U.S. patent application number 14/655958 was filed with the patent office on 2015-12-10 for method of reducing liquid flooding in a transport refrigeration unit.
This patent application is currently assigned to THERMO KING CORPORATION. The applicant listed for this patent is THERMO KING CORPORATION. Invention is credited to Ryan J. DOTZENROD, YoungChan MA, Titilope Zaburat SULE.
Application Number | 20150354879 14/655958 |
Document ID | / |
Family ID | 51022076 |
Filed Date | 2015-12-10 |
United States Patent
Application |
20150354879 |
Kind Code |
A1 |
DOTZENROD; Ryan J. ; et
al. |
December 10, 2015 |
METHOD OF REDUCING LIQUID FLOODING IN A TRANSPORT REFRIGERATION
UNIT
Abstract
A method to reduce/prevent liquid refrigerant flooding in the
compressor is disclosed herein. The method may include closing down
the ETV when there is a risk of compressor flooding. The method may
include closing down the ETV to a desired value when there is a
risk of the compressor flooding. A failure to provide the
superheated refrigerant vapor in a desired superheat temperature by
the compressor may indicate a risk of the compressor being flooded
by liquid refrigerant. The method may include measuring a
refrigerant discharge temperature of the compressor, and closing
down the ETV when a difference between the refrigerant discharge
temperature of the compressor and a refrigerant saturate
temperature is below a desired temperature threshold.
Inventors: |
DOTZENROD; Ryan J.;
(Lakeville, MN) ; MA; YoungChan; (Bloomington,
MN) ; SULE; Titilope Zaburat; (Columbia Heights,
MN) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
THERMO KING CORPORATION |
Minneapolis |
MN |
US |
|
|
Assignee: |
THERMO KING CORPORATION
Minneapolis
MN
|
Family ID: |
51022076 |
Appl. No.: |
14/655958 |
Filed: |
December 27, 2013 |
PCT Filed: |
December 27, 2013 |
PCT NO: |
PCT/US2013/077960 |
371 Date: |
June 26, 2015 |
Related U.S. Patent Documents
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
|
|
61746333 |
Dec 27, 2012 |
|
|
|
Current U.S.
Class: |
62/115 |
Current CPC
Class: |
F25B 41/043 20130101;
F25B 49/02 20130101; F25B 47/022 20130101; F25B 2400/13 20130101;
F25B 2500/04 20130101; B60H 1/3225 20130101; B60H 2001/3257
20130101; F25B 2700/21152 20130101; F25B 49/022 20130101; F25B
2400/19 20130101; F25B 2600/2513 20130101; B60H 1/3214 20130101;
B60H 1/3232 20130101; B60H 1/00364 20130101; F25B 2600/2515
20130101 |
International
Class: |
F25B 49/02 20060101
F25B049/02 |
Claims
1. A method to control an electronic throttle valve (ETV) of a
transport refrigeration unit comprising: determining whether there
is a risk of a compressor of the transport refrigeration unit being
flooded by liquid refrigerant; closing down the ETV when there is a
risk of the compressor being flooded by liquid refrigerant; and
opening up the ETV where there is no risk of the compressor being
flooded by liquid refrigerant, wherein the ETV is configured to
regulate a refrigerant flow into the compressor of the transport
refrigeration unit, and wherein determining whether there is a risk
of a compressor of the transport refrigeration unit being flooded
by liquid refrigerant includes: measuring a refrigerant discharge
temperature from the compressor; comparing the refrigerant
discharge temperature to a saturated discharge temperature of the
refrigerant; when a difference between the refrigerant discharge
temperature and the saturated discharge temperature of the
refrigerant is below or equal to a threshold value, determining
that there is a risk of compressor being flooded; and when the
difference between the refrigerant discharge temperature and the
saturated discharge temperature of the refrigerant is higher than
the threshold value, determining that there is no risk of
compressor being flooded.
2. (canceled)
3. The method of claim 1, wherein the saturated discharge
temperature of the refrigerant is derived from a refrigerant
discharge pressure of the compressor.
4. The method of claim 1, wherein the threshold value is between 10
to 15.degree. R superheat.
5. A method to control an electronic throttle valve (ETV) of a
transport refrigeration unit comprising: determining whether there
is a risk of a compressor of the transport refrigeration unit being
flooded by liquid refrigerant; closing down the ETV when there is a
risk of the compressor being flooded by liquid refrigerant; and
opening up the ETV where there is no risk of the compressor being
flooded by liquid refrigerant, wherein the ETV is configured to
regulate a refrigerant flow into the compressor of the transport
refrigeration unit, and wherein determining whether there is a risk
of a compressor of the transport refrigeration unit being flooded
by liquid refrigerant includes: measuring a refrigerant discharge
temperature from the compressor; when the temperature of the
refrigerant discharge temperature is below or equal to a
temperature threshold value, determining that there is a risk of
compressor being flooded; and when the temperature of the
refrigerant discharge temperature is higher than the temperature
threshold value, determining that there is no risk of compressor
being flooded.
