Heating, ventilation, and air conditioning system with primary and secondary heat transfer loops

1. A heating, ventilation, and air conditioning (HVAC) system, comprising:

a primary heat transfer loop configured to be disposed at least partially outside of a building, comprising:

a heat exchanger;

a compressor configured to compress a refrigerant;

a condenser configured to receive and condense the refrigerant; and

an expansion device configured to reduce a temperature of the refrigerant;

a secondary heat transfer loop configured to circulate a two-phase fluid at least partially inside the building, wherein the secondary heat transfer loop comprises:

the heat exchanger, wherein the heat exchanger is configured to transfer energy from the two-phase fluid circulating in the secondary heat transfer loop to the refrigerant;

an evaporator configured to evaporate the two-phase fluid by exchanging energy with an air supply stream flowing across the evaporator; and

a pump configured to pump the two-phase fluid between the heat exchanger and the evaporator; and

a controller configured to receive feedback from a first sensor indicative of a first pressure of the refrigerant in the primary heat transfer loop, receive additional feedback from a second sensor indicative of a second pressure of the two-phase fluid in the secondary heat transfer loop, and shut down the compressor, the pump, or both, in response to a determination that the second pressure is less than the first pressure.

2. The HVAC system of claim 1 , wherein the first pressure of the refrigerant in the primary heat transfer loop is less than the second pressure of the two-phase fluid in the secondary heat transfer loop during normal operation of the HVAC system to block and/or reduce transfer of the refrigerant into the secondary heat transfer loop.

3. The HVAC system of claim 1 , wherein the two-phase fluid is inert.

4. The HVAC system of claim 3 , wherein the two-phase fluid comprises carbon dioxide.

5. The HVAC system of claim 1 , wherein the expansion device is upstream from the heat exchanger and downstream from the condenser relative to a direction of a flow of the refrigerant through the primary heat transfer loop during operation of the HVAC system.

6. The HVAC system of claim 1 , comprising the first sensor and the second sensor, wherein the first sensor is coupled to the primary heat transfer loop and the second sensor is coupled to the secondary heat transfer loop.

7. The HVAC system of claim 6 , wherein the controller is configured to compare the first pressure and the second pressure to determine a differential pressure between the first pressure and the second pressure.

8. The HVAC system of claim 7 , wherein the controller is configured to transmit a warning message to an electronic device in response to the differential pressure indicating that the second pressure of the two-phase fluid is less than the first pressure of the refrigerant.

9. The HVAC system of claim 1 , wherein the secondary heat transfer loop excludes another expansion device.

10. The HVAC system of claim 1 , wherein the controller is configured to transmit a message to an electronic device in response to the determination that the second pressure is less than the first pressure, wherein the message comprises a request to confirm the shut down of the compressor, the pump, or both.

11. A heating, ventilation, and air conditioning (HVAC) system, comprising:

a primary heat transfer loop configured to be disposed outside of a building, the primary heat transfer loop comprising:

a compressor configured to compress a refrigerant;

a condenser configured to receive and condense the refrigerant; and

an expansion device configured to reduce a temperature of the refrigerant;

a secondary heat transfer loop configured to circulate a two-phase fluid inside the building, wherein the two-phase fluid is inert, and the secondary heat transfer loop comprises:

a heat exchanger configured to transfer energy from the two-phase fluid circulating in the secondary heat transfer loop to the refrigerant;

an evaporator configured to evaporate the two-phase fluid by exchanging energy with an air supply stream flowing over the evaporator; and

a pump configured to pump the two-phase fluid between the heat exchanger and the evaporator;

a first sensor configured to emit a first signal indicative of a pressure of the refrigerant;

a second sensor configured to emit a second signal indicative of a pressure of the two-phase fluid; and

a controller configured to receive the first signal and the second signal, wherein the controller is configured to compare the first signal to the second signal to determine if the pressure of the two-phase fluid is greater than the pressure of the refrigerant, and wherein, in response to a determination that the pressure of the two-phase fluid is less than the pressure of the refrigerant, the controller is configured to shut down the compressor, the pump, or both.

12. The HVAC system of claim 11 , wherein the controller is further configured to regulate operation of the HVAC system to maintain the pressure of the two-phase fluid to be greater than the pressure of the refrigerant during normal operation of the HVAC system.

13. The HVAC system of claim 11 , wherein the controller is further configured transmit a warning message to an electronic device in response to the determination that the pressure of the two-phase fluid is less than the pressure of the refrigerant.

14. The HVAC system of claim 13 , wherein the warning message comprises an audible tone, a written message, an audible message, or a flashing light.

15. The HVAC system of claim 14 , wherein the electronic device comprises a mobile electronic device, a thermostat, or a computer.