Patent Application
20220061626
This application relates generally to warewash machines for washing wares and, more specifically, to a warewash machine drain down process of such a warewash machine.
In some jurisdictions, the plumbing code requires that all hot water to the drains needs to be at most 140° F. In hot operated warewash machines the exiting drain water (e.g., from the wash tank) is commonly over 140 F. This necessitates tempering before discharge through the plumbing network.
For some machines, to temper drain water, a large volume of colder fresh water is directly mixed with the machine exiting hot drain water, such as in a drain box or compartment along the drain line, to bring the temperature to below 140° F. before discharge. These tempering systems are known as direct drain water tempering (DWT). While this DWT process assists in getting the drain to meet the temperature requirements, it is associated with substantial freshwater use, and is not water efficient and economical.
The goal of reducing the amount of freshwater usage caused by DWT systems lead to the development of an alternative, in the form of drain water energy recovery (DWER) systems. DWER systems allow for recovery of heat from the hot waste machine drain water using heat exchangers, while in the process the hot drain water cools to below the 140° F. limit. In most cases, the recovered heat is reused for preheating incoming fresh cold water to the machine especially the rinse water.
The DWER technology is an improvement over the DWT system, requiring significantly less amount of fresh cold water for tempering, which mainly occurs during machine shutdown. Moreover, the tempering water used during the shutdown has the benefit of being used for machine wash tank and DWER system self-cleaning, resulting energy and water savings.
However, improvements that reduce water usage and/or facilitate faster draining of the machine wash tank are still desired.
In one aspect, a method of draining a wash tank of a warewash machine involves: (a) turning off, or maintaining off, both a booster tank heater and a wash tank heater of the machine; (b) simultaneously operating a rinse pump, operating a drain pump and opening a booster fill valve of the machine so that all of the following take place at the same time: (b1) fresh water is delivered through a heat exchanger to the booster tank; (b2) fresh water is delivered by the rinse pump from the booster tank to a rinse spray system and falls down into the wash tank; and (b3) liquid from the wash tank is delivered by the drain pump to a drain flow path and through the heat exchanger to exchange heat with the fresh water delivered through the heat exchanger.
In another aspect, a method is provided for draining a wash tank of a warewash machine that includes a ware spray zone, a wash pump, a wash spray system, a booster tank, a rinse pump, a rinse spray system, a drain pump, a drain flow path, a fresh water input path, a booster fill valve and a heat exchanger. The wash tank is located below the ware spray zone and includes a wash tank heater. The wash pump includes an input connected to receive liquid from the wash tank and an output connected to deliver liquid to the wash spray system. The heat exchanger is located along the fresh water input path and along the drain flow path for heat exchange between liquid traveling along the drain flow path and fresh water traveling along the fresh water input path. The booster tank includes heater, an input connected to receive fresh water from the heat exchanger as controlled by the booster fill valve, and an output connected to deliver fresh water to an input of the rinse pump. The rinse pump includes an output connected to deliver fresh water to the rinse spray system. The drain pump includes an input connected to receive liquid from the wash tank and an output connected to the drain flow path. The method involves, responsive to a wash tank drain down trigger, carrying out a drain down process in which: (a) if the wash tank heater is on, turning off the wash tank heater for the drain down process or, if the wash tank heater is off, maintaining the wash tank heater off for the drain down process; (b) if the booster tank heater is on, turning off the booster tank heater for the drain down process or, if the booster tank heater is off, maintaining the booster tank heater off for the drain down process; and (c) simultaneously operating the rinse pump, operating the drain pump and opening the booster fill valve so that all of the following take place at the same time: (c1) fresh water is delivered through the heat exchanger to the booster tank, (c2) fresh water is delivered by the rinse pump from the booster tank to the rinse spray system and falls down into the wash tank, and (c3) liquid from the wash tank is delivered by the drain pump to the drain flow path and through the heat exchanger to exchange heat with the fresh water delivered through the heat exchanger.
The details of one or more embodiments are set forth in the accompanying drawings and the description below. Other features, objects, and advantages will be apparent from the description and drawings, and from the claims.