6. The method of claim 5, wherein the temperature threshold value
is between 10 to 15.degree. R superheat.
7. A method to control an electronic throttle valve (ETV) of a
transport refrigeration unit comprising: determining whether there
is a risk of a compressor of the transport refrigeration unit being
flooded by liquid refrigerant; closing down the ETV when there is a
risk of the compressor being flooded by liquid refrigerant; opening
up the ETV where there is no risk of the compressor being flooded
by liquid refrigerant; measuring a refrigerant discharge
temperature from the compressor; comparing the refrigerant
discharge temperature to a saturated discharge temperature of the
refrigerant; and controlling the electronic throttle so that a
difference between the refrigerant discharge temperature from the
compressor and the saturated discharge temperature of the
refrigerant is at least at a desired threshold value wherein the
ETV is configured to regulate a refrigerant flow into the
compressor of the transport refrigeration unit.
8. The method of claim 7, wherein controlling the electronic
throttle so that a difference between the refrigerant discharge
temperature from the compressor and the saturated discharge
temperature of the refrigerant is at least at a desired threshold
value includes: when the difference between the refrigerant
discharge temperature and the saturated discharge temperature of
the refrigerant is lower than the desired threshold value, closing
down the ETV; and when the difference between the refrigerant
discharge temperature and the saturated discharge temperature of
the refrigerant is higher than the desired threshold value, opening
up the ETV.
9. The method of claim 1, wherein the ETV is controlled in a
step-wise manner.
10. The method of claim 1, wherein determining whether there is a
risk of a compressor of the transport refrigeration unit being
flooded by liquid refrigerant includes: when the transport
refrigeration unit is in at least one of a heating/defrosting mode
and a transition between a cooling mode and the heating/defrosting
mode, determining there is a risk of the compressor of the
transport refrigeration unit being flooded.
11-12. (canceled)
13. A method of controlling a transport refrigeration unit,
comprising: determining whether there is a risk of the compressor
being flooded; and limiting a refrigerant flow into a compressor of
the transport refrigeration unit when there is a risk of the
compressor being flooded, wherein determining whether there is a
risk of a compressor of the transport refrigeration unit being
flooded by liquid refrigerant includes: measuring a refrigerant
discharge temperature from the compressor; comparing the
refrigerant discharge temperature to a saturated discharge
temperature of the refrigerant; when a difference between the
refrigerant discharge temperature and the saturated discharge
temperature of the refrigerant is below or equal to a threshold
value, determining that there is a risk of compressor being
flooded; and when the difference between the refrigerant discharge
temperature and the saturated discharge temperature of the
refrigerant is higher than the threshold, determining that there is
no risk of compressor being flooded.
14. The method of claim 13, wherein limiting a refrigerant flow
into a compressor of the transport refrigeration unit includes
closing down an electronic throttle valve of the compressor.
15. (canceled)
16. The method of claim 15, wherein the saturated discharge
temperature of the refrigerant is derived from a refrigerant
discharge pressure of the compressor.
17. The method of claim 15, wherein the threshold value is between
10 to 15.degree. R superheat.
18. A method of controlling a transport refrigeration unit,
comprising: determining whether there is a risk of the compressor
being flooded; and limiting a refrigerant flow into a compressor of
the transport refrigeration unit when there is a risk of the
compressor being flooded, wherein determining whether there is a
risk of a compressor of the transport refrigeration unit being
flooded by liquid refrigerant includes: measuring a refrigerant
discharge temperature from the compressor; when the temperature of
the refrigerant discharge temperature is below or equal to a
temperature threshold value, determining that there is a risk of
compressor being flooded; and when the temperature of the
refrigerant discharge temperature is higher than the temperature
threshold value, determining that there is no risk of compressor
being flooded.
19. The method of claim 18, wherein the temperature threshold value
is between 10 to 15.degree. R superheat.
20. The method of claim 13, wherein determining whether there is a
risk of the compressor being flooded includes: when the transport
refrigeration unit is in at least one of a heating/defrosting mode
and a transition between a cooling mode and the heating/defrosting
mode, determining there is a risk of compressor being flooded.
Description
FIELD
[0001] The disclosure herein relates to a transport refrigeration
unit (TRU). More specifically, the disclosure herein relates to a
method of reducing a risk of liquid flooding, such as liquid
refrigerant flooding, in a compressor of the TRU by controlling an
electronic throttle valve of the TRU.
