ADAPTIVE CONTROL METHOD FOR REFRIGERATION SYSTEMS

Abstract

ADAPTIVE CONTROL PROCEDURE FOR REFRIGERATION SYSTEMS which comprises the detection of the frost level in the evaporator by means of a calculation method of NTU rate, allowing to define: the most suitable defrosting time, the energization of the drainage resistors and the adaptive management of the evaporator fan combining different operating modes. An ice-free mode which uses only the cooling capacity of the refrigerant, and different modes with ice which benefits from the latent heat stored in the ice to produce energy savings, depending on the level of frost in the evaporator. For calculating the NTU rate, it uses the evaporator as a reference when it is dry at the beginning, and when the cooling system is in operation, it calculates the NTU rate with a variable frequency operating mode depending on the evaporator performance or level of ice and its comparison with the cited reference.

Claims

1. An adaptive control method for refrigeration systems which, being of the type which manages the fans according to the level of frost in the evaporator, comprising the detection of the level of frost in the evaporator using an NTU rate calculation method, and the adaptive management of the evaporator fan combining different operating modes, comprising an ice-free mode, where solely the refrigeration capacity of the coolant is employed, and different iced modes where the latent heat stored in the ice is employed to provide energy savings, depending on the level of frost in the evaporator; and wherein the method comprises the performance of said detection of the level of frost by by obtaining a dimensionless coefficient fc of the relative level of frost in the evaporator and the monitoring of the temporal evolution of the same, where the method comprises the obtaining of said dimensionless coefficient fc of the relative level of frost in the evaporator: from the calculation of a first value or reference value of the NTU rate, performed when the evaporator is dry at the commencement, with no frost, and from the calculation of second values of the NTU rate, when the refrigeration system is in operation during one of said iced modes of fan management, performing said calculation repeatedly over time, with a non-constant frequency of repetitions which varies depending on the performance of the evaporator or on the level of ice in the same; where said dimensionless coefficient fc of the relative level of frost in the evaporator relates, in a comparative manner, the second values with the first value of the NTU rate.

2. The method of claim 1, wherein fc=UA.sub.ice/UA.sub.dry, where U is a global heat transfer coefficient and A is the area of heat transfer, and they are obtained from the calculation of the aforementioned first and second values of the NTU rate, according to the following expression:
UA=NTU.Math.({dot over (m)}Cp)air where {dot over (m)} is the mass flow of air crossing the fins of the evaporator and Cp is the specific heat of the air, and NTU is obtained from the following expression:
=1e.sup.NTU where is the efficiency of the heat exchange and is defined as .sub.dry to calculate the first value of the NTU rate and as .sub.ice to calculate the second values of the NTU rate, which are in turn related according to the following expression:
.sub.dry.Math.(T.sub.airT.sub.evap).sup.dry=.sub.ice.Math.(T.sub.airT.sub.evap).sup.ice where (T.sub.airT.sub.evap).sup.dry is the temperature difference between the air in the refrigeration chamber and the evaporator when there is no frost/ice in the latter, and (T.sub.airT.sub.evap).sup.ice is the temperature difference between the air in the refrigeration chamber and the evaporator when there is frost/ice in the latter, and where the method comprises the measurement of the values of said temperatures.

3. The method of claim 1, wherein in order to decide on the mode of operation and as to whether a defrosting process is necessary in real time, the value of the fc coefficient is compared with regard to a dimensionless reference performance coefficient fs, indicating that a defrost is necessary, where said value of fs is adapted, subsequent to said comparison of the values of fc with fs, being updated in accordance with the time required for the performance of the defrost by implementing one of said iced operating modes, on the basis of said fc value compared, the first fs value being a default value.

4. The method of claim 3, wherein the method contemplates the existence of a safety indicator to halt the refrigeration system and activate the defrosting process, in the event that this might be the reason for a malfunction.

5. The method of claim 3, wherein thanks to the capacity of predicting the time for defrosting on the basis of the temporal evolution of the fc coefficient, the method contemplates that the heating system for drainage of the evaporator should only be activated prior to defrosting, while it is maintained inactive during the periods where defrosting is not in operation or is not foreseen in the short term.

