U.S. patent application number 11/728315 was filed with the patent office on 2007-10-11 for refrigerant based heat exchange system with compensating heat pipe technology.
Invention is credited to Eric Barger, Larry Defauw, V.J. Patel.
Application Number | 20070235161 11/728315 |
Document ID | / |
Family ID | 38573906 |
Filed Date | 2007-10-11 |
United States Patent
Application |
20070235161 |
Kind Code |
A1 |
Barger; Eric ; et
al. |
October 11, 2007 |
Refrigerant based heat exchange system with compensating heat pipe
technology
Abstract
The present invention comprises an improved refrigerant based
heat exchange system useful in air conditioning and refrigeration
applications. The refrigerant based heat exchange system detects
the presence of a passive heat pipe phenomenon in the refrigeration
circuit and responds by either temporarily shutting off the flow of
refrigerant in the circuit, or by temporarily removing the
evaporator coil of the air conditioning portion of the system from
the path of a forced air flow.
Inventors: |
Barger; Eric; (Plano,
TX) ; Patel; V.J.; (Dallas, TX) ; Defauw;
Larry; (Dallas, TX) |
Correspondence
Address: |
Charles D. Gunter, Jr.;Whitaker, Chalk, Swindle & Sawyer, LLP
Suite 3500
301 Commerce Street
Fort Worth
TX
76102-4186
US
|
Family ID: |
38573906 |
Appl. No.: |
11/728315 |
Filed: |
March 23, 2007 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
60786201 |
Mar 27, 2006 |
|
|
|
Current U.S.
Class: |
165/65 ;
165/61 |
Current CPC
Class: |
F25B 41/00 20130101;
F25B 2400/06 20130101; F25B 2500/27 20130101; F24F 1/0059 20130101;
F25B 2400/0409 20130101; F25B 39/02 20130101 |
Class at
Publication: |
165/065 ;
165/061 |
International
Class: |
F25B 29/00 20060101
F25B029/00 |
Claims
1. A refrigerant based heat exchange system, the system comprising:
a furnace heat exchanger; an evaporating heat exchanger connected
in a refrigeration circuit in which a compressor circulates
refrigerant between a condenser and an evaporator coil; wherein
both the furnace heat exchanger and the evaporator coil include
heat exchange surface areas and wherein air flow from a source of
forced air is used to provide a heat exchange effect over the heat
exchange surface areas; and means for temporarily removing at least
a selected one of the heat exchange surface areas in response to
the detection of a passive heat pipe phenomenon in the
refrigeration circuit.
2. The refrigerant based heat exchange system of claim 1, wherein
the means for temporarily removing at least a selected one of the
heat exchange surface areas is a mechanical actuator which
temporarily repositions the evaporator coil with respect to the
source of forced air.
3. The refrigerant based heat exchange system of claim 2, wherein a
pair of evaporator coils are connected by flexible tubing and
wherein the mechanical actuator pivots the coils between an open
and closed positions relative to the air flow from the source of
forced air.
4. The refrigerant based heat exchange system of claim 3, wherein
the mechanical actuator is a servo motor.
5. The refrigerant based heat exchange system of claim 1, wherein
an evaporator coil and a furnace heat exchanger are located within
a common housing and are separated by a partition, and wherein the
flow of forced air is controlled by means of a movable damper which
selectively directs a flow of air over either the furnace heat
exchanger or over the evaporator coil.
6. A refrigerant based heat exchange system, the system comprising:
a condensing heat exchanger; an evaporating heat exchanger
connected in a refrigerant circuit; a compressor for circulating
refrigerant between the condensing heat exchanger and the
evaporating heat exchanger in the refrigeration circuit; wherein
both the condensing heat exchanger and the evaporating heat
exchanger include heat exchange surface areas and wherein air flow
from a source of forced air is used to provide a heat exchange
effect over at least a selected one of the heat exchange surface
areas; and means for temporarily blocking the flow of refrigerant
in the refrigeration circuit in response to the detection of a
passive heat pipe phenomenon in the refrigeration circuit.
