U.S. patent number RE39,597 [Application Number 10/682,850] was granted by the patent office on 2007-05-01 for variable speed drive chiller system.
This patent grant is currently assigned to Carrier Corporation. Invention is credited to William H. Rousseau.
United States Patent |
RE39,597 |
Rousseau |
May 1, 2007 |
Variable speed drive chiller system
Abstract
The compressor in a refrigeration system is controlled solely by
a variable speed drive which controls the motor of the compressor
by virtue of the varying of the frequency of the electricity
provided to the motor. To minimize the initial cost and to minimize
operating costs, the variable speed drive is cooled by refrigerant
from the refrigeration system which permits the use of a smaller
drive, and the variable speed drive is operated at, or approaching,
a unity power factor.
Inventors: |
Rousseau; William H. (Savannah,
GA) |
Assignee: |
Carrier Corporation
(Farmington, CT)
|
Family
ID: |
25404890 |
Appl.
No.: |
10/682,850 |
Filed: |
October 9, 2003 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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Reissue of: |
09895684 |
Jul 2, 2001 |
06434960 |
Aug 20, 2002 |
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Current U.S.
Class: |
62/228.4; 62/498;
62/259.2; 62/236 |
Current CPC
Class: |
F25B
49/025 (20130101); F25B 1/047 (20130101); F25B
31/006 (20130101); F25B 2700/21173 (20130101); F25B
2400/23 (20130101); F25B 2600/0253 (20130101); F25B
2400/13 (20130101); F25B 2600/024 (20130101); Y02B
30/70 (20130101) |
Current International
Class: |
F25B
49/00 (20060101); F25B 1/00 (20060101); F25B
27/00 (20060101) |
Field of
Search: |
;62/228.4,228.1,236,498,259.2 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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54100510 |
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56121801 |
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4203383 |
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6056104 |
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6151401 |
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115 234 |
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Oct 1945 |
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SE |
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Primary Examiner: Doerrler; William C.
Attorney, Agent or Firm: Carlson, Gaskey & Olds
Claims
What is claimed is:
1. A refrigerant system having: a closed fluid circuit serially
including a screw compressor, a discharge line, a condenser, an
expansion device, a chiller and a suction line leading back to said
compressor; water passing through said chiller in a heat exchange
relationship and being cooled; said compressor being unloaded
solely by regulating the speed of said compressor; motor means for
driving said compressor; means for varying the speed of said motor
means by controlling the frequency of electrical current supplied
to said motor; means for providing cooling to said means for
varying the speed; means for sensing the temperature of water
leaving said chiller; means for controlling said means for varying
the speed responsive to the sensed temperature of water leaving
said chiller.
2. The refrigeration system of claim 1 wherein liquid refrigerant
from said condenser is supplied by said means for providing cooling
to said means for varying the speed of said motor.
3. The refrigeration system of claim 2 wherein liquid refrigerant
used to provide cooling to said means for varying the speed is at
least partially evaporated and supplied to said chiller.
4. The refrigeration system of claim 1 wherein said means for
controlling said means for varying the speed acts solely responsive
to the sensed temperature of water leaving side chiller.
5. The refrigeration system of claim 1 wherein said means for
varying the speed of said motor has a constant output over a range
of frequency and voltage inputs.
6. A refrigeration system having: a closed fluid circuit serially
including a screw compressor, a discharge line, a condenser, a
first expansion device, an economizer, a second expansion device, a
chiller and a suction line leading back to said compressor; a
branch line connected to said economizer and extending into said
compressor; water passing through said chiller in a heat exchange
relationship and being cooled; said compressor being unloaded
solely by regulating the speed of said compressor; motor means for
driving said compressor; means for varying the speed of said motor
means by controlling the frequency of electric current supplied to
said motor; means for providing cooling to said means for varying
the speed; means for sensing the temperature of water leaving said
chiller; means for controlling said means for varying the speed
responsive to the sensed temperature of water leaving said
chiller.
