Refrigerant charge management in a heat pump water heater
View Patent ↗Heat pumps that heat or cool a space and that also heat water, refrigerant management systems for such heat pumps, methods of managing refrigerant charge, and methods for heating and cooling a space and heating water. Various embodiments deliver refrigerant gas to a heat exchanger that is not needed for transferring heat, drive liquid refrigerant out of that heat exchanger, isolate that heat exchanger against additional refrigerant flowing into it, and operate the heat pump while the heat exchanger is isolated. The heat exchanger can be isolated by closing an electronic expansion valve, actuating a refrigerant management valve, or both. Refrigerant charge can be controlled or adjusted by controlling how much liquid refrigerant is driven from the heat exchanger, by letting refrigerant back into the heat exchanger, or both. Heat pumps can be operated in different modes of operation, and segments of refrigerant conduit can be interconnected with various components.
1. A method of managing refrigerant charge in a heat pump that heats or cools a space and that also heats water, the heat pump comprising an outdoor heat exchanger that transfers heat between refrigerant and outdoor air or a heat source/sink, an indoor heat exchanger that transfers heat between the refrigerant and indoor air, a water heat exchanger that transfers heat from the refrigerant to water, a compressor, and at least one expansion device, the method comprising, in any order except where a particular order is explicitly indicated, at least the acts of:
during conditions under which a particular heat exchanger of the heat pump is not needed for transferring heat, delivering refrigerant gas to the particular heat exchanger and driving liquid refrigerant out of the particular heat exchanger and through the at least one expansion device;
while the refrigerant gas is in the particular heat exchanger, isolating the particular heat exchanger against additional refrigerant flowing into the particular heat exchanger; and
while the particular heat exchanger is isolated against additional refrigerant flowing into the particular heat exchanger, operating the heat pump, including running the compressor;
wherein the act of driving liquid refrigerant out of the particular heat exchanger comprises monitoring at least one of: compressor discharge temperature, compressor discharge pressure, or duration of the act of driving liquid refrigerant out of the particular heat exchanger; and the act of driving liquid refrigerant out of the particular heat exchanger is terminated when at least one of: the compressor discharge temperature exceeds a predetermined compressor discharge temperature threshold, the compressor discharge pressure exceeds a predetermined compressor discharge pressure threshold, or the duration of the act of driving liquid refrigerant out of the particular heat exchanger exceeds a predetermined duration of the act of driving liquid refrigerant out of the particular heat exchanger.
2. The method of claim 1 wherein:
the particular heat exchanger is the outdoor heat exchanger;
the act of delivering refrigerant gas to the particular heat exchanger and driving liquid refrigerant out of the particular heat exchanger comprises, during conditions under which the outdoor heat exchanger is not needed for transferring heat, delivering refrigerant gas to the outdoor heat exchanger and driving liquid refrigerant out of the outdoor heat exchanger;
the act of isolating the particular heat exchanger against additional refrigerant flowing into the particular heat exchanger comprises, while the refrigerant gas is in the outdoor heat exchanger, isolating the outdoor heat exchanger against additional refrigerant flowing into the outdoor heat exchanger; and
the act of operating the heat pump comprises, while the outdoor heat exchanger is isolated against additional refrigerant flowing into the outdoor heat exchanger:
heating the water at the water heat exchanger; and
cooling the space using the indoor heat exchanger.
3. The method of claim 1 wherein:
the particular heat exchanger is the indoor heat exchanger;
the act of delivering refrigerant gas to the particular heat exchanger and driving liquid refrigerant out of the particular heat exchanger comprises, during conditions under which the indoor heat exchanger is not needed for transferring heat, delivering refrigerant gas to the indoor heat exchanger and driving liquid refrigerant out of the indoor heat exchanger;
the act of isolating the particular heat exchanger against additional refrigerant flowing into the particular heat exchanger comprises, while the refrigerant gas is in the indoor heat exchanger, isolating the indoor heat exchanger against additional refrigerant flowing into the indoor heat exchanger; and
the act of operating the heat pump comprises, while the indoor heat exchanger is isolated against additional refrigerant flowing into the indoor heat exchanger:
heating the water at the water heat exchanger; and
extracting heat from the outdoor air or from the heat source/sink using the outdoor heat exchanger.
