U.S. patent application number 10/886383 was filed with the patent office on 2006-01-12 for refrigerant system with reheat function provided by auxiliary heat exchanger.
Invention is credited to Alexander Lifson, Michael F. Taras.
Application Number | 20060005571 10/886383 |
Document ID | / |
Family ID | 35539888 |
Filed Date | 2006-01-12 |
United States Patent
Application |
20060005571 |
Kind Code |
A1 |
Lifson; Alexander ; et
al. |
January 12, 2006 |
Refrigerant system with reheat function provided by auxiliary heat
exchanger
Abstract
In disclosed embodiments of this invention, the main flow of
refrigerant is subcooled by another refrigerant stream in an
auxiliary heat exchanger. The auxiliary heat exchanger is either an
economizer heat exchanger or a liquid-suction heat exchanger. In
the case of the economizer heat exchanger, the smaller tapped
portion of the refrigerant is returned into the intermediate
compression stage. In the case of the liquid-suction heat
exchanger, the refrigerant leaving the evaporator subcools the
refrigerant in the main line as it leaves the condenser. In either
case, the refrigerant approaching the evaporator is subcooled and
greater cooling capacity is achieved. At the same time, the reheat
function is provided by passing a stream of air over the auxiliary
heat exchanger. This air additionally cools both refrigerant flows
in the auxiliary heat exchanger, which is desirable as it further
increases the subcooling of the liquid refrigerant and also reduces
the temperature of the vapor refrigerant entering the compressor.
This results in improved system efficiency and capacity, while at
the same time air is being dehumidified in a reheat cycle.
Inventors: |
Lifson; Alexander; (Manlius,
NY) ; Taras; Michael F.; (Fayetteville, NY) |
Correspondence
Address: |
CARLSON, GASKEY & OLDS, P.C.
400 WEST MAPLE ROAD
SUITE 350
BIRMINGHAM
MI
48009
US
|
Family ID: |
35539888 |
Appl. No.: |
10/886383 |
Filed: |
July 7, 2004 |
Current U.S.
Class: |
62/498 ;
62/513 |
Current CPC
Class: |
F25B 40/00 20130101;
F25B 2400/13 20130101 |
Class at
Publication: |
062/498 ;
062/513 |
International
Class: |
F25B 43/02 20060101
F25B043/02; F25B 1/00 20060101 F25B001/00; F25B 41/00 20060101
F25B041/00 |
Claims
1. A refrigerant system comprising: a compressor for compressing
refrigerant and delivering the refrigerant to a condenser; a main
expansion device positioned downstream of said condenser, and an
evaporator positioned downstream of said main expansion device, and
an air moving device for passing air over said evaporator; and an
auxiliary heat exchanger, a first refrigerant stream being
subcooled in said auxiliary heat exchanger by a second refrigerant
stream returning toward said compressor, and at least one of said
first or second refrigerant streams placed in a path of air driven
by said air moving device over said evaporator to provide a reheat
function.
2. The refrigerant system as set forth in claim 1, wherein a flow
control device selectively communicates said second flow stream of
refrigerant downstream of said auxiliary heat exchanger being
returned to said compressor, either through a reheat portion that
is in a path of said air to provide a reheat function, or can
bypass said second flow stream of refrigerant into a bypass line to
be returned directly to said compressor without providing the
reheat function.
3. The refrigerant system as set forth in claim 2, wherein a flow
control device is positioned in each of a line leading to said
reheat portion, and said bypass line.
4. The refrigerant system as set forth in claim 1, wherein said
auxiliary heat exchanger is placed in said path of air to provide
said reheat function.
5. The refrigerant system as set forth in claim 1, wherein said
auxiliary heat exchanger is an economizer heat exchanger, and there
being a tap for said second stream of refrigerant for being tapped
from a first flow of refrigerant and being passed through an
economizer expansion device, said tapped refrigerant exchanging
heat with said first flow of refrigerant in said economizer heat
exchanger.
6. The refrigerant system as set forth in claim 5, wherein said
tapped flow of refrigerant being returned to an intermediate
compression portion in said compressor.
