EP1916490B1 - Thawing control method - Google Patents

Description

The invention relates to a method for controlling the defrosting of an evaporator of a refrigerated cabinet.

Refrigerated cabinets are used, for example, as open sales refrigerated cabinets for the normal refrigeration or deep-freezing of food in supermarkets or the like. The evaporator of the refrigerated cabinet serves to absorb heat from the product to be cooled and the air surrounding the goods. In this case, it comes as a result of the moisture contained in the ambient air over time to icing of the evaporator, which undesirably reduces the efficiency of the device. Particularly serious is this ice formation on the evaporator with open cooling furniture, in which constantly fresh ambient air and thus additional moisture reaches the evaporator. The evaporator must be defrosted regularly.

For this purpose, it is known to equip the evaporator with an optionally activatable electric heater. Especially for the deep-freezing, a so-called hot gas defrosting is known in which heated gaseous refrigerant is passed through the heat exchanger tubes of the evaporator.

However, the problem is the detection of the actual degree of icing of the evaporator. Usually, depending on the particular furniture product, it is defrosted according to predetermined time intervals without taking into account the particular installation or environmental conditions of the furniture. As a result, often unnecessarily often defrosted in practice. The defrost is therefore associated with an unnecessary energy demand, and the goods stored in the refrigerated cabinet may be affected by too frequent or unnecessary defrosting processes. Although the degree of icing can be assessed by the melting time measured during the defrost, which is needed to melt off the ice buildup. The disadvantage here, however, is that the assessment is done only for the past.

From the EP-A-1 367 346 a method for controlling the defrosting process of an evaporator having the features of the preamble of claim 1 is known. In this method, the circulating air volume flow of the evaporator is determined and taken into account.

It is therefore an object of the invention to provide a method by which the actual actual defrosting requirement of a vaporizer of a refrigerated cabinet can be determined using as few additional sensors as possible with high accuracy.

This object is achieved by a method having the features of claim 1.

Thus, two computational estimates are made. On the one hand, an actual ice formation on the evaporator, ie an amount of ice (mass or volume) or an ice formation rate, is estimated. For this purpose, at least the ambient temperature and the ambient humidity (relative or absolute humidity) are measured and taken into account. These measurements usually do not require significant additional effort For example, in supermarkets with a plurality of refrigeration units, a central measurement of the ambient temperature and the humidity is usually carried out anyway, and these measured values are transmitted to the respective control device of the refrigerated cabinets or a central control device.

On the other hand, a nominal ice formation at the evaporator is estimated according to a predetermined nominal operating point of the refrigerated appliance or its evaporator, namely at least in accordance with a nominal ambient temperature and / or a nominal air humidity, whereby the determination of the nominal ice formation is analogous to the determination of the aforementioned actual ice formation is made. Said nominal operating point may for example correspond to the nominal ambient temperature and / or the nominal air humidity of a climate class according to the standard EN441 or a comparable standard (for example EN23953), e.g. 25 ° C and 60% relative humidity for climate class "3".

It is important that a nominal icing rate of the evaporator is known for the rated operating point of the evaporator considered. This rated icing rate may be determined empirically by the operator for the particular refrigerated cabinet and / or specified by the refrigeration cabinet manufacturer. The named rated operating point of the evaporator is chosen in particular such that it corresponds to the worst-case expected environmental conditions (eg highest expected temperature and highest expected relative humidity at the installation site of the refrigerator). In turn, the associated rated icing rate is, in particular, the icing rate that corresponds to these worst case expected environmental conditions. The starting point for the method is therefore a nominal rate of icing, the consideration of which also applies to the most unfavorable environmental conditions to be expected (eg according to the ambient conditions according to a special climate class according to EN441) is sufficient for a timely defrost. The stated nominal icing rate may be a defrost interval (ie a time interval between two consecutive defrosting dates) or else the specification of an ice formation volume or an ice formation mass per unit time.

