U.S. patent application number 11/609656 was filed with the patent office on 2008-06-12 for variable compressor oil return.
Invention is credited to Peter R. Carlsen, Ole Moelgaard Christensen, Bo Hylseback.
Application Number | 20080134701 11/609656 |
Document ID | / |
Family ID | 39310967 |
Filed Date | 2008-06-12 |
United States Patent
Application |
20080134701 |
Kind Code |
A1 |
Christensen; Ole Moelgaard ;
et al. |
June 12, 2008 |
Variable Compressor Oil Return
Abstract
A method includes operating a variable-speed compressor in a
refrigeration system carrying a refrigerant-oil mixture at a
varying compressor speed to provide cooling capacity in proportion
to cooling demand on the refrigeration system, determining that
increased oil return to the compressor compared to a current
oil-return rate is desired, and increasing the speed of the
compressor to be disproportionately high relative to the cooling
demand to provide increased oil return to the compressor.
Inventors: |
Christensen; Ole Moelgaard;
(Haderslev, DK) ; Hylseback; Bo; (Egtved, DK)
; Carlsen; Peter R.; (Aalborg, DK) |
Correspondence
Address: |
TOWNSEND AND TOWNSEND AND CREW, LLP
TWO EMBARCADERO CENTER, EIGHTH FLOOR
SAN FRANCISCO
CA
94111-3834
US
|
Family ID: |
39310967 |
Appl. No.: |
11/609656 |
Filed: |
December 12, 2006 |
Current U.S.
Class: |
62/193 ;
417/42 |
Current CPC
Class: |
F25B 2400/075 20130101;
F25B 2500/16 20130101; F25B 2600/01 20130101; Y02B 30/741 20130101;
F25B 31/002 20130101; Y02B 30/70 20130101; F25B 2600/0253 20130101;
F25B 49/022 20130101 |
Class at
Publication: |
62/193 ;
417/42 |
International
Class: |
F25B 49/02 20060101
F25B049/02; F04B 49/20 20060101 F04B049/20; F25B 31/00 20060101
F25B031/00 |
Claims
1. A refrigeration system comprising: a condenser configured to
condense refrigerant in a refrigerant-oil mixture from first
gas-phase refrigerant to first liquid-phase refrigerant; a pressure
mechanism in liquid communication with the condenser and configured
to receive the first liquid-phase refrigerant from the condenser
and to reduce a pressure of the first liquid-phase refrigerant of
the mixture to produce second liquid-phase refrigerant; an
evaporator in liquid communication with the pressure mechanism and
configured to receive the second liquid-phase refrigerant from the
pressure mechanism and to transfer heat to the second liquid-phase
refrigerant of the mixture to convert the second liquid-phase
refrigerant to second gas-phase refrigerant; a compressor subsystem
in liquid communication with the evaporator and the condenser and
configured to receive the second gas-phase refrigerant from the
evaporator and to compress the second gas-phase refrigerant vapor
refrigerant of the mixture into the first gas-phase refrigerant and
send the first gas-phase refrigerant toward the condenser; and a
controller coupled to the compressor subsystem and configured to
determine that an amount of oil available to the compressor
subsystem is less than desired and to control the compressor
subsystem to increase a speed of the compressor subsystem to cause
more oil to be provided to the compressor subsystem such that the
compressor subsystem has a desirable amount of oil available to the
compressor subsystem.
2. The system of claim 1 wherein the compressor subsystem comprises
a variable-speed compressor.
3. The system of claim 2 wherein the controller is configured to
determine that the amount of oil available to the compressor
subsystem is less than desired if the variable-speed compressor's
speed is below a first speed threshold for longer than a first time
threshold.
4. The system of claim 3 wherein the controller is configured to
cause the variable-speed compressor to increase its speed if the
variable-speed compressor's speed is below a second speed threshold
for longer than a second time threshold, the second speed threshold
being lower than the first speed threshold, the second time
threshold being shorter than the first time threshold.
