is blown, and on the other hand, the condensation temperature and the heating water temperature, in the example considered it is assumed that the condensation temperature and the heating water temperature are approximately the same, and consequently only one of these temperatures has to be taken into account.

In the example under consideration, the correction value is determined using a matrix in which is stored how high at a respective air temperature (first matrix input variable) and a respective condensation temperature (second matrix input variable) with an ice-free evaporator 4th the evaporation temperature should be (matrix output).

The correction value sought is then in each case the difference between the evaporation temperature determined from the matrix taking into account the current air temperature and the current condensation temperature and a more or less long previously determined evaporation temperature from the matrix in the same way. Finally, the threshold value is increased or decreased by this evaporation temperature difference. This can prevent changes in the evaporation temperature t0 cycle or the associated evaporation pressure, which only occur due to a change in the air temperature or a change in the condensation temperature, or a change in the heating water temperature, having an influence on the start of a respective defrosting process.

In the example under consideration, the respective correction values are determined as follows: At the beginning of each heating cycle, a first evaporation temperature is read from the matrix using the current air temperature and the current condensation temperature. In the example considered, the determination of this first evaporation temperature begins as in the determination of the actual evaporation temperature t0 start described 8 minutes after the start of a respective heating cycle. First, the air temperature and the condensation temperature are averaged over 8 minutes, and then, 16 minutes after the start of the heating cycle in question, the assigned (first) evaporation temperature is read from the matrix using these averaged temperatures. Subsequently, further evaporation temperatures are read out from the matrix at more or less large time intervals using newly determined values for the air temperature and the condensation temperature. The newly determined values for the air temperature and the condensation temperature are preferably also averaged values. In the example considered, the values used are values averaged over the two preceding minutes.

The current correction value is then determined by forming the difference between the evaporation temperature last read out of the matrix and the first evaporation temperature read out of the matrix at the beginning of the heating cycle in question.

Alternatively, it could be provided to work with a matrix from which the current correction value can be read out immediately. However, such a matrix would then have four different input variables, namely the averaged values for the air temperature and the condensation temperature, using which the first evaporation temperature was read from the matrix in the example described above, and the respective current values for the air temperature and the condensation temperature, below Use which the further evaporation temperatures were read from the matrix in the example described above.

It should be obvious and requires no further explanation that the correction described does not necessarily have to be carried out using the matrix mentioned. The evaporation temperatures read from the matrix in the example described above can also be determined in another way, for example by means of a corresponding functional equation.

Of course, instead of using evaporation temperatures or evaporation temperature differences, it is possible to work with evaporation pressures or evaporation pressure differences when correcting the threshold value. Regardless of this, there is no imperative to make the correction depending on the air temperature and the evaporation temperature. In addition, or alternatively, any other parameters that can change or change during a heating cycle can be taken into account in the correction. In principle, there is no restriction regarding the selection or the number of parameters to be considered.

In the manner described above, it is possible to start a respective defrosting process exactly when it is actually necessary. The determination of when to start a defrost process is always carried out with the greatest precision. The precision is also not negatively influenced by sensor errors due to long-term drifts that are hardly avoidable in practice, because the mentioned threshold value is not compared with the current absolute evaporation pressure / the current absolute evaporation temperature, but with an evaporation temperature difference or an evaporation pressure difference, and also because of the correction of the threshold is worked with differences. By working with differences, the sensor errors are largely eliminated and, as a result, have no or at most one negligible influence on the start of each defrosting process.

However, there is no imperative to work with differences. In particular, if the sensors mentioned have no or only a very slight long-term drift, or if the long-term drift is compensated for in some other way, it would also be possible to work with absolute temperature or pressure values when determining when a respective defrosting process should be started. More precisely, it could be provided, for example, that a respective defrosting process is started when the difference between the current absolute evaporation temperature and the current absolute air temperature exceeds a predetermined threshold value, this threshold value also being able to be adapted to changes occurring during operation, for example in Depending on the current duration of the current heating cycle can be changed dynamically.

