FIELD OF THE INVENTION
[0001] The present invention relates to a method for operating a vapour compression system,
the vapour compression system comprising at least one evaporator, each evaporator
being arranged in thermal contact with a refrigerated volume for storing goods. The
method according to the invention allows an early warning to be generated in the case
that the temperature inside a refrigerated volume is above a specified level.
BACKGROUND OF THE INVENTION
[0002] Vapour compression systems may be used for providing cooling to refrigerated volumes
or compartments, e.g. in the form of display cases in supermarkets or the like. Such
refrigerated volumes may be used for accommodating goods which need to be stored at
specified low temperatures, e.g. food products, drugs, etc. To this end, one or more
evaporators of the vapour compression system are arranged in thermal contact with
the refrigerated volumes.
[0003] For instance, fresh food products may be subject to bacterial growth, in particular
if the food products are stored at temperatures between 5°C and 60°C, sometimes referred
to as the 'temperature danger zone'. Therefore, it is normally required that fresh
food products are stored at temperatures below 5
°C. It may, however, be acceptable that food products are stored, for a limited time,
at temperatures above 5°C. How much the temperature may be allowed to deviate from
the specified storage temperature, and for how long, depends on the kind of goods
being stored, in particular on the temperature sensitivity of the goods.
[0004] Accordingly, vapour compression systems are normally controlled by controlling the
refrigerant supply to the evaporators in such a manner that the temperature inside
the refrigerated volumes are maintained within a specified temperature interval below
5°C. More specifically, when the temperature inside a refrigerated volume reaches
a specified cut-in temperature, an expansion valve associated therewith is opened,
thereby providing a supply of refrigerant to the corresponding evaporator. This will
cause the temperature inside the refrigerated volume to decrease. The expansion valve
is kept open until a cut-out temperature is reached. Then the expansion valve is closed,
thereby preventing that the refrigerant is supplied to the evaporator. This will cause
the temperature inside the refrigerated volume to increase, and this is allowed to
continue until the cut-in temperature is once again reached. Thereby it is ensured
that the temperature inside the refrigerated volume is maintained substantially within
the temperature interval between the cut-out temperature and the cut-in temperature,
possibly with minor undershoots and/or overshoots.
[0005] In the case that the vapour compression system malfunctions or, for some reason,
is not operating in an optimal manner, it may be difficult to maintain the temperature
inside the refrigerated volume within the specified temperature interval. For instance,
it may not be possible to drive the temperature down below the cut-in temperature,
even if the expansion valve is kept fully open, and the temperature inside the refrigerated
volume may even continue to increase. In order to prevent that the temperature inside
the refrigerated volume increases to an unacceptable level, a high temperature alarm
is normally generated if the temperature inside the refrigerated volume has increased
to a specified elevated temperature level, e.g. 8°C, and has remained above this temperature
level for a specified period of time, e.g. approximately 30 minutes. When such an
alarm is generated, it will normally be necessary to attend to the matter immediately,
in order to prevent or limit degradation of the goods stored in the refrigerated volume.
[0006] In some cases, the vapour compression system may be able to keep the temperature
inside the refrigerated volume below the temperature which triggers the high temperature
alarm, but not below the upper limit of the specified temperature range. In this case,
a high temperature alarm will not be generated, even though the temperature inside
the refrigerated volume is in reality too high. Accordingly, the goods accommodated
in the refrigerated volume are stored at a too high temperature, potentially during
a long time period. This may cause faster degradation of the goods, and possibly result
in more goods than necessary being discarded.
US 2009/093917 A1 discloses a control method which triggers an alarm when the measured temperature
in a predefined position of the refrigerant line is not within a predefined range
after a time delay when the compressor has started. The method first determines, as
reference points, the high and low set points of the measured temperature and the
compressor start point. Then it is determined whether the temperature in the refrigeration
compartment reaches the compressor start point temperature. Once the start point temperature
is reached, the system starts a timer. Once a predetermined time has elapsed, the
measured temperature is recorded. If the temperature is outside of the normal range,
the system notifies an operator or technician that a potential problem exists.
DESCRIPTION OF THE INVENTION
[0007] It is an object of embodiments of the invention to provide a method for operating
a vapour compression system, in which the risk of storing goods at elevated temperatures
is decreased.
[0008] It is a further object of embodiments of the invention to provide a method for operating
a vapour compression system which allows early detection of potential faults in the
vapour compression system.
[0009] The invention provides a method for operating a vapour compression system as defined
in claim 1, the vapour compression system comprising a compressor unit, a heat rejecting
heat exchanger, at least one expansion device and at least one evaporator arranged
in a refrigerant path, each evaporator being arranged in thermal contact with a refrigerated
volume for storing goods, the method comprising the steps of, for at least one of
the refrigerated volumes:
- setting control parameters related to the refrigerated volume, including setting a
cut-in temperature, a high temperature alarm limit and a high temperature alarm delay
time,
- deriving a maximum acceptable relative decay value, based on the high temperature
alarm limit and the high temperature alarm delay time,
- operating the vapour compression system while monitoring a temperature inside the
refrigerated volume and continuously deriving a weighted mean temperature prevailing
inside the refrigerated volume, during a moving time window of a predefined length,
- in the case that the weighted mean temperature inside the refrigerated volume exceeds
the cut-in temperature, starting a timer and continuing to derive the weighted mean
temperature prevailing inside the refrigerated volume, during a moving time window
of a predefined length,
- deriving a delay time, based on the weighted mean temperature and the maximum acceptable
relative decay value, and
- generating a warning when the timer reaches the derived delay time.
[0010] Thus, the method according to the invention is a method for operating a vapour compression
system. In the present context the term 'vapour compression system' should be interpreted
to mean system in which a flow of fluid medium, such as refrigerant, circulates and
is alternatingly compressed and expanded, thereby providing either refrigeration or
heating of a volume. Thus, the vapour compression system may be a refrigeration system,
an air condition system, a heat pump, etc.
[0011] In the present context the term 'operating a vapour compression system' should be
interpreted to mean operating various components of the vapour compression system
in order to provide the required cooling in the refrigerated volumes, while measuring
or monitoring relevant parameters, and ensuring that various parts of the vapour compression
system are performing as expected. It is noted that the method according to the invention
is primarily related to monitoring of the vapour compression system with the purpose
of ensuring that the vapour compression system operates appropriately and as expected.
