U.S. patent application number 13/061576 was filed with the patent office on 2011-07-07 for capacity boosting during pulldown.
This patent application is currently assigned to CARRIER CORPORATION. Invention is credited to Bill Bush, Paul Chen, Biswajit Mitra.
Application Number | 20110162396 13/061576 |
Document ID | / |
Family ID | 42060045 |
Filed Date | 2011-07-07 |
United States Patent
Application |
20110162396 |
Kind Code |
A1 |
Chen; Paul ; et al. |
July 7, 2011 |
CAPACITY BOOSTING DURING PULLDOWN
Abstract
The transcritical refrigeration system is provided with a main
compressor and booster compressor that is made to operate in
parallel with the main compressor only during pulldown conditions.
A single, two stage compressor is provided with valving which is
controlled so as to provide for the two stages operating in series
in normal operation and for operating in parallel during pulldown
conditions.
Inventors: |
Chen; Paul; (Manlius,
NY) ; Bush; Bill; (Skaneateles, NY) ; Mitra;
Biswajit; (Huntersville, NC) |
Assignee: |
CARRIER CORPORATION
Farmington
CT
|
Family ID: |
42060045 |
Appl. No.: |
13/061576 |
Filed: |
September 16, 2009 |
PCT Filed: |
September 16, 2009 |
PCT NO: |
PCT/US2009/057068 |
371 Date: |
March 1, 2011 |
Related U.S. Patent Documents
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
|
|
61100929 |
Sep 29, 2008 |
|
|
|
Current U.S.
Class: |
62/115 ;
62/228.5 |
Current CPC
Class: |
F25B 2600/2507 20130101;
F25B 9/008 20130101; F25B 2400/075 20130101; F25B 2600/02 20130101;
F25B 41/20 20210101 |
Class at
Publication: |
62/115 ;
62/228.5 |
International
Class: |
F25B 1/10 20060101
F25B001/10; F25B 49/02 20060101 F25B049/02 |
Claims
1. A method of operating a transport refrigeration system of the
type having CO.sub.2 as the refrigerant, comprising the steps of:
during normal operation, compressing the refrigerant in the system
by the operation of only a first compression unit; and only during
operation under pulldown conditions, operating a second compressor
unit in parallel with said first compression unit to thereby
increase the system mass flow and improve the overall capacity
thereof.
2. A method as set forth in claim 1 wherein said first compression
unit is a single stage compressor.
3. A method as set forth in claim 1 wherein said second compression
unit is a single stage compressor.
4. A method as set forth in claim 1 wherein said first and second
compression units comprise first and second stages of a two stage
compressor, and further wherein valving is provided to selectively
cause the two stages to operate either in series or parallel
relationship.
5. A method as set forth in claim 4 wherein said valving includes a
valve between the first and second stage, and a valve connected in
parallel across each of said stages.
6. A method as set forth in claim 5 wherein, during normal
operation, the valve between the two stages is open and other
valves are closed, and during pulldown operation, the valve between
the two stages are closed, and the other two valves are open.
7. A transport refrigeration system comprising: a vapor compression
system including a compression unit, a condenser, an expansion
device and an evaporator connected in serial refrigeration flow
relationship and adapted to operate with CO.sub.2 as the
refrigerant; said compression unit being a two stage compressor and
including valving apparatus capable of being selectively operated
such that during normal operation the refrigerant flows through the
two stages in series relationship and during periods of operation
in which greater capacities are desired the refrigerant flows
through the two stages in parallel relationship to thereby boost
the capacity of the system.
8. A transport refrigerant system as set forth in claim 7 wherein
said valving apparatus includes a first valve between the two
stages and second and third valves connected in parallel with the
respective stages, such that for normal operation said first valve
is opened and said second and third valves are closed wherein
during periods in which higher capacities are desired said first
valve is closed and said second and third valves are opened.
Description
TECHNICAL FIELD
[0001] This invention relates generally to transport refrigeration
systems and, more particularly, to a method for boosting compressor
capacity during pulldown operating conditions.
BACKGROUND OF THE INVENTION
[0002] In transcritical refrigeration systems as for example when
using CO.sub.2 as the refrigerant, the capacity at high evaporating
temperatures is limited compared to more conventional subcritical
refrigerants due to the thermodynamic properties of the fluid in
use. Pulldown, the process of starting the system at a high
evaporating temperature and pulling heat out of the area to be
refrigerated, is a critical phase which requires high capacity and
accomplishment in a reasonable time.
DISCLOSURE OF THE INVENTION
[0003] In accordance with one aspect of the invention, during
periods of operation of a transcritical refrigeration system in a
pulldown mode, a second compressor is caused to operate in parallel
with the primary compressor to temporarily boost the capacity of
the system.
[0004] In accordance with another aspect of the invention, a
two-stage compressor arrangement has a plurality of valves that are
operated in such a way as to cause the two-stages to operate in
parallel rather than in series operation to thereby boost the
capacity of the system.
[0005] In the drawings as hereinafter described, a preferred
embodiment is depicted; however, various other modifications and
alternate constructions can be made thereto without departing from
the scope of the invention.
BRIEF DESCRIPTION OF THE DRAWINGS
[0006] FIG. 1 is a schematic illustration of a transcritical
refrigeration system with the present invention incorporated
therein.
[0007] FIG. 2 is a schematic illustration of one embodiment
thereof.
[0008] FIGS. 3 and 4 are a schematic illustrations of another
embodiment thereof.