6. The method of claim 3, wherein the method comprises the following stages: a first stage where the default value of the fs coefficient is predetermined, as is the maximum defrosting time (tmax); a second stage where the evaporator is defrosted; a third stage where a standard operating mode of the fan is executed; a fourth stage, where a measurement operation mode is executed; a fifth stage, where the calculation of said first value or reference value of the NTU rate is performed with the evaporator dry, with no frost; a sixth stage, where an initial/post-defrosting ice-free operating mode of the refrigeration system is executed, wherein solely the refrigeration capacity of the coolant is used; a seventh stage, where the calculation of one of the second values of the NTU rate is carried out, and also obtaining the values of the fc coefficient of the relative level of frost from said second value and said first value; an eighth stage, where the calculation of the value of said fc coefficient is carried out, with three possible options for the following stage: a ninth stage, where the recurrent ice-free mode is executed; that is, using solely the refrigeration capacity of the coolant; subsequently returning to stage where, once again, the calculation of one of the second values of the NTU rate is carried out, to obtain a new value for the fc coefficient of the relative level of frost; a tenth stage, where the appropriate iced operation mode is executed, depending on the value of said fc coefficient; that is, one of the different iced modes is selected, where the latent heat stored in the ice of the frost is employed to provide energy savings; subsequently returning to stage where, once again, the calculation of one of the second values of the NTU rate is carried out, to obtain the new fc coefficient of the level of frost; an eleventh stage of thawing the evaporator; and a twelfth stage, the performance of which is subject to the performance of the eleventh stage, of the adaptation/updating of the value of the fs coefficient of the level of frost, subsequently returning to stage, wherein the initial/post-defrosting ice-free fan operating mode is executed once again.

7. The method of claim 1, wherein the method comprises obtaining said dimensionless coefficient fc of the relative level of frost in the evaporator when the evaporator is cooling the air within the refrigeration chamber of the refrigeration system via evaporation of the coolant circulating within the same.

8. An adaptive control method for refrigeration systems which, being of the type which manages the fans according to the level of frost in the evaporator, comprising the detection of the level of frost in the evaporator by a calculation method of a FVT indicator representing the facility to the variation of temperature of the evaporator, according to the following expression: $F.Math..Math.V.Math..Math.T=\frac{\mathrm{Te\_end}-\mathrm{Te\_ini}}{\mathrm{timestep}.Math..Math.{\mathrm{abs}\left(\left(T_{\mathrm{evap}}-T_{\mathrm{air}}\right)\right)}_i}$ where (Te_endTe_ini) is the difference between the temperatures of the evaporator at the end and at the commencement, respectively, of an evaporator heating process, (T.sub.evapT.sub.air) are the successive samples of the thermal gradient between the temperature of the evaporator T.sub.evap and that of the refrigeration chamber of the refrigeration system T.sub.air occurring during said heating process, measured with each timestep or time in seconds between thermal gradient samples i.

9. The method of claim 8, wherein the method comprises the performance of said detection of the level of frost by obtaining a dimensionless coefficient fc of the relative level of frost in the evaporator and the monitoring of the temporal evolution of the same, where the method comprises obtaining said dimensionless coefficient fc of the relative level of frost in the evaporator the relationship FVT.sub.ice/FVT.sub.dry, where FVT.sub.ice includes the values of the FVT indicator obtained when there is frost in the evaporator, and FVT.sub.dry the values of the same when there is no frost in the evaporator.

Description

DESCRIPTION OF THE DRAWINGS

[0075] As a complement to the description made herein, and for a better understanding of the characteristics of the invention, a drawing is attached to the present specification as an integral part thereof, wherein, by way of illustration but not limitation, the following is portrayed:

[0076] FIG. 1 portrays a flow diagram of the adaptive control method for refrigeration systems which is the object of the present invention, wherein the stages comprised by the method can be observed.

