U.S. patent application number 10/203194 was filed with the patent office on 2003-08-07 for refrigerator.
Invention is credited to Duncan, Gerald David, Lan, Lin, McGill, Ian Campbell.
Application Number | 20030145611 10/203194 |
Document ID | / |
Family ID | 19927760 |
Filed Date | 2003-08-07 |
United States Patent
Application |
20030145611 |
Kind Code |
A1 |
McGill, Ian Campbell ; et
al. |
August 7, 2003 |
Refrigerator
Abstract
A refrigerator has a fresh food compartment (3) adapted for
maintaining the contents at a temperature above freezing. A vapour
compression refrigeration system is operable in one mode so that an
evaporator (7) is operated at a temperature within 10.degree. C. of
the temperature desired in the fresh food compartment (3) and a
supply of air is maintained over the evaporator (7) and in to the
compartment (3). The vapour compression system is used in a defrost
mode in which the vapour compression refrigeration system is
stopped or allowed to operate without significant heat extraction
at the evaporator (7), and a supply of air above 0.degree. C. is
past over it. Operating the fresh food compartment evaporator (7)
at such a high temperature (close to 0.degree. C.) reduces the rate
of frost build up and the under cooling of frost. Frost may be
adequately removed by an ambient air flow without heater
supplementation.
Inventors: |
McGill, Ian Campbell;
(Auckland, NZ) ; Duncan, Gerald David; (Auckland,
NZ) ; Lan, Lin; (Auckland, NZ) |
Correspondence
Address: |
Trexel Bushnell Giangiorgi
Blackstone & Marr
105 West Adams Street
Chicago
IL
60603
US
|
Family ID: |
19927760 |
Appl. No.: |
10/203194 |
Filed: |
December 17, 2002 |
PCT Filed: |
February 28, 2001 |
PCT NO: |
PCT/NZ01/00028 |
Current U.S.
Class: |
62/155 ;
62/278 |
Current CPC
Class: |
F25D 17/062 20130101;
F25D 21/04 20130101; F25D 2400/04 20130101; F25B 2600/2511
20130101; F25D 2317/0682 20130101; F25D 11/022 20130101 |
Class at
Publication: |
62/155 ;
62/278 |
International
Class: |
F25D 021/06; F25B
047/00 |
Foreign Application Data
Date |
Code |
Application Number |
Feb 28, 2000 |
NZ |
503106 |
Claims
1. A refrigerator having a fresh food compartment adapted for
maintaining the contents thereof at a temperature above freezing, a
vapour compression refrigerator system, air circulation means for
causing a circulating airflow between said compartment and the
evaporator of said refrigerator system, and a controller for
controlling said air circulation means and said refrigerator
system, characterised in that in a refrigeration mode with said
refrigeration system and air circulation means active, said
evaporator operates with a surface temperature within 10.degree. C.
of the temperature desired in the said fresh food compartment and a
supply of air is maintained over said evaporator and into said
fresh food compartment, and in a defrost mode said controller
deactivates said vapour compression refrigeration system, or
operates it without significant heat extraction at said evaporator,
and activates said air circulation means to circulate air above
0.degree. C. over said evaporator, and there is no other means of
heating said evaporator.
2. A refrigerator as claimed as claim 1 wherein said refrigerator
includes only said fresh food compartment.
3. A refrigerator as claimed in claim 1 including a frozen food
compartment and a separate vapour compression refrigeration system
for each said compartment, the evaporator of said vapour
compression refrigeration system of said frozen food compartment
operating at a much lower temperature than the evaporator of said
vapour compression system for said fresh food compartment.
4. A refrigerator as claimed in claim 1 including a frozen food
compartment, said vapour compression system including said
evaporator for said fresh food compartment and a second evaporator
adapted to operate at a lower temperature for cooling the frozen
food compartment.
Description
BACKGROUND TO THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to refrigerators and in
particular to refrigerators having only a fresh food compartment or
at least having a fresh food compartment and an associated
evaporator dedicated to cooling the fresh food compartment.
