Note: Descriptions are shown in the official language in which they were submitted.
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Ecological refrigeration unit cooled with outdoor air
Field of Invention
The invention relates to refrigeration units, and especially to energy effi-
cient refrigeration units.
Background
Refrigeration units, such as refrigerators, can significantly improve the
shelf life of perishable products. Nowadays, the refrigerator is a standard
equipment
in homes and, for example in Europe and North America, one is found in almost
every
home. In addition, there are refrigeration units in workplaces and
institutions, and
other private and public spaces where meals are served. Refrigeration units
are a very
significant group of appliances in terms of energy consumption, which is why
signifi-
cant energy savings can be achieved by improving their energy efficiency, both
on an
individual and societal level.
Brief Description
The unit according to the invention is characterized by what is stated in
the independent claims.
The energy consumption of a refrigeration unit can be decreased by uti-
lizing colder outdoor air to maintain the storage space of the refrigeration
unit at a
desired temperature. This can be achieved by circulating cold outdoor air in
an air
space between the interior space of the refrigeration unit and the insulation
of the
outer housing so that the interior space of the unit is cooled down. The
operation of
the unit can be intelligently controlled by means of temperature detecting
sensors,
such that the air circulation automatically starts and stops according to what
is most
appropriate for the refrigeration unit and the energy consumption thereof. In
regions
with a cool climate, significant energy savings can be achieved by utilizing
outdoor
air. For example, in all regions of Finland, the coldness can be utilized at
least during
6 months of the year and in the Northern Finland even longer. The winters are
cold
also in many geographical regions even further south, and there are also
regions, for
example in the mountains, where especially the nights are cold.
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The outdoor temperature is lowest during winters and nights when it is
both cold and dark. During the warmer seasons, when the outdoor air is too
warm
for cooling a refrigerator, there is on the other hand a lot of light, whereby
ecological
solar energy may be utilized for cooling the refrigerator.
At temperatures much below freezing, the refrigeration unit may operate
completely without external energy. Due to the energy required for heating,
the total
societal energy demand is at its highest at freezing temperatures, and in the
produc-
tion thereof there is therefore a need to use all kinds of production methods
(including
the less environmentally friendly ones). The peak in the energy consumption
can be
lowered if there is no electricity demand, or only a very small demand, for
refrigera-
tion units during freezing temperatures.
The refrigeration unit according to the invention may be used all over the
world at regions where the outdoor temperature drops below the temperature of
the
refrigerator for a considerable part of the year. It can be used also at
locations where
the nights are cold, even if the daytime temperatures would be high.
List of Figures
In the following, the invention is described in detail with reference to the
enclosed drawings, wherein:
Figure la and lb present an embodiment of a refrigeration unit according
to the present disclosure,
Figure 2 presents another embodiment of a refrigeration unit according
to the present disclosure, and
Figure 3 presents further another embodiment of a refrigeration unit ac-
cording to the present disclosure.
Detailed Description
This description describes an energy efficient refrigeration unit and a
method for controlling the same. The refrigeration unit comprises a storage
space
arranged within a thermally insulated outer housing for cold storage of
products, and
a refrigeration machinery for lowering the temperature of the storage space to
a
temperature range defined by a minimum temperature and a maximum temperature.
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The thermally insulated outer housing refers to an entity formed by the
thermally
insulated walls surrounding the storage space. The desired storage temperature
de-
pends on the intended use of the refrigeration unit. The refrigeration unit
may, for
example, be a refrigerator, or another storage space equipped with a
refrigeration
machinery, such as a wine storage or chiller unit. In the case of a
refrigerator, the
desired storage temperature range may be +2 C ¨ +6 C, for example. In order
to
improve the energy efficiency of the refrigeration unit, an air space is
arranged within
the outer housing between the storage space and the thermally insulated outer
hous-
ing.
The air space is a cavity or an air channel system that at least partially
surrounds the storage space. Figures la and lb present an embodiment of such a
refrigeration unit.
In Figure la, a simplified cross-section representation of the refrigeration
unit 10 is shown in a front view. Refrigeration unit 10 can be a refrigerator,
for ex-
ample. Figure lb shows the same refrigeration unit 10 as presented from the
side. In
Figures la and lb, a storage space 12 is arranged within the outer housing 11
com-
prising thermal insulation 11.1. In Figure lb, disclosing the side view, also
a refriger-
ation machinery 17 arranged to cool down the storage space is shown.
