U.S. patent application number 15/137122 was filed with the patent office on 2016-08-18 for heat exchanger fault diagnostic.
The applicant listed for this patent is Elstat Limited. Invention is credited to Colin HULL, Philip LAMBERT.
Application Number | 20160238332 15/137122 |
Document ID | / |
Family ID | 49979441 |
Filed Date | 2016-08-18 |
United States Patent
Application |
20160238332 |
Kind Code |
A1 |
LAMBERT; Philip ; et
al. |
August 18, 2016 |
Heat Exchanger Fault Diagnostic
Abstract
A fault diagnostic method for a heat exchanger in which ambient
air temperature and heat exchanger temperature are measured. Also
disclosed is the use of a single temperature sensor, in combination
with a microprocessor, to measure temperature emitted from a heat
exchanger and ambient air temperature surrounding the heat
exchanger.
Inventors: |
LAMBERT; Philip; (Preston,
GB) ; HULL; Colin; (Fleetwood, GB) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Elstat Limited |
Preston |
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GB |
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|
Family ID: |
49979441 |
Appl. No.: |
15/137122 |
Filed: |
April 25, 2016 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
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PCT/GB2014/053524 |
Nov 28, 2014 |
|
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15137122 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
F28F 2265/10 20130101;
F25D 29/008 20130101; F25B 2700/2106 20130101; F28F 27/00 20130101;
F25B 49/005 20130101; F25B 2700/2103 20130101 |
International
Class: |
F28F 27/00 20060101
F28F027/00 |
Foreign Application Data
Date |
Code |
Application Number |
Nov 28, 2013 |
GB |
1320977.0 |
Claims
1. A fault diagnostic method for a heat exchanger in which ambient
air temperature and heat exchanger temperature are measured, the
method comprising: measuring the temperature of the heat exchanger
when the heat exchanger is in operation, measuring the temperature
of ambient air around the heat exchanger when the heat exchanger is
not in operation, comparing the two temperatures, and when the
difference between the two temperatures is greater than a selected
temperature difference, sounding an alarm, alerting an engineer
and/or disabling operation of the heat exchanger.
2. The method according to claim 1 further comprising steps
preceding steps a) to d), wherein: i) a maximum operating
temperature for the heat exchanger is set; and ii) a temperature
difference between the heat exchanger temperature and ambient air
temperature is set for an efficiently operating heat exchange
system.
3. The method according to claim 2, wherein the maximum operating
temperature for the heat exchanger is set within a range of about
50 to 125 degrees Celsius.
4. The method according to claim 1, wherein the temperature
difference is about 30 degrees Celsius.
5. The method according to claim 1, wherein operation of the heat
exchanger is informed by the operation of a compressor or pump
associated with the heat exchanger.
6. The method according to claim 1, wherein the temperature
measurements are stored in a microprocessor.
7. The method according to claim 6, wherein the microprocessor
senses or detects whether or not the pump or compressor is in
operation.
8. The method according to claim 6, wherein the temperature
readings are saved by the microprocessor into separate files as
`heat exchanger temperature` and `ambient air temperature`.
9. The method according to claim 8, wherein the microprocessor
subtracts ambient air temperature from heat exchanger temperature
to ascertain whether or not the heat exchanger is functioning
efficiently.
10. The method according to claim 1, wherein measurement of ambient
air temperature is made after a time period that is sufficient to
enable the heat exchanger to cool to, or near to, ambient
temperature.
11. The method according to claim 10, wherein the time period is
between about 2 and 5 minutes after the heat exchanger has ceased
to operate.
12. The method according to claim 1, wherein the temperatures are
measured by two temperature sensors.
13. The method according to claim 1, wherein the temperatures are
measured by a single temperature sensor.
14. The method according to claim 13, wherein the single
temperature sensor is located on or close to the heat
exchanger.
15. Use of a single temperature sensor, in combination with a
microprocessor, to measure temperature emitted from a heat
exchanger and ambient air temperature surrounding the heat
exchanger.