5. The system of claim 2 wherein the controller is configured to
cause the variable-speed compressor to make its speed approximately
60% or higher of a maximum speed associated with the variable-speed
compressor if the controller determines that the amount of oil
available to the compressor subsystem is less than desired.
6. The system of claim 2 wherein the controller is configured to
determine that the amount of oil available to the compressor
subsystem is less than desired if an oil level at the
variable-speed compressor is below a lower oil-level threshold.
7. The system of claim 6 wherein the controller is configured to
cause the compressor to increase its speed until the oil level at
the compressor reaches an upper oil-level threshold that is higher
than the lower oil-level threshold.
8. The system of claim 1 wherein the compressor subsystem comprises
a first compressor and a second compressor, the first compressor
being a fixed-speed compressor, and wherein the controller is
configured to cause the first compressor to operate if the
controller determines that the amount of oil available to the
compressor subsystem is less than desired and the first compressor
is currently off.
9. A system comprising: a variable-speed compressor including an
input configured to receive a refrigerant-oil mixture with the
refrigerant being in gas phase and at a first pressure, the
compressor including an output configured to transfer the
refrigerant-oil mixture with the refrigerant being in gas phase and
at a second pressure that is higher than the first pressure, the
compressor being further configured to increase the pressure of the
refrigerant received via the input from the first pressure to the
second pressure and to supply the refrigerant-oil mixture with the
refrigerant at the second pressure to the output; and a controller
coupled to the compressor and configured to control the compressor
to increase a speed of the compressor from a first speed to a
second speed if the compressor speed has been below a first
low-speed threshold for longer than a first time, the second speed
being substantially faster than the first speed.
10. The system of claim 9 wherein the second speed is at least
about 60% of a maximum speed of the compressor.
11. The system of claim 10 wherein the second speed is at least
about 90% of the maximum speed of the compressor.
12. The system of claim 11 wherein the second speed is about 100%
of the maximum speed of the compressor and the controller is
configured to control the compressor speed to be the second speed
for a second time that is about 10% of the first time or less.
13. The system of claim 12 wherein the controller is configured to
cause the compressor to increase its speed if the compressor speed
is below a second low-speed threshold for longer than a third time
threshold, the second speed threshold being lower than the first
speed threshold, the third time threshold being shorter than the
first time threshold.
14. The system of claim 13 wherein the second speed is about 100%
of the maximum speed of the compressor and the second speed is
about 10% of the third time or less.
15. A method comprising: operating a variable-speed compressor in a
refrigeration system carrying a refrigerant-oil mixture at a
varying compressor speed to provide cooling capacity in proportion
to cooling demand on the refrigeration system; determining that
increased oil return to the compressor compared to a current
oil-return rate is desired; and increasing the speed of the
compressor to be disproportionately high relative to the cooling
demand to provide increased oil return to the compressor.
16. The method of claim 15 further comprising returning the speed
of the compressor to a speed proportionate to the cooling demand
after increasing the speed of the compressor to be
disproportionately high relative to the cooling demand has resulted
in the compressor being desirably lubricated.
Description
BACKGROUND
[0001] It is often desirable to remove heat from air using a
refrigeration system. For example, in a data center with many
electronic components operating and generating heat, it is
desirable to remove the heat from the data center to help prevent
operational problems with the electronic components.
[0002] The amount of heat produced by the electronic equipment
typically varies over time, e.g., with the amount of use of the
equipment. Thus, variable-speed compressors may be used to help
efficiently and cost effectively remove the heat. With oil mixed
with refrigerant in a refrigeration system, the amount of oil
returned to the compressor varies with the compressor speed. Proper
design of oil return to the compressor is important to avoid issues
such as excessive pressure loss in tubes of the refrigeration
system, low efficiency of the refrigeration system, and low
capacity of the refrigeration system. To help return oil to the
compressor, tubes may be sized to help return oil during times of
low compressor speed, a separate oil return system may be provided,
an extra oil replenishing or holding system may be used, and/or
compressor oil level may be manually checked and replenished. Such
techniques may have associated issues such as high pressure loss,
short lifespan of the compressor due to insufficient or excess oil
return, high fabrication/installation cost, and/or high maintenance
cost.