In order to determine a next required defrost date and / or to establish a suitable type of defrost procedure for the next predetermined defrost date (nominal defrost date), the actual ice formation (based on the measurements) and the estimated (based on the respective nominal values) nominal ice formation are determined. Ice formation in relation to each other, for example - but not necessarily - by quotient formation, and this ratio is in turn set in relation to the aforementioned nominal icing rate, for example by multiplication or division.

This ratio formation ultimately causes a delay in the determined defrosting dates with respect to the nominal icing rate or defrosting dates assumed for the worst-case environmental conditions, or it determines the proportion by which the actual ice formation deviates from the nominal ice formation, respectively depending on the deviation of the measured real conditions from the nominal conditions.

A particular advantage of this method is the consideration of a climate class already specified by the device manufacturer (whereby the nominal ambient temperature and the nominal air humidity are specified) or a nominal freezing rate already known for such a nominal operating point of the evaporator anyway (eg nominal -Abtauintervall). This has the consequence that the volume or mass flow of the ambient air impinging on the evaporator can be indirectly taken into account without the need for a separate measurement of this volume or mass flow. However, only taking into account this volume or mass flow, an accurate estimate of the amount of condensate occurring at the evaporator per unit time is possible.

Fig. 1 und 2

zeigen jeweils eine schematische Seitenansicht eines Kühlmöbels mit einem Verdampfer und verschiedenen Luftströmen.

Possible embodiments of the method according to the invention are explained below, wherein for better understanding, the typical structure of the refrigerator affected here should first be explained.

Fig. 1 and 2

each show a schematic side view of a refrigerated cabinet with an evaporator and different air streams.

In Fig. 1 is a here on its front open cooling cabinet only shown schematically. The refrigerator has an evaporator V. This is integrated in a conventional manner in a known refrigerant circuit, ie, the evaporator V is connected in the flow direction of the refrigerant, for example with a compressor, a condenser and an expansion valve.

Furthermore, in Fig. 1 shown different air flows. Thus, an air flow 1 is guided in the refrigerator to the evaporator V. The air is cooled at the evaporator V and leaves it as air flow 2. At the top of the refrigerator, namely at an air outlet A, the cooled air is discharged as air stream 3. The cooled air flows along the front of the cabinet curtain down (air flow 4), wherein the goods arranged in the refrigerated goods is cooled. In this air stream 4, air from the environment U (air stream 5) mixed. The am For a conventional normal cooling, the air temperature at the outlet A, for example, about + 2 ° C and at the air inlet E of the refrigerator furniture approx. + 5 ° C.

In Fig. 1 In addition, the temperatures at the air outlet A, in the environment U, at the air inlet E and at the evaporator V prevailing temperatures T, the relative humidity rF and the absolute humidity (water content) x are shown. The measured values used in the context of the method according to the invention are each surrounded by a circle, wherein a solid line indicates a mandatory measured value and a dashed line indicates an optional measured value. A respective rectangular border indicates a calculated value, and optional calculations are again indicated by a dashed line. Specifically, the respective water content x (absolute humidity) can be taken as a function of the temperature T and the relative humidity rF the Mollier diagram, wherein simplifying a constant pressure can be assumed.

Hereinafter, a particularly accurate method for determining a defrosting deadline for the evaporator V according to Fig. 1 explained (so-called condensate model). In this process, the in Fig. 1 determined as optional measured values, and the calculations marked as optional are performed. Subsequently, a simplified embodiment of the method according to the invention is explained (so-called linear approach).

(a) Estimate the actual ice formation on the evaporator V:

On the one hand, the (volume or mass specific) actual ice formation on the evaporator is estimated. For this purpose, at least the ambient temperature Tu and the relative humidity rFu of the environment are measured. As a result, the water content x _U of the ambient air stream 5 mixed with the cooling air flow 4 is known (Mollier diagram).

In the context of the so-called condensate model, a difference Δx between the absolute humidity x _E at the evaporator inlet E and the absolute humidity x _A at the air outlet A is ultimately determined for the estimation of the actual ice formation on the evaporator V, it being assumed that the heating of the cooling air between the Air outlet A (air flow 3) and the air inlet E (air flow 1) alone from the admixture of the ambient air (air flow 5) results.

