U.S. patent application number 12/691887 was filed with the patent office on 2010-07-29 for scroll compressors with different volume indexes and systems and methods for same.
This patent application is currently assigned to Bitzer Kuhlmaschinenbau GMGH. Invention is credited to Francesco Galante, Richard G. Kobor.
Application Number | 20100186433 12/691887 |
Document ID | / |
Family ID | 42353034 |
Filed Date | 2010-07-29 |
United States Patent
Application |
20100186433 |
Kind Code |
A1 |
Galante; Francesco ; et
al. |
July 29, 2010 |
Scroll Compressors with Different Volume Indexes and Systems and
Methods for Same
Abstract
A plurality of scroll compressors with different fixed volume
indexes are connected in fluid parallel circuit and configured to
selectively operate to maximize isentropic efficiency at different
condensing temperatures. Different quantities of scroll compressors
of different volume indexes may be selected based upon typical
climate or geographic location environmental conditions to attempt
to maximize efficiency. A controller may selectively operate
different combinations of the compressors of different volume
indexes bases up load demands and condensing temperature
conditions, which may be determined in a variety of ways.
Inventors: |
Galante; Francesco;
(Leonberg, DE) ; Kobor; Richard G.;
(Stuttgart-Sillenbuch, DE) |
Correspondence
Address: |
REINHART BOERNER VAN DEUREN P.C.
2215 PERRYGREEN WAY
ROCKFORD
IL
61107
US
|
Assignee: |
Bitzer Kuhlmaschinenbau
GMGH
Sindelfingen
DE
|
Family ID: |
42353034 |
Appl. No.: |
12/691887 |
Filed: |
January 22, 2010 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
61146947 |
Jan 23, 2009 |
|
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|
Current U.S.
Class: |
62/115 ; 418/1;
418/201.1; 418/55.1; 62/228.1 |
Current CPC
Class: |
F04C 29/04 20130101;
F04C 2240/81 20130101; F04C 18/0215 20130101; F04C 23/001 20130101;
F25B 1/04 20130101; F25B 49/022 20130101; F04C 2230/604 20130101;
F25B 2600/0251 20130101; F25B 2400/06 20130101; F04C 23/008
20130101; F04C 28/065 20130101; F04C 28/02 20130101; F25B 2400/0751
20130101 |
Class at
Publication: |
62/115 ;
418/55.1; 62/228.1; 418/1; 418/201.1 |
International
Class: |
F25B 1/04 20060101
F25B001/04; F04C 18/02 20060101 F04C018/02; F04C 18/08 20060101
F04C018/08 |
Claims
1. A compressor arrangement, comprising: a plurality of refrigerant
compressors connected in parallel circuit, each refrigerant
compressor having a volume index, the plurality of refrigerant
compressors including at least one first compressor and at least
one second compressor, each first compressor having a different
volume index than each second compressor.
2. The compressor arrangement of claim 1, wherein the first and
second compressors are scroll compressors.
3. The compressor arrangement of claim 2, wherein in relative
relation between the first and second compressors, each first
compressor has a higher isentropic efficiency at a high temperature
range for saturated condensing temperature, and wherein each second
compressor has a higher isentropic efficiency at a low temperature
range for saturated condensing temperature, the high temperature
range being higher than the low temperature range.
4. The compressor arrangement of claim 3, wherein each first
compressor is substantially optimized for air cooling, and wherein
each second compressor is substantially optimized for water
cooling.
5. The compressor arrangement of claim 3, further comprising: a
controller in operative communication with the refrigerant
compressors for individually turning refrigerant compressors on and
off; the controller configured to selectively operate the first and
second compressors in response to a demand load and a determination
of different saturated condensing temperature conditions.
6. The compressor of claim 5, wherein the controller selects
between the first and second compressors or combination thereof
based on maximizing isentropic efficiency.
7. The compressor arrangement of claim 6, wherein, when determined
to be in the first high temperature range, the controller operating
the first compressors to the extent necessitated by the demand
load, and operating the second compressors only as necessary to
meet the demand load when all first compressors are already
operating; and when determined to be in the second low temperature
range, the controller operating the second compressors to the
extent necessitated by a demand load, and operating the first
compressors only as necessary to meet the demand load when all
second compressors are already operating.
8. The compressor arrangement of claim 5, further comprising at
least one sensor adapted to sense an environmental condition
indicative of the high and low temperature ranges, the sensor in
communication with the controller, the controller determining
whether a high or low temperature range exists based on sensed
environmental conditions of the at least one sensor.
9. The compressor arrangement of claim 8, wherein the plurality of
refrigerant compressors are integrated in a cooling system, the
cooling system including: an expansion unit including an expansion
valve and a expansion unit heat exchanger, the expansion unit
arranged in fluid series with the plurality of refrigerant
compressors; and a condenser interposed between the expansion unit
and the plurality of refrigerant compressors; wherein the plurality
of refrigerant compressors compress a refrigerant fluid, which is
condensed in the condenser, then expanded in the expansion unit and
then returned to the plurality of refrigerant compressors.
