[0001] The present application and the resultant patent relate generally to refrigeration
systems and more particularly relate to a carbon dioxide based auxiliary cooling system
for a refrigeration system that may be free of the use of hydrofluorocarbons and the
like.
[0002] Cascade refrigeration systems generally include a first side cooling cycle, or a
high side cycle, and a second side cooling cycle, or a low side cooling cycle. The
two cooling cycles interface through a common heat exchanger,
i.e., a cascade evaporator-condenser. The cascade refrigeration system may provide cooling
at very low temperatures in a highly efficient manner.
[0003] Current refrigeration trends promote the use of carbon dioxide and other types of
natural refrigerants as opposed to conventional hydrofluorocarbon based refrigerants.
Unlike hydrofluorocarbons, however, carbon dioxide based systems may lose refrigerant
during power outages. In the case of a power outage, the carbon dioxide based system
may start gaining heat such that the refrigerant pressure may rise and exceed the
design pressure of the overall refrigeration system. The refrigeration system generally
must be vented to the atmosphere in such a situation.
[0004] In order to avoid venting the refrigerant, carbon dioxide based refrigeration systems
may include a backup condensing unit with an independent power source to keep the
carbon dioxide cool. These known backup devices, however, generally use hydrofluorocarbon
based refrigerants such that the refrigeration system as a whole cannot be considered
truly "green" or hydrofluorocarbon free.
[0005] There is thus a desire for a refrigeration system such as cascade refrigeration systems
that provide auxiliary cooling without the use of hydrofluorocarbons. Such an auxiliary
cooling system would provide efficient cooling in a truly hydrofluorocarbon free design.
[0006] The present application and the resultant patent thus provide a cascade refrigeration
system. The cascade refrigeration system may include a first side cycle, a second
side cycle with a second side cycle carbon dioxide refrigerant, and an auxiliary cooling
system to cool the second side cycle carbon dioxide refrigerant in the event of a
power outage. The auxiliary cooling system may include an auxiliary carbon dioxide
refrigerant.
[0007] The present application and the resultant patent further provide a method of providing
auxiliary cooling in a refrigeration system. The method may include the steps of flowing
a natural refrigerant through a first side cycle, flowing a carbon dioxide refrigerant
through a second side cycle, providing an auxiliary cooling system to cool the flow
of the carbon dioxide refrigerant in the case of a power loss, and flowing an auxiliary
carbon dioxide refrigerant through the auxiliary cooling system.
[0008] The present application and the resulting patent further provide a carbon dioxide
based refrigeration system. The carbon dioxide based refrigeration system may include
a receiver, a carbon dioxide refrigerant, and an auxiliary cooling system in communication
with the receiver to cool the carbon dioxide refrigerant in the event of a power outage.
The auxiliary cooling system may include an auxiliary carbon dioxide refrigerant.
[0009] These and other features and improvements of the present application and the resultant
patent will become apparent to one of ordinary skill in the art upon review of the
following detailed description when taken in conjunction with the several drawings,
which illustrate embodiments of the invention by way of example only, and the appended
claims
Fig. 1 is a schematic diagram of a known cascade refrigeration system with a high
side cycle and a low side cycle.
Fig. 2 is a schematic diagram of a cascade refrigeration system with a carbon dioxide
base auxiliary cooling system as may be described herein.
Fig. 3 is a schematic diagram of an alternative embodiment of a carbon dioxide based
auxiliary cooling system as may be described herein.
[0010] Referring now to the drawings, in which like numerals refer to like elements throughout
the several views, Fig. 1 shows an example of a cascade refrigeration system 100.
The cascade refrigeration system 100 may be used to cool any type of enclosure for
use in, for example, supermarkets, cold storage, and the like. The cascade refrigeration
system 100 also may be applicable to heating, ventilation, and air conditioning and/or
different types of industrial applications. The overall cascade refrigeration system
100 may have any suitable size or capacity.
[0011] Generally described, the cascade refrigeration system 100 may include a first or
a high side cycle 110 and a second or a low side cycle 120. The high side cycle 110
may include a high side compressor 130, a high side oil separator 140, a high side
condenser 150, a high side receiver 160, and a high side expansion device 170. The
high side cycle 110 also may include a suction/liquid heat exchanger 180 and a suction
accumulator 190. The high side cycle 110 may include a flow of a natural refrigerant
200. The natural refrigerant 200 may include a flow of ammonia, a flow of hydrocarbons,
and the like. Other components and other configurations may be used herein.