The absolute humidity x _A at the air outlet A can be equated with the water content x _V at the evaporator V. Although the air flow 2 from the evaporator V to the air outlet A heats up, that is, the relative humidity RH changes. The absolute water content x remains constant. It can also be reasonably assumed that the air at the evaporator V cools down to the dew point or below the dew point (relative humidity rFv at the evaporator V of 100%). Thus, the water content x _V or x _A can be determined directly from the temperature Tv at the evaporator V (Mollier diagram). This value in turn can be measured by means of the temperature sensor, which is usually present at the evaporator V anyway. Alternatively, neglecting the above-mentioned heating, the temperature T _A at the air outlet A may be used instead of the temperature Tv at the evaporator V.

The absolute humidity x _E at the air inlet E is - as already mentioned - determined taking into account the fact that the at the air outlet

A output cooling air (air stream 3) an air stream 5 from the environment U is mixed. However, the respective mass flows are not known. The absolute humidity x _E is therefore determined according to a mixing rule (mixture of the air masses located at different temperature levels), whereby the accumulating condensate quantities are specific, ie based in each case on a defined air mass (eg one kilogram).

For a better explanation of the mixing rule used on Fig. 2 referenced, in which the mass flows are drawn. It is assumed that the mass flow in the refrigeration cabinet is constant (m ₁ = m ₃ , ms = m ₆ ). There is thus a mass exchange between the air stream 2 in the refrigerator and the environment U by the amount m ₆ = m ₅ instead. With this condition, the mass flow remains constant in the calculation.

According to the mixing rule, a mixing temperature T ₁ results for the air flow 1 at the air inlet E, which can initially be deduced from the temperatures T ₄ and T _{5 of} the air flows 4 and 5 as well as from the corresponding masses and heat capacities: $${\mathrm{<figure-callout\; id="1"\; label="T"\; filenames="imgf0001.png"\; state="\{\{state\}\}">T</figure-callout>}}_1=\frac{\Sigma m_i\times c_i\times T_i}{\Sigma m_i\times c_i}=\frac{m_4\times c_4\times {\mathrm{<figure-callout\; id="4"\; label="T"\; filenames="imgf0001.png"\; state="\{\{state\}\}">T</figure-callout>}}_4+{\mathrm{<figure-callout\; id="5"\; label="m"\; filenames="imgf0001.png"\; state="\{\{state\}\}">m</figure-callout>}}_5\times c_5\times T_5}{{\mathrm{<figure-callout\; id="4"\; label="m"\; filenames="imgf0001.png"\; state="\{\{state\}\}">m</figure-callout>}}_4\times {\mathrm{<figure-callout\; id="4"\; label="c"\; filenames="imgf0001.png"\; state="\{\{state\}\}">c</figure-callout>}}_4+{\mathrm{<figure-callout\; id="5"\; label="m"\; filenames="imgf0001.png"\; state="\{\{state\}\}">m</figure-callout>}}_5\times {\mathrm{<figure-callout\; id="5"\; label="c"\; filenames="imgf0001.png"\; state="\{\{state\}\}">c</figure-callout>}}_5}$$

Here, c _i denotes the respective specific mixing heat capacity of the air and the water content at a given temperature and relative humidity. As explained above, it can be assumed that m ₄ = m ₃ -m ₆ = m ₃ -m ₅ . In addition, to simplify the respective water content in the partial streams, for example, a maximum of about 2% the total mass, neglected. From equation (1): $${\mathrm{<figure-callout\; id="5"\; label="m"\; filenames="imgf0001.png"\; state="\{\{state\}\}">m</figure-callout>}}_{\mathrm{5}}=\frac{{\mathrm{<figure-callout\; id="3"\; label="m"\; filenames="imgf0001.png"\; state="\{\{state\}\}">m</figure-callout>}}_3\times c_3\times \left(T_1-T_3\right)}{c_5\times T_5-{\mathrm{<figure-callout\; id="3"\; label="c"\; filenames="imgf0001.png"\; state="\{\{state\}\}">c</figure-callout>}}_3\times T_3-{\mathrm{<figure-callout\; id="5"\; label="c"\; filenames="imgf0001.png"\; state="\{\{state\}\}">c</figure-callout>}}_5\times {\mathrm{<figure-callout\; id="1"\; label="T"\; filenames="imgf0001.png"\; state="\{\{state\}\}">T</figure-callout>}}_1+c_3\times {\mathrm{<figure-callout\; id="1"\; label="T"\; filenames="imgf0001.png"\; state="\{\{state\}\}">T</figure-callout>}}_1}$$

