Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
CA 02525360 2005-11-03
VAPOR COMPRESSION SYSTEM WITH DEFROST SYSTEM
BACKGROUND OF THE INVENTION
1. Field of the Invention.
[0001) The present invention relates to vapor compression systems,
particularly, vapor
compression systems having a defrost system.
2. Description of the Related Art.
[0002] 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 transfernng 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.
[0003] 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
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ambient air indoors to the refrigerant within the coil thereby cooling the air
indoors. This
phenomenon is commonly referred to as "cold blow."
[0004] 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.
SUMMARY OF THE INVENTION
[0005] 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
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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.
[0006] 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.
[0007] 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
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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.
[0008] 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.
[0009] 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.
[0010] Additional advantages of the present invention will become apparent
when referencing
the descriptions below.
BRIEF DESCRIPTION OF THE DRAWINGS
[0011] 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:
[0092] FIG. I is a schematic view of a vapor compression system according to
one embodiment
of the present invention wherein the vapor compression system is performing an
operating cycle;
FIG. 2 is a schematic view of the vapor compression system of FIG. 1 wherein
the vapor
compression system is performing a defrost cycle; and
FIG. 3 is a schematic view of the vapor compression system of FIG. I wherein
the vapor
compression system is performing a start-up cycle.
[0013] Corresponding reference characters indicate corresponding parts
throughout the several
views. Although the exemplification set out herein illustrates embodiments of
the invention, in
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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.
DETAILED DESCRIPTION
[0014] 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.
[0015] Referring first to FIG. l, a vapor compression system 10 in accordance
with the present
invention is illustrated. Vapor compression system 10 includes refrigerant
fluid circuit 12
(represented by bold flow lines in FIG. 1 ) through which flows a compressible
refrigerant, such
as carbon dioxide. Operably coupled to fluid circuit 12, in serial order, is
compressor 14, first
heat exchanger 16, second heat exchanger or sub-cooler 18, expansion device
20, third heat
exchanger 22 and accumulator 24. Vapor compression system 10 is depicted in
FIGS. 1-3 as a
heat pump system for heating and/or cooling an interior space defined by
building or other
structure. As such, first heat exchanger 16 is positioned in the interior
space, while third heat
exchanger 22 is positioned exterior to the structure. A blower or fan 26 is
positioned adjacent
interior heat exchanger 16 and is adapted to circulate the ambient air of the
interior space over
interior heat exchanger 16. It should be understood that although the present
invention is
illustrated in FIGS. 1-3 as a heat pump system, the present invention may be
similarly adapted
for use in other heating and cooling systems, water heating systems, and other
heating and
cooling applications.
[0016] 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.
[0017] Turning now to FIGS. 1-3, vapor compression system 10 also includes
first bypass line
28 and second bypass line 34. First bypass line 28 extends from a first point
30 in fluid circuit
12 between interior heat exchanger 16 and second heat exchanger 18 to a second
point 32 in
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fluid circuit 12 between expansion device 20 and third heat exchanger 22. As
illustrated in
FIGS. 2 and 3, first bypass line 28 is adapted to communicate fluid from first
point 30 in fluid
circuit 12 directly to second point 32 in fluid circuit 12, the fluid thereby
bypassing second heat
exchanger 18 and expansion device 20.
[0018] As shown in FIGS. 1-3, a first valve 42 is operably coupled to first
bypass line 28 and has
a first position and a second position. In its first position, depicted in
FIG. 2, first valve 42
permits the refrigerant flowing from interior heat exchanger 16 to flow from
first point 30
through bypass line 28 to second point 32, thereby flowing from interior heat
exchanger 16
directly to exterior heat exchanger 22 without passing through second heat
exchanger 18 and
expansion device 20. In its second position, depicted in FIG. l, first valve
42 prevents the flow
of refrigerant through first bypass line 28. As a result, the refrigerant is
forced to flow through
second heat exchanger 18 and expansion device 20 before flowing to exterior
heat exchanger 22.
[0019] As illustrated in FIG. 2, first valve 42 may be disposed in first
bypass line 28. In this
configuration, when first valve 42 is in the first position, first valve 42 is
open and permits fluid
to flow through bypass line 28 but does not positively prohibit fluid from
also flowing through
second heat exchanger 18 and expansion device 20. Thus, at first point 30
refrigerant flowing
from interior heat exchanger 16 may flow to exterior heat exchanger 22 either
through first
bypass line 28 or through fluid circuit 12 including second heat exchanger 18
and expansion
device 20. However, due to the resistance created by second heat exchanger 18
and expansion
device 20, the natural fluid dynamics of system 10 causes at least a
substantial amount of the
refrigerant flowing from interior heat exchanger 16 to flow to exterior heat
exchanger 22 through
bypass line 28 when first valve 42 is in the first position. First valve 42
may be any conventional
valve capable of controlling the flow of high pressure refrigerant fluid. In
one embodiment, for
example, valve 42 is a solenoid valve.
[0020] 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.
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[0021] Referring to FIGS. 1-3, second bypass line 34 extends from a third
point 36 in fluid
circuit 12 between exterior heat exchanger 22 and accumulator 24 to a fourth
point 38 in fluid
circuit 12 between third point 36 and accumulator 24. Second bypass line 34 is
operably coupled
to, and is in thermal heat exchange with, second heat exchanger 18. Bypass
expansion device 40
is operably coupled to second bypass line 34 and reduces the pressure of the
refrigerant flowing
to second heat exchanger 18.