10. The compressor of claim 9, wherein said at least one sensor is
a pressure sensor in communication with a refrigerant suction line
upstream of the plurality of refrigerant compressors, the
controller determining whether a high or low temperature range
exists based upon sensed pressure.
11. The compressor of claim 10, further comprising an intermediate
temperature range intermediate of the high and low temperature
ranges, wherein the controller selectively operates the first and
second compressors on a factor other than maximizing isentropic
efficiency when in the intermediate range.
12. The compressor of claim 5, wherein the controller uses the
demand load to determine saturated condensing temperature, wherein
the demand load is indicative of saturated condensing temperature
with a relative higher demand load indicating a higher saturated
condensing temperature and a relative lower demand load indicating
a lower saturated condensing temperature.
13. The compressor of claim 5, wherein the controller uses at least
one of a temperature sensor and seasonal date information to
determine saturated condensing temperature.
14. The compressor arrangement of claim 1, wherein the volume index
of the first and second compressors is fixed and thereby not
adjustably variable.
15. The compressor arrangement of claim 1, further comprising a
common refrigerant suction pipe connecting inlet ports of each of
the refrigerant compressors in a bank, and a compressed refrigerant
pipe connecting the outlet ports of each of the refrigerant
compressors in the bank.
16. The compressor arrangement of claim 2, further comprising a
common mounting rail, with both first and second refrigerant
compressors commonly mounted on the mounting rail.
17. A method of compressing refrigerant, comprising: arranging at
least two refrigerant compressors in fluid parallel having
different built in volume indexes; and selectively operating the at
least two refrigerant compressors based on saturated condensing
temperature.
18. The method of claim 17, further comprising: sensing a suction
pressure upstream of the at least refrigerant compressors; and
determining the saturate condensing temperature based on the
suction pressure.
19. The method of claim 17, wherein the saturated condensing
temperature is determined by at least one factor selected from the
group consisting of: demand load, actual temperature, refrigerant
pressure, and seasonal date data.
20. The method of claim 17, further comprising: selectively
operating the refrigerant compressors in response to a load demand;
determining which of the different refrigerant compressors are more
efficient at a present state of the saturated condensing
temperature; operating only the refrigerant compressors determined
to be more efficient at the present state of the saturated
condensing temperature to satisfy the demand load; and operating
the refrigerant compressor determined to be less efficient in the
event the demand load cannot be satisfied by the refrigerant
compressors determined to be more efficient.
21. The method of claim 17, wherein the refrigerant compressors are
scroll compressors, each having a fixed volume index.
22. The method of claim 21, further comprising: selectively
operating the refrigerant compressors in response to a load demand;
operating only the refrigerant compressors having a lowest volume
index at a low load demand; operating all of the refrigerant
compressors at a maximum load demand.
23. The method of claim 22, further comprising: operating a mix of
refrigerant compressors with different volume indexes at an
intermediate load demand between lowest and maximum load demand to
attempt to optimize efficiency.
24. The method of claim 22, further comprising operating only the
refrigerant compressors having the lowest volume index at an
intermediate load demand between lowest and maximum load demand to
attempt to optimize efficiency.
25. The method of claim 22, further comprising operating only the
refrigerant compressors having the highest volume index at an
intermediate load demand between lowest and maximum load demand to
attempt to optimize efficiency.
26. The method of claim 17, further comprising: configuring a
combination of scroll compressors of different index volumes based
upon at least one of climate location and geographic location.
27. The method of claim 26, wherein said configuring comprises
including more scroll compressors of a higher index volume in some
locations and more scroll compressors of a lower index volume in
some locations.
28. The method of claim 17, further comprising: compressing
refrigerant from a common suction refrigerant pipe with at least
some of the compressors and outlet compressed refrigerant along a
common outlet pipe; condensing the refrigerant received from the
outlet pipe with a condenser heat exchanger; expanding the
condensed refrigerant in a expansion heat exchanger; and returning
expanded refrigerant to the refrigerant compressors along the
common suction refrigerant pipe.
29. The compressor arrangement of claim 1, wherein the first and
second compressors are screw compressors.
Description
[0001] CROSS-REFERENCE TO RELATED PATENT APPLICATIONS
[0002] This patent application claims the benefit of U.S.
Provisional Patent Application No. 61/146,947, filed Jan. 23, 2009,
the entire teachings and disclosure of which are incorporated
herein by reference thereto.
