U.S. patent application number 11/528493 was filed with the patent office on 2007-06-21 for heat pump system having a defrost mechanism for low ambient air temperature operation.
Invention is credited to Gang Li.
Application Number | 20070137228 11/528493 |
Document ID | / |
Family ID | 37904964 |
Filed Date | 2007-06-21 |
United States Patent
Application |
20070137228 |
Kind Code |
A1 |
Li; Gang |
June 21, 2007 |
Heat pump system having a defrost mechanism for low ambient air
temperature operation
Abstract
A heat pump system includes a hot gas bypass defrost mechanism
which enables normal heat pump operation at low ambient air
temperatures, and may be used for heating swimming pools. The
bypass defrost mechanism is activated by sensing a drop in
compressor suction line pressure, which occurs at low ambient
temperatures when frost forms on an evaporator in the heat pump,
which disrupts normal heat pump operation. The defrost mechanism
includes a circuit that redirects a portion of hot refrigerant
discharged by a compressor directly to the evaporator, thereby
bypassing other heat pump components and defrosting the
evaporator.
Inventors: |
Li; Gang; (Clemmons,
NC) |
Correspondence
Address: |
MCCARTER & ENGLISH, LLP
FOUR GATEWAY CENTER
100 MULBERRY STREET
NEWARK
NJ
07102
US
|
Family ID: |
37904964 |
Appl. No.: |
11/528493 |
Filed: |
September 27, 2006 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
60721479 |
Sep 28, 2005 |
|
|
|
Current U.S.
Class: |
62/196.4 ;
62/498 |
Current CPC
Class: |
F25B 2400/0411 20130101;
F25B 2400/0403 20130101; F25B 2700/1933 20130101; F25B 30/02
20130101; F25B 2500/31 20130101; F25B 47/022 20130101; F25B
2600/2501 20130101 |
Class at
Publication: |
062/196.4 ;
062/498 |
International
Class: |
F25B 41/00 20060101
F25B041/00; F25B 1/00 20060101 F25B001/00 |
Claims
1. In a heat pump including a compressor; a condenser; a compressor
discharge line connecting said compressor to said condenser; an
expansion device; a condenser discharge line connecting said
condenser to said expansion device; an evaporator; an expansion
device discharge line connecting said expansion device to said
evaporator; a suction line connecting said evaporator to said
compressor; and a by-pass valve having an inlet, which is in fluid
communication with said compressor discharge line, and an outlet,
which is in fluid communication with said expansion device
discharge line, the improvement comprising: controlling means for
controlling said by-pass valve so as to adjust said by-pass valve
between an open position and a closed position in response to
pressure in said suction line.
2. The heat pump of claim 1, wherein said by-pass valve is a
capacity control discharge valve.
3. The heat pump of claim 2, wherein said controlling means
includes an equalization tube extending between said capacity
control discharge valve and said suction line.
4. The heat pump of claim 3, wherein said valve moves into its said
open position in response to the suction line pressure dropping
below a selected value associated with frost formation on said
evaporator, whereby refrigerant flowing from said compressor
discharge line to said evaporator causes the evaporator to
defrost.
5. The heat pump of claim 4, wherein said selected suction line
pressure value is 60 psi.
6. The heat pump of claim 1, wherein said by-pass valve is a
solenoid valve.
7. The heat pump of claim 6, wherein said controlling means
includes a pressure switch adapted to sense pressure in said
suction line, said pressure switch being electrically connected to
said solenoid valve.
8. The heat pump of claim 7, wherein said solenoid valve moves into
its said open position in response to the suction line pressure
dropping below a selected value associated with frost formation on
said evaporator, whereby refrigerant flowing from said compressor
discharge line to said evaporator causes said evaporator to
defrost.
9. The heat pump of claim 8, wherein said selected suction line
pressure value is 60 psi.
