Note: Descriptions are shown in the official language in which they were submitted.
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CLOSED-LOOP DEHUMIDIFICATION CIRCUIT
FOR REFRIGERANT SYSTEM
BACKGROUND OF THE INVENTION
This invention relates to a refrigerant system wherein a closed-loop
dehumidification circuit is incorporated into a system schematic.
Refrigerant systems are utilized to control the temperature and humidity of
air
in various indoor environments to be conditioned. In a typical refrigerant
system
operating in the cooling mode, a refrigerant is compressed in a compressor and
delivered to a condenser (or an outdoor heat exchanger in this case). 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 (or
an
indoor heat exchanger in this case). 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.
In some cases, the temperature level, to which the air is brought to provide
comfort in a conditioned space, may need to be higher than the temperature
that
would provide the ideal humidity level. This has presented challenges to
refrigerant
system designers. One way to address such challenges is to utilize various
schematics
incorporating reheat coils. In many cases, the reheat coils, placed in the
indoor air
stream behind the evaporator, are employed for the purpose of reheating the
air
supplied to the conditioned space after it has been cooled in the evaporator,
and where
the moisture has been removed.
One challenge with integrating these reheat circuits into refrigerant systems
is
that the reheat circuits require connections to the main refrigerant loop
associated with
specific flow control devices. These flow control devices, such as three-way
valves,
check valves or other valve systems, may need additional control functionality
and
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frequently present reliability and refrigerant migration issues. For instance,
as known,
the refrigerant would migrate to a coldest spot within a refrigerant system.
The
coldest spot will change depending on the mode of operation. In the
conventional
cooling mode, the refrigerant would naturally migrate to the non-functioning
reheat
coil and, in a reheat mode, the opposite phenomenon would typically take
place. This
refrigerant re-distribution within the refrigerant system affects amount of
the
refrigerant flowing through the main refrigerant loop that in turn may cause
serious
system malfunctioning and reliability issues. Moreover, since a reheat loop is
closely
coupled to a main refrigerant circuit the system control for both the reheat
function
and conventional cooling becomes more complicated than would be desirable. In
other words, this complexity arises from the fact that the refrigerant is
essentially
shared between the main refrigerant loop and the reheat circuit. Another issue
related
to the reheat concepts employing main circuit refrigerant is associated with
the fact
that refrigerant system operational flexibility is compromised. Consequently,
it
becomes extremely difficult to satisfy a wide range of operational and
environmental
conditions and potential applications.
Separate closed-loop refrigerant circuits have been utilized for various
purposes in the past, however, they have not been utilized in combination with
a
refrigerant system and to provide dehumidification. Thus, there is a need in a
reliable
refrigerant system with a decoupled refrigerant circuit to satisfy market
requirements
and to provide operational flexibility.
SUMMARY OF THE INVENTION
In the present invention, a closed-loop reheat circuit is utilized in
conjunction
with a main refrigerant system. The closed-loop reheat circuit includes a pair
of heat
exchangers, with a reheat heat exchanger providing an effective reheat
function by
being placed in the path of at least a portion of the airflow having passed
over the
evaporator. As is known, this reheat heat exchanger will tend to reheat the
air, such
that the air can be cooled below its desired comfort temperature in the
evaporator to
remove an adequate amount of moisture and thus to provide a comfortable
humidity
level. The air then passes over the reheat heat exchanger, at which its
temperature is
increased to achieve a desired temperature set by an occupant of an
environment to be
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conditioned. As known, in the reheat heat exchanger, heat is transferred from
refrigerant to air to reheat the air.
The other heat exchanger is an auxiliary heat exchanger where, due to heat
transfer interaction, the refrigerant in the closed-loop reheat circuit cools
the
refrigerant in the main refrigerant circuit. In other words, in the auxiliary
heat
exchanger heat is transferred from the main circuit refrigerant to the
refrigerant
circulating through the reheat loop. Therefore, the refrigerant in the closed-
loop reheat
circuit is heated, while the refrigerant in the main refrigerant circuit will
have an
increased cooling potential when it reaches the evaporator. The refrigerant in
the
closed-loop reheat circuit leaves the auxiliary heat exchanger and returns to
the reheat
heat exchanger.
In one disclosed embodiment, a liquid pump is included to drive the
refrigerant through the closed-loop reheat circuit. Further, the liquid pump
may be
provided with a variable speed drive or an external flow control device such
as an
adjustable valve can be used to achieve variable refrigerant flow and
consequently
variable capacity in the reheat heat exchanger.