[0012] The vapour compression system comprises a compressor unit, a heat rejecting heat
exchanger, at least one expansion device and at least one evaporator arranged in a
refrigerant path. Thus, refrigerant flowing in the refrigerant path is compressed
by one or more compressors of the compressor unit, before being supplied to the heat
rejecting heat exchanger. When the refrigerant passes through the heat rejecting heat
exchanger, heat exchange takes place between the refrigerant and the ambient or a
secondary fluid flow across the heat rejecting heat exchanger, in such a manner that
heat is rejected from the refrigerant. The heat rejecting heat exchanger may be in
the form of a condenser, in which case the refrigerant is at least partly condensed
when passing through the heat rejecting heat exchanger. As an alternative, the heat
rejecting heat exchanger may be in the form of a gas cooler, in which case the refrigerant
passing through the heat rejecting heat exchanger is cooled, but remains in a gaseous
or trans-critical state.
[0013] The refrigerant leaving the heat rejecting heat exchanger is supplied to the expansion
device(s), where it is expanded before being supplied to respective evaporator(s).
The refrigerant supplied to the evaporator(s) is in a mixed state of gaseous and liquid
refrigerant. In the evaporator(s), the liquid part of the refrigerant is at least
partly evaporated, while heat exchange takes place between the refrigerant and the
ambient or a secondary fluid flow across the respective evaporator, in such a manner
that heat is absorbed by the refrigerant. Finally, the refrigerant leaving the evaporator(s)
is supplied to the main compressor(s).
[0014] Each evaporator is arranged in thermal contact with a refrigerated volume for storing
goods. Thereby, due to the heat exchange taking place when the refrigerant passes
through an evaporator, cooling is provided to the corresponding refrigerated volume.
[0015] In the method according to the invention, for at least one of the refrigerated volumes,
control parameters for the refrigerated volume are initially set. This includes setting
a cut-in temperature, a high temperature alarm limit and a high temperature alarm
delay time.
[0016] In the present context, the term 'cut-in temperature' should be interpreted to mean
a temperature value which triggers opening of the expansion valve which supplies refrigerant
to the evaporator being arranged in thermal contact with the refrigerated volume.
Thus, when the temperature inside the refrigerated volume reaches the cut-in temperature,
then the expansion device is opened, thereby allowing a supply of refrigerant to the
evaporator, and causing a decrease in the temperature inside the refrigerated volume.
Thus, by setting the cut-in temperature it is determined at which temperature level
the expansion valve should be opened for that particular refrigerated volume.
[0017] As alternative, the expansion device may be a modulating thermostat. In this case,
the temperature inside the refrigerated volume is controlled according to a reference
temperature, e.g. by means of a PI controller. The reference temperature is, in this
case, typically in the middle of a temperature interval between a cut-out temperature
and the cut-in temperature. The cut-in temperature still represents a temperature
limit which it is undesirable that the temperature inside the refrigerated volume
exceeds.
[0018] In the present context the term 'high temperature alarm limit' should be interpreted
to mean a temperature level which triggers that a high temperature alarm is generated.
The high temperature alarm limit is typically somewhat higher than the cut-in temperature,
since it should be selected in such a manner that a high temperature alarm is only
generated if it is certain that an elevated temperature which needs attention is prevailing
inside the refrigerated volume. Thus, by setting the high temperature alarm limit
it is determined to which extent the temperature inside the refrigerated volume can
be allowed to exceed the upper boundary of the normally acceptable temperature interval.
In other words, the high temperature alarm limit defines the highest acceptable temperature
inside the refrigerated volume.
[0019] In the present context the term 'high temperature alarm delay time' should be interpreted
to mean a time period which elapses from the temperature inside the refrigerated volume
exceeds the high temperature alarm limit until a high temperature alarm is generated.
It may be considered acceptable that the temperature inside the refrigerated volume
exceeds the high temperature alarm limit very briefly, and therefore a high temperature
alarm may only be generated if the temperature inside the refrigerated volume remains
above the high temperature alarm limit for some time. Thereby it is ensured that a
high temperature alarm is only generated if it is certain that an elevated temperature
is prevailing inside the refrigerated volume, that the vapour compression system is
not able to decrease the temperature, and that attention is therefore required. Thus,
by setting the high temperature alarm delay time it is determined for how long it
can be accepted that the temperature inside the refrigerated volume is above the high
temperature alarm limit.
[0020] Thus, the control parameters being set all represent threshold values which are applied
when operating the vapour compression system, and they may advantageously be set when
the vapour compression system is installed. When setting the control parameters, the
kind of goods to be stored in the refrigerated volume may be taken into account. For
instance, for very temperature sensitive goods, a low high temperature alarm limit
and/or a short high temperature alarm delay time may be selected, whereas a higher
high temperature alarm limit and/or a longer high temperature alarm delay time may
be selected for goods which are less temperature sensitive.
[0021] It should be noted that the cut-in temperature, the high temperature alarm limit
and the high temperature alarm delay time are control parameters which are commonly
set in prior art vapour compression system. Accordingly, the method according to the
invention relies partly on control parameters which are already applied for other
purposes, and while taking the kind of goods being accommodated in the refrigerated
volume into account.
[0022] Next, a maximum acceptable relative decay value is derived, based on the high temperature
alarm limit and the high temperature alarm delay time. As described above, the high
temperature alarm limit and the high temperature alarm delay time in combination define
how high a temperature is acceptable inside the refrigerated volume, and for how long.
The impact on the stored goods, e.g. in terms of decay, caused by an elevated storage
temperature, is determined by the temperature level as well as by the length of the
time interval at which the goods are stored at a certain temperature level. Thus,
by setting the high temperature alarm limit and the high temperature alarm delay time,
it is also defined for how long it can be accepted that the temperature inside the
refrigerated volume is at or above the high temperature alarm limit. Accordingly,
it is also defined that additional decay of the stored goods, which corresponds to
storing the goods at the high temperature alarm limit for a time period corresponding
to the high temperature alarm delay time, is acceptable. The derived maximum acceptable
relative decay value reflects this.
[0023] Next, the vapour compression system is operated in a normal manner, in order to provide
the required cooling to the respective refrigerated volumes. During this, the temperature
inside the refrigerated volume is monitored. Furthermore, a weighted mean temperature
prevailing inside the refrigerated volume, during a moving time window of a predefined
length, is continuously derived.
[0024] In the present context the term 'weighted mean temperature' should be interpreted
to mean a mean value of the measured temperature inside the refrigerated volume, during
the moving time window, where the measured temperature values are weighted, e.g. by
providing higher temperatures with a higher weight than lower temperatures. Thus,
the weighted mean temperature provides a suitable measure for the temperature conditions
inside the refrigerated volume, during a time interval corresponding to the moving
time window, and without possible rapid fluctuations in the temperature signal, and
which provides greater weight to temperature which are significantly above the cut-in
temperature than to temperatures slightly above the cut-in temperature, thereby reflecting
the severity of the elevated temperature level.
