Classifications

• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
  • F25D—REFRIGERATORS; COLD ROOMS; ICE-BOXES; COOLING OR FREEZING APPARATUS NOT OTHERWISE PROVIDED FOR
  • F25D21/00—Defrosting; Preventing frosting; Removing condensed or defrost water
  • F25D21/002—Defroster control
  • F25D21/008—Defroster control by timer
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
  • F25B—REFRIGERATION MACHINES, PLANTS OR SYSTEMS; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS
  • F25B2500/00—Problems to be solved
  • F25B2500/29—High ambient temperatures
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
  • F25B—REFRIGERATION MACHINES, PLANTS OR SYSTEMS; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS
  • F25B2500/00—Problems to be solved
  • F25B2500/31—Low ambient temperatures
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
  • F25B—REFRIGERATION MACHINES, PLANTS OR SYSTEMS; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS
  • F25B2700/00—Sensing or detecting of parameters; Sensors therefor
  • F25B2700/21—Temperatures
  • F25B2700/2117—Temperatures of an evaporator
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
  • F25D—REFRIGERATORS; COLD ROOMS; ICE-BOXES; COOLING OR FREEZING APPARATUS NOT OTHERWISE PROVIDED FOR
  • F25D2500/00—Problems to be solved
  • F25D2500/04—Calculation of parameters
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
  • F25D—REFRIGERATORS; COLD ROOMS; ICE-BOXES; COOLING OR FREEZING APPARATUS NOT OTHERWISE PROVIDED FOR
  • F25D2700/00—Means for sensing or measuring; Sensors therefor
  • F25D2700/02—Sensors detecting door opening
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
  • F25D—REFRIGERATORS; COLD ROOMS; ICE-BOXES; COOLING OR FREEZING APPARATUS NOT OTHERWISE PROVIDED FOR
  • F25D2700/00—Means for sensing or measuring; Sensors therefor
  • F25D2700/14—Sensors measuring the temperature outside the refrigerator or freezer