The storage space is surrounded by an air space 11.2. The air space 11.2
is situated between the storage space 12 and the thermal insulation 11.1 of
the outer
housing. The wall 12.1 between the air space 11.2 and the storage space 12 is
pref-
erably made of a material having high thermal conductivity, such as aluminum.
Thus,
it is ensured that heat can be efficiently transferred between the storage
space 12
and the air space 11.2. At the same time, because the thermal insulation 11.1
of the
housing 11 is between the air space 11.2 and the air outside the housing 11
(such as
indoor air), the air outside the housing 11 does not considerably heat the air
within
the air space 11.2. The wall between the storage space 12 and the air space
11.2 can
also be formed such that it functions as a heat sink. A sufficiently thick
wall can for
instance function as a cooling plate heat sink. Alternatively, or
additionally, the refrig-
eration unit may be equipped with separate heat sinks, such as cooling plates.
The
heat sinks may be cooled down, for example, during cold nights, whereby they
assist
in cooling the storage space 12 at other times of the day.
The refrigeration unit according to the present disclosure comprises an
inlet and outlet air pipe connected to the air space within the housing to
provide an
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air circulation path within the air space. In Figures la and lb, the inlet air
pipe 13 is
at the bottom part of the refrigeration unit 10 and the outlet air pipe 14 is
at the
upper part. The air flow of the air circulation path is in Figures la and lb
shown with
arrows. The cold or cool outdoor air is drawn into the inlet air pipe 13 and
proceeds
therefrom into the air space 11.2. In the air space 11.2, the cold or cool air
cools
down the storage space 12 via the wall 12.1 and proceeds therefrom warmed up
through the air space 11.2 into the outlet air pipe 14. From the outlet air
pipe 14 the
heated air is discharged to the outdoor air.
The refrigeration unit further comprises measuring means for measuring
the outdoor temperature, the temperatures of the air space arranged within the
hous-
ing and the storage space. The measuring means may be in the form of, e.g.,
tem-
perature sensors. There are preferably at least three sensors, such as shown
in figures
la and lb, for example. The first sensor 15.1 can be outside the building, or
in the
inlet air pipe 13 as close as possible to the outer wall, where it may detect
the tern-
perature of the outdoor air. A second sensor 15.2 can be in the air space of
the
refrigerating unit, where it detects the temperature of the air space 11.2. A
third
sensor 15.3 can be inside the refrigeration unit, where it detects the
temperature of
the interior space 12 of the refrigeration unit.
The refrigeration unit according to the present disclosure further corn-
prises air flow adjustment means arranged in connection with the inlet and/or
outlet
air pipe for adjusting the air circulation. These adjustment means may be
imple-
mented in several ways. They may be, for example, a shutter mechanism in the
form
of a valve or valves. One simple example of a shutter mechanism is a flap
operated
with an electric motor, whereby the flap can be set in two different positions
(closed
and open). In Figure la and lb, such flaps 16.1 and 16.2 functions as
adjustment
means.
The refrigeration unit further comprises control means adapted to control
the refrigeration machinery and the air flow adjustment means as a response to
the
measured temperatures. Outdoor air is circulated in the space between the
interior
space of the refrigeration unit and the insulated outer housing such that the
air cir-
culation of the space in between can be automatically adjusted based on the
outdoor
temperature, the temperature of the air space in the refrigeration unit and
the interior
temperature. The control means may be, for example, in the form of an
electrical
control unit. The control unit may comprise a calculation unit (such as a
processor,
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microcontroller or programmable logic) and a memory. A program that programs
the
calculation unit to control the refrigeration machinery and the air flow
control means
may be stored in the memory. The control unit may be programmed to receive
meas-
urement data from the measuring means and based thereon decide how the refrig-
5 eration machinery and the air flow is utilized in the cooling.
Alternatively, the refrig-
eration unit is cooled only by means of an air stream conducted from the
outside,
only by means of the refrigerator's own refrigeration machinery, or by a
combination
of these. If the interior temperature of the refrigeration unit decreases to
the lower
limit of a desired temperature range, the cooling of the refrigeration unit
will be
stopped completely until the cooling is calculated to be necessary again.