16. Use according to claim 15, wherein the temperature sensor a)
measures the temperature emitted from the heat exchanger when the
heat exchanger is in operation and b) measures the temperature of
ambient air around the heat exchanger when the heat exchanger is
not in operation.
17. Use according to claim 15, wherein ambient air temperature is
subtracted from the temperature emitted from the heat exchanger
and, when the difference between the two temperatures is greater
than about 30 degrees Celsius, the microprocessor issues a fault
alert.
18. Use according to claim 15, wherein operation of the heat
exchanger is informed by the operation of a pump or compressor
associated with the heat exchanger.
19. Use according to claim 18, wherein the microprocessor senses or
detects whether or not the pump or compressor is in operation.
20. Use according to claim 15, wherein the microprocessor saves the
temperature readings.
21. Use according to claim 20, wherein the temperature readings are
saved by the microprocessor into separate files as `heat exchanger
temperature` and `ambient air temperature`.
22. Use according to claim 21, wherein the microprocessor subtracts
ambient air temperature from heat exchanger temperature to
ascertain whether or not the heat exchanger is functioning
efficiently.
23. Use according to claim 15, wherein measurement of ambient air
temperature is made after a time period that is sufficient to
enable the heat exchanger to cool to, or near to, ambient
temperature.
24. Use according to claim 23, wherein the time period between
about 2 and 5 minutes after the heat exchanger has ceased to
operate.
25. Use according to claim 15, wherein the temperature sensor is
located on or close to the heat exchanger.
26. Use according to claim 15 to diagnose a fault in a heat
exchanger.
Description
RELATED APPLICATIONS
[0001] This application is a continuation of PCT/GB2014/053524,
filed Nov. 28, 2014, titled "HEAT EXCHANGER FAULT DIAGNOSTIC," and
which designated the United States, the entire contents of which
are hereby fully incorporated herein by reference for all purposes.
Application PCT/GB2014/053524 claims priority from GB 1320977.0,
filed Nov. 28, 2013, the entire contents of which are hereby fully
incorporated herein by reference for all purposes.
[0002] The present invention relates to the fault diagnosis of a
heat exchanger in which ambient air temperature and heat exchanger
temperature are measured.
[0003] Refrigeration may be defined as lowering the temperature of
an enclosed space by removing heat from that space and transferring
it elsewhere. The work of heat transport is typically driven by
heat, magnetism, electricity, or other means. Refrigeration has
many applications, including, but not limited to: household
refrigerators, industrial freezers, cryogenics, and air
conditioning. Heat pumps may use the heat output of the
refrigeration process and also may be designed to be reversible,
but are otherwise similar to refrigeration units.
[0004] The vapour-compression cycle is used in most household
refrigerators as well as in many large commercial and industrial
refrigeration systems. The vapour-compression cycle uses a
circulating liquid refrigerant as the medium which absorbs and
removes heat from the space to be cooled and subsequently rejects
that heat elsewhere. A typical, single-stage vapour-compression
system has four components: a compressor, a condenser or heat
exchanger, a thermal expansion valve (also called a throttle
valve), and an evaporator.
[0005] Circulating refrigerant enters the compressor in the
thermodynamic state known as a saturated vapour and is compressed
to a higher pressure, resulting in a higher temperature as well.
The hot, compressed vapour is then in the thermodynamic state known
as a superheated vapour and it is at a temperature and pressure at
which it can be condensed with either cooling water or cooling air.
That hot vapour is routed through a condenser or heat exchanger
where it is cooled and condensed into a liquid by flowing through a
coil, fins or tubes with cool water or cool air flowing across the
coil, fins or tubes. This is where the circulating refrigerant
rejects heat from the system and the rejected heat is carried away
by either the water or the air (whichever may be the case).
[0006] The condensed liquid refrigerant, in the thermodynamic state
known as a saturated liquid, is next routed through an expansion
valve where it undergoes an abrupt reduction in pressure. That
pressure reduction results in the adiabatic flash evaporation of a
part of the liquid refrigerant. The auto-refrigeration effect of
the adiabatic flash evaporation lowers the temperature of the
liquid and vapour refrigerant mixture to where it is colder than
the temperature of the enclosed space to be refrigerated.