Definitions

• the present invention relates to a controller and a method for controlling a defrost operation in a refrigerator, according to the preamble of claims 1 and 21.
• a controller and a method of this kind are known from DE 29 45 691.
• a controller for defrosting the evaporator of a refrigerator which adaptively controls a defrost operation for melting ice accumulated on the evaporator during a refrigeration period, that is during a period of normal operation of the refrigerator to maintain a food compartment of the refrigerator at a desired temperature. From this document it is known, that when the compressor of the refrigerator is switched off to start a defrost operation, the time taken for the evaporator to reach a preset temperature above 0°C is approximately proportional to the amount of ice accumulated on the evaporator during the preceding refrigeration period.
• the known controller delays a next defrost operation by a factor dependent on the time the evaporator takes to reach the preset temperature during the defrost operation.
• the known controller measures the duration of a defrost time interval until the evaporator has reached the preset defrost temperature. If this duration is less than a predetermined target defrost duration, the known controller extends the next refrigeration period. If the defrost duration is larger than the target defrost duration, the known controller reduces the next refrigeration period and hence advances the beginning of the next defrost period. In this way, the known controller saves energy by carrying out less defrost operations in conditions of low ice formation rate. Similarly, if the ice formation rate is high, the frequency of defrost operations is increased thus ensuring that the evaporator stays largely ice free and hence operates at high efficiency.
• the time taken by the evaporator to reach the preset defrost temperature above 0°C, signaling the end of a defrost operation is influenced not only by the amount of ice on the evaporator, particularly if no additional source of energy is used for accelerating the defrost operation.
• the duration of the defrost time interval until the evaporator has reached the preset defrost temperature also depends on the thermal dispersion through the refrigerator appliance insulation.
• Fig. la shows a typical behavior of the evaporator temperature T over time in a first condition A when the ambient temperature is low, and in a second condition B when the ambient temperature is high. From Fig.
• the thermal dispersion through the appliance insulation is low such that a defrost time interval t ⁇ _ is comparatively large. If the ambient temperature is high, the thermal dispersion through the appliance insulation is high, resulting in a reduced defrost time interval t2 until the evaporator has reached the same defrost temperature as in condition A. In an ambient temperature condition A, the known controller will detect a defrost time interval TQ_ larger than the target defrost duration and will, accordingly, increase the frequency of defrost operations.
• the known controller is furthermore adapted to initiate a defrost immediately after the calculated refrigeration period time limit has expired.
• This has the disadvantage that the duration of the defrost time interval until the evaporator has reached the preset defrost temperature, depends on the temperature of the evaporator at the end of the refrigeration period.
• Fig. lb shows a first situation A that the refrigeration period ends with the evaporator temperature having a comparatively high value.
• Fig. lb furthermore shows a situation B where the refrigeration period ends with the evaporator temperature being at a comparatively low value .
• the total amount of time required for the evaporator to reach the preset defrost temperature differs in both situations A and B.
• situation A the known controller will set the next refrigeration period time limit different than in situation B, due to the timing error in the defrost time interval. This again results in refrigeration periods less than optimum and in an increased energy consumption of the refrigerator.
• the known controller always reacts to past icing conditions on the evaporator.
• the accumulation of ice on the evaporator generally results from opening the refrigerator door. If after a defrost operation a user frequently opens the refrigerator door in the subsequent refrigeration period, the amount of ice actually accumulating on the evaporator may differ substantially from what was detected during the previous defrost operation.
• the known controller is not able to react appropriately to this situation. It cannot prevent that in the course of the current refrigeration period with many door openings a lot of ice accumulates hence lengthening the time taken for the evaporator to reach the preset defrost temperature. This will cause the known controller to shorten the next refrigeration period even if the rate of ice accumulation returns to normal. This results in an increased energy consumption of the refrigerator.
• the thermal dispersion of the refrigerator is detected, and the target defrost duration is adjusted in accordance with the detected thermal dispersion.
• the thermal dispersion of the refrigerator depends on the ambient temperature of the refrigerator. Therefore, it is convenient to detect the thermal dispersion by means of detecting the ambient temperature of the refrigerator.
• the ambient temperature of the refrigerator can be detected by means of an ambient temperature sensor or by means of estimating the ambient temperature on the basis of the rate of rise of evaporator temperature when the compressor is off, or on the basis of a rate of fall of evaporator temperature when the compressor is on, or preferably, on the basis of a ratio of these rates.
• the present invention allows to adapt the duration of the refrigeration periods to the actual amount of ice accumulated on the evaporator essentially independent from the ambient conditions of the refrigerator.
• the present invention therefore improves the energy efficiency of a refrigerator with an adaptive defrost function and enables an adaptive defrost not requiring a heater at the evaporator for accelerating the defrost operation.
• the optimum target defrost time can be determined during development testing of the refrigerator appliance at a number of different ambient temperatures which the appliance can be expected to see during its use. These various target defrost durations in association with various ambient temperatures can be stored in a memory and can be used at the end of each defrost to calculate a new value for the subsequent refrigeration period. Also, fuzzy logic can be used. Alternatively, the target defrost duration can be calculated through a mathematical formula as a function of the detected thermal dispersion. For example, a nominal target defrost duration of 30 minutes at 25°C can be adjusted by a factor proportional to the temperature deviation from the 25°C. For calculating target defrost durations a linear approximation can be sufficient.
• the target defrost duration is calculated as a function of the thermal dispersion with a linear term and/or a quadratic term.
• a controller according to the present invention is preferably implemented using a microprocessor, and said look up table or said calculation routine of the target defrost duration can be stored in the microprocessor read-only memory or similar non volatile storage medium. The resulting programming complexity is well within the capabilities of a low-cost 4-bit or 8-bit microprocessor .
• the controller according to the present invention measures the refrigeration period in terms of compressor running time rather than in terms of total time between defrost operations.
• the amount of ice accumulated on the evaporator can be regarded as approximately proportional to the accumulated running time of the compressor. It is, however, possible to use the total time, that is ON periods and OFF periods of the compressor during the refrigeration operation, for determining the refrigeration period.