SUMMARY
[0003] In general, in an aspect, the invention provides a
refrigeration system including: a condenser configured to condense
refrigerant in a refrigerant-oil mixture from first gas-phase
refrigerant to first liquid-phase refrigerant; a pressure mechanism
in liquid communication with the condenser and configured to
receive the first liquid-phase refrigerant from the condenser and
to reduce a pressure of the first liquid-phase refrigerant of the
mixture to produce second liquid-phase refrigerant; an evaporator
in liquid communication with the pressure mechanism and configured
to receive the second liquid-phase refrigerant from the pressure
mechanism and to transfer heat to the second liquid-phase
refrigerant of the mixture to convert the second liquid-phase
refrigerant to second gas-phase refrigerant; a compressor subsystem
in liquid communication with the evaporator and the condenser and
configured to receive the second gas-phase refrigerant from the
evaporator and to compress the second gas-phase refrigerant vapor
refrigerant of the mixture into the first gas-phase refrigerant and
send the first gas-phase refrigerant toward the condenser; and a
controller coupled to the compressor subsystem and configured to
determine that an amount of oil available to the compressor
subsystem is less than desired and to control the compressor
subsystem to increase a speed of the compressor subsystem to cause
more oil to be provided to the compressor subsystem such that the
compressor subsystem has a desirable amount of oil available to the
compressor subsystem.
[0004] Implementations of the invention may include one or more of
the following features. The compressor subsystem includes a
variable-speed compressor. The controller is configured to
determine that the amount of oil available to the compressor
subsystem is less than desired if the variable-speed compressor's
speed is below a first speed threshold for longer than a first time
threshold. The controller is configured to cause the variable-speed
compressor to increase its speed if the variable-speed compressor's
speed is below a second speed threshold for longer than a second
time threshold, the second speed threshold being lower than the
first speed threshold, the second time threshold being shorter than
the first time threshold. The controller is configured to cause the
variable-speed compressor to make its speed approximately 60% or
higher of a maximum speed associated with the variable-speed
compressor if the controller determines that the amount of oil
available to the compressor subsystem is less than desired. The
controller is configured to determine that the amount of oil
available to the compressor subsystem is less than desired if an
oil level at the variable-speed compressor is below a lower
oil-level threshold. The controller is configured to cause the
compressor to increase its speed until the oil level at the
compressor reaches an upper oil-level threshold that is higher than
the lower oil-level threshold. The compressor subsystem comprises a
first compressor and a second compressor, the first compressor
being a fixed-speed compressor, and wherein the controller is
configured to cause the first compressor to operate if the
controller determines that the amount of oil available to the
compressor subsystem is less than desired and the first compressor
is currently off.
[0005] In general, in another aspect, the invention provides a
system including: a variable-speed compressor including an input
configured to receive a refrigerant-oil mixture with the
refrigerant being in gas phase and at a first pressure, the
compressor including an output configured to transfer the
refrigerant-oil mixture with the refrigerant being in gas phase and
at a second pressure that is higher than the first pressure, the
compressor being further configured to increase the pressure of the
refrigerant received via the input from the first pressure to the
second pressure and to supply the refrigerant-oil mixture with the
refrigerant at the second pressure to the output; and a controller
coupled to the compressor and configured to control the compressor
to increase a speed of the compressor from a first speed to a
second speed if the compressor speed has been below a first
low-speed threshold for longer than a first time, the second speed
being substantially faster than the first speed.
