Air conditioning system with vapor injection compressor
An air conditioning system can be toggled between a heating mode, in which heat is withdrawn from a source (e.g., a geothermal source) and deposited into a conditioned space (e.g., a building), and a cooling mode, in which heat is withdrawn from the conditioned space and deposited into the source. The air conditioning system uses a combination of efficiency-enhancing technologies, including injection of superheated vapor into the system's compressor from an economizer circuit, adjustable compressor speed, the use of one or coaxial heat exchangers and the use of electronic expansion valves that are continuously adjustable from a fully closed to various open positions. A controller may be used to control the system for optimal performance in both the heating and cooling modes, such as by disabling the economizer circuit and vapor injection when the system is in the cooling mode.
1. A reversible heat pump system housed in a housing for heating and cooling a space, comprising:
a refrigerant circuit through which refrigerant is configured to flow;
a variable speed scroll compressor disposed on the refrigerant circuit, the compressor including a compressor inlet, a compressor outlet, and a vapor infection inlet disposed between the compressor inlet and the compressor outlet;
a liquid-to-liquid coaxial counterflow load heat exchanger disposed on the refrigerant circuit to exchange heat between the refrigerant and either a cooling load or a heating load;
a liquid-to-liquid coaxial counterflow source heat exchanger disposed on the refrigerant circuit to exchange heat between the refrigerant and a source;
a reversing valve disposed on the refrigerant circuit between the compressor and the load and source heat exchangers and selectable to effect a heating mode and a cooling mode, wherein in the heating mode the reversing valve routes the refrigerant from the compressor outlet to the load heat exchanger and routes the refrigerant from the source heat exchanger to the compressor inlet, wherein in the cooling mode the reversing valve routes the refrigerant from the compressor outlet to the source heat exchanger and routes the refrigerant from the load heat exchanger to the compressor inlet;
a diverter disposed on the refrigerant circuit between the load heat exchanger and the source heat exchanger, the diverter configured to selectively divert a portion of the refrigerant to an economizer circuit when the heat pump is in the heating mode and none of the refrigerant when the heat pump is in the cooling mode, wherein the economizer circuit includes
a coaxial counterflow economizer heat exchanger configured to exchange heat between the refrigerant diverted to the economizer circuit and the refrigerant in the refrigerant circuit to create superheated refrigerant vapor for injection into the vapor injection inlet, and
an electronic economizer expansion valve (EEEV) disposed between the diverter and the economizer heat exchanger, the EEEV configured to be continuously adjustable between fully open and fully closed positions to selectively meter and expand the diverted refrigerant when the heat pump is in the heating mode and to selectively cease diversion of the refrigerant to the economizer circuit when the heat pump is in the cooling mode; and
an electronic primary expansion valve (EPEV) disposed on the refrigerant circuit between the diverter and the source heat exchanger to selectively meter the refrigerant discharged from the economizer heat exchanger to the source heat exchanger when the heat pump is in the heating mode and the economizer circuit is active, and to selectively meter the refrigerant discharged from the source heat exchanger to the economizer heat exchanger when the heat pump is in the cooling mode and the economizer circuit is inactive,
wherein in the heating mode, the EPEV receives the refrigerant from the economizer heat exchanger and discharges the refrigerant to the source heat exchanger; and
in the cooling mode, the EPEV receives the refrigerant from the source heat exchanger and discharges the refrigerant to the economizer heat exchanger.
2. The reversible heat pump system of claim 1 , including a controller configured to control the EEEV to meter the diverted refrigerant according to a programmed set of instructions.
3. The reversible heat pump system of claim 2 , wherein the controller is operably connected to the reversing valve and the EEEV, the controller operable to:
toggle the reversing valve into the heating mode and adjustably open the EEEV when the reversible heat pump system is called upon to deposit heat into a conditioned space; and
toggle the reversing valve into the cooling mode and close the EEEV to a fully closed position when the reversible heat pump system is called upon to withdraw heat from the conditioned space.
4. The reversible heat pump system of claim 1 , wherein the coaxial counterflow economizer heat exchanger comprises
a first flow path through which the refrigerant in the refrigerant circuit passes; and
a second flow path through which the refrigerant diverted to the economizer circuit passes, the second flow path coaxial with, but fluidly isolated from, the first flow path such that the first flow path is in heat exchange relationship with the second flow path.
5. The reversible heat pump system of claim 1 , wherein at least one of the load heat exchanger and the source heat exchanger comprises
a first flow path through which the refrigerant passes; and
a second flow path through which a first or second working fluid passes, respectively, the second flow path coaxial with, but fluidly isolated from, the first flow path such that the first flow path is in heat exchange relationship with the second flow path.
6. The reversible heat pump system of claim 1 , further comprising a refrigerant filter/dryer disposed on the refrigerant circuit between the source heat exchanger and the EPEV.
7. The reversible heat pump system of claim 1 , further comprising
a compressor inlet pressure sensor configured to detect refrigerant pressure at the compressor inlet; and
a controller operably connected to the compressor, the EPEV, and the compressor inlet pressure sensor, wherein the controller is operable to
compare a compressor inlet pressure indicated by the compressor inlet pressure sensor to a desired compressor inlet pressure to compute a primary pressure difference, and
if the primary pressure difference is beyond a threshold amount, adjust at least one of a speed of the compressor and a flow rate of the refrigerant through the EPEV to return the primary pressure difference to an amount less than the threshold amount.
