EP0278701B1 - Système de dégivrage d'échangeurs de chaleur - Google Patents

Système de dégivrage d'échangeurs de chaleur Download PDF

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Publication number
EP0278701B1
EP0278701B1 EP88300999A EP88300999A EP0278701B1 EP 0278701 B1 EP0278701 B1 EP 0278701B1 EP 88300999 A EP88300999 A EP 88300999A EP 88300999 A EP88300999 A EP 88300999A EP 0278701 B1 EP0278701 B1 EP 0278701B1
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EP
European Patent Office
Prior art keywords
defrost
heat exchanger
interval
controller
defrost 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.)
Expired - Lifetime
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EP88300999A
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German (de)
English (en)
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EP0278701A3 (en
EP0278701A2 (fr
Inventor
Anthony Robert Fry
Derek Kent
Bernard W. Johnson
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.)
York International Ltd
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York International Ltd
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Publication date
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Priority to AT8888300999T priority Critical patent/ATE105071T1/de
Publication of EP0278701A2 publication Critical patent/EP0278701A2/fr
Publication of EP0278701A3 publication Critical patent/EP0278701A3/en
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Publication of EP0278701B1 publication Critical patent/EP0278701B1/fr
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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
    • F25D21/002—Defroster control
    • 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
    • F25B2700/11—Sensor to detect if defrost is necessary
    • F25B2700/111—Sensor to detect if defrost is necessary using an emitter and receiver, e.g. sensing by emitting light or other radiation and receiving reflection by a sensor