10. In a heat pump including a refrigerant circuit having a
compressor; a condenser; a compressor discharge line connecting
said compressor to said condenser; an expansion device; a condenser
discharge line connecting said condenser to said expansion device;
an evaporator; an expansion device discharge line connecting said
expansion device to said evaporator; and a suction line connecting
said evaporator to said compressor; the improvement comprising: a
defrost circuit including a valve having an inlet and an outlet; an
inlet line in fluid communication with said compressor discharge
line and said inlet; an outlet line in fluid communication with
said outlet and said expansion device discharge line; and
controlling means for controlling said valve so as to adjust said
valve between an open position and a closed position in response to
pressure in said suction line, wherein said valve moves into its
said open position in response to the pressure in said suction line
dropping below a selected value, whereby refrigerant flowing from
said compressor discharge line to said evaporator causes the
evaporator to defrost.
11. The heat pump system of claim 10, wherein said valve is a
capacity control discharge valve.
12. The heat pump system of claim 11, wherein said controlling
means includes an equalization tube in fluid communication with
said suction line and said valve, said equalization tube being
adapted to communicate the pressure in said suction line to said
valve.
13. The heat pump system of claim 10, wherein said valve is a
solenoid valve.
14. The heat pump system of claim 13, wherein said controlling
means includes a transformer electrically connected to said
solenoid valve, and a switch disposed in said suction line and
electrically connected to said transformer.
15. A method for defrosting an evaporator of a heat pump which also
includes a compressor; a condenser; a compressor discharge line
connecting the compressor to the condenser; an expansion device; a
condenser discharge line connecting the condenser to the expansion
device; an expansion device discharge line connecting the expansion
device to the evaporator; a suction line connecting the evaporator
to the compressor; and a by-pass valve having an inlet, which is in
fluid communication with the compressor discharge line, and an
outlet, which is in fluid communication with the expansion device
discharge line, the method comprising the steps of: selecting a
pressure value associated with the formation of frost on the
evaporator; monitoring the pressure in the suction line; opening
the by-pass valve when the pressure in the suction line drops below
the selected value, thereby allowing a flow of refrigerant from the
compressor, through the by-pass valve and into the evaporator,
wherein the refrigerant is of a temperature sufficient to defrost
the evaporator; continuing to monitor the pressure in the suction
line; and closing the by-pass valve when the pressure in the
suction line returns to the selected value.
Description
CROSS REFERENCE TO RELATED APPLICATION
[0001] This application claims priority of U.S. Provisional Patent
Application Ser. No. 60/721,479, filed Sep. 28, 2005, the
disclosure of which is incorporated by reference herein in its
entirety.
FIELD OF THE INVENTION
[0002] The present invention is directed to heat pump systems. More
particularly, the present invention is directed to vapor
compression heat pump systems with hot gas bypass defrosting for
low ambient air temperature operation.
BACKGROUND OF THE INVENTION
[0003] The evaporator element of a vapor compression heat pump
system is subject to a degradation in operating efficiency due to
the frosting of the evaporator coils. Frosting occurs when the
water vapor, in the ambient air surrounding the chilled evaporator,
condenses on the outer surfaces of the evaporator and freezes. One
method utilized to defrost the evaporator, is to reverse the heat
pump cycle, wherein the evaporator becomes the condenser. Another
method utilized to defrost the evaporator, is to direct a portion
of the high temperature and pressure refrigerant vapor, herein
referred to as hot gas, that is discharged from the compressor,
directly through the evaporator, bypassing the condenser.
[0004] The hot gas bypass defrost method is frequently utilized in
heat pump systems which do not require a reversal of the cycle in
normal operation (i.e., the heating function is not required to
become a cooling function), and the hot gas bypass defrost method
is often the least complex method for defrosting the evaporator in
such heat pump systems. In addition, the hot gas bypass defrost
method avoids cooling the heated fluid during the defrosting
operation because the functioning of the condenser is never
reversed to function as the evaporator.
[0005] The frosting of the evaporator generally increases with
decreases in the temperature of the ambient air surrounding the
evaporator. Therefore, decreases in ambient air temperatures also
decrease the ability of the heat pump systems to operate
normally.
[0006] What is needed, but has yet to be provided, is a heat pump
system having a hot gas bypass defrost mechanism, which operates
normally at low ambient air temperatures. This and other
needs/objectives are addressed by the present invention. Additional
advantageous features and functionalities of the present invention
will be apparent from the disclosure which follows, particularly
when reviewed in conjunction with the accompanying drawings.