7. The refrigeration system of claim 6 wherein liquid refrigerant
from said condenser is supplied by said means for providing cooling
to said means for varying the speed of said motor.
8. The refrigeration system of claim 6 wherein said means for
varying the speed of said motor has a constant output over a range
of frequency and voltage inputs.
9. A method for selecting the compressor, motor and variable speed
drive for refrigeration system comprising the steps of: for a given
design refrigeration requirement, selecting a compressor having a
design speed and being capable of providing the necessary
refrigerant delivery; selecting a motor operating at the compressor
design speed with a power factor of at least 0.89 when delivering
the design amount of refrigerant; selecting a variable speed drive
for controlling said motor by varying the frequency of electric
power supplied to said motor such that said variable speed drive
operates at an input power factor of at least 0.99 when driving
said motor to drive said compressor to deliver the design amount of
refrigerant.
10. The method of claim 9 wherein the step of selecting a
compressor includes the selection of a compressor without
mechanical unloading structure.
11. The refrigeration system of claim 3 wherein said motor means
has a power factor of at least 0.89 and said means for varying the
speed of said motor means varies the frequency of electric power
supplied to said motor means such that said means for varying the
speed of said motor means operates at an input power factor of at
least 0.99 when driving said motor means.
12. The refrigeration system of claim 4 wherein said motor means
has a power factor of at least 0.89 and said means for varying the
speed of said motor means varies the frequency of electric power
supplied to said motor means such that said means for varying the
speed of said motor means operates at an input power factor of at
least 0.99 when driving said motor means.
13. The refrigeration system of claim 5 wherein said motor means
has a power factor of at least 0.89 and said means for varying the
speed of said motor means varies the frequency of electric power
supplied to said motor means such that said means for varying the
speed of said motor means operates at an input power factor of at
least 0.99 when driving said motor means.
14. The refrigeration system of claim 7 wherein said motor means
has a power factor of at least 0.89 and said means for varying the
speed of said motor means operates at an input power factor of at
least 0.99 when driving said motor means.
15. The refrigeration system of claim 8 wherein said motor means
has a power factor of at least 0.89 and said means for varying the
speed of said motor means operates at an input power factor of at
least 0.99 when driving said motor means.
16. The method of claim 10 further including the step of selecting
means for cooling said variable speed drive with refrigerant from
said refrigeration system.
17. The method of claim 16 further including the steps of:
selecting means for sensing the temperature of water leaving the
chiller; and selecting means for controlling the speed of said
motor solely responsive to the sensed temperature of the water
leaving the chiller.
.Iadd.18. A refrigeration system having: a closed fluid circuit
serially including a compressor, a discharge line, a condenser, an
expansion device, a chiller and a suction line leading back to said
compressor; water passing through said chiller in a heat exchange
relationship and being cooled; said compressor being unloaded
solely by regulating the speed of said compressor; motor means for
driving said compressor; means for varying the speed of said motor
means by controlling the frequency of electrical current supplied
to said motor; means for providing cooling to said means for
varying the speed; means for sensing the temperature of water
leaving said chiller; means for controlling said means for varying
the speed responsive to the sensed temperature of water leaving
said chiller..Iaddend.
.Iadd.19. The refrigeration system of claim 18 wherein liquid
refrigerant from said condenser is supplied by said means for
providing cooling to said means for varying the speed of said
motor..Iaddend.
.Iadd.20. The refrigeration system of claim 19 wherein liquid
refrigerant used to provide cooling to said means for varying the
speed is at least partially evaporated and supplied to said
chiller..Iaddend.
.Iadd.21. The refrigeration system of claim 18 wherein said means
for controlling said means for varying the speed acts solely
responsive to the sensed temperature of water leaving said
chiller..Iaddend.
.Iadd.22. The refrigeration system of claim 18 wherein said means
for varying the speed of said motor has a constant output over a
range of frequency and voltage inputs..Iaddend.