7. The refrigerant system as set forth in claim 1, wherein a return
line for returning refrigerant to said compressor is placed in said
path of air.
8. The return line as set forth in claim 7, wherein at least a
portion of this line has enhanced heat transfer surfaces to promote
heat transfer between the refrigerant in said return line and air
in said air path.
9. The refrigerant system as set forth in claim 5, wherein a
three-way valve selectively directs refrigerant from said tap and
downstream of said economizer heat exchanger either into said path
of air, or to bypass said path of air when a reheat function is not
desired.
10. The refrigerant system as set forth in claim 5, wherein said
economizer heat exchanger itself is placed in the path of said
air.
11. The refrigerant system as set forth in claim 1, wherein said
two refrigerant flows are maintained separately within said
auxiliary heat exchanger.
12. The refrigerant system as set forth in claim 1, wherein said
auxiliary heat exchanger has said first refrigerant stream
surrounded by said second refrigerant stream, and such that said
second refrigerant stream is exposed to said air.
13. The refrigerant system as set forth in claim 1, wherein said
second refrigerant stream is surrounded by said first refrigerant
stream, and such that said first refrigerant stream is exposed to
said air.
14. The refrigerant system as set forth in claim 1, wherein both
said first and second refrigerant streams in said auxiliary heat
exchanger are exposed to said air.
15. A refrigerant system comprising: a compressor for compressing
refrigerant and delivering the refrigerant to a condenser; a main
expansion device positioned downstream of said condenser, and an
evaporator positioned downstream of said main expansion device, an
air moving device for passing air over said evaporator; and an
auxiliary heat exchanger, said auxiliary heat exchanger cooling a
refrigerant passing from said condenser toward said evaporator,
said refrigerant being cooled by a downstream refrigerant returning
to said compressor downstream of said evaporator, and a refrigerant
line of said downstream refrigerant passing to said compressor
being placed in a path of air driven by said air moving device
downstream of said evaporator to provide a reheat function.
16. The refrigerant system as set forth in claim 15, wherein a flow
control device selectively communicates said second flow of
refrigerant downstream of said auxiliary heat exchanger being
returned to said compressor, either through a reheat portion that
is in a path of said air to provide a reheat function, or can
bypass said second flow of refrigerant into a bypass line to be
returned directly to said compressor without providing the reheat
function.
17. The refrigerant system as set forth in claim 16, wherein a flow
control device is positioned in each of a line leading to said
reheat portion, and said bypass line.
18. The refrigerant system as set forth in claim 15, wherein said
auxiliary heat exchanger is placed in said path of air to provide
said reheat function.
19. A refrigerant system comprising: a compressor for compressing
refrigerant and delivering the refrigerant to a condenser; a main
expansion device positioned downstream of said condenser, and an
evaporator positioned downstream of said main expansion device, an
air moving device for passing air over said evaporator; and an
economizer heat exchanger, said economizer heat exchanger cooling a
first refrigerant stream passing from said condenser toward said
evaporator, said first refrigerant stream being subcooled in said
economizer heat exchanger by a tapped refrigerant which is returned
toward said compressor downstream of said economizer heat
exchanger, and a refrigerant return passing to said compressor
downstream of said economizer heat exchanger being placed in a path
of air driven by said air moving device downstream of said
evaporator to provide a reheat function.
20. The refrigerant system as set forth in claim 19, wherein said
tapped flow of refrigerant being returned to an intermediate
compression portion in said compressor.
21. The refrigerant system as set forth in claim 19, wherein at
least one flow control device selectively directs refrigerant from
said tap and downstream of said economizer heat exchanger either
into said path of air, or to bypass said path of air when a reheat
function is not desired.
22. The refrigerant system as set forth in claim 19, wherein said
economizer heat exchanger itself is placed in the path of said air
driven by said air moving device
23. The refrigerant system as set forth in claim 19, wherein said
refrigerant streams in said economizer exchanger is arranged in
counterflow configuration
24. The refrigerant system as set forth in claim 19, wherein said
refrigerant streams in said economizer exchanger is arranged in
parallel flow configuration
25. The refrigerant system as set forth in claim 19, wherein said
tapped flow of refrigerant is tapped upstream of the said
economizer heat exchanger.
