METHOD FOR REMOVING A DEPOSITION OF SCALE ON A HEATING ELEMENT AND A HOUSEHOLD APPLIANCE CONFIGURED TO PERFORM THE METHOD

Abstract

A method for removing a deposition of scale on a heating element may include turning on the heating element to heat the liquid in the heating space, determining a first value (Tv1) of temperature of the heating element and/or a first time period (tp1) during heating of the liquid. The method may further include turning off the heating element and turning on the heating element at a second value (Tv2) of temperature of the heating element and reheating the liquid in the heating space until temperature of the heating element reaches a third value (Tv3) related to the first value (Tv1) and/or until a second time period (tp2) related to the first time period (tp1) is reached. A household appliance may also be provided.

Claims

1. A method for removing a deposition of scale on a heating element arranged to heat a liquid in a heating space of a household appliance, the method comprises: a) turning on the heating element to heat the liquid in the heating space, b) determining a first value (Tv1) of temperature of the heating element and/or a first time period (tp1) during heating of the liquid, c) turning off the heating element and d) turning on the heating element at a second value (Tv2) of temperature of the heating element and reheating the liquid in the heating space until temperature of the heating element reaches a third value (Tv3) related to said first value (Tv1) and/or until a second time period (tp2) related to said first time period (tp1) is reached.

2. The method according to claim 1, wherein said first value (Tv1) of temperature of the heating element corresponds to a boiling temperature of the liquid and said first time period (tp1) is required to reach said boiling temperature of the liquid.

3. The method according to claim 1 further comprising monitoring a behavior (TB) of temperature of the heating element during heating of the liquid in order to determine said first value (Tv1) of temperature of the heating element and/or in order to determine said first time period (tp1).

4. The method according to claim 1 further comprising: repeating said step c) and d) at least once.

5. The method according to claim 1 further comprising obtaining a start temperature (T0) of the heating element before turning on the heating element.

6. The method according to claim 5, wherein said third value (Tv3) of temperature of the heating element constitutes a first predetermined percentage of said first value (Tv1) of temperature of the heating element, and/or a third time period (tp3) constitutes a second predetermined percentage of said first time period (tp1), wherein said third time period is calculated as a sum of a fourth time period (tp4) required to heat said heating element, during heating of the liquid in the heating space, from the start temperature (T0) to said second value (Tv2) of the temperature of the heating element and of said second time period (tp2).

7. The method according to claim 6, wherein said first predetermined percentage and said second predetermined percentage is between 90% and 110%.

8. The method according to claim 1, wherein the heating element is turned on at the second value (Tv2) of temperature of the heating element if said second value (Tv2) is lower than said first value (Tv1) with a third predetermined percentage of said first value (Tv1) of temperature of the heating element.

9. The method according to claim 8 wherein said third predetermined percentage is at least 10%.

10. The method according to claim 1 further comprising removing the liquid from said heating space.

11. A household appliance comprising a heating element arranged to heat a liquid in a heating space of said household appliance, a sensor arranged to measure temperature of said heating element and a control unit, wherein the household appliance being configured to: turn on the heating element to heat the liquid in the heating space, determine a first value (Tv1) of temperature of the heating element and/or a first time period (tp1) during heating of the liquid, turn off the heating element and turn on the heating element at a second value (Tv2) of temperature of the heating element and reheat the liquid in the heating space until temperature of the heating element reaches a third value (Tv3) related to said first value (Tv1) and/or until a second time period (tp2) related to said first time period (tp1) is reached.

12. The household appliance according to claim 11, wherein said first value (Tv1) of temperature of the heating element corresponds to a boiling temperature of the liquid and said first time period (tp1) is required to reach said boiling temperature of the liquid.

13. The household appliance according to claim 11, further being configured to monitor a behaviour (TB) of temperature of the heating element during heating of the liquid in order to determine said first value (Tv1) of temperature of the heating element and/or in order to determine said first time period (tp1).

14. The household appliance according to claim 11 further being configured to repeat at least once the turning off the heating element and the turning on the heating element at the second value (Tv2) of temperature of the heating element, and reheat the liquid in the heating space until temperature of the heating element reaches the third value (Tv3) related to said first value (Tv1) and/or until the second time period (tp2) related to said first time period (tp1) is reached.