7. The refrigerant based heat exchange system of claim 5, wherein
the means for temporarily blocking the flow of refrigerant in the
refrigeration circuit comprises one or more valves in the
refrigeration circuit which are switched between an open position
when the compressor is on and a closed position when the compressor
is off and there are temperature differentials between portions of
the refrigeration circuit.
8. The refrigerant based heat exchange system of claim 6, wherein a
pair of solenoid valves are located on either side of the
refrigeration circuit between the condensing and evaporating heat
exchangers.
9. The refrigerant based heat exchange system of claim 6, wherein a
check valve is located on one side of the refrigeration circuit
between the condensing and evaporating heat exchangers and a
solenoid valve is located on an opposite side of the refrigeration
circuit.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] The present application claims priority from the earlier
filed provisional application Ser. No. 60/786,201, filed Mar. 27,
2006, by the same inventors.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The present invention relates generally to refrigerant based
heat exchange systems employing a compressor, a condenser, an
evaporator and associated fluid circuitry used for air
conditioning, food storage refrigeration, and similar applications,
and to improvements which result from the recognition of a heat
pipe phenomenon in such systems.
[0004] 2. Description of the Prior Art
[0005] In a typical commercially available mechanical air
conditioning or refrigeration unit, a condensable refrigerant is
circulated in a closed loop. Liquid refrigerant under high pressure
flows from, for example, a liquid receiver to a pressure reducing
valve and into an evaporator. In the evaporator, the pressure of
the refrigerant is greatly reduced. Liquid refrigerant boils and
absorbs heat from the evaporator. Now a vapor, the refrigerant
flows back to the compressor and is compressed to high pressure.
The temperature of the refrigerant is greatly increased and, in the
condenser, heat is transferred to the surrounding air and the
refrigerant cools, becoming liquid again. The refrigerant then
flows back into the liquid receiver and cooling cycle is repeated.
This typical cycle and variations thereof forms the basis for much
of the commercial HVAC industry which exists today and a large body
of patent art and technical literature exists with regard to such
systems. It should be noted, however, that liquid receivers are
optional, and their inclusion in an air conditioning or
refrigeration unit is subject to equipment design.
[0006] A fairly extensive body of knowledge also exists with
respect to what is referred to in the art as "Heat Pipe"
technology. A "Heat Pipe" is a refrigerant based heat exchanger
that is commonly used for passive heat transfer (i.e. there is no
compressor or pump). A heat pipe is typically two heat exchangers
piped together, charged with a refrigerant. The flow of refrigerant
occurs due to pressure differentials from a hot side to a colder
side. As the "hot side" absorbs heat, the heat flows through the
refrigerant tubing to the other side of the heat pipe where it is
exchanged to a heat exchange medium (typically air). This is the
result of a natural tendency of refrigerant to reach equilibrium in
an enclosed circuit.
[0007] One application of heat pipe technology is used in
conjunction with a conventional evaporator coil in an air
conditioning system to improve humidity control
performance--condensing more water from the humid air by means of
creating a stage in the air flow that is colder than would normally
be achieved by the evaporator coil in an air conditioning
system.
[0008] Another example of commercially available "Heat Pipe"
technology is a device used to remove heat from microprocessors,
such as those used in notebook computers. The heat pipe facilitates
the movement of heat from the processor to a fin coil near the edge
of the notebook package to be expunged to the environment. Heat
pipes of this general type can be purchased at electronics
retailers such as "Fry's Electronics."
[0009] Exemplary patents dealing with the heat pipe phenomenon
include U.S. Pat. No. 3,543,839, issued Dec. 1, 1970. This patent
shows a temperature controllable heat pipe with a switching device
between the evaporator and condenser sections of the device.
[0010] U.S. Pat. No. 4,974,667, issued Dec. 4, 1990, shows a
thermally actuated and switchable heat pipe system in which a
condenser is in contact with an automobile engine coolant and an
evaporator is in thermal contact with the exhaust of the
vehicle.