BACKGROUND
[0002] TRUs have been used to regulate a space temperature of a
transport unit, such as a truck, a trailer, a railway car, a
shipping cargo box or a container. The TRU can be configured to
include a compressor, a condenser, an expansion device (e.g. an
expansion valve) and an evaporator, which form a refrigeration
circuit. The refrigeration circuit of the TRU can be configured to
provide cooling and/or heating to an internal space of the
transport unit. Some TRUs may also be configured to have a
defrosting mode to remove icing on the refrigeration circuit.
[0003] The compressor of the TRU may be, for example, a scroll
compressor, a screw compressor, a reciprocating compressor, or
other suitable compressors. The compressor typically requires
lubrication, for example, provided by lubricating oil during
operation. When the TRU is in operation, liquid refrigerant may
flood the compressor in some cases, causing dilution to the
lubricating oil and thus reducing the lubricating effect of the
lubricating oil. Liquid refrigerant flooding may also cause a
foaming action during the TRU start-up, which can, for example,
drive all oil out of the compressor in a short period of time,
causing high loads on bearings, scroll sets, and/or pistons. Liquid
refrigerant may flood the compressor when the TRU for example is in
a heating mode, a defrosting mode, or transition between a cooling
mode to the heating/defrosting mode.
SUMMARY
[0004] A compressor of a TRU may experience liquid refrigerant
flooding, for example, when the TRU is operated in a
heating/defrosting mode, or a transition mode between a cooling
mode and a heating/defrosting mode. Some TRUs may be equipped with
an electronic throttle valve (ETV) that is configured to control a
volume of a refrigerant flowing into the compressor. Embodiments
disclosed herein are directed to controlling the ETV to reduce the
occurrence or risk of the compressor being flooded by liquid
refrigerant.
[0005] In some embodiments, a method to control the ETV may include
determining whether there is a risk of a compressor of the TRU
being flooded by liquid refrigerant; and closing down the ETV to a
desired value when there is a risk for the compressor being flooded
by liquid refrigerant.
[0006] In some embodiments, the method to control the ETV may
include: measuring a refrigerant discharge temperature from the
compressor; comparing the refrigerant discharge temperature to a
saturated discharge temperature of the refrigerant; when the
refrigerant discharge temperature and the saturated discharge
temperature of the refrigerant is below or equal to a desired
value, determining that there is a (unacceptable) risk of the
compressor being flooded; and when the refrigerant discharge
temperature and the saturated discharge temperature of the
refrigerant is higher than the desired value, determining that
there is no (or not an acceptable) risk of the compressor being
flooded.
[0007] In some embodiments, the method may include measuring a
refrigerant discharge temperature from the compressor; comparing
the refrigerant discharge temperature to a saturated discharge
temperature of the refrigerant; and controlling the electronic
throttle so that a difference between the refrigerant discharge
temperature from the compressor and the saturated discharge
temperature of the refrigerant is within a desired threshold.
[0008] Other features and aspects of the fluid management
approaches will become apparent by consideration of the following
detailed description and accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0009] Reference is now made to the drawings in which like
reference numbers represent corresponding parts throughout.
[0010] FIG. 1 illustrates an embodiment of a transport unit, with
which embodiments of the method disclosed herein can be
practiced.
[0011] FIG. 2 illustrates a schematic diagram of a TRU equipped
with an ETV.
[0012] FIG. 3 illustrates a flow chart of a method of controlling
an ETV, according to one embodiment.
[0013] FIG. 4 illustrates a flow chart of another method of
controlling an ETV, according to another embodiment.
DETAILED DESCRIPTION
[0014] A TRU can be used to regulate a space temperature of a
transport unit, such as a truck, a trailer, a railway car, a
shipping cargo box or a container. Some TRUs may include a
compressor, a condenser, an expansion device and an evaporator,
forming a refrigeration circuit. In operation, the compressor
compresses refrigerant and drives the refrigerant through the
refrigeration circuit. In some TRUs, an electronic throttle valve
(ETV) may be positioned in-line between the evaporator and the
compressor. The ETV may be configured to include a variable opening
that allows refrigerant to flow there through. The variable opening
can be controlled electronically so as to control a volume of the
refrigerant that flows through the variable opening.
[0015] The compressor may be, for example, a scroll compressor, a
screw compressor, a reciprocating compressor, etc. The compressor
may require lubrication provided, for example, by oil to operate
properly. In some operation conditions of the TRU, such as in a
heating or defrosting mode, or in a transition between the
heating/defrosting mode and a cooling mode, the liquid refrigerant
may flow into the compressor, causing dilution of the oil. This may
reduce, for example, a lubrication effect provided by the oil,
which can result in a compressor failure. Liquid refrigerant
flowing into the compressor is often called compressor flooding.
Improvements can be made to the TRU to reduce/prevent the risk of
the liquid refrigerant flooding to the compressor so as to help
reduce/prevent compressor failures.
[0016] Embodiments of a method to reduce/prevent liquid refrigerant
flooding to the compressor are disclosed herein. The method
includes closing down (or shutting off) the ETV when there is a
risk of compressor flooding by, for example, liquid refrigerant. In
some embodiments, the method may include closing down the ETV to a
desired value when there is a risk of the compressor flooding.
