WO2007149698A1

WO2007149698A1 - Method of disinfecting items in a dishwasher and dishwasher for carrying out the method

Info

Publication number: WO2007149698A1
Application number: PCT/US2007/070372
Authority: WO
Inventors: Harald Disch; Udo Burkle; Rolf Calmbacher
Original assignee: Premark Feg L.L.C.
Priority date: 2006-06-22
Filing date: 2007-06-05
Publication date: 2007-12-27
Also published as: DE102006028607A1; DE202006020579U1

Abstract

Hand-loaded dishwasher in the form of a box- type warewasher (2), in particular a commercial dishwasher, and method for operating it, with a disinfection phase being carried out between a washing phase and a final rinse phase, and steam being introduced into the treatment chamber (2) of the dishwasher during said disinfection phase in order to disinfect items to be washed, and with said items then being rinsed with final rinse liquid in the final rinse phase, this final rinse liquid being at a temperature which is lower than the steam disinfection temperature.

Description

METHOD OF DISINFECTING ITEMS IN A DISHWASHER AND DISHWASHER

FOR CARRYING OUT THE METHOD

The invention relates to a hand-loaded dishwasher in the form of a box-type warewasher, in particular a commercial dishwasher, and to a method for operating it, according to the patent claims.

WO 2006/037447 Al discloses a dishwasher in which items to be washed are cleaned with washing liquid and then rinsed with fresh water which has been heated up in a boiler. The items to be washed are then subjected to a thermal aftertreatment with steam. The steam for the thermal aftertreatment is generated in the boiler, which is provided to heat up the fresh water, and introduced into the dishwasher through the rinse system which is provided for the final rinse process.

Dishwashers, in particular commercial dishwashers, in the form of a box-type warewasher may be hood-type warewashers or front-loader warewashers. Front-loader warewashers may be under-counter machines or top-counter machines or built-in-counter machines.

Commercial dishwashers used in hospitals in England are subject to a special thermal disinfection regulation which states that an item of tableware is only thermally disinfected if it is subjected to a predetermined temperature for a predetermined time period.

Modern dishwashers satisfy this disinfection regulation mainly as a result of a prolonged final rinse cycle, with fresh water having a temperature of, for example, 85°C being sprayed onto the items being washed for at least 30 seconds. However, this type of process uses a considerable amount of fresh water (approximately 10-12 liters/cycle) and the total program run time of, for example, 6-10 minutes is very long too. Parts of the items being washed or regions of the items being washed which are in so-called shadow zones in the dishwasher have only an inadequate amount of final rinse liquid applied to them and are therefore not sufficiently disinfected. Shadow zones are those regions which the jets of final rinse liquid cannot reach directly. A further disadvantage of the high temperature of the final rinse liquid is that the items being washed are at a very high temperature of, for example, 70⁰C - 80⁰C at the end of the final rinse process and an operator may therefore burn his fingers on the item which has been washed if he removes the item which has been washed immediately after the final rinse cycle of the dishwasher without using gloves.

The aim of the invention is to achieve the object of optimizing cleaning and disinfection of items to be washed. According to the invention, this object is achieved by the features of the independent patent claims.

Further features of the invention can be found in the subclaims.

The invention provides at least one of the following advantages: reduction in the amount of water consumed; reduction in the program run time; improvement of the disinfection result, in particular in shadow zones of the items being washed; reduction in the temperature of the items which have been washed at the end of the final rinse process, as a result of which the items which have been washed can be removed from the dishwasher immediately after the final rinse phase at a lower temperature than in the prior art, and this is more convenient for the operator.

The invention comprises two inventive ideas which can be used both together and also separately and independently of one another. These ideas are disinfection by means of steam in a disinfection phase between the washing phase and the final rinse phase, and the use of steam to heat up the washing liquid during the washing phase. According to the invention, steam can be used as an energy source for heating up the washing liquid during the washing phase and/or as a disinfection medium during the disinfection phase between the washing phase and the final rinse phase. If steam is used to heat up the washing liquid, an additional heating apparatus for heating up the washing liquid can be dispensed with. In special cases, an additional heating apparatus can also be used.

