EP1843111A2 - System und Verfahren zum Bestimmen der von einem Abtauheizer abgegebenen Abtauenergie - Google Patents

System und Verfahren zum Bestimmen der von einem Abtauheizer abgegebenen Abtauenergie Download PDF

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Publication number
EP1843111A2
EP1843111A2 EP07007062A EP07007062A EP1843111A2 EP 1843111 A2 EP1843111 A2 EP 1843111A2 EP 07007062 A EP07007062 A EP 07007062A EP 07007062 A EP07007062 A EP 07007062A EP 1843111 A2 EP1843111 A2 EP 1843111A2
Authority
EP
European Patent Office
Prior art keywords
defrost
defrost heater
amount
sensing element
cycle
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Withdrawn
Application number
EP07007062A
Other languages
English (en)
French (fr)
Inventor
Robert J. Alvord
Leonard W. Jenski
Benjamin N. Lease
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Robertshaw Controls Co
Original Assignee
Robertshaw Controls Co
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Robertshaw Controls Co filed Critical Robertshaw Controls Co
Publication of EP1843111A2 publication Critical patent/EP1843111A2/de
Withdrawn legal-status Critical Current

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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
    • F25D21/06—Removing frost
    • F25D21/08—Removing frost by electric heating
    • 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
    • F25D21/006—Defroster control with electronic control circuits
    • 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
    • F25B2700/15—Power, e.g. by voltage or current
    • 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
    • F25D2600/00—Control issues
    • F25D2600/02—Timing

