Patent Grant
10285562
This application relates generally to warewashers such as those used in commercial applications such as cafeterias and restaurants and, more particularly, to a heat recovery system that adapts to operating conditions of the warewasher.
Commercial warewashers commonly include a housing area which defines washing and rinsing zones for dishes, pots, pans and other wares. Heat recovery systems have been used to recover heat from the machine that would ordinarily be lost to the machine exhaust.
Waste heat recovery systems such as a heat pump or refrigeration system uses evaporator(s), compressor(s) and condenser(s) such that the operation involves thermal fluids (including refrigerant) for recovering waste energy and re-using captured energy at areas of interest. The systems require the thermal fluid to operate within a specified envelope to prevent system shut down from high or low pressure, hence, the need for effective controls.
It would be desirable to provide a heat recovery system that adapts to machine operating condition in order to make more effective use of heat recovery. It would also be desirable to provide a heat recovery system that is able to more effectively maintain desired subcooled condition of refrigerant medium.
In one aspect, a warewash machine includes a chamber for receiving wares, the chamber having at least one wash zone. A waste heat recovery unit is arranged to transfer heat from exhaust air of the machine to incoming water traveling along a water flow path through the waste heat recovery unit to a booster heater of the machine. A refrigerant medium circuit includes at least a first condenser arranged to deliver refrigerant medium heat to the incoming water. A bypass arrangement is provided for causing at least some incoming water to selectively bypass the waste heat recovery unit based upon subcooled refrigerant medium condition.
In implementation, the bypass arrangement includes a valve upstream of the waste heat recovery unit, and a bypass path from the valve to a downstream side of the waste heat recovery unit.
In one example, the bypass arrangement further includes a refrigerant medium temperature sensor and a refrigerant medium pressure sensor downstream of all condensers in the refrigerant medium circuit and upstream of a thermal expansion valve in the refrigerant medium circuit. A controller is connected with the refrigerant medium temperature sensor and the refrigerant medium pressure sensor, the controller configured to determine a subcooled condition of the refrigerant medium and to control the valve based upon the subcooled condition.
In one embodiment, the controller is configured to switch the valve to flow water along the bypass path when the subcooled condition is below a set threshold.
In certain implementations, the controller is also configured such that, if the subcooled condition remains below the set threshold for a predetermined time period after the valve is switched to flow water along the bypass path, the controller operates a second valve to increase a flow rate of the incoming water.
In another aspect, a warewash machine for washing wares includes a chamber for receiving wares, the chamber having at least one wash zone. A refrigerant medium circuit includes a condenser to deliver refrigerant medium heat to incoming water that is being delivered into the machine. A first flow path for incoming water runs through a waste heat recovery unit to the condenser and a second flow path for incoming water runs in bypass of the waste heat recovery unit to the condenser. A valve is provided for selectively controlling whether at least some incoming water flows along the first flow path or the second flow path based upon subcooled refrigerant medium condition.
In a further aspect, a method is provided for controlling a flow of incoming water to a warewash machine that includes a chamber for receiving wares, the chamber having at least one wash zone, a refrigerant medium circuit including at least one condenser, and a waste heat recovery unit for heating incoming water to the machine. The method involves: flowing incoming water through both the waste heat recovery unit and then the condenser; and identifying an under-condensed condition of subcooled refrigerant medium in the refrigerant medium circuit and responsively causing at least some incoming water to flow in bypass around the waste heat recovery unit to the condenser.
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
The racks proceed to a next curtain 38 into a main wash chamber or zone 40, where the wares are subject to sprays of cleansing wash liquid (e.g., typically water with detergent) from upper and lower wash manifolds 42 and 44 with spray nozzles 47 and 49, respectively, these sprays being supplied through a supply conduit 46 by a pump 48, which draws from a main tank 50. A heater 58, such as an electrical immersion heater provided with suitable thermostatic controls (not shown), maintains the temperature of the cleansing liquid in the tank 50 at a suitable level. Not shown, but which may be included, is a device for adding a cleansing detergent to the liquid in tank 50. During normal operation, pumps 32 and 48 are continuously driven, usually by separate motors, once the warewash system 10 is started for a period of time.