[0011] U.S. Pat. No. 4,494,595, issued Jan. 22, 1985, shows a
temperature controllable heat valve which illustrates many of the
basic principles of the heat pipe phenomenon. The patent discloses
a means for interrupting and modulating the return of liquid
condensate to the evaporator end of the heat pipe.
[0012] The above patent references are merely intended to be
illustrative of the general state of the art of heat pipes and heat
pipe systems. A number of references can also be found in the
technical literature. See, for example, P. S. Dunn and D. A. Reay,
"Heat Pipes", 2.sup.nd edition (Pergamon, N.Y., 1978).
[0013] The present invention does not deal with improvements in
heat pipe systems per se, but rather to the application of certain
basic heat pipe principles to traditional heating, ventilating, air
conditioning, and refrigeration (HVAC-R) type systems.
SUMMARY OF THE INVENTION
[0014] Applicants' have discovered that in HVAC and refrigeration
systems, there exists an undiscovered "heat pipe effect" when one
or more refrigerant circuits in the system are in an idle state,
i.e. the compressor(s) are off. This effect occurs, in one
instance, because nothing is restricting refrigerant flow and there
are temperature differentials between parts of the air conditioning
or refrigeration circuit.
[0015] In one broad aspect, the present invention comprises a
furnace heat exchanger and an evaporative heat exchanger in series,
as in a typical HVAC system. The evaporative heat exchanger is
connected in a refrigeration circuit in which a compressor
circulates refrigerant between a condenser and an evaporator coil.
Both the furnace heat exchanger and the evaporator coil include
heat exchange surface areas and wherein air flow from a source of
forced air is used to provide a heat exchange effect over the heat
exchange surface areas. Means are provided for temporarily removing
or shielding the heat exchange surface area of the evaporative heat
exchanger in response to the detection of a passive heat pipe
phenomenon in the air conditioning circuit.
[0016] The means for temporarily removing or shielding the heat
exchange surface area of the evaporative heat exchanger can be a
mechanical actuator which temporarily repositions the evaporator
coil with respect to a source of forced air. In one embodiment of
the invention, the system can include a pair of evaporator coils
which are connected by flexible tubing and wherein the mechanical
actuator pivots the coils between an open and closed position
relative to the forced air flow. In the closed position, the air
must go through the coils. In the open position, the air can
proceed unimpeded. In one form, the mechanical actuator can
comprise an electronically controlled servo motor.
[0017] In a second version, the system of the invention can also be
configured so that the evaporator coil and furnace heat exchanger
are located within a common duct or housing and are separated by a
partition. In this case, the flow of forced air is controlled by
means of a movable damper which selectively directs a flow of air
over either the heat exchanger or over the evaporator coil.
[0018] In a third version of the system of the invention, a means
is provided for temporarily blocking the flow of refrigerant in a
refrigeration circuit in response to the detection of a passive
heat pipe phenomenon in the refrigeration circuit. For example, the
means for temporarily blocking the flow of refrigerant in the
refrigeration circuit can comprise one or more valves in the
refrigeration circuit which are switched between an open position
or open state when the compressor is on and a closed position or
closed state when the compressor is off and there are temperature
differentials between portions of the refrigeration circuit.
[0019] Any of a number of convenient valving schemes can be
employed. For example, a pair of solenoid valves can be located on
either side of the refrigeration circuit between the condensing and
evaporating heat exchangers. Alternatively, a check valve is
located on one side of the refrigeration circuit between the
condensing and evaporating heat exchangers and a solenoid valve is
located on an opposite side of the refrigeration circuit.
[0020] In each of the above versions of the system of the
invention, mechanical elements are introduced into the refrigerant
based air conditioner or refrigeration circuit in order to
compensate for the "heat pipe effect" which has been found to exist
when the refrigerant circuit is in an idle state, refrigerant flow
is unrestricted, and temperature differentials exist between parts
of the refrigeration circuit.
[0021] Additional objects, features and advantages will be apparent
in the written description which follows.
