Variable Refrigerant Flow Cooling System

Abstract

A variable flow refrigerant system having a compressor and one or a plurality of evaporators. The suction at one or the plurality of evaporators for the input to the compressor is monitored and generally corresponds to the minimum pressure of the refrigerant. The pressure is associated with a temperature and is controlled to always be above the dew point temperature of the room.

What is claimed is: 
     
         1 . A variable refrigerant flow cooling system comprising:
 a compressor having an inlet and an outlet, the inlet generating a first pressure, and the outlet generating a second pressure higher than the first pressure;   a condenser having an inlet and an outlet, the inlet of the condenser communicating with the outlet of the compressor, the condenser receiving fluid provided by the outlet of the compressor and removing heat from the fluid;   an expansion valve having an inlet and an outlet, the inlet of the expansion valve communicating with the outlet of the condenser, the expansion valve enabling expansion of the liquid at its outlet and varying a flow of liquid between its inlet and outlet;   an evaporator having an inlet and an outlet, the inlet of the evaporator communicating with the outlet of the expansion valve, the evaporator absorbing heat into the fluid as the fluid passes from its inlet to outlet; and   a controller monitoring a pressure at the outlet of the evaporator and varying the output of the compressor in accordance with the monitored pressure, wherein the monitored pressure indicates a saturation temperature and the control maintains the saturation temperature above a dew point temperature.   
     
     
         2 . The variable refrigerant flow system of  claim 1  wherein the expansion valve is responsive to the superheat of the evaporator. 
     
     
         3 . The variable refrigerant flow system of  claim 1  further comprising a suction line communicating with the outlet of the evaporator at a first end and the inlet of the compressor at a second end for fluid flow between the outlet of the evaporator and the inlet of the compressor. 
     
     
         4 . The variable refrigerant flow system of  claim 3  further comprising an accumulator interposed in the suction line between the evaporator and the compressor. 
     
     
         5 . The variable refrigerant flow system of  claim 4  wherein fluid flowing from the outlet of the condenser to the inlet of the expansion valve passes through the accumulator in order to reduce the temperature of the liquid flowing therethrough. 
     
     
         6 . The variable refrigerant flow system of  claim 1  further comprising a liquid receiver having an inlet and an outlet, the inlet of the liquid receiver communicating with the outlet of the condenser and the outlet of the liquid receiver communicating with the expansion valve. 
     
     
         7 . The variable refrigerant flow system of  claim 6  wherein the outlet of the liquid receiver is in thermal communication with a suction line interconnecting the output of the evaporator with the input of the compressor, thereby cooling the liquid output by the liquid receiver prior to input to the expansion valve. 
     
     
         8 . The variable flow refrigerant system of  claim 1  further comprising:
 a plurality of expansion valves, each having an inlet and an outlet, the inlet of the each expansion valve communicating with the outlet of the condenser, each expansion valve enabling expansion of the liquid at its outlet and varying a flow of liquid between its inlet and outlet; and 
 a plurality of evaporators, each evaporator having an inlet and an outlet, the inlet of each evaporator communicating with a respective outlet of the expansion valve, each evaporator absorbing heat into the fluid as the fluid passes from its inlet to outlet. 
 
     
     
         9 . A variable refrigerant flow cooling system comprising:
 a compressor generating a first pressure and a second pressure higher than the first pressure;   a condenser communicating with the second pressure, the condenser receiving fluid provided at the second pressure and reducing the temperature of the fluid;   a liquid line communicating with the condenser and receiving the liquid;   an expansion valve communicating with the liquid line, the expansion valve enabling expansion of the fluid in the liquid line;   an evaporator communicating with the fluid output by the expansion valve, the fluid absorbing heat as it passes through the evaporator;   a vapor line communicating with the evaporator and returning fluid output from the evaporator to the compressor; and   a controller monitoring a pressure in the vapor line and varying the output of the compressor in accordance with the monitored pressure, wherein the monitored pressure indicates a saturation temperature of the vapor line, and the output of the compressor is varied to maintain the saturation temperature above a dew point temperature for the vapor line.   
     
     
         10 . The variable refrigerant flow system of  claim 9  wherein the expansion valve is responsive to the superheat of the evaporator. 
     
     
         11 . The variable refrigerant flow system of  claim 9  further comprising an accumulator interposed in the vapor line between the evaporator and the compressor. 
     
     
         12 . The variable refrigerant flow system of  claim 11  wherein liquid line passes through the accumulator in order to reduce the temperature of the fluid flowing therethrough. 
     
     
         13 . The variable refrigerant flow system of  claim 9  further comprising a liquid receiver interposed in the liquid line. 
     
     
         14 . The variable refrigerant flow system of  claim 13  wherein the output of the liquid receiver is in thermal communication with the vapor line, thereby cooling the liquid output by the liquid receiver prior to input to the expansion valve. 
     
     
         15 . The variable flow refrigerant system of  claim 9  further comprising:
 a plurality of expansion valves communicating with the liquid line, each expansion valve enabling expansion of the fluid in the liquid line; and 
 a plurality of evaporators communicating with the fluid output by a respective expansion valve, the fluid absorbing heat as it passes through the evaporator. 
 
     
     
         16 . A method for controlling an output of a compressor in a cooling system comprising:
 providing an evaporator;   monitoring a suction pressure at the output of the evaporator;   comparing the suction pressure against a predetermined threshold, wherein the predetermined threshold is determined in accordance with a saturation temperature of a fluid output by the evaporator; and   decreasing the output of the compressor if the suction pressure is below the predetermined threshold.   
     
     
         17 . The method of  claim 16  further comprising increasing the output of the compressor if the suction pressure is above a predetermined threshold. 
     
     
         18 . The method of  claim 17  further comprising maintaining the suction pressure unchanged if the suction pressure is equal to the predetermined threshold. 
     
     
         19 . The method of  claim 16  further comprising maintaining the suction pressure unchanged if the suction pressure is equal to the predetermined threshold.