Note: Descriptions are shown in the official language in which they were submitted.
CA 02436367 2003-08-04
- 1 -
ENERGY STORAGE WITH REFRIGERAT30N SYSTEMS AND METHOD
TECHNICAL FIELD
The present invention generally relates to
refrigeration systems and, more particularly, to energy
storage with refrigeration systems to reduce electricity
consumption costs.
BACKGROUND ART
With the constant evol~ztion of technology, the
demand for electricity has greatly increased in
industrialized countries over the last decades. A major
portion of households and offices of industrialized
countries are now equipped with electrical appliances that
did not exist a few decades ago. Computers, air-
conditioning units, microwave ovens and home entertainment
systems are a few of these appliance~> that are widely used
in the industrialized countries.
In these industrialized countries, a major
portion of the industries have adopted a Monday-to-Friday
daytime work schedule. As a consequence, a generally
corresponding part of the population has similar hours of
activity and this has created peak-hour periods for energy
demand. Accordingly, electricity consumption is higher
during these hours of activity. In typical supply-and-
demand logic following this peaked daytime demand, power
companies have adopted two-way electricity i~ariffs, with
cheaper rates at night.
Another field that generally involves greater
daytime electricity consumption is refrigeration and air-
conditioning of commercial establishments. In the warmer
months of a year, refrigeration systerr~s and air. -conditioning
systems operate at full capacity during the daytime hours.
During these hours, sunlight causes the outside temperature
to peak. Accordingly, refrigerant head pressure in
compression stages of such systems must be increased so as
' CA 02436367 2003-08-04
- 2 -
to enable heat exchange in a condensation stage between the
refrigerant and outside air. Therefore, air-conditioning
units and refrigeration systems operate at hic;her capacity
during these warmer hours. For instance, referring to
Fig. lA, a graph A demonstrates the head pressure of
refrigerant at the condensation stage throughout a summer
day for a refrigeration cycle. As described previously, the
head pressure peaks during the warmer part of the day.
Electricity consumption is directly proportional to the head
pressure. Referring to Fig. 1B, a graph B is similar to the
graph A of Fig. lA, but represents fall/spring days.
Although the head pressure is relatively lower, the graph B
also displays a peaked daytime head pressure.
Accordingly, energy-storage systems have been
provided to be used with air-conditioning systems in order
to store energy at night when the electricity rates are low,
to then use the stored energy during the warmer hours of the
day, to avoid daytime rates. For instance, in warmer
countries, energy-storage systems having complete
refrigeration cycles have been specifically designed to
store energy at night in the form of a solid. The solid
(e. g., ice) is then used to condense an air-conditioning
refrigerant of an adjacent air-conditioning system.
These energy-storage systems comprise compres
sion, condensation, expansion and evaporation stages, with
the evaporation stage being used to coo7_ a liquid
(e. g., water) for solidification. Such er~ergy-storage
refrigeration systems are valuable investments in warmer
countries, as air-conditioning systems are often used
throughout the year. In cooler countries, energy-storage
systems to be used with air-conditioning systems have longer
return-on-investment periods, as they are used only for a
few warm months during the year. It: would, however, be
desirable to lower the equipment costs of this technology to
render same a better investment in cooler countries.
CA 02436367 2003-08-04
- 3 -
S'UNIMARY OF INVENTION
Therefore, it is a feature of the present
invention to provide energy storage to be used in
combination with existing commercial refrigeration systems.
It is a further feature of the present invention
to provide a method for storing energy with existing
refrigeration systems.
It is a still further feature of the present
invention to provide a combination of refrigeration system
and air-conditioning system cooperating in storing energy.
According to the above feature of the present
invention, and from a broad aspect thereof, the present
invention provides a refrigeration system of the type having
a main refrigeration circuit, wherein a refrigerant goes
through at least a compression stage having at least one
compressor, wherein said refrigerant is compressed to a
high-pressure gas state to then reach a condensation stage,
wherein said refrigerant in said high-pressure gas state is
condensed at least partially to a high-pressure liquid state
to then reach an expansion stage, wherein said refrigerant
in said high-pressure liquid state is expanded to a first
low-pressure liquid state ~to then reach an evaporation
stage, wherein said refrigerant in said first low-pressure
liquid state is evaporated at least partially to a first
low-pressure gas state by absorbing heat, to then return to
said compression stage, said refrigeration system comprising
an energy-storage stage in parallel to the evaporation stage
between the expansion stage and the compression stage, the
energy-storage stage having a container in which a medium is
disposed in heat exchange relationship with said refrigerant
such that said refrigerant absorbs heat from said medium
during a period of a day where the air least one compressor
is less in demand, said medium being used in heat exchange
thereafter to cause condensation of an air-conditioning
refrigerant.
