U.S. patent application number 12/936449 was filed with the patent office on 2011-02-10 for start-up procedure for refrigerant systems having microchemical consensor and reheat cycle.
Invention is credited to Eric B. Fraser, Michael F. Taras.
Application Number | 20110030397 12/936449 |
Document ID | / |
Family ID | 41417041 |
Filed Date | 2011-02-10 |
United States Patent
Application |
20110030397 |
Kind Code |
A1 |
Taras; Michael F. ; et
al. |
February 10, 2011 |
START-UP PROCEDURE FOR REFRIGERANT SYSTEMS HAVING MICROCHEMICAL
CONSENSOR AND REHEAT CYCLE
Abstract
A refrigerant system has a condenser of microchannel design and
construction and includes a reheat cycle. The reheat cycle includes
a refrigerant flow control device, such as a three-way valve, for
selectively routing at least a portion of refrigerant through a
reheat heat exchanger from a location between a compressor and
expansion device. A control for the refrigerant system selectively
actuates this refrigerant flow control device to route at least a
portion of refrigerant through the reheat heat exchanger at system
start-up.
Inventors: |
Taras; Michael F.;
(Fayetteville, NY) ; Fraser; Eric B.; (Canastota,
NY) |
Correspondence
Address: |
CARLSON, GASKEY & OLDS, P.C.
400 WEST MAPLE ROAD, SUITE 350
BIRMINGHAM
MI
48009
US
|
Family ID: |
41417041 |
Appl. No.: |
12/936449 |
Filed: |
May 7, 2009 |
PCT Filed: |
May 7, 2009 |
PCT NO: |
PCT/US09/43070 |
371 Date: |
October 5, 2010 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
61061142 |
Jun 13, 2008 |
|
|
|
Current U.S.
Class: |
62/90 ;
62/513 |
Current CPC
Class: |
F28D 1/05391 20130101;
F25B 2600/2521 20130101; F25B 2400/075 20130101; F25B 2500/26
20130101; F24F 3/153 20130101; F28F 2260/02 20130101 |
Class at
Publication: |
62/90 ;
62/513 |
International
Class: |
F25B 41/00 20060101
F25B041/00 |
Claims
1. A refrigerant system comprising: a compressor for delivering a
compressed refrigerant to a condenser, refrigerant from said
condenser passing through an expansion device, and from said
expansion device through an evaporator, and from said evaporator
being returned to said compressor; and said condenser being a
microchannel heat exchanger; a reheat cycle including a refrigerant
flow control device for selectively routing at least a portion of
refrigerant through a reheat heat exchanger, said refrigerant flow
control device being positioned to route said at least portion of
refrigerant through said reheat heat exchanger from a location
between said compressor and said expansion device, and said reheat
heat exchanger being positioned in a path of air that has passed
over said evaporator; and a control for the system selectively
actuating said switch to route at least a portion of refrigerant
through said reheat heat exchanger at refrigerant system
start-up.
2. The refrigerant system as set forth in claim 1, wherein said
control is also routing said at least a portion of refrigerant
through said reheat heat exchanger when at least one of a start-up,
compressor speed change, tandem compressor activation or high
ambient temperature conditions occur.
3. The refrigerant system as set forth in claim 2, wherein said
conditions are programmed in the control to identify when to
selectively actuate said refrigerant flow control device to route
refrigerant through said reheat heat exchanger.
4. The refrigerant system as set forth in claim 1, wherein a bypass
is provided around said condenser to selectively bypass at least a
portion of refrigerant around said condenser.
5. The refrigerant system as set forth in claim 1, wherein said
refrigerant flow control device routes said at least portion of
refrigerant from a location between said compressor and said
expansion device, and downstream of said compressor.
6. The refrigerant system as set forth in claim 1, wherein said
refrigerant flow control device is actuated to selectively allow
for refrigerant flow through the reheat heat exchanger for at least
a predetermined period of time after said condition is
identified.