• the controller preferably starts a defrost at a fixed evaporator temperature thus ensuring that the defrost operation is always timed between two fixed temperatures.
• the fixed evaporator temperature at which the defrost may be started can vary according to the type of appliance.
• the fixed evaporator temperature at which a defrost is started is preferably programmed into the memory of the microcontroller at the time of manufacture, for example by the use of an EEPROM or other non volatile programmable memory.
• a compartment heater can be switched on.
• the compartment heater can take the form of a resistive heating element or can be the interior light within the food compartment. This will cause the evaporator temperature to rise to the desired preset defrost temperature at which point the defrost is terminated and normal temperature regulation is resumed.
• Fig. la shows time charts for illustrating the dependency of the duration of a defrost time interval on the ambient temperature
• Fig. lb shows time charts for illustrating the dependency of the duration of a defrost time interval on the evaporator temperature at the end of a refrigeration period
• Fig. 2 shows an embodiment of a controller for controlling a defrost operation in a refrigerator in accordance with the present invention
• Fig. 3 shows a second embodiment of a controller for controlling a defrost operation according to the present invention
• Fig. 4a shows a third embodiment of a controller for controlling a defrost operation according to the present invention
• Fig. 4b shows a time chart for illustrating the function of the controller according to the embodiment of
• Fig. 4a; and Fig. 5 shows a fourth embodiment of a controller for controlling a defrost operation according to the present invention.
• Fig. 2 shows a first embodiment of a controller for controlling a defrost operation in a refrigerator in accordance with the present invention.
• Reference numeral 1 in Fig. 2 denotes the controller.
• Reference numeral 2 denotes an evaporator connected via pipe means 3a and 3b to a compressor 3 for circulating cooling fluid through the evaporator 2 to achieve a cooling effect.
• Reference numeral 22 denotes a temperature sensor mounted in thermal contact with the evaporator 2.
• Reference numeral 4 denotes a refrigeration controller for performing normal temperature regulation inside a food compartment of the refrigerator. The refrigeration controller 4 receives an input from evaporator temperature sensor 22 and controls the operation of compressor 3.
• This refrigeration controller can be any kind of temperature controller, for instance a well-known 2 -point controller which keeps the evaporator temperature during a refrigeration period between a low temperature threshold and a high temperature threshold.
• Reference numeral 5 denotes a user-adjustable temperature dial for setting a desired temperature in the food compartment.
• Reference numeral 6 denotes a timer means for inhibiting normal temperature regulation of the refrigeration controller 4 after expiry of a refrigeration period time limit.
• the timer means 6 has a trigger input for triggering the timer. It furthermore has an input for setting a value for the refrigeration period time limit. After the timer has been triggered through its trigger input, it will output an inhibit signal to the refrigeration controller 4 after expiry of the set refrigeration period time limit.
• the timer has a trigger input for triggering the timer. It furthermore has an input for setting a value for the refrigeration period time limit. After the timer has been triggered through its trigger input, it will output an inhibit signal to the refrigeration controller 4 after expiry of the set refrigeration period
• the timer 6 receives from the refrigeration controller an indication on the operating state of the compressor.
• Reference numeral 7 denotes a unit for measuring a defrost duration.
• Unit 7 receives an input from evaporator temperature sensor 22. It furthermore receives a preset defrost temperature value. It also receives an input from timer 6 indicating when a refrigeration period time limit has been reached and a defrost operation starts.
• Unit 7 for measuring a defrost duration begins a time measurement whenever this indication has been received from timer 6.
• Unit 7 ends the measurement of the defrost time interval when the temperature measured by sensor 22 at the evaporator has reached the preset defrost temperature.
• Comparator 8a compares the actual defrost duration measured by unit 7 with a target defrost duration and outputs a difference between the actual defrost duration and the target defrost duration to a unit 8b which calculates a new refrigeration period time limit based on the deviation of the actual defrost duration from the target defrost duration. The calculated time limit in turn is input into timer 6 for setting the next refrigeration period time limit.
• Reference numeral 9 denotes a means for detecting an ambient temperature of the refrigerator.
• the ambient temperature detected by unit 9 is input into a unit 10 for determining a target defrost duration on the basis of the detected ambient temperature.
• the target defrost duration thus determined is input into comparator 8a.
• the ambient temperature detector 9 is a temperature sensor mounted at the refrigerator in a location suitable for measuring the ambient temperature.
• Unit 10 for determining a target defrost duration receives the detected ambient temperature and converts the detected temperature into a digital value. This digital temperature value is then used by unit 10 to look up a table storing target defrost duration values for a variety of different ambient temperature values.
• the target defrost duration looked up in the table of unit 10 is either input into comparator 8a for digitally determining a deviation between the actual defrost duration and the target defrost duration, or unit 10 converts a value read from its look up table into an analogue value for further processing in comparator 8a.
• the controller 1 of this embodiment is implemented in digital technology by means of programming the functions of the timer 6, the unit 7 for measuring the defrost duration, the comparator 8a, the unit 8b for calculating a new refrigeration time limit and the unit 10 into a microcontroller.
• the microcontroller preferably has A/D conversion means on the chip, for processing the analogue signals provided by temperature sensor 22 and the temperature sensor 9 for detecting the ambient temperature .
• the microcontroller furthermore implements the control functions of refrigeration controller 4.
• Fig. 3 shows a second embodiment of a controller for controlling a defrost operation of a refrigerator in accordance with the present invention.
• the embodiment of Fig. 3 differs from the embodiment of Fig. 2 in the ambient temperature detection means 9.
• the ambient temperature detection means 9 receives a signal from temperature sensor 22 on the evaporator 2. It furthermore receives a signal from refrigeration controller 4 indicating the operating state of the compressor, that is whether the compressor is currently in the ON state or in the OFF state.
• the embodiment of Fig. 3 is advantageous in that the ambient temperature detection means 9 does not require a separate temperature sensor for sensing the ambient temperature. Rather, the ambient temperature detection means 9 estimates thermal dispersion of the refrigerator based on the temperature curve of the evaporator temperature 22.
• the ambient temperature detection means 9 calculates a rate of rise of evaporator temperature when the compressor is off. It furthermore calculates a rate of fall of evaporator temperature when the compressor is on. It then calculates the ratio of said rate of rise to said rate of fall. This ratio indicates the thermal dispersion of the refrigerator largely independent of food load variations in the food compartment of the refrigerator.
• the thermal dispersion ratio is preferably calculated by unit 9 on a continuous basis in the course of every refrigeration period.
• unit 9 provides a new value for the thermal dispersion ratio to unit 10.