FIELD OF THE INVENTION
[0003] The present invention relates to scroll compressors for
compressing refrigerant and more particularly to efficiency
improvements relative to a bank of two or more compressors that may
be implemented in a cooling/refrigeration circuit, and is
particularly advantageous for such compressors that have a built-in
fixed volume index such as scroll or screw compressors.
BACKGROUND OF THE INVENTION
[0004] A scroll compressor is a certain type of compressor that is
used to compress refrigerant for such applications as
refrigeration, air conditioning, heat pumps, industrial cooling and
freezer applications, and/or other applications where compressed
fluid may be used. Such prior scroll compressors are known, for
example, as exemplified in U.S. Pat. Nos. 6,398,530 to Hasemann;
6,814,551, to Kammhoff et al.; 6,960,070 to Kammhoff et al.; and
7,112,046 to Kammhoff et al., all of which are assigned to a Bitzer
entity closely related to the present assignee. As the present
disclosure pertains to improvements that can be implemented in
these or other scroll compressor designs, the entire disclosures of
U.S. Pat. Nos. 6,398,530; 7,112,046; 6,814,551; and 6,960,070 are
hereby incorporated by reference in their entireties.
[0005] As is exemplified by these patents, scroll compressors
conventionally include an outer housing having a scroll set
contained therein. A scroll compressor, and more particularly a
scroll set, includes first and second scroll compressor members. A
first compressor member is typically arranged stationary and fixed
in the outer housing. A second scroll compressor member is moveable
relative to the first scroll compressor member in order to compress
refrigerant between respective scroll ribs which rise above the
respective bases and engage in one another. Conventionally the
moveable scroll compressor member is driven about an orbital path
about a central axis for the purposes of compressing refrigerant.
An appropriate drive unit, typically an electric motor, is provided
usually within the same housing to drive the movable scroll
member.
[0006] Scroll compressors and/or other types of compressors are
positive displacement machines and thereby may have a fixed and
therefore non-adjustable "volume index". Such compressors trap a
fixed volume of fluid (e.g. typically a pure gas state) on the
suction side and increase the pressure by reducing the volume
occupied by the fluid in a compression chamber, thereby raising the
fluid pressure on the discharge side. The volume index is the ratio
of the volume of suction gas in the compression chamber cavity
(when it closes) to the volume of gas in the compressor chamber
cavity (when it opens). This Volume index (Vi) provides for the
internal pressure ratio for the compressor.
[0007] One drawback with employing such fixed positive displacement
compressors is that the efficiency curve is fixed relative to
operating temperature or to part load operation (e.g. due to
condensing temperature differences due to seasonal changes as
between summer and winter). While making variable geometry
compressors is possible, these adjustable machines have other
drawbacks such as increased parts (e.g. controls and actuators and
mechanical geometry adjustment structure) and thereby increased
complexity and typically a substantial increased cost.
BRIEF SUMMARY OF THE INVENTION
[0008] A general objective of the present invention is to increase
efficiency of compressors systems operating in both full or part
load conditions. Further, the system can be optimized depending on
various environmental conditions.
[0009] It is a further subsidiary objective according to the above
objective to provide such efficiency gains in compressors that have
a fixed volume index. However, it will be recognized from the
description herein that this subsidiary objective is not limited to
fixed volume index compressors alone.
[0010] In accordance with either or both of the objectives above,
one aspect of the present invention is directed toward a compressor
arrangement comprising a plurality of refrigerant compressors
connected in parallel circuit in which each refrigerant compressor
has a volume index. The compressors include at least one first
compressor and at least one second compressor in which each first
compressor has a volume index different than each second
compressor.
[0011] According to the above aspect, the first and second
compressors may be fixed volume index compressors, e.g. scroll or
screw compressors. Each of the first and second compressors have a
volume index different from the other. For example, in one
embodiment, the first compressor has a higher volume index than the
second compressor. There may be a relation between the first and
second compressor in which each first compressor has a higher
isentropic efficiency at a high temperature range for saturated
condensing temperature. In contrast, each second compressor may
have a higher isentropic efficiency at a low temperature range for
saturated condensing temperature. There may be an intermediate
range between the high temperature and low temperature range where
efficiencies are roughly equivalent or of relatively small
difference.
[0012] According to the above aspect, one of the compressors may be
substantially optimized for air cooling (thereby having a higher
condensing temperature) and the other type of compressor
substantially optimized for water cooling (thereby having a lower
condensing temperature). Different volume indexes generally
indicate different condenser optimizations. Notwithstanding the
same, even if the system is selected for air cooling, it may
include a combination of air-cooled optimized compressors and
water-cooled optimized compressors; or if it is water or liquid
cooled, the arrangement may also include compressors optimized for
air cooling in combination with compressors optimized for water
cooling. The combination of compressors selected is based upon at
least, in part, maximizing isentropic efficiency due to operating
conditions that are anticipated to be used at a given geographic
location. The combination of compressors selected is also based
upon at least, in part, maximizing the Seasonal Energy Efficiency
Ratio (SEER) and the Integrated Part Load Value (IPLV).