[0017] The compressor of the TRU is generally configured to
compress a low-pressure refrigerant vapor to high-pressure
superheated refrigerant vapor. When the compressor of the TRU is
flooded or at a risk of being flooded by the liquid refrigerant,
liquid refrigerant may flow into the compressor. As a result, the
compressor may not be able to provide the superheated refrigerant
vapor because of the presence of the liquid refrigerant. Therefore,
the failure to provide the superheated refrigerant vapor by the
compressor may indicate that the compressor may be at a risk of
being flooded or flooded by the liquid refrigerant. In some
embodiments, the method may include measuring a refrigerant
discharge temperature of the compressor, and closing down the ETV
when a difference between the refrigerant discharge temperature of
the compressor and a refrigerant saturated discharge temperature is
below a temperature threshold. In some embodiments, the threshold
is about 10 to 15.degree. R.
[0018] References are made to the accompanying drawings that form a
part hereof, and in which is shown by way of illustration of the
embodiments in which the embodiments may be practiced. The phrases
"upstream" and "downstream" are referred relatively to a flow
direction. The term "in line" generally means in fluid
communication. The terms "compressor flooding," "refrigerant
flooding in the compressor" and the alike terms are used
interchangeably. The term "closing down" generally means reducing a
size of an opening of an ETV; and the term "opening up" generally
means increasing the size of the opening of the ETV. It is to be
noted that the term "closing down" also includes fully shutting off
the opening; and the term "opening up" also includes fully opening
the opening. It is to be understood that the terms used herein are
for the purpose of describing the figures and embodiments and
should not be regarding as limiting the scope of the present
application.
[0019] FIG. 1 illustrates a transport unit 100, with which the
embodiments disclosed herein can be used. The transport unit 100
(for example a trailer unit) is configured to be transported by a
tractor unit 110. A TRU 120 is configured to be attached to an end
wall 102 of the transport unit 100. The TRU 120 is configured to
regulate a space temperature of an internal space 104 of the
transport unit 100.
[0020] It is appreciated that the embodiments disclosed herein can
be used with other transport units, such as a railway car, or a
cargo container/box.
[0021] FIG. 2 illustrates a schematic diagram of a TRU 200. The TRU
200 includes a compressor 202, a three way valve 220, a condenser
204, an expansion device 206 (e.g. an expansion valve), and an
evaporator 207 connected by refrigerant lines 209 to form a
refrigeration circuit. The TRU 200 includes a TRU controller 250.
The TRU 200 also includes an accumulator 208 and an ETV 210
positioned in-line with the refrigerant line 209 between the
accumulator 208 and the compressor 202.
[0022] It is known to the art that by controlling the refrigerant
flow directions, for example, via controlling a three-way valve
220, the TRU 200 can be configured to work in a plurality of modes,
including a cooling mode and a heating/defrosting mode. It is also
known in the art that the refrigerant circuit can also include
other components, such as a refrigerant dryer and/or a suction line
heat exchanger. The embodiments as shown herein are exemplary.
[0023] The compressor 202 is configured to compress refrigerant
vapor. In operation, the compressor 202 generally sucks refrigerant
vapor from an inlet 212, compresses the refrigerant vapor, then
discharges the compressed refrigerant vapor out of the compressor
202 through an outlet 214.
[0024] In the cooling mode, the compressed refrigerant is generally
directed to the condenser 204 first, then through the expansion
device 206 into the evaporator 207. In the cooling mode, the TRU
200 generally is configured to provide cooling to an internal space
(such as the internal space 104 in FIG. 1) of a transport unit
(such as the transport unit 100 in FIG. 1).
[0025] In the heating/defrosting mode, the compressed refrigerant
is generally directed into the evaporator 207 first and then into
the compressor 202. The TRU 200 is generally configured to provide
heating to the internal space (the heating mode) or melt icing on
the evaporator 207 (the defrosting mode).
[0026] The TRU 200 also includes a probe 230 that is positioned
close to the outlet 214 of the compressor 202. In some embodiments,
the probe 230 may be positioned at a compressor top cap (not shown)
of the compressor 202. The probe 230 can be a temperature and/or a
pressure probe, which may be configured to measure a discharge
temperature (T.sub.dis) and/or a discharge pressure (P.sub.dis.) of
the refrigerant compressed by the compressor 202. It is generally
known in the art that a saturated discharge temperature (T.sub.sat)
of the refrigerant discharged from the compressor 202 can be
derived from the P.sub.dis measured, for example, by the probes
230.
