METHOD FOR CONTROLLING DEFROST OPERATION OF A REFRIGERATION SYSTEM

Abstract

The invention relates to a method for controlling a refrigeration system by establishing a defrost period during an initial defrost period. One or more compressors of the refrigeration system are monitored to establish if the one or more compressors are running, and a parameter representative of the one or more compressors running is monitored. The monitoring establishes at least one parameter limit value representative of whether a defrost period or a non-defrost period is to be initiated. The invention also relates to a method for controlling a refrigeration system subsequent to an electrical power interruption. The invention also relates to control units for applying one or both of the methods according to the invention, and to a refrigeration system having one or more control units controlling the refrigeration system according to one or both of the methods.

Claims

1. A method for controlling a refrigeration system, said method comprising the steps of: establishing a defrost period, and when one or more compressors of the refrigeration system is running, monitoring a parameter representative of the one or more compressors running, said monitoring establishing at least one parameter limit value representative of whether a defrost period or a non-defrost period is to be initiated, and if the parameter being monitored is above a parameter limit value, determining that a defrost period is not to be initiated subsequent to the compressor running, if the parameter being monitored is below a parameter limit value, determining that a defrost period is to be initiated subsequent to the compressor running.

2. The method according to claim 1, wherein the parameter limit value, when monitoring if the parameter being monitored is above a parameter limit, is the same as the parameter limit value, when monitoring if the parameter being monitored is below a parameter limit, so that no value gap is present between former and the latter parameter.

3. The method according to claim 1, wherein the parameter limit value, when monitoring if the parameter being monitored is above a parameter limit value, is greater than the parameter limit value, when monitoring if the parameter being monitored is below a parameter limit value, so that a value gap is present between former and the latter parameter value.

4. The method according to claim 1, wherein the at least one parameter value being representative of the compressor running being a number of compressor cycles, and if the number of compressor cycles is above a number limit, determining that a defrost period is not to be initiated subsequent to the compressor running, and if the number of compressor cycles is below a number limit, determining that a defrost period is to be initiated subsequent to the compressor running.

5. The method according to claim 4, the upper limit of compressor cycles being between 2 cycles and 100 cycles, possibly being between 2 cycles and 50 cycles, possibly being 20 cycles.

6. The method according to claim 1, wherein the at least one parameter value being representative of the compressor running is a temperature of the compressor, and if the temperature of the compressor is above a temperature limit, determining that a defrost period is not to be initiated subsequent to the compressor running, and if the number of compressor cycles is below a temperature limit, determining that a defrost period is to be initiated subsequent to the compressor running.

7. The method according to claim 1, wherein the at lest one parameter value being representative of the compressor running is electrical power applied to the compressor, and if the electrical power applied to the compressor is above a power limit, determining that a defrost period is not to be initiated subsequent to the compressor running, and if the electrical power applied to the compressor is below a power limit, determining that a defrost period is to be initiated subsequent to the compressor running.

8. A control unit for controlling a refrigeration system, said control unit capable of controlling the refrigeration system according to claim 1.

9. A refrigeration system comprising at least one control unit, said at least one control unit being a control unit according to claim 8.

10. The method according to claim 2, wherein the at least one parameter value being representative of the compressor running being a number of compressor cycles, and if the number of compressor cycles is above a number limit, determining that a defrost period is not to be initiated subsequent to the compressor running, and if the number of compressor cycles is below a number limit, determining that a defrost period is to be initiated subsequent to the compressor running.

11. The method according to claim 3, wherein the at least one parameter value being representative of the compressor running being a number of compressor cycles, and if the number of compressor cycles is above a number limit, determining that a defrost period is not to be initiated subsequent to the compressor running, and if the number of compressor cycles is below a number limit, determining that a defrost period is to be initiated subsequent to the compressor running.

12. The method according to claim 2, wherein the at least one parameter value being representative of the compressor running is a temperature of the compressor, and if the temperature of the compressor is above a temperature limit, determining that a defrost period is not to be initiated subsequent to the compressor running, and if the number of compressor cycles is below a temperature limit, determining that a defrost period is to be initiated subsequent to the compressor running.

