Note: Descriptions are shown in the official language in which they were submitted.
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APPARATUS AND METHOD FOR CONTROLLING REFRIGERANT TEMPERATURE
IN A HEAT PUMP OR REFRIGERATION APPARATUS
FIELD OF TECHNOLOGY
[0001] The present disclosure relates to compressors for heat pump or
refrigeration
apparatus.
BACKGROUND
[0002] A typical refrigeration cycle is a closed loop system which uses a
refrigerant
having a low boiling point to produce a relative coldness. A compressor
compresses the
refrigerant in order to increase its pressure. As the pressure increases, the
refrigerant
gas temperature also rises and subsequently the gas then flows through a heat
exchanger to transfer heat to the adjacent medium in the heat exchanger. As
the heat
dissipates, the refrigerant cools and condenses to a liquid. The liquid then
flows through
an expansion valve which causes the refrigerant to expand and change phases
into a
gas. The cold gas then circulates into a second heat exchanger and absorbs
heat and
then passes into the compressor where the cycle repeats.
[0003] Lubricant is provided in the compressor 12 to lubricate the compressor
crankcase and other compressor components. Proper lubrication helps to avoid
compressor failures, which can be costly both in terms of production down time
and part
replacement. The lubricant is intended to remain primarily in the compressor
crankcase,
however, the lubricant often migrates to other parts of a refrigeration
apparatus.
[0004] In general, the temperature output of a refrigeration apparatus is
limited by the
effective temperature range of the lubricant and the compression process of
the
compressor. When operating above the effective temperature range, lubricants
may
break down over time in response to the high temperatures in the compressor.
When the
lubricant breaks down, the degraded lubricant may flow throughout the
compressor and
may cause compressor failure.
SUMMARY
[0005] In an aspect there is provided, an apparatus including: a compressor
comprising
a pair of ports in fluid communication with first and second heat exchangers
and a
reduced temperature refrigerant inlet for receiving reduced temperature
refrigerant; and
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an expansion device coupled between the first and second heat exchangers for
reducing
a pressure of refrigerant flowing from one of the first and second heat
exchangers to the
other of the first and second heat exchangers; wherein the compressor, the
first heat
exchanger, the expansion device and the second heat exchanger are arranged in
a loop
to operate as a refrigeration or heat pump apparatus.
[0006] In another aspect there is provided a method including: compressing a
refrigerant during a compression step of a refrigeration cycle; and injecting
a reduced
temperature refrigerant into a compressor part-way through the compression
step.
BRIEF DESCRIPTION OF THE DRAWINGS
[0007] Embodiments of the present disclosure will now be described, by way of
example only, with reference to the attached figures, wherein:
[0008] FIG. 1 is a cycle diagram of an apparatus according to an embodiment;
and
[0009] FIG. 2 is a schematic top sectional view of a scroll compressor.
DETAILED DESCRIPTION
[0010] The following describes an apparatus and method of compressing a
refrigerant
during a compression step of a refrigeration cycle; and injecting a reduced
temperature
refrigerant into a compressor part-way through the compression step.
[0011] For simplicity and clarity of illustration, reference numerals may
be repeated
among the figures to indicate corresponding or analogous elements. Numerous
details
are set forth to provide an understanding of the embodiments described herein.
The
embodiments may be practiced without these details. In other instances, well-
known
methods, procedures, and components have not been described in detail to avoid
obscuring the embodiments described. The description is not to be considered
as limited
to the scope of the embodiments described herein.
[0012] Referring to FIG. 1, an apparatus 10 is schematically shown by way of a
cycle
diagram. The apparatus 10 is generally a refrigeration apparatus, which may
also be
referred to as a heat pump. In general, the components of the apparatus 10 are
arranged
in a loop and refrigerant flows through the apparatus 10 in a first direction
to generate
heat at a first side of the apparatus 10. The flow may be reversed to switch
the side of
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the apparatus 10 at which heat is generated.
[0013] The apparatus 10 includes a compressor 12, first heat exchanger 14 and
second heat exchanger 16. A four-way reversing valve 18 is located between the
compressor 12 and the heat exchangers 14, 16 to reverse the direction of fluid
flow. First
heat exchanger 14 and second heat exchanger 16 are both operable as an
evaporator
and a condenser depending on the direction of fluid flow through the apparatus
10. A first
heat exchange conduit 28 communicates with the first heat exchanger 14 to
transfer heat
to the first heat exchanger 14 when the first heat exchanger 14 is operating
as an
evaporator and remove heat from the first heat exchanger 14 when the first
heat
exchanger 14 is operating as a condenser. Similarly, a second heat exchange
conduit 30
communicates with the second heat exchanger 16 to transfer heat to the second
heat
exchanger 16 when the second heat exchanger 16 is operating as an evaporator
and
remove heat from the second heat exchanger 16 when the second heat exchanger
16 is
operating as a condenser. The apparatus 10 further includes drive mechanisms
(not
shown) for pumping fluid through the first and second heat exchange conduits
28, 30.
[0014] A receiver 20 is located between the heat exchangers 14, 16.