[0006] Implementations of the invention may include one or more of
the following features. The second speed is at least about 60% of a
maximum speed of the compressor. The second speed is at least about
90% of the maximum speed of the compressor. The second speed is
about 100% of the maximum speed of the compressor and the
controller is configured to control the compressor speed to be the
second speed for a second time that is about 10% of the first time
or less. The controller is configured to cause the compressor to
increase its speed if the compressor speed is below a second
low-speed threshold for longer than a third time threshold, the
second speed threshold being lower than the first speed threshold,
the third time threshold being shorter than the first time
threshold. The second speed is about 100% of the maximum speed of
the compressor and the second speed is about 10% of the third time
or less.
[0007] In general, in another aspect, the invention provides a
method including: operating a variable-speed compressor in a
refrigeration system carrying a refrigerant-oil mixture at a
varying compressor speed to provide cooling capacity in proportion
to cooling demand on the refrigeration system; determining that
increased oil return to the compressor compared to a current
oil-return rate is desired; and increasing the speed of the
compressor to be disproportionately high relative to the cooling
demand to provide increased oil return to the compressor.
[0008] Implementations of the invention may include one or more of
the following features. The method further includes returning the
speed of the compressor to a speed proportionate to the cooling
demand after increasing the speed of the compressor to be
disproportionately high relative to the cooling demand has resulted
in the compressor being desirably lubricated.
[0009] In accordance with implementations of the invention, one or
more of the following capabilities may be provided. A variable
speed compressor can be provided with appropriate amounts of
returned oil. Proper amounts of oil may be returned to a compressor
despite variations in compressor speed. Cooling efficiency of a
variable-speed compressor refrigeration system may be improved.
Proper amounts of oil may be returned to a variable-speed
compressor refrigeration systems using different tube sizes. A
variable-speed compressor refrigeration system can have a simple
construction, low cost, and/or high compressor reliability.
[0010] These and other capabilities of the invention, along with
the invention itself, will be more fully understood after a review
of the following figures, detailed description, and claims.
BRIEF DESCRIPTION OF THE FIGURES
[0011] FIG. 1 is a block diagram of a data center.
[0012] FIG. 2 is a block diagram of a refrigeration system shown in
FIG. 1.
[0013] FIG. 3 is a block flow diagram of a process of altering a
speed of a compressor shown in FIG. 2 to provide desired oil return
to the compressor.
[0014] FIGS. 4-5 are block diagrams of other refrigeration
systems.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
[0015] Embodiments of the invention provide techniques for
regulating oil return to a variable-speed compressor. For example,
a controller can monitor a refrigeration system to determine and/or
infer amounts of oil return to a variable-speed compressor. The
controller can control the speed of the compressor to interrupt a
period of relatively low speed with a period of relatively high
speed as desired to increase the oil return to the compressor, and
then return to a lower speed. The controller can repeat this as
appropriate. This system is exemplary, however, and not limiting of
the invention as other implementations in accordance with the
disclosure are possible.
[0016] Referring to FIG. 1, a system 10 includes a data center 12
that includes equipment racks 14 and a refrigeration system 16. The
racks 14 are, here, arranged in two rows 18, 20, although other
configurations are possible. The equipment racks 14 contain
electronic components such as servers or other information
technology equipment. The electronic components produce heat that
is expelled from backs 21 of the racks 14 between the rows 18, 20
and the refrigeration system 16 is configured to cool the hot air
and provide cool air to fronts 22 of the racks 14.
[0017] Referring to FIG. 2, the refrigeration system 16 includes a
condenser 24, an expansion valve 26, an evaporator 28, a
variable-speed compressor 30, and a controller 32. Not all of the
components of the refrigeration system 16 may be contained in a
rack. For example, the condenser 24 may be located outside of the
rack, e.g., external to the data center 10 outside. The condenser
24, expansion valve 26, and evaporator 28 operate in typical
fashion, and are not discussed here. Refrigerant lines 34, 36, 38,
40 contain and transport a refrigerant and oil mixture between the
devices 24, 26, 28, 30. Here, the lines/tubes 34, 36, 38, 40 are
configured for optimum oil return to the compressor 30 at 80% of
maximum compressor speed, although other configurations may be
used. The compressor 30 is configured to operate a different speeds
to accommodate different cooling capacities as desired (e.g.,
during peak and off-peak hours of use of, and thus heat production
by, the equipment in the racks 14). The compressor 30 is coupled to
the controller 32 and configured to vary its speed in response to a
control signal from the controller 32. The controller 32 is
configured to increase and lower the speed of the compressor in
accordance with cooling demand on the refrigeration system 16 by
the racks 14.