BRIEF DESCRIPTION OF THE DRAWINGS
[0022] FIG. 1A is a schematic diagram of one version of the
improved HVAC heat exchange system of the invention in the cooling
mode showing the closed position of the evaporative coils.
[0023] FIG. 1B is a view similar to FIG. 1A, but showing the
evaporator coils in the open position.
[0024] FIG. 2A is a schematic representation of one version of a
refrigerant circuit employing the principles of the present
invention.
[0025] FIG. 2B is a schematic representation of an alternative
refrigerant circuit, similar to FIG. 2A.
[0026] FIG. 3A is a schematic representation of another version of
the heat exchange system of the invention, showing the system
operating in the cooing mode.
[0027] FIG. 3B is a schematic representation, similar to FIG. 3A,
but showing the system operating in the heating mode.
[0028] FIG. 4 is a schematic representation of another version of
the system of the invention, showing a system with multiple
refrigerant circuits.
DETAILED DESCRIPTION OF THE INVENTION
[0029] The improved refrigerant based heat exchange system of the
invention can be utilized to improve the efficiency of a
conventional refrigerant type air conditioning system where a
refrigerant such as Freon is circulated by compressor between an
evaporator section and a condenser section, wherein it is
respectively changed between liquid and gaseous states to effect
cooling in the evaporator unit.
[0030] As briefly discussed in the "Background" section of the
application, the conventional Freon type air conditioning circuit
includes a compressor, condenser, a metering device and an
evaporator connected in series in a refrigerant circuit. The air
conditioning circuit may also include an optional liquid receiver.
The system is charged with refrigerant, which circulates through
each of the components in order to remove heat from the evaporator
and transfer heat to the condenser. The compressor compresses the
refrigerant from a low pressure superheated vapor state to a high
pressure superheated vapor state, thereby increasing the
temperature and pressure of the refrigerant. The refrigerant medium
leaves the compressor and enters the condenser as a vapor at an
elevated pressure. The condenser condenses the refrigerant vapor at
a higher pressure to a saturated liquid state as a result of the
heat transfer in the condenser, typically accomplished with either
cooling water or to ambient air. The refrigerant then leaves the
condenser as a high pressure liquid. The pressure of the liquid is
decreased as it flows through a metering device, such as an
expansion type valve, causing the refrigerant to change to mixed
liquid-vapor state. The remaining liquid, now at low pressure, is
vaporized in the evaporator section of the system resulting in heat
transfer from the space being cooled. This vapor then enters the
compressor to complete the cycle.
[0031] The above described type vapor-compression refrigeration
cycle has, for many years, been the pattern for the majority of
commercially available air conditioning and refrigeration systems
in the marketplace. The present invention is directed to
improvements in such systems, particularly when the refrigerant
circuit is in an idle state during a normal part of the operating
cycle of the system.
[0032] Applicants' have discovered that, in HVAC and refrigeration
systems, there exists an undiscovered "heat pipe effect" when one
or more refrigerant circuits are in an idle state, i.e. the
refrigerant circuit's compressor(s) are off. This effect occurs
because there is nothing restricting refrigerant flow and there are
temperature differentials between parts of the refrigeration
circuit.
[0033] The "heat pipe effect" is exacerbated if the exchange
medium, such as air, is actively circulated with a part of the
refrigeration circuit. The degree of the "heat pipe effect" is
installation specific and usually significant. The utility of
reducing or eliminating the phenomenon of an idle refrigerant
circuit acting as a "heat pipe" is central to the present inventive
concept. By preventing or reducing the effects of this phenomenon,
efficiency gains can be achieved in both existing and future
heating and/or cooling systems. Examples #1-3 below are intended to
illustrate the heat pipe phenomenon in heating and cooling
systems.
EXAMPLE #1
Heating via a HVAC System
[0034] A typical HVAC system combines both a cooling circuit and a
heating system to provide a solution that satisfies the demand for
climate control in all expected climate conditions. This is usually
implemented by placing the heating system in series with the
evaporative coil portion of the air conditioning circuit. For
example, in FIGS. 1A and 1B, the furnace heat exchanger 11 is
located in series with the evaporator coil 13 of the air
conditioning circuit. This series arrangement allows the use of a
single air flow mechanism to facilitate air circulation for both
cooling and heating operation. As a result, air flow from a forced
air source 15 crosses both the heating element 11 and the
evaporator coil 13, regardless of system operating mode.