In another embodiment, the invention may be utilized with the option of
bypassing at least a portion of refrigerant around the condenser to achieve a
variable
cooling potential in the evaporator. This control feature may be employed
separately
or in conjunction with a variable speed liquid pump or/and with adjustable
reheat
circuit valve.
In still another embodiment, a refrigerant different from the refrigerant
circulating through the main circuit is used in the closed-loop reheat
circuit. Further,
the refrigerant composition in the reheat circuit can be formulated to sustain
a liquid
phase throughout the circuit or to change phases from vapor to liquid in the
reheat
heat exchanger and back from liquid to vapor in the auxiliary heat exchanger.
In yet another embodiment, a natural convection or thermosiphon is employed
for refrigerant circulating through the reheat circuit in place of a forced
fluid flow by
the liquid pump. Obviously, in this embodiment refrigerant phase change would
be
required.
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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
Figure 1A shows a first schematic of the present invention.
Figure 1B shows an alternate schematic of the Figure lA schematic.
Figure 2A shows a second schematic of the present invention.
Figure 2B shows an alternate schematic of the Figure 2A schematic.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
Figure 1A shows a refrigerant system 20 incorporating a compressor 22,
compressing refrigerant and delivering it through a condenser 24. A fan 26
moves air
over the condenser 24. Refrigerant flow through a bypass line 28 is controlled
by a
flow control device such as a valve 30. Another optional valve 25 may be
positioned
upstream of the condenser 24 (but downstream of the diversion point of the
bypass
line 28) to assist in refrigerant routing through the condenser 24 and bypass
line 28. A
control 21 can control the valves 30 and 25 to selectively bypass at least a
portion of
the refrigerant around the condenser 24. Such a bypass will typically be
utilized when
full cooling capacity of the refrigerant system 20 in the reheat mode of
operation is
not required. The two refrigerant flows mentioned above are combined
downstream
of the condenser 24. Of course, the control 21 controls other components of
the
refrigerant system 20 such as the compressor 22 and fans 26 and 48.
An auxiliary heat exchanger 32 is positioned on a liquid refrigerant line
downstream of the condenser 24. An expansion device 34 is positioned
downstream
of the auxiliary heat exchanger 32, and an evaporator 36 is located downstream
of the
expansion device 34. The refrigerant in the main circuit of the refrigerant
system 20
flows through the auxiliary heat exchanger 32, through the expansion device 34
to the
evaporator 36 and then is returned to the compressor 22.
A closed-loop reheat circuit 38 is also incorporated into the refrigerant
system
20. The refrigerant in the closed-loop reheat circuit flows through a reheat
heat
exchanger 42. As shown, a fan 48 blows air over the evaporator 36, and then
over the
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reheat heat exchanger 42. As is known, a reheat function allows the evaporator
to be
controlled to cool the air to a lower temperature than would be desired by an
environment into which the air is being delivered. This permits the removal of
an
adequate amount of moisture (significantly more than might otherwise be
available
given the desired temperature) and thus to provide a comfortable humidity
level in an
environment to be conditioned. Once the air has passed over the evaporator 36,
it
next encounters the reheat heat exchanger 42. The refrigerant in the reheat
heat
exchanger 42 reheats this air, such that when the air approaches the
environment to be
conditioned, it will be at the desired temperature. During this heat transfer
interaction
in the reheat heat exchanger 42, the heat is transferred from the refrigerant
in the
reheat loop to the conditioned air.
A liquid pump 44 circulates the refrigerant through the closed-loop reheat
circuit 38 from the reheat heat exchanger 42, through an optional flow control
device
such as valve 43, through the auxiliary heat exchanger 32 and then returns it
back to
the reheat heat exchanger 42. In the reheat heat exchanger 42 the heat is
transferred
from the refrigerant in the reheat circuit to the conditioned air and in the
auxiliary heat
exchanger 32 the heat is transferred from the refrigerant in the main circuit
to the
refrigerant in the reheat circuit (in this case, to cool the refrigerant in
the main circuit).
It has to be pointed out that the preferred flow configuration in the
auxiliary heat
exchanger 32 is a counterflow arrangement.
