Method and Apparatus of Optimizing the Cooling Load of an Economized Vapor Compression System

Abstract

A vapor compression system includes a variable speed single stage compressor, a heat rejecting heat exchanger, an expansion device, and a heat accepting heat exchanger. The speed of the compressor is varied to control the refrigerant flow rate and match the cooling load requirements of the vapor compression system. A temperature sensor measures an air temperature in the refrigerated container. When the temperature sensor detects that the air temperature is above a threshold temperature, the microcontroller increases the speed of the compressor to increase the refrigerant flow rate and the cooling capacity of the vapor compression system. When the air temperature sensor detects that the air temperature is within a predetermined range from the set point temperature, the microcontroller sends a signal to slightly decrease the speed of the compressor, allowing fine adjustment of the cooling capacity of the vapor compression system to prevent overcooling of the refrigerated container.

1 . A vapor compression system comprising:
 a variable speed single stage compressor to compress a refrigerant to a high pressure;   a heat accepting heat exchanger for exchanging heat between the refrigerant and an airflow to heat the refrigerant and cool the airflow, wherein the airflow is provided to an area;   a temperature sensor to detect an air temperature of air in the area; and   a controller that adjusts a speed of the variable speed single stage compressor based on the air temperature to match a cooling load requirement of the vapor compression system to cool the area.   
   
   
       2 . The system as recited in  claim 1  further including a heat rejecting heat exchanger for cooling the refrigerant and a main expansion device to expand the refrigerant to a low pressure. 
   
   
       3 . The system as recited in  claim 2  further including an economizer heat exchanger,
 wherein the refrigerant from the heat rejecting heat exchanger is split into an economized path which is reduced to an intermediate pressure in an economizer expansion device and a main path,   wherein the refrigerant in the main path and the refrigerant in the economized path exchange heat therebetween in the economizer heat exchanger, and   wherein the refrigerant in the economized path is injected into an economizer port of the variable speed single stage compressor and the refrigerant in the main path is expanded in the main expansion device.   
   
   
       4 . The system as recited in  claim 3  wherein the variable speed single stage compressor includes a compression chamber and a piston that moves in the compression chamber, wherein the piston moves in a first direction to expand a volume of the compression chamber during a suction stroke and prevent the refrigerant in the economized path from entering the compression chamber and the piston moves in an opposing second direction to reduce the volume of the compression chamber during a discharge stroke to compress the refrigerant and prevent the refrigerant in the economized path from entering the compression chamber. 
   
   
       5 . The system as recited in  claim 4  wherein the compression chamber is a single compression chamber. 
   
   
       6 . The system as recited in  claim 1  further including a motor to control the speed of the variable speed single stage compressor and adjust a mass flow rate of the refrigerant through the vapor compression system. 
   
   
       7 . The system as recited in  claim 1  wherein the controller increases the speed of the variable speed single stage compressor when the air temperature detected by the temperature sensor is greater than a threshold temperature programmed in the controller to reduce the air temperature to a set point temperature. 
   
   
       8 . The system as recited in  claim 7  wherein the controller decreases the speed of the variable speed single stage compressor when the air temperature is less than a second threshold temperature programmed in the controller, and the second threshold temperature is greater than the set point temperature. 
   
   
       9 . The system as recited in  claim 1  wherein the air temperature is a return air temperature of the air drawn from the refrigerated container. 
   
   
       10 . A vapor compression system comprising:
 a variable speed single stage compressor to compress a refrigerant to a high pressure;   a motor to control a speed of the variable speed single stage compressor and adjust a mass flow rate of the refrigerant through the vapor compression system;   a heat rejecting heat exchanger for cooling the refrigerant;   a main expansion device to expand the refrigerant to a low pressure;   an economizer heat exchanger, wherein the refrigerant from the heat rejecting heat exchanger is split into an economized path which is reduced to an intermediate pressure in an economizer expansion device and a main path, wherein the refrigerant in the main path and the refrigerant in the economized path exchange heat therebetween in the economizer heat exchanger, and wherein the refrigerant in the economized path is injected into an economizer port of the variable speed single stage compressor and the refrigerant in the main path is expanded in the main expansion device;   a heat accepting heat exchanger for exchanging heat between the refrigerant and an airflow to heat the refrigerant and cool the airflow, wherein the airflow is provided to an area;   a temperature sensor to detect an air temperature of air in the area; and   a controller that adjusts the speed of the variable speed single stage compressor based on the air temperature to match a cooling load requirement of the vapor compression system to cool the area.   
   
   
       11 . The system as recited in  claim 10  wherein the controller increases the speed of the variable speed single stage compressor when the air temperature detected by the temperature sensor is greater than a threshold temperature programmed in the controller to reduce the air temperature to a set point temperature. 
   
   
       12 . The system as recited in  claim 11  wherein the controller decreases the speed of the variable speed single stage compressor when the air temperature is less than a second threshold temperature programmed in the controller, and the second threshold temperature is greater than the set point temperature. 
   
   
       13 . The system as recited in  claim 10  wherein the variable speed single stage compressor includes a single compression chamber. 
   
   
       14 . A method of optimizing a cooling capacity of a vapor compression system comprising the steps of:
 compressing a refrigerant to a high pressure in a variable speed single stage compressor;   heating the refrigerant in a heat accepting heat exchanger by accepting heat from an airflow to cool the airflow;   providing the airflow to cool an area;   detecting an air temperature of air in the area; and   controlling a speed of the variable speed single stage compressor based on the air temperature to match a cooling load requirement of the vapor compression system to cool the area.   
   
   
       15 . The method as recited in  claim 14  further including the steps of cooling the refrigerant in a heat rejecting heat exchanger and expanding the refrigerant to a low pressure in a main expansion device. 
   
   
       16 . The method as recited in  claim 15  further including the steps of:
 splitting the refrigerant from the heat rejecting heat exchanger into an economized path and a main path;   expanding the refrigerant in the economized path to an intermediate pressure in an economizer expansion device,   exchanging heat between the refrigerant in the main path and the refrigerant in the economized path,   injecting the refrigerant in the economized path into an economizer port of the variable speed single stage compressor, and   expanding the refrigerant in the main path in the main expansion device.   
   
   
       17 . The method as recited in  claim 14  further including the step of increasing the speed of the variable speed single stage compressor when the air temperature is greater than a threshold temperature to reduce the air temperature to a set point temperature. 
   
   
       18 . The method as recited in  claim 17  further including the step of then decreasing the speed of the variable speed single stage compressor when the air temperature is less than a second threshold temperature, wherein the second threshold temperature is greater than the set point temperature.