15. The household appliance according to claim 11, further being configured to obtain a start temperature (T0) of the heating element before turning on the heating element.

16. The household appliance according to claim 15, wherein said third value (Tv3) of temperature of the heating element constitutes a first predetermined percentage of said first value (Tv1) of temperature of the heating element, and/or a third time period (tp3) constitutes a second predetermined percentage of said first time period (tp1), wherein said third time period is calculated as a sum of a fourth time period (tp4) required to heat said heating element, during heating of the liquid in the heating space, from the start temperature (T0) to said second value (Tv2) of the temperature of the heating element and of said second time period (tp2).

17. The household appliance according to claim 16, wherein said first predetermined percentage and said second predetermined percentage is between 90% and 110%.

18. The household appliance according to claim 11, wherein the heating element is turned on at the second value (Tv2) of temperature of the heating element if said second value (Tv2) is lower than said first value (Tv1) with a third predetermined percentage of said first value (Tv1) of temperature of the heating element.

19. The household appliance according to claim 18 wherein said third predetermined percentage is at least 10%.

20. The household appliance according to claim 11, further being configured to remove the liquid from said heating space.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0041] The various aspects mentioned above, including their particular features and advantages, will be readily understood from the following detailed description and the accompanying drawings, in which:

[0042] FIG. 1 is a flow chart illustrating a method for removing a deposition of scale on a heating element,

[0043] FIG. 2 is a diagram illustrating behaviour of temperature of a heating element during implementing of some steps of the method in FIG. 1 and

[0044] FIG. 3 is a plane view of a household appliance.

DETAILED DESCRIPTION

[0045] The embodiments herein will now be described in more detail with reference to the accompanying drawings, in which example embodiments are shown. Disclosed features of example embodiments may be combined. Like numbers refer to like elements throughout. Well-known functions or constructions will not necessarily be described in detail for brevity and/or clarity.

[0046] FIG. 1 illustrates an example of actions in a procedure for implementing a method 100 for removing a deposition of scale on a heating element in a heating space of a household appliance. The method 100 may for example be carried by a control unit connected to or arranged at the household appliance. Such a control unit is shown in FIG. 3 and its function will be described in details in conjunction to description of FIG. 3. In conjunction to the FIG. 3 also other details of the household appliance and theirs function for the method will be described.

[0047] The method 100 comprises: turning on 101 the heating element to heat the liquid in the heating space, determining 103 a first value of temperature of the heating element and/or a first time period during heating of the liquid, turning off 105 the heating element and turning on 107 the heating element at a second value of temperature of the heating element and reheating the liquid in the heating space until temperature of the heating element reaches a third value related to the first value and/or until a second time period related to the first time period is reached.

[0048] The liquid may for example be water or water comprising a detergent.

[0049] The method 100 may comprise monitoring 109 a behaviour of temperature of the heating element during heating of the liquid in order to determine the first value of temperature of the heating element and/or in order to determine the first time period.

[0050] The behaviour is obtained by measuring values of temperature of the heating element. The temperature of the heating element may be measured using a sensor arranged at the heating element. The sensor is described in details in conjunction to FIG. 3.

[0051] Further, the method 100 may comprise: repeating 111 at least once the turning off 105 the heating element and the turning on 107 the heating element at the second value of temperature of the heating element and reheating the liquid in the heating space until temperature of the heating element reaches the third value related to the first value and/or until the second time period related to the first time period is reached.

[0052] The method 100 may also comprise obtaining 113 a start temperature of the heating element before turning on 101 the heating element and removing 115 the liquid from the heating space.

[0053] FIG. 2 is a diagram illustrating a behaviour TB of temperature T of a heating element, which temperature T is measured by a sensor.