[0003] 2. Summary of Prior Art
[0004] Most domestic refrigerators operate using a vapour
compression refrigeration system. In this system the refrigerant
passes in turn from a compressor to a condenser, through an
expansion device, through an evaporator and back to the compressor.
Evaporation of the refrigerant in the evaporator draws heat from
the surroundings of the evaporator. In early refrigerators (which
may be referred to as ice box refrigerators) an evaporator was
incorporated directly within the refrigeration compartment as the
wall of an ice box, and cooling of fresh food compartment
(surrounding the ice box) occurred by natural convection. More
recently cooling has been achieved by forcing the flow of air
across surfaces of the evaporator to cool the air and passing this
cooled air into the refrigerated space. In each case the vapour
compression refrigeration system has been operated such that the
surface of the evaporator is held at a very low temperature, for
example -18.degree. C., some 25.degree. C. lower than the desired
temperature of the produce compartment. In the latter form this
allows airflow to be utilised both in cooling the fresh food and
frozen food compartments.
[0005] Operating a refrigeration system with the surface of the
evaporator at such low temperatures results in a rapid accumulation
of frost on the evaporator from the passing airflow. This requires
periodic defrosting by the user, or automatic heater assisted
defrosting by the refrigeration device. In the case of a forced air
evaporator, which generally has a compact arrangement of
refrigerant tubing and cooling fins, removal of frost either takes
considerable time, leaving the refrigerated compartments uncooled
for considerable periods, or requires the inclusion of an auxiliary
defrost heating or element in the evaporator structure, and
associated wiring and controls.
SUMMARY OF THE INVENTION
[0006] It is an object of the present invention to provide a
refrigerator which at least goes some way towards overcoming the
above disadvantages or which will at least provide the public with
a useful choice.
[0007] Accordingly the present invention consists in a refrigerator
having a fresh food compartment adapted for maintaining the
contents thereof at a temperature above freezing and a vapour
compression refrigerator system, characterised in that in said
vapour compression refrigeration system in one mode an evaporator
is operated at a temperature within 10.degree. C. of the
temperature desired in said fresh food compartment and a supply of
air is maintained over said evaporator and into said fresh food
compartment, and in a second, defrost, mode said vapour compression
refrigeration system is stopped or allowed to operate without
significant heat extraction at said evaporator and a supply of air
above 0.degree. C. is passed over said evaporator.
BRIEF DESCRIPTION OF THE DRAWINGS
[0008] FIG. 1 is a side view in partial cutaway of a refrigerator
according to a first embodiment of the present invention,
[0009] FIG. 2 is a schematic representation of the refrigeration
system according to the first embodiment of the present
invention,
[0010] FIG. 3 is a side view in partial cutaway of a
refrigerator/freezer including a refrigeration system according to
a second or third embodiment of the present invention,
[0011] FIG. 4 is a schematic representation of the refrigeration
system according to the second embodiment of the present invention,
and
[0012] FIG. 5 is a schematic representation of the refrigeration
system according to the third embodiment of the present
invention.
DETAILED DESCRIPTION
[0013] In the present invention the refrigeration system at least
of the produce or fresh food compartment is characterised in that
the operating temperature of the evaporator of the vapour
compression refrigeration system is not overly cold as has been the
case in prior art systems. In particular the evaporator is
preferably operated at a temperature within 10.degree. C. of the
temperature desired in the produce compartment. Generally the
temperature desired in the produce compartment will range between
4.degree. C. and 7.degree. C. Consequently the temperature of the
evaporator may in fact (if the temperature difference is say
6.degree. C.) be above freezing.
[0014] With the evaporator operating at a temperature of 0.degree.
C. or just below 0.degree. C., say -5.degree. C. to 0.degree. C.,
the amount of condensation that freezes on the evaporator (frost)
is dramatically less than where the evaporator operates at
-18.degree. C., and the amount of sub cooling of that frost (the
difference between the temperature of the frost and its freezing
temperature) is also greatly reduced. Furthermore the evaporator
itself, and its components such as refrigerant tubing and fins, is
at this higher evaporator temperature.