[0027] The ETV 210 is positioned upstream of the inlet 212, and is
positioned in-line with the refrigerant line 209. The ETV 210 is
generally known in the art. The ETV 210 can have a variable opening
(not shown) that is configured to allow a fluid to flow there
through. A size of the variable opening can be controlled
electronically. Controlling the size of the variable opening of the
ETV 210 of the TRU 200 can regulate a volume of the refrigerant
flowing into the inlet 212 of the compressor 202.
[0028] In some embodiments, the variable opening of the ETVs 210
can be controlled in a step-wise manner from a fully open state to
a fully closed state. For example, in one particular example of the
ETV 210 sold by Danfoss Global Group, there are 800 steps between
the fully open state and the fully closed state, with 0 being the
fully closed state and 800 being the fully open state. A value
between 0 and 800 corresponds to a particular size of the variable
opening between the fully open state and the fully closed state,
with a larger value corresponding generally to a larger opening
size. The ETV 210 can be controlled for example by the TRU
controller 250.
[0029] The compressor 202 of the TRU 200 is generally configured to
compress refrigerant vapor flowing into the inlet 212. The
compressor 202 may experience liquid refrigerant flooding during
operation. The liquid refrigerant flooding generally refers to a
condition when liquid refrigerant enters the inlet 212 of the
compressor 202 and is compressed by the compressor 202. Liquid
refrigerant flooding can cause mechanical failures of the
compressor 202. Flooding may happen when the TRU 200 is operated in
the heating/defrosting mode, or when the TRU 200 transitions from
the cooling mode to the heating mode. In these operation
conditions, liquid refrigerant in the evaporator 207 may flow into
the inlet 212 of the compressor 202, causing the compressor 202 to
become flooded by the liquid refrigerant. Reducing/preventing the
occurrence or risk of liquid refrigerant flooding in the compressor
can help prevent/reduce mechanical failures of the compressor
202.
[0030] In the embodiment as illustrated in FIG. 2, the TRU 200 is
equipped with the ETV 210 to control refrigerant flow into the
inlet 212 of the compressor 202. A method of reducing refrigerant
flooding may include: when the compressor 202 of the TRU 200 is at
a risk of being flooded by liquid refrigerant flowing into the
inlet 212, closing down the ETV 210 to limit the amount of liquid
refrigerant flowing into the inlet 212 of the compressor 202 so as
to reduce/prevent the occurrences/risk of liquid refrigerant
flooding to the compressor 202.
[0031] FIG. 3 illustrates a flow chart of a method 300 to
reduce/prevent compressor flooding in a compressor of a TRU. The
method may be used with, for example, the compressor 202 in the TRU
200 in FIG. 2. The method 300 can be executed by, for example, the
controller 250 in FIG. 2.
[0032] At 310, the TRU is configured to determine whether there is
a (unacceptable) risk of compressor flooding. The determination can
be made based on, for example, the TRU operation modes and/or
parameters of the TRU operation. In some embodiments, it can be
determined that the compressor is at the (unacceptable) risk of
compressor flooding when the TRU is in a heating/defrosting mode,
or in a transition between a cooling mode and the
heating/defrosting mode. The determination can also be made based
on other operation modes or parameters of the TRU.
[0033] If the TRU is at the (unacceptable) risk of compressor
flooding, the method 300 proceeds to 320. At 320, an ETV, such as
the ETV 210 in FIG. 2, can be controlled to close down (or in some
embodiments, to shut off) so as to limit the amount of refrigerant
flowing into the compressor, such as the compressor 202 in FIG. 2.
The ETVs can be controlled in a step-wise manner. Closing down the
ETV can be performed by setting the ETV to a per-determined step
value or the ETV operation can be limited to a desired step range.
The desired step value or the per-determined step range can be
values or ranges obtained in a laboratory setting. For example, the
desired step value or range can be a value or range that shows
effect on reducing the occurrences of compressor flooding, or
reduce the risk of compressor flooding to an acceptable level, in
the laboratory setting.
[0034] The method 300 then returns to 310 to keep monitoring
whether there is a risk of compressor flooding risk.
[0035] If there is no risk (or acceptable risk) of compressor
flooding at 310, the method 300 does not command the ETV to close
down. The method 300 proceeds to 330 to fully open the ETV. For
example, if an ETV with 800 steps is used, the ETV is commanded to
open to 800. The ETV may then return to a normal operation mode, in
which the ETV may be controlled based on other operational
parameters of the TRU. The method 300 then returns to 310 to check
the risk of compressor flooding.
[0036] It is noted that at 320 and/or 330, the method 300 can wait
for a desired amount of time, such as one second before proceeding
to 310 to check the risk of compressor flooding.