Refrigerant
flowing from the first heat exchanger 14 enters the receiver 20 before flowing
into the
second heat exchanger 16. Similarly, when flow is reversed, fluid flowing from
the second
heat exchanger 16 enters the receiver 20 before flowing into the first heat
exchanger 18.
The receiver 20 is a reservoir for storing high pressure liquid. A volume of
the receiver 20
is sized to compensate for expansion and contraction of the refrigerant in the
constant
volume apparatus 10.
[0015] A first valve 22 is located between the first heat exchanger 14 and the
receiver
20 and a second 24 valve is located between the second heat exchanger 16 and
the
receiver 20. Both valves 22, 24 are capable of operating as expansion valves
or as check
valves, which are also referred to as one-way valves. The mode of operation of
the
valves 22, 24 depends on the direction of fluid flow through the apparatus 10.
The valve
22, 24 that is located adjacent to an inlet of the heat exchanger operating as
an
evaporator operates as an expansion valve to reduce a pressure of the fluid
entering the
heat exchanger 14, while the valve 22, 24 that is located adjacent to an exit
of the
condenser operates as a check valve.
[0016] An accumulator 26 is located between the four-way reversing valve 18
and the
compressor 12. The accumulator 26 is an optional component of the apparatus 10
and is
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generally provided to store excess liquid refrigerant and lubricant that may
not have
boiled off during evaporation.
[0017] Conduits, such as pipes, for example, are disposed between components
of the
apparatus 10 for conveying refrigerant therethrough. Conduit 32 is coupled
between the
compressor 12 and the four-way reversing valve 18. Conduit 34 is coupled
between the
four-way reversing valve 18 and the first heat exchanger 14. Conduits 36 and
38 are
coupled between the first heat exchanger 14 and the valve 22 and the valve 22
and the
receiver 20, respectively. Conduits 40 and 42 are coupled between the receiver
20 and
the valve 24 and the valve 24 and the second heat exchanger 16, respectively.
Conduit
44 is coupled between the second heat exchanger 16 and the four-way reversing
valve
18. Conduit 46 is coupled between the four-way reversing valve 18 and the
accumulator
26 and conduit 48 is coupled between the accumulator 26 and the compressor 12.
[0018] Conduits 32 and 48 are coupled to ports 50 and 52, respectively, of the
compressor 12. The port 50 is an outlet port and the port 52 in an inlet port.
The
compressor 12 may have more than one inlet port 52.
[0019] A scroll compressor, which is shown schematically in FIG. 2, generally
includes
two inlet ports for receiving refrigerant from the evaporator. In a scroll
compressor,
refrigerant is compressed between two scroll plates that are nested together.
One plate
may be stationary while the other plate moves in an orbital path. Refrigerant
is received
through inlet ports at the perimeter of the scroll and as the plate orbits, an
enclosed
volume containing the refrigerant is transferred toward a decreased volume
region at the
center of the scroll. As the volume decreases, the refrigerant is compressed
and
discharged through an outlet port.
[0020] The compressor 12 further includes an injection inlet 54 for receiving
a reduced
temperature refrigerant from the receiver 20. Conduit 56 is coupled between
the receiver
20 and an expansion valve 58 and conduit 60 is coupled between the expansion
valve 58
and inlet 54 of the compressor 12 to facilitate delivery of the refrigerant to
the compressor
12. The expansion valve 58 reduces a pressure of the refrigerant prior to the
refrigerant
entering the compressor 12. In a scroll compressor, the injection inlet 54 is
located in
interior or middle scrolls of the flanks of the scroll compressor.
[0021] The injection inlet 54 facilitates injection of refrigerant into
the compressor 12
through the inlet 54 part-way through the compression step of the
refrigeration cycle. In
general, compressor outlet temperature is maintained below 300 F in order to
avoid
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damage due to lubricant breakdown. One or more of compressor outlet
temperature,
compressor motor temperature and compressor flank temperature are measured in
order
to determine when and how much of the reduced temperature refrigerant may be
injected
into the injection inlet 54. Methods for measuring compressor temperatures are
well
known in the art and therefore will not be described further.
[0022] The injection of reduced temperature refrigerant reduces the
temperature of the
refrigerant proceeding through the compression step and exiting the compressor
12. The
reduced temperature refrigerant is less likely to cause the lubricant in the
compressor to
break down, which may result in an increased operating life of the compressor
12.
[0023] The refrigerant used in the apparatus 10 is Trifluoroiodomethane
(CF3I), which
may also be referred to as lodotrifluoromethane, Monoiodotrifluoromethane,
Trifluoromethyl iodide, Perfluoromethyl iodide or Freon 13T1. The chemical
composition
of the Trifluoroiodomethane includes one carbon atom combined with 3 flourine
atoms
and one Iodine atom. Sesquiterpene, which is a stabilizer may be added to the
refrigerant
[0024] Alternatively, the refrigerant may be one of other blends fluorinated
carbon
compounds to facilitate the higher efficiency and work well with mid-
compression
refrigeration injection. The refrigerants generally have a low GWP (global
warming
potential) and are ozone friendly.
[0025] Operation of the apparatus 10 will now be described with reference to
FIG. 1. In
this example, heat exchanger 14 is operating as a condenser and heat exchanger
16 is
operating as an evaporator.
