GB2139083A

GB2139083A - Waste heat utilisation in the operation of a dishwashing machine

Info

Publication number: GB2139083A
Application number: GB08406093A
Authority: GB
Inventors: Ernst Stickel; Rudiger Eiermann
Original assignee: Individual
Current assignee: Individual
Priority date: 1983-05-06
Filing date: 1984-03-08
Publication date: 1984-11-07
Also published as: IT8420792A0; IT8420792A1; IT1174072B; GB2139083B; DE3316716C2; FR2545348A1; FR2545348B1; DE3316716A1; GB8406093D0

Abstract

In a dishwashing machine, a water reserve container (2) is thermally conductively connected with a rinsing container (1) of the machine for heat exchange purposes. The dishwashing machine may be operated employing a programme comprising preliminary rinse, cleaning, intermediate rinse, clear rinse and drying stages. The water in the container (2) is used partly for the preliminary rinse and partly for cleaning, and in the latter stage the part transferred to container (1) is heated to 65 DEG C. When the latter temperature is reached, the container may be re-filled with water, which is heated by heat exchange with the cleaning water in container (1). The water thus heated is partly used for the intermediate rinse and partly for clear rinsing in the following stages. <IMAGE>

Description

SPECIFICATION Waste heat utilisation in the operation of a dishwashing machine The present invention relates to a method operating a dishwashing machine, especially so as to utilise waste heat, and to a dishwashing machine for carrying out such method.

In a method known from DE-OS 2730489 for operation of a dishwashing machine, in a preliminary rinse program portion water from a freshwater feed duct or from a water reserve container is fed to a rinsing container, circulated through spray equipment and thereafter pumped away. In a cleaning program section, water from the freshwater duct or from the reserve container is fed to the rinsing container, heated up to a predetermined cleaning temperature by a heater and circulated. After a certain time, the reserve container is filled with water, which is preheated through thermal contact with the rinsing container as well as through a circulating duct conducted through the reserve conainer to an upper part of the spray equipment, the heater being switched off, and the spent rinsing liquid of the rinsing container is pumped away after the heat exchange.With the start of an intermediate rinse program section, the preheated water is let out of the reserve container into the rinsing container, and at the end of the clear rinse program section and after the emptying of the clear rinse liquid out of the rinsing container, the reserve container is filled up again with water for cooling of the rinsing container and for precipitation of water vapour forming in the drying program section. The water disposed in the reserve container is stored for the preliminary rinse or cleaning program section of a new program.

In this method, heat energy is withdrawn from the spent heated rinsing liquid and the fresh water used in subsequent program steps is heated up so that, apart from an appreciable energy saving, a careful treatment of crockery with respect to temperature fluctuations is achieved. Since the reserve container, designed for a rinsing container filling quantity of one rinsing operation, is emptied after the preliminary rinse, the rinsing container filling for the cleaning phase consists of fresh water and must be heated up from the fresh water temperature to the cleaning temperature. The reserve container is also emptied for the intermediate rinse so that filling of the rinsing container with cold or soft water takes place for the clear rinse and then has to be heated up to the clear rinse temperature.

In a dishwashing machine loadable at the front side as disclosed in DE-GM 75 00 904, a balancing weight is mounted in the rearward region at the machine housing to ensure stability of the machine even when loaded crockery baskets are pulled out onto extended rails. Through this fixed additional weight, the overall weight of the machine is appreciably increased, which is disadvantageous for transport of the machine.

In DE-GM 80 951 there is disclosed a dishwashing machine which, in place of a balancing weight, has a water reserve container consisting of a blow-moulded synthetic material part which is filled with water only at the place of installation of the machine. This water container is arranged between the ion exchanger and the soft water inlet opening of the rinsing container, so that it is disposed in the pressure-free region of the water inlet into the rinsing container and can be constructed to be thin-walled. Moreover, the water container is always kept filled.Through a cooling coil arranged at the rinsing container shell and connected with the water container, it is possible in the drying program section to convey the water stored in the water containerthrough the cooling coil for the coiling of the rinsing container shell.

In relation to the known machines and methods of operation thereof, it would be desirable to reduce energy and water consumption even further and make possible a shortening of the running time of the rinse programs.