[0007] The cold mixture is then routed through the coil or tubes in
the evaporator. A fan circulates the warm air in the enclosed space
across the coil or tubes carrying the cold refrigerant liquid and
vapour mixture. That warm air evaporates the liquid part of the
cold refrigerant mixture. At the same time, the circulating air is
cooled and thus lowers the temperature of the enclosed space to the
desired temperature. The evaporator is where the circulating
refrigerant absorbs and removes heat which is subsequently rejected
in the condenser and transferred elsewhere by the water or air used
in the condenser.
[0008] To complete the refrigeration cycle, the refrigerant vapour
from the evaporator is again a saturated vapour and is routed back
into the compressor.
[0009] A refrigeration unit, such as a refrigerated beverage
merchandising unit (RBMU), comprises a refrigeration system
(electromechanical compressor pump, refrigerant, evaporator, heat
exchanger and an expansion valve) fitted with a means of
controlling when a compressor runs to control the temperature of a
chilled compartment.
[0010] Control of a compressor may be carried out in a variety of
ways. At its most simple, control is via an electromechanical
device, sited inside a chilled compartment, which detects the
temperature and contains a contact to switch the compressor on and
off. More complex electronic devices have a temperature sensor in
the chilled compartment linked to an electronic control device
positioned outside the chilled compartment, which contains the
mechanism for switching the compressor on and off.
[0011] A heat exchanger is the part of a refrigeration system that
expels heat gathered from the chilled compartment. Typically, the
heat exchanger is located outside the cooling compartment and is
cooled with air drawn through it from the ambient surroundings via
an electrical fan or via convection.
[0012] For a refrigeration unit, the extent to which heat transfer
occurs is a function of two things:
[0013] The temperature difference between the ambient air
surrounding the heat exchanger and the temperature of the
circulating liquid/gas.
[0014] The mass of ambient air that can exchange with the heat
exchanger.
[0015] Poor heat exchange occurs when the amount of air passing
through the heat exchanger (and the extent of heat transfer)
reduces significantly due to blockage with dust, debris etc. At
such a time, the refrigeration unit usually sounds an alarm, shuts
itself down and an engineer is alerted.
[0016] Inefficient heat exchange also occurs when the ambient
temperature is too high, i.e. the temperature difference between
the ambient air and the heat exchanger is too small. In such a
situation, the refrigeration unit will shut down and an engineer
will be called out on the assumption that the heat exchanger is
faulty and/or needs cleaning. Beverages, perishable food items etc.
are also removed from sale. In reality, there is no fault and so a)
an engineer is called out unnecessarily and b) saleable goods are
unnecessarily removed from sale.
[0017] Accordingly, it is desirable to measure the temperature of
the ambient air in the vicinity of a refrigeration unit (ambient
air temperature) and the temperature of the heat exchanger itself
(heat exchanger temperature) for fault diagnostics.
[0018] For example, where a refrigeration unit is experiencing
higher than normal heat exchanger temperatures, it is important to
know the ambient air temperature to obtain the correct diagnosis of
what is causing an above-normal heat exchanger temperature (heat
exchanger overheating). A heat exchanger is designed to get rid of
heat and is usually constructed in a way that facilitates this.
There are many different designs (plate, fin and coil, static,
roll) but, in essence, all have the same objective--to create a
large surface area that can be used to exchange heat to a medium
(air, water etc) held at a lower temperature.
[0019] Thus, there is a need to distinguish between a genuine fault
with a heat exchanger and when inefficient heat exchange is due to
an insufficient temperature difference to enable heat exchange to
occur.
[0020] The present invention seeks to solve this problem and thus
resides in a fault diagnostic for a heat exchanger in which ambient
air temperature and heat exchanger temperature are measured.