The use of steam has the following advantages:

a) very efficient heat transfer on account of a high heat-transfer coefficient in the case of film condensation of steam on the surface of the items being washed,

b) efficient energy transfer to the items being washed when the steam condenses, on account of the released condensation enthalpy,

c) ideal and uniform distribution of the steam (gas) to all parts of the items being washed, even in shadow zones,

d) low water consumption on account of a high specific volume of steam, with, according to the invention, preferably the entire interior of the dishwasher being completely filled with steam and it being possible to generate the steam with much less water for this purpose,

e) injection of steam during the washing phase leads to 100% saturation of the atmospheric moisture in the interior of the dishwasher, and this results in a significant reduction in evaporation losses during the washing phase.

According to one preferred embodiment of the invention, the dishwasher is designed for the following process sequence, but without the invention being restricted to the values stated in the text which follows:

1. Washing process during the washing phase: the dishwasher starts the washing process at a washing temperature of between 40⁰C and 80⁰C, preferably between 60⁰C and 70⁰C. Steam is introduced, for example sprayed, into the treatment chamber during the washing process. As a result, the temperature of the washing liquid is increased. This process is continued until the washing liquid reaches a temperature of approximately 70⁰C. This process step can be carried out over 2-4 minutes, depending on the initial temperature of the washing liquid. This therefore lasts somewhat longer for the very first run through a program cycle (run through a washing, disinfection and final rinse program) than for program cycles which are carried out subsequently.

2. After the washing process, a thermal disinfection process using steam, preferably saturated steam, is carried out during a disinfection phase until the required temperature of, for example, 90⁰C is achieved in the region of the items being washed in the treatment chamber for 1 second, for example. This thermal disinfection process lasts for 1 to 2 minutes, for example.

3. The thermal disinfection process (disinfection phase) is followed by a final rinse cycle (final rinse phase) using final rinse liquid, preferably fresh water, which is at a final rinse liquid temperature of, for example, between 10⁰C and 70⁰C or more preferably between 20⁰C and 50⁰C. The quantity of final rinse liquid required for this purpose is, for example, between 2 and 3 liters per washing program. On account of this relatively low temperature of the final rinse liquid, firstly the items which have been washed are cooled to such an extent that they can be easily handled by an operator, and secondly the steam condenses on the relatively cold spray mist and the energy remains in the dishwasher and is not lost by opening the door of the treatment chamber at the end of the program cycle. This process step or the final rinse phase lasts for between 5 seconds and 20 seconds, for example.

The following advantages can be achieved by the invention: reduction in the amount of water consumed; reduction in the total program run time; improvement of the disinfection result, in particular in shadow zones; reduction in the temperature of the items which have been washed at the end of the program cycle, so that an operator can handle said items more easily.

The invention is described below using preferred embodiments as examples, with reference to the attached drawings, in which

Fig. 1 schematically shows a vertical section through a hand-loaded dishwasher according to the invention, and

Fig. 2 schematically shows a vertical section through a further embodiment of a hand- loaded dishwasher according to the invention.

The inventive dishwashers 2 and, respectively, 102 illustrated in figs 1 and 2 are box-type warewashers, preferably commercial dishwashers. Said dishwashers comprise a treatment chamber 2 in a chamber housing 4 for holding items to be washed (not shown). Items to be washed include, for example, plates, cups, pots and pans, trays, knives, forks, spoons and similar kitchen utensils. A washing tank 6 for collecting washing liquid and a final rinse liquid which has been sprayed and which flows from the treatment chamber 2 into the washing tank 6 due to the force of gravity is located beneath the treatment chamber 2. A washing liquid supply device 8 comprises a washing pump 10 in a washing liquid line system 12 for supplying washing liquid from the washing tank 6 to upper washing nozzles 14 above the items to be washed and to lower washing nozzles 16 below the items to be washed. In this case, said washing nozzles are spray nozzles for the washing liquid. Washing nozzles of this type can be arranged in the treatment chamber 2 at the top and bottom, as in the drawings, or only at the top or only at the bottom and/or on the sides of the treatment chamber 2.