According to a first aspect of the present invention there is provided a method of operating a dishwashing machine comprising a rinsing chamber, spray means for spraying water into the chamber, and a reservoir thermally conductively connected to the chamber and storing water, the method comprising the steps of carrying out a preliminary rinsing operation by feeding a part of the stored water into the chamber, circulating the fed water through the spray means and discharging the circulated water from the chamber, carrying out a cleaning operation by feeding the rest of the stored water into the chamber, heating such water to a predetermined temperature, circulating the heated water through the spray means, filling the reservoir with water after attainment of said temperature or after a predetermined time so as to permit the newly stored water to be preheated by thermal conduction from the chamber, and discharging from the chamber the water therein after the preheating of the newly stored water, carrying out an intermediate rinsing operation by feeding part of the preheated newly stored water into the chamber, circulating such water through the spray means, and discharging the circulated water from the chamber, and carrying out a clear rinsing operation by feeding the rest of the newly stored water into the chamber, heating such fed water to a predetermined temperature, circulating the heated water through the spray means, discharging the circulated water from the chamber after attainment of that temperature or after a predetermined time and simultaneously refilling the reservoir with water so as to permit cooling of the chamber by thermal conduction from the reservoir.

In a preferred example of the method, in particular for the recovery of waste heat in a household dishwashing machine with a rinsing container, an electrical heater arranged therein for the heating of rinsing liquid which is sprayable by means of a pump through a lower and an upper spray device onto crockery, and a water reserve conainer which acts as a heat exchanger and is thermally conductively connected with the rinsing coritainer, the method comprises the following steps:: a) in a preliminary rinse program section, a part of the water stored in the reserve container is fed to the rinsing container, circulated through the spray devices and thereafter pumped away; b) in a cleaning program section, the remaining water is fed out of the reserve container to the rinsing container, heated up to a predetermined cleaning temperature and circulated, and after attaining the cleaning temperature or after a certain action time the reserve container is filled with water, the filling of the reserve container being preheated through thermal contact with the rinsing container while the heater is switched off and the spent rinsing liquid of the rinsing container being pumped away after the heat exchange;; c) on the start of an intermediate rinse program section, a part of the preheated water is let out of the reserve container into the rinsing container, circulated through the spray devices and thereafter pumped away; d) in a clear rinse program section, the remaining water is fed out of the reserve container to the rinsing container, heated up to the predetermined clear rinse temperature and circulated; e) after reaching the clear rinse temperature or after a certain action time, the clear rinse liquid is pumped out of the rinsing container and the reserve container is simultaniously filled again with water for the cooling of the rinsing container and precipitation of the water vapour forming in the drying program section; and f) the water disposed in the reserve container is stored for the preliminary rinse and cleaning program sections or for the cleaning steps of a new program.

Such a method exemplifying the invention is applicable in the normal program as well as in the economy-care programs or the economy-fine programs for sensitive crockery and in the intensive program for particularly dirty crockery. By means of this method, energy is withdrawn before pumping away of the spent rinsing liquid and is transferred to following rinsing operations so that the crockery experiences a more careful treatment through the avoidance of large temperature fluctuations. The saved energy assists the heating-up operations and thereby contributes to reduction in the running time of the overall program.Due to the large temperature difference at the end of the clear rinse program section between the temperature of the hot crockery and the cold water flowing into the reserve container, the rinsing container surface lying against the reserve container forms a condensation surface which accelerates the drying of the crockery. Since the reserve container is always filled during the loading and unloading of the machine, an additional balancing weight for the stability of the machine is not needed.

According to a second aspect of the present invention there is provided a dishwashing machine for carrying out the method of the first aspect of the invention, the machine comprising a rinsing chamber, spray means for spraying water into the chamber, a water reservoir thermally conductively connected to the chamber, and water softening means comprising an ion exchanger and a salt container and being separated by a free flow path from fresh water inlet means of the machine, the volume of the reservoir being sufficient to permit charging of the chamber from the reservoir on each of at least two occasions with a predetermined quantity of water for a respective operating phase of the machine.

in a preferred embodiment, the machine comprises softening equipment which comprises an ion exchanger and a salt vessel and is separated by a free flow path from a fresh water connection, the volume of the reservoir being designed for at least two rinsing chamberfillingsforthe preliminary rinse and cleaning program sections or the intermediate rinse and clear rinse program sections.

The reservoir may be arranged upstream or downstream of the free flow path or may include the free flow path. The reservoir is preferably formed by a double-walled wall portion of a container defining the rinsing chamber or by a flat blow-moulded synthetic material part. The reservoir preferably has an aeration stub pipe and a feed stub pipe, which is connected with the ion exchanger, in the upper region, as well as an emptying duct, which opens into an outflow trough of the rinsing container and is blockable by a valve, in the base region. The rinsing container and the outside, remote from the rinsing container, of the reservoir can be provided with a noise-insulating and heat-insulating layer.