[0021] When a heat exchanger is in operation, its temperature will
rise to a steady state, usually not reaching more than around
50.degree. C. or around +20.degree. C. above the temperature of the
surrounding ambient air. Once heat exchange is no longer required
by the associated device (for example, the refrigeration unit has
reached its desired chilled compartment temperature), operation of
the heat exchanger ceases and its temperature drops to the
temperature of the ambient air temperature.
[0022] If the heat exchanger is surrounded by dust and dirt, the
return to ambient air temperature is impeded as the dust and dirt
act as an insulator and the heat exchanger retains some of its
operating heat. Alternatively, if the ambient air temperature is
close to the operating temperature of the heat exchanger, the heat
exchanger will not be able to cool sufficiently.
[0023] By measuring the ambient air temperature when the heat
exchanger is not in operation, it is possible to distinguish
between a genuine fault with the heat exchanger, such as a need for
a clean, and a simple elevation in ambient air temperature, under
which circumstances the unit simply requires additional time to
cool down before restarting the heat exchange process.
Distinguishing between the two situations enables the efficient use
and call-out of engineers. Indeed, the majority of unnecessary
engineer call-outs are to RBMUs operating in high ambient air
conditions rather than heat exchanger blockages.
[0024] In one embodiment, the present invention encompasses a heat
exchanger fault diagnostic method comprising:
[0025] measuring the temperature of the heat exchanger when the
heat exchanger is in operation,
[0026] measuring the temperature of ambient air around the heat
exchanger when the heat exchanger is not in operation,
[0027] comparing the two temperatures, and
[0028] when the difference between the two temperatures is greater
than a selected temperature difference, sounding an alarm, alerting
an engineer and/or disabling operation of the heat exchanger.
[0029] By measuring both the temperature of the ambient air around
the heat exchanger and the heat exchanger temperature, it is
possible to make a judgement on whether the heat exchanger
overheating is being caused by high ambient air temperature or heat
exchanger blockage, or a combination of the two.
[0030] In current usage, a heat exchanger temperature above a
certain set point, say 80 or 100 degrees Centigrade, triggers an
alarm in the unit and the unit is switched off to prevent
overheating. However, according to the present invention, where the
high temperature is a result of a high ambient temperature, rather
than a blockage or fault, if the unit is able to self-diagnose that
the high heat exchanger temperature is due to a high ambient
temperature, the machine is instructed to take additional time to
cool down before restarting the heat exchange process, rather than
shutting the machine down unnecessarily. In this way, the
refrigeration unit is able to keep itself open for business and
reduces the need for an engineer to be called out.
[0031] Where high ambient temperature is consistently recorded, the
unit may provide an alert so that the siting of the unit may be
changed to allow better air flow around the heat exchanger.
[0032] In accordance with the present invention, the method further
comprises initial set-up steps in which a maximum operating
temperature for the heat exchanger is set and an acceptable
temperature difference between the heat exchanger temperature and
ambient air temperature (Delta) is set for an efficiently operating
heat exchange system.
[0033] For example, the heat exchanger high temperature may be set
at, say, 100 degrees Centigrade and Delta is 30 degrees
Centigrade.
[0034] In one embodiment, an alarm may be triggered when the heat
exchanger high temperature exceeds the maximum set temperature and
subtraction of ambient air temperature gives a difference (Delta)
of less than 30 degrees Centigrade. However, if subtraction of
ambient air temperature gives a Delta reading of greater than 30
degrees Centigrade then a different alarm is sounded, an engineer
is alerted and/or operation of the heat exchanger is disabled. As
the heat exchanger becomes blocked with debris, for example, the
heat exchanger has a reduced ability to remove heat and so the
difference between ambient air temperature and the high temperature
of the heat exchanger will increase.
[0035] In one embodiment, operation of the heat exchanger is
informed by the operation of a compressor, such as a pump,
associated with the heat exchanger.
[0036] Ideally the temperature measurements are stored in a
microprocessor, wherein a microprocessor is understood to be a
multipurpose, programmable device that accepts digital and/or
analogue data as input, processes it according to instructions
stored in its memory, and provides results as output.
