U.S. patent application number 12/902200 was filed with the patent office on 2011-05-05 for two-phase single circuit reheat cycle and method of operation.
Invention is credited to Michael L. Balistreri, Alexander Lifson, Michael F. Taras.
Application Number | 20110100035 12/902200 |
Document ID | / |
Family ID | 43923943 |
Filed Date | 2011-05-05 |
United States Patent
Application |
20110100035 |
Kind Code |
A1 |
Taras; Michael F. ; et
al. |
May 5, 2011 |
TWO-PHASE SINGLE CIRCUIT REHEAT CYCLE AND METHOD OF OPERATION
Abstract
A refrigerant system has a refrigerant circuit comprising a
compressor for compressing a refrigerant and delivering it
downstream to a condenser. A bypass line is provided around the
condenser for selectively allowing at least a portion of
refrigerant to bypass the condenser. Valves are provided on a line
leading to the condenser and on the bypass line to individually
control the flow of refrigerant. An expansion device is located
downstream of the condenser, and an evaporator is located
downstream of the expansion device. A reheat cycle is incorporated
into the system. The reheat cycle includes a valve for selectively
delivering at least a portion of refrigerant through a reheat heat
exchanger, which is positioned in the path of air downstream of the
evaporator. A control is provided for the system to achieve a
desired level of dehumidification and temperature control to air
being delivered into the environment to be conditioned.
Inventors: |
Taras; Michael F.;
(Fayetteville, NY) ; Lifson; Alexander; (Manlius,
NY) ; Balistreri; Michael L.; (Baldwinsville,
NY) |
Family ID: |
43923943 |
Appl. No.: |
12/902200 |
Filed: |
October 12, 2010 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
61257598 |
Nov 3, 2009 |
|
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|
Current U.S.
Class: |
62/90 ; 62/192;
62/196.1; 62/229; 62/278; 62/333; 62/498 |
Current CPC
Class: |
F25B 2600/2519 20130101;
F25B 2400/0403 20130101; F24F 3/153 20130101; F25B 2700/21173
20130101; F25B 31/002 20130101; F25B 2400/06 20130101 |
Class at
Publication: |
62/90 ; 62/498;
62/278; 62/229; 62/333; 62/192; 62/196.1 |
International
Class: |
F25D 17/06 20060101
F25D017/06; F25B 1/00 20060101 F25B001/00; F25B 47/00 20060101
F25B047/00; F25B 49/02 20060101 F25B049/02; F25D 17/00 20060101
F25D017/00; F25B 31/00 20060101 F25B031/00; F25B 41/00 20060101
F25B041/00 |
Claims
1. A refrigerant system comprising: at least one refrigerant
circuit comprising at least one compressor for compressing a
refrigerant and delivering it downstream to a heat rejection heat
exchanger; a bypass line provided around said heat rejection heat
exchanger for selectively allowing at least a portion of
refrigerant to bypass said heat rejection heat exchanger; a first
valve controlling flow to said heat rejection heat exchanger and a
second valve on said bypass line to individually control the flow
of refrigerant through said heat rejection heat exchanger and
around said heat rejection heat exchanger; an expansion device
positioned downstream of said heat rejection heat exchanger, and an
evaporator positioned downstream of said expansion device,
refrigerant from said evaporator passing back to said at least one
compressor; a reheat cycle incorporated into said refrigerant
system, including a third valve for selectively delivering at least
a portion of refrigerant through a reheat heat exchanger, said
reheat heat exchanger being positioned in the path of air
downstream of said evaporator; and a control for said system being
operable in a dehumidification mode to achieve a desired level of
dehumidification and temperature control to air being delivered
over said evaporator and said reheat heat exchanger and into an
environment to be conditioned, said control initially opening said
first valve on said bypass line to a relatively open position to
achieve additional reheat control, and said control then beginning
to close said second valve on said line leading to said heat
rejection heat exchanger to achieve additional reheat control.
2. The refrigerant system as set forth in claim 1, wherein said
reheat cycle incorporates an inlet positioned between said heat
rejection heat exchanger and said expansion device, and a return
line downstream of said inlet, but upstream of said expansion
device.
3. The refrigerant system as set forth in claim 1, wherein said
first valve on said bypass line is initially substantially fully
open, and said second valve leading to said heat rejection heat
exchanger then begins to be closed.
4. The refrigerant system as set forth in claim 1, wherein said
control changes a level of capacity provided by said compressor to
achieve evaporator discharge air temperature control, in
combination with changing the position of said first and second
valves to achieve a desired level of reheat control.