Referring to
A wash pump 30 includes an input connected to receive liquid from the wash tank 14 and an output connected to deliver liquid to a wash spray system 32 (e.g., one or more spray nozzles that spray the wash liquid onto wares for cleaning the wares). A heat exchanger 34 is located along a fresh water input path 36 and along a drain flow path 38 for heat exchange between liquid traveling along the drain flow path and fresh water traveling along the fresh water input path. A booster tank 40 includes an input connected to receive fresh water from the heat exchanger 34 as controlled by a booster fill valve 42, an output connected to deliver fresh water to an input of a rinse pump 44, and also includes a booster tank heater 46 for heating the fresh water in the tank to a desired rinse temperature (e.g., between 180° F. and 192° F.). The rinse pump 44 includes an output connected to deliver fresh water to a rinse spray system 48 (e.g., one or more spray nozzles that spray the fresh water (e.g., potable water or potable water with rinse agent) as rinse liquid onto wares for rinsing). A drain pump 50 includes an input connected to receive liquid from the wash tank 14 and an output connected to the drain flow path 38 to deliver liquid from the wash tank to the heat exchanger 34. Temperature sensors 52 may also be provided for detecting the temperature of draining wash tank liquid both before and after passing through the heat exchanger 34. The drain flow path 38 connects to a site drain 55.
A controller 200 controls the various machine components for cleaning cycles (e.g., wash phase followed by a rinse phase) and other purposes, including machine-startup, machine cleaning and machine shutdown. As used herein, the term controller is intended to broadly encompass any circuit (e.g., solid state, application specific integrated circuit (ASIC), an electronic circuit, a combinational logic circuit, a field programmable gate array (FPGA)), processor(s) (e.g., shared, dedicated, or group—including hardware or software that executes code), software, firmware and/or other components, or a combination of some or all of the above, that carries out the control functions of the device or the control functions of any component thereof.
Complete or substantially complete draining of the wash tank 14 may typically occur during either a machine cleaning operation (as initiated by an operator pushing a machine clean input button associated with a user interface 202 during the day) or a machine shutdown operation (as initiated by an operator turning off the machine via the interface 202 at the end of the day).
Referring to
Line 102 represents the point in time when the drain down process is triggered. As shown, the booster heater 46 and wash tank heater 20 are both immediately turned off (or maintained off if not on), and then the drain pump 50 and rinse pump 44 are both turned on to operate simultaneously, while at the same time the booster fill valve 42 is opened. As a result, fresh water is delivered through the heat exchanger 34 to the booster tank 40, and fresh water is delivered by the rinse pump 44 from the booster tank 40 to the rinse spray system 44 and falls down into the wash tank 14, and liquid from the wash tank 14 is delivered by the drain pump 50 to the drain flow path 38 and through the heat exchanger 34 to exchange heat with the fresh water delivered through the heat exchanger, all at the same time. In the exemplary embodiment, the drain pump 50 and rinse pump 44 are both turned on at the same time as the booster fill valve 42 in order to achieve the simultaneous operation described above. However, it is recognized that a slight staggering between pump start times and valve opening could also be implemented to achieve the simultaneous pump operation that overlaps with the fill valve open condition (e.g., open booster fill valve 42 first, then turn on rinse pump 44 and then turn on drain pump 50).
Even though the fresh water delivered from the booster tank 40 to the wash spray system 32 may initially be above the temperature of the liquid in the wash tank (e.g., for the first 20-30 seconds following initiation of the drain down), heat exchange of the draining tank liquid with the incoming fresh water assures that the temperature of water reaching the site drain 55 is below the set code limit (e.g., typically 140° F.). The incoming fresh water to the booster tank eventually (e.g., after the 20-30 seconds) lowers the temperature of the water in the booster sufficiently so that the fresh water delivered via the wash spray system 32 also brings down the temperature of the liquid in the wash tank during the draining.
After a set time period, or once the temperature of the liquid in the wash tank is detected to be below the set code limit, the rinse pump is turned off, as indicated at 104. Here, the booster fill valve is maintained in the open state because the booster tank needs to be filled so that the machine is ready for operation following completion of the draining. The drain pump 50 also continues to operate until to assure substantially complete draining of the wash tank 14. For example, the drain pump may operate until water is below a sensor, then for an additional time period 106 and then with a sequence of pulse operations 108. The booster heater is also turned on again, as at 110, to begin to get the water up to needed temperatures. The booster water can then be used to refill the machine to get the machine ready for subsequent cleaning cycles.
An exemplary wash tank draining process as part of a machine shutdown operation is shown in a time graph 120 (similar to graph 100) where time is on the horizontal. This process is very much the same as that of graph 100, except that, when the rinse pump 44 is turned off at 104, the booster fill valve 42 is also closed, because refilling of the booster tank is not needed. In addition, the booster heater is not turned back on.
Variations in the drain down process are possible. For example, as optionally suggested in
Moreover, optionally, per
It is to be clearly understood that the above description is intended by way of illustration and example only, is not intended to be taken by way of limitation, and that other changes and modifications are possible. For example, for any wash tank drain down process, the controller 200 may first check the temperature of liquid in the wash tank and, if such temperature is already below the applicable code limit, the drain down could be implemented solely by operation of the drain pump 50, because reduction of the temperature of the draining wash tank liquid is not needed. Still other modifications and variations are possible.