[0054] A start temperature T0 of the heating element is measured before turning on the heating element at a first point in time t1 and after the liquid has been supplied to the heating space. According to some embodiments the start temperature T0 may be measured after for example 10 seconds from supplying of the liquid to the heating space. After this time, i.e. for example 10 seconds the liquid in the heating space will reach steady state which means that there is essentially no movement of the liquid within the heating space resulting in that temperature of the liquid and temperature of the heating element reach an average value common both for the heating element and the liquid in the heating space. Therefore, by measuring the start temperature T0 of the heating element before turning on of the heating element a liquid start temperature T0L may be achieved. According to the example illustrated in FIG. 2 the start temperature T0 of the heating element has been measured to 20 C. Thus, the liquid start temperature T0L is also 20 C.

[0055] At the first point in time t1 the heating element is turned on to heat the liquid and simultaneously a first time period tp1 from the first point in time t1 is started to be measured by a time measuring device.

[0056] During heating of the liquid in the heating space the behaviour TB of the measured temperature T of the heating element is monitored i.e. is studied in order to determine a first value Tv1 of the temperature of the heating element and/or the first time period tp1. The first value Tv1 of temperature of the heating element corresponds to a boiling temperature of the liquid and the first time period tp1 is required to heat the liquid to said boiling temperature of the liquid.

[0057] The temperature T of the heating element increases from the start temperature T0 with approximately a constant derivate up to the first value Tv1. In the example shown in FIG. 2 the first value is approximately 120 C.

[0058] When a liquid heated by a heating element starts boiling the temperature of the heating element continues to increase with a different derivate than up to start boiling. With start boiling of the liquid is meant for example when first air bubbles begin to be formed in the direct vicinity of the heating element.

[0059] Thus, a temperature of the heating element corresponding to start boiling temperature of the liquid may be determined by detecting a boiling point at behaviour of the temperature of the heating element, which boiling point is detected by monitoring the behaviour. FIG. 2 illustrates a boiling point K corresponding to the first value Tv1 of temperature T of the heating element.

[0060] Start boiling of the liquid in the heating space i.e. boiling point K at the behaviour TB occurs at a boiling time tk. The measured time period from the first point in time t1 to the boiling time tk define the first time period tp1.

[0061] After the boiling point K has been detected the heating element is turned off. The heating element may be turned off for example after 2 second from detecting boiling point K. As can be seen in FIG. 2, the temperature T of the heating element decreases after the heating element has been turned off.

[0062] Further, the heating element is turned on at a second point in time t2 and at a second value Tv2 of the temperature T of the heating element. The heating element is turned on when temperature of the heating element T has decreased to the second value Tv2 which second value Tv2 is lower than the first value Tv1 with a third predetermined percentage of the first value Tv1, for example with at least 10% of the first value Tv1 of temperature of the heating element. With other words, the heating element is turned on when temperature T of the heating element has decreased with at least 10% of the first value Tv1 of temperature of the heating element.

[0063] The liquid is then reheated and simultaneously a second time period tp2 from the second point in time t2 is started to be measured.

[0064] The first time period tp1 and the second time period tp2 are measured by a time measuring device that may be comprised in a control unit described in conjunction to FIG. 3.

[0065] The liquid is reheated in the heating space until a third value Tv3 related to the first value Tv1 is reached. According to embodiments illustrated in FIG. 2 the third value Tv3 corresponds to approximately 90% of the first value Tv1 of temperature of the heating element, which third value Tv3 is approximately 108 C.

[0066] Alternatively, the liquid in the heating space is reheated until the second time period tp2 related to the first time period tp1 is reached. The second time period tp2 is related to the first time period tp1 by being comprised in a third time period and by a second predetermined percentage used to calculate the third time period so that the third time period constitutes the second predetermined percentage of the first time period. According to FIG. 2, the second predetermined percentage is approximately 90%.

[0067] The third time period is calculated by a control unit as a sum of the second time period tp2 a fourth time period tp4 according to equation (1) below:

tp3=tp2+tp4 (1)

[0068] Where, the fourth time period tp4 is a time period that is required to heat the heating element during heating of the liquid in the heating space without interruption from the first point in time t1 and from the start temperature T0 to the second value Tv2 of the temperature of the heating. With other words the heating element is not turned off when determining the fourth time period tp4.