[0012] The low side cycle 120 similarly may include a low side compressor 210, a low side
oil separator 220, a low side receiver 230, a low side expansion device 240, and one
or more low side evaporators 250. The low side cycle 120 may include a medium temperature
loop 260 with a pump 270 and a number of flow valves 280 as well as a low temperature
loop 290. An accumulator 300 also may be used therein. The low side cycle 120 may
include a flow of a carbon dioxide based refrigerant 310 and the like. Other components
and other configurations may be used herein.
[0013] The two cycles 110, 120 may interface through a cascade evaporator/condenser 320.
The respective flows of the refrigerants 200, 310 may exchange heat via the cascade
evaporator/condenser 320. The cascade evaporator/condenser 320 may have any suitable
size or capacity. Other components and other configurations may be used herein.
[0014] The natural refrigerant 200 may be compressed by the high side compressor 130 and
condensed in the high side condenser 150. The refrigerant 200 may be stored in the
high side receiver 160 and may be withdrawn as needed to satisfy the load on the cascade
evaporator/condenser 320. The refrigerant 200 then may pass through the high side
expansion device 170 and returns to the high side compressor 130. The suction/liquid
heat exchanger 180 may be used to sub-cool the refrigerant 200 before entry into the
cascade evaporator/condenser 320.
[0015] The low side cycle 120 may be similar. The carbon dioxide based refrigerant 310 may
be compressed by the low side compressor 210 and then pass through the cascade evaporator/condenser
320. The refrigerant 310 may be stored within the low side receiver 230 and withdrawn
as needed. The refrigerant 310 may pass through one or more low side expansion devices
240 and one or more low side evaporators 250. The low side cycle 120 may be separated
into the low temperature loop 290 and the medium temperature loop 260.
[0016] The cascade refrigeration system 100 also may include an auxiliary cooling system
330. The cooling auxiliary system 330 may be used to cool the flow of the carbon dioxide
refrigerant 310 via an interface with the low side receiver 230 or elsewhere. The
auxiliary cooling system 330 may include an auxiliary compressor 340, an auxiliary
condenser 350, and an auxiliary expansion device 360. The cooling auxiliary system
330 may include a generator 370 or other type of independent power supply. The auxiliary
cooling system 330 may interface with the low side cycle 120 via an auxiliary condenser/evaporator
380. Known auxiliary cooling systems 330 generally use a hydrofluorocarbon based refrigerant
390 such as R404A or R407A. Other components and other configurations may be used
herein.
[0017] Fig. 2 shows a cascade refrigeration system 400 as may be described herein. The cascade
refrigeration system 400 may include the same or a similar high side cycle 110 and
low side cycle 120. The two cycles may interface via the cascade evaporator/condenser
320 and the like. As described above, the low side cycle 120 includes the flow of
the carbon dioxide based refrigerant 310.
[0018] The cascade refrigeration system 400 also may include a carbon dioxide based auxiliary
cooling system 410. The carbon dioxide auxiliary cooling system 410 may include an
auxiliary compressor 420, an auxiliary condenser 430, and an auxiliary expansion device
440. The carbon dioxide auxiliary cooling system 410 may include an auxiliary generator
450 or other type of independent power supply. The carbon dioxide auxiliary cooling
system 410 may interface with the low side cycle 120 via an auxiliary condenser/evaporator
460 or other type of heat exchange device. The carbon dioxide auxiliary cooling system
410 includes a flow of a carbon dioxide based refrigerant 470 therein. Other types
of natural refrigerants also may be used herein. Other components and other configurations
may be used herein.
[0019] In the event of the loss of power, the carbon dioxide auxiliary cooling system 410
may be used to cool the flow of the carbon dioxide refrigerant 310 in the low side
cycle 120 via the carbon dioxide refrigerant 470 circulating therein and interfacing
at the auxiliary condenser/evaporator 460. The cascade refrigeration system 400 thus
is truly a hydrofluorocarbon free system. The carbon dioxide based auxiliary cooling
system 410 may provide a faster overall response time in a proactive method of cooling
the flow of carbon dioxide refrigerant 310 without venting. Multiple carbon dioxide
auxiliary cooling systems 410 may be used herein.
[0020] Fig. 3 shows an alternative embodiment of a carbon dioxide auxiliary cooling system
500 as may be described herein. The carbon dioxide auxiliary cooling system 500 may
include an auxiliary compressor 510, an auxiliary gas cooler 520 or condenser, and
an auxiliary expansion device 530. The carbon dioxide auxiliary cooling system 500
also may include an auxiliary generator or other type of independent power source.
