Warewasher with heat recovery system

Abstract

A warewash machine for washing wares 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 control arrangement monitors subcooled refrigerant medium condition and responsively modifies operation of one or more of: (i) speed of a compressor of the refrigerant medium circuit, (ii) speed of an exhaust fan that causes air flow across the waste heat recovery unit or (iii) speed of a pump that controls incoming water flow along the water flow path.

What is claimed is: 
     
         1 . A warewash machine for washing wares, comprising:
 a chamber for receiving wares, the chamber having at least one wash zone;   a waste heat recovery unit 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 including at least a first condenser arranged to deliver refrigerant medium heat to the incoming water; and   a control arrangement for monitoring subcooled refrigerant medium condition and for responsively modifying operation of one or more of: (i) speed of a compressor of the refrigerant medium circuit, (ii) speed of an exhaust fan the causes air flow across the waste heat recovery unit or (iii) speed of a pump that controls incoming water flow along the water flow path.   
     
     
         2 . The machine of  claim 1  wherein the control arrangement includes a refrigerant medium temperature sensor and a refrigerant medium pressure sensor downstream of all condensers in the refrigerant medium circuit. 
     
     
         3 . The machine of  claim 2  wherein the control arrangement includes a controller 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 responsively control at least one of: (i) the speed of the compressor, (ii) the speed of the exhaust fan or (iii) the speed of the pump. 
     
     
         4 . The machine of  claim 3  wherein the subcooled condition of the refrigerant medium is a difference between an actual temperature indicated by the refrigerant medium temperature sensor less a condenser saturation temperature corresponding to a pressure indicated by the refrigerant medium pressure sensor. 
     
     
         5 . The machine of  claim 4  wherein the controller is configured to identify a predefined subcooled condition indicative of under-condensing of the refrigerant medium and to responsively effect at least one of: (i) a reduction in the speed of the compressor, (ii) a reduction in the speed of the exhaust fan or (iii) an increase in the speed of the pump. 
     
     
         6 . The machine of  claim 4  wherein the controller is configured to identify a predefined subcooled condition indicative of over-condensing of the refrigerant medium and to responsively effect at least one of: (i) an increase in the speed of the compressor, (ii) an increase in the speed of the exhaust fan or (iii) a decrease in the speed of the pump. 
     
     
         7 . The machine of  claim 1  wherein the control arrangement is further configured to monitor temperature and flow rate of exhaust air and to responsively adjust the speed of the exhaust fan speed to maintain a set temperature drop across the waste heat recovery unit. 
     
     
         8 . A warewash machine for washing wares, comprising:
 a chamber for receiving wares, the chamber having at least one wash zone;   a waste heat recovery unit 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 into the machine;   a refrigerant medium circuit including a condenser arranged to deliver refrigerant medium heat to the incoming water; and   a control arrangement including one or more sensors and a controller for determining a condition of subcooled refrigerant medium in the refrigeration medium circuit, the controller configured to vary, based at least in part upon the condition of the subcooled refrigerant medium, one or more of: (i) a speed of a compressor of the refrigerant medium circuit, (ii) a speed of an exhaust fan that causes air flow across the waste heat recovery unit or (iii) a speed of a pump that controls incoming water flow along the water flow path.   
     
     
         9 . The machine of  claim 8  wherein the controller is configured to identify a predefined under-condensing condition of the refrigerant medium and to responsively effect at least one of: (i) a reduction in the speed of the compressor, (ii) a reduction in the speed of the exhaust fan or (iii) an increase in the speed of the pump. 
     
     
         10 . The machine of  claim 8  wherein the controller is configured to identify a predefined over-condensing condition of the refrigerant medium and to responsively effect at least one of: (i) an increase in the speed of the compressor, (ii) an increase in the speed of the exhaust fan or (iii) a decrease in the speed of the pump. 
     
     
         11 . In 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 through which the incoming water to the machine flows, and a waste heat recovery unit through which incoming water to the machine flows, a method of adaptively controlling the machine, the method comprising:
 identifying an under-condensed condition of subcooled refrigerant medium in the refrigerant medium circuit or an over-condensed condition of subcooled refrigerant medium in the refrigeration medium circuit; and   in response to identification of the under-condensed or over-condensed condition, varying at least one of (i) a speed of a compressor of the refrigerant medium circuit, (ii) a speed of an exhaust fan the causes air flow across the waste heat recovery unit or (iii) a speed of a pump that controls incoming water flow through the waste heat recovery unit and the condenser.   
     
     
         12 . The method of  claim 11  wherein the identifying step includes sensing a refrigerant medium temperature and a refrigerant medium pressure downstream of all condensers in the refrigerant medium circuit. 
     
     
         13 . The method of  claim 12  wherein the identifying step includes determining a difference between the sensed refrigerant medium temperature less a condenser saturation temperature corresponding to the sensed refrigerant medium pressure. 
     
     
         14 . The method of  claim 13  wherein, if the under-condensed condition of subcooled refrigerant medium is identified, the varying step involves at least one of: (i) reducing the speed of the compressor, (ii) reducing the speed of the exhaust fan or (iii) increasing the speed of the pump. 
     
     
         15 . The method of  claim 13  wherein, if the over-condensed condition of subcooled refrigerant medium is identified, the varying step involves at least one of: (i) increasing the speed of the compressor, (ii) increasing the speed of the exhaust fan or (iii) decreasing the speed of the pump. 
     
     
         16 . The method of  claim 11 , further including:
 monitoring temperature and flow rate of exhaust air and responsively adjusting the speed of the exhaust fan to maintain a set temperature drop across the waste heat recovery unit.