[0015] In general operation of a refrigerator there are long
periods when the heat load on a refrigeration space (the
combination of heat migrating through the refrigerator walls, heat
introduced by new produce placed within the refrigeration
compartment, and heat entering the refrigerator while the door is
open) is low. In these periods the refrigeration system generally
cycles on and off to maintain the temperature within the
refrigerator within a specified range. This may for example in a
simplest form comprise an "on" temperature, being the upper limit
of the temperature range and an "off" temperature being the lower
limit of the temperature range. In refrigeration systems where the
evaporator is maintained at a very low temperature (for efficiency
of operation of the refrigeration system, or because the evaporator
is also required to cool the air sufficiently to cool the freezing
compartment which is at approximately -18.degree. C. (some
25.degree. C. less than desired temperature in the produce
compartment)), the evaporator still experiences a significant frost
build up and this frost is cooled to a very low temperature.
Consequently during the "off" period of the compressor operation
the built up frost does not usually rise to its melting temperature
without the assistance of a defrosting heater. The process of
defrosting is further hindered by the significant thermal mass of
the evaporator at -18.degree. C. absorbing substantial amounts of
the heat which could otherwise be utilised in melting the ice
frozen onto the evaporator surfaces.
[0016] With the evaporator of the present invention operating at a
temperature only slightly below freezing, the frost that forms is
not significantly sub cooled and quickly rises to the melting
temperature and drips off the evaporator. Furthermore, the
evaporator, being maintained much closer to the melting temperature
of the frost, does not significantly hinder defrosting.
[0017] In the invention this is further assisted by operating the
fan to continue to circulate air from the produce compartment over
the evaporator during the defrost cycle. The air from the produce
compartment is marginally above freezing and consequently will lose
heat to the frost on the evaporator, at once cooling the air of the
produce compartment and defrosting the evaporator.
[0018] A further advantage of the present invention is the
reduction in frost formation on the evaporator reduces the
dehumidifying effect that the evaporator has on the refrigerator
air flow.
[0019] Particular embodiments of the invention are described now
with reference to FIGS. 1-5.
[0020] Referring to FIG. 1 a refrigerator has a cabinet 1 and a
door 2 enclosing the cabinet 1. This is a single temperature
refrigerator, having only a produce compartment 3. A compressor 4
is mounted on a compressor tray 5 in a compressor enclosure 6 at
the lower back portion of the refrigerator cabinet 1. An evaporator
7 is mounted above a condensate collection guide 8. The condensate
collection guide 8 emits collected condensate onto a evaporation
tray 9 mounted on the top of the compressor 4. A fan 10 draws air
flow over the evaporator 7, and expels it into a vertically
extending distribution duct 11 rearward of the produce compartment
3. The distribution duct 11 has a series of air flow openings 12
into the produce compartment 3. An opening 13 is provided at a
lower part of the produce compartment for air intake to the
evaporator chamber. Thus when air is circulated by the fan 10 it
passes into the evaporator chamber as indicated by arrow 14 across
the evaporator as indicated by arrow 15 out past the fan as
indicated by arrow 16 and up through the distribution duct as
indicated by arrows 18 to exit into the produce compartments base
as indicated by arrows 17.
[0021] Referring then to FIG. 2 this represents the refrigeration
system incorporated in the refrigerator of FIG. 1 in a diagrammatic
form. The refrigeration system comprises a compressor 4, a
condenser 21, a flow control valve 22 and evaporator 7 in series
connection. These components are all well known in the art. They
are connected by connecting tubes 23, 24, 25 and 26, through which
the gas or liquid refrigerant travels as indicated by arrows 20.
The refrigeration system is run in the conventional manner except
that the system is configured such that the evaporator 7 is run as
previously referred to at a temperature which is at only 0.degree.
C. or just below.
[0022] The evaporator operating temperature requires greater
evaporator operating effectiveness. A larger evaporator surface
and/or higher air flow rates over the evaporator surface are two
ways to achieve the higher evaporation temperature in accordance
with the present invention. The lower heat transfer to the moving
air (due to the reduced temperature difference) per unit area of
evaporator surface or per unit volume for air flow than if the
evaporator operated at say -18.degree. C., is compensated by
greater heat transfer surface and/or volume flow rate. Evaporator
operating effectiveness may also be increased (where not already
done) by providing boundary layer interrupters on the heat transfer
surface.