The refrigeration unit is intelligently controlled by means of temperature
sensors such that air is circulated when the cooling of the interior space
benefits from
air circulation. In general, air is circulated when the temperature of the
outdoor air is
lower than the temperature of the air space. The air circulation is stopped
when the
temperature of the outdoor air becomes so high that circulation of air no
longer facil-
itates cooling of the refrigeration unit. In one embodiment, the control means
of the
refrigeration unit are adapted to control the refrigeration machinery and the
adjust-
ment means for the air flow such that the temperature of the storage space is
pri-
marily cooled with the air flow. When the outdoor air is too warm to keep the
refrig-
eration unit at a desired temperature range, the refrigeration machinery is
used. The
refrigeration unit can also be adjusted to simultaneously use both the air
flow and the
refrigeration machinery. This is convenient for example when the refrigeration
unit
has just been loaded with warm food products and the temperature of the
storage
space of the refrigeration unit has increased above a maximum temperature of
the
desired temperature range. It is thus important to cool down the interior
space to the
desired temperature as quickly as possible.
When the temperature of the outdoor air becomes so high that the air
circulation does not provide an advantageous effect anymore, the air
circulation is
automatically stopped, and the air circulation openings are closed tightly. A
corn-
pletely sealed air space provides good thermal insulation, thereby improving
the ther-
mal economy of the refrigeration unit.
In a refrigerator, the desired minimum temperature of the storage space
is generally about +2 C, and it is important that the temperature does not
become
too low, thereby causing freezing. When the outdoor air is very cold, the
programmed
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refrigeration unit prevents the interior space from cooling down too much by
auto-
matically stopping the air circulation at a stage where the temperature
decreases to
a lower limit of the desired temperature range. In that case, no cooling
method is
used until the temperature of the storage space has increased above the
minimum
temperature of the temperature range, whereby the air circulation is started
again.
The air circulation can be arranged in different ways. In one embodiment,
gravity-assisted air circulation is utilized. Gravity-assisted air circulation
may be most
easily arranged when the refrigeration unit is placed against an outer wall of
the
building. The air is put into motion by means of gravity when outdoor air is
brought
into the bottom part of the refrigeration unit and the air outlet can be
arranged in the
upper part of the refrigeration unit. The air circulates vertically because
the air that
has been warmed up raises upwards. The air moves by means of gravity when the
air comes from below and leaves from above and the air inlet and outlet are
far
enough apart and their horizontal portions are short. The refrigeration unit
may fur-
ther be equipped with a blower that improves the gravity-assisted ventilation.
The
control means of the refrigeration unit may be defined to detect when it is
beneficial
to assist the gravity-assisted air circulation with a blower. The blower may
be low-
power, having a nominal power of, e.g., less than 2 W. The example of Figures
la
and lb represents an embodiment based on gravity-assisted air flow. The inlet
air
pipe 13 is at the bottom part of the refrigeration unit 10 and the outlet air
pipe 14 is
on top of the refrigeration unit 10. It can be seen from Figure lb that the
refrigeration
unit 10 is placed in immediate proximity to the wall 18.
If the refrigeration unit is far from the outer wall, it might be challenging
to achieve a gravity-assisted air circulation. In that case the refrigeration
unit may
comprise a blower which provides the main part of the air flow or the air flow
in its
entirety. The refrigeration unit may in such embodiments not operate
completely
without electricity, but the electricity demand of the blower is very low.
When the air
flow is produced with a blower, it is not necessary to place the inlet and
outlet air
pipes separately, but they can be placed close to each other, whereby the
pipes can
be drawn side by side or on top of each other indoors. Figure 3 presents a
schematic
picture of such an embodiment.
The air circulation may also be implemented utilizing the ventilation sys-
tem of the building. In some embodiments of the refrigeration unit, the outlet
air pipe
of the refrigeration unit may for example be adapted to be connected to the
exhaust
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duct of the ventilation system of a building. The ventilation may be gravity-
assisted,
equipped with mechanical exhaust ventilation, or it may be fully mechanical.