A final rinse liquid supply device 20 is provided for supplying final rinse liquid to upper final rinse nozzles 24 and to lower final rinse nozzles 26. The final rinse nozzles are spray nozzles for spraying final rinse liquid onto the items being washed. The final rinse nozzles can be arranged in the treatment chamber 2 at the top, above the items being washed, and at the bottom, below the items being washed, as in the drawings, or only at the top or only at the bottom and/or on the side of the treatment chamber 2. The final rinse liquid supply device 20 comprises a final rinse line system 28 which connects a final rinse pump 30 to the final rinse nozzles 24 and 26. The intake side of the final rinse pump 30 is connected to a fresh water connection 34 by means of a return-prevention means 32. A controllable valve 36 is preferably located between the fresh water connection 34 and the return- prevention means 32. The return-prevention means 32 has an air gap in order to prevent liquid from being able to return to the fresh water connection 34 from the dishwasher 2 or 102 and thus being able to enter the public drinking water supply system.

The final rinse liquid is preferably pure water of drinking water quality, preferably from the drinking water supply system. Final rinse aid can be added to the water. This can be done automatically upstream or downstream of the final rinse pump 30.

The washing liquid in the washing tank 6 is preferably water to which cleaner is added. Cleaner is preferably added to the water automatically.

In the two embodiments from figs 1 and 2, a steam generating device 40 is provided, according to the invention, for generating steam and for supplying the steam to the treatment chamber 2. The steam generating device 40 comprises a steam generator 42 whose steam discharge side 44 issues into the treatment chamber 2 directly or via a steam supply line 46 (and/or via said or other nozzles). The steam generator 42 is connected to a fresh water supply line 48 through which said steam generator can be automatically supplied with the quantity of fresh water required to generate steam.

The steam generator 42 may be arranged inside or outside the chamber housing 4, preferably outside the chamber housing 4 but inside a machine housing (not shown) of the dishwasher. Furthermore, the steam generator 42 may also be arranged outside the machine housing.

The dishwashers from figs 1 and 2 each comprise a program-control device 50 which contains at least one washing program. A washing program is designed to control at least one program cycle. A program cycle is made up of at least one washing cycle during a washing phase, at least one steam cycle during a disinfection phase, and at least one final rinse cycle during a final rinse phase. A user interface (not shown) may be associated with the program-control device. According to the invention, the program-control device 50 is designed in such a way that items to be washed are cleaned during a washing phase by washing liquid being conveyed by means of the washing pump 10 from the washing tank 6 to the washing nozzles 14 and 16 and being sprayed onto the items to be washed; that a disinfection phase is carried out after the washing phase and the items to be washed are disinfected in the treatment chamber 2 by means of steam from the steam generator 42 during said disinfection phase; and that the final rinse phase is carried out after the disinfection phase and final rinse liquid is sprayed through the final rinse nozzles 24 and 26 onto the items being washed during said final rinse phase, with the final rinse liquid being at a temperature which is lower than the steam disinfection temperature and is preferably at most 70°C or less.

During the disinfection phase, a temperature of at least 80⁰C or of at least 90°C is generated in the region of the area for holding items to be washed in the treatment chamber 2 by means of the steam. This minimum temperature is maintained by means of the steam for a predetermined minimum time period which preferably lasts at least 1 second.

The steam is preferably introduced into the treatment chamber 2 in such a quantity that it fills the entire treatment chamber 2.

The final rinse liquid may be at room temperature or lower, for example only a few degrees above 0⁰C. The temperature is lower than the disinfection temperature which is generated by means of steam during the disinfection phase.

According to the preferred embodiment of the invention, the program -control device 50 is designed and connected to the functional elements of the dishwasher in such a way that steam from the steam generator 42 is also introduced into the treatment chamber 2 during the washing phase, and the washing liquid which is sprayed by the washing nozzles 14 and 16 is heated up by means of this steam. The washing liquid can additionally be heated up by a heat source which is provided in the washing tank 6 for heating up the washing liquid. However, according to the preferred embodiment which is illustrated in the drawings, only the steam generator 42, which also generates the steam for the disinfection phase, is provided for heating up the washing liquid.