.Iadd.23. A refrigeration system having: a closed fluid circuit
serially including a compressor, a discharge line, a condenser, a
first expansion device, an economizer, a second expansion device, a
chiller and a suction line leading back to said compressor; a
branch line connected to said economizer and extending into said
compressor; water passing through said chiller in a heat exchange
relationship and being cooled; said compressor being unloaded
solely by regulating the speed of said compressor; motor means for
driving said compressor; means for varying the speed of said motor
means by controlling the frequency of electric current supplied to
said motor; means for providing cooling to said means for varying
the speed; means for sensing the temperature of water leaving said
chiller; means for controlling said means for varying the speed
responsive to the sensed temperature of water leaving said
chiller..Iaddend.
.Iadd.24. The refrigeration system of claim 23 wherein liquid
refrigerant from said condenser is supplied by said means for
providing cooling to said means for varying the speed of said
motor..Iaddend.
.Iadd.25. The refrigeration system of claim 23 wherein said means
for varying the speed of said motor has a constant output over a
range of frequency and voltage inputs..Iaddend.
Description
.Iadd.A second reissue application, 11/397,888, for U.S. Pat. No.
6,434,960, has been filed on Apr. 4, 2006..Iaddend.
BACKGROUND OF THE INVENTION
In screw compressors the bores for the rotors overlap. The
overlapping bores create cusps in the nature of the waist of a
figure eight. One of the cusps in the normal lactation for one form
of a mechanical unloader which forms a portion of the bore and
coacts with the rotors as it moves axially in the cusp to unload
and to control the V.sub.1 or discharge volume to suction volume
ratio, of the compressor. The unloader is normally driven by a
solenoid. To provide a greater degree of control, it is common to
provide a variable speed drive which controls the motor by changing
the frequency of the electric power being supplied to the motor by
the variable speed drive.
SUMMARY OF THE INVENTION
The cost of a variable speed drive is on the order of that of a
compressor. So, adding a variable speed drive to a conventional
compressor greatly increases the cost and adds a degree of
redundancy since the unloader valve, or other mechanical unloading
structure, has some functional overlap with the variable speed
drive in that both can control compressor capacity. While the
variable speed drive is external to the compressor, an unloader
valve is internal to the compressor. Being internal to the
compressor, the unloader valve requires additional manufacturing
steps to accommodate it in the compressor. Specifically, the
unloader valve is located in a cusp and effectively forms a portion
of the bores. This requires precision machining to achieve the
requisite sealing with the rotors and introduces a leakage path
along the interface of the unloader valve with the rotor bores.
Other types of mechanical unloaders such as poppets also require
additional manufacturing steps in order to be accommodated in a
compressor.
The present invention eliminates the mechanical unloader structure
and thereby simplifies the manufacture of the compressor while
reducing costs. All of the control of the compressor is through the
variable speed drive so that further efficiency increases and cost
reductions can be achieved by properly selecting the variable speed
drive, motor, compressor and chiller for a particular application.
The required drive amperage of the variable speed drive, and also
its cost, is directly related to the chiller performance and to the
motor power factor. Improvements in the chiller performance and
motor power factor lowers the average cost of a variable speed
drive for an application.
In the case of the compressor, considerations for unloading include
the amperage or load requirements over the range of operation,
efficiency over the range of operation and the minimum speed
requirements for bearing life which is dependent upon lubrication
circulation with the refrigerant. The motor must be matched with
both the variable speed drive and the compressor in order to
optimize the speed of the compressor. For example, the ideal
compressor speed for a given load is not usually the same as the
synchronous speed. Also, the variable speed drive may be required
to compensate for the various input frequencies and voltages used
around the world and one motor voltage can be used for all
applications over a range of supply voltages. For example, one
variable speed drive and motor combination might be efficiently
used for power supplied at 50 Hz or 60 Hz and over a voltage range
of 346 volts to 480 volts since the variable speed drive output
would remain the same. The system current usage can be minimized
through a unity, or approaching unity, input power factor of the
variable speed drive. The variable speed drive output can be
increased by using system refrigerant for cooling such as is taught
in commonly assigned U.S. Pat. No. 6,116,040. This permits the use
of a smaller and therefore less expensive variable speed drive to
produce a desired output.
