U.S. patent application number 15/176415 was filed with the patent office on 2016-12-15 for method of controlling combustion apparatus.
This patent application is currently assigned to RINNAI CORPORATION. The applicant listed for this patent is RINNAI CORPORATION. Invention is credited to Hideo Okamoto.
Application Number | 20160363348 15/176415 |
Document ID | / |
Family ID | 57515780 |
Filed Date | 2016-12-15 |
United States Patent
Application |
20160363348 |
Kind Code |
A1 |
Okamoto; Hideo |
December 15, 2016 |
METHOD OF CONTROLLING COMBUSTION APPARATUS
Abstract
A combustion apparatus having a burner, a combustion box, a
combustion fan for supplying combustion air, and a regulator for
regulating the amount of combustion fan, an inspection operation is
performed in a state in which an operational quantity of the
regulator (fan rotational speed) is kept at a maximum amount Nmax.
When a deviation between a maximum set combustion amount YQmax
corresponding to supply/exhaust resistances as detected in the
inspection operation and an actually measured maximum combustion
amount Qmax is outside an allowable range, a secondary inspection
operation is performed by lowering the fan rotational speed down to
a value Now which is lower than Nmax by a predetermined rate. Based
on the rate of decrease of Qlow relative to Qmax as detected by the
secondary inspection operation, computation is made of a fan
rotational speed Nsat at which the burner combustion amount ceases
to increase even if the fan rotational speed is increased. The
upper limit value of fan rotational speed is then changed to
Nsat.
Inventors: |
Okamoto; Hideo; (Nagoya-shi,
JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
RINNAI CORPORATION |
Nagoya-shi |
|
JP |
|
|
Assignee: |
RINNAI CORPORATION
Nagoya-shi
JP
|
Family ID: |
57515780 |
Appl. No.: |
15/176415 |
Filed: |
June 8, 2016 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
F24H 9/2035 20130101;
F23L 1/00 20130101; F24H 1/145 20130101; F23N 1/00 20130101; F23K
1/00 20130101 |
International
Class: |
F24H 9/20 20060101
F24H009/20; F24H 1/14 20060101 F24H001/14 |
Foreign Application Data
Date |
Code |
Application Number |
Jun 11, 2015 |
JP |
2015-117969 |
Claims
1. A method of controlling a combustion apparatus, the combustion
apparatus comprising: a burner; a combustion box for disposing
therein a to-be-heated object that is heated by combustion gas from
the burner; a combustion fan for supplying combustion air to the
burner; at least one of an air supply tube communicated with a
suction side of the combustion fan, and an exhaust pipe
communicated with an exhaust port of the combustion box; and a gas
amount regulating means for regulating an amount of fuel gas supply
to the burner, the method comprising: searching in advance for
change characteristics of a maximum set combustion amount due to
change in flow resistance through an auxiliary tube, where the
maximum set combustion amount is defined to be such a burner
combustion amount as will originally be obtainable when a primary
pressure of the fuel gas is normal and when an operational quantity
of the gas amount regulating means is at an upper limit value at
which the fuel gas supply amount becomes maximum, and where the
auxiliary tube is defined to be whichever of the air supply tube
and the exhaust pipe the combustion apparatus is provided with;
performing an inspection operation while operating the combustion
apparatus in a state in which the operational quantity of the gas
amount regulating means is kept at the upper limit value, in order
to detect the flow resistance through the auxiliary tube and the
burner combustion amount; obtaining, from the change
characteristics, the maximum set combustion amount that corresponds
to the flow resistance, as detected in the inspection operation,
through the auxiliary tube; when a deviation between the maximum
set combustion amount and the actually measured maximum combustion
amount that is the burner combustion amount as detected in the
inspection operation is outside a predetermined allowable range,
performing a secondary inspection operation to obtain a saturated
value which is such a value of the operational quantity of the gas
amount regulating means as the burner combustion amount will cease
to increase even if the operational quantity of the gas amount
regulating means is increased; and changing the upper limit value
of the operational quantity of the gas amount regulating means to
the obtained saturated value.