[0037] The microprocessor is able to sense or detect whether the
compressor is running or not, by way of any conventional means such
as a switch, and save the temperature readings. Preferably the
temperature readings are saved by the microprocessor into separate
files (heat exchanger temperature and ambient air temperature). The
second temperature is then subtracted from the first and a
diagnosis made on whether or not the heat exchanger is functioning
efficiently.
[0038] It will be appreciated that the heat exchanger requires time
to cool down after operation and so, in a preferred embodiment, the
ambient air temperature around the heat exchanger is measured after
a time period that is sufficient to enable the heat exchanger to
cool to, or near to, ambient temperature. For example, such a time
period may be approximately 2 to 5 minutes after the heat exchanger
has ceased to operate.
[0039] In one embodiment, the two temperatures are measured by two
temperature sensors: one to measure the temperature of the heat
exchanger and a second to measure the temperature of the ambient
air.
[0040] In an alternative embodiment, the two temperatures are
measured by a single temperature sensor. The temperature sensor may
be mounted on or close to the heat exchanger. Because temperature
is measured and recorded over time, two sensors may be replaced by
a single sensor. The difference in temperature recordings is
sufficient to enable the microprocessor to determine whether or not
the heat exchanger is functioning efficiently and, if not, whether
there is a fault or the inefficiency is due to a high ambient air
temperature.
[0041] In another aspect, the present invention resides in the use
of a single temperature probe or sensor, in combination with a
microprocessor, to measure temperature emitted from a heat
exchanger and ambient air temperature surrounding the heat
exchanger. By measuring and recording temperature readings when the
heat exchanger is in operation and when it has stopped, it is
possible to establish two separate, discrete temperature
measurements using the same temperature sensor.
[0042] In particular, the single sensor is used to assess the
efficiency of the heat exchanger such that, when the difference
between the two temperatures falls below a critical level, the
microprocessor is able to ascertain whether the inefficiency is due
to a high ambient air temperature and so keep the unit functioning,
rather than raising an alarm and/or shutting down the associated
refrigeration system.
[0043] In addition, the use of a single sensor, in place of two
sensors, reduces the complexity and cost in construction of devices
such as refrigerator units while retaining the diagnostic
capability of two separate temperature sensors.
BRIEF DESCRIPTION OF THE DRAWINGS
[0044] The present invention will now be described in detail by way
of example as illustrated in the accompanying figures in which:
[0045] FIG. 1 is a scheme setting out the flow of instructions for
the method and single sensor of the invention when installed in a
refrigeration unit such as a RBMU; and
[0046] FIG. 2 is a scheme setting out the flow of instructions for
overheating of a heat exchanger in a refrigeration unit.
[0047] It will be understood that a refrigeration unit includes a
heat exchanger and a compressor in which the compressor compresses
and vaporises circulating refrigerant. The unit also includes a
microprocessor.
[0048] As shown in FIG. 1, on initial start-up of the unit, the
microprocessor begins a two-pronged routine to enable dual sensing
of heat exchanger temperature and ambient air temperature. First,
the microprocessor enquires whether or not the compressor is
running.
[0049] If the compressor is running, the microprocessor starts a
High Temperature routine to ascertain the temperature of the heat
exchanger. If the parameter DTS (dual temperature sensor) is equal
to 1, the dual temperature sensor is enabled on the refrigeration
unit. The compressor is then confirmed to be running and the
temperature sensor is instructed to record the current temperature
(HT) of the heat exchanger.
[0050] If the parameter DTS does not equal 1 and the compressor is
running, the microprocessor simply instructs the recording of the
heat exchange temperature because the dual temperature sensing
feature is not enabled.
[0051] As illustrated in FIG. 2, when the compressor is running and
the temperature of the heat exchanger exceeds a maximum pre-set
threshold, for example a temperature between 50 and 125 degrees
Celsius, the compressor is switched off. Following this, the
microprocessor subtracts the stored ambient air temperature from
the high heat exchanger temperature. If the difference between the
two temperatures is less than a programmed value (for example, 30
degrees Celsius), the high ambient temperature is flagged as a
warning and the heat exchanger continues to operate after an
extended period of cooling down.