5. The refrigerant system as set forth in claim 1, wherein there
are at least a pair of refrigerant circuits within said refrigerant
system, with a first of said refrigerant circuits incorporating
said reheat heat exchanger, and said bypass around said heat
rejection heat exchanger, and a second of said refrigerant circuits
including airflow downstream of an evaporator passing over said
reheat heat exchanger in said first of said refrigerant
circuits.
6. The refrigerant system as set forth in claim 1, wherein said
control provides head pressure control when said position of said
at least one of first and second valves is such that head pressure
control is deemed desirable.
7. The refrigerant system as set forth in claim 1, wherein at
start-up, said control moves said second and third valves to at
least a partially open position.
8. The refrigerant system as set forth in claim 1, wherein said
control operates in oil return mode when at least one of said first
and second valves is in a position to indicate a need for oil
return.
9. The refrigerant system as set forth in claim 8, wherein said
control enters said oil return mode if said first valve is closed
below a minimum position, and said control opens said first valve
when in said oil return mode.
10. The refrigerant system as set forth in claim 1, wherein at a
transition to a cooling mode, said control cycling said third valve
on and then off periodically.
11. The refrigerant system as set forth in claim 1, wherein a check
valve is provided on said bypass line, and adjacent to a location
where said bypass line re-enters a main flow line.
12. The refrigerant system as set forth in claim 1, wherein said
second valve is positioned upstream of said heat rejection heat
exchanger.
13. A method of operating a refrigerant system including the steps
of: operating a refrigerant circuit and incorporating a reheat
cycle into said system; and providing a desired level of
dehumidification and temperature control to air being delivered
over an evaporator and a reheat heat exchanger in a
dehumidification mode by initially opening a first valve to bypass
refrigerant around a heat rejection heat exchanger, and allowing
the bypassed refrigerant to enter a reheat heat exchanger, and to
move said valve to a relatively open position to achieve additional
reheat control, and then beginning to close a second valve on a
line leading to the heat rejection heat exchanger to achieve
additional reheat control.
14. The method as set forth in claim 11, including the step of
changing a level of capacity provided by a compressor to achieve
evaporator discharge air temperature control, in combination with
changing the position of said valves to achieve a desired level of
reheat control.
15. The method as set forth in claim 11, wherein head pressure
control is provided when the bypass valve is passing the majority
of refrigerant around the heat rejection heat exchanger.
16. The method as set forth in claim 11, wherein said valve on said
bypass line is moved to at least a partially open position at
start-up.
17. The method as set forth in claim 11, wherein when at least one
of said first and second valves is in a position to indicate a need
for oil return, an oil return mode is provided.
18. The method as set forth in claim 17, wherein said oil return
mode includes opening said first valve.
19. The method as set forth in claim 17, further including the
steps of entering the oil return mode when the system is in a
cooling mode, but not a dehumidification mode, after a period of
time, and includes the steps of opening said first valve on said
bypass line.
20. The method as set forth in claim 11, wherein during a
transition to a cooling mode, cycling a reheat valve is cycled on
and then off periodically to allow and then block flow of
refrigerant to the reheat heat exchanger.
Description
RELATED APPLICATION
[0001] This application claims priority to U.S. Provisional
Application No. 61/257,598, which was filed Nov. 3, 2009.
BACKGROUND OF THE INVENTION
[0002] This application relates to refrigerant system controls for
providing a reheat function to accurately tailor environmental
conditions to desired conditions.
[0003] Refrigerant systems are known, and typically employ a
compressor which compresses a refrigerant and delivers it
downstream to a heat rejection heat exchanger. Heat is removed from
the refrigerant at the condenser, and the refrigerant then passes
through an expansion device. From the expansion device, the
refrigerant passes through an evaporator, where heat is typically
added to the refrigerant. From the evaporator, the refrigerant
returns to the compressor. For simplicity, the heat rejection heat
exchanger may be referred to as a condenser, although it is
understood that this term only applies to a sub-critical cycle,
while it is replaced by a gas cooler term for a trans-critical
cycle.
[0004] Many system features have been utilized in combination with
the basic structure mentioned above. One feature is a so-called
reheat cycle. In a reheat cycle, a heat exchanger is positioned in
the path of air downstream of the evaporator. The air is cooled in
the evaporator to a temperature below that desired for the
environment to be conditioned. In this manner, additional humidity
is removed from the air. The air then passes over the reheat heat
exchanger where it is heated back toward the target temperature for
the environment.