[0025] In the present context the term 'moving time window' should be interpreted to mean
a time interval ending at the current point in time, and extending backwards in time
for the predefined length. Thus, the beginning of the time interval moves continuously
forward in time. Accordingly, the derived weighted mean temperature at all times represents
a mean temperature prevailing inside the refrigerated volume during a time interval
of the predefined length, immediately preceding the current point in time.
[0026] The predefined length of the moving time window may be a few minutes, or it may be
as long as several days or even several weeks.
[0027] In the case that the weighted mean temperature inside the refrigerated volume exceeds
the cut-in temperature, a timer is started. Furthermore, monitoring the temperature
inside the refrigerated volume and deriving the weighted mean temperature prevailing
inside the refrigerated volume, in the manner described above, is continued.
[0028] When the weighted mean temperature inside the refrigerated volume increases to a
level above the cut-in temperature, this is an indication that the vapour compression
system is unable to keep the temperature inside the refrigerated volume within the
specified temperature interval. However, this may also simply be due to a temporary
condition which the vapour compression system is able to overcome. Therefore, a warning
is not generated immediately.
[0029] Next, a delay time is derived, based on the weighted mean temperature and the maximum
acceptable relative decay value. As described above, the maximum acceptable relative
decay value represents a decay resulting from storing the goods at the high temperature
alarm limit for a time period corresponding to the high temperature alarm delay time,
and thereby to a decay which was accepted when the control parameters were set initially.
Thus, the delay time is derived based on the weighted mean temperature, which reflects
the current temperature level inside the refrigerated volume, and takes the decay,
which was accepted when the control parameters were set initially into account.
[0030] The derived delay time could thereby correspond to a storage time, at the current
weighted mean temperature, which results in an expected decay which is identical or
similar to the maximum acceptable relative decay value. Accordingly, it is considered
acceptable that the temperature inside the refrigerated volume is at the weighted
mean temperature for a time period corresponding to the derived delay time, in the
same manner as it is considered acceptable that the temperature inside the refrigerated
volume is at the high temperature alarm limit for a time period corresponding to the
high temperature alarm delay time, since this is expected to result in identical or
similar relative decay values.
[0031] The derived delay time can therefore be applied as a warning delay time, in the same
manner as the hight temperature alarm delay time is applied, and as described above.
Accordingly, a warning is generated when the timer reaches the derived delay time.
[0032] Thus, the method according to the invention allows a warning to be generated if the
temperature inside the refrigerated volume is above a desired upper temperature limit,
but below a high temperature alarm limit, which would normally trigger an alarm. This
allows possible faults or non-optimal operation of the vapour compression system,
e.g. need for defrosting, refrigerant charge loss, etc., to be detected early. Thereby
service or maintenance can be scheduled timely before the vapour compression system
is in a critical state which requires immediate attention and possibly results in
stored goods having to be discarded.
[0033] According to one embodiment, the timer may be of a kind which has fixed time steps.
In this case the derived delay time may specify a number of time steps which the timer
needs to count before the delay time has been reached.
[0034] According to another embodiment, the timer may be of a kind which has variable time
steps, and the size of the time steps may depend on the weighted mean temperature,
in the sense that a high temperature corresponds to smaller time steps than a lower
temperature. In this case the delay time may correspond to a fixed number of steps
of the timer, and deriving the delay time includes deriving the size of the time steps
of the timer.
[0035] The step of deriving a maximum acceptable relative decay value may be performed using
a mathematical model.
[0036] According to this embodiment, a suitable mathematical model is applied when the maximum
acceptable relative decay value is derived. The mathematical model may advantageously
take the kind of goods to be stored in the refrigerated volume into account, in the
sense that the mathematical model may reflect how the specific kind of goods would
normally decay when stored at various temperatures. Thus, the mathematical model may
reflect the temperature sensitivity of the stored goods, the specific heat capacity
of the stored goods, etc. For instance, for very temperature sensitive goods, a fast
decay may be expected. Furthermore, goods with a high specific heat capacity may be
expected to maintain a low temperature inside the goods for some time, even if stored
at elevated temperatures, and this will slow the decay.
[0037] The mathematical model may, e.g., be a relative rate of spoilage (RRS) model. Such
models are developed on the basis of shelf-life data obtained at different storage
temperatures in experiments where shelf-life was determined by sensory evaluation.
These models do not take into account the types of reactions which cause spoilage
at different temperatures, and this may be considered an advantage in the sense that
RRS models can be valid for a wide range of storage temperatures. RRS models are very
simple, but still most useful for calculation of shelf-life at different storage temperatures,
since it is only necessary to provide the product shelf-life for a single known and
constant storage temperature. The RRS model then allows shelf-life to be predicted
at different temperatures.
[0038] The mathematical model may, e.g., be an Arrhenius RRS model, e.g. in the form of:
![](https://data.epo.org/publication-server/image?imagePath=2024/13/DOC/EPNWB1/EP22156342NWB1/imgb0001)
[0039] The method may further comprise the step of deriving combinations of mean storage
temperature and storage time resulting in a relative decay value corresponding to
the derived maximum acceptable relative decay value, and the step of deriving a delay
time may be based on the weighted mean temperature and the combinations of mean storage
temperature and storage time.
[0040] According to this embodiment, once the maximum acceptable relative decay value has
been derived, suitable combinations of mean storage temperature and storage time are
derived. Each of the combinations of mean storage temperature and storage time results
in a relative decay value which corresponds to the maximum acceptable relative decay
value. This could, e.g., be done upfront, for instance when the control parameters
are initially set and the maximum acceptable relative decay value is derived.
[0041] Subsequently, during operation of the vapour compression system, a delay time can
easily be derived, based on the weighted mean temperature, simply by consulting the
previously derived combinations of mean storage temperature and storage time, and
selecting the combination which includes the weighted mean temperature. This allows
for fast and reliable determination of the delay time which is relevant under the
given circumstances.
[0042] The step of deriving combinations of mean storage temperature and storage time resulting
in a relative decay value corresponding to the derived maximum acceptable relative
decay value may be performed using a mathematical model.
[0043] This is similar to the situation regarding deriving the maximum acceptable relative
decay value described above, and the remarks set forth in this regard are therefore
equally applicable here. The applied mathematical model may, e.g., be the same in
both cases.
[0044] The step of deriving combinations of mean storage temperature and storage time resulting
in a relative decay value corresponding to the derived maximum acceptable relative
decay value may comprise generating a look-up table and/or a graph.
