Compressor control for heat transfer system

Abstract

A compressor is connected with an evaporator, a condenser, and an electrically controlled valve for circulating a working fluid in a system for recovering waste heat to provide heated water. A controller can be configured to adjust an operating capacity of the compressor to maintain output of a condenser temperature sensor at a condenser temperature set point, except when output of a compressor discharge pressure sensor indicates that a maximum operating pressure of the compressor has been exceeded. In such case the controller reduces the operating capacity of the compressor. The controller may further be configured to shut down the compressor when the discharge pressure sensor indicates that a shutdown pressure has been exceeded.

What is claimed is: 
     
         1 . A heat transfer system comprising:
 a compressor for circulating a working fluid, the compressor having an inlet and an outlet, the compressor operable at a controllable operating capacity;   a condenser connected to the outlet of the compressor;   an electrically controlled valve positioned to receive working fluid from the outlet of the condenser;   an evaporator connected between an outlet of the electrically controlled valve and the inlet of the compressor;   a discharge pressure sensor located between the outlet of the compressor and the inlet of the electrically controlled valve;   a condenser temperature sensor positioned to measure a temperature at the condenser; and   a controller connected to the compressor, the discharge pressure sensor, and the condenser temperature sensor, the controller configured to adjust the operating capacity of the compressor to maintain output of the condenser temperature sensor at a condenser temperature set point, the controller further configured to reduce the operating capacity of the compressor when output of the discharge pressure sensor indicates that a maximum operating pressure of the compressor has been exceeded, the maximum operating pressure having a saturation temperature higher than the condenser temperature set point.   
     
     
         2 . The system of  claim 1 , wherein the controller is configured to shut down the compressor when the output of the discharge pressure sensor indicates that a shutdown pressure has been exceeded, the shutdown pressure having a saturation temperature higher than the saturation temperature of the maximum operating pressure. 
     
     
         3 . The system of  claim 1 , further comprising a discharge temperature sensor located at the outlet of the compressor, wherein the controller is configured to incrementally close the electrically controlled valve when output of the discharge temperature sensor falls below a minimum discharge superheat temperature determined from output of the discharge pressure sensor. 
     
     
         4 . The system of  claim 1 , further comprising a subcooler connected between the condenser and the electrically controlled valve. 
     
     
         5 . The system of  claim 1 , wherein the condenser is configured to receive flow of potable water to be heated. 
     
     
         6 . The system of  claim 5 , wherein the evaporator is configured to receive flow of waste-heat bearing fluid. 
     
     
         7 . A method of controlling a heat transfer system, the method comprising:
 determining a condenser temperature at a condenser connected with an electrically controlled valve, an evaporator, and a compressor for circulating a working fluid, the compressor operable at a controllable operating capacity;   adjusting the operating capacity of the compressor to maintain the condenser temperature at a condenser temperature set point;   reducing the operating capacity of the compressor when a discharge pressure of the compressor indicates that a maximum operating pressure of the compressor has been exceeded, the maximum operating pressure corresponding to a saturation temperature that is higher than the condenser temperature set point; and   returning to adjusting the operating capacity of the compressor to maintain the condenser temperature at the condenser temperature set point after the discharge pressure of the compressor returns to below the maximum operating pressure.   
     
     
         8 . The method of  claim 7 , further comprising shutting down the compressor when the discharge pressure sensor indicates that a shutdown pressure has been exceeded, the shutdown pressure having a saturation temperature higher than the saturation temperature of the maximum operating pressure. 
     
     
         9 . The method of  claim 7 , further comprising incrementally closing the electrically controlled valve when a compressor discharge temperature falls below a minimum discharge superheat temperature. 
     
     
         10 . The method of  claim 7 , further comprising receiving flow of potable water to be heated at the condenser. 
     
     
         11 . The method of  claim 10 , further comprising receiving flow of waste-heat bearing fluid at the evaporator. 
     
     
         12 . A heat transfer system comprising:
 a compressor for circulating a working fluid, the compressor having an inlet and an outlet, the compressor operable at a controllable operating capacity;   a condenser connected to the outlet of the compressor, the condenser configured to receive flow of water to be heated;   an electrically controlled valve positioned to receive working fluid from the outlet of the condenser;   an evaporator connected between an outlet of the electrically controlled valve and the inlet of the compressor, the evaporator configured to receive flow of waste-heat bearing fluid;   a discharge pressure sensor located between the outlet of the compressor and the inlet of the electrically controlled valve;   a condenser temperature sensor positioned to measure a temperature of the flow of water to be heated; and   a controller connected to the compressor, the discharge pressure sensor, and the condenser temperature sensor, the controller configured to adjust the operating capacity of the compressor to maintain output of the condenser temperature sensor at a condenser temperature set point, except when output of the discharge pressure sensor indicates that a maximum operating pressure of the compressor has been exceeded, in which case the controller reduces the operating capacity of the compressor.   
     
     
         12 . The system of  claim 11 , wherein the controller is configured to shut down the compressor when the output of the discharge pressure sensor indicates that a shutdown pressure has been exceeded, the shutdown pressure being higher than the maximum operating pressure. 
     
     
         13 . The system of  claim 12 , further comprising a discharge temperature sensor located at the outlet of the compressor, wherein the controller is configured to incrementally close the electrically controlled valve when output of the discharge temperature sensor falls below a minimum discharge superheat temperature determined from output of the discharge pressure sensor.