[0052] If the difference between the two temperatures is greater
than the programmed value (for example, about 30 degrees Celsius),
this may be used to trigger an alarm or a service request for an
engineer, and/or the refrigeration unit is kept switched off until
a service call is answered.
[0053] Returning to FIG. 1, if the parameter DTS does not equal 1
and the compressor is not running, the high temperature enquiry
finishes.
[0054] If the compressor is not running, the second part of the
routine is initiated. If the parameter DTS is not equal to 1, the
dual temperature sensor is not enabled and the routine ends.
[0055] If the parameter DTS is equal to 1, the dual temperature
sensor is confirmed to be enabled. The microprocessor then enquires
whether the compressor is off. If the compressor is recorded as
running, this part of the routine finishes and the temperature
sensor simply records the temperature of the heat exchanger
according to the first prong of the routine.
[0056] If the compressor is confirmed to be off, the microprocessor
enquires whether Rest Time has expired.
[0057] Rest Time is the minimum amount of time for which the
compressor must be off between cycles. This is to prevent the
compressor cycling too often, which results in mechanical damage.
Rest Time is set within the microprocessor and is dependent on the
compressor and its expected load. Rest Time starts when the
compressor is switched off and a typical time for a RBMU is between
2 and 5 minutes.
[0058] If Rest Time has not expired, the routine waits until this
time period has expired.
[0059] Once Rest Time has expired, the microprocessor instructs the
temperature sensor to take a temperature reading and to write that
reading to the memory of the microprocessor as ambient air
temperature. The ambient air temperature timer is also started.
[0060] The ambient air temperature timer is the additional time
allowed from end of the pre-set Rest Time to enable the
microprocessor to record ambient air temperature. If the
refrigeration compartment in the unit reaches a temperature at
which the compressor needs to be run, the refrigeration compartment
will start the compressor and over-ride the ambient air temperature
timer. The temperature sensor will then revert to the high
temperature sensor routine described above where the temperature of
the heat exchanger is recorded.
[0061] Until the compressor is restarted and/or the ambient air
temperature timer expires, further ambient air temperature readings
are taken. The ambient air temperature reading is only stored to
memory while the compressor is off and the ambient air temperature
timer is running if the temperature reading is less than the
previous reading stored in the microprocessor memory. When the
lower temperature reading is stored to memory, the previous value
stored in the memory value is over-written with the new value. This
is to prevent rogue spikes in temperature from being erroneously
recorded, caused by residual heat in the heat exchanger.
[0062] As soon as the ambient air temperature timer finishes or is
overridden by the refrigeration compartment, the microprocessor
instructs the temperature sensor to take a temperature reading.
This reading is stored to the microprocessor memory and over-writes
the previously stored value, regardless of whether it is higher or
lower than the stored value. Ambient air temperature is thus
recorded as the last temperature stored.
[0063] Once the ambient air temperature timer has expired or been
overridden by the refrigeration compartment, the routine returns to
the beginning and enquires whether the compressor is on or off.
Thus, the compressor and the temperature recordings act in
parallel, with the compressor being thermostat controlled and the
temperature sensor recording ambient air temperature as and when
the opportunity allows.
[0064] In summary, when the compressor is running, the temperature
sensor acts as a high temperature sensor and continuously records
the temperature of the heat exchanger with no rules. The rules
outlined above only apply when the compressor is not running and
Rest Time has expired. The rules enable the microprocessor to
determine the ambient air temperature around the heat exchanger
from the temperature of the heat exchanger itself once the
compressor and heat exchanger have not been in operation for at
least the pre-set Rest Time period.
[0065] Various modifications and variations of the described
aspects and embodiments of the present invention will be apparent
to those skilled in the art without departing from the scope of the
present invention. Although the present invention has been
described in connection with specific preferred embodiments, it
should be understood that the invention as claimed should not be
unduly limited to such specific embodiments.
* * * * *