Patent Description:
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 conditions in order to make more effective use of heat recovery. It would also be desirable to support such heat recovery systems to enable operation continuously or semi-continuously at startup, at steady state or at the standby or idle mode while simultaneously recovering waste energy and tempering the exhaust gas hot stream to an acceptable temperature by the use of thermal fluid(s).

In one aspect, a warewash machine includes a chamber for receiving wares, the chamber having at least one wash zone. A refrigerant medium circuit includes a first condenser and a second condenser, the first condenser located upstream of the second condenser in the refrigerant medium circuit. The refrigerant medium circuit includes a primary flow path through the first condenser and a secondary flow path in bypass of the first condenser, and a valve for selectively controlling whether at least some refrigerant medium flows along the primary flow path or the secondary flow path,. wherein the valve is selectively controlled based upon monitored heat demand on the second heat exchanger.

In a further aspect, a method is provided for controlling refrigerant flow in a refrigerant circuit of a warewash machine that includes a chamber for receiving wares, the chamber having at least one wash zone, the refrigerant circuit including a first condenser and a second condenser, the first condenser located upstream of the second condenser in the refrigerant circuit. The method involves: flowing refrigerant through both the first condenser and the second condenser; and selectively bypassing at least some refrigerant flow around the first condenser based upon a monitored heat demand of the second condenser, wherein the predefined refrigerant medium circuit condition is a heat demand condition of the second condenser.

Referring to <FIG>, an exemplary conveyor-type warewash machine, generally designated <NUM>, is shown. Warewash machine <NUM> includes a housing <NUM> that can receive racks <NUM> of soiled wares <NUM> from an input side <NUM>. The wares are moved through tunnel-like chambers from the input side toward a blower dryer unit <NUM> at an opposite exit end <NUM> of the warewash system by a suitable conveyor mechanism <NUM>. Either continuously or intermittently moving conveyor mechanisms or combinations thereof may be used, depending, for example, on the style, model and size of the warewash system <NUM>. Flight-type conveyors in which racks are not used are also possible. In the illustrated example, the racks <NUM> of soiled wares <NUM> enter the warewash system <NUM> through a flexible curtain <NUM> into a pre-wash chamber or zone <NUM> where sprays of liquid from upper and lower pre-wash manifolds <NUM> and <NUM> above and below the racks, respectively, function to flush heavier soil from the wares. The liquid for this purpose comes from a tank <NUM> and is delivered to the manifolds via a pump <NUM> and supply conduit <NUM>. A drain structure <NUM> provides a single location where liquid is pumped from the tank <NUM> using the pump <NUM>. Via the same drain structure, liquid can also be drained from the tank and out of the machine via drain path <NUM>, for example, for a tank cleaning operation.

The racks proceed to a next curtain <NUM> into a main wash chamber or zone <NUM>, where the wares are subject to sprays of cleansing wash liquid (e.g., typically water with detergent) from upper and lower wash manifolds <NUM> and <NUM> with spray nozzles <NUM> and <NUM>, respectively, these sprays being supplied through a supply conduit <NUM> by a pump <NUM>, which draws from a main tank <NUM>. A heater <NUM>, such as an electrical immersion heater provided with suitable thermostatic controls (not shown), maintains the temperature of the cleansing liquid in the tank <NUM> at a suitable level. Not shown, but which may be included, is a device for adding a cleansing detergent to the liquid in tank <NUM>. During normal operation, pumps <NUM> and <NUM> are continuously driven, usually by separate motors, once the warewash system <NUM> is started for a period of time.

The warewash system <NUM> may optionally include a power rinse (also known as post-wash) chamber or zone (not shown) that is substantially identical to main wash chamber <NUM>. In such an instance, racks of wares proceed from the wash chamber <NUM> into the power rinse chamber, within which heated rinse water is sprayed onto the wares from upper and lower manifolds.

The racks <NUM> of wares <NUM> exit the main wash chamber <NUM> through a curtain <NUM> into a final rinse chamber or zone <NUM>. The final rinse chamber <NUM> is provided with upper and lower spray heads <NUM>, <NUM> that are supplied with a flow of fresh hot water via pipe <NUM> running from a hot water booster <NUM> under the control of a solenoid valve <NUM> (or alternatively any other suitable valve capable of automatic control). A rack detector <NUM> may be actuated when a rack <NUM> of wares <NUM> is positioned in the final rinse chamber <NUM> and through suitable electrical controls (e.g., the controller mentioned below), the detector causes actuation of the solenoid valve <NUM> to open and admit the hot rinse water to the spray heads <NUM>, <NUM>. The water then drains from the wares and is directed into the tank <NUM> by gravity flow. The rinsed rack <NUM> of wares <NUM> then exits the final rinse chamber <NUM> through curtain <NUM>, moving into dryer unit <NUM>, before exiting the outlet end <NUM> of the machine.

An exhaust system <NUM> for pulling hot moist air from the machine (e.g., via operation of a blower <NUM>) may be provided. As shown, a cold water input <NUM> line may run through a waste heat recovery unit <NUM> (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 <NUM>. The water line or flow path <NUM> then runs through one or more condensers <NUM> and <NUM> (e.g., in the form of plate heat exchangers or shell-and-tube heat exchangers, though other variations are possible), before delivering the water to the booster <NUM> for final heating. A condenser <NUM> may be located in the wash tank and a condenser <NUM> may be located in the blower dryer unit <NUM>. A second waste heat recovery unit <NUM> may also be provided.