The carbon dioxide auxiliary cooling system 500 also includes a flow of a carbon dioxide
based refrigerant 540 therein. Other components and other configurations may be used
herein.
[0021] The carbon dioxide auxiliary system 500 may tie directly into the low side cycle
120 via the low side cycle receiver 230 for heat exchange therewith. The carbon dioxide
auxiliary system 500 thus avoids the need for an auxiliary condenser/evaporator and/or
pump in a truly a hydrofluorocarbon free system. The carbon dioxide based auxiliary
system 500 also may provide a faster overall response time in a proactive method of
cooling the flow of carbon dioxide refrigerant 310 without venting.
[0022] Although the carbon dioxide based auxiliary cooling systems have been shown in the
context of a cascade refrigeration system, the carbon dioxide based auxiliary cooling
systems may be used in any type of carbon dioxide refrigeration system. Specifically,
any type of carbon dioxide refrigeration system using a large receiver tank and the
like.
[0023] It should be apparent that the foregoing relates only to certain embodiments of the
present application and the resultant patent. Numerous changes and modifications may
be made herein by one of ordinary skill in the art without departing from the general
spirit and scope of the invention as defined by the following claims and the equivalents
thereof.
1. A cascade refrigeration system (100), comprising:
a first side cycle (110);
a second side cycle (120);
the second side cycle comprising a second side cycle carbon dioxide refrigerant (310);
and
an auxiliary cooling system (330) to cool the second side cycle carbon dioxide refrigerant
in the event of a power outage;
the auxiliary cooling system comprising an auxiliary carbon dioxide refrigerant.
2. The cascade refrigeration system (100) of claim 1, wherein the auxiliary cooling system
(330) comprises an auxiliary compressor (340) and an auxiliary expansion valve (360);
and/or
an auxiliary condenser (310) or an auxiliary gas cooler; and/or
an auxiliary condenser/evaporator (380); and/or
an auxiliary generator (370).
3. The cascade refrigeration system (100) of claim 1 or 2, wherein the second side cycle
(120) comprises a second side cycle receiver (230) and wherein the auxiliary cooling
system (330) is in communication with the second side cycle receiver.
4. The cascade refrigeration system (100) of claim 1, 2 or 3, wherein the first side
cycle (110) and the second side cycle (120) interface via a cascade evaporator/condenser
(320).
5. The cascade refrigeration system (100) of any preceding claim, wherein the first side
cycle (110) comprises a flow of an ammonia or a hydrocarbon refrigerant (200).
6. The cascade refrigeration system (100) of any preceding claim, wherein the first side
cycle (110) comprises a suction/liquid heat exchanger (180).
7. The cascade refrigeration system (100) of any preceding claim, wherein the first side
cycle (110) comprises a first side compressor (130), a first side condenser (150),
and a first side expansion device (170).
8. The cascade refrigeration system (100) of any preceding claim, wherein the second
side cycle (120) comprises a second side compressor (210), a second side expansion
device (240), and a second side evaporator (250).
9. The cascade refrigeration system (100) of any preceding claim, wherein the second
side cycle (120) comprises a low temperature loop (290) and a medium temperature loop
(260).
10. The cascade refrigeration system (100) of any preceding claim, further comprising
a plurality of auxiliary cooling systems (330).
11. A method of providing auxiliary cooling in a refrigeration system, comprising:
flowing a natural refrigerant (200) through a first side cycle (110);
flowing a carbon dioxide refrigerant (310) through a second side cycle (120);
providing an auxiliary cooling system (330) to cool the flow of the carbon dioxide
refrigerant in the case of a power loss; and
flowing an auxiliary carbon dioxide refrigerant (470) through the auxiliary cooling
system.
12. A carbon dioxide based refrigeration system, comprising:
a receiver (230);
a carbon dioxide refrigerant (310); and
an auxiliary cooling system (410) in communication with the receiver to cool the carbon
dioxide refrigerant in the event of a power outage;
the auxiliary cooling system comprising an auxiliary carbon dioxide refrigerant (470).
13. The carbon dioxide refrigeration system of claim 12, wherein the auxiliary cooling
system comprises an auxiliary condenser (430) or an auxiliary gas cooler; and/or
an auxiliary generator (450).
14. The carbon dioxide refrigeration system of claim 12 or 13, wherein the carbon dioxide
refrigeration system comprises a cascade refrigeration system (400).