26. The refrigerant system as set forth in claim 19, wherein the
said tapped flow of refrigerant is tapped downstream of the said
economizer heat exchanger.
27. A method of operating a refrigerant system comprising the steps
of: (1) providing a compressor for compressing refrigerant and
delivering to a condenser, a main expansion device downstream of
said condenser and an evaporator downstream of said main expansion
device, and an air moving device for passing air over the
evaporator; (2) providing an auxiliary heat exchanger with a first
refrigerant stream being subcooled in said auxiliary heat exchanger
by a second refrigerant stream that is returned to said compressor;
(3) placing a portion of said second refrigerant stream in a path
of air moved by said air moving device; and (4) operating said
refrigerant system, and passing said second refrigerant stream in
said path of said air, and passing air over said portion, prior to
said second refrigerant stream being returned to said compressor,
when reheat function is desired and bypassing said portion when
reheat function is not desired.
Description
BACKGROUND OF THE INVENTION
[0001] This application relates to the provision of a reheat
function in a refrigerant system wherein an auxiliary heat
exchanger is utilized to subcool refrigerant approaching an
evaporator.
[0002] Refrigerant systems are utilized to control the temperature
and humidity of air in various environments. In a typical
refrigerant system, a refrigerant is compressed in a compressor and
delivered to a condenser. In the condenser, heat is exchanged
between outside ambient air and the refrigerant. From the
condenser, the refrigerant passes to an expansion device, at which
the refrigerant is expanded to a lower pressure and temperature,
and then to an evaporator. In the evaporator heat is exchanged
between the refrigerant and the indoor air, to condition the indoor
air. When the refrigerant system is operating, the evaporator cools
the air that is being supplied to the indoor environment. In
addition, as the temperature of the indoor air is lowered, moisture
usually is also taken out of the air. In this manner, the humidity
level of the indoor air can also be controlled.
[0003] In some cases, the air, that is brought to provide a comfort
environment in a conditioned space, may need to be additionally
dehumidified to provide the desired humidity level. This has
presented design challenges to refrigerant cycle designers. One way
to address such challenges is to utilize various schematics
incorporating reheat coils. In many cases, the reheat coils, placed
on the way of indoor air stream are employed for the purpose of
reheating at least a portion of the air supplied to the conditioned
space after it has been overcooled in the evaporator, where the
moisture has been removed.
[0004] One of the options available to a refrigerant system
designer to increase efficiency and capacity of the refrigerant
system is to employ an auxiliary economizer circuit. In the
economizer circuit, a portion of the refrigerant flowing from the
condenser is tapped and passed through an economizer expansion
device and then to an economizer heat exchanger. This tapped
refrigerant subcools a main refrigerant flow that also passes
through the economizer heat exchanger. The tapped refrigerant
leaves the economizer heat exchanger, usually in a vapor state, and
is injected back into the compressor at an intermediate compression
point (or in case of two compressors connected in series, the
injection is taken place into the point between the low and high
pressure compressors). The main portion of refrigerant flow leaving
the condenser is additionally subcooled after passing through the
economizer heat exchanger. The main portion of the refrigerant flow
then passes through a main expansion device and then to an
evaporator. This main flow will have a higher cooling capacity
because it was additionally subcooled in the economizer heat
exchanger. An addition of economizer circuit thus provides enhanced
system performance. In an alternate arrangement, a portion of the
refrigerant is tapped and passed through the economizer expansion
device after being passed through the economizer heat exchanger
(along with the main flow). In all other aspects this arrangement
is identical to the configuration described above.
[0005] Another option to increase the system capacity and
efficiency is to utilize a liquid-suction heat exchanger. The
purpose of the liquid-suction heat exchanger is to boost system
performance by providing extra subcooling to liquid refrigerant
exiting the condenser coil through the heat transfer interaction
with the refrigerant vapor exiting the evaporator. Although during
this heat transfer interaction the refrigerant density and
subsequently mass flow rate at the compressor suction are
undesirably reduced, in general, the combined effect of the
liquid-suction heat exchanger addition allows for overall system
performance enhancement.