CA 02436367 2003-08-04
- 4 -
According to a further feature of the present
invention, there is provided a comb-ination of a
refrigeration system and an air-conditioning system with
heat storage therebetween, comprising: a refrigeration
system having a refrigeration circuit, wherein a first
refrigerant goes through at least a compression stage having
at least one compressor, wherein said first refrigerant is
compressed to a high-pressure gas state to then reach a
condensation stage, wherein said first refrigerant in said
l0 high-pressure gas state is condensed at least partially to a
high-pressure liquid state to then reach an expansion stage,
wherein said first refrigerant in said high-pressure liquid
state is expanded to a first low-pressure liquid state to
then reach an evaporation stage, wherein said first
refrigerant in said first low-pressure liquid state is
evaporated at least partially to a first low-pressure gas
state by absorbing heat, to then return to said compression
stage; an air-conditioning system having a main air-
conditioning circuit, wherein a second refrigerant goes
through at least a compression stage, wherein said second
refrigerant is compressed to a high-pressure gas state to
then reach a condensation stage, wherein said second
refrigerant in said high-pressure gas state is condensed at
least partially to a high-pressure liquid state to then
reach an expansion stage, wherein said. second refrigerant in
said high-pressure liquid state is expanded to a first low-
pressure liquid state to then reach an evaporation stage,
wherein said second refrigerant in said first low-pressure
liquid state is evaporated at least partially to a first
low-pressure gas state by absorbing heat, to then return to
said compression stage; and an energy-storage stage having a
container retaining a medium, the medium being in heat-
exchange relationship with said first refrigerant in the
evaporation stage of the refrigeration system such that said
first refrigerant absorbs heat from said medium during a
period of a day where the at least one compressor is less in
CA 02436367 2003-08-04
- 5 -
demand, said medium being in heat-e:~change relation with
said second refrigerant of the air-conditioning system to
absorb heat from said first refrigerant. to cause
condensation in the air-conditioning s;rstem.
S According to a still further feature of the
present invention, there is provided a method for storing
energy from a refrigeration system having a refrigerant
undergoing compression, condensation, expansion and
evaporation stages of a refrigeration cycle, comprising the
l0 steps of: i) providing a container having a medium in a
first state and heat exchange means for heat exchange with
said medium; ii) directing a portion of said refrigerant
from the expansion stage to the heat exchange means to
absorb heat from said medium during a period of a day where
1S the compression is less in demand, such that said medium in
said container is in a second state wherein said medium is
cooled with respect to the first st:.ate; and iii) causing
condensation of an air-conditioning refrigerant by heat
exchange with said medium in said second state such that
24 said medium generally returns to said first state.
BRIEF DESCRIPTION OF DRAWINGS
A preferred embodiment of the present invention
will now be described with reference to the accompanying
drawings in which:
2S FIG.. lA is a graph illustrating a refrigerant
head pressure as a function of the time for a summer day for
a refrigeration system, in accordance with the prior art;
FIG. 1B is a graph illustrating a refrigerant
head pressure as a function of the time for a fall/spring
30 day for a refrigeration system, in accordance with the
prior art;
FIG. 2 is a block diagram i7_lustrating a
refrigeration system cooperating with an air-conditioning
system for energy storage in accordance with the present
3S invention; and
CA 02436367 2003-08-04
- 6 -
FIG. 3 is a schematic view of an energy-storing
unit in accordance with the present invention.
DESCRIPTION OF PREFERRED EMBODIMENTS
Referring to the drawings and, more particularly
to Fig. 2, a refrigeration system in accordance with the
present invention is generally shown at Z0. The
refrigeration system 10 has a typical refrigeration cycle
having a compression stage 12, a condensation stage 14, an
expansion stage 16, and an evaporation stage 18. The stages
l0 12, 14, 16 and 18 are interconnected for fluid connection
therebetween, such that a refrigerant can be circulated
therebetween.
More precisely, refrigerant in a low-pressure
gas state is compressed in the compression stage 12.