13. The method according to claim 3, wherein the at least one parameter value being representative of the compressor running is a temperature of the compressor, and if the temperature of the compressor is above a temperature limit, determining that a defrost period is not to be initiated subsequent to the compressor running, and if the number of compressor cycles is below a temperature limit, determining that a defrost period is to be initiated subsequent to the compressor running.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0031] The invention will hereafter be described with reference to the drawings where

[0032] FIG. 1 is a chart showing control of a refrigeration system during so-called initial defrost,

[0033] FIG. 2 is a chart showing one mode of operation of a refrigeration system after a power interruption, and

[0034] FIG. 3 is a chart showing another mode of operation of a refrigeration system after a power interruption,

[0035] FIG. 4 is a chart showing an example of a mode of control of a refrigeration system after a power loss of certain duration and at a certain time of day.

DETAILED DESCRIPTION

[0036] The figures show possible relationships between time along the x-axis and temperature along the y-axis. There are different intervals along the x-axis, each interval representing a certain mode of operation of the refrigeration system.

[0037] FIG. 1 shows a chart of a mode of control during a so-called initial defrost. An initial defrost interval is used for factory testing to test that the defrost circuit works as intended. Initial defrost can be programmed to one of the following modes of control: Expire after a number of compressor cycles (initial defrost duration at a number between, e.g., 1 and 99 cycles, possibly between 1 and 998 cycles), or number of compressor cycles not used as a mode of control (initial defrost duration 0 cycles), or number of compressor cycles always used (initial defrost duration, of e.g., 100 cycles, possibly of 999 cycles)

[0038] A defrost counter is restored after power-loss, so that during normal operation the initial defrost is not needed, and in case of poor power-quality, it can lead to too often defrosting. After the initial defrost, the next defrost interval will be either a minimum defrost interval or a pull-down defrost interval.

[0039] FIG. 2 is a chart of one mode of control after power interruption, marked by a hatched rectangle, resulting in an intermediate power-loss. After a power-interruption, cabinet or evaporator temperature of the refrigeration system is measured and compared with a defrost reset temperature. If the temperature of the cabinet or evaporator is higher than the defrost reset temperature, it can be assumed that the evaporator is free of ice and no defrost is needed. A defrost counter is therefore reset, next defrost will happen after the minimum defrost interval, or if the control enters pull-down mode, after the pull-down defrost interval. Cut-out temperature is the temperature at which the refrigeration system is cut-out, i.e., where the refrigeration temperature as initially set is reached. Defrost terminate temperature is the temperature, where defrost is terminated, i.e., where it can be assumed that any ice formed on the evaporator has melted.

[0040] FIG. 3 is a chart of another mode of control after power interruption, marked by a hatched rectangle, resulting in an intermediate power-loss. After a power-interruption, cabinet or evaporator temperature of the refrigeration system is measured and compared with a defrost reset temperature. If the temperature measure is lower than the defrost reset temperature, there is a risk of ice having formed on the evaporator, and a defrost counter will be restored and next defrost will happen after the accumulated time before and after the power-interruption. Cut-out temperature is the temperature at which the refrigeration system is cut-out, i.e., where the refrigeration temperature as initially set is reached. Defrost terminate temperature is the temperature, where defrost is terminated, i.e., where it can be assumed that any ice formed on the evaporator has melted.

[0041] The mode of operation shown in FIG. 2 and the mode of operation shown in FIG. 3, respectively, may be implemented into a control unit for each of the modes of control. Alternatively and preferably, the mode of operation shown in FIG. 2 and the mode of operation shown in FIG. 3, respectively, may be implemented into a control unit common for both of the modes of control. The one or more control units may be provided as part of a refrigeration system thus being controlled according to one, or according to both, of the modes of control as shown in FIG. 2 and FIG. 3.

[0042] FIG. 4 is a specific example related to the general description referred to in FIG. 2 and FIG. 3. A first interval has a duration of approximately 7 hours, extending from time zero hours to time 7 hours. The first interval is a normal mode of operation of the refrigeration system with sequential active cooling and non-active cooling. Active cooling is where the compressor is running, illustrated by the temperature decreasing until a certain lower temperature limit. The mode of operation switches to non-active cooling, when the lower temperature limit is reached. Non-active cooling is where the compressor is not running, illustrated by the temperature increasing to a certain upper temperature limit. When the certain upper temperature limit during normal mode of operation is reached, the mode of operation switches to active cooling until a certain lower temperature limit is reached and so on, i.e., a sequential active and non-active cooling of a normal mode of operation.

[0043] The upper temperature limit and the lower temperature limit during normal mode of operation is not the upper and lower temperature limits being part of the scope of the invention. Accordingly, the mode of operation shown form time zero hours to time 7 hours is not within the scope of the method according to the invention.