The warewash system 10 may optionally include a power rinse (also known as post-wash) chamber or zone (not shown) that is substantially identical to main wash chamber 40. In such an instance, racks of wares proceed from the wash chamber 40 into the power rinse chamber, within which heated rinse water is sprayed onto the wares from upper and lower manifolds.
The racks 12 of wares 14 exit the main wash chamber 40 through a curtain 52 into a final rinse chamber or zone 54. The final rinse chamber 54 is provided with upper and lower spray heads 56, 57 that are supplied with a flow of fresh hot water via pipe 62 running from a hot water booster 70 under the control of a solenoid valve 60 (or alternatively any other suitable valve capable of automatic control). A rack detector 64 may be actuated when a rack 12 of wares 14 is positioned in the final rinse chamber 54 and through suitable electrical controls (e.g., the controller mentioned below), the detector causes actuation of the solenoid valve 60 to open and admit the hot rinse water to the spray heads 56, 57. The water then drains from the wares and is directed into the tank 50 by gravity flow. The rinsed rack 12 of wares 14 then exits the final rinse chamber 54 through curtain 66, moving into dryer unit 18, before exiting the outlet end 17 of the machine.
An exhaust system 80 for pulling hot moist air from the machine (e.g., via operation of a blower 81) may be provided. As shown, a cold water input 72 line may run through a waste heat recovery unit 82 (e.g., a fin-and-tube heat exchanger through which the incoming water flows, though other variations are possible) to recover heat from the exhaust air flowing across and/or through the unit 82. The water line or flow path 72 then runs through one or more condensers 84 (e.g., in the form of a plate heat exchanger or shell-and-tube heat exchangers, though other variations are possible), before delivering the water to the booster 70 for final heating. A condenser 88 may be located in the wash tank and a condenser 90 may be located in the blower dryer unit 18. A second waste heat recovery unit 92 may also be provided.
Referring now to
Generally, condenser 88 may take the form of coil submerged in the wash tank 50 to deliver refrigerant heat to the wash water, condenser 90 may take the form of a coil over which the drying air blows to deliver some refrigerant heat to the drying air and condenser 84, which may be a plate-type heat exchanger, delivers residual refrigerant heat to the incoming fresh water. The incoming water to the booster heater passes through both the waste heat recovery unit 82 and condenser 84. However, this flow may be altered based upon warewash machine conditions.
In this regard, one or more sensors 110 are provided to monitor the conditions of the subcooled refrigerant. The monitoring may be continuous, periodic or triggered by some event (e.g., identification of a rack at a certain location in the machine). By way of example, both a temperature sensor and a pressure sensor may be used to monitor the subcooled refrigerant medium downstream of the last condenser 84 and upstream of the thermal expansion valve 101. If the monitoring indicates that the condition of the subcooled refrigerant medium has departed from a set specification, then corrective action can be take. For example, if the condition of the subcooled refrigerant medium falls below a desired condition operating range (indicating the refrigerant medium is not sufficiently condensed) then a two way valve 112 is controlled to cause the incoming fresh water to bypass heat recovery unit 82 along a bypass path 114 so as to flow directly to condenser 84, causing the water delivered to condenser 84 to be cooler and therefore causing more heat to be removed from the refrigerant medium on its path to the monitoring location of sensor(s) 110, thus increasing the amount of condensation of the refrigerant medium that takes place. Check valves 116 and 118 are provided respectively on the primary water path and the bypass path 114. If the condition of the subcooled refrigerant medium remains below the desired condition operating range for a predetermined time period after initiating bypass of the waste heat recovery unit 82, some additional action may be taken, such as increasing the incoming water flow (e.g., where valve 60 enables variable flow control). Once the condition rises back up into the desired operating range (e.g., to a mid-point of the operating range) the valve 112 can switched to turn off the bypass and, if applicable, the valve 60 controlled to reduce the incoming water flow to a standard flow.