Since the reheat circuit 38 is physically decoupled from the main circuit (the
communication between the circuits is conducted through direct and indirect
heat
transfer interactions in the heat exchangers 32 and 42 respectively), the
refrigerant
flow in the reheat circuit can be controlled independently by the system
control 21
through the adjustable valve 43 or by a variable speed drive 46 for the liquid
pump
44. Therefore, the reheat capacity can be controlled. A variable flow of the
reheat
circuit refrigerant circulating through the heat exchangers 32 and 42 can be
utilized in
conjunction with the control 21 controlling the bypass valve 30 and valve 25
to
achieve a desired temperature of the air leaving the reheat heat exchanger 42
and
supplied to the conditioned space. The valves 30 and 25 will control the
amount of
sub-cooling of the refrigerant entering the auxiliary heat exchanger 32 and
consequently, to a great extent, its cooling potential in the downstream
evaporator.
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For instance, if humidity control with lower cooling is desired, then, as is
known, the
amount of refrigerant bypassing the condenser 24 is increased. The reheat
circuit
subsystem consisting of the liquid pump 44 and upstream valve 43 could be also
placed upstream of the reheat heat exchanger 42 (downstream of the auxiliary
heat
exchanger 32). In this case, the refrigerant flowing through the entire reheat
circuit 38
has to be in a liquid phase. This position is illustrated in phantom at X.
Further, in the schematic shown in Figure 1A, the refrigerant in the reheat
circuit can undergo phase transformation and change from liquid to vapor in
the
auxiliary heat exchanger 32 and from vapor to liquid in the reheat heat
exchanger 42.
In this case, (as explained below) an additional expansion device may be
required,
and the cavitation conditions at the entrance to the liquid pump 44 should be
prevented to ensure reliable operation.
Moreover, since the reheat circuit is physically decoupled from the main
circuit, the refrigerant in the reheat circuit may be different in nature,
have different
constituents and/or composition and may have substantially different operating
parameters (such as pressure, controlled by the refrigerant charge).
Another schematic 120 shown in Figure 1B has the auxiliary heat exchanger
132 positioned upstream of the condenser 24 in the main refrigerant circuit.
In this
case, heat transfer interaction in the auxiliary heat exchanger 132 is between
the
refrigerant in the reheat circuit 138 and a discharge line refrigerant vapor
(in
comparison to a liquid line refrigerant in Figure 1A). As mentioned before, a
reheat
circuit expansion device 47 may be required if the reheat circuit refrigerant
changes
phases (between liquid and vapor), and a liquid refrigerant state is to be
maintained at
the entrance of the liquid pump 44 to prevent cavitation. In all other aspects
this
embodiment is identical to the Figure 1A embodiment.
Another embodiment 50 is shown in Figure 2A, wherein the forced flow of
refrigerant in the reheat circuit 38 provided by the liquid pump 44 of Figures
1A and
1B is substituted by the natural convection phenomenon or so-called
thermosiphon
action. Therefore, in this case, a liquid pump 44 is not anymore required,
but, for this
concept to function properly, the refrigerant in the reheat circuit should
change phases
between liquid and vapor. In this embodiment, a closed-loop reheat circuit 52
incorporates a shutoff valve 54, the auxiliary heat exchanger 32, and a reheat
heat
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exchanger 58. As before, the reheat heat exchanger 58 is placed in the path of
at least
a portion of airflow blown by a fan 56 over the evaporator 36. The refrigerant
within
the reheat circuit 52 circulates due to the force of gravity. The refrigerant
condenses
in the reheat heat exchanger 58 and naturally flows down due to the force of
gravity.
This refrigerant then gets drawn to the auxiliary heat exchanger 32 where it
evaporates and raises due to the density difference. Then the refrigerant,
once again,
enters the reheat heat exchanger 58 and the cycle repeats itself. In this
manner,
natural circulation is accomplished throughout the reheat circuit 52.
Another embodiment 150 is shown in Figure 2B. This embodiment is
analogous to the embodiment 50, with the exception that the reheat heat
exchanger
158 utilizes refrigerant vapor in the discharge line of the main circuit as a
source of
heat for the refrigerant in the reheat circuit 152.
The present invention provides the reheat function as a separate closed-loop
circuit decoupled form the main refrigerant circuit. A control of such a
system is less
complex and more flexible than the control for a refrigerant system that
selectively
taps refrigerant from the main refrigerant circuit to,provide the reheat
function. The
control and operation of the known systems is less relbable and frequently
needs
additional components due to changing environmental conditions and refrigerant
migration issues. By utilizing the separate closed-loop reheat circuit, these
concerns
are eliminated, and the system is better suited for a variety of environments
and
potential applications.
A worker of ordinary skill in the 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.
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