As already mentioned at the beginning, it is equally important that the defrosting process is ended exactly when there is no more ice on the evaporator 4th located.

The following describes the conditions that must be met in order for a respective reverse cycle defrosting process to be ended, that is to say the refrigerant circuit is available again for heating.

In the method presented here, it is made dependent on the condensation pressure or the condensation temperature when a particular defrosting process is ended.

In the example considered, the procedure is such that the sensor 9 the condensation pressure is recorded, then the recorded condensation pressure is converted into the condensation temperature using a vapor pressure curve previously created and stored in the system, and it is then made dependent on the condensation temperature when a respective defrosting process is ended.

At this point it should already be pointed out that the conversion of the condensation pressure into the condensation temperature is not absolutely necessary. It could also be the same through the sensor 9 detected condensation pressure can be made dependent on when a respective defrosting process is terminated. However, it could also be provided that the condensation temperature is detected immediately by a temperature sensor and that it is dependent on the condensation temperature obtained in this way when a respective defrosting process is ended.

Since the condensation pressure and the condensation temperature can be converted into one another using the vapor pressure curve or the like, these are mutually corresponding variables that can be replaced. This means that the condensation pressure and the condensation temperature are to be regarded as equivalents.

In the method presented here, it is not only dependent on the current condensation temperature whether a respective defrosting process is ended, but at least partly also on the duration during which a specific condensation temperature is present.

More specifically, in the example under consideration, the defrosting process is ended at the latest when the condensation temperature has reached 42 ° C. or more, in which case it does not matter how long this condition lasts (check 1 ).

• - wenn die Kondensationstemperatur mindestens 1 Minute lang mindestens 40°C beträgt (Überprüfung 2), oder
• - wenn die Kondensationstemperatur mindestens 2 Minuten lang mindestens 36°C beträgt (Überprüfung 3), oder
• - wenn die Kondensationstemperatur mindestens 3 Minuten lang mindestens 30°C beträgt (Überprüfung 4).

A defrosting process can also be ended before this condensation temperature is reached. More specifically, in the example under consideration, a respective defrosting process is already ended when a lower condensation temperature is available for a temperature-dependent minimum period. In the example considered, a defrosting process is already ended,

• - if the condensation temperature is at least 40 ° C for at least 1 minute (check 2nd ), or
• - if the condensation temperature is at least 36 ° C for at least 2 minutes (check 3rd ), or
• - if the condensation temperature is at least 30 ° C for at least 3 minutes (check 4th ).

It should be obvious and does not require any further explanation that the temperatures and durations mentioned are preferably empirically determined device-specific values and can be of different sizes in different refrigerant circuits and can also depend on the operating conditions and other parameters. When determining the temperature / duration combinations used, the first step is to determine how long the condensation temperature must have at least a certain value before it reaches the evaporator 4th ice is completely defrosted, and then this time period is used as the temperature-related time period.

It should also be clear, and requires no further explanation that 30 ° C, 36 ° C, 40 ° C, and 42 ° C can be used instead of the temperatures mentioned any other temperatures. A respective defrosting process can also be ended when the condensation temperature has reached another value, for example 38 ° C. or any other value and no longer falls below this for an assigned period of time.

In addition, more or less than those mentioned 4th Checks are carried out.

The different, in the example considered, the four different checks (check 1 until review 4th ) are preferably carried out in parallel. A respective defrosting process is ended as soon as one of the checks shows that the assigned defrosting criterion (the assigned condensation temperature / duration - combinations) has been met. Of course, there is no imperative, exactly 4th Carry out checks, the number of checks can also be larger or smaller.

In the manner described, it can be reliably achieved that a respective defrosting process is ended exactly when there is no more ice on the evaporator.

The control device initiates and ends a respective defrosting process as well as checks and stipulations as to when a respective defrosting process is to be started or ended 6 .

The methods described above prove to be advantageous regardless of the details of the practical implementation. They allow the evaporator to be defrosted precisely according to actual needs. This means that a respective defrosting process is reliably started exactly when it is actually required, and the respective defrosting process is reliably ended exactly when the ice on the evaporator is completely removed from it. As a result, both the time intervals between successive defrosting processes and the duration of the defrosting processes are optimally adjusted to the given conditions, and consequently the average heating output and the efficiency of the heat pump heating system are maximized.

