1. Field of the Invention
The present invention relates to vapor compression systems, particularly, vapor compression systems having a defrost system.
2. Description of the Related Art
Vapor compression systems, such as heat pumps, typically include a refrigerant circuit through which a compressible refrigerant flows and which fluidly connects, in serial order, a compressor, an indoor heat exchange coil, a sub-cooler, an expansion valve, and an outdoor heat exchange coil. When the heat pump is in the heating mode, the indoor heat exchange coil acts as a condenser transferring thermal energy from the compressed refrigerant flowing therein to the ambient air indoors to warm the air and condense the refrigerant. In the meantime, the outdoor heat exchange coil acts as an evaporator transferring the thermal energy from the ambient air outdoors to the refrigerant flowing through the coil. However, if the temperature of the outdoor heat exchange coil falls below the dew point, condensation may form on the coil. Under certain conditions, this condensation may freeze thus causing frost to build-up on the outdoor heat exchange coil. The build-up of ice and frost on the outdoor coil may impair the ability of the outdoor coil to transfer thermal energy, thus resulting in reduced efficiency.
In order to melt the ice on the outdoor coil, conventional heat pumps are often configured to switch to the cooling mode when ice is detected on the outdoor coil. In the cooling mode, the flow of the refrigerant is reversed and the indoor coil acts as an evaporator, while the outdoor coil acts as a condenser. As a result, hot refrigerant discharged from the compressor flows directly to the outdoor coil thereby heating the outdoor coil and melting the ice. Once the ice is melted, the heat pump switches back to the heating mode. Unfortunately, when the heat pump is in the cooling mode the indoor coil acts as an evaporator transferring thermal energy from the ambient air indoors to the refrigerant within the coil thereby cooling the air indoors. This phenomenon is commonly referred to as “cold blow.”
In order to alleviate the effects of cold blow, heat pump systems often include supplemental electric or gas heaters to heat the air that circulates over the indoor coil. However, these supplemental heaters often increase overall power consumption, can reduce the efficiency and reliability of the system, and can often cause temperature fluctuations. Accordingly, a need remains for a vapor compression system having an effective and efficient defrost system for defrosting the outdoor coil.
The present invention provides a vapor compression system with defrost system for use with a refrigerant to heat and/or cool an interior space defined by a structure. The system, in one form, includes a fluid circuit having operably coupled thereto, in serial order, a compressor, a first heat exchanger located in the interior space, a second heat exchanger, an expansion device, a third heat exchanger located exterior to the structure, and an accumulator. A first bypass line extends from a first point in the fluid circuit between the first heat exchanger and the second heat exchanger to a second point in the fluid circuit between the expansion device and the third heat exchanger. A second bypass line extends from a third point in the fluid circuit between the third heat exchanger and the accumulator to a fourth point in the fluid circuit between the third point and the accumulator, and is operably coupled to the second heat exchanger. A bypass expansion device is operably coupled to the second bypass line between the third point and the second heat exchanger. A first valve is disposed in the fluid circuit between the first heat exchanger and the second heat exchanger and is in communication with the first bypass line. The first valve has a first position wherein at least a substantial amount of the refrigerant flowing from the first heat exchanger flows to the third heat exchanger through the first bypass line without passing through the second heat exchanger and the expansion device thereby defrosting the third heat exchanger, and a second position wherein the refrigerant flowing from the first heat exchanger flows to the second heat exchanger though the fluid circuit without passing through the first bypass line. A second valve is disposed between the third heat exchanger and the accumulator, and has a first position restricting the flow of refrigerant from the third heat exchanger to the accumulator through the fluid circuit without flowing through the second bypass line, and a second position wherein the refrigerant flowing from the third heat exchanger flows through the second bypass line and thereby passes through the bypass expansion device and the second heat exchanger before entering the accumulator. During an operating cycle the first valve is in the second position and the second valve is in the first position, and during a defrost cycle the first valve is in the first position and the second valve is in the second position.