• the thermal dispersion detection means 9 In order to avoid an adverse influence of disturbing factors like frequent or long door openings or the introduction of extremely or cold goods into the food compartment, onto the evaluation of the thermal dispersion, it is advantageous to provide the thermal dispersion detection means 9 with means for detecting whether said calculated thermal dispersion ratio is stable or not.
• unit 9 can be provided with memory locations for storing a predetermined number of preceding thermal dispersion ratios, and with means for investigating whether the stored thermal dispersion ratios differ from each other by more than a predetermined threshold variance.
• unit 10 Each time a new thermal dispersion ratio is calculated by unit 9, the oldest thermal dispersion ratio in said memory locations is replaced by the newest. If the differences between the stored thermal dispersion ratios is smaller than said predetermined variance threshold, the detected thermal dispersion ratio will then be used by unit 10 for calculating an updated target defrost duration on the basis of the detected ambient conditions. Otherwise, unit 10 will maintain the target defrost duration output to unit 8a unchanged until the conditions for detecting a thermal dispersion ratio have been stabilized, that is, until all thermal dispersion ratios stored in unit 9 differ from each other by no more than said predetermined variance threshold.
• Unit 8b for determining an updated refrigeration period time limit based on a deviation of the actual defrost duration from the target defrost duration given by unit 10, can be provided to increase the refrigeration period time limit each time the actual defrost duration is smaller than the target defrost duration, and to decrease the refrigeration period time limit each time the actual defrost duration has been found to be larger than the target defrost duration.
• unit 8b may contain a look up table storing a plurality of refrigeration period time limits in association with respective defrost duration deviation values.
• Unit 7 for measuring the actual defrost duration comprises a time counter the operation of which is started when receiving an end of refrigeration period signal from timer 6.
• the time counter stops counting when a comparator for comparing the actual evaporator temperature from temperature sensor 22 with a preset defrost temperature value indicates that the evaporator temperature 22 has reached the preset defrost temperature.
• unit 7 outputs the end of defrost signal to trigger timer 6 for starting a new refrigeration period.
• Unit 7 then furthermore outputs the actual defrost duration value to comparator 8a.
• Fig. 4a shows a third embodiment of a controller according to the present invention. This embodiment differs from the embodiment shown in Fig. 2 in the provision of a unit 11 for updating the refrigeration period time limit set in timer 6. Unit 11 for updating the time limit of timer 6 receives an input from a door position sensor 12. All remaining elements of Fig. 4a are identical with the corresponding elements of Fig. 2 and are denoted with the same reference numerals, such that their description need not be repeated.
• Fig. 4a addresses the problem that the refrigeration period time limit calculated in unit 8b and set in timer 6, has been determined on the basis of the duration of the preceding defrost operation. If in the course of the refrigeration period there are frequent or long lasting door openings, the time limit for the refrigeration period calculated by unit 8b is no longer up to date.
• Unit 11 for updating the refrigeration period time limit counts the total time for which the door of the food compartment of the refrigerator is open during the refrigeration period. The total time count is received by timer 6, and the timer 6 subtracts the current total time count from the current period of time left until the refrigeration period time limit is reached. As soon as the updated refrigeration period time limit has been reached, the defrost period starts and the timer means 6 outputs a signal to unit 11 to reset the open door time counter.
• the controller according to this embodiment is able to reduce the refrigeration period based on an estimation of additional ice accumulation due to door openings without waiting for the next measurement of a defrost duration. A controller according to this embodiment can, therefore, quickly cope with changes in the actual icing conditions of the evaporator and keep the defrost operation of the refrigerator energy-efficient .
• unit 11 can be provided to count the number of door openings during the refrigeration period. This alternative is, however, inferior to counting the total door open time period in that it will not be able to appropriately react to the situation that the door of the food compartment is opened and left open. While the embodiment of Fig. 4a includes a unit 10 for calculating a target defrost duration and a unit 9 for detecting an ambient temperature of the refrigerator, the units 9 and 10 are not mandatory for solving the problem, to enable to controller for controlling a defrost operation of a refrigerator to quickly react to changes of the icing conditions of the evaporator due to frequent or long lasting door openings.
• Fig. 4b is a time chart illustrating the behavior of the evaporator temperature and the sequence of refrigeration periods and defrost periods according to the third embodiment shown in Fig. 4a.
• the time chart of Fig. 4b shows a refrigeration period n and the evaporator temperature T in the course of that refrigeration period n. No door openings take place during that period n.
• an n tn defrost operation takes place.
• the measured duration of the n fc k defrost period influences the duration of the subsequent refrigeration period (n+1) .
• door openings take place, as indicated in the bottom part of Fig. 4b.
• Updating the refrigeration period time limit on the basis of door openings furthermore has the effect that also the (n+l) st defrost duration is not significantly different from the n tn defrost duration since the increased accumulation of ice on the evaporator due to the door of the refrigerator having been open, is compensated by means of advancing the next defrost operation, such that both in refrigeration period n and in refrigeration period n+1 the peak amount of ice accumulated on the evaporator is substantially the same.
• Fig. 5 shows a fourth embodiment of a controller for controlling a defrost operation according to the present invention.
• the embodiment of Fig. 5 differs from the embodiment of Fig. 2 in the provision of a time-out unit 13 in the path of the inhibit signal output by timer 6.
• This embodiment addresses the problem that if the refrigerator appliance is operated in an ambient temperature lower than the preset defrost temperature, the defrost operation will not terminate because the evaporator 2 will possibly not reach the preset defrost temperature which is used by unit 7 for measuring the defrost duration.
• unit 7 Under the condition that the ambient temperature of the refrigerator is lower than the preset defrost temperature, unit 7 will thus not indicate an end of the defrost period and timer 6 will not be retriggered to start a new refrigeration period.
• the embodiment of Fig. 5 outputs the inhibit signal of timer 6 to time-out unit 13.
• the time-out unit 13 passes the inhibit signal onto the refrigeration controller 4 as long as a preset time-out interval for unit 13 beginning with the arrival of the inhibit signal has not been exceeded.
• Fig. 5 While the embodiment of Fig. 5 has been described including the units 9 and 10 for detecting an ambient temperature of the refrigerator and for calculating a target defrost duration on the basis of the thermal dispersion of the refrigerator, these units are not mandatory for solving the problem addressed by the embodiment of Fig. 5. For solving this problem it is, therefore, possible to replace in Fig. 5 the unit 9 for detecting an ambient temperature and the unit 10 for determining a target defrost duration by a means for providing a preset target defrost duration.