[0018] The controller 32 is configured to regulate the speed of the
compressor 30 to help ensure adequate oil return to the compressor
30. Here, the controller 32 includes a timer 42. The controller 32
is configured to monitor the speed of the compressor 30 and to
actuate the timer 42 if the compressor speed reaches or drops below
one or more threshold speeds. The timer 42 can track multiple
times. Here, the controller 32 is configured to actuate the timer
42 to track amounts of time that the compressor speed drops below
low-speed thresholds, e.g., 75 Hz and 50 Hz where a maximum speed
is about 85 Hz. The controller 32 is configured to reset the
corresponding times tracked by the timer 42 if the compressor speed
exceeds 50 Hz or 75 Hz, respectively. The controller 32 is
configured to send control signals to the compressor 30 to cause
the compressor 30 to increase its speed if the timer 42 reaches a
low-speed threshold time since the corresponding compressor speed
dropped below the corresponding low-speed threshold. For example,
the controller 32 can cause the compressor 30 to increase its speed
to about 100% of its maximum speed if the speed has been below 50
Hz for more than 30 minutes, or below 75 Hz for more than 12 hours.
The compressor 30 can have its speed increased to other percentages
of the maximum speed, e.g., between about 60% and 100%. The
controller 32 is configured to cause the compressor 30 to increase
its speed to a desired speed that is substantially higher than the
current speed and to actuate the timer 42 again. The controller 32
is configured to monitor the timer 42 and, in response to the timer
reaching one or more increased-speed threshold times, to cause the
compressor 30 to return to its previous speed or whatever speed is
dictated by current demand on the refrigeration system 16. For
example, the controller 32 can cause the compressor to run at 100%
of its maximum speed for an increased-speed time before returning
the compressor speed to a speed dictated by cooling demand. The
increased-speed time is preferably less than about 10% of the
threshold time for the compressor 30 to be running at a lowest
speed threshold before triggering acceleration of the compressor
speed, and preferably less than about 8% of this time, e.g., about
7% or two minutes for the example of a 30-minute time threshold for
the lower speed threshold of 50 Hz. The increased-speed time is
preferably longer if the speed to which the compressor 30 is
increased is less than 100% of the maximum speed for the
compressor. Thus, the controller 32 can cause the compressor to
interrupt periods of relatively low speed with periods of
relatively high speed, and then return to a relatively low speed to
help ensure adequate oil return to the compressor 30 while
providing efficient amounts of cooling corresponding to demands on
the refrigeration system 16.
[0019] The controller 32 may take a variety of forms. For example,
the controller 32 may provide digital or analog signals, or
combinations of these, to the compressor 30. The controller 32 may
comprise a mechanical device, a thermo-mechanical device, or
combinations of these. The controller 32 may comprise a processor
and memory that stores computer program code instructions that are
readable and executable by the processor to perform functions as
described here. Further, the controller 32 may comprise a
combination of two or more of the techniques mentioned.
[0020] In operation, referring to FIG. 3, with further reference to
FIGS. 1-2, a process 50 for cooling the data center 12 while
helping to ensure adequate oil return to the compressor 30 includes
the stages shown. The process 50, however, is exemplary only and
not limiting. The process 50 may be altered, e.g., by having stages
added, removed, or rearranged.
[0021] At stage 52, the controller 32 causes the compressor speed
to vary in accordance with (proportional to) cooling demand on the
refrigeration system 16. The controller 32 may receive indicia from
various sources, e.g., air temperature sensors, refrigerant
pressure sensors, etc. to determine the cooling demand on the
system 16 and send control signals to the compressor 30 to vary its
speed accordingly.
