U.S. patent application number 09/817942 was filed with the patent office on 2002-10-03 for control device for a refrigeration plant, and control method.
Invention is credited to Meyer, Friedhelm.
Application Number | 20020139131 09/817942 |
Document ID | / |
Family ID | 25224260 |
Filed Date | 2002-10-03 |
United States Patent
Application |
20020139131 |
Kind Code |
A1 |
Meyer, Friedhelm |
October 3, 2002 |
Control device for a refrigeration plant, and control method
Abstract
A method of and apparatus for controlling a refrigeration plant
having a cooler for cooling cooling air, the surface temperature of
the cooler being measured by a single sensor and the cooling-air
temperature being derived from the surface temperature of the
cooler via a correction factor, the refrigeration plant then being
controlled an the basis of the measured temperature value and the
derived temperature value.
Inventors: |
Meyer, Friedhelm; (Bad
Berleburg, DE) |
Correspondence
Address: |
Schnader Harrison Segal & Lewis
1600 Market Street, 36th Floor
Philadelphia
PA
19103
US
|
Family ID: |
25224260 |
Appl. No.: |
09/817942 |
Filed: |
March 27, 2001 |
Current U.S.
Class: |
62/156 ;
62/229 |
Current CPC
Class: |
F25D 21/002 20130101;
F25D 29/005 20130101; Y02B 30/743 20130101; F25B 2700/2117
20130101; F25B 2600/02 20130101; F25B 2600/2519 20130101; F25D
21/08 20130101; F25B 49/022 20130101; Y02B 30/70 20130101; F25B
2600/112 20130101 |
Class at
Publication: |
62/156 ;
62/229 |
International
Class: |
F25D 021/06; F25B
001/00; F25B 049/00 |
Claims
1. Method of controlling a refrigeration plant having a cooler (8)
for cooling cooling air, the surface temperature (t.sub.K) of the
cooler (8) being measured by means of a single sensor (2) and the
cooling-air temperature (t.sub.L) being derived from the surface
temperature (t.sub.K) of the cooler via a correction factor, the
refrigeration plant then being controlled on the basis of the
measured temperature value (t.sub.K) and the derived temperature
value (t.sub.L).
2. Method according to claim 1, in which, after a predetermined
tire after detection via the temperature sensor (2), according to
which the cooling-air temperature incorporating the correction
factor is in the desired range, the refrigeration unit is switched
off or remains switched off and a fan (3) on the cooler (8) is
switched on in order to lead cooling air to the cooler (8), and the
actual temperature (t.sub.L) of the cooling air is checked by the
temperature sensor (2) in this way.
3. Control device for a refrigeration plant having a cooler (8) for
cooling cooling air, for example in a cold storage room, by means
of which device the cooling-air temperature (t.sub.L) is kept at a
predefined value, comprising a single sensor (2) for determining
the surface temperature (t.sub.K) on the cooler (8) and a control
unit (1) which derives the cooling-air temperature (t.sub.L) from
the measured surface temperature of the cooler (8) via a correction
factor (K) and controls the refrigeration plant on the basis of the
cooling-air temperature (t.sub.L) determined in this way, in
conjunction with the measured surface temperature (t.sub.K) of the
cooler (8).
4. Control device according to claim 3, the temperature sensor (2)
being arranged between the cooling fins (17) of the cooler (8) in
the evaporator (9) of the refrigeration plant.
5. Control device according to claims 3 and 4, the control unit (1)
controlling the compressor (4), the defrost heater (6) and the fan
(3) in the evaporator (9) of a refrigeration plant as a function of
the measured temperature value (t.sub.K) on the cooler surface.
6. Control device according to claims 3 to 5, the control unit (1)
displaying the cooling-air temperature (t.sub.L), detected via the
correction value, in a display as the room air temperature and, if
appropriate, storing and logging the said cooling-air
temperature.
7. A method of controlling a refrigeration plant having a cooler
for cooling cooling air comprising: measuring surface temperature
(t.sub.K) of the cooler with a single sensor; determining
cooling-air temperature (t.sub.L) from the surface temperature
(t.sub.K) of the cooler with a correction factor; and controlling
operation of the cooler on the basis of the measured temperature
value (t.sub.K) and the cooling-air temperature value
(t.sub.L).