Since the volume of the reservoir suffices for rinsing chamber fillings for two rinsing operations, a preliminary rinsing operation and a cleaning operation or two cleaning operations, for example, can be performed with the water stored from a preceding rinse program in the reservoir, in which case the rinsing liquor has to be heated up in the cleaning operation merely from the storage temperature to the desired cleaning temperature. Since the reservoir is empty during the heating sections, no heat energy is withdrawn from the rinsing chamber.The water filling of the reservoir, which is heated up from the waste heat of the cleaning liquid before it is pumped away, again suffices for the intermediate rinse and clear rinse, in case the clear rinse quantity of liquid has to be heated up in the clear rinse program section, with the reservoir emptied, merely from the storage temperature to the clear rinse temperature. The process run-down is simple to control. The heater is loaded less, whilst an additional air heating can be dispensed with because of the cooling of the rinsing chamber during the drying. As a result, a special overheat protection of the heater, which for example may consist of a throughflow heater or a heater plate arranged in the outlet trough, is not necessary. If the reservoir is filled merely with soft warer from the ion exchanger, then long transit times are available for the regeneration of the ion exchanger and make possible the rngener- ation of the ion exchange material with less salt solution.

An example of the method and an embodiment of the dishwashing machine of the present invention will now be more particularly described byway of example with reference to the accompanying drawings, in which: Figure 1 is a schematic sectional view of a dishwashing machine embodying the invention; and Figure 2 is a diagram of water temperature in the performance of a method exemplifying the invention.

Referring now to the drawings, there is shown a dishwashing machine which comprises a rinsing container 1, which is made from thin sheet metal and the rear wall of which is, in the illustrated embodiment, constructed to be double-walled so as to form a reserve container 2. The reserve container 2 is provided at its top with an aeration stub pipe 3, onto which an aeration hose 4 is plugged. In addition, a feed stub pipe 5, which is connected with the soft water outlet of an ion exchanger (not shown), opens into the reserve container somewhat below the aeration stub pipe 3. Associated with the ion exchanger is a salt vessel, the ion exchanger and salt vessel together form water s#oftening equipment which is separated from a fresh water inlet of the machine by a free flow path.The reserve container is disposed in the pressure-free region of the water inlet into the rinsing container so that it can be constructed to be thin-walled. Since the reserve container is filled only with soft water, there is hardly any risk of calcification. For the emptying of the reserve container 2 into the rinsing container 1, an emptying duct 8, which can be opened and closed by a valve 7, leads from the rinsing container bottom into an outlet trough 6 of the rinsing container. Also associated with the rinsing container 1 are a heater for heating water therein and upper and lower spray devices for spraying water onto crockery in the rinsing chamber.

The temperature-time course of a dishwashing operation exemplifying the invention, and performable by the machine of Figure 1, is shown in Figure 2.

Forthe performance of a program consisting of the sections of "preliminary rinse", "cleaning", "intermediate rinse", "clear rinse" and "drying", the following program course results: The program starts with a filling program step 11, during which the valve 7 is opened under the control of time or level and the rinsing container 1 is filled from the full reserve container 2 with the water quantity needed for the preliminary rinse, this quantity being only part of the content of the container 2. The water stored in the reserve containerfrom a preceding rinse program has, for example, a temperature of 200C corresponding to the room temperature.After running-in of the needed water quantity, the valve 7 is closed and, in the preliminary rinse phase 12, the rinsing container filling is circulated through the spray equipment of the machine for the rinsing of crockery and thereafter pumped away into a discharge system.

After completion of the preliminary rinse program section, the reserve container is emptied into the rinsing container during a further filling program step 13, in which case this residual water quantity corresponds to the rinsing container filling needed for cleaning. The cleaning liquid is heated up to a temperature of, for example, 650C with the preliminary rinse container empty and in that case circulated with the addition of a cleaning agent.

On attainment of the cleaning temperature of 650C or after a certain action time, the reserve container 2 is filled in the program step 14 through the feed stub pipe 5 with the valve 7 still closed, in which case the displaced air can escape through the aeration stub pipe 3 and the aeration hose 4. A heat exchange with the water of the reserve container takes place through the cleaning liquid which continues to be circulated up to the end of the cleaning phase 15 and is then pumped away.In that case, heat is withdrawn from the cleaning liquor and the water of the reserve container is heated to, for example, 40 C. Since the cleaning liquor conducted out into the discharge system is cooled down to this temperature, the outflow pipes and the environment are not subjected to hot liquor and an additional cold water feed for cooling of the liquor can be dispensed with.

In a third filling program step 16, a part of the preheated water is again fed from the reserve container into the rinsing container for the intermediate rinse program section. Since the temperature transition from cleaning to intermediate rinse is relatively small by reason of the heat exchange, the crockery is not subjected to substantial temperature change. In the intermediate rinse phase 17, the rinsing container filling is circulated and pumped away thereafter.