[0037] Whether the compressor is at the (unacceptable) risk of
compressor flooding can be monitored by measuring a refrigerant
discharge temperature of a compressor in a TRU. (Such as the
temperature measured by the probe 230 positioned close to the
outlet 214 in FIG. 2.) The compressor of the TRU is generally
configured to compress a low-pressure refrigerant vapor into
high-pressure refrigerant superheat. Refrigerant superheat refers
to a refrigerant vapor having a temperature that is higher than the
saturated discharge temperature. The temperature of the refrigerant
superheat can be measured by the probe 230, while the saturated
discharge temperature can be calculated from the measure discharge
pressure (T.sub.sat). When the discharge temperature of the
refrigerant is higher than the T.sub.sat, the refrigerant is
generally in a vapor state and may likely include little liquid
refrigerant. When the discharge temperature of the refrigerant is
lower than the T.sub.sat, the refrigerant may generally include
some liquid refrigerant. When the discharge temperature of the
refrigerant is sufficiently above the saturate temperature, such as
10-15.degree. R above T.sub.sat, the refrigerant is generally
refrigerant vapor. In normal operation condition, the refrigerant
discharged from the compressor is generally refrigerant superheat
vapor.
[0038] When liquid refrigerant flows into the compressor (e.g. the
compressor 202 in FIG. 2) of the TRU, which is associated with a
risk of compressor flooding, the liquid refrigerant can cause
temperature reduction and/or also reduction of the refrigerant
superheat in the refrigerant discharged from the compressor.
Therefore, temperature reduction and/or loss of the refrigerant
superheat in the refrigerant discharge temperature of the
compressor may indicate a risk of compressor flooding.
[0039] When the refrigerant discharge temperature of the compressor
is substantially higher than the T.sub.sat, such as for example
about 10-15.degree. R higher than the T.sub.sat, the discharged
refrigerant may be generally in a vapor state. Under this
condition, even though a small amount of liquid refrigerant may
flow into the compressor via the ETV, the risk of the compressor
being flooded by the liquid refrigerant is low. In this state, the
ETV can be fully open.
[0040] FIG. 4 illustrates a flow chart of another method 400 that
is configured to monitor the refrigerant discharge temperature and
control the ETV based on the refrigerant discharge temperature of
the compressor. The method 400 may be executed, for example, by a
controller of the TRU (such as the TRU controller 250 in FIG. 2).
The refrigerant discharge temperature (T.sub.dis) and/or pressure
(P.sub.dis) may be measured, for example, by a temperature probe,
such as the probes 230 in FIGS. 2.
[0041] At 410 and 412, T.sub.dis and P.sub.dis of the refrigerant
discharged from the compressor are measured (for example, by the
probes 230 in FIG. 2), and the measured values are provided to the
controller.
[0042] It is known in the art that T.sub.sat of the refrigerant can
have an association with the pressure of the refrigerant.
Therefore, T.sub.sat of the refrigerant discharged by the
compressor can be obtained or derived based on the P.sub.dis of the
discharged refrigerant. The T.sub.sat may be obtained by the
controller, for example, by calculation based on a formula or a
look up table.
[0043] At 420, a difference between the T.sub.sat and T.sub.dis is
measured. Generally, if T.sub.dis is higher than T.sub.sat, the
refrigerant discharged by the compressor may contain refrigerant
superheat. At 420, the difference between the T.sub.sat and
T.sub.dis is compared to a desired threshold temperature value
.DELTA.T.sub.thd.
[0044] .DELTA.T.sub.thd can be determined, for example, in a
laboratory setting. In the laboratory setting, it can be determined
a minimal .DELTA.T.sub.thd or a range of .DELTA.T.sub.thd that is
associated with a reduced (or an acceptable) risk of refrigerant
flooding in the compressor. Generally, the higher the
.DELTA.T.sub.thd is, the less the risk of the refrigerant flooding
in the compressor. In the laboratory setting, the .DELTA.T.sub.thd
can be determined that when the refrigerant discharge temperature
is higher than the T.sub.sat by the .DELTA.T.sub.thd, the
refrigerant is generally refrigerant superheated vapor. This may
indicate that the risk of compressor flooding is low (or
acceptable). In some embodiments, the .DELTA.T.sub.thd is about
10-15.degree. R.
[0045] If the difference between the T.sub.sat and T.sub.dis is
larger than .DELTA.T.sub.thd, which indicates that there is a low
(or acceptable) risk of compressor flooding, the method 400
proceeds to 425. At 425, the ETV is commanded to a fully open
status (e.g. open to 800 in an ETV with 800 steps.) After the ETV
being fully opened, the ETV may return to a normal operation mode
and be controlled by other operational parameters of the TRU.
[0046] The method 400 then proceeds back to 410 and 412 to measure
P.sub.dis and T.sub.dis, and determine T.sub.sat. It is noted that
the method 400 can wait for a desired period of time, such as one
second, before the method 400 proceeding to 410 and 412 at 425.