Definitions

  • the present invention relates to the defrosting of heat exchangers particularly, but not exclusively, to the defrosting of a heat pump system.
  • a fin-and-tube air-to-refrigerant heat exchanger is used as an evaporator in heat pump systems to collect heat from the air.
  • frosting or icing up of the heat exchanger may occur.
  • Such frosting both lowers (and, indeed, may stop) the throughput of air and acts as a barrier to the transfer of heat between the air and the primary and secondary surface material of the heat exchanger. It is conventional, therefore, to make provision for the heat exchanger to be defrosted from time to time where it is operating in low temperature humid air conditions where frosting occurs.
  • a typical defrosting technique used with heat exchangers is the "hot-gas" technique; in this, by operation of suitable valving in the refrigerant circuit, the heat exchanger is injected with hot compressor discharge gas, the air-to-refrigerant evaporator thus operating temporarily as a condenser, thereby rejecting heat to the outside and causing the frosting or ice to be melted. Operation in this way obviously detracts from the overall efficiency of the heat pump since while the defrost cycle is in operation the evaporator is not able to fulfil its normal function of collecting heat from the surrounding air.
  • a sensor is provided to detect frosting or icing up of the evaporator - this may be done, for example, by measuring the temperature of the primary or secondary surface of the evaporator, the refrigerant temperature or pressure, the air pressure difference across the coil, the optical reflectivity of the evaporator and so on.
  • a control circuit periodically samples the output of this sensor to determine whether a defrost cycle should be initiated. The defrosting cycle may either be of fixed duration or terminated by sensing that the frost or ice has been melted.
  • EP-A-0063178 discloses a heat pump defrost control system in which a defrost controller operates to adjust the interval to the initiation of the next defrost cycle on the basis of the difference in the times of the two preceding defrost cycles. This difference is multiplied by a constant and added to a basic time interval to determine the interval before the next defrost.
  • EP-A-0021151 discloses a heat pump defrosting system corresponding to the precharacterising part of claim 1.
  • the invention seeks to provide an improved way of controlling the interval between defrost cycles and provides a heat exchanger defrosting system comprising a heat exchanger liable to frosting, means operable to carry out a defrost cycle of the heat exchanger and a controller for controlling defrosting comprising means for initiating a defrost cycle on detection of an operating parameter having a value indicative of the need for defrosting of the heat exchanger, the controller in use sampling the values of one or more operating parameters of the system at intervals to determine whether a defrost cycle is required, and being operative to vary the interval between the end of one defrost cycle and the enablement of the start of the next depending on the length of said one defrost cycle to establish a longer interval when said length is shorter and vice versa, characterised in that the controller is operative to improve the overall operating efficiency of the system by increasing the interval between successive samplings if and only if the durations of the two preceding defrost cycles are both below a predetermined optimum range of durations for the
  • the present invention provides, inter alia, a defrost controller for a heat exchanger which is operative to adapt the defrosting operation to prevailing conditions by increasing or decreasing the intervals between defrosting cycles as appropriate.
  • Fig 1 shows an example of a heat pump to which the present invention may be applied and which comprises a compressor 1 for driving refrigerant around a refrigerant circuit comprising an air-to-refrigerant fin-and-tube evaporator 2 which is exposed to outside air, a condenser 3 in which the refrigerant cools and rejects heat to another medium such as water in a hot-water supply circuit or space air, a refrigerant expansion device 4 which may be a thermostatic expansion valve or an electronically controlled expansion valve and a hot gas injection valve 12.
  • a compressor 1 for driving refrigerant around a refrigerant circuit comprising an air-to-refrigerant fin-and-tube evaporator 2 which is exposed to outside air
  • a condenser 3 in which the refrigerant cools and rejects heat to another medium such as water in a hot-water supply circuit or space air
  • a refrigerant expansion device 4 which may be a thermostatic expansion valve or an electronically controlled expansion valve and
  • the system has associated with it a system controller 5 which incorporates electronic circuitry and appropriate interfaces to enable the system to operate under the control of one or more inputs generally designated 6 which may, for example, be used to signal to the system controller 5 a set point value for one or more relevant operating parameters of the system.
  • An example of such a parameter is the temperature of the secondary medium leaving the condenser 3 where the system is intended primarily for heating purposes.
  • a set point for air or water leaving the evaporator can be applied by one of the inputs 6 to the system controller 5.
  • the system controller 5 has various sensors associated with it and distributed around the elements of the refrigerant circuit are electro-mechanical devices such as solenoid valves for controlling the refrigerant flow around the refrigerant circuit and to control the progressive loading and unloading of the compressor 1 in response to increasing and decreasing cooling or heating demands.
  • electro-mechanical devices such as solenoid valves for controlling the refrigerant flow around the refrigerant circuit and to control the progressive loading and unloading of the compressor 1 in response to increasing and decreasing cooling or heating demands.
  • One of the functions of the system controller 5 is, in appropriate operating conditions, periodically to determine whether defrosting of the evaporator 2 is required and, if so, to initiate and control a defrosting cycle.
  • the evaporator 2 (or each evaporator where there is a number of them) has associated with it a sensor 7 which can supply to the system controller 5 a signal (such as an analogue voltage) which when compared with a reference value is indicative of the need or otherwise for the initiation of a defrost cycle.
  • the sensor 7 may detect the temperature of the primary or secondary surface of the evaporator 2, the air pressure difference across the evaporator coil (which will increase as the evaporator coil frosts up), the pressure in, or pressure difference across, an appropriate part of the refrigerant system (such as at the exit of the evaporator 2), the optical reflectivity of the exterior of the evaporator or by any other variable indicative of the actual or likely occurrence of frosting.
  • the system controller 5 may be implemented using discrete electronic components, IC digital logic circuits or be based around a suitably programmed micro-computer.
  • the system controller 5 is to be implemented using a microprocessor (MPU) and associated interfacing and support circuitry.
  • MPU microprocessor
  • the MPU 10 will execute a suitable program stored in a non-volatile, usually read only memory (ROM), have random access memory (RAM) available as program workspace and be provided with suitable interfaces to accept control and information signals and emit data and commands signals in a form electrically compatible with the controlled or controlling equipment of the heat pump system.
  • the program for the MPU 10 will be such as to cause a desired control algorithm for the heat pump to be carried into effect. In particular, this program may be used in implementing the present invention.