[0005] One feature that is provided in combination with the reheat
circuit is a bypass of refrigerant around the condenser. In this
manner, the thermodynamic state of the refrigerant being delivered
into the reheat heat exchanger can be controlled.
SUMMARY OF THE INVENTION
[0006] A refrigerant system has a refrigerant circuit comprising a
compressor for compressing a refrigerant and delivering it
downstream to a condenser. A bypass line is provided around the
condenser for selectively allowing at least a portion of
refrigerant to bypass the condenser. Valves are provided on a
refrigerant line leading to the condenser and on the bypass line to
individually control the flow of refrigerant through the two
branches. An expansion device is positioned downstream of the
condenser, and an evaporator is located downstream of the expansion
device. A reheat cycle is incorporated into the refrigerant system.
The reheat cycle includes a three-way valve for selectively
delivering refrigerant through a reheat heat exchanger, which is
positioned in the path of air downstream of the evaporator. A
control is provided for the system to achieve a desired level of
dehumidification and temperature control to air being delivered
into the environment to be conditioned at any ambient conditions as
well as internal latent and sensible thermal load demands. The
control is operable to initially open the valve on the bypass line,
and to move the valve to a relatively open position to achieve
additional dehumidification and reheat capacity control. The
control next closes the valve on the refrigerant line leading to
the condenser to achieve additional dehumidification and reheat
capacity control.
[0007] 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
[0008] FIG. 1A shows an exemplary refrigerant system.
[0009] FIG. 1B shows a P-h graph of the refrigerant system
operation.
[0010] FIG. 1C schematically shows a control feature of the
invention.
[0011] FIG. 2 shows a main system control flowchart.
[0012] FIG. 3 shows a sub-routine operating in parallel with the
FIG. 2 control.
[0013] FIG. 4 shows another sub-routine operating in parallel with
the FIG. 2 control.
[0014] FIG. 5A shows another sub-routine operating in parallel with
the FIG. 2 control.
[0015] FIG. 5B shows another sub-routine operating in parallel with
the FIG. 2 control.
[0016] FIG. 6A shows another sub-routine operating in parallel with
the FIG. 2 control.
[0017] FIG. 6B shows another sub-routine operating in parallel with
the FIG. 2 control.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
[0018] A refrigerant system 20 is illustrated in FIG. 1A
incorporating a pair of circuits 22 and 23. Of course, more than
two circuits can be integrated into the refrigerant system 20.
Circuit 22 is provided with a compressor 24, a condenser 26, an
expansion device 28 and an evaporator 30. Air flow 32 passing over
the evaporator 30 then passes downstream as shown on path 34, over
a reheat heat exchanger 40 of the circuit 23. Thus, the single
reheat heat exchanger 40 in the circuit 23 provides a reheat
function for both circuits 22 and 23. The refrigerant circuits 22
and 23 may provide similar cooing capacities or may have components
of different sizes.
[0019] Circuit 23 is provided with its own compressor 24, expansion
device 28, and evaporator 30. In addition, a condenser 38 in the
circuit 23 has a modulating valve 52 controlling the flow of
refrigerant through the condenser downstream of the compressor. A
bypass line 46 allows bypass of at least a portion of refrigerant
around the condenser 38. A modulating valve 48 controls the flow
through the bypass line 46, and to a check valve 50 before being
returned to a main flow line for the circuit 23. The condenser
modulating valve 52 may be positioned downstream of the condenser
38. The check valve 50 allows for minimal refrigerant charge
migration in and out of the bypass line, in case the bypass line
modulating valve 48 is position further upstream on the bypass
line.
[0020] A reheat circuit includes a three-way valve 42 which
selectively diverts at least a portion of refrigerant downstream of
the condenser 38, but upstream of the expansion device 28. This
refrigerant passes through the reheat heat exchanger 40, and back
through a return line and check valve 44 to the main refrigerant
circuit at a location upstream of the expansion device 28. The
three-way valve 42 can be replaced by a pair of conventional
two-way valves. The three-way valve 42 and a pair the two-way
valves can be of an on/off or adjustable type.
[0021] Temperature sensor T.sub.1 senses the air temperature
downstream of the evaporator, and a temperature sensor T.sub.2
senses the temperature of the air downstream of the reheat heat
exchanger 40.
[0022] A control 100 controls all of the components mentioned
above. The controls set forth below are disclosed in a system with
dual circuits 22/23. However, the control features extend to a
single circuit system or a multi-circuit system having more than
two refrigerant circuits and more than one refrigerant circuit
equipped with the reheat capability.