2. The method of controlling a combustion apparatus according to
claim 1, wherein the inspection operation is performed at a time of
trial operation after having placed in position the combustion
apparatus, the method further comprising: when the flow resistance
through the auxiliary tube as detected in the inspection operation
is outside a predetermined reference range, displaying "auxiliary
tube abnormal" which means that the auxiliary tube is abnormal; and
when a deviation between the maximum set combustion amount that
corresponds to the flow resistance through the auxiliary tube as
detected in the inspection operation and the actually measured
maximum combustion amount is within the allowable range, displaying
"primary pressure normal" which means that the primary pressure of
the fuel gas is normal.
3. The method of controlling a combustion apparatus according to
claim 1, wherein the secondary inspection operation is performed by
detecting the burner combustion amount while operating the
combustion apparatus in a state in which the operational quantity
of the gas amount regulating means is lowered by a predetermined
rate from the upper limit value, the method further comprising
computing the saturated value based on the rate of decrease of the
burner combustion amount as detected in the secondary inspection
operation relative to the actually measured maximum combustion
amount.
4. The method of controlling a combustion apparatus according to
claim 3, wherein, when the rate of decrease of the burner
combustion amount as detected in the secondary inspection operation
relative to the actually measured maximum combustion amount is
below a predetermined threshold value, displaying "primary pressure
abnormal" is made showing that the primary pressure of the fuel gas
is abnormal.
5. The method of controlling a combustion apparatus according to
claim 1, further comprising: when the upper limit value of the
operational quantity of the gas amount regulating means is changed
to the saturated value, displaying the upper limit value which
shows the changed upper limit value.
Description
BACKGROUND
[0001] 1. Technical Field
[0002] This invention relates to a method of controlling a
combustion apparatus which is provided with: a burner; a combustion
box containing therein an object that is heated by combustion gas
from the burner (this "object" is hereinafter also referred to as a
"to-be-heated object"); a combustion fan for supplying combustion
air to the burner; at least one of an air supply tube communicated
with a suction side of the combustion fan and an exhaust pipe
communicated with an exhaust port of the combustion box; and a gas
amount regulating means for regulating an amount of fuel gas supply
to the burner.
[0003] 2. Related Art
[0004] As long as a primary pressure of the fuel gas is normal, the
fuel gas supply amount increases in proportion to an increase in an
operational quantity (amount of manipulation) of the gas amount
regulating means. Suppose that the operational quantity of the gas
amount regulating means in which the fuel gas supply amount becomes
maximum that is necessary for control purpose is defined as an
upper limit value. Then the operational quantity of the gas amount
regulating means is managed to be varied within a range below the
upper limit value depending on the required combustion amount.
However, if the primary pressure of the fuel gas becomes
insufficient due, for example, to clogging in a gas pipe, and the
like, the fuel gas supply amount will increase to a certain degree
when the operational quantity of the gas amount regulating means is
increased. Thereafter, the fuel gas supply amount ceases to
increase even if the operational quantity of the gas amount
regulating means is increased further.
[0005] As a solution, the following art is known. That is, when the
difference between the burner combustion amount that can originally
be obtained when the operational quantity of the gas amount
regulating means is increased to the upper limit value (maximum set
combustion amount) and the burner combustion amount that is
detected in a state in which the operational quantity of the gas
amount regulating means is at the upper limit value (actually
measured maximum combustion amount) exceeds a predetermined
allowable range, a judgment is made that the primary pressure of
the fuel gas is insufficient. Then, there is obtained a saturated
value which is a value of the operational quantity of the gas
amount regulating means at which the burner combustion amount
ceases to increase even if the operational quantity of the gas
amount regulating means is increased. The upper limit value of the
operational quantity of the gas amount regulating means is then
changed to the obtained saturated value (see, for example, JP
1995-198129A).
[0006] By the way, as the gas amount regulating means, largely
classified, there are the following two systems, i.e., one is of
proportional valve system and the other is of zero governor system.