[0026] Low pressure refrigerant enters the compressor 12 through port 52 and
is
compressed. Part-way through compression, reduced temperature refrigerant,
which has
a lower temperature than the refrigerant that is in the compressor 12, is
injected through
inlet 54. The reduced temperature refrigerant flows from the receiver 20,
through the
expansion valve 58, to enter the compressor 12 with a pressure that is lower
than the
pressure of the refrigerant in the receiver 20. The refrigerant entering the
compressor 12
through the inlet 54 has an absolute pressure that is approximately mid-way
between the
absolute pressure at the inlet port 52 and the absolute pressure at the outlet
port 50. The
reduced temperature refrigerant mixes with the refrigerant in the compressor
12 and exits
the compressor 12 through conduit 32 as a high pressure, high temperature gas.
The
refrigerant exiting the compressor 12 is at a high temperature, however, the
temperature
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is less than the temperature would have been without the addition of the
reduced
temperature refrigerant, which facilitates protection of the lubricant and the
moving
mechanical parts of the compressor and other components of the apparatus 10.
[0027] The gas exiting the compressor 12 flows through the four-way reversing
valve
18, through conduit 34 and enters the first heat exchanger 14. As the
refrigerant flows
through the first heat exchanger 14, the refrigerant is in indirect contact
with fluid flowing
through the first heat exchange conduit 28 to remove heat from the
refrigerant. The
condensed refrigerant exits the heat exchanger 14, flows through conduit 36
and travels
past valve 22, which functions as a check valve. The condensed refrigerant
then flows
through conduit 38 and into the receiver 20.
[0028] The condensed refrigerant exits the receiver 20, flows through conduit
40 and
travels past the valve 24, which functions as an expansion valve where the
pressure of
the refrigerant is reduced to facilitate expansion and lowering of the
refrigerant
temperature. The refrigerant then flows through conduit 42 and into the second
heat
exchanger 16. As the refrigerant flows through the second heat exchanger 16,
the
refrigerant is in indirect contact with fluid flowing through the second heat
exchange
conduit 30 and heat is absorbed by the refrigerant. As heat is absorbed, the
refrigerant
vaporizes and exits the second heat exchanger 16 through conduit 44 and flows
into the
four-way reversing valve 18. From the four-way reversing valve 18, the
refrigerant flows
through conduit 46 to enter the accumulator 26. The refrigerant then exits the
accumulator 26 through conduit 48 and flows into the compressor 12 to begin
the cycle
again.
[0029] In general, the refrigerant temperature is maintained below a breakdown
temperature of the lubricant. In one example, the refrigerant temperature is
maintained
25 to 50 degrees Fahrenheit below the lubricant breakdown temperature. When
Polyolester (POE), which is a common lubricant used with Hydro fluorocarbon
(HFC)
refrigerants, is used, the breakdown temperature is approximately 300 degrees
Fahrenheit. Therefore, in this example, the temperature at the outlet port 50
of the
compressor 12 may be between 250 and 275 degrees Fahrenheit.
[0030] In one embodiment, the four-way reversing valve 18 is eliminated from
the
embodiment of FIG. 1 and the apparatus 10 is operable in a single direction.
[0031] In another embodiment, a motor of the compressor 12 includes a
frequency
drive for controlling the compressor motor speed. There is a large difference
between
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refrigeration densities at opposite ends of the operating conditions as
determined by the
refrigerant gas specific volumes and resultant density. For example, a
compressor may
need to move significantly more pounds of refrigerant gas for a particular
pressure
increase, which may consequently overload the connected refrigerant compressor
motor.
By slowing down the motor using a frequency drive, power input may be reduced.
Control over the motor speed may improve the service life of the compressor
12.
[0032] In another embodiment, the reduced temperature refrigerant may be
injected
into the compressor 12 in response to a temperature at the outlet port 50 of
the
compressor 12 being within a predetermined temperature range. In one example,
the
reduced temperature refrigerant is injected into the compressor when the
temperature at
the outlet port 50 is between 250 and 275 degrees Fahrenheit.
[0033] The apparatus 10 described herein may include any type of compressor
that is
capable of compound and/or inter-stage compression. A scroll compressor is
provided as
an example and is not intended to be limiting.
[0034] By reducing the temperature of the refrigerant exiting the compressor
12, the
operating life of the lubricant and therefore the operating life of the
compressor 12 and
other components of the heat pump/refrigeration apparatus may be extended.
[0035] In addition, by reducing the temperature of the refrigerant exiting the
compressor 12, the efficiency of the refrigeration apparatus 10 may be
increased. By
achieving cooling/heating results more efficiently, the operating time of the
refrigeration
apparatus 10 may be reduced resulting in less energy consumed.
[0036] The present disclosure may be embodied in other specific forms without
departing from its spirit or essential characteristics. The described
embodiments are to
be considered in all respects only as illustrative and not restrictive. The
scope of the
present disclosure is, therefore, indicated by the appended claims rather than
by the
foregoing description. All changes that come within the meaning and range of
equivalency of the claims are to be embraced within their scope.
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