  • the system controller 5 includes a defrost interval timer 8 which is used to generate a defrost-enable signal 9 which is used to signal the microprocessor 10 that the time has been reached at which a determination is to be made of whether a defrost cycle should be initiated.
  • the timer 8 may be implemented by means of a MPU register or RAM memory location in which a timing count is loaded, its value being incremented or decremented at appropriate intervals and a time-out determination made i.e. by the start of the timing interval, the time 8 can be loaded with a number representing the interval in, say, minutes or seconds with this value then being decremented periodically (for example every second or minute as appropriate) and then a determination be made by the microprocessor 10 to whether the count has reached zero.
  • the MPU 10 makes a determination, from the output of one of more of the sensors 7, as to whether a defrost cycle is to be initiated. If the determination is that a defrost cycle is required, the system controller 5 sends the appropriate control signals to the electro-mechanical devices controlling operation of the heat pump to initiate a hot-gas defrost cycle, in this case by the hot gas defrost in which hot, gaseous refrigerant is delivered to the evaporator 2 via valve 12.
  • the defrost cycle length timer 11 is activated and this is used to record the time that the defrost cycle actually takes to complete. This may be achieved by initially storing a count of zero in the timer 11 and having the MPU 10 increment this at regular intervals. At appropriate intervals during the defrost cycle the MPU checks the output of the sensor(s) 7 to determine whether the defrost cycle is completed. At the end of the defrost cycle, the timer 11 will contain information as to the time which was taken to carry out the defrost cycle. This value is then used to determine whether an adjustment needs to be made of the defrost sampling interval in the next cycle.
  • This determination can be made on the basis that a long defrost time suggest adverse operating conditions making more frequent defrost cycles desirable while a shorter than expected defrost cycle, indicating that defrosting is completing in less time than was expected, suggests that a longer defrost interval can be tolerated (and in the interests of efficiency this determination should be followed by an increase in the defrost interval).
  • the adjustment of the defrost interval can be done in a step-wise or linear manner or, indeed, in accordance with any other law appropriate to the circumstances.
  • Figures 3 and 4 illustrate one arrangement in which adjustment is made in a series of steps.
  • the controller 5 issues a command for defrost to be carried out. It may be carried out by any of the standard methods such as the hot gas mentioned above, electric heating elements, warm water, etc, until defrost completion is detected by any one of the sensing methods described above.
  • the controller 5 can provide control facilities through which each of the parameter set points may be varied, for example, defrost initiation occurring between 3°C and 9°C, the higher value enabling evaporator coil secondary surface temperatures to be effectively monitored; in the case of defrost termination temperatures between 5°C and 15°C may be selected.
  • the controller 5 includes a control facility in which the maximum optimum defrost period may be preset, for example between 1 and 6 minutes in the example shown in fig 3, and as described below. Below optimum band, 0 to 75% of preset maximum optimum defrost period Optimum band within 75% to 100% of the present maximum optimum defrost period, Above optimum band 100% to 200% of preset maximum optimum defrost period.
  • the actual defrost time taken as established by the defrost duration timer 11 is compared by the controller 5 with those defined parameters in fig 3 to determine in which band the defrost termination signal occurred.
  • the controller 5 has a control facility in which the 100% parameter for the interval time between defrost initiations may be set, for example between 30 and 90 minutes as another set point.
  • the subsequent interval between defrost will be incremented by a discrete percentage value i.e. to 120% of the original preset interval. If the system interval time for a defrost initiation is reached and the defrost initiation sensor temperature is greater than that at which defrost is required then no defrosting will take place and the control system will automatically increment the control defrost interval time.
  • the interval between defrost is again incremented to a longer time interval until a maximum value is reached, for example if fig 4, up to 160%. If the actual defrost period terminates within the "optimum band", in the illustrated example 75 to 100% of the set point (period Y), then no change will occur to the controlled interval time between defrost initiations. Thus, in this condition the controller 5 takes account of the defrost times necessary and the time interval between defrosts to achieve an optimum operating condition.
  • the subsequent interval between defrost will be decremented and if necessary after subsequent defrosts further decremented, until a minimum time between defrosts is reached.
  • defrost termination will occur irrespective of the signal from the defrost termination sensor, i.e. this is a maximum defrost time override condition.
  • the defrost interval time can return to the 100% set point or remain at the previous operating set point.
  • the above logic is applicable to any evaporator coil circuit that is defrosted in total.
  • Fig 5 shows part of a heat-pump system having a number of evaporators EVAP1, EVAP2, EVAPN, with associated solenoid valves SV, refrigerant expansion devices tev and defrost sensors SI...SN.
  • the controller 5 can cause defrosting of some circuits while others continue operation as evaporators.
  • the controller 5 is arranged to have the capability of dictating the defrost logic such that coincident defrosting of all the evaporators is inhibited.
  • the defrost cycle for this type of evaporator coil arrangement is determined on the basis of previous defrost times.
  • the actual defrost time for a particular evaporator EVAPX is compared to the parameters as defined in fig 2 to determine in which band the defrost termination signal occurred. This information is then related to the information obtained for the previous defrost time on the other coil(s) and the following decision table can be used to update the defrost interval time:-
  • controller 5 dictates that each circuit is sensed for defrost in sequence within the time interval between defrost as shown in fig 6.
  • the time interval at which the next coil defrost cycle is initiated in the case of two coils, will be half the defrost time interval determined by fig 4.
  • the actual time interval is divided evenly amongst the number of coils involved.
  • each evaporator has its own sensor designated S1...Sn; when evaporator EVAP1 has terminated its defrost, the time taken D1, is used for the controller 5 to select the time interval T1 between defrosts (fig 4) based on table 1. The time then allocated before defrost initiation of the next evaporator EVAP2, is in the case shown in, T1/2 (fig 6). After the second evaporator EVAP2 has defrosted then the defrost time D2 is used for the controller to select the revised time interval T2 between defrost initiation (fig 4) based on table 1.
  • the revised time before defrost initiation of the first evaporator EVAP1 again is T2/2.
  • two such sensors may be provided at opposite sides (in the direction of air flow through the evaporator) of the evaporator and means may be provided to select for monitoring purposes, whichever of those sensors whose output indicates the greater likelihood of frosting.
  • the output used would be the one from the sensor 7 indicating the lower evaporator temperature.
  • the time to defrost is variable dependent upon the capacity load being generated at that time (eg 1/2 or 1/4 load) - the greater the unloading, the higher the evaporating temperature which in turn reduces the likelihood of frost formation.