In the proportional vale system, a proportional valve is interposed
in a fuel gas supply passage so that the fuel gas supply amount is
regulated by the proportional valve. In the zero governor system,
on the other hand, a downstream end of the fuel gas supply passage
is connected to the air suction passage on the upstream side of the
combustion fan, and the zero governor which maintains the secondary
pressure at the atmospheric pressure, is interposed in the fuel gas
supply passage. In this arrangement, the suction negative pressure
on the upstream side of the combustion fan varies in proportion to
the rotational speed of the combustion fan (strictly speaking, the
amount of air supply by the combustion fan). The fuel gas supply
amount that is determined by the differential pressure between the
atmospheric pressure, that is the secondary pressure of the fuel
gas, and the suction negative pressure, varies in proportion to the
rotational speed of the combustion fan.
[0007] Here, let us define whichever of the air supply tube and the
exhaust pipe is disposed in the combustion apparatus, as an
auxiliary tube. Then, in the gas amount regulating means of the
proportional valve system, when the flow resistance through the
auxiliary tube increases, the pressure rises in the combustion box
having disposed therein the gas nozzle. Therefore, the amount of
gas to be ejected from the gas nozzle decreases and consequently
the burner combustion amount decreases. In the gas amount
regulating means of the zero governor system, when the flow
resistance through the auxiliary tube increases, the air supply
amount becomes smaller than the normal amount that corresponds to
the rotational speed of the combustion fan. As a consequence of
decrease in the suction negative pressure, the fuel gas supply
amount decreases and the burner combustion amount decreases.
[0008] However, conventionally no attention has been paid to the
decrease in the burner combustion amount due to an increase in the
flow resistance through the auxiliary tube. If the flow resistance
through the auxiliary tube is large even in case the primary
pressure of the fuel gas is normal, the difference between the
maximum set combustion amount and the actually measured maximum
combustion amount exceeds an allowable range. A judgment is then
made that the primary pressure of the fuel gas is insufficient and,
consequently, the upper limit value of operational quantity of the
gas amount regulating means is unnecessarily lowered.
SUMMARY
[0009] In view of the above points, it is an advantage of this
invention to provide a method of controlling a combustion apparatus
in which there can be prevented unnecessary lowering, under the
influence of the flow resistance through the auxiliary tube, in the
upper limit value of the operational quantity of the gas amount
regulating means.
Means for Solving the Problems
[0010] In order to solve the above-mentioned problems, this
invention is a method controlling a combustion apparatus. The
combustion apparatus comprises: a burner; a combustion box for
disposing therein a to-be-heated object that is heated by
combustion gas from the burner; a combustion fan for supplying
combustion air to the burner; at least one of an air supply tube
communicated with a suction side of the combustion fan, and an
exhaust pipe communicated with an exhaust port of the combustion
box; and a gas amount regulating means for regulating an amount of
fuel gas supply to the burner. The method comprises: searching in
advance for change characteristics of a maximum set combustion
amount due to change in flow resistance through an auxiliary tube,
where the maximum set combustion amount is defined to be such a
burner combustion amount as will originally be obtainable when a
primary pressure of the fuel gas is normal and when an operational
quantity of the gas amount regulating means is at an upper limit
value at which the fuel gas supply amount becomes maximum, and
where the auxiliary tube is defined to be whichever of the air
supply tube and the exhaust pipe the combustion apparatus is
provided with; performing an inspection operation while operating
the combustion apparatus in a state in which the operational
quantity of the gas amount regulating means is kept at the upper
limit value, in order to detect the flow resistance through the
auxiliary tube and the burner combustion amount; obtaining, from
the change characteristics, the maximum set combustion amount that
corresponds to the flow resistance, as detected in the inspection
operation, through the auxiliary tube; when a deviation between the
maximum set combustion amount and the actually measured maximum
combustion amount that is the burner combustion amount as detected
in the inspection operation is outside a predetermined allowable
range, performing a secondary inspection operation to obtain a
saturated value which is such a value of the operational quantity
of the gas amount regulating means as the burner combustion amount
will cease to increase even if the operational quantity of the gas
amount regulating means is increased; and changing the upper limit
value of the operational quantity of the gas amount regulating
means to the obtained saturated value.