[0047] If the difference between the T.sub.sat and T.sub.dis is
equal to or lower than the .DELTA.T.sub.thd, which indicates that
there is a high (or unacceptable) risk of compressor flooding, the
method 400 proceeds to 430. At 430, the ETV is commanded to reduce
a size of an opening of the ETV to a desired value (or a desired
range). Reducing the size of the opening of the ETV can reduce
liquid refrigerant flowing into the compressor, reducing the risk
of refrigerant flooding in the compressor. The desired value (or
range) may be determined, for example, in a laboratory setting. The
per-determined value (or range) can be a value (or range) where the
ETV can limit the liquid refrigerant flow to the compressor so that
the difference between T.sub.sat and T.sub.dis is at least
.DELTA.T.sub.thd.
[0048] The method 400 then proceeds back to 410 and 412 after 430
to measure P.sub.dis and T.sub.dis, and determine T.sub.sat. It is
noted that the method 400 can wait for a desired period of time,
such as one second, before the method 400 proceeding to 410 and 412
at 430.
[0049] The method 400 may optionally proceed to a feedback control
of the ETV after 430, which includes 440, 442, 450, 460 and 470 as
shown in FIG. 4. The feedback control may be configured to control
the ETV so that the difference between the refrigerant discharge
temperature and the T.sub.sat of the compressor is at least
.DELTA.T.sub.thd.
[0050] At 440 and 442, T.sub.dis and P.sub.dis of the refrigerant
discharged from the compressor are measured, and the measured
values are provided to the controller. The saturated discharge
temperature T.sub.sat is obtained or derived at 442 based on the
P.sub.dis of the refrigerant discharged from the compressor.
[0051] At 450, a difference between the T.sub.sat and T.sub.dis is
measured. If the difference is at least .DELTA.T.sub.thd, which
indicates that the risk of compressor flooding is low (or
acceptable), the method 400 proceeds to 460. If the difference is
smaller than .DELTA.T.sub.thd, which indicates that the risk of
compressor flooding is high (or unacceptable), the method 400
proceeds to 470.
[0052] At 460, the ETV is commanded to maintain its opening or open
up to increase the opening of the ETV.
[0053] At 470, the ETV is commanded to close down its opening so as
to reduce the amount of refrigerant allowed through the ETV.
[0054] After 460 and 470, the method 400 proceeds back to 440 and
442 to continue the feedback control of the ETV.
[0055] It is appreciated that the embodiments as disclosed herein
are exemplary. The general principle is to use the ETV to limit an
amount of refrigerant flowing into the compressor when there is a
(unacceptable) risk of compressor flooding. In some embodiments,
the superheat temperature of the refrigerant discharged by the
compressor can be used to monitor whether there is a (unacceptable)
risk of compressor flooding. It is appreciated that other
parameters can be used to monitor whether there is a risk of
compressor flooding.
[0056] The embodiments disclosed herein are generally directed to
measuring discharge temperature from the compressor. It is
appreciated that the embodiments disclosed herein may also be
adapted to use suction temperature and/or suction saturated
temperature of the compressor to determine the risk of compressor
flooding.
Aspects
[0057] Any of aspects 1-10 can be combined with any of aspects
11-20. Any of aspects 11-12 can be combined with any of aspects
13-20.
Aspect 1. A method to control an electronic throttle valve (ETV) of
a transport refrigeration unit comprising:
[0058] determining whether there is a risk of a compressor of the
transport refrigeration unit being flooded by liquid
refrigerant;
[0059] closing down the ETV when there is a risk of the compressor
being flooded by liquid refrigerant; and
[0060] opening up the ETV where there is no risk of the compressor
being flooded by liquid refrigerant,
[0061] wherein the ETV is configured to regulate a refrigerant flow
into the compressor of the transport refrigeration unit.
Aspect 2. The method of aspect 1, wherein determining whether there
is a risk of a compressor of the transport refrigeration unit being
flooded by liquid refrigerant includes:
[0062] measuring a refrigerant discharge temperature from the
compressor;
[0063] comparing the refrigerant discharge temperature to a
saturated discharge temperature of the refrigerant;
[0064] when a difference between the refrigerant discharge
temperature and the saturated discharge temperature of the
refrigerant is below or equal to a threshold value, determining
that there is a risk of compressor being flooded; and
[0065] when the difference between the refrigerant discharge
temperature and the saturated discharge temperature of the
refrigerant is higher than the threshold value, determining that
there is no risk of compressor being flooded.
Aspect 3. The method of aspect 2, wherein the saturated discharge
temperature of the refrigerant is derived from a refrigerant
discharge pressure of the compressor. Aspect 4. The method of any
of aspects 2-3, wherein the threshold value is between 10 to
15.degree. R superheat. Aspect 5. The method of any of aspects 1-4,
wherein determining whether there is a risk of a compressor of the
transport refrigeration unit being flooded by liquid refrigerant
includes:
[0066] measuring a refrigerant discharge temperature from the
compressor;
[0067] when the temperature of the refrigerant discharge
temperature is below or equal to a temperature threshold value,
determining that there is a risk of compressor being flooded;
and
[0068] when the temperature of the refrigerant discharge
temperature is higher than the temperature threshold value,
determining that there is no risk of compressor being flooded.