[0013] Yet a further subsidiary aspect of the present invention may
include a controller that is in operative communication with both
types of refrigerant compressors for individually turning the
refrigerant compressors on and off (including optionally modulating
and otherwise controlling the compressors). The controller can be
configured to selectively operate the first and second compressors
in response to a demand load and a determination of different
saturated condensing temperature conditions. Preferably the
controller selects between the first and second compressors or
combination thereof based upon maximizing isentropic efficiency.
For example, when it is determined to be in the first high
temperature range, the controller may operate the first compressors
to the extent necessitated by the demand load and operate the
second compressors only as necessary to meet the demand load when
all of the first compressors are already operating. However, when
temperatures are typically lower and it is determined to be in the
second low temperature range, the controller may operate the second
compressors to the extent necessitated by a demand load and operate
the first compressors only as necessary to meet the demand load
when all of the second compressors are already operating. If there
is an intermediate range between high and low temperature ranges,
different logic or different combinations may either be
pre-selected for the compressors depending on other considerations,
while still maximizing efficiency given the negligible efficiency
differences that may be provided in an intermediate range.
[0014] Various ways may be used to provide a determination of the
temperature range of condensing temperatures. For example, the
sensed pressure of a refrigeration system detected using a pressure
sensor can be indicative of the saturated condensing temperature.
Alternatively, actual temperature detected using temperature
sensors and/or other such data, i.e. date or seasonal information
indicative of the current environment or climate, can be used to
determine whether the compressor arrangement is in a higher
temperature range or lower temperature range of condensing
temperatures. The operating load demand may also itself indicate
the operating condensing temperature such as for an air conditioner
system when lower demand loads indicate a lower condensing
temperature range and higher demand loads indicate a higher
condensing temperature range. Combinations of such sensors and
other data or information may be used to derive such a
determination.
[0015] The compressor arrangement may comprise two, three or four
or more compressors operating in one, two or more banks and one,
two or more different refrigerants circuits, but it is extensible
to all different compressor arrangements and technologies with a
fixed volume index. Further, the compressors may be arranged in a
single bank or divided up among different banks of scroll
compressors that may be commonly mounted with common suction and
discharge pipes and common mounting rails. Separate or combined
circuits may be used with the banks.
[0016] Another aspect is directed toward a method of compressing
refrigerant comprising arranging at least two refrigerant
compressors in fluid parallel having different built in volume
indexes; and selectively operating the at least two refrigerant
compressors based on saturated condensing temperature.
[0017] The saturated condensing temperature may be determined by at
least one factor selected from the group consisting of: demand
load, actual temperature, refrigerant pressure, and seasonal date
data. Preferably, it is pressure based information that can include
sensing a suction pressure upstream of the at least refrigerant
compressors; and determining the saturate condensing temperature
based on the suction pressure (e.g. with a known refrigerant,
suction pressure correlates to and is thus indicative of saturated
condensing temperature).
[0018] The above method may further include the subsidiary aspect
of: selectively operating the refrigerant compressors in response
to a load demand; determining which of the different refrigerant
compressors are more efficient at a present state of the saturated
condensing temperature; operating only the refrigerant compressors
determined to be more efficient at the present state of the
saturated condensing temperature to satisfy the demand load; and
operating the refrigerant compressor determined to be less
efficient in the event the demand load cannot be satisfied by the
refrigerant compressors determined to be more efficient.
[0019] According to the subsidiary aspect, the method may further
include: selectively operating the refrigerant compressors in
response to a load demand; operating only the refrigerant
compressors having a lowest volume index at a low load demand; and
operating all of the refrigerant compressors at a maximum load
demand. If an intermediate load demand is provided, the method may
further involve operating a mix of refrigerant compressors with
different volume indexes at an intermediate load demand between
lowest and maximum load demand to attempt to optimize
efficiency.
[0020] Other aspects, objectives and advantages of the invention
will become more apparent from the following detailed description
when taken in conjunction with the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0021] The accompanying drawings incorporated in and forming a part
of the specification illustrate several aspects of the present
invention and, together with the description, serve to explain the
principles of the invention. In the drawings:
[0022] FIG. 1 is an isometric view of multiple scroll compressor
assemblies that are mounted in parallel fluid circuit and in a
common bank that may further be mounted on a common pair of
mounting rails in accordance with an embodiment of the present
invention;
[0023] FIG. 2 is a cross section of one of the scroll compressors
shown in FIG. 1;
[0024] FIG. 3 is a schematic view of a cooling system employing at
least one bank of scroll compressors;
[0025] FIG. 4 is a schematic view of a cooling system employing at
least one bank of scroll compressors, according to an alternative
embodiment of FIG. 3, but with similar reference numbers indicated
to indicate like components; and
[0026] FIG. 5 is a graph illustrating the isentropic efficiencies
of a low volume index compressor and a high volume index compressor
at different operating condensing temperatures.