[0006] Recently, the assignee of this application has developed a
system that combines the reheat coil and economizer cycle. However,
variations of this basic concept have yet to be fully
developed.
SUMMARY OF THE INVENTION
[0007] In disclosed embodiments of this invention, an auxiliary
heat exchanger is provided and placed on the way of predominantly
liquid refrigerant flow downstream of the condenser and upstream of
the evaporator, and this main flow of refrigerant in the auxiliary
heat exchanger is further subcooled by another refrigerant stream.
In the case of the economizer heat exchanger, the latter, smaller
portion of the refrigerant is evaporated and returned into the
intermediate compression stage. In case of liquid-suction heat
exchanger, the refrigerant in the main suction line, that is
predominantly in a vapor state, before flowing into the compressor
suction port, subcools the refrigerant in the main liquid line, as
it leaves the condenser. In either case, the refrigerant
approaching the evaporator is subcooled such that a greater cooling
capacity is provided. With these arrangements, the refrigerant flow
returning to the compressor through the intermediate port, in the
case of the economizer heat exchanger, or through the suction port,
in case of the liquid-suction heat exchanger, is being preheated by
the opposite stream that is being subcooled. The present invention
utilizes this preheating effect to provide a reheat function.
[0008] More specifically in the embodiment dealing with the
liquid-suction heat exchanger, refrigerant downstream of the
evaporator is utilized to subcool the refrigerant approaching the
evaporator. In this case, a portion of the suction line leading to
the compressor inlet or liquid suction heat exchanger itself is
placed in the path of at least a portion of an airflow passing over
the evaporator. As described above, the reheat function is operable
to heat the air to a desired temperature, while providing the air
dehumidification in the evaporator. As the air is heated while
passing over the liquid-suction heat exchanger, it cools the
refrigerant in this liquid-suction heat exchanger, which is
desirable, as it improves the system capacity and efficiency.
[0009] In other embodiments, the subcooling function is provided by
an economizer circuit. As is known, an economizer circuit includes
a heat exchanger receiving a main flow of refrigerant and a
smaller, tapped flow of refrigerant. The tapped flow of refrigerant
subcools the main flow of refrigerant. The tapped flow of
refrigerant is returned to an intermediate point in the compression
cycle of the compressor. Since the smaller, or tapped flow, has
subcooled the main flow of refrigerant, this tapped refrigerant is
being evaporated or pre-heated, as it passes through the economizer
heat exchanger. Thus, if the economizer heat exchanger or its
return line to the compressor are placed in the heat transfer
relationship with the airflow passing over the evaporator, then the
refrigerant in this line is cooled by this airflow. This additional
cooling of refrigerant vapor, as it enters the intermediate
injection port, is desirable, as it improves system capacity and
efficiency. At the same time, the reheating of the airflow is
accomplished and dehumidification function is provided.
[0010] These and other features of the present invention can be
best understood from the following specification and drawings, the
following of which is a brief description.
BRIEF DESCRIPTION OF THE DRAWINGS
[0011] FIG. 1 shows a first schematic of a refrigerant system.
[0012] FIG. 2 shows a second schematic of a refrigerant system.
[0013] FIG. 3 shows a third schematic of a refrigerant system.
[0014] FIG. 4 shows a fourth schematic of a refrigerant system.
[0015] FIG. 5 shows an exemplary heat exchanger.