[0044] A second interval has a duration of approximately two hours, extending form time 7 hours to time 9 hours. The second interval is a defrost period, where control of the refrigeration system is such that the temperature is allowed to increase and to pass the upper temperature limit of the first interval. The second interval is an interval of non-active cooling. During the second interval, ice having formed on the evaporator of the refrigeration system is melting. When the temperature has increased to e certain increased temperature limit, the compressor is started to initiate active cooling.

[0045] A third interval is subsequent to the second interval, i.e., subsequent to the defrost period. The third interval is an interval where active cooling is performed, and the third interval has a duration of approximately 1 hour, from time 9 hours to time 10 hours.

[0046] The second interval and the third interval are also intervals of normal mode of operation. Accordingly, the mode of operation shown from time 7 hours to time 10 hours is not within the scope of the method according to the invention.

[0047] A fourth interval, subsequent to the third interval, is similar to the first interval. However, the fourth interval is disrupted by a loss of electrical power, said loss of electrical power happening at approximately time 13 hours.

[0048] A fifth interval, subsequent to the fourth interval, is an interval where loss of electrical power is prevailing. The refrigeration system has no electrical power to run the compressor, and therefore the temperature is constantly increasing during the fifth interval. In the diagram shown, the fifth interval has a duration of approximately 4 hours, from time 14 hours to time 17 hours. At time 17 hours, electrical power is re-applied and the compressor may run again to provide cooling.

[0049] A sixth interval, subsequent to the fifth interval, is where the compressor is running again, after electrical power has been re-applied. Cooling is performed to a lower temperature limit similar to the lower temperature limit as set in the first interval. The fifth interval has a duration of approximately 3 hours, from time 17 hours to time 20 hours. When the compressor has been running for approximately 3 hours, the temperature has decreased to a lower temperature limit similar to the lower temperature limit as set in the first interval.

[0050] A seventh interval, subsequent to the sixth interval, is where normal mode of operation is re-established, the seventh interval being similar to the first interval. The seventh interval ends at 24 hours, i.e., after a full day, and the seventh interval leads to start of the first interval.

[0051] As mentioned, the seventh interval is an interval of normal mode of operation. Accordingly, the mode of operation shown from time 20 hours to time 24 hours is not within the scope of the method according to the invention.

[0052] An upper temperature limit, X, and set in accordance to the method of the invention, is set between the fifth interval and the seventh interval, i.e., the upper temperature limit, X, is set between the interval where loss of electrical power is prevailing and the interval where electrical power is re-applied to the refrigeration system.

[0053] If the temperature during the fifth interval increases to a temperature only below the upper temperature limit, X, the control of the defrost mode of operation as applicable during the first interval is saved for future intervals of normal mode of operation. Saving the defrost timer is possible because the temperature increase during the fifth interval is only below the upper temperature limit, X.

[0054] Therefore, the defrost timer as applicable during the first interval may be used in intervals subsequent to the fifth interval and sixth interval, although the compressor may run for a prolonged period of time during the sixth interval, compared to the period of time when the compressor is running during active cooling in the first interval. The prolonged period of time is for decreasing the temperature to a lower temperature limit similar to that of the first interval.

[0055] If the temperature during the fifth interval increases to a temperature above the upper temperature limit, X, the control of the defrost mode of operation as applicable during the first interval cannot be used for future intervals of normal mode of operation. Therefore, the defrost timer has to be reset to a timer condition similar to a first start-up of the refrigeration system, because the temperature increase during the fifth interval is above the upper temperature limit, X.

[0056] As mentioned, the defrost timer as applicable during the first interval cannot be used for intervals subsequent to the fifth interval and sixth interval, because the compressor will run for a period of time resembling a first start of the refrigeration system. In order to decrease the temperature to a lower temperature limit similar to that of the first interval, the defrost timer applicable in the first interval must be overruled by the control of the refrigeration system, allowing the compressor to run for a much longer prolonged period of time, compared to the period of time when the compressor is running during active cooling in the first interval. The even longer prolonged period of time is a period of time more resembling the compressor running like during first start of the refrigeration system than a period of time where the compressor is running like during active cooling in the first interval. First start of the refrigeration system will normally take place form a temperature above the upper temperature limit X.

[0057] Although various embodiments of the present invention have been described and shown, the invention is not restricted thereto, but may also be embodied in other ways within the scope of the subject-matter defined in the following claims.