[0011] According to this invention, even in case the flow
resistance through the auxiliary tube is large although the primary
pressure of the fuel gas is normal, thereby resulting in a decrease
in the actually measured maximum combustion amount, a comparison is
made between the set maximum combustion amount that corresponds to
such a flow resistance through the auxiliary tube as was detected
in the inspection operation and the actually measured maximum
combustion amount. Therefore, the deviation between the two amounts
falls within an allowable range. In this manner, the upper limit
value of the operational quantity of the gas amount regulating
means will not be changed in the secondary inspection operation. As
a consequence, unnecessary lowering, under the influence of the
flow resistance through the auxiliary tube, in the upper limit
value of the operational quantity of the gas amount regulating
means can be prevented.
[0012] In this invention, preferably, the inspection operation is
performed at a time of trial operation after having placed in
position the combustion apparatus. The method further comprises:
when the flow resistance through the auxiliary tube as detected in
the inspection operation is outside a predetermined reference
range, displaying "auxiliary tube abnormal" which means that the
auxiliary tube is abnormal; and when a deviation between the
maximum set combustion amount that corresponds to the flow
resistance through the auxiliary tube as detected in the inspection
operation and the actually measured maximum combustion amount is
within the allowable range, displaying "primary pressure normal"
which means that the primary pressure of the fuel gas is normal.
According to this arrangement, the person in charge of installing
the combustion apparatus ready for use can advantageously
discriminate as to whether there is a problem such as clogging to,
and/or loose connection in, the auxiliary tube and the gas piping.
If there is such a problem, the person in question can easily
discriminate where the problem lies.
[0013] Further, in this invention, preferably, the secondary
inspection operation is performed by detecting the burner
combustion amount while operating the combustion apparatus in a
state in which the operational quantity of the gas amount
regulating means is lowered by a predetermined rate from the upper
limit value. In this case, the saturated value can be computed
based on the rate of decrease of the burner combustion amount as
detected in the secondary inspection operation relative to the
actually measured maximum combustion amount. Further, in this case,
when the rate of decrease of the burner combustion amount as
detected in the secondary inspection operation relative to the
actually measured maximum combustion amount is below a
predetermined threshold value, preferably displaying "primary
pressure abnormal" is made to show that the primary pressure of the
fuel gas is abnormal.
[0014] Further, in this invention, when the upper limit value of
the operational quantity of the gas amount regulating means is
changed to the saturated value, preferably displaying is made of
the upper limit value which shows the changed upper limit value.
According to this arrangement, even if the upper limit value of the
operational quantity of the gas amount regulating means is changed
low and consequently the heating capacity is lowered, the user is
informed of the fact of lowering in the heating capacity. In this
manner, the user can be prevented from mistaking the phenomenon for
a mechanical trouble in the combustion apparatus.
BRIEF DESCRIPTION OF THE DRAWINGS
[0015] FIG. 1 is a schematic diagram of an example of a combustion
apparatus for carrying out the method of control according to an
embodiment of this invention.
[0016] FIG. 2 is a flow chart showing the method of control
according to the embodiment of this invention.
[0017] FIG. 3 is a graph showing the relationship between the
operational quantity (rotational speed of a combustion fan) and the
combustion amount of a gas amount regulating means.
DESCRIPTION OF EXEMPLARY EMBODIMENTS
[0018] With reference to FIG. 1, reference numeral 1 denotes a
closed type of housing of a combustion apparatus. Inside the
housing 1 there are housed: a burner 2; a combustion box 4
containing therein a heat exchanger 3 for supplying hot water, the
heat exchanger serving the purpose as an object that is heated by
the combustion gas of the burner 2 ("to-be-heated object"); and a
combustion fan 5 for supplying the burner 2 with combustion air.