Therefore, the refrigerant reaches the condensation stage 14
in a high-pressure gas state. In the condensation stage 14,
heat exchange is performed such that the high.-pressure gas
refrigerant releases energy by changing phases to a high-
pressure liquid state and by lowering temperature. This is
achieved by typically having rooftop condensers in which
outside air absorbs heat from the high-pressure gas
refrigerant. It is known that the change of phase absorbs
or releases a substantial amount of energy (latent heat) at
a constant temperature. Therefore, the compressor head
2S pressure, i.e., the refrigerant pressure downstream of the
compression stage 12, is a function of the temperature of
the heat exchange fluid, e.g., outside air, to enable
changes of phase.
A heat-reclaim loop 13 is shown in parallel to
the condensation stage 14. The heat-reclaim loop 13 is used
to recuperate heat rather than releasing the heat to the
atmosphere, as is the case with condensers of the
condensation stage 14. The heat reclaimed by the heat
reclaim loop 13 is typically used for heating the
ventilation air in the winter months and for
CA 02436367 2003-08-04
dehumidification of the ventilation air in the warmer
months.
In the expansion stage 16, expansion valves
reduce the pressure of the refrigerant. Therefore, high-
s pressure liquid from the condensation stage 14 goes through
the expansion stage 16 to have its pressure lowered.
Thereafter, the expanded refrigerant reaches the evaporation
stage 18, wherein the refrigerant will absorb heat through a
heat exchanger to cool air that. is used to cool
l0 refrigeration enclosures and display cases. The refrigerant
changes phases from liquid to gas to absorb heat from the
air that cools the refrigeration enclosures and display
cases. The refrigeration system 10 is not limited to uses
as heat absorber for refrigeration enclosures and display
15 cases. For instance, the refrigeration system 10 may be
used in arenas to create an ice surface.
It is pointed out that many additional
components may be added to the refrigeration system 10, the
latter being illustrated in Fig. 2 in a basic configuration.
20 As an example, the refrigeration system 10 may be provided
with defrost systems to remove solid build-up on the
evaporators of the evaporation stage. Also, reservoirs,
suction headers, and oil separators are well known in
refrigeration systems.
25 Moreover, the refrigeration system 10 can be of
various sizes. In the present invention, the refrigeration
system 10 preferably has commercia7_ capacities, e.g., a
plurality of compressors in the compression stage 12 and
evaporators in the evaporator stage 18. This will enable a
30 more profitable return on investment for the energy-storage
system, as will be described hereinafter.
In a preferred embodiment of the present
invention, the refrigeration system 10 is used in
combination with an air-conditioning evaporation stage 20.
35 The evaporation stage 20 has heat exchangers positioned in
ventilation ducts that absorb heat from ventilation air, as
CA 02436367 2003-08-04
-
known in the art. In the present invention, refrigerant in
suitable condition for the evaporation stage 20 is provided
by an energy-storage unit 30, as shown in Fig. 2. Referring
to Fig. 3; the energy-storage unit 30 is schematically
illustrated. The energy-storage unit 30 has a reservoir 32
containing an energy-storing medium 34. The reservoir 32 is
thermally insulated. A refrigeration heat exchanger 36 goes
through the reservoir 32 for heat exchange between the
refrigerant circulating in the heat exchanger- 36 and the
medium 34. Lines 38 and 39 are in fluid connection with the
reservoir 32. The line 39 will direct the medium 34 and
direct same to the evaporation stage 20, whereas the line 38
will return the medium 34 to the reservoir 32 thereafter.
The refrigeration heat exchanger 36 is supplied
with refrigerant from the refrigeration system 10: More
precisely, the refrigerant is conveyed from the expansion
stage 16. It is understood that the refrigerant being fed
to the heat exchanger 36 can be supplied directly from the
condensation stage 14, with an expansion valve 40 (included
in the present invention as part of the expansion stage 16)
being provided upstream of the heat exchanger 36 to enable
adequate expansion of the refrigerant as a function of the
energy-storing medium 34. Considering the pressure of the
medium 34, the refrigerant temperature supplied to the heat
exchanger 36 must preferably be below the solidification
temperature of the medium 34. The expansion, whether it be
via the expansion stage 16 or the valve 40 of the expansion
stage 16, must create these conditions. Refrigerant exiting
the heat exchanger 36 has absorbed heat from the medium 34
in the reservoir 32 , whereby refrigerant will change phases
by evaporating, and the medium 34, e.g., water or any other
suitable refrigerant, will be cooled and will possibly
solidify upon reaching freezing point.