8. The method according to claim 7, wherein after a predetermined
time after detection via the temperature sensor, according to which
the cooling-air temperature incorporating the correction factor is
in a selected range, the refrigeration unit is switched off or
remains switched off and a fan associated with the cooler is
switched on to lead cooling air to the cooler, and actual
temperature (t.sub.L) of the cooling air is checked by the
temperature sensor.
9. A control device for a refrigeration plant having a cooler for
cooling cooling air, wherein cooling-air temperature (t.sub.L) is
kept at a selected value comprising: a single sensor for
determining the surface temperature (t.sub.K) on the cooler; and a
controller which determines the cooling-air temperature (t.sub.L)
from measured surface temperature of the cooler with a correction
factor (K) and controls the refrigeration plant on the basis of the
cooling-air temperature (t.sub.L) in conjunction with the measured
surface temperature (t.sub.K) of the cooler.
10. The control device according to claim 8, wherein the sensor is
arranged between cooling fins of the cooler in an evaporator
connected to the refrigeration plant.
11. The control device according to claim 9, wherein the control
unit controls a compressor, a defrost heater and a fan in an
evaporator of the refrigeration plant as a function of the measured
temperature value (t.sub.K) on a surface of the cooler.
12. The control device according to claim 10, wherein the control
unit controls a compressor, a defrost heater and a fan in an
evaporator of the refrigeration plant as a function of the measured
temperature value (t.sub.K) on a surface of the cooler.
13. The control device according to claim 9, wherein the control
device displays the cooling-air temperature (t.sub.L), detected via
the correction value, on a display as the room air temperature and,
optionally, stores and logs the cooling-air temperature.
14. The control device according to claim 10, wherein the control
device displays the cooling-air temperature (t.sub.L), detected via
the correction value, on a display as the room air temperature and,
optionally, stores and logs the cooling-air temperature.
15. The control device according to claim 11, wherein the control
device displays the cooling-air temperature (t.sub.L), detected via
the correction value, on a display as the room air temperature and,
optionally, stores and logs the cooling-air temperature.
16. The control device according to claim 12, wherein the control
device displays the cooling-air temperature (t.sub.L), detected via
the correction value, on a display as the room air temperature and,
optionally, stores and logs the cooling-air temperature.
Description
FIELD OF THE INVENTION
[0001] The invention relates to a control device for a
refrigeration plant, especially for cold storage rooms, and to a
method of controlling the temperature of the cold storage room.
BACKGROUND
[0002] In a refrigeration plant by means of which the temperature
in a cold storage room is kept to a predefined value, it is known
to provide a sensor to determine the temperature of the cold
storage room, the said sensor generally being arranged in the air
inlet upstream of the evaporator, and also to provide a sensor for
determining the temperature of the cooler in the evaporator, this
sensor generally being arranged on the surface of the cooler.
During the design of a refrigeration plant, a temperature
difference .DELTA.t.sub.1 in Kelvin between the desired cold
storage room temperature and evaporator temperature or else the
temperature at which the refrigerating medium evaporates is
defined. In the case of deep-frozen goods, for example, a
temperature difference .DELTA.t.sub.1 of 10 K is defined when
designing the plant; in the refrigeration of foodstuffs such as
vegetables, for example, a .DELTA.t.sub.1 of 7.degree. K. From this
temperature difference, defined from the outset, the power
calculation for the evaporator is carried out.
[0003] In such a refrigeration plant, the sensor for the cold
storage room temperature controls, via a control unit, a fan for
the passage of air through the cooler and the refrigerant circuit,
for example the compressor, while the sensor on the cooler surface
controls the final defrost temperature for a defrost heater and the
like. At the end of defrosting, the compressor is then switched on
first by the sensor for determining the cold storage room
temperature and, after a predefined temperature has been reached,
the fan of the evaporator is switched on by the sensor on the
cooler surface. In the cooling cycles which then follow the fan of
the evaporator and the compressor are again controlled by the
sensor for the cold storage room temperature.
SUMMARY OF THE INVENTION
[0004] The invention is based on the advantage of constructing a
temperature control system such that it keeps the cold storage room
temperature to the predefined set point in a reliable way with a
simple construction.
[0005] A single sensor is provided on the cooler surface, by means
of which the cold storage room temperature is determined via a
correction factor and the refrigeration plant is controlled on the
basis of the determined cold storage room temperature, which
results in a more simple construction as a result of omitting a
second sensor for the cold storage room temperature. The fact that
a single sensor is responsible for controlling the refrigeration
plant reduces the investment costs, the outlay on installation and
possible service costs. Fault sources are minimized by the fact
that confusion between the sensors and the sensor connection lines
is ruled out. Line-bound input coupling resulting from
electromagnetic interference, such as can be coupled in sensor
connecting lines and then have a detrimental effect on a control
unit, is reduced by half by omitting one sensor. A control unit
having only one sensor is considerably better in terms of its
functional reliability as compared with the prior art, since all
the measured variables are determined by a single sensor.