The heat capacity c _i can be assumed to be constant as a simplification. It can be estimated that the errors caused by neglecting the unequal heat capacities of air and water are minor and that the above simplifications only make equation (2) "safer" as they ultimately lead to larger calculated condensate quantities at the evaporator V.

From this, the compounding amount m ₅ can then ambient air will be approximately calculated as: $$\frac{{\mathrm{m}}_{\mathrm{5}}}{{\mathrm{<figure-callout\; id="3"\; label="m"\; filenames="imgf0001.png"\; state="\{\{state\}\}">m</figure-callout>}}_{\mathrm{3}}}=\frac{{\mathrm{T}}_{\mathrm{1}}-{\mathrm{T}}_{\mathrm{3}}}{{\mathrm{T}}_{\mathrm{5}}-{\mathrm{<figure-callout\; id="3"\; label="T"\; filenames="imgf0001.png"\; state="\{\{state\}\}">T</figure-callout>}}_{\mathrm{3}}}$$

Due to the aforementioned equation (3), the mass ratio m ₅ / m _{3 is} known. The temperature T ₁ corresponds to that in connection with Fig. 1 said inlet temperature T _E and can be measured by means of a arranged at the air inlet E of the refrigerator furniture temperature sensor. The temperature T ₃ corresponds to the outlet temperature T _{A of} the air outlet A according to Fig. 1 ; An associated temperature sensor can also be provided for this purpose, or the outlet temperature T _A is equated with the temperature T _V at the evaporator V for the sake of simplicity. The temperature T ₅ finally corresponds to the ambient temperature Tu according to Fig. 1 , Thus, from the mentioned equation (3) by measuring the temperatures T _E , T _A (or T _V ) and T _U, the mass ratio m ₅ / m _{3 of} the proportionate Admixture of the ambient air (air flow 5 according to Fig. 1 ) in the cooling air flow 3 known.

The absolute humidity x _E at the air inlet E, ie the prevailing water content (g / kg), is the sum of the water content of the air flows 4 and 5 according to Fig. 1 , The absolute humidity x _E thus results from the product of the absolute humidity x _A at the air outlet A with the air mass m _{3 there} , from which the product of the absolute humidity x _A at the air outlet A with the mass m _{6 is} to be subtracted (to the environment discharged water quantity), in which case again the product of the absolute humidity x _U of the ambient air is to be added to the mass m ₅ supplied by the environment U, and wherein this function is of course to be standardized with respect to the total mass m ₁ = m ₃ : $${\mathrm{x}}_{\mathrm{e}}=\frac{x_A\times m_3-x_A\times m_6+x_U\times m_5}{{\mathrm{<figure-callout\; id="3"\; label="m"\; filenames="imgf0001.png"\; state="\{\{state\}\}">m</figure-callout>}}_3}$$

Overall, it follows that the absolute humidity x _E can be calculated as a value related to the recirculated air mass. The absolute humidity x _A at the air outlet A can namely be set equal to the water content x _{V of} the air at the evaporator V, which in turn can be estimated from the temperature Tv measured at the evaporator V and from the assumption that the dew point is reached or undershot, as already explained above. The absolute humidity x _{U of} the ambient air can be calculated from the measured ambient temperature Tu and relative humidity rFu (Mollier diagram). The aforementioned mass m ₆ corresponds to the mass m ₅ at a constant mass flow (cf. Fig. 2 ). The mass ratio m ₅ / m ₃ is obtained according to equation (3) from the measured temperatures T ₁ = T _E , T ₃ = T _A (or T ₃ = T _V ) and T ₅ = T _U.