Therefore, the energy-storage unit 30 will store
energy in the form of a cooled medium, using the
refrigeration system 10. It has been shown in Figs. lA and
CA 02436367 2003-08-04
_ g _
1B that the head pressure of refrigerant is lower at night,
and so is the electricity consumption. Accordingly, the
compressors of the compression stage 12 are not used to full
capacity at night. The heat exchanger 36 is to be cooled at
night to store energy in the form of the cooled medium 34,
when the electricity tariffs are low (e.g., 9:00 p.m. to
7:00 a.m.). The insulated reservoir 32 ensures that this
energy is not lost by the warming effect of the ambient air.
The air-conditioning loop, including the
evaporation stage 20 and the lines 38 and 39, on the other
hand, is used during the warmer hou-.rs of the day (e. g.,
7:00 a.m. to 9:00 p.m. ) , when the demand for cooled air and
the electricity tariffs are high.
In the evaporation stage 20, th.e medium 34
absorbs heat from ventilation air to cool the ventilation
air. A pump 42 ensures the circulation of refrigerant in
this closed loop. The highest electricity consumption in a
refrigeration cycle is that required to operate the
compressors. By storing energy at night, electricity
consumption is increased at night and lowered during the
day, as air-conditioning compressors will not be used,
thereby substantially reducing electricity costs. Moreover,
the use of the compressors of the compression. stage 12 is
optimized, as these compressors, which were for the most
part inoperative at night due to the cooler outdoor
temperature and the closing of, e.g., the supermarket (and
thus no opening of refrigeration cabinets) is now optimized
by the compression stage 12 being used at night to cool the
medium 34.
Therefore, by providing a reservoir 32 of
sufficient volume, enough medium 34 can be provided to
suppress any air-conditioning system. In such a case, the
above-described closed loop between the evaporation stage 20
and the energy-storage unit 30 would be sufficient to supply
the full air-conditioning load. However, the energy-storage
unit 30 is also contemplated as an auxiliary system to
CA 02436367 2003-08-04
- 10 -
provide additional capacity to a combination of
refrigeration system and air-conditioning system
(not shown) .
The energy-storage unit 30 can help reduce
equipment costs in addition to the energy savings. As
mentioned previously, if the energy--storage unit 30 has
sufficient volume, it can store enough energy for a day's
load of air-conditioning, whereby an air-conditioning system
having a full refrigeration cycle (e. g., the air-
l0 conditioning system 20) is not required.
The energy-storage unit 30 uses refrigerant that
has gone through the compression stage 12, whereby no
additional compressor is necessary andl thus equipment costs
are minimized. Therefore, the energy-storage unit 30 is
added to existing refrigeration systems (e.g., the
refrigeration system 10). Moreover, the use of the
compressors of the refrigeratian system is optimized, as the
typically unoccupied nights are now used for storing energy.
The medium 34 may be any given type of
refrigerant having adequate properties to store energy.
More specifically, the medium 34 must be able to change
phase at a temperature above that of the refrigerant of the
refrigeration system, whereby solid build-ups are
anticipated about the heat exchanger 36. Water, for
instance, changing phase at 0°C at atmospheric pressure, and
having an enthalpy of about 144 Btu.jlb, can be used as
medium 34. It is pointed out that the evaporator stage 20
need not be part of a loop with the e:n.ergy-storage unit 30.
For instance, if water is the medium 34, it may be rejected
after having gone through the evaporation stage 20, so as
not to warm up the rest of the medium 34 in the energy-
storage 34. In such a case, the reservoir 32 would simply
be refilled before' every night . Moreover, a reservoir (not
shown) may be provided downstream of the evaporation stage
20 so as to temporarily contain the medium 34 that has
absorbed heat. This reservoir would then be emptied into
CA 02436367 2003-08-04
- 11 -
the reservoir 32, when air conditioning is no longer
required (e. g., at the end of a day).
The heat reclaim 13 can have a loop that extends
to the ventilation ducts, with a heat exchanger positioned
downstream of the evaporation heat exchanger, to dehumidify
the cooled air.
It is within the ambit of the present invention
to cover any obvious modifications of the embodiments
described herein, provided such modifications fall within
the scope of the appended claims.