BRIEF DESCRIPTION OF THE DRAWINGS
[0006] The invention will be explained in more detail by way of
example using the drawings, in which:
[0007] FIG. 1 shows a refrigeration plant for cooling in a cold
storage room, in schematic form,
[0008] FIG. 2 is a graph illustrating control of the cold storage
room temperature, and
[0009] FIG. 3 is a graph for determining the correction value.
DETAILED DESCRIPTION
[0010] FIG. 1 shows a cold storage room 100 and a refrigeration
plant 12 having an evaporator 9 for the air cooling, in the housing
of which there are arranged a fan 3 for the passage of air and also
a cooler 8 comprising piping through which refrigerating medium
flows and which has cooling fins 17, which preferably consist of
aluminum. The numeral "6" designates an example of an electrical
defrost heater, by means of which the cooler 8 is defrosted when
iced up. The numeral "7" designates an expansion valve. Instead of
electrical defrost heating, another form of defrost heating can
also be provided.
[0011] In addition, the refrigeration plant 12 comprises a
compressor 4, an air-cooled liquefier 10 and a refrigerating-medium
collector 11. Arranged in the air-cooled liquefier 10 is a fan 13
and piping with cooling fins 16. Via a suction line 15, gaseous
refrigerating medium flows from the cooler 8 in the evaporator 9 to
the compressor 4, and liquid refrigerating medium flows through the
liquefier 10 and the refrigerating-medium collector 11, through a
line 14 and via solenoid valve 5, to the expansion valve 7.
[0012] Arranged on the cooler 8 of the evaporator 9 is a
temperature sensor 2, by means of which the surface temperature
t.sub.K of the cooler 8 is determined. In a known refrigeration
plant, a second sensor (not illustrated) is arranged in the room to
be cooled or in the air inlet upstream of the evaporator, wherein
the sensor measures the temperature of the cooling air.
[0013] In the configuration of a refrigeration plant according to
the invention and shown in FIG. 1, only a single temperature sensor
2 is provided on the cooler surface, preferably between the cooling
fins 17, by means of which sensor the surface temperature t.sub.K
of the cooler 8 is determined.
[0014] The numeral "1" designates a control unit TC which accepts
the temperature value measured by the sensor 2 and, via an
electronic control device, switches the fan 3, the compressor 4 and
the defrost heater 6.
[0015] A program provided in the control unit 1 registers the
surface temperature t.sub.K of the cooler 8 and, in addition,
determines the temperature of the cooling air or the cold storage
room temperature via a correction value.
[0016] The correction value is determined as follows. For example,
the refrigeration plant is to be designed for cooling vegetables to
a cold storage room temperature of +2.degree. C. In this case, the
refrigeration plant is designed by the plant constructor in such a
way that, for the set point of +2.degree. C., an evaporation
temperature to of -5.degree. C. is ensured so that during practical
operation, a .DELTA.t.sub.1 of 7.degree. K. is established. The
.DELTA.t.sub.1 is determined in a known way as the difference
between the air inlet temperature t.sub.L1 and the evaporation
temperature t.sub.0. This is defined in the standards DIN 8955 and
ENV 328 for determining cooler capacity. Values from experience
show that a specific evaporation temperature t.sub.0 of the
refrigerating medium in the evaporator is to be allocated a
specific value of the surface temperature t.sub.K of the cooler in
the evaporator.
[0017] FIG. 3 shows in schematic form the relationship between
evaporation temperature to of the refrigerating medium and surface
temperature t.sub.K of the cooler. Such a relationship can be
stored, for example, in the form of a table, in the electronic
control unit 1. After the temperature difference .DELTA.t.sub.1 has
been defined from the outset, the predefinition of the desired
temperature of + 2.degree. C. and the resulting evaporation
temperature of the refrigerating medium of -5.degree. C. can be
used to derive a surface temperature of the cooler t.sub.K of
-1.degree. C. from FIG. 3.