Definitions

  • the present invention relates generally to defrost heaters for consumer and commercial appliances, and more particularly to defrost cycle control methods to control the defrost cycle in such appliances.
  • Consumer and commercial refrigeration systems typically utilize a compressor driven refrigeration cycle to provide the cooling necessary to maintain the internal temperature of the freezer compartment of a refrigerator or freezer at a particular selected temperature.
  • a damper door is typically utilized to allow some of the cold air from the freezer compartment to flow into the fresh food compartment to maintain the fresh food compartment at a different selected temperature.
  • Such a compressor refrigeration system includes an evaporator positioned within or in close proximity to the freezer compartment. The evaporator is a heat exchanger through which is blown recirculated air within the freezer compartment to reduce the temperature thereof. This heat exchanger is typically a coiled arrangement of refrigeration line with fins connected thereto to increase the surface area and therefore the efficiency of the heat transfer.
  • any moisture in the air in the freezer compartment tends to freeze on the evaporator during operation.
  • This frost build-up on the evaporator reduces the amount of surface area over which the air may be blown. Indeed, if this condition were allowed to continue, the frost would build to ice that would completely block off the air flow paths through the evaporator.
  • the compressor is required to run, potentially continuously, in order to try to maintain the temperature of the freezer compartment at the appropriate level. This greatly increases the cost of operating this refrigeration equipment, and reduces the owner's satisfaction as the noise generated by the continuously running compressor may well be annoying to the consumer.
  • a defrost heater that is placed in proximity to the evaporator heat exchanger.
  • This defrost heater is controlled by a controller, which may take the form of an electromechanical defrost timer or may utilize a microprocessor or microcontroller.
  • the defrost heater is utilized to provide a small amount of heating of the evaporator coil after the refrigeration cycle has stopped to defrost the heat exchanger, i.e. melt the ice or frost that may have formed thereon during the refrigeration cycle.
  • the efficiency of the refrigeration system is maintained at a high level so as to reduce the cost of operation of the appliance and to increase the owner's satisfaction as the refrigeration cycles may be kept short due to the high efficiency energy transfer through the defrosted evaporator coils.
  • the heating from the defrost heater tends to increase the temperature in the freezer compartment. Since a rough rule of thumb is that twice the amount of cooling is required to remove each unit of heat from the freezer compartment, the defrost heater should be operated for the least amount of time to provide the defrosting of the evaporator coils. Otherwise, the temperature of the freezer compartment may be unnecessarily increased, which increases the amount of cooling necessary to remove this unnecessary heat in the next refrigeration cycle.
  • Electromechanical defrost timers are used in an attempt to limit the amount of time that the defrost heater is energized. This energization time is set based on experimentations with the particular appliances to determine how long the defrost heater should operate to remove a typical amount of frost that would build up during a typical refrigeration cycle within that particular appliance. This timing is selected to optimally remove this amount of frost. If the defrost heater is run for too long, unnecessary heating of the freezer compartment occurs without any added benefit to the removal of frost from the evaporator coils.
  • Adaptive control utilizes a temperature sensing element on the evaporator, and monitors the temperature and time of the defrost cycle. That is, after the refrigeration cycle when the defrost heater is energized, the controller monitors the temperature of the evaporator. Once the temperature reaches a predetermined point, the controller assumes that it has been fully defrosted. The time that this process takes is then used by the controller to adjust the subsequent refrigeration cycle, hence the "adaptive" nature of the controller.
  • the calculation and testing to program the adaptive control to provide an optimized time for operation of the refrigeration and defrost cycle is based on a given voltage to be applied to the defrost heater. Since defrost heaters are typically resistive heating elements, the amount of power that is dissipated, i.e. turned into heat, through the resistive heating element is affected by variations in the line voltage.
  • a typical controller assumes that a known amount of heating is provided during the particular defrost cycle based on a predetermined line voltage and the value of the resistive heating element. Therefore, if all of these were to remain constant, the defrost cycle time on which the adaptive controller bases the next refrigeration cycle would operate in the field as it does in the lab.
  • the line voltage at a consumer or commercial installation may vary greatly from that of the laboratory in which the cycle time was determined, and may, in fact, vary greatly over its operational life. These variations are not symptomatic of any problem in the electrical distribution system, but are, typically, within the specifications for power delivery. Unfortunately, as the input line voltage varies, so does the amount of heat generated or power delivered by the defrost heater. This will directly affect the time it takes to raise the temperature of the evaporator to the set point under identical frost conditions.
  • a line voltage lower than that utilized in the development of the adaptive cycles will result in less heat being delivered to melt the frost and ice from the evaporator, and therefore will result in a longer time needed to raise the temperature of the evaporator to the predetermined level.
  • the adaptive controller may well reduce the refrigeration cycle time thinking that the last refrigeration cycle time severely frosted the evaporator.
  • an increase in the line voltage over that utilized in the development of the adaptive cycles will result in more heat being delivered by the heater.
  • the time to reach the predetermined temperature of the evaporator will be shorter. This will cause the adaptive controller to believe that very little frost accumulated on the previous refrigeration cycle. As a result, the controller will likely lengthen the next refrigeration cycle.
  • the amount of power delivered when the line voltage is a nominal 117 volts AC is approximately 400 watts. If the line voltage increases, within its specifications, to 132 volts AC, the amount of power delivered during the same defrost cycle will increase to approximately 600 watts. Conversely, if the line voltage were to be at the low end of the specification, for example 102 volts AC, the amount of power delivered during the same defrost cycle will drop to only approximately 350 watts.
  • the present invention provides a new and improved defrost heater control system and method that overcomes one or more of the problems existing in the art. More particularly, the present invention provides a new and improved defrost cycle control that monitors or calculates the defrost cycle to determine an actual amount of heating during the defrost cycle regardless of variations of the input line voltage.
  • a system for determining an amount of energy delivered by a defrost heater in accordance with the invention is defined in claim 1.
  • a method of determining an amount of energy delivered by a defrost heater is defined in claim 14.
  • FIG. 1 is a simplified single line schematic diagram of one embodiment of a defrost heater control circuit constructed in accordance with the teachings of the present invention
  • FIG. 2 is a simplified single line schematic diagram of an alternate embodiment of a defrost heater control circuit constructed in accordance with the teachings of the present invention
  • FIG. 3 is a simplified single line schematic diagram of a further alternate embodiment of a defrost heater control circuit constructed in accordance with the teachings of the present invention illustrating additionally physical features thereof;