[0022] At stage 54, the controller 32 determines whether the
compressor speed drops below a first low-speed threshold. For
example, the first low-speed threshold may be 75 Hz. If the speed
has not gone below the first low-speed threshold, then the
controller 32 continues to monitor the compressor speed. If,
however, the compressor speed decreases below the first low-speed
threshold, then the process 50 proceeds to both stage 56 and stage
64.
[0023] At stage 56, the controller 32 resets and starts a first
timer using the timer 42. The controller 32 causes the timer 42 to
start a first timer for tracking an amount of time that the
compressor 30 runs at a speed less than the first low-speed
threshold.
[0024] At stage 58, an inquiry is made as to whether the compressor
speed exceeds the first low-speed threshold. The controller 32
determines whether the compressor speed now exceeds the first
low-speed threshold (e.g., by being increased at stage 60 via stage
72 as discussed below). If so, then the process returns to stage
54, and otherwise proceeds to stage 60.
[0025] At stage 60, the controller 32 determines whether the time
indicated by the first timer exceeds a first time threshold
associated with the first low-speed threshold. For example, the
first time threshold may be 12 hours. If the first timer does not
exceed the first time threshold, then the process 50 returns to
stage 58, and otherwise proceeds to stage 62.
[0026] At stage 62, the compressor speed is increased. The
controller 32 sends a control signal to the compressor 30 in
response to which the compressor increases its speed, e.g., to 100%
of its maximum speed. The controller 32 causes the compressor 30 to
operate at this speed for a predetermined amount of time, e.g., two
minutes.
[0027] At stage 64, with the compressor speed being below the first
low-speed threshold, the controller 32 determines whether the
compressor speed drops below a second, lower low-speed threshold.
For example, the second low-speed threshold may be 50 Hz. If the
speed has not gone below the second low-speed threshold, then the
process 50 proceeds to stage 66. If, however, the compressor speed
decreases below the second low-speed threshold, then the process 50
proceeds to stage 68.
[0028] At stage 66, the controller 32 determines whether the
compressor speed exceeds the first low-speed threshold. If the
compressor speed does not exceeded the first low-speed threshold,
then the process 50 returns to stage 64, and otherwise returns to
stage 52. For example, if the compressor speed is increased at
stage 62, then the process returns from stage 66 to stage 52.
[0029] At stage 68, the controller 32 actuates a second timer. The
controller 32 causes the timer 42 to actuate a second timer for
tracking an amount of time that the compressor 30 runs at a speed
less than the second low-speed threshold.
[0030] At stage 70, the controller 32 determines whether the
compressor speed exceeds the second low-speed threshold. If the
compressor speed exceeds the second low-speed threshold, then the
process 50 returns to stage 64, and returns to stage 52 if the
compressor speed exceeds the second low-speed threshold.
[0031] At stage 72, the controller 32 determines whether the time
indicated by the second timer exceeds a second time threshold
associated with the second low-speed threshold. For example, the
second time threshold may be 30 minutes. If the second timer does
not exceed the second time threshold, then the process 50 returns
to stage 70, and otherwise proceeds to stage 62.
[0032] Other embodiments are within the scope and spirit of the
invention. For example, due to the nature of software, functions
described above can be implemented using software, hardware,
firmware, hardwiring, or combinations of any of these. Features
implementing functions may also be physically located at various
positions, including being distributed such that portions of
functions are implemented at different physical locations.
[0033] In exemplary embodiments of refrigeration systems, instead
of different compressor speed thresholds and corresponding
threshold times, the controller could monitor the compressor speed
for an average compressor speed dropping below a threshold speed
for a threshold time. For example, the controller is configured to
reset its timer if the average compressor speed drops below a
low-speed threshold and to send control signals to the compressor
to cause the compressor to increase its speed if the timer reaches
a low-speed threshold time since the average compressor speed
exceeded the threshold speed. Alternatively, the controller could
determine whether the average speed over different periods of time
has not exceeded corresponding, different average speed values and
cause the compressor to increase speed if the average speed
violates any speed-time pair.