[0027] While the invention will be described in connection with
certain preferred embodiments, there is no intent to limit it to
those embodiments. On the contrary, the intent is to cover all
alternatives, modifications and equivalents as included within the
spirit and scope of the invention as defined by the appended
claims.
DETAILED DESCRIPTION OF THE INVENTION
[0028] An embodiment of the present invention has been illustrated
in FIG. 1 as at least one bank 10 of compressors of at least two
different volume indexes, such as scroll compressors 12, connected
in fluid parallel circuit. Each scroll compressor as illustrated in
FIG. 1 may be a fixed positive displacement machine that has a
non-adjustable built in fixed volume index in that the geometry of
scrolls and the compressor chambers that are formed are not
adjustable during operation. The bank 10 of scroll compressors may
be used in a variety of systems to include air conditioning or
chillers, reversible heat pumps, refrigeration units, industrial
cooling applications and other such refrigerant circuits (herein
cooling and refrigeration and other similar words are used
interchangeably and mean the same thing and apply broadly to all
such applications indicated).
[0029] Before turning to the details of the parallel circuit bank
with different volume indexes, some background about a scroll
compressor 12 as shown in FIG. 2 will be provided for orientation
and description purposes, although it is understood that this
invention may be applicable to other compressor configurations such
as those discussed in the background for example, especially such
configurations with a fixed (e.g. no adjustable) volume index. The
scroll compressor 12 generally includes an outer housing 14 that
typically comprises one or more stamp-formed sheet steel shell
sections 16 that are welded together. Contained within the housing
14 is a drive unit 18 that may take the form of an electrical motor
and a pair of scroll compressor bodies to include a fixed scroll
compressor body 20 and a movable scroll compressor body 22. The
scroll compressor bodies 20, 22 have respective bases 24 and
respective scroll ribs 26 that project from the respective bases 24
and which mutually engage for compression of fluid. The drive unit
18 has a rotational output on a drive shaft 28 that is operable to
drive the movable scroll compressor body 22 about an orbital path
relative to the fixed scroll compressor body 20 and thereby
facilitates the compression of fluid. The drive unit 18 is
electrically connected via wiring to a local electrical panel and
box 30 that is carried on the housing 14. Further details of such a
scroll compressor arrangement are further described in the
aforementioned patents which have been hereby incorporated by
reference in their entireties.
[0030] Referring again to FIG. 1, each scroll compressor 12 may be
commonly mounted on common mounting rails 32 via mounting bases 40
to form at least one bank 10 of scroll compressors. Multiple banks
(as schematically indicated in FIGS. 3 and 4) may be employed, with
the compressors 12 connected among each other in parallel circuit
as shown. To facilitate parallel connection, each scroll compressor
may have a suction inlet connected to a common low pressure suction
pipe 34, and a discharge outlet connected to a common high pressure
outlet pipe 36. The lubricating oil sumps may also optionally be
connected via a common line 38.
[0031] As also indicated in FIG. 1, different scroll compressors
may be different models, sizes or types (e.g. with different scroll
member geometry) to provide different fixed built in volume indexes
(Vi). For example, in FIG. 1, one of the illustrated scroll
compressors is shown to have a Vi of 2.3 and in an embodiment may
be optimized for water cooling applications (e.g. in which the
condensing temperature is lower). Also shown in FIG. 1 is that two
of the illustrated scroll compressors are shown to have a Vi of 2.6
and in an embodiment may be optimized for air cooling applications
(i.e. in which the condensing temperature is higher). The volume
index is the ratio of the volume of suction gas in the compression
chamber 42 when it closes (i.e. see chambers 42 formed between
scroll members in FIG. 2) to the volume of gas in the compressor
chamber 42 when it opens. This Volume index (Vi) provides for the
internal pressure ratio for the compressor. In a scroll compressor
(with reference to FIG. 1) the volume of each compression chamber
42 progressively decreases in volume during operation as the
compression chamber is moved radially inward due to the movement
until it discharges into a discharge port and through a check valve
44.
[0032] The present invention contemplates using compressors of
different volume indexes (Vi) for purposes of increasing efficiency
due to different condensing temperatures that may be experienced in
a given application and/or geographic region. Embodiments
contemplate different combinations of compressors with Vi depending
upon the typical load demand at different temperature ranges and
the time % during a year that will typically be spent in that
range.