7. The refrigerant system as set forth in claim 6, wherein said
predetermined period of time is preferably from 15 seconds to 3
minutes.
8. The refrigerant system as set forth in claim 1, wherein said
refrigerant flow control device is one of adjustable type through
modulation or pulsation or of an on/off type.
9. The refrigerant system as set forth in claim 1, wherein said
microchannel heat exchanger includes a plurality of heat exchange
tube each having a plurality of parallel refrigerant channels.
10. The refrigerant system as set forth in claim 9, wherein said
microchannel heat exchanger having flow channels with a hydraulic
diameter less than or equal to 5 mm.
11. The refrigerant system as set forth in claim 1, wherein all of
the refrigerant passes through said reheat heat exchanger.
12. A method of operating a refrigerant system comprising the steps
of: a) delivering a compressed refrigerant to a condenser,
refrigerant from said condenser passing through an expansion
device, and from said expansion device through an evaporator, and
from said evaporator being returned to said compressor; b) said
condenser being a microchannel heat exchanger; c) selectively
routing at least a portion of refrigerant through a reheat heat
exchanger from a location between said compressor and said
expansion device, and passing at least a portion of air over said
reheat heat exchanger after the air has passed over said
evaporator; and d) selectively actuating a refrigerant flow control
device to route said at least portion of refrigerant through said
reheat heat exchanger at system start-up.
13. The method as set forth in claim 12, further comprising the
step of routing said at least a portion of refrigerant through said
reheat heat exchanger when at least one of a start-up, compressor
speed change, tandem compressor activation or high ambient
temperature occurs.
14. The method as set forth in claim 12, further comprising the
step of selectively allowing refrigerant flow through the reheat
heat exchanger for at least a predetermined period of time after
refrigerant system start-up.
15. The method as set forth in claim 12, wherein all of the
refrigerant passes through said reheat heat exchanger.
Description
RELATED APPLICATIONS
[0001] This application claims priority to U.S. Provisional Patent
Application No. 61/061,142, which was filed Jun. 13, 2008.
BACKGROUND OF THE INVENTION
[0002] Refrigerant systems utilize a refrigerant to condition a
secondary fluid, such as air, delivered to a climate-controlled
space. In a basic refrigerant system, the refrigerant is compressed
in a compressor, and flows downstream to a condenser in a
subcritical refrigerant cycle or to a gas cooler in a transcritical
refrigerant cycle, where heat is typically rejected from the
refrigerant to ambient environment, during heat transfer
interaction with this ambient environment. Then refrigerant flows
through an expansion device, where it is expanded to a lower
pressure and temperature, and to an evaporator, where during heat
transfer interaction with a secondary fluid (e.g., indoor air), the
refrigerant is evaporated and typically superheated, while cooling
and often dehumidifying this secondary fluid.
[0003] In recent years, much interest and design effort has been
focused on the efficient operation of the heat exchangers
(condenser and evaporator) of the refrigerant systems. One
relatively recent advancement in heat exchanger technology is the
development and application of parallel flow, or so-called
microchannel or minichannel, heat exchangers (these two terms will
be used interchangeably throughout the text), as the condensers and
evaporators.
[0004] These heat exchangers are provided with a plurality of
parallel heat exchange tubes, typically of a non-round shape, among
which refrigerant is distributed and flown in a parallel manner.
The heat exchange tubes are orientated generally substantially
perpendicular to a refrigerant flow direction in the inlet,
intermediate and outlet manifolds that are in flow communication
with the heat exchange tubes. The heat exchange tubes typically
have a multi-channel construction, with refrigerant distributed and
flowing within these multiple channels in a parallel manner. Heat
transfer fins are inter-disposed in between and rigidly attached to
heat exchange tubes. The primary reasons for the employment of the
parallel flow heat exchangers, which usually have aluminum
furnace-brazed construction, are related to their superior
performance, high degree of compactness, structural rigidity, lower
weight, lower refrigerant charge and enhanced resistance to
corrosion.