DETAILED DESCRIPTION OF THE INVENTION
[0009] Shown in FIG. 1, is a CO.sub.2 refrigerant vapor compression
system which includes a primary compression device 11 driven by a
motor 12 operatively associated therewith, a refrigerant heat
rejecting heat exchanger 13, and a refrigerant heat absorbing heat
exchanger 14, also referred to herein as an evaporator, all
connected in a closed loop refrigerant circuit in series
refrigerant flow arrangement by various refrigerant lines 16, 17
and 18. Additionally, the refrigerant vapor compression system 10
includes a filter drier 19 and a flash tank receiver 21 disposed in
refrigerant line 17 of the refrigerant circuit downstream with
respect to refrigerant flow of the refrigerant heat rejecting heat
exchanger 13 and upstream with respect to refrigerant flow of the
evaporator 14, and an evaporator expansion device 22, operatively
associated with the evaporator 14, disposed in refrigerant line 17
downstream with respect to refrigerant flow of the flash tank
receiver 21 and upstream with respect to refrigerant flow of the
evaporator 14.
[0010] The primary compression device 11 functions to compress and
circulate CO.sub.2 refrigerant through the refrigerant circuit, and
may be a single or a multi-stage compressor such as, for example, a
scroll compressor or a reciprocating compressor. In the case of a
multiple stage compressor, both compression stages would be driven
by the single motor 12 operatively associated in driving
relationship with the compression mechanism of the compressor
11.
[0011] The CO.sub.2 refrigerant vapor compression system is
designed to operate in a subcritical cycle. Thus, the refrigerant
heat rejecting heat exchanger 13 is designed to operate as a
refrigerant condensing heat exchanger through which hot, high
pressure refrigerant vapor discharge from the compression device 11
passes in heat exchange relationship with a cooling medium to
condense the refrigerant passing therethrough from a refrigerant
vapor to refrigerant liquid. The refrigerant heat rejecting heat
exchanger 13, which may also be referred to herein as a gas cooler
or a condenser, may comprise a finned tube heat exchanger, such as,
for example, a fin and round tube heat exchange coil or a fin and
flat mini-channel tube heat exchanger. In transport refrigeration
system applications, the typical cooling medium is ambient air
passed through the condenser 13 in heat exchange relationship with
the refrigerant by means of fan(s) 31 operatively associated with
the condenser 13.
[0012] The evaporator 14 constitutes a refrigerant evaporating heat
exchanger which, in one form, may be a conventional finned tube
heat exchanger, such as, for example, a fin and round tube heat
exchange coil or a fin and mini-channel flat tube heat exchanger,
through which expanded refrigerant, having traversed the expansion
device 22, passes in heat exchange relationship with a heating
fluid, whereby the refrigerant is vaporized and typically
superheated. The heating fluid passed in heat exchange relationship
with the refrigerant in the evaporator 14 may be air passed through
the evaporator 14 by means of fan(s) 24 operatively associated with
the evaporator 14, to be cooled and also commonly dehumidified, and
thence supplied to a climate controlled environment which may
include a perishable cargo, such as, for example, refrigerated or
frozen food items, placed in a storage zone associated with a
transport refrigeration system.
[0013] The expansion device 22, which is normally an electronic
expansion valve, operates to control the flow of refrigerant
through the refrigerant line 33 to the evaporator 14 in response to
the refrigerant suction temperature and pressure sensed by the
sensors (not shown) on the suction side of the compression device
11. A bypass valve 27 is provided to supplement the refrigerant
flow through the expansion device 22 when higher mass flow is
required by the refrigeration system. During normal operation, the
primary compression device 11 is sufficient to meet the capacity
requirements of the system.
[0014] A control logic diagram is shown in FIG. 2 to illustrate
this operation.
[0015] During normal operation, which is indicated in block 33, the
controller 28 causes the motor 11 to drive the primary compression
device 11 only. When operation is desired in the pulldown mode, the
controller 28 moves to block 36 so as to then operate the motor 29
to drive the booster compressor 31, in parallel with and in
addition to the primary compression device 11. When the pulldown
mode operation is completed, the control 28 then proceeds to block
33 for normal operation.
[0016] Having described the invention in one form as comprising two
separate compressors, another embodiment thereof is shown in FIGS.
3 and 4, wherein a single, two-stage compressor is operated in such
a manner as to perform as a pair of compressors operating in
parallel.
[0017] The two-stage compressor is shown generally at 38 and
comprises a first stage 39 and a second stage 41. A valve 42 is
disposed therebetween. During normal operation, the valve 42 is
open and the two-stage compressor 38 operates as a conventional
two-stage compressor. Also provided are valves 43 and 44, which are
arranged in parallel relationship with the stage one 39 and stage
two 41, respectively. When the operational needs are such that
higher capacities are required, such as at pulldown operating
conditions, the valve 42 is closed and the valves 43 and 44 are
opened. The effect is to place the two stages 39 and 41 in parallel
relationship as shown in FIG. 4 to thereby temporarily boost
capacity of the system.
[0018] When operating in the above manner, with either the FIG. 1
or FIG. 3 embodiments, a smaller main compressor is allowed to be
used for normal operating conditions, which is desirable in terms
of overall power consumption.
[0019] Operating in parallel stages will increase the system mass
flow and thereby improve capacity of the system. The multi-stages
compressor can be turned into a regular compressor when the
pulldown is achieved or almost achieved, or when the distance
between the suction and discharge pressures are too high and
causing overheating of the discharge gas.
[0020] While the present invention has been particularly shown and
described with reference to the preferred mode as illustrated in
the drawing, it will be understood by one skilled in the art that
various changes in detail may be effected therein without departing
from the spirit and scope of the invention as defined by the
claims.
* * * * *