The foregoing factors are optimized to achieve a given performance
at a minimized installed cost with the following being affected:
the compressor size, speed and configuration; the variable speed
drive size, input, output and cooling configuration; the motor size
and speed; and the input wire sizes.
It is an object of this invention to control compressor output in a
refrigeration system solely by use of a variable speed drive.
It is another object of this invention to reduce the initial cost
of a refrigeration system employing a variable speed drive.
It is an additional object of this invention to add a variable
speed drive to a refrigeration system at a cost penalty no greater
than 5% of the cost of a compressor with mechanical unloading.
It is a further object of this invention to integrate a variable
speed drive into a refrigeration system. These objects, and others
as will become apparent, hereinafter, are accomplished by the
present invention.
Basically, the compressor in a refrigeration system is controlled
solely by a variable speed drive which controls the motor of the
compressor by virtue of the varying of the frequency of the
electric current provided to the motor. To minimize the initial
cost and to minimize operating costs, the variable speed drive is
cooled by refrigerant from the refrigeration system which permits
the use of a smaller drive, and the variable speed drive is
operated at, or approaching, a unity power factor.
BRIEF DESCRIPTION OF THE DRAWINGS
For a fuller understanding of the present invention, reference
should now be made to the following detailed description thereof
taken in conjunction with the accompanying= drawing wherein:
The FIGURE is a schematic representation of a refrigeration system
employing the present invention.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
For a refrigeration system a particular system capacity is the
starting point in designing the system. A compressor capable of
producing the required capacity will be chosen based upon factors
such as cost, efficiency and operating speed. The selection of the
compressor will be in conjunction with the selection of the motor.
Motors are available having power factors in the range of 0.80 to
0.93 and the motor will be selected based upon cost, power factor,
efficiency at design compressor speed. Variable speed drives are
available which have power factors running from 0.99 to unity.
However, the differences between the standard sizes of the variable
speed drives are relatively large such that a considerably
oversized variable speed drive might be the smallest standard drive
available sufficient to meet design requirements. By cooling the
variable speed drive with refrigerant from the condenser, it may be
operated at higher than its air cooled drive design capacity
because of the greater cooling available. For example, a 100 ampere
drive that supplies 80 amperes when air cooled could supply from 80
to 100 amperes for driving the compressor when refrigerant
cooled.
In the FIGURE, the numeral 10 generally designates a refrigeration
system. Refrigeration system 10 has a screw compressor 12 which has
no mechanical unloading structure. Refrigeration system 10 includes
a closed fluid circuit serially including compressor 12, discharge
line 14, condenser 16, line 18 containing expansion device 20 and
flash tank economizer 22, line 24 containing expansion device 26,
chiller 28 and suction line 30. Line 32 branches from flash tank
economizer 22 and provides fluid communication with a trapped
volume in compressor 12 at an intermediate pressure.
Compressor 12 is driven by motor 11 under the control of variable
speed drive 40 which is connected to the electrical power grid (not
illustrated). Variable speed drive 40 controls the alternating
frequency of the current supplied to motor 11 thereby controlling
the speed of motor 11 and the output of compressor 12. In chiller
28, water is chilled by refrigerant circulating in the closed fluid
circuit of refrigeration system 10. The chilled water provides the
cooling to the zones. The temperature of the water leaving chiller
28 via line 29 is sensed by thermal sensor 50 and supplied to
microprocessor 100. Microprocessor 100 controls variable speed
drive 40 and thereby motor 11 and compressor 12 to maintain a
desired water temperature for the water leaving chiller 28.