[0018] This relationship results from the cooler construction and
the design of the evaporator. From the surface temperature t.sub.K
of the cooler 8 in the evaporator 9, determined in this way, in
this example a correction value of 3.degree. K. is determined from
the difference between the set point +2.degree. C. and surface
temperature t.sub.K of -1.degree. C. In other words, it is assumed
that, according to the design of the refrigeration plant based on
.DELTA.t.sub.1, the cooling-air temperature t.sub.L in this example
lies above the surface temperature t.sub.K of the cooler by the
correction value of 3.degree. K.
[0019] While for the purpose of cooling vegetables, for example, a
set point of +2.degree. C. and a correction value of 3.degree. K.
are used for example for the deep-frozen range, a set point of
-20.degree. C. is predefined, from which, via the predefined value
of .DELTA.t.sub.1=10.degree.K., a correction value of 5.degree. K.
results. The value of .DELTA.t.sub.1 has to be set on the control
unit 1. The control unit 1 then determines the correction value
from the set .DELTA.t.sub.1.
[0020] FIG. 2 shows the temperature variation of the cold storage
room temperature t.sub.L and the surface temperature t.sub.K at the
cooler 8 over time, a set point for the cold storage room
temperature t.sub.L of +2.degree. C. being assumed, such as is
provided, for example, for vegetables as refrigerated goods.
Starting from a switched-off state of the refrigeration plant, in
which both the cooler surface temperature t.sub.K and the cold
storage room temperature t.sub.L have a value lying above
+2.degree. C., the refrigeration unit 12 and the fan 3 in the
evaporator 9 are switched on first by the control unit to bring the
cold storage room temperature t.sub.L to the set point. When the
refrigeration unit 12 is running, the surface temperature on the
cooler 8 is lowered as a result of circulation of the refrigerating
medium in the refrigerant circuit. At the same time, the cold
storage room temperature t.sub.L is lowered by the running fan 3 in
the evaporator 9. As soon as the sensor 2 detects a surface
temperature t.sub.K of -1.degree. C., the control unit 1 determines
that the set point t.sub.L of +2.degree. C. has been reached, by
adding on the correction value of 3.degree. K. This means that the
control unit 1 switches off the compressor 4 and the fan 3. The fan
3 is switched on again when the sensor 2 indicates, via the
correction value, a desired temperature t.sub.L at the upper
temperature value of +2.5.degree. C. of a predefined tolerance
range of .+-.0.5.degree. K. about the desired temperature
+2.degree. C. in the control unit 1.
[0021] In FIG. 2, the tolerance range about the desired temperature
+2.degree. C. is reproduced by means of dash-dotted lines above and
below the desired temperature. The compressor 4 is expediently
switched off via the control unit 1 when the cooling air
temperature t.sub.L, determined via the correction value, reaches
the tolerance value lying below the desired temperature. The
surface temperature t.sub.K on the cooler 8 then rises again, the
said temperature being determined via the sensor 2, the fan 3 of
the evaporator 9 then being switched on again first, and then the
compressor 4 being switched on again via the control unit 1 when
the surface temperature t.sub.K of the cooler 8 determined by the
sensor 2 indicates the tolerance value of +0.5.degree. K. lying
above the desired temperature.
[0022] These cycles are repeated until, for example, as a result of
icing of the cooler 8, the sensor 2 determines a surface
temperature t.sub.K from which icing of the cooler 8 can be derived
in the control unit 1 by means of a comparison with predefined
values or by means of a predefined program. At this point, the
control unit 1 switches off the compressor 4 and the fan 3 and
switches on the defrost heater 6 until the predefined final defrost
temperature on the cooler 8 is again displayed via the temperature
sensor 2. The defrost heater 6 is then switched off by the control
unit 1, and the refrigeration unit 12 with the compressor 4 is
switched on again. The cooling cycle illustrated in FIG. 2 begins
again after the fan 3 of the evaporator 9 is likewise switched on
again by the control unit 1 in accordance with a previously defined
surface temperature of the cooler 8.
[0023] The temperature sensor 2 arranged in the cooler 8
constitutes a neutral measuring point which cannot be falsified by
parameters such as is the case, for example, in a room temperature
sensor whose measured value can be falsified, for example, by the
fact that the room temperature sensor is covered by wrongly stacked
refrigerated goods in the cold storage room. In this way, on
account of the above-described control using only one sensor 2 via
a correction factor starting from the previously determined
.DELTA.t.sub.1, the result is more reliable control than is the
case in known refrigeration plants with two sensors of which the
cooling-air sensor can be falsified by various parameters and false
cooling-air temperatures can be determined. The temperature sensor
2 is arranged so as it is protected between the cooling fins, and
cannot be damaged by putting refrigerated goods into storage and
removing them.