[0005] One concern with utilizing microchannel heat exchangers,
also related to their advantage, is their low internal volume. Due
to low internal volume, microchannel heat exchangers are more
susceptible to refrigerant pressure variations due to instantaneous
changes in refrigerant flow throughout the refrigerant circuit.
Microchannel heat exchangers are also very sensitive to refrigerant
charge amounts, with even a small amount of extra refrigerant
charge in the system leading to higher than desirable discharge
operating pressures and instantaneous pressure spikes. These
problems are especially pronounced during start-ups. Nuisance
interruptions of the refrigerant system operation can be a result
of emergency shutdown by control software on a high pressure alarm
or by mechanical safety, such as a high pressure switch, leading to
complete inability to operate the refrigerant system, if a
discharge pressure spike exceeded predetermined allowable safe
limit (typically for a preset number of times). This consequently
would results in a failure to keep a climate-controlled environment
within desirable temperature and humidity ranges, leading to
occupant discomfort and liability claims. Under certain
circumstances, repeated starts and shutdowns in short periods of
time can potentially lead to a compressor failure.
[0006] Another refrigerant cycle component is a reheat cycle
utilizing primary refrigerant circulating throughout the main
refrigerant circuit. In the reheat cycle, at least a portion of
refrigerant passes through a reheat heat exchanger which is
positioned in the path of air flowing across the evaporator. The
reheat heat exchanger is typically positioned in the path of the
air downstream of the evaporator. With a reheat cycle actuated, air
can be cooled in the evaporator below normally desirable
temperature, allowing for a greater amount of moisture removal from
the air stream. The air then passes over the reheat heat exchanger
and is heated back toward the target temperature. Typically, reheat
cycles are provided with a refrigerant flow control device, such a
three-way valve, that can selectively route at least a portion of
refrigerant through the reheat heat exchanger when reheat is
desired. The reheat cycle has not been operated at system start-up,
in order to prevent high pressure spikes and nuisance refrigerant
system shutdowns.
SUMMARY OF THE INVENTION
[0007] A refrigerant system has a compressor delivering a
compressed refrigerant to a condenser. Refrigerant from the
condenser passes through an expansion device and an evaporator.
From the evaporator it is returned to the compressor. The condenser
is a microchannel heat exchanger. A reheat cycle includes a
refrigerant flow control device for selectively routing at least a
portion of refrigerant through a reheat heat exchanger. The reheat
heat exchanger is positioned in a path of air that has passed over
the evaporator. A control for the refrigerant system selectively
actuates a switch to route refrigerant through a reheat heat
exchanger at system start-up.
[0008] In one embodiment, the reheat cycle may also be actuated at
certain environmental and operating conditions, when high pressure
spikes are expected to occur. Such conditions may include, for
instance, high ambient temperatures, higher operating speeds of
variable speed compressors and a higher number of active tandem
compressors. These environmental and operating conditions may be
pre-programmed and stored in the memory of the refrigerant system
controller.
[0009] 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
[0010] FIG. 1A shows a first embodiment schematic.
[0011] FIG. 1B shows an alternative embodiment.
[0012] FIG. 2A shows an exemplary microchannel heat exchanger.
[0013] FIG. 2B is a cross-section through a portion of FIG. 2A.
[0014] FIG. 3 is a graph showing start-up utilizing the disclosed
method.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
[0015] A refrigerant system 20 is illustrated in FIG. 1A and
includes a compressor 22 delivering refrigerant into a discharge
line heading to a condenser 24. The condenser 24 is a parallel flow
heat exchanger, and in one disclosed embodiment is a microchannel
or minichannel heat exchanger. As mentioned above, these terms are
used interchangeably here.