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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)
  • Air Conditioning Control Device (AREA)

Claims (5)

  1. Système de dégivrage d'échangeur de chaleur comprenant un échangeur de chaleur pouvant être dégivré, un moyen pouvant fonctionner pour exécuter un cycle de dégivrage de l'échangeur de chaleur et un dispositif de commande pour commander le dégivrage comprenant un moyen pour déclencher un cycle de dégivrage lors de la détection d'un paramètre de fonctionnement présentant une valeur indiquant qu'un dégivrage de l'échangeur de chaleur est nécessaire, ce dispositif de commande échantillonnant pendant l'utilisation les valeur d'un ou plusieurs paramètres de fonctionnement du système à des intervalles pour déterminer si un cycle est nécessaire et étant apte à modifier l'intervalle entre la fin d'un cycle de dégivrage et le démarrage du cycle suivant en fonction de la longueur dudit cycle de dégivrage afin d'établir un intervalle plus long quand ladite longueur est plus courte et vice versa, caractérisé en ce que le dispositif de commande sert à améliorer le rendement de fonctionnement global du système en augmentant l'intervalle entre des échantillonnages successifs si, et seulement si, les durées des deux cycles de dégivrage précédents se trouvent toutes deux en dessous d'une plage optimale prédéterminée de durées pour le cycle de dégivrage, tandis que le dispositif de commande sert à diminuer les intervalles entre les échantillonnages si la durée du cycle de dégivrage le plus récent se trouve au dessus d'une plage optimale prédéterminée de durées pour le cycle de dégivrage.
  2. Système de dégivrage d'échangeur de chaleur selon la revendication 1, dans lequel le dispositif de commande sert à augmenter ou diminuer l'intervalle d'échantillonnage d'une fraction en fonction de la durée de dégivrage mesurée.
  3. Système selon l'une quelconque des revendication précédentes dans lequel le dispositif de commande comprend au moins un capteur pour mesurer la température de la surface de l'air de l'échangeur de chaleur, ou le pouvoir réflecteur, ou la différence de pression de l'air entre l'entrée et la sortie de l'échangeur de chaleur pour déterminer si le dégivrage est nécessaire.
  4. Système selon l'une quelconque des revendications dans lequel l'échangeur de chaleur comporte deux côtés alternativement plus aptes à être dégivrés selon les conditions qui prévalent, et dans lequel des capteurs sont prévus à ces deux côtés de l'échangeur de chaleur afin qu'un intervalle de dégivrage soit imposé par le capteur qui est placé dans la position où la formation de givre prédomine.
  5. Système de pompe à chaleur comprenant un circuit de réfrigérant comportant un compresseur de réfrigérant, un condenseur de réfrigérant et au moins un évaporateur de réfrigérant comprenant un système de dégivrage d'échangeur de chaleur selon l'une quelconque des revendications précédentes.
EP88300999A 1987-02-06 1988-02-05 Système de dégivrage d'échangeurs de chaleur Expired - Lifetime EP0278701B1 (fr)

Priority Applications (1)

Application Number Priority Date Filing Date Title
AT8888300999T ATE105071T1 (de) 1987-02-06 1988-02-05 Abtauanlage fuer waermeaustauscher.