SUMMARY OF THE INVENTION
[0007] A heat pump is provided which includes a compressor, a
condenser, a compressor discharge line connecting the compressor to
the condenser, an expansion device, a condenser discharge line
connecting the condenser to the expansion device, an evaporator, an
expansion device discharge line connecting the expansion device to
the evaporator, a suction line connecting the evaporator to the
compressor, and a by-pass valve having an inlet, which is in fluid
communication with the compressor discharge line, and an outlet,
which is in fluid communication with the expansion valve discharge
line. Controlling means are provided for controlling the by-pass
valve so as to adjust the by-pass valve between an open position
and a closed position in response to pressure in the suction line,
so as to defrost the evaporator.
BRIEF DESCRIPTION OF THE DRAWINGS
[0008] For a more complete understanding of the present invention,
reference is made to the following detailed description of various
exemplary embodiments considered in conjunction with the
accompanying drawings, in which:
[0009] FIG. 1 is a schematic diagram of a heat pump, illustrating a
hot gas bypass defrost circuit equipped with a capacity control
discharge valve mechanism;
[0010] FIG. 2 is an elevational view of the capacity control
discharge valve mechanism shown schematically in FIG. 1;
[0011] FIG. 3 is a schematic diagram of the heat pump shown in FIG.
1, illustrating a hot gas bypass defrost circuit equipped with a
solenoid valve mechanism;
[0012] FIG. 4 is an electrical schematic of the solenoid valve
mechanism shown in FIG. 3;
[0013] FIG. 5 is a perspective view of an exterior design for the
heat pump illustrated in FIGS. 1-4;
[0014] FIG. 6 is a front elevational view of the heat pump shown in
FIG. 5;
[0015] FIG. 7 is a side elevational view of the heat pump shown in
FIG. 5; and
[0016] FIG. 8 is an exploded perspective view of the heat pump
illustrated in FIGS. 5-7.
DETAILED DESCRIPTION OF THE INVENTION
[0017] Tests conducted on a heat pump adapted to heat swimming pool
water have demonstrated that the heat pump, operating at low
ambient temperatures in the range of from about 40 degrees to about
50 degrees Fahrenheit (.degree. F.), usually encounters frosting of
the entire evaporator, which produces a reduction in the compressor
suction pressure, thereby causing the heat pump compressor
low-pressure switch to cease operation of the compressor. Tests
have also demonstrated that, in order for the heat pump to continue
to operate at low ambient air temperatures, the compressor suction
pressure is required to be maintained at, or above, about 50 pounds
per square inch (psi) and compressor suction temperature is
required to be maintained above about 32.degree. F.
[0018] A first exemplary embodiment of the present invention is
illustrated in FIGS. 1-2. Referring now to FIG. 1, a heat pump
system 10 includes a refrigerant circuit 12 and a defrost circuit
14. The refrigerant circuit 12 is constructed and operates in a
manner similar to that of a conventional heat pump. The refrigerant
(not shown) which flows though the heat pump 10 may be any suitable
compressible refrigerant, such as carbon dioxide or a hydrocarbon
refrigerant.
[0019] The refrigerant circuit 12 includes in serial order and
operatively coupled, a compressor 16, a condenser 18, an expansion
device 20, and an evaporator 22. The compressor 16, condenser 18,
expansion device 20, and evaporator 22 are fluidly interconnected
by a compressor discharge line 24, a condenser discharge line 26,
an expansion device discharge line 28, and a compressor suction
line 30. The expansion device may be a thermostatic expansion valve
(TXV) or other suitable expansion device.