Aspect 6. The method of aspect 5, wherein the temperature threshold
value is between 10 to 15.degree. R superheat. Aspect 7. The method
of any of aspects 1-6, further comprising:
[0069] measuring a refrigerant discharge temperature from the
compressor;
[0070] comparing the refrigerant discharge temperature to a
saturated discharge temperature of the refrigerant; and
[0071] controlling the electronic throttle so that a difference
between the refrigerant discharge temperature from the compressor
and the saturated discharge temperature of the refrigerant is at
least at a desired threshold value.
Aspect 8. The method of aspect 7, wherein
[0072] controlling the electronic throttle so that a difference
between the refrigerant discharge temperature from the compressor
and the saturated discharge temperature of the refrigerant is at
least at a desired threshold value includes:
[0073] when the difference between the refrigerant discharge
temperature and the saturated discharge temperature of the
refrigerant is lower than the desired threshold value, closing down
the ETV; and
[0074] when the difference between the refrigerant discharge
temperature and the saturated discharge temperature of the
refrigerant is higher than the desired threshold value, opening up
the ETV.
Aspect 9. The method of any of aspects 1-8, wherein the ETV is
controlled in a step-wise manner. Aspect 10. The method of any of
aspects 1-9, wherein
[0075] determining whether there is a risk of a compressor of the
transport refrigeration unit being flooded by liquid refrigerant
includes: [0076] when the transport refrigeration unit is in at
least one of a heating/defrosting mode and a transition between a
cooling mode and the heating/defrosting mode, determining there is
a risk of the compressor of the transport refrigeration unit being
flooded. Aspect 11. A method of controlling a transport
refrigeration unit, comprising:
[0077] restricting refrigerant flow to the compressor when the
transport refrigeration unit is in at least one of a
heating/defrosting mode and a transition between a cooling mode and
the heating/defrosting mode.
Aspect 12. The method of aspect 11, wherein restricting refrigerant
flow to the compressor includes closing down an electronic throttle
valve of the compressor. Aspect 13. A method of controlling a
transport refrigeration unit, comprising:
[0078] determining whether there is a risk of the compressor being
flooded; and
[0079] limiting a refrigerant flow into a compressor of the
transport refrigeration unit when there is a risk of the compressor
being flooded.
Aspect 14. The method of aspect 13, wherein limiting a refrigerant
flow into a compressor of the transport refrigeration unit includes
closing down an electronic throttle valve of the compressor. Aspect
15. The method of any of aspects 13-14, wherein determining whether
there is a risk of a compressor of the transport refrigeration unit
being flooded by liquid refrigerant includes:
[0080] measuring a refrigerant discharge temperature from the
compressor;
[0081] comparing the refrigerant discharge temperature to a
saturated discharge temperature of the refrigerant;
[0082] when a difference between the refrigerant discharge
temperature and the saturated discharge temperature of the
refrigerant is below or equal to a threshold value, determining
that there is a risk of compressor being flooded; and
[0083] when the difference between the refrigerant discharge
temperature and the saturated discharge temperature of the
refrigerant is higher than the threshold, determining that there is
no risk of compressor being flooded.
Aspect 16. The method of aspect 15, wherein the saturated discharge
temperature of the refrigerant is derived from a refrigerant
discharge pressure of the compressor. Aspect 17. The method of any
of aspects 15-16, wherein the threshold value is between 10 to
15.degree. R superheat. Aspect 18. The method of any of aspects
13-17, wherein determining whether there is a risk of a compressor
of the transport refrigeration unit being flooded by liquid
refrigerant includes:
[0084] measuring a refrigerant discharge temperature from the
compressor;
[0085] when the temperature of the refrigerant discharge
temperature is below or equal to a temperature threshold value,
determining that there is a risk of compressor being flooded;
and
[0086] when the temperature of the refrigerant discharge
temperature is higher than the temperature threshold value,
determining that there is no risk of compressor being flooded.
Aspect 19. The method of aspect 18, wherein the temperature
threshold value is between 10 to 15.degree. R superheat. Aspect 20.
The method of any of aspects 13-19, wherein determining whether
there is a risk of the compressor being flooded includes:
[0087] when the transport refrigeration unit is in at least one of
a heating/defrosting mode and a transition between a cooling mode
and the heating/defrosting mode, determining there is a risk of
compressor being flooded.
[0088] With regard to the foregoing description, it is to be
understood that changes may be made in detail, without departing
from the scope of the present invention. It is intended that the
specification and depicted embodiments are to be considered
exemplary only, with a true scope and spirit of the invention being
indicated by the broad meaning of the claims.
* * * * *