  • FIG. 4 illustrates a portion of a defrost heater power trace and electrical connection pads for a thermistor that may be used in one embodiment of the present invention, such as in the circuit illustrated in FIG. 3.
  • FIG. 1 illustrates a simplified single line schematic diagram of an adaptive defrost control circuit 10 constructed in accordance with the teachings of the present invention.
  • the adaptive defrost control (ADC) circuit utilizes an ADC controller 12, which is preferably a microcontroller, microprocessor, programmable logic device, etc., that may adaptively change the refrigeration cycle time based upon how long the defrost heater 14 is energized before the evaporator temperature reaches a predetermined temperature.
  • the ADC controller 12 controls the start and stop of a defrost cycle by closing or opening a power control switch 16. This is well known in the art, such a power control switch 16 may take the form of an electromechanical relay, a power switching semiconductor, etc.
  • the defrost heater 14 is a resistive heating element, the power delivered by which may be calculated as the amount of current provided therethrough varies over the defrost cycle.
  • the ADC controller 12 is programmed with these values. The ADC controller 12 utilizes this information to determine the duration of the defrost cycle and adjust the refrigeration cycle to ensure continued efficient operation of the refrigeration system.
  • the system of the present invention utilizes a current sensor 20 placed in circuit with the defrost heater 14 to monitor an amount of instantaneous current being supplied through the defrost heater 14, which current will vary depending on the line voltage.
  • the ADC controller 12 multiplies the square of this monitored current by the known resistance of the defrost heater to calculate an instantaneous power supplied by the defrost heater 14.
  • the ADC controller 12 then calculates the total amount of energy supplied by accumulating the instantaneous power during the defrost cycle.
  • the ADC controller 12 commands the switching element 16 to open to stop the flow of current to the heater 14.
  • a fixed defrost cycle time need not be used as was the case with the electromechanical timers.
  • the length of the succeeding refrigeration cycle need not be based simply on the elapsed time of the defrost cycle as was the case with the adaptive controls of the prior art.
  • the ADC controller 12 can adapt the length of the refrigeration cycle based either on the total energy delivered by the defrost heater 14 over the defrost cycle or on the elapsed time of the defrost cycle adjusted for the total energy delivered.
  • CT current transformer
  • FIG. 2 illustrates such a circuit utilizing a thermistor 22 to provide the current sensing function for use by the ADC controller 12.
  • the thermistor 22 is placed on the power trace 26 for the defrost heater 14.
  • This power trace 26 has a known resistance, and therefore the flow of current therethrough will result in a temperature rise thereof.
  • This temperature rise is detected by thermistor 22.
  • the ADC controller 12 then performs a calculation that takes into account the temperature rise over time to calculate the amount of current flowing through the trace 26, and therefore the amount of current flowing through defrost heater 14.
  • This current value is then utilized to calculate the instantaneous power delivered by the defrost heater 14, which values are accumulated until the desired temperature of the evaporator is reached, i.e. until the proper amount of energy has been delivered to melt the frost and/or ice that may have accumulated on the evaporator in the prior refrigeration cycle.
  • the ADC controller 12 will command the switching element 16 to terminate the defrost cycle. While various types of thermistors may be used, a preferred embodiment of the present invention utilizes surface mount thermistors, such as NTC thermistors, Linear PTC thermistors, etc.
  • a second thermistor 24 is utilized to provide an indication of the ambient temperature of the control circuitry.
  • the second thermistor 24 is used to provide a correcting factor based upon a change in the ambient temperature that may occur due to the heating caused by the defrost heater 14. Such an increase in ambient temperature will also be sensed by thermistor 22. If this rise in ambient temperature is not compensated, the ADC controller 12 may think that the increased temperature sensed by thermistor 22 is due to an increased current flow through the defrost heater 14 as measured on trace 26.
  • the adaptive defrost controller 12 compensates the temperature sensed by thermistor 22 by the temperature sensed by thermistor 24. This net temperature rise, therefore, is due only to the temperature rise of the trace 26. It is this net temperature rise that is used by the ADC controller 12 to calculate the amount of current flowing through the defrost heater 14 and the trace 26.
  • thermistor 22 While the utilization of a thermistor 22 to sense the temperature rise of the power trace 26 solves both the variation in power delivered and cost of sensing current flowing to the defrost heater 14, typical power traces, and indeed wiring for power devices in general, have a very low linear resistance. This is particularly true in configurations as are typically used in such circuitry. As such, and to enhance the ability of the thermistor 22 to actually sense a temperature rise, a preferred embodiment of the present invention utilizes a physical layout that provides such enhanced sensing ability.
  • FIG. 3 One such circuit layout that will provide this enhanced sensitivity is illustrated in FIG. 3. While the circuit components remain the same, a physical configuration of the power trace 26 on which the thermistor 22 is placed in thermal contact is chosen to enhance, or increase its linear resistance so that the temperature rise to be sensed by the thermistor may be provided with better resolution. Since a typical power trace is fairly wide, it was determined that if the power trace at the point of thermistor 22 placement could be narrowed, the thermistor 22 would be able to better sense a temperature rise.
  • the width of the power trace is calculated based on transient and maximum current carrying capability. As such, it was important not to minimize the ability of the power circuit itself to carry such maximum currents.
  • a secondary current carrying path 28 was added into the circuit to provide an alternate path for current flow at the point of thermistor placement. Such an alternate path 28 insures the ability of the overall circuit to carry such high transient currents.
  • an alternate path would also allow the current actually flowing through the defrost heater 14 to take different paths, and therefore the temperature rise sensed by thermistor 22 would not be representative of the actual current flowing through the defrost heater 14.
  • the length, and therefore the resistance, of the alternate path 28 was made to ensure that under normal operating conditions, the majority of the current flowing through the defrost heater 14 will flow through the power trace 26 path as opposed to the alternate path 28. In this way, the calculation within the ADC controller 12 maintains accuracy. Indeed, in one embodiment of the present invention the current ratio flow between paths 26 and 28 may also be taken into account with the ADC 12 to ensure that the full current flow is taken into consideration.
  • FIG. 4 illustrates an exemplary embodiment of a physical implementation of a section of the power trace 30 of FIG. 3.
  • the width of the power trace 30 is greatly reduced in the branch 26 over which the thermistor will be positioned to sense temperature rise thereacross.
  • This FIG. 4 also illustrates the alternate path 28 that is provided to ensure that the overall current carrying capability of the trace 30 is not lessened by the modification to provide an enhanced thermal sensing capability through branch 26.
  • attachment pads 32, 34 are provided on either side of branch 26 for surface mount placement of the thermistor 22 (see FIG.3). the electrical connection from attachment pad 34 is jumpered over branch 26 to trace 36.
  • the actual configuration of the alternate branch 28 may vary widely, but preferably provides an increased resistance to current flow so as to maximize the ability of the thermistor placed over branch 26 to sense a temperature rise.
  • the resistance of branch 26 is known and utilized by the ADC controller 12 to perform the temperature rise to current calculation.

