# US 2019/0170405 A1 · Heating, ventilation, and air conditioning system with primary and secondary heat tranfer loops > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 2019/0170405 A1 - Document ID: US20190170405A1 - Status: Published application - Kind: A1 - Application number: 15/890,120 - Filed: 2018-02-06 - Published: 2019-06-06 - Earliest claimed: 2017-12-01 - Assignees: Johnson Controls Technology Company - Applicants: Johnson Controls Technology Company - Inventors: Douglas A. Kester - Web page: https://patentgrep.com/patent/US20190170405A1 ## CPC - F25B 25/005: {using primary and secondary systems} - F24D 1/00: Steam central heating systems (district heating systems F24D10/00; central heating systems using heat accumulated in storage masses F24D11/00) - F25B 9/008: {the refrigerant being carbon dioxide} - F25B 49/005: {of safety devices (F25B49/02 and F25B49/04 take precedence)} - F25B 49/022: {Compressor control arrangements} - F25B 7/00: Compression machines, plants or systems, with cascade operation, i.e. with two or more circuits, the heat from the condenser of one circuit being absorbed by the evaporator of the next circuit (F25B9/00 takes precedence) - F25B 41/31: Expansion valves - F25B 2309/06: Compression machines, plants or systems characterised by the refrigerant being carbon dioxide - F25B 2327/00: Compressor driving means - F25B 2400/054: between the suction tube of the compressor and another part of the cycle - F25B 2600/0271: the discharge pressure - F25B: REFRIGERATION MACHINES, PLANTS OR SYSTEMS; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS - F24D: DOMESTIC- OR SPACE-HEATING SYSTEMS, e.g. CENTRAL HEATING SYSTEMS; DOMESTIC HOT-WATER SUPPLY SYSTEMS; ELEMENTS OR COMPONENTS THEREFOR (using steam or condensate extracted or exhausted from steam engine plants for heating purposes F01K17/02) ## Abstract The present disclosure relates to a heating ventilation and air conditioning (HVAC) system. The system includes a primary heat transfer loop configured to be disposed at least partially outside of a building, and the primary heat transfer loop includes a heat exchanger, a compressor configured to compress a refrigerant, where the refrigerant is reactive, a condenser configured to receive and condense the refrigerant, and an expansion device configured to reduce a temperature of the refrigerant. The system further includes a secondary heat transfer loop configured to circulate a two-phase fluid at least partially inside the building, wherein the two-phase fluid is less reactive than the refrigerant. The secondary heat transfer loop includes the heat exchanger, where the heat exchanger is configured to transfer energy from the two-phase fluid circulating in the secondary heat transfer loop to the refrigerant, and an evaporator configured to evaporate the two-phase fluid by exchanging energy with an air supply stream flowing across the evaporator. ## Claims ### Claim 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, wherein the refrigerant is reactive; a condenser configured to receive and condense the refrigerant; and an expansion device configured to reduce a temperature of the refrigerant; and a secondary heat transfer loop configured to circulate a two-phase fluid at least partially inside the building, wherein the two-phase fluid is less reactive than the refrigerant, and 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; and an evaporator configured to evaporate the two-phase fluid by exchanging energy with an air supply stream flowing across the evaporator. ### Claim 2 (depends on 1) The system of claim 1, wherein a first pressure of the refrigerant in the primary heat transfer loop is less than a second pressure of the two-phase fluid in the secondary heat transfer loop to block and/or reduce transfer of the refrigerant into the secondary heat transfer loop. ### Claim 3 (depends on 1) The system of claim 1, wherein the two-phase fluid is inert. ### Claim 4 (depends on 3) The system of claim 3, wherein the two-phase fluid comprises carbon dioxide. ### Claim 5 (depends on 1) The system of claim 1, comprising a pump configured to pump the two-phase fluid from the heat exchanger to the evaporator. ### Claim 6 (depends on 1) The system of claim 1, wherein the expansion device is upstream of the heat exchanger relative to a flow path of the refrigerant. ### Claim 7 (depends on 1) The system of claim 1, comprising a sensor coupled to the primary heat transfer loop, wherein the sensor is configured to emit a signal indicative of a pressure of the refrigerant. ### Claim 8 (depends on 7) The system of claim 7, wherein the sensor is a first pressure sensor, the signal is a first signal, and the pressure is a first pressure, and wherein the system comprises a second pressure sensor