[0069] When the third value Tv3 of temperature of the heating element has been reached and/or when the second time period tp2 has been reached, the heating element is turned off at an off-point in time toff and the temperature T of the heating element decreases again.

[0070] It has been observed that by implementing a heating-cooling cycle of a heating element which heating-cooling cycle is at least partly illustrated by the behaviour TB in FIG. 2 a deposition of scale on the heating element is removed in a simple and effective manner and without need of heating the heating element to high temperatures that may cause damage of the heating element.

[0071] After the heating element has been turned off, at said off-point in time toff, it may be turned on again when the temperature T of the heating element has decreased to the second value Tv2.

[0072] Thus, by repeating at least once, for example several times, the turning off and on of the heating element, the heating element is exposed to several oscillation cycles of temperature of the heating element, i.e. heating-cooling cycles or shift of temperature cycles. By this a further improved method for removing a deposition of scale on a heating element is provided.

[0073] When repeating the turning off and on of the heating element the first predetermined percentage may be equal or different each time the repeating procedure is performed. In a similar way the second predetermined percentage and the third predetermined percentage may be equal or different each time the repeating procedure is performed.

[0074] FIG. 3 illustrates an example of a household appliance which may be a dishwasher 5 comprising a heating element 1 arranged to heat a liquid in a heating space 3 of the dishwasher 5. Further the dishwasher 5 comprises a sensor 7 arranged to measure temperature of the heating element 1. The dishwasher 5 comprises also a control unit 9.

[0075] The heating space 3 that may also be called heating cavity is connected to a sump 4 of the dishwasher 5 by a channel 6 enabling transport of the liquid from the sump 4 to the heating space 3. This may be achieved by a pump 8 arranged to transport the liquid from the sump to the heating space 3. As illustrated in the example in FIG. 3, the pump 8, which may be any suitable pump for pumping liquid, may be arranged within the heating space 3.

[0076] The sump 4 is arranged to receive the liquid supplied to the dishwasher 5 through an inlet 11. The inlet 11 may be connected to a pipe network (not shown) for supplying water.

[0077] The heating element 1 is arranged to heat the liquid in the heating space 3, i.e. the heating element 1 is arranged in the heating space 3 so that a transfer of thermal energy between the liquid supplied to the heating space 3 and the heating element 1 is possible and sufficient for example for heating the liquid for use in the dishwasher 5. In a normal use the liquid is heated by the heating element 1 to about 70-80 C. The heating element 1 may be arranged to have direct contact with the liquid supplied to the heating space.

[0078] During an operation of the dishwasher 5, water is heated by the heating element 1 and is then pumped to a wash arm arrangement 10 of the dishwasher 5. The heating element 1 is connected to a power grid through the control unit 9. The heating of the heating element 1 is electrical and is achieved in a regular manner, which is therefore not necessary to described in detail.

[0079] The control unit 9 is connected to the sensor 7, which may be a temperature sensor of any suitable kinds. The control unit 9 is arranged to receive information data regarding temperature measured by the sensor 7. Further, the control unit 9 is arranged to process the information data from the sensor 7 in order to create behaviour of temperature of the heating element. The behaviour is shown in FIG. 2. Further the control unit 9 is arranged to enable monitoring i.e. evaluating of the behaviour of the temperature of the heating element.

[0080] The control unit 9 may further comprise a voltage measuring device (not shown), as for example an ADC, and a time measuring device, as for example a crystal oscillator (not shown). The control unit 9 may also comprise a voltage adapting means (not shown) for adjusting voltage to the heater.

[0081] According the embodiments in FIG. 3 the sensor 7 is arranged to measure temperature of the heating element 1. The sensor 7 may be arranged at a distance from the heating element 1, which distance enables sufficient measurement of temperature of the heating element 1. As illustrated in FIG. 3 the sensor 7 may be arranged directly on a surface of the heating element 1. If the heating element 1 is arranged to have contact with the liquid supplied to the heating space 3, for example by a first surface 12 the sensor 7 is arranged on a second surface 14 of the heating element 1, which second surface 14 does not have contact with the liquid supplied to the heating space 3. The sensor 7 may for example be attached to the second surface 14 by an adhesive.