Multi-circuit hvac systems and methods

Abstract

A heating, ventilation, and air conditioning (HVAC) system includes a primary heat transfer circuit having a first heat exchanger fluidly coupled to an ambient environment and a compressor fluidly coupled to the first heat exchanger and configured to circulate a refrigerant through the primary heat transfer circuit. The HVAC system also includes a secondary heat transfer circuit having a second heat exchanger fluidly coupled to a thermal load and a pump fluidly coupled to the second heat exchanger and configured to circulate a heat transfer fluid through the secondary heat transfer circuit, where the heat transfer fluid is a non-volatile or inert fluid. The HVAC system further includes an intermediate heat exchanger disposed along the primary heat transfer circuit and the secondary heat transfer circuit, where the intermediate heat exchanger is configured to transfer heat between the refrigerant and the heat transfer fluid, and the primary heat transfer circuit is entirely external to a perimeter of the thermal load.

1 . A heating, ventilation, and air conditioning (HVAC) system, comprising:
 a primary heat transfer circuit, comprising:
 a first heat exchanger fluidly coupled to an ambient environment; 
 an intermediate heat exchanger fluidly coupled to the first heat exchanger; and 
 a compressor configured to circulate a refrigerant through the primary heat transfer circuit; 
   a secondary heat transfer circuit, comprising:
 a second heat exchanger fluidly coupled to a thermal load; 
 the intermediate heat exchanger, wherein the intermediate heat exchanger is fluidly coupled to the second heat exchanger; and 
 a pump configured to circulate a heat transfer fluid through the secondary heat transfer circuit; 
   a sensor configured to provide feedback indicative of an operational parameter of the heat transfer fluid; and   a controller communicatively coupled to the compressor and the pump, wherein the controller is configured to receive the feedback and adjust operation of the compressor, the pump, or both, based on the feedback.   
     
     
         2 . The HVAC system of  claim 1 , wherein the controller is configured to:
 determine, based on the feedback, a temperature of the heat transfer fluid;   compare the temperature to a lower operating temperature threshold for the heat transfer fluid; and   execute a remedial operation in response to a determination that the temperature is less than the lower operating temperature threshold.   
     
     
         3 . The HVAC system of  claim 2 , wherein the controller is configured to execute a temperature-increase control scheme as the remedial operation, and wherein, to execute the temperature-increase control scheme, the controller is configured to:
 decrease an operational speed of the compressor;   increase an operational speed of the pump;   or both.   
     
     
         4 . The HVAC system of  claim 2 , wherein the controller is configured to deactivate the compressor, the pump, or both, in response to a determination that the temperature of the heat transfer fluid is below an additional lower operating temperature threshold that is less than the lower operating temperature threshold. 
     
     
         5 . The HVAC system of  claim 2 , wherein the controller is configured to:
 determine, based on additional feedback from an additional sensor, a composition of the heat transfer fluid; and   determine, based on the composition, the lower operating temperature threshold.   
     
     
         6 . The HVAC system of  claim 1 , wherein the controller is configured to:
 detect, based on the feedback, an amount of the refrigerant mixed in the heat transfer fluid; and   in response to detection of the amount, deactivate the compressor, the pump, or both.   
     
     
         7 . The HVAC system of  claim 1 , wherein the controller is configured to:
 determine, based on the feedback, a pressure of the heat transfer fluid;   compare the pressure to a target operating pressure range of the heat transfer fluid; and   execute a remedial operation in response to a determination that the pressure deviates from the target operating pressure range by a threshold amount.   
     
     
         8 . The HVAC system of  claim 1 , wherein the heat transfer fluid comprises a non-volatile or inert fluid. 
     