[0045] According to this embodiment, the derived combinations are stored in the form of
a look-up table and/or a graph, which can be consulted when the delay time needs to
be derived during operation of the vapour compression system.
[0046] The step of deriving a delay time may be performed continuously, based on the continuously
derived weighted mean temperature, thereby obtaining a dynamically updated delay time.
[0047] According to this embodiment, the temperature inside the refrigerated volume is continuously
monitored in order to continuously derive the weighted mean temperature, after the
temperature has increased above the cut-in temperature. This continuously derived
weighted mean temperature is then used for continuously deriving a delay time, which
corresponds to the currently occurring weighted mean temperature. Thereby the derived
delay time is continuously adjusted to reflect the actually occurring temperature
inside the refrigerated volume. For instance, in the case that the temperature inside
the refrigerated volume continues to increase, this is taken into account, and the
delay time is decreased, thereby causing the warning to be generated earlier.
[0048] The method may further comprise the step of, in the case that the weighted mean temperature
inside the refrigerated volume decreases below the cut-in temperature, stopping and
resetting the timer.
[0049] According to this embodiment, if the weighted mean temperature decreases below the
cut-in temperature before the delay time is reached, this is an indication that the
vapour compression system is in fact capable of maintaining an acceptable temperature
level inside the refrigerated volume, even though the weighted mean temperature was
temporarily above the cut-in temperature. Accordingly, in this case it is not necessary
to generate a warning. Therefore, the timer is stopped and reset, the delay time will
accordingly not be reached, and a warning is not generated.
[0050] The weighted mean temperature may be a mean kinetic temperature (MKT). The MKT is
defined by the International Conference on Harmonization (ICH) as a single derived
temperature, which, if maintained over a defined period, would afford the same thermal
challenge to a pharmaceutical product as would have been experienced over a range
of both higher and lower temperatures for an equivalent defined period. The MKT yields
a higher temperature than a simple arithmetic mean, and may be calculated using the
Arrhenius equation mentioned above. The MKT quantifies the cumulative thermal stress
to which a product has been subjected when placed at varying temperatures during transport
or storage. The MKT provides higher temperatures with greater weights by computing
the natural logarithm of the absolute temperature. For instance, the MKT may be calculated
using Haynes' formula:
![](https://data.epo.org/publication-server/image?imagePath=2024/13/DOC/EPNWB1/EP22156342NWB1/imgb0002)
where T
k is MKT in kelvin, ΔH is the heat of activation or activation energy, R is the universal
gas constant, T
i is the temperature in kelvin during the i'th time period, and n is the total number
of equal time periods over which data has been collected.
[0051] The method may further comprise the step of scheduling inspection or maintenance
of the vapour compression system in response to a generated warning.
[0052] As described above, when a warning is generated, this is an indication that the vapour
compression is, for some reason, not capable of maintaining the temperature inside
the refrigerated volume within a desired temperature range. This could, e.g., be due
to ice formation on the evaporator, refrigerant loss, malfunctioning components, e.g.
fans, valves, sensors, compressors, etc. in any event, this may require inspection,
and possibly maintenance or repair, of the vapour compression system. Therefore, this
may advantageously be scheduled in response to a generated warning.
[0053] Since the warning is generated before the high temperature alarm limit is reached,
and thereby before the state of the vapour compression system is critical, scheduling
the inspection or maintenance is not urgent, and it can therefore be scheduled at
a convenient time, e.g. during normal working hours of the maintenance personnel,
during closing hours of a store accommodating the vapour compression system, during
a time slot where relevant maintenance personnel is available, etc.
[0054] The method may further comprise the step of resetting the moving time window upon
completion of the scheduled inspection or maintenance.
[0055] According to this embodiment, when maintenance personnel has arrived at the site,
the inspection will be performed, and the cause of the elevated temperature will typically
be identified and alleviated. Thus, when the maintenance personnel has completed the
task, it can be assumed that the vapour compression system is now operating correctly.
Therefore, in order to avoid that a new warning is generated, based on temperature
measurements performed before the inspection or maintenance was performed, the moving
time window may be reset, thereby ensuring that, going forward, the weighted mean
temperature is derived based on measurements performed after completion of the inspection
or maintenance, thereby reflecting the new conditions prevailing in the vapour compression
system.
[0056] In addition, the warning may be reset, thereby indicating that the issue causing
the elevated temperature inside the refrigerated volume has been dealt with.
[0057] Alternatively or additionally, the warning may be reset if the weighted mean temperature
inside the refrigerated volume decreases below the cut-in temperature, even if inspection
or maintenance has not been scheduled. Furthermore, a scheduled inspection may be
cancelled if the weighted mean temperature decreases below the cut-in temperature
after the inspection has been scheduled, but before it has been performed. In this
case it can be assumed that the vapour compression system has been able to overcome
the issues which caused the elevated temperature inside the refrigerated volume, and
that inspection or maintenance is therefore not required.
[0058] The step of setting control parameters related to the refrigerated volume may further
comprise setting a cut-out temperature.
[0059] According to this embodiment, a cut-out temperature is set in addition to the cut-in
temperature, the high temperature alarm limit and the high temperature alarm delay
time. In the present context the term 'cut-out temperature' should be interpreted
to mean a temperature value which triggers closing of the expansion valve which supplies
refrigerant to the evaporator being arranged in thermal contact with the refrigerated
volume. Thus, when the temperature inside the refrigerated volume has decreased to
the cut-out temperature, then the expansion valve is closed, thereby preventing a
flow of refrigerant to the evaporator. This will cause the temperature inside the
refrigerated volume to increase. Thus, by setting the cut-out temperature it is determined
at which temperature level the expansion valve should be closed for that particular
refrigerated volume. As an alternative, in the case that the expansion device is controlled
in accordance with a reference temperature, the cut-out temperature forms the lower
boundary of a temperature interval between the cut-out temperature and the cut-in
temperature, with the reference temperature in the middle of the temperature interval.
[0060] The cut-in temperature and the cut-out temperature may be set in dependence of each
other. For instance, a specific absolute temperature may be selected for the cut-out
temperature, and the cut-in temperature may be specified as a certain temperature
interval above the cut-out temperature, e.g. 2°C or 3°C above the cut-out temperature.
[0061] The vapour compression system may comprise at least two expansion devices and at
least two evaporators, each expansion device controlling a refrigerant supply to one
of the evaporators, and the method may further comprise the step of performing diagnosis
of the vapour compression system based on one or more warnings originating from the
refrigerated volumes being arranged in thermal contact with the evaporators.