Thus, the aforementioned difference .DELTA.x of the absolute humidity x _E and x _{A is} known, which corresponds to the condensation or ice formation on the evaporator V, namely as a relative to the circulated air mass value (eg g / kg). In other words, the actual ice formation .DELTA.x at the evaporator V has hitherto only been estimated as a volume or mass-specific value by taking account of the described mixing rule, namely based on the volume or the mass of the airflow circulating in the refrigeration appliance. However, this is not known and should not be measured if possible.

(b) Estimating a nominal ice formation on the evaporator:

The thus lacking mass flow or volume flow in the refrigerator is therefore taken into account indirectly, namely in the form of a nominal rate of icing of the cabinet or its evaporator. This nominal icing rate, for example a nominal defrost interval, may have been determined empirically by the operator of the refrigerated cabinet or - also on the basis of empirical determination - may be specified by the refrigeration cabinet manufacturer. In particular, the rated icing rate corresponds to the worst possible expected real ambient conditions at the installation site of the refrigerated cabinet, and it may correspond to a specific climate class according to the EN441 standard. The rated icing rate is associated with a nominal ambient temperature and nominal air humidity as the rated operating point of the evaporator.

On the basis of this nominal ambient temperature and nominal air humidity, the nominal ice formation x _nominal is estimated at the evaporator V, with the actual ice formation being estimated analogously to the above-described estimation. For example, only the actually measured ambient temperature T _U and air humidity rFu are replaced by the corresponding nominal values (rated ambient temperature or nominal air humidity). The further calculation of the nominal ice formation x _nominal takes place as explained in detail above for the calculation of the actual ice formation, in particular taking into account the same measured values (eg T _A , T _E , Tv).

As an alternative to replacing the actual measured ambient temperature Tu and air humidity rF _U by the corresponding nominal values, only one of these measured values can be replaced by the corresponding nominal value of the nominal operating point of the evaporator. For example, it is sufficient to replace only the measured air humidity rFu of the environment by the rated humidity of the cooling cabinet, ie for the calculation of nominal ice formation x _nominal analogous to the calculation of the actual ice formation, the measured ambient temperature Tu = T ₅ (and not the nominal ambient temperature). This means according to the above equation (3) that the same mass ratio m ₅ / m ₃ (ratio of the air flow 5 supplied from the environment U to the air flow 3 at the outlet A) is assumed as in the calculation of the actual ice formation, and not of a reduced such mass ratio at a higher temperature T ₅ .

Thus, the nominal ice formation x _nominal is now available as a volume or mass-specific value (eg g / kg).

(c) Ratio of actual ice formation and nominal ice formation on the evaporator:

Finally, the (volume or mass specific) estimated actual ice formation Δx at the evaporator and the (volume or mass specific) estimated nominal ice formation x _nominal are set in relation to each other, for example by quotient Δx / x _nominal . By taking account of the aforementioned nominal icing rate, the missing knowledge of the air volume flow or air mass flow is taken into account.

Thus, a ratio V of the actual ice formation X to the estimated nominal ice formation X _nominal, which is no longer dependent on the volume flow or mass flow, can be formed from the corresponding volume- or mass-specific quantities Δx or x _nominal as follows: $$V=\frac{X}{X_{\mathit{nominal}}}=\frac{\mathrm{\Delta }\mathit{x}\times \dot{V}\times {\rho }_{\mathit{air}}}{{\mathrm{\Delta }\mathit{x}}_{\mathit{nominal}}\times \dot{V}\times {\rho }_{\mathit{air}}}$$

With V̇ in this case the volume flow (m ³ / min) is referred to in the refrigerator. ρ _Air is the density of the air (kg / m ³ ). It can be seen that the specific values of the actual ice formation Δx and the nominal ice formation x _nominal relate to a mass (eg 1 kg of air) circulating around the refrigerated cabinet. Since the calculation of the actual ice formation X and the calculation of the nominal ice formation X _{nominal are} analogous to one another and the volume flow and the density of the air shorten out of the calculation of the ratio V, the volume flow and the density of the air can change without this affects the ratio V The volume flow and the density of the air need not be known.