[0024] Since the evaporator 9 represents a cold reservoir, and the
surface temperature of the cooler 8 does not always reliably
reproduce the cooling-air temperature in the room via the
correction factor, for example, because the cold storage room
temperature rises as a result of the transmission of heat from the
refrigerated goods, without this having an immediate effect on the
surface temperature t.sub.K of the cooler 8, after a predefined
time after the control unit 1 has established that the sensor 2 is
indicating a set point in the tolerance range, the fan 3 is
switched on so that room air is lead through the cooler 8 to check
the actual room air temperature.
[0025] In this case, the compressor 4 is still switched off, since
there is on the control unit 1 a signal from the sensor 2 which
reproduces the cold storage room temperature within the tolerance
range of the set point. Given warmer cooling-air temperature within
the cold storage room in which, for example, good which have not
yet been cooled have been subsequently store, the surface
temperature t.sub.K of the cooler 8 rises as a result of the warmer
air brought up by the fan 3, until the surface temperature of the
cooler has assumed the temperature of the room air. As a result,
the sensor 2--without taking into account the correction
factor--reports a current value of the room temperature which does
not lie in the tolerance range of the desired temperature, for
which reason the control until 1 switches on the refrigeration unit
and the compressor 4 to take the surface temperature t.sub.K of the
cooler 8 back to a value which, with the correction factor, lies
within the tolerance range of the desired temperature.
[0026] The room air temperature is measured indirectly by means of
the sensor 2 via the surface temperature t.sub.K of the cooler 8
and the correction factor. However, since the room air temperature
can change more rapidly after reaching the desired temperature than
can be determined by the only slowly following surface temperature
on the cooler 8, the room air temperature must be repeatedly
checked in this way or checked at specific time intervals by
switching on the fan 3 again so that the control unit 1 can measure
the actual room temperature via the sensor 2.
[0027] The fact that, after the desired temperature has been
reached with the compressor 4 switched off, the fan 3 of the
evaporator 9 is switched on first and the control unit 1 uses the
sensor 2 to follow the temperature variation without correction
factor, and the compressor 4 remains switched off until the control
unit 1 uses the sensor 2 to determine a surface temperature t.sub.K
above the set point of +2.degree. C., it being assumed that the
surface temperature t.sub.K of the cooler 8 has assumed the cold
storage room temperature and only then is the compressor 4 switched
on by the control unit 1, means that this method prevents the
surface of the cooler 8 falling below the dew point at the time at
which the compressor is switched on.
[0028] The advantageous features of the method outlined above are:
considerably lower loss of mass of the refrigerated goods as result
of reduced dehumidification of the cold storage room air.
Considerable reduction in the energy consumption and, therefore,
reduction in the operating costs as a result of utilizing the
developed ice crystals as an energy store for cooling the room air.
This results in an improved efficiency of the air cooler, shorter
compressor running within the cooling cycles and, therefore, a
longer useful life (service life) of the compressor. Defrost
intervals are suspended by the pre-running of the fan, or the
defrost cycles are reduced.
[0029] The above-described control of a refrigeration plant can be
applied not only to cold storage rooms and deep-freeze rooms, but
also to refrigerated and deep-freeze cabinets in which the fan
corresponding to the fan 3 is permanently operating, and the cold
air delivered by the fan corresponds to the room air, whose
temperature is determined, via the correction factor, by means of
the temperature sensor 2 fitted to the cooler 8. Refrigerated and
deep-freeze cabinets of this type are used as island sales cabinets
and chilled counters in commercial refrigeration and the like. This
also applies in particular to room air-conditioning plant in the
air-conditioning sector.
[0030] The above-described control of the room air temperature by
means of a single sensor does not depend on the refrigeration media
respectively used. For example, the evaporator 9 may also be an air
cooler, which is operated not with direct expansion but with pumped
refrigeration media in the form of liquid solutions, for example
NH.sub.3, or cold sols in two-circuit refrigeration plants, or Flo
Ice or in CO.sub.2 plants.
[0031] By means of the control unit 1, the solenoid valve 5 in
composition refrigeration plants can also be driver in a manner
known per se, be it simultaneously with driving of the compressor 4
or else separately therefrom.
* * * * *