[0022] A second valve 44 is disposed in refrigerant circuit 12 between third
and fpurth points 36,
38, and has a first position and a second position. In the first position,
depicted in FIG. l, second
valve 44 is open and refrigerant is permitted to flow from exterior heat
exchanger 22 directly to
accumulator 24 through fluid circuit 12 without flowing through second bypass
line 34. In this
position second valve 44 does not positively prohibit fluid from flowing to
accumulator 24
through second bypass line 34. Thus, at third point 36 refrigerant flowing
from exterior heat
exchanger 22 may flow to accumulator 24 either through second bypass line 34
including bypass
expansion device 40 and second heat exchanger 18 or through fluid circuit 12.
However, due to
the resistance created by bypass expansion device 40 and second heat exchanger
18, when
second valve is in the first position, the fluid dynamics of system 10 causes
at least a substantial
amount of the refrigerant to flow directly to accumulator 24 via refrigerant
fluid circuit 12
without flowing through second bypass line 34. In the second position,
depicted in FIG. 2,
second valve 44 is closed thereby positively prohibiting refrigerant from
flowing directly to
accumulator 24 via fluid circuit 12. As a result, the refrigerant flowing from
exterior heat
exchanger 22 is forced to flow through second bypass line 34. Second valve 44
may be any
conventional valve capable of controlling the flow of high pressure
refrigerant. In one
embodiment, for example, second valve 44 is a solenoid valve.
[0023] 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.
[0024] 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
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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.
[0025] During the heating mode, vapor compression system 10 performs an
operating cycle,
illustrated by the bold flow lines in FIG. 1. During the operating cycle,
first valve 42 is in the
second position while second valve 44 is in the first position. The
refrigerant fluid is compressed
in compressor 14 to a high pressure and high temperature. The resulting hot
compressed fluid
discharged from compressor 14 flows through fluid circuit 12 to interior heat
exchanger 16.
Interior heat exchanger 16 acts as a condenser extracting heat from the hot
compressed fluid and
transferring it to the ambient air forced over interior heat exchanger 16 by
blower 26. As a
result, the compressed refrigerant is cooled and the ambient air within the
interior space of the
structure is heated. Although cooled in interior heat exchanger 16, the
refrigerant exiting interior
heat exchanger 16 is still quite hot and retains a significant amount of
thermal energy. The hot
refrigerant fluid then flows to second heat exchanger 18 where additional
thermal energy is
extracted to thereby further cool the refrigerant. The second heat exchanger
18 stores the
extracted thermal energy and, ultimately, transfers the thermal energy to
refrigerant flowing in
another area of system 10 during a defrost cycle, which is discussed further
below. The cooled
refrigerant flows from second heat exchanger 18 to expansion device 20 which
reduces the
pressure of the compressed refrigerant and meters the refrigerant to exterior
heat exchanger 22.
Exterior heat exchanger 22 acts as an evaporator wherein thermal energy is
transferred from the
ambient air outside of the structure to the refrigerant, thereby cooling the
air outside of the
structure and evaporating the compressed refrigerant fluid. The refrigerant
then flows through
fluid circuit 12 to accumulator 24 which stores any liquid refrigerant
remaining in the fluid
exiting exterior heat exchanger 22 and meters the liquid refrigerant to
compressor 14 or to
another location in refrigerant circuit 12. The evaporated refrigerant flows
through accumulator
24 and back to compressor 14 and the operational cycle is repeated.
[0026] 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
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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.
[0027] During the defrost cycle the refrigerant circulates through system 10
along the flow path
illustrated in bold in FIG. 2. More particularly, hot refrigerant flowing from
interior heat
exchanger 16 flows to first point 30 at which point a majority of the hot
refrigerant flows through
first bypass line 28 directly to exterior heat exchanger 22 bypassing second
heat exchanger 18
and expansion device 20. As a result, the hot fluid exiting interior heat
exchanger 16 flows
directly to exterior heat exchanger 22, wherein the hot refrigerant flows
through exterior heat
exchanger 22 thawing any frost that has formed on exterior heat exchanger 22
and cooling the
refrigerant. The refrigerant then flows from exterior heat exchanger 22 to
third point 36 at which
point the refrigerant is forced to flow through second bypass line 34. The
refrigerant is expanded
in expansion device 40 and is metered to second heat exchanger 18. In second
heat exchanger 18
the cool refrigerant absorbs the sensible heat of second heat exchanger 18
(e.g. the thermal
energy stored in second heat exchanger 18 during the operational cycle),
thereby warming the
refrigerant and cooling second heat exchanger 18. The warm refrigerant then
flows to
accumulator 24 and then to compressor 14 and the defrost cycle continues.
[0028] 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.
[0029] 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
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hydrates including, for example, NaOH, CaCl2, NaZS04, NazHP04, Ca(N03)2 or
NaZS203.
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.
[0030] 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 FIG. 3. During initial start-up of
vapor compression
system 10, controller 46 initiates the start-up cycle by switching first valve
42 to the first position
and maintaining second valve 44 in the first position. The refrigerant flows
from compressor 14
to interior heat exchanger 16. From interior heat exchanger 16, the
refrigerant flows through
first bypass line 28 to exterior heat exchanger 12, thereby bypassing second
heat exchanger 18
and expansion device 20. The refrigerant then flows from exterior heat
exchanger 12 to
accumulator 24, bypassing second bypass line 34, expansion valve 40 and second
heat exchanger
18. From accumulator 24, the refrigerant flows to compressor 14 and the cycle
is repeated until
the system is warmed up. By directing the refrigerant to bypass expansion
device 20, the torque
load placed on compressor 14 by the refrigerant during start-up is reduced. As
a result, the start-
up cycle reduces the stress on compressor 14 and the power spike caused by the
compressor
during start-up, thereby promoting the life of compressor 14. Once vapor
compression system
is fully operating, controller 46 switches system 10 to the operational cycle,
illustrated in FIG.
1, by moving first valve 42 from the first position to the second position.
[0031] 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.
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