coupled to the secondary heat transfer loop, wherein the second pressure sensor is configured to emit a second signal indicative of a second pressure of the two-phase fluid. ### Claim 9 (depends on 8) The system of claim 8, comprising a controller configured to receive and compare the first signal and the second signal to determine if the first pressure is less than the second pressure. ### Claim 10 (depends on 9) The system of claim 9, wherein the controller is configured transmit a warning message to an electronic device in response to the second pressure being less than the first pressure. ### Claim 11 (depends on 1) The system of claim 1, wherein the secondary heat transfer loop excludes another expansion device. ### Claim 12 A heating ventilation and air conditioning (HVAC) system, comprising: a primary heat transfer loop configured to be disposed outside of a building, comprising: a heat exchanger; a compressor configured to compress a refrigerant, wherein the refrigerant is reactive; a condenser configured to receive and condense the refrigerant; and an expansion device configured to reduce a temperature of the refrigerant; and a secondary heat transfer loop configured to direct a two-phase fluid inside the building, wherein the two-phase fluid is inert, and the secondary heat transfer loop comprises: a heat pipe configured to carry the two-phase fluid, wherein the two-phase fluid is configured to absorb energy from a supply airstream; and the heat exchanger, wherein the heat exchanger is configured to exchange energy between the refrigerant circulating in the primary heat transfer loop and the two-phase fluid in the heat pipe. ### Claim 13 (depends on 12) The system of claim 12, wherein the refrigerant is at a first pressure and the two-phase fluid is at a second pressure, and wherein the first pressure is less than the second pressure to block and/or reduce transfer of the refrigerant from the primary heat transfer loop into the secondary heat transfer loop. ### Claim 14 (depends on 12) The system of claim 12, wherein the expansion device is upstream of the heat exchanger relative to a flow path of the refrigerant. ### Claim 15 (depends on 12) The system of claim 12, wherein the heat pipe comprises a first end and a second end, and wherein the first end is coupled to the heat exchanger and the second end is configured to be disposed within a duct of the building to exchange energy with an air supply stream passing through the duct. ### Claim 16 (depends on 12) The system of claim 12, wherein the secondary heat transfer loop excludes another expansion device. ### Claim 17 A heating ventilation and air conditioning (HVAC) system, comprising: a primary heat transfer loop configured to be disposed outside of a building, comprising: a compressor configured to compress a refrigerant, wherein the refrigerant is reactive; 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; and an evaporator configured to evaporate the two-phase fluid by exchanging energy with an air supply stream flowing over the evaporator; a first sensor configured to emit a first signal indicative of a first pressure of the refrigerant; a second sensor configured to emit a second signal indicative of a second pressure of the two-phase fluid; and a controller configured to receive the first signal and the second signal. ### Claim 18 (depends on 17) The system of claim 17, wherein the controller is configured to compare the first signal to the second signal to determine if the second pressure of the two-phase fluid is greater than the first pressure of the refrigerant. ### Claim 19 (depends on 18) The system of claim 18, wherein the controller is configured to regulate operation of the HVAC system to maintain the second pressure to be greater than the first pressure. ### Claim 20 (depends on 18) The system of claim 18, wherein the controller is configured to adjust operation of the compressor in response to the second pressure being less than the first pressure. ### Claim 21 (depends on 18) The system of claim 18, wherein the controller is configured to adjust operation of a pump that pumps the two-phase fluid through the secondary heat transfer loop in response to the second pressure being less than the first pressure. ### Claim 22 (depends on 18) The system of claim 18, wherein the controller is configured transmit a warning message to an electronic device in response to the second pressure being less than the first pressure. ### Claim 23 (depends on 22) The system of claim 22, wherein the warning message comprises an audible tone, a written message, an audible message, or a flashing light. ### Claim 24 (depends on 23) The system of claim 23, wherein the electronic device comprises a mobile electronic device, a thermostat, or a computer.