Referring now to <FIG>, the flow configuration for both incoming fresh cold water and for refrigerant are shown. Cold fresh water is first heated by the hot air passing through the waste heat recovery unit <NUM>, then heated further by refrigerant when passing through condenser <NUM> and finally heated further by superheated refrigerant when passing through condenser <NUM>. The heated water then enters the booster <NUM> for final heating. The refrigerant medium circuit <NUM> includes a thermal expansion valve <NUM>, which leads to a waste heat recovery unit <NUM> to recover heat from warm waste air (e.g., the exhaust air flow) after some heat has already been removed from the exhaust air flow by unit <NUM>. A compressor <NUM> compresses the refrigerant to produce superheated refrigerant, which then flows sequentially through the condensers <NUM>, <NUM>, <NUM> and <NUM>.

Generally, condenser <NUM> delivers refrigerant heat to the incoming fresh water, condenser <NUM> may take the form of coil submerged in the wash tank <NUM> to deliver refrigerant heat to the wash water, condenser <NUM> may take the form of a coil over which the drying air blows to deliver some refrigerant heat to the drying air and condenser <NUM>, which may be a plate-type heat exchanger, delivers residual refrigerant heat to the incoming fresh water. However, this flow may be altered based upon warewash machine conditions.

In this regard, a temperature sensor <NUM> is provided to monitor the temperature of the wash tank condenser <NUM>. The temperature sensor may be in direct contact with the condenser <NUM> or may simply monitor the surrounding wash tank liquid temperature, which in either case represents a temperature condition of the water in the tank and is therefore indicative of heat demand on the condenser <NUM>. If the monitored temperature falls below a specified threshold temperature, a two way valve <NUM> is controlled to cause superheated refrigerant to bypass condenser <NUM> along bypass path <NUM> so as to flow directly to condenser <NUM>, causing more heat to be transferred from the refrigerant to the wash tank wash liquid. This operation assures that more refrigerant heat is transferred to the wash tank wash liquid when needed, so as to more effectively augment the heating performed by heater <NUM> (<FIG>), and thus more quickly bring the wash tank wash liquid up to desired or required temperature. Check valves <NUM> and <NUM> are provided respectively on the primary refrigerant path and the bypass path <NUM>. When the heat demand on the condenser <NUM> is no longer deemed high (e.g., when the temperature sensor <NUM> indication rises above the specified threshold temperature or a temperature slightly higher than the specified temperature threshold), the valve <NUM> can be switched back to again provide refrigerant flow through the condenser <NUM>.

In one example valve <NUM> is configured to switch an entirety of the refrigerant medium flow between the path through condenser <NUM> and the bypass path. However, valve <NUM> could alternatively be a proportional valve that is capable of partially splitting the flow between the two paths in variable amounts (e.g., <NUM>/<NUM>, <NUM>/<NUM>, <NUM>/<NUM> or any desired split). This latter arrangement could provide for more precisely responding to heat demand on condenser <NUM>.

A controller <NUM> may be provided to effect switching of the valve <NUM> (or varied control of the valve) based upon temperature output of sensor <NUM>, as well as for controlling other functions and operations of the machine. 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.

Thus, the system provides an advantageous method of refrigerant flow in a warewash machine that includes a chamber for receiving wares, where the chamber has at least one wash zone, and the refrigerant circuit includes a first condenser and a second condenser, the first condenser located upstream of the second condenser in the refrigerant circuit. The method involves: flowing refrigerant through both the first condenser and the second condenser; and selectively bypassing refrigerant flow around the first condenser based upon a monitored heat demand of the second condenser. Heat demand of the second condenser may be monitored by sensing a temperature condition of an environment of the second condenser. The monitoring may be continuous, periodic or triggered by some event (e.g., identification of a rack at a certain location in the machine). Refrigerant flow may be selectively bypassed around the first condenser in response to identification of a low temperature condition of the environment of the second condenser. The low temperature condition may be identified when a temperature sensor indicates a temperature below a set threshold temperature. In some machines, the set threshold temperature can be varied (e.g., via an operator interface associated with the controller <NUM> or via a restricted service/maintenance personnel interface).

Claim 1:
A warewash machine (<NUM>) for washing wares (<NUM>), comprising:
- a chamber for receiving wares (<NUM>), the chamber having at least one wash zone (<NUM>);
- a refrigerant medium circuit (<NUM>) including a first condenser (<NUM>) and a second condenser (<NUM>), the first condenser (<NUM>) located upstream of the second condenser (<NUM>) in the refrigerant medium circuit (<NUM>), the refrigerant medium circuit (<NUM>) including a first flow path through the first condenser (<NUM>),
characterized in that
the refrigerant medium circuit (<NUM>) includes a second flow path (<NUM>) in bypass of the first condenser (<NUM>), and a valve (<NUM>) for selectively controlling whether at least some refrigerant medium flows along the first flow path or the second flow path (<NUM>),
wherein the valve (<NUM>) is selectively controlled based upon monitored heat demand on the second condenser (<NUM>).