[0023] By selectively controlling the amount of refrigerant passing
through the valve 48 and the valve 52, a designer can achieve
control such that the two-phase refrigerant being delivered to the
reheat circuit is of a desired quality. Valves 48 and 52, for
example, can be step motor valves. Of course, similar control logic
can be utilized for a refrigerant system operating in a
trans-critical regime (vs. a sub-critical regime). In this case,
the temperature of single-phase refrigerant (rather than quality of
two-phase refrigerant) will be a controlled parameter, while the
condenser becomes a gas cooler.
[0024] As an example, if the percentage of bypass fluid compared to
the percentage of fluid having passed through the condenser is
increased, then the overall quality of the mixed refrigerant shifts
into a higher vapor quality region inside the two-phase dome, as
illustrated in FIG. 1B. This in turn enhances the reheat coil
capacity. On the other hand, decreasing the bypass flow causes the
opposite effect.
[0025] FIG. 1C schematically shows a feature of the present
invention, wherein an air flow discharge temperature is sensed
(T.sub.1) downstream of the evaporator, and a supply air
temperature is sensed (T.sub.2) downstream of the reheat coil 40. A
desired temperature is calculated for both locations, and the
sensed temperatures are fed back to the control.
[0026] When dehumidification is desired, the control 100 will
change a compressor cooling capacity upwardly or downwardly to
maintain the evaporator exit air temperature at a dehumidification
cooling set point. This set point is configured in software and
will be set to a temperature low enough to meet the latent capacity
needs in the conditioned space positioned downstream of the reheat
heat exchanger 40. Alternatively, the dehumidification cooling set
point could be dynamic and be reset automatically based on input
from a return air temperature sensor and a relative humidity
sensor. In this way, the dehumidification cooling set point could
be continuously reset, such as to the dew point temperature minus
an offset. Further, such controls can be used to control the amount
of moisture removed per a specified time interval, such as an hour
or a minute.
[0027] Once a dehumidification cooling set point is established,
the control 100 stages the compressor to meet the set point based
on an algorithm that is an adaptive PID style of control. The PID
is programmed within the control. The capacity control algorithm
uses a modified PID algorithm, with a self-adjusting gain which
compensates for varying conditions, including changing flow rates
across the evaporator coil. This control uses a "rise per percent
capacity" technique in the calculation. For each jump, up or down,
in capacity the control knows beforehand the exact capacity change
brought on. As the compressors stage up and down to meet the
dehumidification cooling set point, the refrigerant valves (46/52)
modulate refrigerant flow to meet the required supply air
temperature entering the conditioned space.
[0028] The valves operate to provide two distinct stages of reheat
capacity. In the first stage, the condenser bypass valve 48 begins
to open to increase supply air temperature. If the supply air
temperature is still too low (T.sub.2), once valve 48 reaches a
particular relatively high open percentage (in an example, 100%
open), then the valve 52 at the entrance to the condenser will
provide a second stage of reheat capacity. Valve 52 begins to
close, moving the mixing point even further into the high vapor
region. Both valves operate through their full range of motion to
meet the supply air temperature requirement. The valves will move
in series from Stage 1 (condenser bypass valve) to Stage 2
(condenser entrance valve) and back down again as the unit control
logic runs a PID loop to meet the required supply air temperature.
This avoids the valves "fighting" with each other when adjusting
refrigerant flows through different flow paths.
[0029] FIG. 2 shows these method steps in an ordered fashion. In
situations where there is only a need for latent capacity removal
(no sensible load), the valves 48/52 modulate refrigerant flow so
that the air can be reheated to either the return air temperature
minus a return air temperature offset (configurable) or to a
pre-set reheat set point. In situations where there is a need for
both sensible and latent capacity (cooling and dehumidification),
the valves 48/52 modulate refrigerant flow so that the air can be
reheated to the required supply air temperature for cooling (or
heating). This allows the unit to bring the evaporator down to a
lower temperature for enhanced dehumidification, while reheating
the air to the required supply air temperature. As the valves
modulate to meet the required supply air temperature, the latent
capacity of the unit remains nearly constant. This dynamics allows
the system to provide a variable sensible heat ratio (SHR) that can
be matched to the thermal load in the space to be conditioned.
[0030] Several additional logic sub-routines are developed to
ensure reliable system operation, given the valve operation on the
bypass line and the line leading to the condenser.