The combustion apparatus is provided, as tubes which are auxiliary
with the combustion apparatus, with: an air supply tube 6 which is
communicated with the suction side of the combustion fan 5 through
an inner space of the housing 1; and an exhaust pipe 7 which is
communicated with an exhaust port 4a of the combustion box 4. The
combustion apparatus is further provided with a gas amount
regulating means 8 for regulating an amount of fuel gas supply to
the burner 2; and a controller 9 which serves as a control means.
The controller 9 has connected thereto a remote control unit
9a.
[0019] The gas amount regulating means 8 is of a zero governor
system which is arranged such: that a downstream end of a fuel gas
supply passage 81 is connected to a venturi section 52 which is
provided in an air suction passage 51 on an upstream side of the
combustion fan 5; and that the fuel gas supply passage 81 has
interposed therein a zero governor 82 which maintains the secondary
pressure at atmospheric pressure. According to this arrangement,
the suction negative pressure at the venturi section 52 varies in
proportion to the rotational speed of the combustion fan 5
(strictly speaking, the amount of air supply by the combustion fan
5). Also the fuel gas supply amount to be determined by the
differential pressure between the atmospheric pressure that is the
secondary pressure of the fuel gas and the suction negative
pressure varies in proportion to the rotational speed of the
combustion fan 5. By means of the controller 9 computation is made
of the combustion amount (required combustion amount) of the burner
2 required for delivering hot water at a set temperature from the
heat exchanger 3. By controlling the rotational speed of the
combustion fan 5 so as to obtain an air supply amount corresponding
to the required combustion amount, the amount of fuel gas supply to
the burner 2 is also adjusted to the amount corresponding to the
required combustion amount.
[0020] By the way, if the primary pressure of the fuel gas is
normal, the fuel gas supply amount, i.e., the combustion amount of
the burner 2, will increase in proportion to the rotational speed
of the combustion fan 5, as illustrated by line "a" in FIG. 3,
until the rotational speed of the combustion fan 5, that is an
operational quantity of the gas amount regulating means 8, reaches
a predetermined upper limit value Nmax. On the other hand, if the
primary pressure of the fuel gas becomes insufficient due, for
example, to clogging in the gas pipe, etc., as illustrated by line
"b" in FIG. 3, the combustion amount of the burner 2 ceases to
increase any further, at a point where the combustion amount of the
burner 2 has increased to a certain degree as a result of increase
in the rotational speed of the combustion fan 5. Any further
increase in the rotational speed of the combustion fan 5 will not
increase the combustion amount. Suppose that the value of the
rotational speed of the combustion fan 5 at which the combustion
amount of the burner 2 ceases to increase despite the increase in
the rotational speed of the combustion fan 5, is defined as a
saturated value Nsat. Then, if the rotational speed of the
combustion fan 5 is increased to a value exceeding the saturated
value Nsat, the air supply amount becomes excessive, so that the
combustion at the burner 2 becomes instable.
[0021] Suppose that such a combustion amount of the burner 2 as
will originally be obtainable when the rotational speed of the
combustion fan 5 is made to be an upper limit value Nmax is defined
as a maximum set combustion amount, and that such a combustion
amount of the burner 2 as will be detected when the rotational
speed of the combustion fan 5 is made to be the upper limit value
Nmax is defined as an actually measured maximum combustion amount
of the burner 2. Then, it is conceivable to change the upper limit
value of rotational speed of the combustion fan 5 to the saturated
value Nsat, based on a judgment that the primary pressure of the
fuel gas is insufficient when the deviation between the maximum set
combustion amount and the actually measured maximum combustion
amount is outside the predetermined allowable range. However, if
the supply/exhaust resistances that are total ventilation
resistances in the air supply tube 6 and in the exhaust pipe 7
increase, the air supply amount becomes smaller than the regular
amount that corresponds to the rotational speed of the combustion
fan 5. As a consequence of decrease in the suction negative
pressure, the fuel gas supply amount will also decrease.
