Low temperature heat pump

A reverse cycle heat pump system operably connected to a forced air system ducted to provide heated and/or cooled air into a residential, commercial or industrial space other than a space used to test or evaluate heat pump systems or components;

• wherein said system has an indoor coil, an outdoor coil, and a compressor, and is operable in an indoor heating mode and an indoor cooling mode for the residential, commercial or industrial space;
• wherein the outdoor coil is substantially larger than the indoor coil, and the compressor is a variable capacity compressor;
• and
• wherein the system includes:
• a) a sensor for determining one or more characteristics of the refrigerant in the compressor discharge line when the system is operating in its indoor heating mode, and b) a controller that adjusts the capacity of the compressor to maintain a sensor output value within a desired range of values when the system is operating in its indoor heating mode.

A reverse cycle heat pump having an indoor heating mode and an indoor cooling mode, comprising:

• a) an indoor heat exchanger (condenser/evaporator coil);
• b) an outdoor heat exchanger (condenser/evaporator coil);
• wherein the refrigeration capacity of said outdoor heat exchanger is greater than the refrigeration capacity of said indoor heat exchanger;
• c) a compressor effective for compressing a refrigerant fluid;
• wherein said compressor is operable at a first/lower operating capacity that is substantially equal to the refrigeration capacity of said indoor heat exchanger;
• and
• wherein said compressor is operable at a second/greater operating capacity that is substantially equal to the refrigeration capacity of said outdoor heat exchanger;
• d) a refrigerant fluid;
• e) refrigerant line linking said indoor heat exchanger, outdoor heat exchanger, and compressor in a closed refrigeration circuit containing said refrigerant fluid;
• f) a reversing valve for directing the flow of said refrigerant fluid through said refrigeration circuit in a first direction when operating in an indoor heating mode, and for directing the flow of said refrigerant fluid through said refrigeration circuit in a second direction when operating in an indoor cooling mode;
• g) a sensor effective for sensing the temperature and/or pressure of the refrigerant fluid in the discharge line of the compressor when the system is operating in its indoor heating mode, and effective for sending a signal indicating said temperature and/or pressure to a compressor controller;
• and
• h) a compressor controller operationally linked to said sensor and effective for controlling the pumping capacity of said compressor in response to said sensor signal,
• wherein said controller is adapted to adjust the operating capacity of said compressor to its first/lower operating capacity when the system is operating in its indoor cooling mode, and
• wherein said controller is adapted to adjust the operating capacity of said compressor to its second/greater operating capacity when the temperature and/or pressure of the refrigerant fluid in the discharge line of the compressor is below a predetermined value when the system is operating in its indoor heating mode.

A reverse cycle heat pump having an indoor heating mode and an indoor cooling mode, the heat pump having functional elements consisting essentially of:

• a) an indoor heat exchange coil;
• b) an outdoor heat exchange coil;
• wherein the refrigeration capacity of said outdoor heat exchange coil is greater than the refrigeration capacity of said indoor heat exchange coil;
• c) a compressor effective for compressing a refrigerant fluid;
• wherein said compressor is operable at a first/lower operating capacity that is substantially equal to the refrigeration capacity of said indoor heat exchange coil;
• and
• wherein said compressor is operable at a second/greater operating capacity that is substantially equal to the refrigeration capacity of said outdoor heat exchange coil;
• d) a refrigerant fluid;
• e) refrigerant line linking said indoor heat exchanger, outdoor heat exchanger, and compressor in a closed refrigeration circuit containing said refrigerant fluid;
• f) a reversing valve for directing the flow of said refrigerant fluid through said refrigeration circuit in a first direction when operating in an indoor heating mode, and for directing the flow of said refrigerant fluid through said refrigeration circuit in a second direction when operating in an indoor cooling mode;
• g) a sensor effective for sensing a parameter selected from the group consisting of temperature, pressure, density, and a combination thereof, as to the refrigerant fluid in the discharge line of the compressor when the system is operating in its indoor heating mode, and effective for sending a signal indicating said temperature and/or pressure to a compressor controller;
• h) a compressor controller operationally linked to said sensor and effective for controlling the pumping capacity of said compressor in response to said sensor signal;
• i) a first check valve and a first expansion valve in said refrigerant line adjacent said outdoor heat exchanger, wherein said first check valve is effective for directing the flow of refrigerant from said indoor heat exchanger through said first expansion valve when operating in an indoor heating mode, and wherein said first check valve is effective for preventing refrigerant from flowing into said first expansion valve when operating in an indoor cooling mode, and
• j) a second check valve and a second expansion valve in said refrigerant line adjacent said indoor heat exchanger, wherein said second check valve is effective for directing the flow of refrigerant from said outdoor heat exchanger through said first expansion valve when operating in an indoor cooling mode, and wherein said second check valve is effective for preventing refrigerant from flowing into said second expansion valve when operating in an indoor heating mode;
• wherein said controller is adapted to adjust the operating capacity of said compressor to its first/lower operating capacity when the system is operating in its indoor cooling mode, and
• wherein said controller is adapted to adjust the operating capacity of said compressor to its second/greater operating capacity in response to the output of said sensor.