[0031] In a case where the discharge refrigerant downstream of the
compressor is all bypassed, the reheat heat exchanger effectively
becomes a condenser. In some applications and conditions, the
indoor air flow across the reheat heat exchanger can be reduced to
a level where the resulting discharge pressure increases beyond the
limits of a compressor operating envelope. In such situations, a
head pressure control is desirable as the outdoor fans will no
longer have any impact on the discharge pressure. An additional
head pressure control sub-routine is then activated. As shown in
FIG. 3, should the modulating valve position indicate the need for
alternative head pressure control, then a discharge pressure is
compared to a bypass upper limit. If the discharge pressure is
greater than the upper limit, then refrigerant flow is adjusted
through controlling valves 52 and 48 to reduce the discharge
pressure. This will continue until the valve 48/52 positions have
changed to indicate no need for alternative head pressure control,
or until the discharge pressure drops below the upper limit.
[0032] An additional start-up sub-routine is disclosed in FIG. 4.
The disclosed refrigerant system contains more refrigerant than a
normal cooling circuit is required. This additional refrigerant is
stored in the reheat coil during normal cooling mode of operation.
Charge migration during an off-cycle may result in excess
refrigerant in the main refrigerant circuit than required during
normal cooling mode of operation. This can create an overcharge
situation that can in turn lead to unit shutdown due to high
discharge pressure. To ensure that refrigerant is in the correct
part of the system at start-up, the sub-routine shown in FIG. 4 is
provided. Generally, the bypass valve 48 is open, and the reheat
three-way valve 42 is open. The compressor is then started. The
bypass valve 48 is closed once the bypass line is purged. Then, the
reheat valve is also closed after the time required to migrate the
refrigerant from the main refrigerant circuit into the reheat coil
is complete.
[0033] Reduction in the flow through the condenser during the
reheat mode of operation can result in flow rates being too low to
adequately carry oil through the condenser. Thus, a sub-routine as
shown in FIGS. 5A and 5B is disclosed. In the FIGS. 5A and 5B
sub-routine, several steps are disclosed for ensuring that the oil
return to the compressor is adequate. Further, the FIGS. 5A and 5B
sub-routine will also ensure adequate oil return from the reheat
coil, if the dehumidification portion of the refrigerant circuit
has not been in operation for a prolonged period of time.
Generally, as shown in the FIGS. 5A and 5B flowchart, in a cooling
mode, if the time elapsed since entering the cooling mode is
greater than a maximum time, then the system moves into charge/oil
return mode. The reheat valve 42 is opened, as is the bypass valve
48. This occurs through a control loop as shown in the FIGS. 5A and
5B, and for a preset period of time. In this way, not only adequate
oil return to the compressor is assured, and the refrigerant charge
is also properly re-balanced/re-distributed.
[0034] On the other hand (FIG. 5B), if the system is in a
dehumidification or reheat mode already, then the position of the
condenser valve 52 is compared to a minimum position for adequate
oil return. If the condenser valve position is less than the
minimum position, then the oil return flag is set. The condenser
valve 52 position is changed to a more open position required to
ensure adequate oil return. Again, the operation will then continue
for a predetermined period of time. Further details are shown in
the flowchart.
[0035] Finally, a sub-routine shown in FIGS. 6A and 6B is utilized
when a transition to cooling occurs. There may be discharge
pressure spikes, as the unit switches from a dehumidification mode
to a cooling mode. The circuit thus includes a control logic
routine in which the three-way valve 42 is repeatedly cycled to
push additional refrigerant into the reheat coil, thus reducing the
amount of refrigerant in the cooling circuit and effectively
managing pressure spikes. Thus, as shown in the FIGS. 6A and 6B
sub-routine, the three-way valve 42 is repeatedly cycled between
open and closed positions.
[0036] In general, the flowcharts shown in FIGS. 2-6 include
additional details that may enhance but not limit the methods as
claimed in this application. The claims should be studied to
determine the true scope of the coverage of this application
relative to these methods. However, the methods and sub-routines as
shown in the several flow charts are those which are most preferred
at this time.
[0037] It should be pointed out that many different compressor
types could be used in this invention. For example, scroll, screw,
rotary, or reciprocating compressors can be employed. Also, rather
than a single compressor, plural compressors including multi-stage
or plural compressors in series could be used.
[0038] The refrigerant systems that utilize this invention can be
used in many different applications, including, but not limited to,
air conditioning systems, heat pump systems, marine container
units, refrigeration truck-trailer units, and supermarket
refrigeration systems.
[0039] 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.
* * * * *