The present invention also provides a method for defrosting a heat exchanger of a vapor compression system. The method, in one form, includes the step of circulating a refrigerant during an operational cycle through, in serial order, a compressor, a first heat exchanger located in an interior space defined by a structure, a second heat exchanger, an expansion device, a third heat exchanger located exterior to the structure, and an accumulator. The method also includes the step of circulating the refrigerant during a defrost cycle through, in serial order, the compressor, the first heat exchanger, the third heat exchanger, a bypass expansion device, the second heat exchanger, and the accumulator. During the defrost cycle at least a substantial amount of the refrigerant flowing from the first heat exchanger flows through a first bypass line to the third heat exchanger without passing through the second heat exchanger to thereby defrost the third heat exchanger. During the operational cycle the refrigerant flowing from the first heat exchanger bypasses the first bypass line and flows to the second heat exchanger without passing through the first bypass line.
The vapor compression system, in another form, includes a fluid circuit having operably coupled thereto, in serial order, a compressor, a first heat exchanger located in the interior space, a second heat exchanger, an expansion device, a third heat exchanger located exterior to the structure, and an accumulator. A first bypass line is fluidly coupled to the fluid circuit and provides fluid communication between the first heat exchanger and the third heat exchanger without passing through the second heat exchanger and the expansion device. A second bypass line is fluidly coupled to the fluid circuit and is in thermal communication with the second heat exchanger. The second bypass line provides fluid communication between the third heat exchanger and the accumulator. A bypass expansion device is operably coupled to the second bypass line between the third heat exchanger and the second heat exchanger. A first valve is operably coupled to the first bypass line, and has a first position restricting the flow of refrigerant to the second heat exchanger and communicating the refrigerant to the first bypass line, and a second position restricting the flow of the refrigerant through the first bypass line and communicating the refrigerant toward the second heat exchanger. A second valve is operably coupled to the fluid circuit between the third heat exchanger and the accumulator, and has a first position and a second position. In the first position, second valve restricts the flow of the refrigerant through the second bypass line and the refrigerant flows to the accumulator without flowing through the bypass expansion device and the second heat exchanger. In the second position, the refrigerant flowing from the third heat exchanger flows through the second bypass line and thereby passes through the bypass expansion device and the second heat exchanger before entering the accumulator. During an operating cycle the first valve is in the second position and the second valve is in the first position. During a defrost cycle the first valve is in the first position and the second valve is in the second position.
One advantage of the present invention is that the defrost cycle melts the ice on the exterior heat exchanger without converting the system to cooling mode. As a result, the interior heat exchanger does not act as an evaporator during the defrost cycle and, therefore, does not produce cool air or a “cold blow” effect.
Another advantage of the present invention is that it does not require the use of supplemental heaters to eliminate the effect of cold blow and, thus, efficiency is maintained.
Additional advantages of the present invention will become apparent when referencing the descriptions below.
The above-mentioned and other features and objects of this invention, and the manner of attaining them, will become more apparent and the invention itself will be better understood by reference to the following description of embodiments of the invention taken in conjunction with the accompanying drawings, wherein:
Corresponding reference characters indicate corresponding parts throughout the several views. Although the exemplification set out herein illustrates embodiments of the invention, in several forms, the embodiments disclosed below are not intended to be exhaustive or to be construed as limiting the scope of the invention to the precise forms disclosed.
The embodiments hereinafter disclosed are not intended to be exhaustive or limit the invention to the precise forms disclosed in the following description. Rather the embodiments are chosen and described so that others skilled in the art may utilize its teachings.
Referring first to
Compressor 14 may be any known single-stage or multi-stage compressor suitable for compressing a refrigerant fluid, such as carbon dioxide. Such suitable compressors may include one or more compressor mechanisms, including rotary vane mechanisms, reciprocating piston mechanisms, orbiting scroll mechanisms and centrifugal impeller mechanisms. Interior and exterior heat exchangers 16, 18 may be of any conventional condenser/evaporator design and may include a series of evaporator/condenser coils. The structure and design of second heat exchanger 18 is discussed in further detail below. Expansion device 20 may be any conventional expansion device or valve suitable for use in heating and/or cooling systems.