[0062] According to this embodiment, the vapour compression system is of a kind which comprises
at least two refrigerated volumes, each being cooled by a separate evaporator. The
vapour compression system could, e.g., be of the kind which may be installed in a
supermarket, comprising several display cases.
[0063] When a warning is generated in the manner described above, this may be due to issues
related to the individual refrigerated volumes, e.g. ice formation on the evaporator,
a malfunctioning fan, etc. However, it may also be due to issues which are related
to the entire vapour compression system, and which may therefore affect several refrigerated
volumes. Such issues may include loss of refrigerant charge, a malfunctioning condenser
fan, a malfunctioning compressor, etc. By simultaneously monitoring warnings originating
from the various refrigerated volumes, information may be derived regarding the nature
of the issues causing the warnings. For instance, if only one refrigerated volume
generates a warning, then the cause of the warning is most likely related to that
refrigerated volume. On the other hand, if several refrigerated volumes generate warnings,
then the cause of the warnings may be related to the entire vapour compression system,
e.g. loss of refrigerant charge. Accordingly, analysing the generated warnings in
this manner may provide an indication for the maintenance personnel with regard to
identifying the cause of the warning(s), thereby leading to a faster conclusion and
alleviation of the issue.
[0064] Thus, the step of performing diagnosis of the vapour compression system may comprise
determining that a system related fault is occurring in the case that warnings originating
from two or more refrigerated volumes occur within a predefined time interval, e.g.
if warnings originating from two or more refrigerated volumes are active simultaneously.
BRIEF DESCRIPTION OF THE DRAWINGS
[0065] The invention will now be described in further detail with reference to the accompanying
drawings in which
Fig. 1 is a diagrammatic view of a vapour compression system being operated in accordance
with a method according to a first embodiment of the invention,
Fig. 2 is a diagrammatic view of a vapour compression system being operated in accordance
with a method according to a second embodiment of the invention,
Fig. 3 illustrates temperature inside a refrigerated volume as a function of time,
including various temperature limits,
Fig. 4 illustrates deriving a delay time in accordance with a method according to
an embodiment of the invention,
Fig. 5 illustrates temperature inside a refrigerated volume as a function of time
while ice formation is building up on the evaporator,
Fig. 6 illustrates generated warnings and alarms as a function of time in a vapour
compression system comprising multiple refrigerated volumes, and being operated in
accordance with a method according to an embodiment of the invention, and
Fig. 7 is a detail of the graph of Fig. 6.
DETAILED DESCRIPTION OF THE DRAWINGS
[0066] Fig. 1 is a diagrammatic view of a vapour compression system 1 being operated in
accordance with a method according to a first embodiment of the invention. The vapour
compression system 1 comprises a compressor unit 2, a heat rejecting heat exchanger
3, an expansion device 4 and an evaporator 5 arranged in a refrigerant path. A fan
6 is arranged to drive a secondary fluid flow across the heat rejecting heat exchanger
3.
[0067] During operation of the vapour compression system 1, refrigerant flowing in the refrigerant
path is compressed by means of the compressor(s) of the compressor unit 2 before being
supplied to the heat rejecting heat exchanger 3. When the refrigerant passes through
the heat rejecting heat exchanger 3, heat exchange takes place between the refrigerant
and the secondary fluid flow driven by the fan 6, in such a manner that heat is rejected
from the refrigera nt.
[0068] The refrigerant leaving the heat rejecting heat exchanger 3 is supplied to the expansion
device 4, where it undergoes expansion before being supplied to the evaporator 5.
When passing through the evaporator 5, heat exchange takes place between the refrigerant
and air inside a refrigerated volume arranged in thermal contact with the evaporator
5, in such a manner that heat is absorbed by the refrigerant, while the liquid part
of the refrigerant is at least partly evaporated. Accordingly, cooling is thereby
provided to the refrigerated volume. Finally, the refrigerant is once again supplied
to the compressor unit 2.
[0069] The supply of refrigerant to the evaporator 5 is controlled by means of the expansion
device 4. The supply of refrigerant is controlled in order to obtain a temperature
inside the refrigerated volume which is within a desired temperature interval. Accordingly,
when the temperature inside the refrigerated volume reaches a specified cut-in temperature,
the expansion device 4 is opened, thereby allowing a supply of refrigerant to the
evaporator 5 and causing the temperature inside the refrigerated volume to decrease.
When the temperature inside the refrigerated volume reaches a cut-out temperature,
the expansion device 4 is closed, thereby preventing a supply of refrigerant to the
evaporator 5, and causing the temperature inside the refrigerated volume to increase
again, until the cut-in temperature is reached, etc. As described above, the expansion
device 4 may alternatively be controlled in accordance with a reference temperature
in the middle of a temperature interval between the cut-out temperature and the cut-in
temperature.
[0070] Initially, at least the cut-in temperature, the cut-out temperature, a high temperature
alarm limit and a high temperature alarm delay time are set. The high temperature
alarm limit represents a temperature value, above the desired temperature interval,
which triggers generation of a high temperature alarm, and the high temperature alarm
delay time defines a delay time which is allowed to elapse from the high temperature
alarm limit is reached and until the high temperature alarm is actually generated.
Accordingly, the high temperature alarm delay time represents a dwelling time during
which it is considered acceptable that a temperature at or above the high temperature
alarm limit is occurring inside the refrigerated volume.
[0071] Furthermore, a maximum acceptable relative decay value is derived, based on the high
temperature alarm limit and the high temperature alarm delay time. Thus, the maximum
acceptable relative decay value represents an expected decay of goods stored in the
refrigerated volume, when the temperature inside the refrigerated volume is at a level
corresponding to the high temperature alarm for a time period corresponding to the
high temperature alarm delay time.
[0072] While the vapour compression system 1 is operated in the manner described above,
the temperature inside the refrigerated volume is monitored, and a weighted mean temperature
prevailing inside the refrigerated volume is continuously derived, during a moving
time window of a predefined length.
[0073] In the case that the weighted mean temperature inside the refrigerated volume exceeds
the cut-in temperature, a timer is started. Furthermore, the weighted mean temperature
is continuously derived, based on the monitored temperature inside the refrigerated
volume, and a delay time is dynamically derived, based on the weighted mean temperature
and the previously derived maximum acceptable relative decay value. The delay time
represents a storage time at the weighted mean temperature, which results in a relative
decay value corresponding to the maximum acceptable relative decay value.
[0074] When the timer reaches the delay time, a warning is generated. Based on the generated
warning, inspection or maintenance of the vapour compression system 1 may be scheduled,
in order to remove the cause of the elevated temperature.