[0016] FIG. 6 shows a second embodiment heat exchanger.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
[0017] A refrigerant system 20 is illustrated in FIG. 1 having a
compressor 22 delivering a refrigerant to a condenser 24. An
auxiliary heat exchanger 26 (liquid-suction heat exchanger in this
case) is positioned downstream of the condenser 24, and upstream of
a main expansion device 28. The refrigerant passes through an
evaporator 30 downstream of the main expansion device 28, and an
air moving device 32 moves air over the evaporator 30, with the air
then being moved into an environment to be conditioned. As can be
seen in FIG. 1, downstream of the evaporator 30, the refrigerant
once again enters an auxiliary liquid-suction heat exchanger 26 at
point 34, and exits at point 36, subcooling the refrigerant passing
to the main expansion device 28. Thus, when the refrigerant reaches
the evaporator 30, it will have a greater cooling capacity than it
otherwise would possess. As can be appreciated, the refrigerant
passing from the condenser 24 to the main expansion device 28 is
generally in a liquid state, while the refrigerant passing from
point 34 to 36 is generally a vapor.
[0018] As shown in FIG. 5, the heat exchanger 80, receives the
liquid refrigerant passing to the main expansion device 28 through
a central tube 82 (or multiple tubes), and receives the vapor
refrigerant through an inlet port 84. The vapor refrigerant then
enters the space confined between a heat exchanger shell 86 and the
central tube 82. After heat transfer interaction with the liquid
refrigerant inside the tube, the heated vapor refrigerant exits
through an outlet port 88. Thus, the two flows of refrigerant are
maintained separated within the heat exchanger 80 and communicate
with each other through the heat transfer interaction only. It is
known to a person ordinarily skilled in the art that, the heat
exchanger can have enhanced heat transfer surfaces (such as fins,
ribs, etc) located on the outside or inside portion of the heat
exchanger shell 86 in order to improve the heat transfer between
the two refrigerant flows and surrounding air. The internal and
external surfaces of the tube 82 can also be similarly enhanced to
boost the heat transfer between the two refrigerant streams. In the
heat exchanger exhibited in FIG. 5, the refrigerant vapor, being on
the shell side, is in direct heat transfer interaction with
surrounding air. Another heat exchanger configuration, with the
refrigerant liquid being on the shell side, is also possible, and
selection of a particular design depends on the application
requirements and specifics. Thus, the connections can simply be
reversed such that the liquid refrigerant is on the shell side.
Finally, as shown in FIG. 6, in an embodiment 200, both the vapor
and the liquid are exposed to the outside environment or air, with
a vapor flow path 202, and a liquid flow path 204. Obviously, the
heat exchanger 200 can have various flow patterns and
configurations, including multiple channels on both liquid and
vapor sides. It should be noted that the heat exchanger designs
shown in FIGS. 5 and 6 are exemplary and many other concepts and
configuration variations are also permissible to obtain full
benefits of the invention teachings.
[0019] Downstream of the point 36, the refrigerant passes into a
suction line 41 leading back to a line 44 to direct the refrigerant
back to the compressor 22. An enhanced heat transfer surface 42 is
preferably placed on or built into the suction line 44. This heat
transfer surface and the portion of the suction line are placed in
the airflow having passed over the evaporator 30. A worker of
ordinary skill in the art would recognize how and when to control
flow control devices, such valves 40 and 48, to either bypass the
heat exchange portion 42, or pass the refrigerant through the heat
exchange portion 42 when a reheat function is desired. It should
also be noted that valves 40 and 48 and line 46 can be removed
altogether if the reheat option is to remain operational all the
time. The valves 48 and 42 can also be combined into a single
three-way valve. Also, the valves 40 and 48 could be fixed or
regulating flow control devices.
[0020] While the air reheating function is provided, the
temperature of the refrigerant in the heat exchange portion 42 will
be reduced as air temperature is expected to be colder than
refrigerant temperature in the heat exchange portion 42. This
reduction in the refrigerant temperature is desirable, as it will
improve capacity and efficiency of the refrigerant system by
increasing the density and consequently the mass flow rate of the
refrigerant entering the compressor 22.
[0021] FIG. 2 shows a refrigerant system 50 that is similar to the
FIG. 1 embodiment, however, the auxiliary liquid-suction heat
exchanger 126 is itself placed in the path of the airflow provided
by the air moving device 32. The temperature of the refrigerant
vapor is reduced by the airflow, which is beneficial to improving
the system performance, as it reduces the temperature of the
refrigerant entering the compressor, as well as provides additional
subcooling of the liquid refrigerant entering the expansion device
to boost system performance. Depending on the liquid-suction heat
exchanger configuration, either vapor refrigerant or liquid
refrigerant is placed on a shell side of the auxiliary heat
exchanger 26 into direct heat transfer interaction with the air
form air moving device 32.