[0020] When the heat pump 10 is operating, the refrigerant in the
refrigerant circuit 12 flows continuously, and in serial order,
through the compressor 16, the compressor discharge line 24, the
condenser 18, the condenser discharge line 26, the expansion device
20, the expansion device discharge line 28, the evaporator 22, the
suction line 30, and again through the compressor 16. More
particularly, the low pressure and temperature refrigerant vapor
exiting the evaporator 22 is drawn by suction pressure into the
compressor 16 where the refrigerant is compressed and discharged
from the compressor 16 as hot gas, and then flows through the
compressor discharge line 24 and through the condenser 18. As the
hot gas flows through the condenser 18, thermal energy is removed
from the refrigerant and transferred to a fluid, such as swimming
pool water, surrounding the condenser 18, wherein the hot gas is
condensed to a liquid. The refrigerant then flows through the
condenser discharge line 26 and through the expansion device 20,
which reduces the pressure of the liquid refrigerant. The
refrigerant then flows through the expansion device discharge line
28 and through the evaporator 22, wherein thermal energy is
transferred from the ambient air surrounding the evaporator 22 to
the evaporator 22. The liquid refrigerant in the evaporator 22 is
then evaporated into a vaporous state. The refrigerant vapor,
exiting the evaporator 22, then flows through the compressor
suction line 30 and is again drawn by suction pressure into
compressor 16, where the cycle is repeated.
[0021] Because thermal energy is transferred from the ambient air
surrounding the evaporator 22, water vapor in the ambient air
condenses on the chilled outer surface of the evaporator 22,
forming frost. When sufficient quantities of frost are formed on
the outer surface of the evaporator 22, the heat transfer
functioning of the evaporator 22 becomes impaired. The defrost
circuit 14 is employed to defrost the evaporator 22 and restore the
normal heat transfer functioning of the evaporator 22. The defrost
circuit 14 directs a portion of the hot gas, which is discharged
from the compressor 16, directly into the evaporator 22, thereby
bypassing the condenser 18 and the expansion device 20. The defrost
circuit 14 includes a capacity control discharge valve 32, which
will be described in greater detail below.
[0022] Referring to FIGS. 1-2, in general, but FIG. 2, in
particular, the capacity control discharge valve 32 has an inlet
34, an outlet 36, and an equalization tube connection 38. The valve
32 may be any suitable capacity control discharge valve such as
Valve Model No. ASDRSE-2-0/80 manufactured by the Sporlan Valve
Company (Washington, Mo.). An inlet line 40 is in fluid
communication with the discharge valve inlet 34 and the compressor
discharge line 24, for conveying hot gas to the valve 32. An outlet
line 42 is in fluid communication with the valve outlet 36 and the
expansion device discharge line 28, for conveying hot gas from the
valve 32 to the expansion device discharge line 28. An equalization
tube 44 is in fluid communication with the suction line 30 and the
connection 38, for communicating the suction pressure to the valve
32.
[0023] In operation, when the evaporator 22 becomes frosted, the
suction pressure at the compressor suction line 30 is reduced, it
being understood that the pressure at the connection 38 is
substantially the same as the pressure in the suction line 30. When
the valve 32, which is normally closed, senses the suction line
pressure at the connection 38 to be lower than a selected pressure
value (e.g., 60 psi in this embodiment), the valve 32 is opened
proportionately, such proportionate opening being greater for lower
sensed pressures at the connection 38. More particularly, when the
discharge valve 32 is opened, a portion of the hot gas flows from
the discharge line 24, in serial order, through the inlet line 40,
the discharge valve 32, the outlet line 42, and the evaporator 22,
thereby bypassing the condenser 18 and the expansion device 20. The
opening of the valve 32 thereby defrosts the evaporator 22, and
simultaneously raises the suction pressure, thus enabling the
evaporator 22, the compressor 16, and the heat pump 10 to operate
at low ambient air temperatures in a normal manner. During the
aforesaid operation of the valve 32, a portion of the hot gas
continues to flow through the condenser 18, thereby continuing to
transfer thermal energy to the fluid (such as swimming pool water)
surrounding the condenser 18, thus continuing to heat such
fluid.