The washing liquid can be heated up to any suitable temperature by means of the steam from the steam generator 42, for example to a temperature of between 40⁰C and 80⁰C, preferably to a temperature of between 60⁰C and 70⁰C. The steam which is provided to heat up the washing liquid is preferably introduced into the treatment chamber 2 during the washing phase in such a way that it fills the entire treatment chamber 2.

A valve 52 which can be controlled by the program-control device 50 is preferably arranged in the fresh water supply line 48 of the steam generator 42.

Furthermore, a non-return valve 54 can be arranged between this controllable valve 52 and the steam generator 42, which non-return valve prevents fresh water returning from the steam generator 42 by closing in the direction of the steam generator 42 to the controllable valve 52.

The steam generator 42 may be provided with a relief valve 56 through which it can be emptied if required.

A discharge line 60 is connected to the base or to a sump 58 of the washing tank 6, through which discharge line the washing tank 6 can be emptied and particles of dirt can be removed, preferably by means of a discharge pump 62 which is arranged in the discharge line 60.

Differences between the dishwasher 2 from fig. 1 and the dishwasher 102 from fig. 2:

In addition to a fresh water connection 34, the dishwasher 2 from fig. 1 has a second fresh water connection 64 from which fresh water can be supplied to the steam generator 42 independently of the fresh water connection 34. Fresh water can be supplied to the final rinse liquid supply device 20 by the fresh water connection 34 independently of the second fresh water connection 64 of the steam generator 42.

The dishwasher 2 from fig. 1 may also comprise a fresh water supply line 66 with a valve 68 which can be controlled by the program-control device 50, which line has a downstream end 70 which issues into the treatment chamber 2 or into the washing tank 6 and is used to fill the washing tank 6 with fresh water for the first time. According to fig. 1, the upstream start 72 of this fresh water supply line 66 may be connected to the second fresh water connection 64 or, according to an embodiment which is not shown, be connected to the fresh water connection 34. Only the fresh water connection 34 is provided in the dishwasher 102 from fig. 2. The upstream start 74 of the fresh water supply line 48 which leads to the steam generator 42 is connected to the delivery side of the final rinse pump 30 at a point which is situated between the final rinse pump 30 and a valve 76 which can be controlled by the program- control device 50. This controllable valve 76 is located in a line 78 which connects the delivery side of the final rinse pump 30 to the final rinse line system 28. The upstream start 72 of the fresh water supply line 76, which is used to fill the washing tank 6 for the first time, may also be connected to this connecting line 78 between the final rinse pump 30 and the controllable valve 76. The final rinse pump 30 from fig. 2 is therefore not only provided to convey the final rinse liquid but also to supply fresh water to the steam generator 42 and to the fresh water supply line 76 for filling the washing tank 6 for the first time.

A washing phase may comprise one or more washing cycles; a disinfection phase may comprise one or more disinfection cycles; and a final rinse phase may comprise one or more final rinse cycles.

Claims

1. A method for cleaning items to be washed in a hand-loaded dishwasher in the form of a box-type warewasher, in particular a commercial dishwasher, with the items to be washed being washed in a treatment chamber (2) during a washing phase and rinsed during a final rinse phase, wherein the items to be washed are disinfected by means of steam during a disinfection phase, with the disinfection phase being carried out after the washing phase but before the final rinse phase, and wherein the items to be washed are rinsed with final rinse liquid during the final rinse phase, this final rinse liquid being at a temperature which is lower than the temperature generated by means of the steam for disinfection during the disinfection phase.

2. The method as claimed in claim 1, wherein a temperature of at least 80⁰C, preferably of at least 90⁰C, is generated in the region of the area for holding items to be washed in the treatment chamber by means of the steam, and wherein this minimum temperature is maintained by means of the steam for a predetermined minimum time period which preferably lasts at least 1 second.