[0075] Since the warning is generated when the temperature inside the refrigerated volume
has been above a desired upper temperature limit for a certain time, but before a
high temperature alarm limit has been reached, it is possible to detect issues which
affect the operation of the vapour compression system 1 to the effect that it is difficult
to maintain the temperature inside the refrigerated volume within a desired temperature
interval, at an early stage. Thereby such issues can be addressed before the operation
of the vapour compression system 1 becomes critical.
[0076] Fig. 2 is a diagrammatic view of a vapour compression system 1 being operated in
accordance with a method according to a second embodiment of the invention. The vapour
compression system 1 of Fig. 2 is very similar to the vapour compression system 1
of Fig. 1, and it will therefore not be described in detail here.
[0077] The vapour compression system 1 comprises a number of expansion devices 4, two of
which are shown, each being arranged to supply refrigerant to a separate evaporator
5. Each of the evaporators 5 is arranged in thermal contact with a separate refrigerated
volume. Thus, each of the expansion devices 4 is controlled in order to allow or prevent
a flow of refrigerant to the respective evaporators 5, in order to maintain the temperature
inside the respective refrigerated volumes within respective specified temperature
intervals, essentially in the manner described above with reference to Fig. 1. Furthermore,
warnings may be generated with respect to each of the refrigerated volumes, independently
of the other refrigerated volumes, essentially in the manner described above with
reference to Fig. 1.
[0078] In the vapour compression system 1 of Fig. 2, the entire vapour compression system
1 is further monitored by simultaneously monitoring the warnings generated in relation
to all of the refrigerated volumes. In the case that several refrigerated volumes
generate warnings substantially simultaneously, or within a limited time interval,
this may be an indication that the issue causing the warnings may be system related,
e.g. loss of refrigerant charge or malfunctioning of the condenser fan 6. On the other
hand, if only one of the refrigerated volumes generates a warning, then it is more
likely that the issue causing the warning is related to that specific refrigerate
volume, e.g. defrost requiring ice formation on the corresponding evaporator 5.
[0079] Fig. 3 is a graph illustrating weighted mean temperature inside a refrigerated volume
as a function of time. A cut-out temperature of 2°C, a cut-in temperature of 4°C and
a high temperature alarm limit of 8°C are marked. Furthermore, a maximum desirable
temperature value of 5
°C is marked. The temperature curve 7 represents temperature variations inside the
refrigerated volume when the vapour compression system is operated in accordance with
a prior art method.
[0080] Initially, the temperature 7 is kept within a temperature interval between the cut-out
temperature and the cut-in temperature, i.e. the vapour compression system is performing
as expected. However, at t=t
1, the temperature 7 exceeds the cut-in temperature, and continues to increase above
the 5°C limit at t=t
2. The temperature 7 remains above the 5°C temperature limit for a long period of time,
while slowly increasing, and reaches the high temperature alarm limit at t=t
3. Then a timer is started, and an alarm is generated when the specified high temperature
alarm delay time has elapsed, at t=t
4.
[0081] It can be seen that the slow increase in temperature after t=t
1 has the consequence that the temperature inside the refrigerated volume is above
the 5
°C limit for a very long period of time before the alarm is generated, and the operator
is thereby made aware of the elevated temperature. This may have an undesirable impact
on the shelf-life or quality of the goods being stored in the refrigerated volume.
[0082] If, on the other hand, the vapour compression system had been operated in accordance
with a method according to an embodiment of the invention, the following would have
happened.
[0083] When the temperature 7 exceeds above the cut-in temperature at t=t
1, a timer is started, and a delay time is dynamically derived, based on the weighted
mean temperature and a maximum acceptable relative decay, which corresponds to storing
goods at 8°C for a period of time corresponding to the high temperature alarm delay
time. When the delay time is reached, indicated at t=t
5, a warning is generated. Thus, the operator is warned of the increased temperature
level at a significantly earlier point in time, and before the elevated temperature
becomes critical. This allows inspection or maintenance of the vapour compression
system to be timely scheduled, and may improve the quality and/or shelf-life of goods
being stored in the refrigerated volume.
[0084] Fig. 4 illustrates deriving a delay time in accordance with a method according to
an embodiment of the invention. Similarly to the situation illustrated in Fig. 3,
a cut-in temperature of 4°C and a high temperature alarm limit of 8°C are selected.
Furthermore, the hight temperature alarm delay time is set to 30 minutes.
[0085] A maximum acceptable relative decay value is derived, based on the high temperature
alarm limit and the high temperature alarm delay time. Thus, the maximum acceptable
relative decay value corresponds to an expected decay of stored goods when stored
at the high temperature alarm limit, i.e. at 8°C, for a period of time corresponding
to the high temperature alarm delay time, i.e. for 30 minutes. This may, e.g., include
applying a suitable mathematical model.
[0086] The derived maximum acceptable relative decay value is then used for deriving delay
times as a function of storage temperature, in such a manner that a relative decay
value corresponding to the maximum acceptable relative decay value is obtained for
each pair or combination of storage temperature and delay time. This may also include
applying an appropriate mathematical model. The curve 8 of Fig. 4 represents these
values. It can be seen that a storage temperature corresponding to the cut-in temperature,
i.e. 4°C results in a delay time of 50 minutes. As the storage temperature increases,
the delay time decreases, indicating that a high storage temperature is acceptable
for a shorter time period than a lower storage temperature.
[0087] When a delay time is to be derived during operation of the vapour compression system,
the graph of Fig. 4 is simply consulted, and a delay time can be readily determined,
based on the weighted mean temperature.
[0088] Fig. 5 illustrates temperature inside a refrigerated volume as a function of time
while ice formation is building up on the evaporator. Curve 9 represents measured
temperature, and curve 10 represents weighted mean temperature, in the form of MKT,
during a moving time window. Line 11 represents high temperature alarm state, and
line 12 represents a warning state in accordance with the present invention. The cut-out
temperature is set to 0°C, the cut-in temperature is set to 2°C, and the high temperature
alarm limit is set to 8°C.
[0089] It can be seen that the vapour compression system is initially performing as expected,
and the temperature is kept between the cut-out temperature and the cut-in temperature.
However, on 11 September around noon, ice starts to build up on the evaporator, causing
the temperature 9 inside the refrigerated volume to gradually increase, and exceeding
the cut-in temperature at approximately 6 pm. A bit later the MKT 10 also starts to
increase, and the MKT 10 exceeds the cut-in temperature around midnight. This starts
a timer, and a delay time is dynamically derived, in the manner described above, and
a warning is generated, setting the warning state 12 to '1', when the delay time is
reached.