After completion of the intermediate rinse, the reserve container is completely emptied into the rinsing container in the program step 18, in which case the resultant rinsing container filling corresponds to the quantity of water needed for the clear rinse. The water already heated to 400C is circulated by way of the spray equipment subject to the addition of a clear rinsing agent and after or during the heating to a clear rinse temperature of, for example, 70 C. After attainment of the clear rinse temperature or after run-down of an action time 19, the empty reserve container is again filled up with cold water so that a heat exchange between the rinsing container and the reserve container takes place again at or towards the end of the clear rinse phase 20 or 21.In that case, the clear rinse liquid can be pumped away immediately after attainment of the clean rinse temperature or after run-down of the action time 19 then cooled down somewhat. A heat transfer to a reserve container water temperature of substantially above 200C is not aimed at in this program section. Due to the large temperature difference 22 between the crockery temperature of about 65 C and the reserve container water temperature of about 20"C, a condensation surface favouring the drying of the crockery arises in the drying phase 23 at the rinsing container wall associated with the reserve container. As a result, the actuation of an additional radiant heater in the drying phase 23 becomes redundant. It is in that case possible to insulate the rinsing container and the outside surface, remote from the rinsing container, of the reserve container without the function oftheconde- nsation surface being restricted or the drying operation being significantly impaired. Apart from heat insulation, noise insulation can also be provided at the same time.

The curves 24, 25 and 26 indicate the temperature course of the water in the reserve container after filling with cold water at about 1 0 C.

Claims

1. A method of operating a dishwashing machine comprising a rinsing chamber, spray means for spraying water into the chamber, and a reservoir thermally conductively connected to the chamber and storing water, the method comprising the steps of carrying out a preliminary rinsing operation by feeding a part of the stored water into the chamber, circulating the fed water through the spray means and discharging the circulated water from the chamber, carrying out a cleaning operation by feeding the rest of the stored water into the chamber, heating such water to a predetermined temperature, circulating the heated water through the spray means, filling the reservoir with water after attainment of said temperature or after a predetermined time so as to permit the newly stored water to be preheated by thermal conduction from the chamber, and discharging from the chamber the water therein after the preheating of the newly stored water, carrying out an intermediate rinsing operation by feeding part of the preheated newly stored water into the chamber, circulating such water through the spray means, and discharging the circulated water from the chamber, and carrying out a clear rinsing operation by feeding the rest of the newly stored water into the chamber, heating such fed water to a predetermined temperature, circulating the heated water through the spray means, discharging the circulated water from the chamber after attainment of that temperature or after a predetermined time and simultaneously refilling the reservoir with water so as to permit cooling of the chamber by thermal conduction from the reservoir.

2. A method as claimed in claim 1,wherein the water filled into the reservoir in both the cleaning and clear rinsing operations is one of fresh water and softened water.

3. A method as claimed in claim 1, wherein the water filled into the reservoir in the cleaning operation is fresh water and in the clear rinsing operation softened water.

4. A method substantially as hereinbefore described with reference to the accompanying drawings.

5. A dishwashing machine for carrying out the method claimed in claim 1,the machine comprising a rinsing chamber, spray means for spraying water into the chamber, a water reservoir thermally conductively connected to the chamber, and water softening means comprising an ion exchanger and a salt container and being separated by a free flow path from fresh water inlet means of the machine, the volume of the reservoir being sufficient to permit charging of the chamber from the reservoir on each of at least two occasions with a predetermined quantity of water for a respective operating phase of the machine.

6. A dishwashing machine as claimed in claim 5, wherein the reservoir is arranged upstream of the free flow path.

7. A dishwashing machine as claimed in claim 5, wherein the reservoir is arranged downstream of the free flow path.

8. A dishwashing machine as claimed in claim 5, wherein the reservoir includes the free flow path.

9. A dishwashing machine as claimed in any one of claims 5 to 8, wherein the chamber is defined by a housing and the reservoir by a double-walled portion of the housing or a shaped hollow member arranged at the housing, the reservoir having a water inlet and an air outlet in an upper portion thereof and a water outlet in a lower region thereof.

10. A dishwashing machine as claimed in claim 9, comprising a water transfer duct connecting the water outlet of the reservoir to an outflow trough of the chamber, and valve means to control water flow through the duct.

11. Adishwashing machine as claimed in any one of claims 5 to 10, comprising insulating means at least partially insulating the chamber and the reservoir against transmission of noise and heat externally of the machine.

12. A dishwashing machine as claimed in claim 5 and substantially as hereinbefore described with reference to the accompanying drawings.