PREFERRED EMBODIMENT OF THE INVENTION

[0077] In view of the described and unique FIG. 1, and in accordance with the numbering adopted, it can be seen how the adaptive control method for refrigeration systems of the present invention contemplates the following stages in the order shown: [0078] A first stage (1) wherein the default value of the fs coefficient is predetermined, as is the maximum defrosting time (tmax), which comprises reasonable values for the defrosting of an evaporator of a refrigeration chamber (between 45 and 5 min). For example, a default value of tmax=18 minutes is assigned, this being parametrizable. The fs coefficient is adjusted until the defrosting time reaches the value of tmax, which is adjustable (parametrizable); [0079] A second stage (2) where the evaporator is defrosted; [0080] A third stage (3) where a standard operating mode of the fan is executed, during a pre-set time or a time typical of the normal operation of the regulation (control) of the cooling generation within the refrigeration chamber. Said time is necessary for the stabilisation of temperatures during the start-up of the refrigeration chamber. It is generally set at half an hour, although it is parametrizable; [0081] A fourth stage (4), where the measurement operation mode is executed, during a pre-set time; [0082] A fifth stage (5), where the calculation of said first value or reference value of the NTU rate is performed with the evaporator dry, with no frost; a calculation performed at the commencement of the regulation of cooling, subsequent to a defrost and always subsequent to the pre-set time. Thus, it is ensured that the evaporator is frost-free (thanks to the defrost) but the chamber is under the thermal conditions stabilized to its normal application (thanks to the pre-set time); [0083] A sixth stage (6), where an initial/post-defrosting ice-free operating mode of the refrigeration system is executed, wherein solely the refrigeration capacity of the coolant is used; [0084] A seventh stage (7), where the calculation of one of the second values of the NTU rate is carried out, and also the obtaining of the values of the fc coefficient of the relative level of frost from said second value and said first value; [0085] An eighth stage (8), where the calculation of the value of said fc coefficient is carried out, with three possible options for the following stage: [0086] A ninth stage (9), where if the evaporator is frost-free, the recurrent ice-free mode is executed; that is, using solely the refrigeration capacity of the coolant; subsequently returning to stage (7) where, once again, the calculation of one of the second values of the NTU rate is carried out, to obtain a new value of the fc coefficient of the relative level of frost; [0087] A tenth stage (10), where if the evaporator has a little frost, the appropriate iced operation mode is executed, depending on the value of said fc coefficient; that is, one of the different iced modes is selected, where the latent heat stored in the ice of the frost is employed to provide energy savings; subsequently returning to stage (7) where, once again, the calculation of one of the second values of the NTU rate is carried out, to obtain the new fc coefficient of the level of frost; [0088] An eleventh stage (11) of thawing the evaporator, should this have excessive frost; and [0089] A twelfth stage (12), the performance of which is subject to the performance of the eleventh stage (11), in which the value of the fs coefficient of the level of frost is assessed and, if deemed necessary, its value is adapted/updated, subsequently returning to stage (6) wherein the initial/post-defrosting ice-free fan operating mode is executed once again.

[0090] It should be noted that in order to perform said operating stages, the adaptive control method contemplates the input into the system of the following parameters: [0091] Temperature of the evaporator [0092] Temperature of the refrigerated space [0093] Real Time Clock [0094] Compressor ON/OFF signal [0095] Solenoid ON/OFF signal [0096] Defrost ON/OFF signal [0097] Maximum acceptable defrosting time [0098] Initial defrost activation coefficient (fs) [0099] Safety time without defrosting [0100] Hysteresis related to the temperature setpoint of the refrigerated space [0101] Maximum out-of-setpoint acceptable time

[0102] The nature of the present invention having been sufficiently described, as well as the manner of putting it into practice, it is not considered necessary to make the explanation thereof more extensive for any expert skilled in the art to understand its scope and the advantages to be derived therefrom; it is therefore stated that within its essential nature it may be put into practice in other embodiments which may differ in detail from that indicated by way of an example, embodiments which will be equally covered by the protection which is sought, provided that its fundamental principle is not altered, changed or modified.