[0090] However, inspection is not scheduled fast, and the temperature 9 as well as the MKT
10 continues to increase until the temperature 9 exceeds the high temperature alarm
limit shortly after noon on 12 September. This causes an alarm to be generated when
the high temperature alarm delay time has lapsed shortly thereafter, setting the alarm
state 11 to '1'.
[0091] On 13 September shortly before noon, maintenance staff arrives at the site and performs
a defrost procedure which removes the cause of the elevated temperature. Afterwards,
the alarm state 11 and the warning state 12 are reset to '0'. Furthermore, the moving
time window is reset, thereby ensuring that the MKT 10 is subsequently derived based
on temperature measurements 9 performed after the defrost procedure was completed.
[0092] Fig. 6 illustrates generated warnings and alarms as a function of time in a vapour
compression system comprising multiple refrigerated volumes, and being operated in
accordance with a method according to an embodiment of the invention. The vapour compression
system could, e.g., be the vapour compression system illustrated in Fig. 2. More specifically,
curve 13 represents number of warnings generated in accordance with a method according
to the invention, and curve 14 represents number of generated high temperature alarms.
It can be seen that the number of generated warnings 13 is generally higher than the
number of generated high temperature alarms 14. Furthermore, in some periods of time,
the number of generated warnings 13 is relatively high. This indicates that the issue
or issues causing the warnings may be system related, in the sense that it may be
something which affects several refrigerated volumes, e.g. loss of refrigerant charge.
This can be detected by viewing the warnings 13 generated from all of the refrigerated
volumes in combination, rather than handling them separately. Furthermore, this could
not have been detected on the basis of the generated high temperature alarms 14.
[0093] Fig. 7 is a detail of the graph of Fig. 6. It can be seen that before the first high
temperature alarm is generated on 18 July, 4-5 refrigerated volumes have already generated
warnings, thereby allowing relevant actions to be taken in a timely manner.
1. Verfahren zum Betreiben eines Dampfkompressionssystems (1), wobei das Dampfkompressionssystem
(1) eine Kompressoreinheit (2), einen wärmeableitenden Wärmetauscher (3), mindestens
eine Expansionsvorrichtung (4) und mindestens einen Verdampfer (5), der in einem Kältemittelpfad
angeordnet ist, umfasst, wobei jeder Verdampfer (5) in thermischem Kontakt mit einem
gekühlten Volumen zur Lagerung von Waren angeordnet ist, wobei das Verfahren für mindestens
eines der gekühlten Volumina die folgenden Schritte umfasst:
- Einstellen von Steuerparametern in Bezug auf das gekühlte Volumen, einschließlich
Einstellen einer Einschalttemperatur, einer Alarmgrenze für hohe Temperaturen und
einer Verzögerungszeit für einen Alarm bei hohen Temperaturen,
- Ableiten eines maximal akzeptablen relativen Abklingwerts auf Basis der Alarmgrenze
für hohe Temperaturen und der Verzögerungszeit für einen Alarm bei hohen Temperaturen,
- Betreiben des Dampfkompressionssystems (1), während eine Temperatur innerhalb des
gekühlten Volumens überwacht und kontinuierlich eine gewichtete Durchschnittstemperatur
abgeleitet wird, die innerhalb des gekühlten Volumens während eines beweglichen Zeitfensters
einer vordefinierten Länge besteht,
- für den Fall, dass die gewichtete Durchschnittstemperatur innerhalb des gekühlten
Volumens die Einschalttemperatur überschreitet, Starten eines Timers und Fortfahren
mit dem Ableiten der gewichteten Durchschnittstemperatur, die innerhalb des gekühlten
Volumens während eines beweglichen Zeitfensters einer vordefinierten Länge besteht,
- Ableiten einer Verzögerungszeit auf Basis der gewichteten Durchschnittstemperatur
und des maximal akzeptablen relativen Abklingwerts, und
- Erzeugen einer Warnung, wenn der Timer die abgeleitete Verzögerungszeit erreicht.
2. Verfahren nach Anspruch 1, wobei der Schritt des Ableitens eines maximal akzeptablen
relativen Abklingwerts unter Verwendung eines mathematischen Modells durchgeführt
wird.
3. Verfahren nach Anspruch 1 oder 2, das ferner den Schritt des Ableitens von Kombinationen
aus Durchschnittslagertemperatur und Lagerzeit umfasst, die zu einem relativen Abklingwert
führen, der dem abgeleiteten maximal akzeptablen relativen Abklingwert entspricht,
und wobei der Schritt des Ableitens einer Verzögerungszeit auf der gewichteten Durchschnittstemperatur
und den Kombinationen aus Durchschnittslagertemperatur und Lagerzeit basiert.
4. Verfahren nach Anspruch 3, wobei der Schritt des Ableitens von Kombinationen aus Durchschnittslagertemperatur
und Lagerzeit, die zu einem relativen Abklingwert führen, der dem abgeleiteten maximal
akzeptablen relativen Abklingwert entspricht, unter Verwendung eines mathematischen
Modells durchgeführt wird.
5. Verfahren nach Anspruch 3 oder 4, wobei der Schritt des Ableitens von Kombinationen
aus Durchschnittslagertemperatur und Lagerzeit, die zu einem relativen Abklingwert
führen, der dem abgeleiteten maximal akzeptablen relativen Abklingwert entspricht,
das Erzeugen einer Nachschlagetabelle und/oder eines Diagramms umfasst.
6. Verfahren nach einem der vorhergehenden Ansprüche, wobei der Schritt des Ableitens
einer Verzögerungszeit kontinuierlich auf Basis der kontinuierlich abgeleiteten gewichteten
Durchschnittstemperatur durchgeführt wird, wodurch eine dynamisch aktualisierte Verzögerungszeit
erhalten wird.
7. Verfahren nach einem der vorhergehenden Ansprüche, das ferner den Schritt des Stoppens
und Zurücksetzens des Timers umfasst, für den Fall, dass die gewichtete Durchschnittstemperatur
innerhalb des gekühlten Volumens unter die Einschalttemperatur sinkt.
8. Verfahren nach einem der vorhergehenden Ansprüche, wobei die gewichtete Durchschnittstemperatur
eine kinetische Durchschnittstemperatur (MKT) ist.
9. Verfahren nach einem der vorhergehenden Ansprüche, das ferner den Schritt des Planens
einer Inspektion oder Wartung des Dampfkompressionssystems (1) als Reaktion auf eine
erzeugte Warnung umfasst.
10. Verfahren nach Anspruch 9, das ferner den Schritt des Zurücksetzens des beweglichen
Zeitfensters nach Abschluss der geplanten Inspektion oder Wartung umfasst.