The ratio V thus corresponds to a degree of icing. It indicates the ratio of actual ice formation to nominal ice formation. Of the Nominal ice formation, in turn, is assigned to the nominal icing rate. The ratio V thus denotes the proportion by which the rated icing rate has fallen below due to the (more favorable) real conditions or a nominal defrost interval T _defrost can be exceeded.

The ratio V can be determined periodically, for example, with the individual determined values V _{i being} added up. The estimated actual ice formation and the estimated nominal ice formation are therefore cumulated. Preferably, the individual determined values V _i (or the sum formed) are additionally normalized with regard to the nominal icing rate, in particular by forming a ratio with the rated icing rate. For example, the determined values V _i can be multiplied by the ratio of the respective measurement interval Δt _{meas, i} (time duration between two measurements) to the nominal defrost interval T _defrost (defrost interval for nominal conditions): $$\mathrm{v}\left(\mathrm{n}\right)={\displaystyle \underset{i=1}{\overset{n}{\Sigma }}}{V}_i\frac{{\mathrm{\Delta }\mathit{t}}_{\mathit{measuring}.i}}{T_{\mathit{defrost}}}$$

Of course, instead of a summation, an integration can also take place.

Once this accumulated and normalized degree of icing V (n) reaches or exceeds a predetermined threshold, such as 100%, the next defrost is initiated, either immediately or after a programmed defrost release deadline (eg defrost only to allow for certain night or weekend times). Thus, if more favorable environmental conditions exist than the nominal conditions, one or even several nominal defrosting dates are skipped. The comparison the normalized degree of icing V (n) with a predetermined threshold value (such as 100%) corresponds indirectly to a comparison of the degree of icing with the nominal icing rate (eg with the nominal defrost interval T _defrost ).

It is also possible to convert the currently determined degree of icing into a time prognosis of the next actually required defrosting date, for example by the icing _{degree being set} in relation to the nominal defrost interval T _defrost .

As an alternative to the initiation of the next defrosting explained above, it can also be provided that the predetermined regular defrosting dates (nominal defrosting appointments) are maintained, ie not skipped, independently of the determined degree of icing. However, depending on the detected degree of icing, only the type of defrosting method may be changed. In this case, a summation of the degrees of icing therefore does not take place over several nominal defrost intervals. In particular, if, when a nominal defrost interval has elapsed, the determined degree of icing has exceeded a threshold value of 100% (calculated from the last defrosting operation), an energetic defrosting method can be selected instead of an otherwise provided non-energetic defrosting method. For example, - especially in the case of plus cooling (> 0 ° C) - provided for the expected ambient conditions for each nominal defrosting a Umluft Abtauung (temporary shutdown of the cooling, ie only the air circulating in the cabinet air provides for de-icing of the evaporator). However, if less favorable environmental conditions occur (which lead to an increased determined degree of icing), an electric defrost will be carried out at the nominal defrosting time instead of the circulating air defrosting. In this case, the evaporator, for example, electric Heating energy supplied; Thus, an increased energy consumption is accepted, but a more effective de-icing is guaranteed, ie the evaporator is reliably completely de-iced.

(d) Summary of the condensate model:

• Es wird von einem konstanten Luftdruck ausgegangen (z.B. 1 bar). Die Erwärmung der Luft zwischen Austritt und Eintritt am Kühlmöbel erfolgt nur über die Umgebungsluft. Der kälteste Punkt des Luftkreislaufs im Kühlmöbel wird mittels eines Temperatursensors gemessen, wobei an diesem Punkt die relative Luftfeuchte 100 % beträgt. Der Massenstrom im Kühlmöbel ist konstant. Die Temperatur und Feuchte der Umgebungsluft sind bekannt bzw. werden gemessen.

In summary, the assumptions underlying the condensate model explained above should once again be mentioned:

• It is assumed that the air pressure is constant (eg 1 bar). The heating of the air between the outlet and the entrance to the refrigerator is done only through the ambient air. The coldest point of the air circulation in the refrigerator is measured by means of a temperature sensor, at which point the relative humidity is 100%. The mass flow in the refrigerator is constant. The temperature and humidity of the ambient air are known or measured.