Landscapes

• Engineering & Computer Science (AREA)
• Chemical & Material Sciences (AREA)
• Combustion & Propulsion (AREA)
• Physics & Mathematics (AREA)
• Mechanical Engineering (AREA)
• Thermal Sciences (AREA)
• General Engineering & Computer Science (AREA)
• Defrosting Systems (AREA)

Priority Applications (1)

Applications Claiming Priority (4)

Publications (1)

Family

ID=8237551

Family Applications (2)

Family Applications Before (1)

Country Status (5)

Families Citing this family (4)

Family Cites Families (12)

• 1999
  • 1999-02-19 ES ES99102741T patent/ES2236975T3/es not_active Expired - Lifetime
  • 1999-02-19 EP EP19990102741 patent/EP1030137B1/de not_active Expired - Lifetime
  • 1999-02-19 DE DE1999623531 patent/DE69923531T2/de not_active Expired - Fee Related
• 2000
  • 2000-02-18 EP EP00912486A patent/EP1157245A1/de not_active Withdrawn
  • 2000-02-18 AU AU34242/00A patent/AU3424200A/en not_active Abandoned
  • 2000-02-18 WO PCT/EP2000/001364 patent/WO2000049350A1/en not_active Application Discontinuation

Non-Patent Citations (1)

Also Published As

Similar Documents

Legal Events