4. The method of claim 1 wherein:
in a first mode of operation:
the particular heat exchanger is the outdoor heat exchanger;
the act of delivering refrigerant gas to the particular heat exchanger and driving liquid refrigerant out of the particular heat exchanger comprises, during conditions under which the outdoor heat exchanger is not needed for transferring heat, delivering refrigerant gas to the outdoor heat exchanger and driving liquid refrigerant out of the outdoor heat exchanger;
the act of isolating the particular heat exchanger against additional refrigerant flowing into the particular heat exchanger comprises, while the refrigerant gas is in the outdoor heat exchanger, isolating the outdoor heat exchanger against additional refrigerant flowing into the outdoor heat exchanger; and
the act of operating the heat pump, including running the compressor, comprises, while the outdoor heat exchanger is isolated against additional refrigerant flowing into the outdoor heat exchanger, operating the heat pump, including:
running the compressor;
heating domestic hot water at the water heat exchanger; and
cooling the space using the indoor heat exchanger; and
in a second mode of operation:
the particular heat exchanger is the indoor heat exchanger;
the act of delivering refrigerant gas to the particular heat exchanger and driving liquid refrigerant out of the particular heat exchanger comprises, during conditions under which the indoor heat exchanger is not needed for transferring heat, delivering refrigerant gas to the indoor heat exchanger and driving liquid refrigerant out of the indoor heat exchanger;
the act of isolating the particular heat exchanger against additional refrigerant flowing into the particular heat exchanger comprises, while the refrigerant gas is in the indoor heat exchanger, isolating the indoor heat exchanger against additional refrigerant flowing into the indoor heat exchanger; and
the act of operating the heat pump, including running the compressor, comprises, while the indoor heat exchanger is isolated against additional refrigerant flowing into the indoor heat exchanger, operating the heat pump, including:
running the compressor;
heating domestic hot water at the water heat exchanger; and
extracting heat from the outdoor air or from the heat source/sink using the outdoor heat exchanger.
5. The method of claim 1 wherein:
the act of isolating the particular heat exchanger against additional refrigerant flowing into the particular heat exchanger comprises closing a particular electronic expansion valve that is connected to the particular heat exchanger with a first refrigerant conduit; and
the act of operating the heat pump comprises keeping the particular electronic expansion valve closed for at least a majority of the act of operating the heat pump.
6. The method of claim 1 wherein the act of isolating the particular heat exchanger against additional refrigerant flowing into the particular heat exchanger comprises actuating a refrigerant management valve located in a refrigerant conduit that connects the water heat exchanger to a reversing valve that is used to switch the heat pump between a heating mode, in which the heat pump heats the space, and a cooling mode, in which the heat pump cools the space.
7. The method of claim 6 wherein the act of isolating the particular heat exchanger against additional refrigerant flowing into the particular heat exchanger comprises closing a particular electronic expansion valve that is connected to the particular heat exchanger with a first refrigerant conduit; and wherein the act of operating the heat pump comprises keeping the particular electronic expansion valve closed for at least a majority of the act of operating the heat pump.
8. The method of claim 7 further comprising an act of adjusting the refrigerant charge, wherein:
the act of adjusting the refrigerant charge takes place after the act of isolating the particular heat exchanger against additional refrigerant flowing into the particular heat exchanger;
the act of adjusting the refrigerant charge takes place during the act of operating the heat pump; and
the act of adjusting the refrigerant charge comprises using at least one of the particular electronic expansion valve or the refrigerant management valve to let refrigerant into the particular heat exchanger.
9. The method of claim 8 wherein the act of adjusting the refrigerant charge comprises monitoring refrigerant subcooling at a water heat exchanger outlet and letting refrigerant into the particular heat exchanger if the subcooling at the water heat exchanger outlet exceeds a predetermined subcooling threshold.
10. The method of claim 1 wherein the act of driving liquid refrigerant out of the particular heat exchanger comprises monitoring: compressor discharge temperature, compressor discharge pressure, and duration of the act of driving liquid refrigerant out of the particular heat exchanger; and the act of driving liquid refrigerant out of the particular heat exchanger is terminated when the compressor discharge temperature exceeds a predetermined compressor discharge temperature threshold, the compressor discharge pressure exceeds a predetermined compressor discharge pressure threshold, or the duration of the act of driving liquid refrigerant out of the particular heat exchanger exceeds a predetermined duration of the act of driving liquid refrigerant out of the particular heat exchanger, whichever occurs first.
11. The method of claim 1 wherein, during conditions under which a certain heat exchanger of the heat pump is used as an evaporator, the evaporator being different than the particular heat exchanger, the act of driving liquid refrigerant out of the particular heat exchanger comprises monitoring refrigerant superheat between the evaporator and the compressor, and if the refrigerant superheat between the evaporator and the compressor is less than a predetermined bottom superheat threshold, starting or accelerating an evaporator fan that blows air through the evaporator; and if the refrigerant superheat between the evaporator and the compressor exceeds a predetermined top superheat threshold, stopping or decelerating the evaporator fan that blows air through the evaporator.