[0033] The benefits of using different compressors of different Vi
in combination can be realized with the performance efficiency
distinctions experienced by the different compressors. In this
regard and referring to FIG. 5, it is seen that different
compressors may perform differently at different saturated
condensing temperatures. As shown, the efficiency graphs for two
different compressors are shown, one having a higher volume index
(Vi) and another having a lower volume index (Vi). Maximum
efficiencies may be separated by at least 5 degrees F. of
temperature. Additionally, it is seen that at lower temperatures
the low Vi compressor is significantly more efficient (preferably
at least 2% more efficient, and at some temperatures at least 5%
more efficient); and in contrast at higher temperatures the higher
Vi compressor is significantly more efficient. Further there may
optionally be an intermediate range (that may or may not start and
stop at the maximum efficiencies as shown) over which there may be
marginal or relatively insignificant efficiency differences such
that other logic may be used over that range relative to
operation.
[0034] Turning to FIGS. 3 and 4, different refrigeration cooling
systems are illustrated showing different embodiments of a system
incorporating one or more banks 10 of the scroll compressors 12.
FIG. 3 illustrates a system employing separate refrigeration
circuits for each bank, and FIG. 4 illustrates a system wherein the
banks are connected in parallel feeding a common refrigeration
circuit.
[0035] Referring to FIG. 3, the illustrated cooling system includes
two separate banks 10 of scroll compressors 12 connected in
parallel circuit, but each feeding a separate dedicated
refrigeration circuit 46. Each refrigeration circuit 46 includes a
condenser 48 connected in series to the high pressure outlet pipe
36 of the scroll compressor bank 10. The condenser 48 is
illustrated to have fluid flow heat exchanger 50 (e.g. air, or in
another embodiment liquid) flow across to cool and thereby condense
high pressure refrigerant. A pressure sensor 52 may be interposed
to sense high pressure refrigerant pressure along the outlet pipe
36 (e.g. upstream of the condenser and downstream of the scroll
compressors). The pressure sensor 52 provide electrical feedback
indicative of sensed pressure to an electronic controller 60.
[0036] At least one cooling expansion unit 54 (if multiple units 54
on a circuit then arranged typically in parallel) is also arranged
in fluid series downstream of the condenser 48. Optional control
valve unit 56 (e.g. as in US Patent Publication 2008/0011014) or
other controls may optionally be interposed between the expansion
unit 54 and the condenser 48. The expansion unit 54 typically will
include an on/off stop valve 58 controlled by a controller 60 to
allow for operation of the expansion unit to produce cooling when
necessitated by a demand load or to preclude operation of the
expansion unit when not necessitated. The expansion unit 54 also
includes an expansion valve 62 that may be responsive or in part
controlled by pressure downstream of the expansion unit heat
exchanger) that controls discharge of refrigerant into a heat
exchanger 64, wherein due to the expansion, heat is absorbed to
expand the refrigerant to a gas state thereby creating a
cooling/refrigeration effect at the heat exchanger 64.
[0037] The expansion unit 54 returns the expanded refrigerant in a
gas state along the low pressure suction pipe 34 to the bank 10 of
scroll compressors 12. A pressure sensor 66 is interposed along the
return between the expansion unit 54 and the scroll compressors 12
to sense pressure along the suction side as experienced in the
suction pipe 34. The pressure sensor 66 provides electrical
feedback indicative of sensed pressure to the controller 60. The
controller 60 is also electrically connected to each electrical box
30 for each of the scroll compressors 12 to individually turn the
compressors on and off, and to otherwise control the compressors as
may be appropriate.
[0038] Referring to FIG. 4, it is seen that both banks 10 of
compressors 12 may collectively be arranged in parallel in the same
circuit alternatively feeding a common condenser 48 that may output
to one or more expansion units 54 as illustrated. This circuit also
work with the same refrigeration cycle as does the first through
compression of refrigerant, condensing of refrigerant, expansion of
refrigerant and return of the refrigerant to the beginning of the
cycle. This illustrates that different circuit configurations are
possible.
[0039] In either refrigeration circuit configuration of FIG. 4 or
FIG. 3, the controller 60 can operate according to embodiments of
the invention as discussed below. As noted, the controller that is
in individual operative communication with both types of
refrigerant compressors (both high Vi and low Vi compressors), to
individually and selectively control different compressors
depending upon load demand and environmental conditions (e.g.
condensing temperature). The controller 60 can thus individually
turn the refrigerant compressors 12 on and off (including
optionally modulating and otherwise controlling the compressors).
The controller 60 will be preconfigured with logic that
automatically selects the compressors based upon demand load and
the temperature conditions (as may be determined by being actual or
calculated from other data).
[0040] In an embodiment, the controller 60 is be configured to
selectively operate the high Vi or low Vi compressors 12 in
response to a demand load and a determination of different
saturated condensing temperature conditions. In combination with
what is shown in FIG. 5, preferably the controller 60 selects
between the high Vi or low Vi compressors 12 or combination thereof
based upon maximizing isentropic efficiency. For example, when it
is determined to be in the first high temperature range (see FIG.