[0024] Referring to the Graph 1 and Table 1 below, laboratory tests
have demonstrated that the heat pump 10 operates normally at
ambient air temperatures as low as 40.degree. F. TABLE-US-00001
TABLE 1 TEST RESULT OBSERVATIONS: Graph 1 shows the testing results
of the defrost mechanism, wherein a manual shut off valve was
installed to activate and deactivate the discharge valve mechanism
of the heat pump: Graph 1: From left to right: --->Room
temperature went from 80 F. to 50 F. without defrost mechanism,
suction temperature sank below frozen point --->Defrost
mechanism was activated, suction temperature rose above frozen
point --->Room temperature went down to 45 F. and defrost
mechanism was turned off. Suction temperature went down to about 26
F. --->Room temperature maintained at 45 F. and the defrost
mechanism was activated. Suction temperature rose above frozen
point --->Room Temperature went down to 40 F. with defrosting
mechanism activated. Suction temperature maintain around the frozen
point --->Defrost was turned off, suction temperature took a
dive --->Room went down to 35 F. and defrost mechanism was
activated, suction temperature maintained at about 27 to 28 F. From
the test results, the unit can operate at 40 F. ambient without
frost issues. The unit will begin # to frost once the ambient
temperature is below 40 F. depending on the humidity conditions. As
we can see # that the suction pressure still maintained about 50
psi even the room went to 40 F. and about 48 psi when the # room
went to 35 F. So the unit would continue to operate with ambient in
30s, but the low-pressure switch # will shut down the unit once
severe frost covered large part of the coil.
[0025] Another exemplary embodiment of the present invention is
illustrated in FIGS. 3-4. Elements illustrated in FIGS. 3-4 which
correspond to the elements described above with reference to FIGS.
1-2 have been designated by corresponding reference numerals
increased by one hundred, while new elements are designated by
odd-numbered reference numerals in the one hundreds. The embodiment
of the present invention shown in FIGS. 3-4 operates and is
constructed in a manner consistent with the embodiment of FIGS.
1-2, unless it is stated otherwise.
[0026] Referring to FIG. 3, a heat pump system 110 includes a
refrigerant circuit 112 and a defrost circuit 114. The defrost
circuit 114, which operates in conjunction with a high pressure
switch 115 disposed in a compressor suction line 130, includes a
solenoid valve 117, which is disposed between an inlet line 140 and
an outlet line 142.
[0027] FIG. 4 illustrates a transformer 119 for powering the valve
117. Wires 121 (shown as solid lines) electrically interconnect the
valve 117, the switch 115, and the transformer 1 19.
[0028] In operation, the switch 115 senses the suction pressure at
the compressor suction line 130. More particularly, the switch 115
is set up to open at a selected suction line pressure value (e.g.,
60 psi in this embodiment). When the suction line 130 pressure is
higher than 60 psi, the switch 115 is open, the transformer 119 is
not activated, and the valve 117 is not energized. When the valve
117 is not energized, the valve 117 is closed to the flow of hot
gas therethrough. When the switch 115 senses the suction line 130
pressure to be lower than 60 psi, the switch 115 is closed, the
transformer 119 is activated, and the valve 117 is energized. When
the valve 117 is energized, the valve 117 is opened to the flow of
hot gas therethrough. As described above, the bypass flow of hot
gas defrosts the evaporator 122 while simultaneously raising the
pressure in the suction line 130, thereby enabling the heat pump
110 to operate at low ambient air temperatures in a normal
manner.
[0029] Elements of the present invention are illustrated in FIGS.
5-8. Elements illustrated in FIGS. 5-8 which correspond to the
elements described above with reference to FIGS. 1-2 have been
designated by corresponding reference numerals increased by two
hundred, while new elements are designated by odd-numbered
reference numerals in the two hundreds. The embodiment of the
present invention shown in FIGS. 5-8 operates and is constructed in
a manner consistent with the embodiment of FIGS. 1-2, unless it is
stated otherwise.
[0030] Referring to FIGS. 5-7, there is shown a heat pump 210
having an exterior design 211. Referring to FIG. 8, there are shown
disassembled elements of the heat pump 210, including a compressor
216, a condenser 218, an expansion device 220, and an evaporator
222. Referring still to FIG. 8, there are shown disassembled
elements of the heat pump 210, including a fan top assembly 223, an
evaporator support 225, an evaporator guard 227, a base pan
assembly 229, a side panel 231, a control box assembly 233, and a
cover assembly 235.
[0031] It will be understood that the embodiments of the present
invention described herein are merely exemplary and that a person
skilled in the art may make many variations and modifications
without departing from the spirit and scope of the invention. All
such variations and modifications, including those discussed above,
are intended to be included within the scope of the invention as
defined in the appended claims.
* * * * *