[0035] In such HVAC systems, while operating in heating mode, the
air conditioning circuit is in an idle state while the heated air
flow passes through the air conditioning circuit's evaporator coil
13. The refrigerant in the evaporator coil 13 absorbs some of the
heat energy from the supply air 15 and then passively moves it to
another part of the refrigerant circuit and dissipates it. As a
result, some of the heat energy introduced by the active heating
circuit is removed by the idle cooling circuit.
[0036] The idle refrigerant circuit operates as a passive "heat
pipe" between the evaporator coil 13 and the condensing unit,
comprising the compressor and the condenser, of the air
conditioning circuit. The refrigerant while in the evaporator coil
13 increases in temperature, and therefore pressure. This increase
in pressure differs from the rest of the refrigerant circuit
especially the cold outdoor condenser unit. Naturally, the pressure
in the system will attempt to equalize, moving the heat absorbed by
the evaporator coil outside. This phenomenon reduces the net
heating efficiency of the overall HVAC system.
EXAMPLE #2
Cooling via a Food Storage Refrigeration System
[0037] Most, if not all evaporator coil units in refrigeration
systems are implemented as a forced air heat exchanger designed to
facilitate the absorption of heat energy from the controlled
environment. The heat in such a situation is pumped and expunged to
an environment external to the controlled environment.
[0038] In this type of system, the "heat pipe effect" occurs once
the refrigeration circuit becomes idle. The condenser portion (17
in FIGS. 2A and 2B) of the circuit is relatively hot compared to
the evaporative portion (19 in FIGS. 2A and 2B) which is located in
the cool controlled environment. The temperature differential
creates a pressure differential which causes the refrigerant to
flow. The net effect is a passive "heat pipe" between the condenser
17 and the evaporator 19. This phenomenon introduces heat into the
controlled environment which results in an increased demand for
refrigeration time.
[0039] Also in this type of system, there is a need to keep air
circulating in the controlled environment even when the
refrigeration circuit is off. The additional circulation increases
the heat exchange between the controlled environment and the "heat
pipe" thereby increasing the net amount of heat introduced.
EXAMPLE #3
Systems with Multiple Refrigerant Circuits
[0040] Many roof-top packaged HVAC units above 5 ton air
conditioning capacity achieve the designed capacity by implementing
multiple refrigerant circuits in a single package. In doing so, the
evaporator coil comprises multiple refrigerant circuits, one per
compressor, in a single coil assembly. Such a system is typically
controlled as a two stage system, allowing one or both compressors
to run based on system demand.
[0041] FIG. 4 illustrates the heat pipe effect in such systems.
There is shown a typical 10 ton package unit operating in cooling
mode, implemented using two 5-ton compressors (51, 53) each having
separate refrigerant circuits (55, 57) wherein each heat exchange
coil 58 per circuit shares a common assembly 59 with the
corresponding heat exchange coil 58 in the other circuit. The
compressors 51, 53 and their corresponding refrigerant circuits 55,
57 shall be denoted as circuits "A" and "B," respectively.
[0042] When the control system calls for 10 ton operation, both
refrigerant circuits A and B are active and operate as expected to
facilitate heat exchange. However, when the control system calls
for 5 ton operation, one refrigerant circuit is active (i.e.,
compressor A is ON) while the other is in an idle state (i.e.,
compressor B is off).
[0043] In this mode, idle refrigerant circuit B acts as a heat
pipe, introducing heat from condenser B and compressor B and
introducing it into the indoor air stream 61 via evaporator B. The
result is that heat added to the circulated indoor air stream 61
via evaporator B will partially offset the cooling effect intended
by the heat absorption of evaporator A. Depending on the mechanical
assembly that houses evaporators A and B, this may also have an
adverse effect on removing humidity from the indoor air stream
61.