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  • 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)
EP07007062A 2006-04-06 2007-04-04 System und Verfahren zum Bestimmen der von einem Abtauheizer abgegebenen Abtauenergie Withdrawn EP1843111A2 (de)

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
US11/399,157 US20070234748A1 (en) 2006-04-06 2006-04-06 System and method for determining defrost power delivered by a defrost heater

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EP1843111A2 true EP1843111A2 (de) 2007-10-10

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Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US20220003479A1 (en) * 2018-10-02 2022-01-06 Lg Electronics Inc. Refrigerator

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US7343227B1 (en) * 2006-08-31 2008-03-11 Dell Products, Lp Current sensing temperature control circuit and methods for maintaining operating temperatures within information handling systems
WO2012070404A1 (ja) * 2010-11-25 2012-05-31 シャープ株式会社 電力制御装置、電力制御方法、電力制御プログラム及び記録媒体
US9127875B2 (en) * 2011-02-07 2015-09-08 Electrolux Home Products, Inc. Variable power defrost heater
US9175872B2 (en) 2011-10-06 2015-11-03 Lennox Industries Inc. ERV global pressure demand control ventilation mode
US9404668B2 (en) 2011-10-06 2016-08-02 Lennox Industries Inc. Detecting and correcting enthalpy wheel failure modes
US20130118188A1 (en) 2011-11-10 2013-05-16 Justin McKie Method of defrosting an energy recovery ventilator unit
US9671122B2 (en) 2011-12-14 2017-06-06 Lennox Industries Inc. Controller employing feedback data for a multi-strike method of operating an HVAC system and monitoring components thereof and an HVAC system employing the controller
KR102220911B1 (ko) * 2014-01-06 2021-02-25 엘지전자 주식회사 냉장고, 및 홈 어플라이언스

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Cited By (1)

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Publication number Priority date Publication date Assignee Title
US20220003479A1 (en) * 2018-10-02 2022-01-06 Lg Electronics Inc. Refrigerator

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