[0034] Referring to FIG. 4, a controller 82 is configured to
monitor an oil level indicator 84 in a compressor 80. In accordance
with a current oil level and a desired oil level, the controller 32
can send a control signal to increase its speed such that more oil
is returned to the compressor 30. For example, if the compressor 30
runs at a low speed for a period of time, the oil level in the
compressor 30 may drop. The controller 32 is configured to
determine when a higher rate of oil return than the present rate is
desired, e.g., when the oil level reaches or drops below a lower
threshold level and to respond by signaling to the compressor 30 to
increase its speed. The controller 32 may cause the compressor 30
to increase its speed to a desired speed for a desired amount of
time. Alternatively, the controller 32 may cause the compressor 30
to increase its speed to a desired speed until the oil level
reaches a higher threshold level (higher than the lower threshold
level), at which time the controller 32 can cause the compressor 30
to return to its previous speed or whatever speed is dictated by
current demand on the refrigeration system 16. Thus, the controller
32 can cause the compressor to interrupt periods of relatively low
speed with periods of relatively high speed, and then return to a
relatively low speed to help ensure adequate oil return to the
compressor 30 while providing efficient amounts of cooling
corresponding to demands on the refrigeration system 16.
[0035] As a further example, a controller could use a timer to
periodically cause a compressor to operate at a high speed,
regardless of the historical speed of the compressor. For example,
the controller could cause the compressor to operate at its maximum
speed for two minutes every 30 minutes. The speed and duration of
the high-speed interval and the length of time between high-speed
intervals are preferably selected to guard against foreseeable
unacceptable oil return scenarios. In this example, the durations
and speed are selected to equal the shorter time interval,
corresponding to the compressor speed below 50 Hz, discussed
above.
[0036] Further, a controller could monitor other properties and
control a compressor accordingly. For example, referring to FIG. 5,
a controller 92 can monitor a pressure sensor 94, a temperature
sensor 96, and a gas speed sensor 98. The sensors 94, 96, 98 shown
are exemplary only, and other sensors for detecting other
characteristics, more of any of the types of sensors shown, and/or
different locations for sensing system characteristics, may be
used. In this example, the controller 92 can monitor pressure,
temperature, and gas speed and determine when a compressor 100
should operate at a higher speed to guard against undesirably low
oil return to the compressor 100. The controller 92 can control the
compressor 100 to increase its speed as desired to boost oil return
to the compressor 100 appropriately.
[0037] Further, combinations of techniques discussed above for
determining when and how to control a compressor speed, and
controlling the compressor speed, may be used.
[0038] Further still, the techniques described can be applied to
various system configurations. For example, multiple variable speed
compressors with a shared oil distribution (e.g., an oil leveling
tube or the like) may have their speeds increased to help ensure
adequate oil return for the compressors. A multiple compressor
setup preferably would us an oil level control like in FIG. 4,
where the controller gets feedback from an oil level sensor in the
compressor. Two or more constant speed compressors with shared oil
distribution (with an oil equalization tube) can be regulated to
help ensure adequate oil return. For example, if a constant speed
compressor is not running and oil return drops to an undesired
level, then the compressor can be actuated to its constant speed to
provide adequate oil return. Further, techniques described can be
applied to systems with a compressor employing unloading to reduce
compression capacity of the compressor. Techniques described may
also be used with multi-compressor systems that employ unloading
and that have shared oil distribution. Techniques described can
also be applied to systems with a compressor with a hot gas bypass,
multi-compressor systems with a hot gas bypass, unloading, and
shared oil distribution, systems with a compressor with varying
capacity, multi-compressor systems with varying capacity,
unloading, and shared oil distribution, etc. Further combinations
of these systems or other cooling devices may be used. Also, the
techniques described can be applied to other systems not
listed.
[0039] Also, while the description above refers to "the invention,"
more than one invention may be disclosed.
* * * * *