3. The method as claimed in either of the preceding claims, wherein so much steam is introduced into the treatment chamber during the disinfection phase that said steam spreads throughout the entire treatment chamber.

4. The method as claimed in one of the preceding claims, wherein final rinsing is carried out during the final rinse phase with final rinse liquid having a temperature of 70⁰C or less.

5. The method as claimed in one of the preceding claims, wherein steam is introduced into the treatment chamber (2) during the washing phase and the washing liquid is heated up by means of this steam.

6. The method as claimed in claim 5, wherein the washing liquid is heated up to a washing temperature of between 40⁰C and 80⁰C, preferably between 60⁰C and 70⁰C, by means of the steam.

7. The method as claimed in claim 5 or 6, wherein steam is introduced into the treatment chamber during the washing phase until the temperature of the washing water has reached the predetermined value.

8. The method as claimed in at least one of the preceding claims, wherein the washing process of the washing phase is started when the temperature of the washing liquid is between 40⁰C and 80⁰C, preferably between 60⁰C and 70⁰C, with the temperature of the washing liquid being increased by the introduction of steam into the treatment chamber until the washing liquid has reached a predetermined setpoint temperature; wherein the disinfection phase is carried out after the washing phase and steam is introduced into the treatment chamber during the disinfection phase and a setpoint temperature of at least 80⁰C, preferably of at least 90⁰C, is generated in the treatment chamber by means of the steam, and this setpoint temperature is maintained for a predetermined minimum time period; and wherein no longer steam but only final rinse liquid having a temperature of 70⁰C or less is introduced into the treatment chamber during the final rinse phase which follows the disinfection phase.

9. A hand-loaded dishwasher in the form of a box-type warewasher, in particular a commercial dishwasher, comprising a treatment chamber (2) for holding items to be washed; a washing tank (6) for collecting washing liquid and final rinse liquid which has been sprayed; a washing liquid supply device (8) with a washing pump (10) for supplying washing liquid from the washing tank (6) to spray nozzles (14, 16) in the treatment chamber (2); a final rinse liquid supply device (20) for supplying final rinse liquid to spray nozzles (24, 26) in the treatment chamber (2); a program-control device (50) for controlling the washing liquid supply device (8) and for controlling the final rinse liquid supply device (20) to automatically carry out at least one program cycle which comprises at least one washing phase and at least one final rinse phase; wherein a steam generating device (40), which is controlled by the program-control device (50), is provided for generating steam and for supplying the steam to the treatment chamber (2); and wherein the dishwasher is designed to automatically carry out the method as claimed in at least one of the preceding claims by means of the program-control device (50).

10. The dishwasher as claimed in claim 9, wherein the steam generating device (40) has a steam generator (42) and a valve (52) which can be controlled by the program-control device (50), with the controllable valve (52) being arranged upstream of the steam generator in a fresh water supply line (48) of the steam generator (42).

11. The dishwasher as claimed in claim 10, wherein a non-return valve (54) is arranged between the controllable valve (52) and the steam generator (42) in the fresh water supply line (48), said non-return valve closing in the direction of the steam generator (42) toward the controllable valve (52).

12. The dishwasher as claimed in one of claims 9 to 11, wherein two fresh water connections (34, 64) which are separate from one another are provided, one of these fresh water connections being provided for the fresh water supply to the final rinse liquid supply device (20) and the other fresh water connection being provided for the fresh water supply to the steam generating device (40).

13. The dishwasher as claimed in claim 12, wherein a return-prevention means (32) is arranged between the final rinse liquid supply device (20) and its fresh water connection (34).

14. The dishwasher as claimed in one of claims 9 to 11, wherein a fresh water connection (34) is provided to which a return-prevention means (32) is connected, and wherein the final rinse liquid supply device (20) and the steam generating device (40) are connected to the downstream end of the return-prevention means (32).

15. The dishwasher as claimed in one of claims 9 to 14, wherein a fresh water supply line (66) is provided which issues into the treatment chamber (2) or into the washing tank (6) separately from the spray nozzles in order to rapidly fill the washing tank (6).