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
GB878702722A GB8702722D0 (en) 1987-02-06 1987-02-06 Defrosting of heat exchangers
GB8702722 1987-02-06

Publications (3)

Publication Number Publication Date
EP0278701A2 EP0278701A2 (fr) 1988-08-17
EP0278701A3 EP0278701A3 (en) 1989-10-04
EP0278701B1 true EP0278701B1 (fr) 1994-04-27

Family

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Family Applications (1)

Application Number Title Priority Date Filing Date
EP88300999A Expired - Lifetime EP0278701B1 (fr) 1987-02-06 1988-02-05 Système de dégivrage d'échangeurs de chaleur

Country Status (5)

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EP (1) EP0278701B1 (fr)
AT (1) ATE105071T1 (fr)
DE (1) DE3889237D1 (fr)
ES (1) ES2055736T3 (fr)
GB (1) GB8702722D0 (fr)

Families Citing this family (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP1180652B1 (fr) * 2000-08-18 2006-09-27 Ranco Incorporated of Delaware Dispositif de commande et procédé pour commander l'opération de dégivrage dans un réfrigérateur
US9562757B2 (en) 2009-10-02 2017-02-07 The Controls Group, Inc. Removal of an accumulated frozen substance from a cooling unit
FR3101137B1 (fr) * 2019-09-19 2022-03-18 Guinault Sa Unité de conditionnement d’air pour aéronef

Family Cites Families (14)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4206612A (en) * 1977-07-15 1980-06-10 Emhart Industries, Inc. Refrigeration system control method and apparatus
DE2850198A1 (de) * 1978-11-18 1980-05-29 Hamadeh Steueranlage zum abtauen von kuehlstellen
US4251988A (en) * 1978-12-08 1981-02-24 Amf Incorporated Defrosting system using actual defrosting time as a controlling parameter
US4680940A (en) * 1979-06-20 1987-07-21 Vaughn Eldon D Adaptive defrost control and method
US4328680A (en) * 1980-10-14 1982-05-11 General Electric Company Heat pump defrost control apparatus
DE3043459A1 (de) * 1980-11-18 1982-07-08 Linde Ag, 6200 Wiesbaden Bedarfsabtauung der kuehlmoebel
DE3110042A1 (de) * 1981-03-16 1982-09-30 Gesellschaft für Wärmepumpen und Energierückgewinnungsanlagen mbH, 7311 Holzmaden Verfahren und anordnung zum abtauen von eis an einem luftkuehler einer waermepumpe oder kaeltemaschine
DE3115599C2 (de) * 1981-04-16 1986-07-10 KKW Kulmbacher Klimageräte-Werk GmbH, 8650 Kulmbach Abtausteuerung für eine Wärmepumpe
US4395887A (en) * 1981-12-14 1983-08-02 Amf Incorporated Defrost control system
DE3235642A1 (de) * 1982-09-25 1984-03-29 3 E Elektronik-Elektro-Energieanlagen Baugesellschaft mbH, 5500 Trier Einrichtung zur elektrischen abtauregelung fuer den verdampfer einer kaelteanlage
DE3238354A1 (de) * 1982-10-15 1984-04-19 Siemens AG, 1000 Berlin und 8000 München Verfahren zum abtauen des verdampfers einer beispielsweise als waermepumpe betriebenen kaeltemaschine
US4538420A (en) * 1983-12-27 1985-09-03 Honeywell Inc. Defrost control system for a refrigeration heat pump apparatus
US4563877A (en) * 1984-06-12 1986-01-14 Borg-Warner Corporation Control system and method for defrosting the outdoor coil of a heat pump
US4627245A (en) * 1985-02-08 1986-12-09 Honeywell Inc. De-icing thermostat for air conditioners

Also Published As

Publication number Publication date
EP0278701A3 (en) 1989-10-04
ES2055736T3 (es) 1994-09-01
ATE105071T1 (de) 1994-05-15
EP0278701A2 (fr) 1988-08-17
DE3889237D1 (de) 1994-06-01
GB8702722D0 (en) 1987-03-11

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