By applying a mass mixing rule, the amount of condensate can be calculated on the evaporator V mass or volume specific, namely based on the air circulating in the refrigerator. By considering a device specific rated icing rate with associated rated ambient temperature and nominal humidity, the mass flow of the circulating air, i. the time dependence of the estimated condensate formation are taken into account.

The condensate model takes into account lower evaporation temperatures (ie lower than normal operating conditions) with a larger condensate (earlier defrost date). Covered refrigerated cabinets or times in which the refrigerated cabinets are temporarily covered or closed is taken into account with a lower condensate quantity (later defrost date).

(e) Linear Approach:

The estimation of ice formation can also be made according to a simplified linear approach, so that the in Fig. 1 dashed bordered values do not necessarily have to be measured or determined. For this purpose, the actual formation of ice on the evaporator V is estimated on the basis of the absolute humidity x _{U of} the ambient air U. This is calculated from the measured ambient temperature T _U and the measured relative humidity rFu of the environment. In addition, a nominal ice formation on the evaporator V is estimated by calculating a reference humidity x _Ref for a nominal ambient temperature and / or a nominal air humidity. These nominal conditions can in turn correspond to a climate class according to the standard EN441. It is important that these nominal conditions are assigned a known nominal icing rate.

The estimated actual ice formation (actual moisture xu) is then related by quotient formation to the nominal ice formation (reference moisture x _Ref ) and the value obtained is compared with the nominal ice formation rate. As a result, for example - as in the illustrated condensate model - a degree of icing can be determined in order to initiate a defrosting process when an ice degree of 100% is reached.

In particular, a current degree of icing is formed by summing up and normalizing the measured values, or a time average of the estimated actual ice formation is determined and taken into account, for example, by integration.

In addition, correction parameters can be provided in the quotient formation, in particular a gradient correction value and / or an offset correction value.

Finally, it should be noted that in both the illustrated condensate model and the simplified linear approach by appropriate measurement of the ambient pressure can be taken into account in order to achieve an even higher accuracy of the underlying estimates.

LIST OF REFERENCE NUMBERS

1 - 5

airflow

A

air outlet

e

air inlet

U

Surroundings

V

Evaporator

Claims (20)

1. A method of controlling the defrosting of an evaporator (V) of a piece of refrigeration equipment, in which

   (a) an actual frost formation at the evaporator is estimated by measuring at least the environmental temperature (T_U) and the air humidity (rF_U) of the environment (U),

   characterized in that

   (b) a nominal frost formation at the evaporator is estimated for a nominal operating point of the refrigeration equipment, with a nominal frosting rate being known for the nominal operating point and with the estimation of the nominal frost formation taking place analog to the estimation of the actual frost formation; with

   - the measured environmental temperature (T_U) being replaced with a nominal environmental temperature; or

   - the measured air humidity (rF_U) of the environment being replaced with a nominal air humidity; or

   - the measured environmental temperature (T_U) being replaced by a nominal environmental temperature and the measured air humidity (rF_U) being replaced with a nominal air humidity; and