11. Verfahren nach einem der vorhergehenden Ansprüche, wobei der Schritt des Einstellens
von Steuerparametern in Bezug auf das gekühlte Volumen ferner das Einstellen einer
Abschalttemperatur umfasst.
12. Verfahren nach einem der vorhergehenden Ansprüche, wobei das Dampfkompressionssystem
(1) mindestens zwei Expansionsvorrichtungen (4) und mindestens zwei Verdampfer (5)
umfasst, wobei jede Expansionsvorrichtung (4) eine Kältemittelzufuhr zu einem der
Verdampfer (5) steuert, wobei das Verfahren ferner den Schritt des Durchführens einer
Diagnose des Dampfkompressionssystems (1) auf Basis einer oder mehrerer Warnungen
umfasst, die von den gekühlten Volumina stammen, die in thermischem Kontakt mit den
Verdampfern (5) angeordnet sind.
13. Verfahren nach Anspruch 12, wobei der Schritt des Durchführens einer Diagnose des
Dampfkompressionssystems (1) das Bestimmen umfasst, dass ein systembezogener Fehler
auftritt, für den Fall, dass Warnungen, die von zwei oder mehr gekühlten Volumina
stammen, innerhalb eines vordefinierten Zeitintervalls erfolgen.
1. Procédé de fonctionnement d'un système de compression de vapeur (1), le système de
compression de vapeur (1) comprenant une unité de compresseur (2), un échangeur de
chaleur de rejet de chaleur (3), au moins un dispositif d'expansion (4) et au moins
un évaporateur (5) agencé dans un chemin de fluide frigorigène, chaque évaporateur
(5) étant agencé en contact thermique avec un volume réfrigéré de stockage de marchandises,
le procédé comprenant, pour au moins l'un des volumes réfrigérés, les étapes suivantes
:
- réglage de paramètres de contrôle liés au volume réfrigéré, y compris le réglage
d'une température d'enclenchement, d'une limite d'alarme de température élevée et
d'une temporisation d'alarme de température élevée,
- dérivation d'une valeur de décroissance relative maximale acceptable, sur la base
de la limite d'alarme de température élevée et de la temporisation d'alarme de température
élevée,
- fonctionnement du système de compression de vapeur (1) tout en surveillant une température
à l'intérieur du volume réfrigéré et en dérivant en continu une température moyenne
pondérée régnant à l'intérieur du volume réfrigéré, durant une fenêtre temporelle
mobile d'une durée prédéfinie,
- dans le cas où la température moyenne pondérée à l'intérieur du volume réfrigéré
dépasse la température d'enclenchement, démarrage d'une minuterie et poursuite de
la dérivation de la température moyenne pondérée régnant à l'intérieur du volume réfrigéré,
durant une fenêtre temporelle mobile d'une durée prédéfinie,
- dérivation d'une temporisation, sur la base de la température moyenne pondérée et
de la valeur de décroissance relative maximale acceptable, et
- génération d'un avertissement quand la minuterie atteint la temporisation dérivée.
2. Procédé selon la revendication 1, dans lequel l'étape consistant à dériver une valeur
de décroissance relative maximale acceptable est mise en œuvre en utilisant un modèle
mathématique.
3. Procédé selon la revendication 1 ou 2, comprenant en outre l'étape consistant à dériver
des combinaisons de température moyenne de stockage et de durée de stockage, résultant
en une valeur de décroissance relative qui correspond à la valeur de décroissance
relative maximale acceptable dérivée, et dans lequel l'étape consistant à dériver
une temporisation est basée sur la température moyenne pondérée et les combinaisons
de température moyenne de stockage et de durée de stockage.
4. Procédé selon la revendication 3, dans lequel l'étape consistant à dériver des combinaisons
de température moyenne de stockage et de durée de stockage résultant en une valeur
de décroissance relative qui correspond à la valeur de décroissance relative maximale
acceptable dérivée est mise en œuvre en utilisant un modèle mathématique.
5. Procédé selon la revendication 3 ou 4, dans lequel l'étape consistant à dériver des
combinaisons de température moyenne de stockage et de durée de stockage résultant
en une valeur de décroissance relative qui correspond à la valeur de décroissance
relative maximale acceptable dérivée comprend la génération d'une table de correspondance
et/ou d'un graphique.
6. Procédé selon l'une quelconque des revendications précédentes, dans lequel l'étape
consistant à dériver une temporisation est mise en œuvre en continu, sur la base de
la température moyenne pondérée dérivée en continu, obtenant ainsi une temporisation
mise à jour de manière dynamique.
7. Procédé selon l'une quelconque des revendications précédentes, comprenant en outre
l'étape consistant, dans le cas où la température moyenne pondérée à l'intérieur du
volume réfrigéré diminue en dessous de la température d'enclenchement, à arrêter et
à réinitialiser la minuterie.
8. Procédé selon l'une quelconque des revendications précédentes, dans lequel la température
moyenne pondérée est une température cinétique moyenne (MKT, soit Mean Kinetic Température).
9. Procédé selon l'une quelconque des revendications précédentes, comprenant en outre
l'étape consistant à planifier une inspection ou une maintenance du système de compression
de vapeur (1) en réponse à un avertissement généré.
10. Procédé selon la revendication 9, comprenant en outre l'étape consistant à réinitialiser
la fenêtre temporelle mobile à la fin de l'inspection ou de la maintenance planifiée.
11. Procédé selon l'une quelconque des revendications précédentes, dans lequel l'étape
consistant à régler des paramètres de contrôle liés au volume réfrigéré comprend en
outre le réglage d'une température de déclenchement.
12. Procédé selon l'une quelconque des revendications précédentes, dans lequel le système
de compression de vapeur (1) comprend au moins deux dispositifs d'expansion (4) et
au moins deux évaporateurs (5), chaque dispositif d'expansion (4) contrôlant une alimentation
en fluide frigorigène vers l'un des évaporateurs (5), dans lequel le procédé comprend
en outre l'étape consistant à mettre en œuvre un diagnostic du système de compression
de vapeur (1) sur la base d'un ou plusieurs avertissements provenant des volumes réfrigérés
agencés en contact thermique avec les évaporateurs (5).
13. Procédé selon la revendication 12, dans lequel l'étape consistant à mettre en œuvre
un diagnostic du système de compression de vapeur (1) comprend la détermination du
fait qu'un défaut lié au système se produit dans le cas où des avertissements provenant
de deux ou plusieurs volumes réfrigérés se produisent dans un intervalle de temps
prédéfini.