Reference list

1

compressor

2nd

Condenser

3rd

Expansion valve

4th

Evaporator

5

fan

6

Control device

7

Four-way valve

8th

Low pressure sensor

9

High pressure sensor

Claims (13)

Method for controlling the defrosting of an evaporator (4) of a refrigerant circuit, whereby it is made dependent on the evaporation pressure or the evaporation temperature, when a respective defrosting process is started, and wherein a respective defrosting process is started when the difference between a starting evaporating temperature and the current evaporation temperature, or the difference between a starting evaporation pressure and the current evaporation pressure exceeds a predetermined threshold value, characterized in that it is made dependent on the evaporation pressure averaged over a certain preceding time period or on the evaporation temperature averaged over a certain previous time period defrosting is started. Method for controlling the defrosting of an evaporator (4) of a refrigerant circuit, whereby it is made dependent on the evaporation pressure or the evaporation temperature, when a respective defrosting process is started, and wherein a respective defrosting process is started when the difference between a starting evaporating temperature and the current evaporation temperature, or the difference between a start evaporation pressure and the current evaporation pressure exceeds a predetermined threshold, characterized in that the threshold value is dynamically adapted to the given conditions, the threshold value depending on the time since the start of the current Heating cycle has passed, is changed. Procedure according to Claim 2 , characterized in that the threshold value is reduced as the duration of the current heating cycle progresses. Procedure according to Claim 3 , characterized in that the threshold is reduced so that its decrease follows a hyperbolic function. Method according to one of the preceding claims, characterized in that the evaporation pressure or the evaporation temperature are determined by a sensor (8) provided in the refrigerant circuit and the evaporation pressure and the evaporation temperature are converted into one another if necessary using a vapor pressure curve. Method according to one of the preceding claims, characterized in that that evaporation pressure or that evaporation temperature is used as the start evaporation pressure or as the start evaporation temperature as soon as a stable one after the start of a heating cycle in the evaporator (4) Overheating is reached. Procedure according to Claim 6 , characterized in that the start evaporation pressure or the start evaporation temperature is determined a predetermined time after the start of a heating cycle. Method according to one of the preceding claims, characterized in that the start evaporation pressure or the start evaporation temperature is newly determined in each heating cycle, and is determined only once per heating cycle. Method for controlling the defrosting of an evaporator (4) of a refrigerant circuit, whereby it is made dependent on the evaporation pressure or the evaporation temperature, when a respective defrosting process is started, and additionally on the temperature of the air passing through the evaporator (4) and / or depending on the condensation temperature and / or the heating water temperature, when a respective defrosting process is started, characterized in that, taking into account the current air temperature and / or the current condensation temperature and / or the current heating water temperature, it is determined which evaporation temperature would occur, if the evaporator (4) were not iced up and that it is dependent on the change in this evaporation temperature when a respective defrosting process is to be started. Procedure according to Claim 9 , characterized in that when determining when a respective defrosting process is to be started, the changes in the evaporation pressure or the evaporation temperature are determined which are caused by changes in the air temperature and / or by changes in the condensation temperature and / or by changes in the heating water temperature. Method for controlling the defrosting of an evaporator of a refrigerant circuit, characterized in that a respective defrosting process is ended when the condensation pressure or the condensation temperature have at least a predetermined value for a predetermined period of time. Procedure according to Claim 11 , characterized in that a respective defrosting process is ended when the condensation pressure or the condensation temperature has at least a predetermined first value for a predetermined first time period, or when the condensation pressure or the condensation temperature has at least a predetermined second value for a predetermined second time period. Procedure according to Claim 11 or 12th , characterized in that a respective defrosting process is also ended when the condensation pressure or the condensation temperature has reached a predetermined value which is above the first value and the second value, it being irrelevant how long this value is reached when this higher value is reached Value is held.

Images