5), the controller 60 may operate the high Vi compressors to the
extent necessitated by the demand load and operate the low Vi
compressors only as necessary to meet the demand load when all of
the high Vi compressors are already operating.
[0041] However, when temperatures are determined to be in the
second low temperature range (see e.g. FIG. 5), the controller 60
may operate the high Vi compressors to the extent necessitated by a
demand load and operate the low Vi compressors only as necessary to
meet the demand load when all of the second compressors are already
operating. In this manner, efficiency is maximized. If there is an
intermediate range between high and low temperature ranges,
different logic or different combinations may either be
pre-selected for the compressors depending on other
considerations.
[0042] Various ways may be used to provide a determination of the
temperature range of condensing temperatures. For example, the
pressure sensors 52, 66 provide the pressure of the system which is
indicative of the saturated condensing temperature. In particular,
for a given refrigerant, an AC system will evaporate at a certain
temperature which is linked to a precise pressure for the given
refrigerant. Thus, the pressure signal(s) may be used to determine
temperature. Alternatively, actual temperature sensors and/or other
such data such as date or seasonal information that would be
indicative of the current environmental client and thereby whether
the compressor arrangement is in a higher temperature range or
lower temperature range. For example, at mid summer for an air
cooled system, it would be presumed and thereby determined that a
high temperature is experienced. The operating load demand may also
itself indicate the operating condensing temperature such as for an
air conditioner system when lower demand loads indicate a lower
condensing temperature range and higher demand loads indicate a
higher condensing temperature range. Thus a determination of
temperature may simply be derived from demand load. Combinations of
such sensors and other data or information may be used to derive
such a temperature determination.
[0043] With this understanding a working contemplated example below
will be explained implementing an embodiment of the present
invention.
CONTEMPLATED EXAMPLE
[0044] To demonstrate the above concept, a practical contemplated
example is discussed below for a conditioning chiller that is
optimized for efficiency using two types scroll compressors having
different volume indexes (Vi). For purposes of demonstration, it
will be assumed the following application environment parameters:
[0045] System: air cooled chiller supplying around 360 kW (max
cooling capacity nominally required) double circuit with a trio
operating on each circuit [0046] Geographical area: Southern Europe
(Italy, Spain) [0047] Objective: to optimize the system in terms of
both EER (full load) and SEER (part load), in agreement to a
customer and application requirements
[0048] Given these application and environmental parameters, a
total of 6 scroll compressors will be therefore used: of them one
compressor per circuit will be chosen with a V.sub.i=2.3 (i.e. a
Bitzer model # GSD8-295VW, water cooled/low condensing temperature
optimized) while the other two with a V.sub.i=2.6 (i.e. a Bitzer
model # GSD8-295VA, air cooled/high condensing temperature
optimized).
[0049] During the year several operating conditions will alternate,
as consequence of a different cooling request. The system control
will regulate the supplied cooling capacity by switching off/on the
number of compressors required, as commonly already done. The
advantage of the "scroll mix" is that the system will possibly
select only the compressors that are more performing under the
required conditions.
[0050] Based on this configuration, it is possible to illustrate
the efficiency benefit below for three situations, among the six in
this case possible: 100%, 83.3%, 66.7%, 50%, 33.3% and 16.7% of the
full load.
[0051] A. Full load, 100%: all 6 compressors are switched on.
[0052] The season is hot summer/mid summer which typically
experience the highest condensing temperatures.
[0053] In terms of total energy efficiency, in this case, the
"weight" of the 4 compressors with V.sub.i=2.6 will be prevailing.
The performance of the whole AC system will be therefore tending to
the values of the compressors optimized for higher condensing
temperatures (V.sub.i=2.6). The two compressors with lower V, are
capable of running also in these conditions.
[0054] Considering the relatively short (in relation to the whole
year for the given region) period on which the system is running at
full load, the slight decrease of efficiency due the influence of
the two compressors with lower V.sub.i will be very little compared
to the efficiency of an equivalent system mounting all six "air
cooled" compressors.
[0055] The efficiency of this system, by the way, is greatly higher
than the one of an equivalent system mounting all six compressors
with a lower V.sub.i=2.3; this in the case that we would have
chosen to optimize the AC system only in terms of part load
operations.
[0056] B. Part Load, 66.7%: 2 compressors V.sub.i=2.3 and 2
compressors V.sub.i=2.6 switched on, 2 compressors V.sub.i=2.6
switched off.
[0057] The season is "fresh summer" beginning of summer and the end
of summer, which typically provides for medium condensing
temperatures and part load demands. Further, because the condenser
size remains fixed, the condensing temperature is lower in part
load operation.