8. The reversible heat pump system of claim 7 , further comprising a vapor injection pressure sensor configured to detect refrigerant pressure at the vapor injection inlet, wherein the controller is operably connected to the EEEV and to the vapor injection pressure sensor and is operable in the heating mode to
compare a vapor injection inlet pressure indicated by the vapor injection pressure sensor to a desired vapor injection inlet pressure to compute an economizer pressure difference, and
if the economizer pressure difference is beyond a threshold amount, adjust at least one of the speed of the compressor and a flow rate of the diverted refrigerant through the EEEV to return the economizer pressure difference to an amount less than the threshold amount.
9. The reversible heat pump system of claim 1 , wherein the refrigerant is R410A and the heat pump system operates the refrigerant in sub-critical and super-critical states.
10. The reversible heat pump system of claim 1 , wherein
the source is a geothermal source, and
a working fluid circulates between the source heat exchanger and the geothermal source to exchange heat between the refrigerant and the geothermal source.
11. A method of controlling a reversible heat pump system housed in a housing, the method comprising:
toggling a reversing valve into one of a heating mode or a cooling mode, the reversing valve being disposed on a refrigerant circuit between a variable speed scroll compressor disposed on the refrigerant circuit, a liquid-to-liquid coaxial counterflow load heat exchanger disposed on the refrigerant circuit to exchange heat between a refrigerant and either a heating load or a cooling mode, and a liquid-to-liquid coaxial counterflow source heat exchanger disposed on the refrigerant circuit in a heat exchanging arrangement with a source, wherein
in the heating mode, the reversing valve
routes the refrigerant from a compressor outlet of the compressor to the load heat exchanger and
routes refrigerant from the source heat exchanger to a compressor inlet of the compressor, and
in the cooling mode, the reversing valve
routes the refrigerant from the compressor outlet to the source heat exchanger and
routes the refrigerant from the load heat exchanger to the compressor inlet;
controlling an electronic economizer expansion valve (EEEV) configured to be continuously adjustable between fully open and fully closed positions to selectively divert a portion of refrigerant from the refrigerant circuit to a coaxial counterflow economizer heat exchanger, the EEEV being disposed on an economizer circuit between a diverter and the coaxial counterflow economizer heat exchanger, the diverter being disposed on the refrigerant circuit, the coaxial counterflow economizer heat exchanger being configured to exchange heat between the refrigerant diverted to the economizer circuit and the refrigerant in the refrigerant circuit to create superheated refrigerant vapor for injection into a vapor injection inlet of the compressor, including
in the heating mode, adjusting the EEEV to meter and expand the diverted refrigerant and
in the cooling mode, fully closing the EEEV to cease diversion of the refrigerant; and
controlling a speed of the compressor to circulate the refrigerant through the load heat exchanger, the economizer heat exchanger, the source heat exchanger, and an electronic primary expansion valve (EPEV) disposed on the refrigerant circuit between the diverter and the source heat exchanger to match compressor output to a heating load and a cooling load, including
in the heating mode, metering the refrigerant discharged from an active economizer heat exchanger to the source heat exchanger by the EPEV, and
in the cooling mode, metering the refrigerant discharged from the source heat exchanger to an inactive economizer heat exchanger by the EPEV.
12. The method of claim 11 , wherein toggling the reversing valve, controlling the EEEV, and controlling the speed of the compressor are performed by an electronic controller for the heating mode and for the cooling mode.
13. The method of claim 12 , wherein, in the heating mode:
the controller compares a pressure of a vapor injection line with a desired economizer pressure to generate a pressure differential;
the controller compares the pressure differential with a predetermined threshold pressure differential; and
the controller adjusts at least one of the speed of the compressor and a flow rate of the diverted refrigerant when the pressure differential is outside the predetermined threshold pressure differential.
14. The method of claim 12 , wherein in the heating mode and in the cooling mode the controller
compares a pressure in the refrigerant circuit between the reversing valve and the compressor inlet with a desired compressor inlet pressure to generate a pressure differential;
the controller compares the pressure differential with a predetermined threshold pressure differential; and
the controller adjusts at least one of the speed of the compressor and a flow rate of the refrigerant through the EPEV when the pressure differential is outside the predetermined threshold pressure differential.
15. The method of claim 12 , wherein, in the heating mode, the controller controls at least one of the speed of the compressor, a flow rate of the refrigerant through the EPEV, and a flow rate of the diverted refrigerant through the EEEV to maintain the refrigerant in a mixed liquid-and-vapor phase state between the EEEV and the economizer heat exchanger and between the EPEV and the source heat exchanger.
16. The method of claim 12 , wherein, in the cooling mode, the controller controls at least one of the speed of the compressor and a flow rate of the refrigerant through the EPEV to maintain the refrigerant in a mixed liquid-and-vapor phase state between the EPEV and the load heat exchanger.
17. The method of claim 12 , wherein, in the heating mode, the controller controls at least one of the speed of the compressor, a flow rate of the refrigerant through the EPEV, and a flow rate of the refrigerant through the EEEV to maintain the refrigerant in a superheated vapor phase between the load heat exchanger and the compressor, and to maintain the refrigerant in a subcooled liquid phase between the economizer heat exchanger and the EPEV.
18. The reversible heat pump system of claim 7 , wherein the controller controls the compressor to operate at a slower speed in the cooling mode than in the heating mode.
19. The reversible heat pump system of claim 1 , wherein the load heat exchanger heats or cools potable water.