[0022] FIG. 3 shows yet another embodiment 52 wherein a tap 55 taps
a refrigerant through an economizer expansion device 58. The tapped
refrigerant from the line 55 passes through an economizer heat
exchanger 54. A main portion of the flow (or all the flow, if the
tap is located downstream of the economizer heat exchanger 54, on
its main leg) also passes through the economizer heat exchanger 54
toward the main expansion device 28. As is known, the refrigerant
in the main flow is subcooled within the economizer heat exchanger
54. A three-way valve 56 downstream of the economizer heat
exchanger 54 on the tap line 55 selectively taps the refrigerant
into a line 59, if the reheat function is desired, or taps
refrigerant into the by-pass line 60, if no reheat function is
desired. If the three-way valve 56 activates the reheat function,
then a heat exchange portion 90 will be in the path of air having
passed over the evaporator 30 as it has been driven by the air
moving device 32. While the air reheating function is provided, the
temperature of the refrigerant in the heat exchange portion 90 will
be reduced, as air passing over the heat exchange portion 90 is
colder than refrigerant in the 90. This is desirable, as it will
improve capacity and efficiency of the refrigerant system by
increasing the density and lowering the temperature of the
refrigerant entering the compressor 22 through its intermediate
compression port. On the other hand, if the reheat function is not
desired, the three-way valve 56 is positioned to direct the
refrigerant through a bypass line 60, at which it will re-enter the
line 64 at a point 62. This refrigerant is thus returned to an
intermediate compression point in the compressor 22 without having
provided the reheat function. Again, an appropriate control manages
the three-way valve 56 to either provide the reheat function or
avoid it, depending upon sensible and latent capacity demands. It
should also be noted that the valve 56 and line 60 can be removed
altogether, if the reheat option to remain operational all the
time. Of course, the three-way valve 56 can be substituted by a
pair of the conventional valves as well as be of the metering
nature by either modulation or pulsation techniques.
[0023] FIG. 4 shows a refrigerant system 70, again having an
economizer heat exchanger 154. In this embodiment, the auxiliary
economizer heat exchanger itself is placed in the path of the
airflow from the air moving device 32, providing the desired
reheating function. At the same time, as the air temperature
passing over the auxiliary economizer heat exchanger is expected to
be colder than the temperature of the refrigerant passing through
the heat exchanger, the temperature of the refrigerant in the heat
exchanger is reduced. The refrigerant temperature reduction is
beneficial to the system performance (resulting in enhanced system
capacity and efficiency), as it increases refrigerant subcooling
entering the main expansion device as well as reducing the
temperature of the refrigerant vapor entering the compressor
intermediate compression port.
[0024] The refrigerant flow through the economizer heat exchanger
can be arranged in either counterflow or parallel flow
configuration (only parallel flow arrangement is illustrated in the
schematics). Also, with another variation, the tapped portion of
the refrigerant can be tapped either upstream of the economizer
heat exchanger (as shown in the schematics) or downstream of the
economizer heat exchanger. If it is tapped upstream, then only a
portion of the refrigerant exiting the condenser will pass through
the main leg of the economizer heat exchanger, with the remaining
portion of the refrigerant passing through the secondary leg
leading to the intermediate compression port. In case of the tap
located downstream of the economizer heat exchanger, the main leg
of the economizer heat exchanger will carry all the flow exiting
the condenser. In this case, the tapped portion of the refrigerant
will enter the economizer heat exchanger on the secondary leg
downstream of the economizer heat exchanger, subcooling the
refrigerant in the main leg.
[0025] Although preferred embodiments of this invention have been
disclosed, a worker of ordinary skill in this art would recognize
that certain modifications would come within the scope of this
invention. For that reason, the following claims should be studied
to determine the true scope and content of this invention.
* * * * *