Microprocessor 100 can control variable speed drive 40 solely
responsive to the temperature sensed by thermal sensor 50 or it may
also receive zone inputs from the zones being cooled and regulate
the rate of water circulation through the chiller 26, and thereby
the amount of available cooling. If desired, microprocessor 100 may
also control expansion devices 20 and 26.
While refrigeration system 10, as described above, has many
features common with conventional refrigeration systems, there are
a number of significant differences. Screw compressor 12 is simpler
than conventional refrigeration compressors in that it has no
mechanical unloading structure. Accordingly, the rotors only seal
with each other and the bores. There is no slide valve which
replaces portions of the bores in the region of a cusp with the
attendant extra manufacturing costs and potential for leakage
between the slide valve and adjacent structure or any other
mechanical unloading structure. The output of compressor 12 is
controlled through motor 11 whose speed is controlled by variable
speed drive 40. The motor 11 is matched to the variable speed drive
40 and compressor 12. There is an ideal compressor speed for the
design compressor output. So the motor is chosen to have efficient
operation at the ideal compressor speed and to have an optimized
power factor. On the input side of the variable speed drive, a near
unity power factor reduces energy usage and the cost of the energy
because of the reduced energy demand at, or approaching, unity
power factor. This is because the power factor of the variable
speed drive, not the power factor of the motor, is seen by the
utility, since the variable speed drive isolates the motor from the
utility.
In the operation of refrigeration system 10, gaseous refrigerant is
induced into compressor 12 via suction line 30 and compressed with
the resultant hot, high pressure refrigerant gas being supplied via
discharge line 14 to condenser 16. In condenser 16, the gaseous
refrigerant condenses as it gives up heat due to heat transfer via
air, water or brine-cooled heat exchangers (not illustrated). The
condensed refrigerant passes from condenser 16 into line 18 and
serially passes through expansion device 20 into flash tank
economizer 22. A portion of the refrigerant flowing into economizer
22 is diverted into line 32 at an intermediate pressure and passes
via line 32 to a trapped volume in compressor 12. The remaining
liquid refrigerant in economizer 22 passes through expansion device
26 thereby undergoing a pressure drop and partially flashing as it
passes via line 24 into chiller 28. In chiller 28, the remaining
liquid refrigerant evaporates due to heat transfer to the water
passing through chiller 28 via line 29. The economizer flow into
compressor 12 via line 32 increases the capacity of compressor in
that it increases the mass of refrigerant gas being compressed.
Microprocessor 100 receives a signal form thermal sensor 50
indicative of the temperature of the water leaving chiller 28 via
line 29 to provide cooling to one or more zones (not illustrated).
Responsive to the water temperature sensed by sensor 50, the
microprocessor 100 sends a signal to variable speed drive 40 to
cause it to change the speed of motor 11 to increase or decrease
the cooling capacity of compressor 12, as required. Variable speed
drive 40 increases or decreases the speed, and therefore the
capacity, of compressor 12 by changing the frequency of the current
supplied to power motor 11. By having a motor 11 operating at an
optimum power factor the electrical usage and demand are minimized
and the size of the variable speed drive 40 required is reduced.
Additionally, a portion of the liquid refrigerant in condenser 16
is diverted via line 17 to the variable speed drive 40 where the
electronic components are cooled and the refrigerant evaporated.
The evaporated refrigerant passes from variable speed drive 40 via
line 41 to chiller 28. The rate of flow of refrigerant to variable
speed drive 40 from condenser 16 is controlled by valve 42
responsive to the temperature of the refrigerant leaving variable
speed drive sensed by sensor 43. Because the variable speed drive
40 is cooled by the liquid refrigerant, a still smaller variable
speed drive 40 can be used.
Although a preferred embodiment of the present invention has been
illustrated and described, other changes will occur to those
skilled in the art. For example, the economizer may be omitted
and/or zone temperature, water flow rates, the expansion devices
can be connected to the microprocessor. It is therefore intended
that the present invention is to be limited only by the scope of
the appended claims.
* * * * *