Turning now to
As shown in
As illustrated in
In an alternative embodiment, first valve may be positioned at first point 30. Furthermore, first valve may be a three way valve. In this configuration, when in the first position, the three way valve permits refrigerant to flow from first point 30 through first bypass line 28, while positively prohibiting refrigerant from flowing to second heat exchanger 18 and expansion device 20. In the second position, the three way valve directs the flow of refrigerant through second heat exchanger 18 and expansion device.
Referring to
A second valve 44 is disposed in refrigerant circuit 12 between third and fourth points 36, 38, and has a first position and a second position. In the first position, depicted in
Alternatively, second valve 44 may be positioned at third point 36 and may be a three way valve. In this embodiment the second valve has a first position positively directing the flow of refrigerant through second bypass line 34 and a second position positively directing the flow of refrigerant through second bypass line 34.
Vapor compression system 10 also includes sensor 48. Sensor 48 is operably coupled to either exterior heat exchanger 22, or fluid circuit 12 near the outlet of exterior heat exchanger 22. Sensor 48 is adapted to sense the temperature of the refrigerant in, or flowing from, exterior heat exchanger 22. Alternatively, sensor 48 may be adapted to sense the pressure of the refrigerant flowing from exterior heat exchanger 22. A controller 46 is electronically coupled to sensor 48 and is adapted to receive the sensed temperature from sensor 48. Controller 46 is also operably coupled to first and second valves 42, 44 and is adapted to affect the movement of valves 42, 44 between their first and second positions.
During the heating mode, vapor compression system 10 performs an operating cycle, illustrated by the bold flow lines in
Meanwhile, sensor 48 senses the temperature and/or pressure of the refrigerant in, or flowing from, exterior heat exchanger 22 and communicates the sensed temperature and/or pressure to controller 46. A sensed temperature below a certain level could be an indication of frost build-up on exterior heat exchanger 22. Similarly, a sensed pressure below a certain level may also indicate inefficient/ineffective evaporation due to frost build-up on exterior heat exchanger. Therefore, when the sensed temperature and/or pressure falls below a pre-determined value, controller 46 initiates a defrost cycle by switching first valve 42 to the first position and second valve 44 to the second position.
During the defrost cycle the refrigerant circulates through system 10 along the flow path illustrated in bold in
During the defrost cycle, sensor 48 continues to sense the temperature and/or pressure of the refrigerant in, or flowing from, exterior heat exchanger 22. When the sensed temperature and/or pressure of the refrigerant reaches a pre-determined value, controller 46 ceases the defrost cycle and initiates the operating cycle.
Second heat exchanger or sub-cooler 18 may be any conventional heat exchanger capable of exchanging thermal energy between the refrigerant flowing in fluid circuit 12 and the refrigerant flowing in second bypass line 34. Because second heat exchanger 18 extracts and stores thermal energy during the operational cycle, second heat exchanger 18 is preferably constructed of a material having significant thermal storage potential. Such materials include metals, such as steel and copper. In one embodiment, a mass of material capable of storing heat may be added onto the body of second heat exchanger 18 in order to increase the thermal storage potential of the heat exchanger. Alternatively, or additionally, second heat exchanger 18 may incorporate a layer or section of phase change material, such as water, paraffin wax, or salt hydrates including, for example, NaOH, CaCl2, Na2SO4, Na2HPO4, Ca(NO3)2 or Na2S2O3. Second heat exchanger 18 may alternatively include adsorption/desorption pairs capable of storing and releasing heat. Examples of such pairs are ammonia/strontium chloride, carbon/water, activated carbon/ammonia, zeolites/water and methenol/metal hydrides. Chemicals capable of undergoing a reversible exothermic process may also be used to increase their heat storage potential.
In addition to the operational and defrost cycles, the vapor compression system 10 may be adapted to perform a start-up cycle, during which the refrigerant circulates through system 10 along flow lines illustrated in bold in
While this invention has been described as having an exemplary design, the present invention may be further modified within the spirit and scope of this disclosure. This application is therefore intended to cover any variations, uses, or adaptations of the invention using its general principles. Further, this application is intended to cover such departures from the present disclosure as come within known or customary practice in the art to which this invention pertains.