     
         9 . A heating, ventilation, and air conditioning (HVAC) system, comprising:
 a first primary heat transfer circuit, comprising a first heat exchanger fluidly coupled to an ambient environment, an intermediate heat exchanger fluidly coupled to the first heat exchanger, and a first compressor configured to circulate a first refrigerant through the first heat exchanger and the intermediate heat exchanger;   a second primary heat transfer circuit, comprising a second heat exchanger fluidly coupled to the ambient environment, the intermediate heat exchanger, and a second compressor, wherein the intermediate heat exchanger is fluidly coupled to the second heat exchanger, and the second compressor is configured to circulate a second refrigerant through the second heat exchanger and the intermediate heat exchanger;   a secondary heat transfer circuit, comprising a third heat exchanger fluidly coupled to a thermal load, the intermediate heat exchanger, and a pump, wherein the intermediate heat exchanger is fluidly coupled to the third heat exchanger, and the pump is configured to circulate a heat transfer fluid through the third heat exchanger and the intermediate heat exchanger; and   a controller communicatively coupled to the first compressor and the second compressor, wherein the controller is configured to operate the first compressor and block operation of the second compressor in a first operating mode of the HVAC system and to operate the second compressor and to block operation of the first compressor in a second operating mode of the HVAC system.   
     
     
         10 . The HVAC system of  claim 9 , wherein the first refrigerant and the second refrigerant are different types of refrigerant. 
     
     
         11 . The HVAC system of  claim 9 , wherein the first operating mode is a cooling mode, and the second operating mode is a heating mode. 
     
     
         12 . The HVAC system of  claim 9 , wherein the controller is configured to operate the HVAC system in the first operating mode in response to a first demand level of the HVAC system, and the controller the controller is configured to operate the HVAC system in the second operating mode in response to a second demand level of the HVAC system that is greater than the first demand level. 
     
     
         13 . The HVAC system of  claim 12 , wherein the controller is configured to operate both the first compressor and the second compressor to operate the HVAC system in a third operating mode of the HVAC system, and the controller is configured to operate the HVAC system in the third operating mode in response to a third demand level of the HVAC system that is greater than the second demand level. 
     
     
         14 . The HVAC system of  claim 9 , wherein the heat transfer fluid comprises a non-volatile or inert fluid. 
     
     
         15 . The HVAC system of  claim 9 , comprising a sensor configured to detect an operating parameter of the heat transfer fluid, wherein the controller is configured to receive feedback indicative of the operating parameter from the sensor and to adjust operation of the first compressor, the second compressor, the pump, or any combination thereof, based on the feedback. 
     
     
         16 . The HVAC system of  claim 15 , wherein the operating parameter is a temperature of the heat transfer fluid, and the controller is configured to:
 compare the temperature to a lower operating temperature threshold for the heat transfer fluid; and   increase a first speed of the first compressor, increase a second speed of the second compressor, decrease a third speed of the pump, or any combination thereof, in response to a determination that the temperature is less than the lower operating temperature threshold.   
     
     
         17 . A heating, ventilation, and air conditioning (HVAC) system, comprising:
 a primary heat transfer circuit, comprising:
 a first heat exchanger fluidly coupled to an ambient environment; and 
 a compressor fluidly coupled to the first heat exchanger and configured to circulate a refrigerant through the primary heat transfer circuit; 
   a secondary heat transfer circuit, comprising:
 a second heat exchanger fluidly coupled to a thermal load; and 
 a pump fluidly coupled to the second heat exchanger and configured to circulate a heat transfer fluid through the secondary heat transfer circuit, wherein the heat transfer fluid is a non-volatile or inert fluid; 
   an intermediate heat exchanger disposed along the primary heat transfer circuit and the secondary heat transfer circuit, wherein the intermediate heat exchanger is configured to transfer heat between the refrigerant and the heat transfer fluid,   wherein the primary heat transfer circuit is entirely external to a perimeter of the thermal load.   
     
     
         18 . The HVAC system of  claim 17 , comprising a sensor configured to detect an operating parameter of the heat transfer fluid, wherein the controller is configured to receive feedback indicative of the operating parameter from the sensor and to adjust operation of the compressor, the pump, or both, based on the feedback. 
     
     
         19 . The HVAC system of  claim 18 , wherein the operating parameter is a pressure of the heat transfer fluid, and the controller is configured to:
 compare the pressure to a target pressure range for the heat transfer fluid; and   suspend operation of the compressor, the pump, or both, in response to a determination that the pressure is below the target pressure range.   
     
     
         20 . The HVAC system of  claim 17 , comprising a sensor configured to detect a pressure of the refrigerant, wherein the controller is configured to:
 receive feedback indicative of the pressure from the sensor;   compare the pressure to a target pressure range for the refrigerant; and   suspend operation of the compressor, the pump, or both, in response to a determination that the pressure is below the target pressure range.