In grav-
ity-assisted exhaust ventilation, the exhaust duct draws air out most
efficiently when
the outdoor air is significantly colder than the indoor air. Thereby, the
exhaust duct
draws air most efficiently when the outdoor air can be used for cooling the
refrigera-
tion unit. In gravity-assisted exhaust ventilation, the air circulation may be
improved
with a low-power blower when necessary.
In buildings having mechanical exhaust ventilation or fully mechanical
ventilation, the air circulation is made to function by use of an
underpressure pro-
duced by a machine, and a separate blower is not necessarily needed in
connection
with the unit.
Figure 2 presents an example of such an embodiment. Figure 2 shows a
side view of a refrigerator 20 placed next to the outer wall 28. Like in
Figures la and
lb, air is brought from outside through the inlet pipe 23 into the bottom part
of the
unit 20. However, in contrast to Figures la and 2b, the air is led from the
upper part
of the unit to an exhaust duct 24.1 in Figure 2. When the exhaust ventilation
operates
mechanically, the air circulation of the refrigeration unit is functioning by
means of
the underpressure produced by the exhaust ventilation without the need of a
blower
in connection with the refrigeration unit.
When the refrigeration unit is used in connection with mechanical venti-
lation, it is beneficial to keep the volume of the air space relatively small,
such that
the unit can be cooled down effectively with a small amount of air. Thereby
variations
in the air circulation have almost no effect on other indoor ventilation or
heat recov-
ery.
When the refrigeration unit is a refrigerator, it typically has horizontal di-
mensions somewhat greater than 500 x 500 mm. When the insulation of the
housing
is reduced from the external dimensions, the horizontal dimensions of the air
space
thereby fall below 500 x 500 mm. If air is brought from outside into the lower
part of
the refrigerator with a pipe having a diameter of 80 mm into a 100 mm high air
space,
then the volume of the air space in the lower part of the refrigerator is
about 25 dm3
and the height of the lower part can even be lowered in some parts of the
space,
whereby its volume may be estimated to about 15 dm3. At the sides of the
refrigera-
tor, the thickness of the air space may be, e.g., about 10 mm, whereby the air
space
at the sides is 10-20 dm3 in total, depending on the size of the refrigerator.
At the
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upper part of the refrigerator, a suitable height of the air space may be
around 20
mm, whereby the volume of the air space there is about 5 dm3. The total volume
of
the air space in a high refrigeration unit is thus about 40 dm3. If the amount
of air is,
e.g., 0,8 dm3/s, which means 2880 dm3/h, the amount of air is sufficient to
exchange
the air of the whole air space of a large refrigerator more than 60 times an
hour, that
is more than once every minute.
In Figure 3, the refrigeration unit 30, which may be for example a refrig-
erator, comprises a storage space 32 and an outer housing 31 surrounding it.
The
outer housing comprises thermal insulation 31.1 and an air space 31.2. The
storage
space 32 and the air space 31.2 are separated by a case formed by the walls
32.1
defining the storage space. The walls 32.1 are made from thermally conducting
ma-
terial. An inlet air pipe 33 and an outlet air pipe 34 are connected to the
air space
31.2. The pipes 33 and 34 are next to each other in the upper part of the
refrigeration
device 30. The outlet air pipe 34 comprises a blower 34.1. The air space 31.2
is
divided by a partitioning wall 31.3 such that the air coming from the inlet
air pipe 33
needs to circulate around the storage space 32 in order to get to the outlet
air pipe
34. In this way, cool air is arranged to cool down the air space 32. Like in
the em-
bodiments presented above, the refrigeration unit 30 comprises several
temperature
sensors. The first sensor 35.1 can be outdoors or in the inlet air pipe 33,
the second
sensor 35.2 is in the air space 31.2 and the third sensor 35.3 is in the
storage space
32. The control means for the refrigeration unit are adapted to control the
air flow
adjustment means 36.1 and 36.2 of the refrigeration unit as well as the
refrigeration
machinery based on temperature data provided by the measuring sensors 35.1,
35.2
and 35.3, for example in a same manner than previously presented in this
description.
The refrigeration unit according to the present disclosure may be imple-
mented in several ways, and the methods of implementation are not limited to
the
examples presented above.
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