[0016] Heat is transferred in the condenser 24 from the refrigerant
to a secondary fluid, such as ambient air. The high pressure,
desuperheated, condensed and typically subcooled, refrigerant
passes from the condenser 24 into an expansion device 38, where it
is expanded to a lower pressure and temperature. Downstream of the
expansion device 38, refrigerant flows through an evaporator 36 and
back to the compressor 22. As known, the heat exchanger 24 operates
as a condenser in subcritical applications and as a gas cooler in
transcritical applications. Nevertheless, although both
applications are within the scope of the invention, the heat
exchanger 24 will be referred throughout the text as a
condenser.
[0017] A reheat cycle is incorporated into the refrigerant system
20. As known, a refrigerant flow control device such as a three-way
valve 30 selectively routes at least a portion of refrigerant
downstream of the condenser 24 and through a reheat heat exchanger
32. An air-moving device such as a fan 34 blows air over an
evaporator 36, and over the reheat heat exchanger 32. That is, the
reheat heat exchanger 32 is positioned indoors, along with the
evaporator 36, and downstream, with respect to the air flow, of the
evaporator 36. As mentioned above, essentially, the reheat cycle is
selectively actuated by opening (fully or partially) the three-way
valve 30 to direct at least a portion of refrigerant through the
reheat heat exchanger 32 when dehumidification in a
climate-controlled environment X is desired. Under such
circumstances, the refrigerant system is controlled such that the
evaporator 36 cools the air to a temperature below that is desired
in the environment to be conditioned X, which allows removing an
additional amount of moisture from the air to be delivered to the
conditioned environment X. As the air passes over the reheat heat
exchanger 32, it is reheated toward the target temperature. As a
result, temperature and humidity control are achieved in the
climate-controlled environment X.
[0018] Downstream of the reheat heat exchanger 32, there is an
optional check valve 40. Further, as shown, a condenser bypass line
26 selectively bypasses at least a portion of refrigerant around
the condenser 24 and includes a refrigerant flow control device
such as a valve 28. This allows for achieving variable
dehumidification capability, or variable sensible heat ratios. The
valve 28 can be adjustable (through modulation or pulsation) or of
an on/off type.
[0019] FIG. 1B shows an alternative embodiment wherein the reheat
cycle three-way valve 42 is positioned upstream of the condenser 24
and delivers at least a portion of refrigerant through a reheat
refrigerant line 44 to a reheat heat exchanger (not shown). For
purposes of this application, the exact location of the three-way
valve 42 and the reheat heat exchanger 32 is not critical, provided
they are both located on the high pressure side of the refrigerant
system 20. Also, as known, the three-way valves 30 and 42 can be
replaced by a pair of conventional valves performing identical
refrigerant routing function.
[0020] As shown in FIG. 2A, an inlet line 146 downstream of the
compressor 22 delivers refrigerant into a first bank of parallel
heat exchange tubes 148, and then across the condenser core to a
first chamber of an intermediate manifold structure 133. From the
intermediate manifold structure 133, the refrigerant passes back
through a second bank of parallel heat exchange tubes 150 to an
intermediate chamber in the manifold 147. Refrigerant then passes
through yet another bank of parallel heat exchange tubes 152,
returning to the intermediate manifold 133. From the intermediate
manifold 133, the refrigerant passes through another bank of heat
exchange tubes 154 back to the manifold 147, and an outlet
refrigerant line. Of course, this is simply one illustrated
embodiment. It should be noted that, in practice, there may be more
or less refrigerant passes than the four illustrated passes 148,
150, 152, and 154. Further, it should be understood that, although
for simplicity purposes, each refrigerant pass is represented by a
single heat exchange tube, typically there are many heat exchange
tubes within each pass amongst which refrigerant is distributed
while flowing within the pass. In condenser applications, a number
of the heat exchange tubes within each bank may decrease in a
downstream direction, with respect to refrigerant flow. For
instance, there could be 12 heat exchange tubes in the first bank,
8 heat exchange tubes in the second bank, 5 heat exchange tubes in
a third bank and only 2 heat exchange tubes in the last forth bank.
Separator plates 143 are placed within the manifolds 133 and 147 to
separate the chambers positioned within the same manifold
structure.
