Heat exchanger freeze protection

Abstract

Preventing freezing in a heat exchanger can include passing first and second cooling fluids through the heat exchanger, monitoring a temperature and/or pressure of the second cooling fluid entering the heat exchanger, heating the second cooling fluid entering the heat exchanger by opening a valve when the monitored temperature and/or monitored pressure is below a trigger temperature and/or trigger pressure, and closing the valve when a condition is met. The first cooling fluid can have a first freezing temperature and the second cooling fluid can have a second, lower freezing temperature. Opening the valve can cause the second cooling fluid, in gaseous phase, to mix with the second cooling fluid, in liquid phase, upstream of the heat exchanger.

What is claimed is: 
     
         1 . A system, comprising:
 a heat exchanger configured to have a first cooling fluid and a second cooling fluid passed there through, the first cooling fluid having a first freezing temperature and the second cooling fluid having a second freezing temperature, wherein the second freezing temperature is lower than the first freezing temperature;   a temperature sensor and/or pressure sensor in sensing communication with a fluid path by which the second cooling fluid enters the heat exchanger;   a valve; and   a controller;   wherein the controller is configured to
 monitor a monitored temperature and/or a monitored pressure of the second cooling fluid entering the heat exchanger; 
 open the valve when the monitored temperature and/or monitored pressure is below a trigger temperature and/or trigger pressure, thereby raising the monitored temperature and/or monitored pressure of the second cooling fluid entering the heat exchanger; and 
 close the valve when a condition is met. 
   
     
     
         2 . The system of  claim 1 , wherein the first cooling fluid comprises water and the second cooling fluid comprises a two-phase refrigerant. 
     
     
         3 . The system of  claim 1 , wherein the trigger temperature and/or a second cooling fluid temperature at the trigger pressure is above a point at which the first cooling fluid would freeze as it moves into the heat exchanger. 
     
     
         4 . The system of  claim 1 , wherein the controller is further configured to open the valve and thereby cause the second cooling fluid, in gaseous phase, to mix with the second cooling fluid, in liquid phase, upstream of the heat exchanger. 
     
     
         5 . The system of  claim 1 , wherein the condition comprises a predetermined time, and wherein the controller is configured to close the valve once the predetermined time has elapsed following the valve opening. 
     
     
         6 . The system of  claim 1 , wherein the condition comprises a predetermined temperature and/or predetermined pressure, and wherein the controller is configured to close the valve once the monitored temperature and/or monitored pressure of the second cooling fluid entering the heat exchanger rises to the predetermined temperature and/or predetermined pressure. 
     
     
         7 . The system of  claim 6 , wherein the predetermined temperature and/or predetermined pressure is higher than the trigger temperature and/or trigger pressure. 
     
     
         8 . The system of  claim 6 , wherein the predetermined temperature and/or a second cooling fluid temperature at the predetermined pressure is higher than the first freezing temperature. 
     
     
         9 . The system of  claim 1 , wherein the heat exchanger comprises at least one of a liquid to air heat exchanger and an evaporator. 
     
     
         10 . The system of  claim 1 , wherein the heat exchanger comprises a liquid to air heat exchanger configured to remove heat from a space. 
     
     
         11 . The system of  claim 1 , wherein the heat exchanger comprises an evaporator, and wherein the trigger temperature and/or a second cooling fluid temperature at the trigger pressure is above a point at which the first cooling fluid would freeze as it moves into the evaporator. 
     
     
         12 . The system of  claim 1 , wherein the heat exchanger comprises an evaporator, and wherein the system is configured to raise the temperature and/or pressure of at least a portion of the second cooling fluid to an elevated temperature and/or elevated pressure, and to cause the second cooling fluid, at the elevated temperature and/or elevated pressure, to mix with the second cooling fluid, at a lower temperature and/or lower pressure, upstream of the evaporator, thereby raising the monitored temperature and/or monitored pressure of the second cooling fluid entering the evaporator. 
     
     
         13 . The system of  claim 1 , wherein
 the heat exchanger comprises a liquid to air heat exchanger and an evaporator;   the system is configured to pass water through the liquid to air heat exchanger to remove heat from a space, the liquid to air heat exchanger being located within the space; and   the system is configured to pass a two-phase refrigerant through the evaporator, thereby cooling the water as at least a portion of the refrigerant changes from liquid phase to gaseous phase.   
     
     
         14 . The system of  claim 13 , wherein the system is configured to
 pass the refrigerant through a pump, thereby increasing a refrigerant temperature of the refrigerant to an elevated temperature, when the condition is met;   pass the refrigerant through a compressor, thereby increasing the refrigerant temperature of the refrigerant to the elevated temperature, when the condition is not met and a space temperature, of the space, is above a setpoint; and   close the valve when a second condition is met.   
     
     
         15 . The system of  claim 14 , wherein the second condition comprises a predetermined time, and wherein the controller is configured to close the valve once the predetermined time has elapsed following the valve opening. 
     
     
         16 . The system of  claim 14 , wherein the second condition comprises a predetermined temperature and/or predetermined pressure, and wherein the controller is configured to close the valve once the monitored temperature and/or monitored pressure of the refrigerant entering the evaporator rises to the predetermined temperature and/or predetermined pressure. 
     
     
         17 . The system of  claim 14 , wherein the second condition comprises a predetermined temperature and/or refrigerant temperature at the predetermined pressure, and wherein the controller is configured to close the valve once the predetermined temperature and/or refrigerant temperature at the predetermined pressure is higher than the water freezing temperature and the trigger temperature and/or refrigerant temperature at the trigger pressure. 
     
     
         18 . A method for preventing freezing in a heat exchanger, the method comprising the steps of:
 passing a first cooling fluid and a second cooling fluid through a heat exchanger, the first cooling fluid having a first freezing temperature and the second cooling fluid having a second freezing temperature, wherein the second freezing temperature is lower than the first freezing temperature;   monitoring a monitored temperature and/or monitored pressure of the second cooling fluid entering the heat exchanger;   opening a valve when the monitored temperature and/or monitored pressure is below a trigger temperature and/or trigger pressure, thereby raising the monitored temperature and/or monitored pressure of the second cooling fluid entering the heat exchanger; and   closing the valve when a condition is met.   
     
     
         19 . The method of  claim 18 , wherein passing the first cooling fluid through the heat exchanger comprises passing the first cooling fluid through a liquid to air heat exchanger to remove heat from a space, and wherein passing the second cooling fluid through the heat exchanger comprises passing the second cooling fluid through an evaporator, thereby cooling the first cooling fluid as at least a portion of the second cooling fluid changes from liquid phase to gaseous phase. 
     
     
         20 . The method of  claim 19 , wherein the trigger temperature and/or a second cooling fluid temperature at the trigger pressure is above a point at which the first cooling fluid would freeze as it moves into the evaporator.