[0023] Air is thus supplied by the fan 10 through the duct 11 at
the back of the refrigerator between the baffle 19 and the rear
face of the cabinet 1 to reach the produce compartment 3.
[0024] Referring now to FIGS. 3-5 the present invention may also be
incorporated into refrigerator/freezer combinations, such as
depicted in FIG. 3 wherein a cabinet 29 has a freezer compartment
30 and a produce compartment 31 separated by a intermediary wall 32
with a door 33 and 34 to each of the compartments 30 and 31
respectively. In this embodiment, for example, each of the freezer
and refrigerator compartments include a baffle 35, 36 respectively
at the rear thereof to form respective ducts between the baffles
and the rear wall 37 of the cabinet 29. An evaporator enclosure 38
meets the baffle 36 to form an enclosure for the evaporator. An
evaporator is separately provided in each of the two evaporator
enclosures. Each of the evaporators supplies only its respective
compartment with cooled or chilled air, and each has a
corresponding and independently driven fan. The produce compartment
evaporator 40 runs as indicated above at a temperature only just
below 0.degree. C. The freezer evaporator 39 however runs at a
temperature which is much lower, for example -18.degree. C. Thus
the air supplied to the produce compartment 31 by the produce
compartment fan 41 is at a temperature suitable for the produce
compartment, while the air supplied by the freezer compartment fan
42 to the freezer compartment 30 is supplied at a temperature
suitable for the freezer compartment. This air is circulated by the
respective fans 41 or 42 as indicated by the arrows 43 and, 44
respectively. The produce compartment air flows through respective
openings 45 in the baffle 36. The circulating air for the freezer
compartment flows through openings 46 and the freezer compartment
baffle 35.
[0025] Supply of liquid refrigerant to the respective evaporators
39 and 40 are by a range of alternatives.
[0026] In a first alternative, as depicted in FIG. 4, each of the
evaporators are supplied by an entirely independent refrigeration
system. Each refrigeration system has a respective compressor,
condenser, flow control valve and evaporator. In FIG. 4 this is
indicated by separate refrigeration circuits. Evaporator 39 of the
freezer compartment 30 includes a first compressor 50, first
condenser 51 which extracts heat 52, first flow control valve or
capillary 53 and associated connecting conduits. A second
refrigeration system for the produce compartment evaporator 40
includes a second compressor 55, a second condenser 56 extracting
heat 57, a second flow control valve 58 and associated connecting
conduit. The two refrigeration systems are essentially run
independently with the produce compartment system being run
entirely as described earlier. This arrangement allows for each of
the systems to be ideally tuned to its respective compartment and
may be particularly suitable with variable speed compressors where
the compressor capacity can be made to accurately match the
required heat pump capacity at any given time.
[0027] Alternatively an arrangement, such as that depicted in FIG.
5, could be adopted where both refrigeration systems include common
components, in particular a common compressor 60 and condenser 61.
One possible embodiment is depicted in FIG. 5 in which a selection
valve 62 selectively incorporates either the freezer compartment
evaporator or the produce compartment evaporator into the
refrigeration system. In that case the flow control valves 63 or 64
for each of the respective evaporators 39 or 40 may be provided
individually for each of the evaporator parts of the circuit or may
be provided as shown such that the flow control valve for
evaporator 39 is actually a combination of valves 63 and 64, while
for evaporator 40 is only the single flow control valve 64. It is
considered that, for this embodiment, to allow effective control of
the refrigeration system the compressor 60 would be required to be
of variable capacity, for example, a linear compressor operating at
varying stroke or frequency. The return flow from the suction side
of the evaporators 39 or 40 combine back into the main circuit at
junction 65. Junction 65 may include a further selection valve 62
operated in unison with valve 62, if desired, to ensure that
continuing suction is not provided to the evaporator not connected
into the main refrigeration circuit.
* * * * *