   (c) in that the estimated actual frost formation and the estimated nominal frost formation are set into relationship with one another in order to determine a next defrosting time or to fix a type of defrosting from the relationship and from the known nominal frosting rate.
2. A method in accordance with claim 1
   characterized in that
   a difference of the air humidity (x_E) at the evaporator inlet (E) and of the air humidity (x_A) at the evaporator outlet (A) is determined for the estimation of the actual frost formation.
3. A method in accordance with claim 2,
   characterized in that
   at least the environmental temperature (Tu) and the air humidity (rFu) of the environment (U) are taken into account for the determination of the air humidity (x_E) at the evaporator inlet (E).
4. A method in accordance with one of the claims 2 or 3,
   characterized in that
   the determination of the air humidity (x_E) at the evaporator inlet (E) takes place in accordance with a mass mixing rule, with at least the temperature (T_E) at the evaporator inlet (E) and the temperature (T_A) at the evaporator outlet or the temperature (Tv) at the outlet additionally being taken into account.
5. A method in accordance with claim 4,
   characterized in that
   the mass mixing rule takes account of an admixing of environmental air (5) into a cooling air flow (4) of the refrigeration equipment.
6. A method in accordance with any one of the claims 2 to 5,
   characterized in that
   the temperature (T_V) at the evaporator or the temperature (T_A) at the evaporator outlet (A) is taken into account for the determination of the air humidity (x_A) at the evaporator outlet, with a relative air humidity (rFv) at the evaporator (V) or at the evaporator outlet (A) of substantially 100% being assumed.
7. A method in accordance with any one of the preceding claims,
   characterized in that
   the estimation of the actual frost formation takes place in a manner specific to the air volume or in a manner specific to the air mass.
8. A method in accordance with any one of the preceding claims,
   characterized in that
   the environmental air pressure is additionally taken into account for the estimation of the actual frost formation.
9. A method in accordance with any one of the preceding claims,
   characterized in that
   the nominal operating point of the refrigeration equipment is at least determined

   - by a nominal environmental temperature; or

   - by a nominal air humidity; or

   - by a nominal environmental temperature and a nominal air humidity.
10. A method in accordance with any one of the preceding claims,
    characterized in that
    the nominal operating point of the refrigeration equipment corresponds to the most unfavorable environmental conditions to be expected at the installation site of the refrigeration equipment.
11. A method in accordance with any one of the preceding claims,
    characterized in that
    the nominal frosting rate is a nominal defrosting interval or a frost formation volume or a frost formation mass per unit of time.
12. A method in accordance with any one of the preceding claims,
    characterized in that
    the relationship of an estimated actual frost formation and an estimated nominal frost formation is set into relationship with the nominal frosting rate to determine the next defrosting time or to fix the type of defrosting.
13. A method in accordance with any one of the preceding claims,
    characterized in that
    the estimated actual frost formation and the estimated nominal frost formation are accumulated starting from the last defrost event; or in that the relationship of estimated actual frost formation and estimated nominal frost formation is accumulated from the last defrost event.
14. A method in accordance with any one of the preceding claims,
    characterized in that
    the estimated actual frost formation and the estimated nominal frost formation are standardized using the nominal frosting rate; or in that the relationship of estimated actual frost formation and estimated nominal frost formation are standardized using the nominal frosting rate.
15. A method in accordance with any one of the preceding claims,
    characterized in that
    the relationship of estimated actual frost formation and estimated nominal frost formation is standardized with respect to the nominal frosting rate, with this standardized relationship being compared with a threshold value.
16. A method in accordance with any one of the preceding claims,
    characterized in that
    the relationship of estimated actual frost formation and estimated nominal frost formation is accumulated from the last defrost event, with the accumulated relationship being standardized with respect to the nominal frosting rate, and with this accumulated and standardized relationship being compared with a threshold value.
17. A method in accordance with any one of the preceding claims, characterized in that
    the next defrosting time or the type of defrosting is determined by the condition that the estimated actual frost formation corresponds to the estimated nominal frost formation or exceeds the estimated nominal frost formation.
18. A method in accordance with any one of the preceding claims,
    characterized in that
    a next defrosting time is determined on the basis of the relationship of estimated actual frost formation and estimated nominal frost formation and on the basis of the nominal frosting rate, with said defrosting time differing from a nominal defrosting time which corresponds to the nominal operating point of the refrigeration equipment.
19. A method in accordance with any one of the preceding claims,
    characterized in that
    one of a plurality of predefined defrost types, which effect a defrosting of the evaporator of different degrees, is fixed on the basis of the relationship of estimated actual frost formation and estimated nominal frost formation and on the basis of the nominal frosting rate.
20. A method in accordance with any one of the preceding claims,
    characterized in that
    a selection is made between an energetic and a non-energetic defrost type on the basis of the relationship of estimated actual frost formation and estimated nominal frost formation and on the basis of the nominal frosting rate.

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