[0044] Additionally, the fact that condenser coils A and B share a
common physical assembly and therefore are simultaneously exposed
to the same air stream 61 intended to facilitate heat exchange from
an active refrigerant circuit exacerbates the heat pipe effect. In
similar fashion, the fact that evaporators A and B share a common
physical assembly results in a reduction of cooling capacity and
humidity control.
[0045] A recognition of the heat pipe phenomenon, as explained
above, has allowed Applicants' to implement several solutions to
the problem which act to increase the overall system efficiency.
Generally speaking, the solutions which have been implemented to
address the heat pipe phenomenon include combinations of the
following concepts:
[0046] 1. Move a selected heat exchanger out of the path of a
selected exchange medium. This design change will reduce the
efficiency of heat transfer from the exchange medium to the
refrigerant thus limiting the overall effect of the "heat
pipe."
[0047] 2. Stop the refrigerant from flowing. This will prevent a
"heat pipe" from being set up but the refrigerant will still absorb
some heat.
[0048] 3. Redirect the exchange medium around heat exchanger. This
will also reduce the efficiency of heat transfer from the exchange
medium to the refrigerant thus limiting the overall effect of the
"heat pipe."
[0049] FIGS. 1A-3B illustrate the above solutions in partly
schematic fashion as applied to the above discussed Example
#1--Heating via HVAC System.
Design 1:
[0050] The first design is a mechanical apparatus that physically
moves the evaporator coil to a configuration that significantly
reduces or prevents the flow of air through the evaporator coil
during heating mode. With reference to FIGS. 1A and 1B, the
evaporator coil 13 is actually provided as a pair of coils
connected by a flexible refrigerant hose 21. A means is provided
for temporarily removing the heat exchange surface area presented
by the evaporator coils from the path of the air flow in response
to detection of a passive heat pipe phenomenon in the refrigerant
circuit of the evaporator coil. In the example, this is
accomplished by mounting a servo motor 23 within the furnace
enclosure 25 which can be electronically actuated to pivot the
evaporator coil halves between and open and a closed position
(illustrated in FIGS. 1A and 1B, respectively).
Design 2:
[0051] This design utilizes valves to ensure that the refrigerant
is prohibited from flowing passively when the refrigeration circuit
(30 in FIGS. 2A and 2B) is not in the air conditioning mode. This
may be implemented using two solenoid valves (27 and 29 in FIG.
2A), or one solenoid valve (31 and a check valve 33 in FIG. 2B).
The solenoid valve in either case may be replaced by a pressure
relief valve that opens only when pressures are high enough to
indicate cooling mode (pressure introduced by the compressor in the
refrigeration circuit).
Design 3:
[0052] In this design, dampers are utilized to direct air flow
depending upon whether the system is operating in either the
cooling or the heating mode. With reference to FIGS. 3A and 3B, the
furnace heat exchanger 35 and the evaporator coil 37 of the air
conditioning circuit are located within a common enclosure or duct
wall 39 and are separated by an internal partition 41. A movable
damper 43 is electronically controlled and selectively positioned
to direct a flow of air over either the heat exchanger or over the
evaporator coil, depending upon whether the unit is in the cooling
mode or the heating mode.
[0053] It will be appreciated that any of the above three "Design"
concepts can be implemented with the Example 3 above in which the
system is comprised of multiple refrigerant circuits.
[0054] An invention has been provided with several advantages. The
recognition of the heat pipe phenomenon in conventional HVAC and
refrigeration systems allows simple mechanical solutions to be
implemented which increase the efficiency of these systems,
sometimes dramatically. The mechanical components added to the
systems are simple in design and economical to manufacture and, as
a result, do not add greatly to the manufacturing costs. The
resulting systems effectively compensate for the heat pipe
phenomenon which otherwise exists in such systems when any
refrigerant circuit in the system is in an idle state.
[0055] While the invention has been shown in only three of its
forms, it is not thus limited but is susceptible to various changes
and modifications without departing from the spirit thereof.
* * * * *