[0021] As shown in FIG. 2B, the heat exchange tubes within the tube
banks 148, 150, 152, and 154 may consist of a plurality of parallel
channels 100 separated by walls 101. The FIG. 2B is a
cross-sectional view of the heat exchange tubes shown in FIG. 2A.
The channels 100 allow for enhanced heat transfer characteristics
and assist in improved structural rigidity of the heat exchanger.
The cross-section of the channels 100 may take different forms, and
although illustrated as a rectangular in FIG. 2B, may be, for
instance, of triangular, trapezoidal, oval or circular
configurations. The size of the channels 100 in a microchannel heat
exchanger is quite small. As disclosed, the channels could have a
hydraulic diameter of less than or equal to 5 mm, and more
narrowly, less than or equal to 3 mm. Notably, the use of
"hydraulic diameter" does not imply the channels are circular.
[0022] As mentioned above, when microchannel heat exchangers are
utilized as condensers, pressure spikes which can be particularly
observed at the refrigerant system start-up, can provide a
challenge to a refrigerant system designer. One concern with
microchannel heat exchangers is that their internal volume is
relatively small, and thus they are particularly susceptible to
pressure spikes and extremely sensitive to refrigerant charge
amounts. Although pressure spikes are particularly pronounced at
refrigerant system start-up, they can be also observed at changes
of operating conditions such as, for instance, a sharp increase of
the compressor speed or activating a larger number of tandem
compressors, in order to satisfy thermal load demands in the
conditioned space X.
[0023] In this invention, the reheat circuit is actuated at
refrigerant system start-up. Now, when the refrigerant is passing
through both the condenser 24, and through the reheat heat
exchanger 32, there is a larger combined internal volume on a high
pressure side of the refrigerant system, and the amplitude of the
pressure spike is thus reduced. In some instances, all of the
refrigerant could pass through the reheat heat exchanger 32.
[0024] As shown in FIG. 3, with a conventional start-up S, and
without the reheat circuit being actuated, a pressure spike can be
relatively high, and may exceed the safety limit Y. With the
present application, and as shown at Z in FIG. 3, the amplitude of
the pressure spike is greatly reduced, due to the combined internal
volume of the heat exchangers 24 and 32. In this manner, the
pressure spike may well be below the safety limit Y, and nuisance
shutdowns, caused by control software operating on a high pressure
alarm or by mechanical safety, such as a high pressure switch, can
be avoided. This provides uninterrupted control of temperature and
humidity within the desired ranges and occupant comfort in the
climate-controlled environment. Furthermore, repeated starts and
shutdowns of the refrigerant system in short periods of time will
be avoided, leading to improved compressor reliability and
temperature/humidity variation reduction in the conditioned
space.
[0025] The reheat heat exchanger 32 can be any type of a heat
exchanger, including standard heat exchangers or a microchannel
heat exchanger.
[0026] A control 110 for the refrigerant system may be of any
appropriate electronic control type, as is known in the art. The
control would typically control all system components, and not only
the three-way valve 30 that can be adjustable (through modulation
or pulsation) or of an on/off type. The control 110 can actuate the
reheat cycle at certain environmental and operating conditions,
when high pressure spikes are likely to occur. Such conditions may
include, for instance, high ambient temperatures, higher operating
speeds of variable speed compressors and a higher number of active
tandem compressors. These environmental and operating conditions
may be pre-programmed and stored in the memory of the refrigerant
system control 110. Further, under some environment and operating
conditions, it may be that there is less likelihood of a pressure
spike at system start-up. Thus, the control may be programmed to
not actuate the reheat cycle in these instances.
[0027] In addition, after some period of time following refrigerant
system start-up, the three-way valve 30 is deactivated to block
flow of refrigerant through the reheat heat exchanger 32, unless
dehumidification mode of operation is desired. This period of time
can be on the order of 15 seconds to 3 minutes.
[0028] Although an embodiment of this invention has 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.
* * * * *