By way of example, the subcooled condition may be a difference between the actual temperature indicated by the temperature sensor 110 less a condenser saturation temperature corresponding to the pressure indicated by pressure sensor 110. An exemplary acceptable subcooled condition operating range may be between 10° F. and 15° F., though variations are possible. Above 15° F. indicates the refrigerant medium has been overly condensed, and below 10° F. indicates that the refrigerant medium has not been condensed enough (e.g., gas may be present). The condenser saturation temperature may be determined by reading the pressure indicated by pressure sensor 110 and (i) using a refrigerant pressure/temperature chart or table (e.g., stored in controller memory) to convert the pressure reading to the condenser saturation temperature or (ii) using an equation fitted to a refrigerant medium pressure/temperature chart to convert the pressure reading to the condenser saturation temperature.
In one example valve 112 is configured to switch an entirety of the incoming water flow between the path between waste heat recovery unit 82 and the bypass path. However, valve 112 could alternatively be a proportional valve that is capable of partially splitting the flow between the two paths in variable amounts (e.g., 80/20, 50/50, 20/80 or any desired split). This latter arrangement could provide for more precisely impacting the sub-cooled condition of the refrigerant medium.
A controller 150 may be provided to effect switching of the valve 112 based upon indications from the temperature sensor and pressure sensor as described above, as well as for controlling other functions and operations of the machine as discussed above (e.g., controlling the valve 60 and the heater 58). 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 (e.g., shared, dedicated, or group—including hardware or software that executes code) or other component, or a combination of some or all of the above, that carries out the control functions of the machine or the control functions of any component thereof. The controller may include variable adjustment functionality that enables, for example, the acceptable subcooled condition operating range to be varied (e.g., via an operator interface associated with the controller 150 or via a restricted service/maintenance personnel interface).
Ensuring that the refrigerant medium remains in a desired operating range as indicated above can help system operation by (i) assuring that the refrigerant medium is fully condensed to assist efficient operation of the thermal expansion valve 101, and/or (ii) reducing or eliminating the presence of gas in the refrigerant medium at the upstream side of the thermal expansion valve as the presence of such gas will tend to restrict refrigerant medium flow hence starving the evaporator of refrigerant medium, and/or (ii) assuring that the refrigerant medium is not overcooled coming out of the condenser chain, as such overcooling will require more energy delivery to the refrigerant medium at the evaporator in order to raise the refrigerant medium to desired compressor suction conditions, and if the evaporator is unable to deliver sufficient energy the performance and/or life of the compressor may be adversely impacted.
The above machine provides an advantageous method of controlling incoming water flow to enable correction of undesired conditions of a refrigerant medium circuit. In particular, the method involves flowing incoming water through both the waste heat recovery unit and then the condenser, identifying an under-condensed condition of subcooled refrigerant medium in the refrigerant medium circuit and responsively causing incoming water to flow in bypass around the waste heat recovery unit to the condenser. The responsive bypass could be immediate or delayed for some time period. The under-condensed condition is identified by detecting both a temperature of subcooled refrigerant medium and a temperature of subcooled refrigerant medium upstream of a thermal expansion valve of the refrigerant medium circuit. More specifically, the under-condensed condition is identified by comparing a difference between an actual temperature indicated by the pressure sensor less a condenser saturation temperature corresponding to a pressure indicated by the pressure sensor. If the difference is below a set threshold, the under-condensed condition is identified. In some implementations, if the under-condensed condition persists for a predetermined time period after the bypass is initiated, a flow rate of the incoming water is increased. By causing incoming water to flow in bypass around the waste heat recovery unit to the condenser and/or by increasing the flow rate of the incoming water, the degree of condensation of the refrigerant medium can be increased to a more desirable and effective level.
It is to be clearly understood that the above description is intended by way of illustration and example only and is not intended to be taken by way of limitation, and that changes and modifications are possible. Accordingly, other embodiments are contemplated and modifications and changes could be made without departing from the scope of this application. For example, the term refrigerant commonly refers to known acceptable refrigerants, but other thermal fluids could be used in refrigerant type circuits. The term “refrigerant medium” is intended to encompass all such traditional refrigerants and other thermal fluids.
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