[0058] In this case the efficiency of the system will be already
influenced by the higher efficiency of the 2 compressors with
V.sub.i=2.3. The two compressors with higher V.sub.i will still
offer acceptable performances. Possibly the efficiency increase due
to the two compressors with lower V.sub.i will be bigger than the
efficiency decrease due to the two compressors with higher V.sub.i,
or--in the worse case--the two effects will mutually compensate
each other (this is function of the real condensing temperature and
also depends on the exact behavior of the isentropic efficiency
curves of the compressors).
[0059] By the way, the total efficiency of the system in this case
will be certainly higher than the one of an equivalent system
equipped with all four compressors with V.sub.i=2.6. This is the
efficiency advantage offered by the "scroll mix" at the given
conditions.
[0060] C. Part Load, 33.3%: 2 compressors V.sub.i=2.3 on, 4
compressors V.sub.i=2.6 off.
[0061] The season is spring, autumn, or very early or very late
summer in which low condensing temperatures are typically
expected.
[0062] These temperature conditions are similar to those of a water
cooled chiller and therefore the advantage, in terms of efficiency,
becomes in this case even more conspicuous.
[0063] The efficiency of the system in these conditions is
certainly much higher than the one of an equivalent system equipped
with compressors optimized for air cooled conditions (V.sub.i=2.6).
Practically, one will obtain exactly the same efficiency of a
system only equipped with compressors with lower V.sub.i=2.3 but
without giving up the high efficiency of the system at full load
conditions.
[0064] Other Operating Capacities
[0065] In the above example, we have in total 6 compressors, split
into 2 circuits (3 compressors per circuit). The configurations
100%, 66.7% and 33.3% are indicated above, but it is also possible
to run other part load configurations. For example, at 83.3%
operating capacity, 5 compressors are switched on, with the first
bank/circuit operating with 3 compressors in full load and the
second bank/circuit with 2 compressors--part load 66.7%. At 50%, 3
compressors are switched on; the first circuit operates with 2
compressors (66.7% part load), and the second with 1 compressor
33.3% part load). At 16.7% operating capacity, only 1 compressor is
switched on with one circuit is operating with 1 compressor at
33.3% part load and the other one is completely switched off. It is
noted that the exact behavior in this case depends on the lay-out
and design of the system (one condenser or two separate
condensers).
[0066] Conclusions from Example
[0067] After quantifying, if the efficiencies of the system are
summed at the different operating conditions during the whole year,
one can expect that the total efficiency will be higher for a
system with a "scroll mix" than for an equivalent system using all
compressors with the same V.sub.i (either higher or lower). This is
explainable because, in terms of efficiency, the "scroll mix"
relies on the most efficient compressors, in correspondence of a
certain operating condition. Similarly if in another case an
optimization weighted toward part load conditions, i.e. low
condensing temperatures, is required, more compressors (i.e. 3 or
4) with lower V.sub.i will be selected in order to increase the
"weight" of the compressors optimized for lower condensing
temperatures. In each case the exact mix is to be readily
calculated.
[0068] All references, including publications, patent applications,
and patents cited herein are hereby incorporated by reference to
the same extent as if each reference were individually and
specifically indicated to be incorporated by reference and were set
forth in its entirety herein.
[0069] The use of the terms "a" and "an" and "the" and similar
referents in the context of describing the invention (especially in
the context of the following claims) is to be construed to cover
both the singular and the plural, unless otherwise indicated herein
or clearly contradicted by context. The terms "comprising,"
"having," "including," and "containing" are to be construed as
open-ended terms (i.e., meaning "including, but not limited to,")
unless otherwise noted. Recitation of ranges of values herein are
merely intended to serve as a shorthand method of referring
individually to each separate value falling within the range,
unless otherwise indicated herein, and each separate value is
incorporated into the specification as if it were individually
recited herein. All methods described herein can be performed in
any suitable order unless otherwise indicated herein or otherwise
clearly contradicted by context. The use of any and all examples,
or exemplary language (e.g., "such as") provided herein, is
intended merely to better illuminate the invention and does not
pose a limitation on the scope of the invention unless otherwise
claimed. No language in the specification should be construed as
indicating any non-claimed element as essential to the practice of
the invention.
[0070] Preferred embodiments of this invention are described
herein, including the best mode known to the inventors for carrying
out the invention. Variations of those preferred embodiments may
become apparent to those of ordinary skill in the art upon reading
the foregoing description. The inventors expect skilled artisans to
employ such variations as appropriate, and the inventors intend for
the invention to be practiced otherwise than as specifically
described herein. Accordingly, this invention includes all
modifications and equivalents of the subject matter recited in the
claims appended hereto as permitted by applicable law. Moreover,
any combination of the above-described elements in all possible
variations thereof is encompassed by the invention unless otherwise
indicated herein or otherwise clearly contradicted by context.
* * * * *