Accordingly, if the supply/exhaust resistances are large even if
the primary pressure of the fuel gas is normal, the difference
between the maximum set combustion amount and the actually measured
maximum combustion amount exceeds the allowable range. A judgement
will thus be made that the primary pressure of the fuel gas is
insufficient, and the upper limit value of the rotational speed of
the combustion fan 5 will unnecessarily be lowered.
[0022] In order to eliminate this kind of disadvantages, the
following arrangement has been made in this embodiment. In other
words, suppose that the primary pressure of the fuel gas is normal
and that such a combustion amount of the burner 2 as will
originally be obtainable when the rotational speed of the
combustion fan 5 is made to be the upper limit value Nmax is
defined to be a maximum set combustion amount. Change
characteristics of the maximum set combustion amount due to the
change in the supply/exhaust resistances were studied and these
change characteristics were stored in memory on the controller
9.
[0023] Then, as shown in FIG. 2, at the time of trial operation of
the combustion apparatus after it has been placed in position,
i.e., when a switch for trial operation is discriminated to have
been pushed in STEP 1, the process proceeds to STEP 2, where (i.e.,
in STEP 2), while keeping the combustion apparatus in operation in
a state in which the rotational speed of the combustion fan 5 is
maintained at the upper limit value Nmax, an inspection operation
is performed to detect the supply/exhaust resistances and the
combustion amount of the burner 2. By the way, the supply/exhaust
resistances can be computed by detecting the amount of air to flow
through the combustion fan 5 based on electric current of the motor
for the combustion fan 5, on the differential pressure between the
internal pressure of the housing 1 and the suction negative
pressure of the combustion fan 5, or the like. Further, the
combustion amount of the burner 2 can be computed based on such an
amount of heating in the heat exchanger 3 as can be obtained from
the amount of water flow through the heat exchanger 3, the
temperature of water feed to the heat exchanger 3, and the
temperature of water discharge from the heat exchanger 3.
[0024] The process then proceeds to STEP 3, where a discrimination
is made as to whether the supply/exhaust resistances as detected in
the inspection operation are within a predetermined reference range
or not. If abnormalities of the air supply tube 6 and the exhaust
pipe 7 such as clogging, disconnection and the like are present in
the air supply tube 6 and the exhaust pipe 7, the detected
supply/exhaust resistances will be outside the reference value. In
such a case, the process proceeds to STEP 4, where displaying is
made by using the remote control unit 9a to show that the air
supply tube 6 and the exhaust pipe 7 are abnormal.
[0025] On the other hand, if the detected supply/exhaust
resistances are within the reference range, the process proceeds to
STEP 5, where searching is made to obtain a maximum set combustion
amount YQmax corresponding to the supply/exhaust resistances as
detected in the inspection operation based on the change
characteristics held in memory. Then, the process proceeds to STEP
6, where a discrimination is made as to whether a deviation between
the obtained maximum set combustion amount YQmax and the actually
measured maximum combustion amount Qmax that is the combustion
amount of the burner 2 as detected in the inspection operation, is
within the predetermined allowable range (e.g., within .+-.5% of
the maximum set combustion amount) or not. Then, if the deviation
between the maximum set combustion amount YQmax and the actually
measured maximum combustion amount Qmax is within the allowable
range, the process proceeds to STEP 7, where displaying of "primary
pressure normal" is made by using the remote control unit 9a to
show that the primary pressure of the fuel gas is normal.
[0026] If, on the other hand, the deviation between the maximum set
combustion amount YQmax and the actually measured maximum
combustion amount Qmax is outside the allowable range, the process
proceeds to STEP 8, where a secondary inspection operation is
performed to obtain the saturated value Nsat. In concrete, the
secondary inspection operation is performed, while operating the
combustion apparatus with the rotational speed of the combustion
fan 5 being lowered to a value Nlow which is lower by a
predetermined rate (e.g., by 20%) than the upper limit value Nmax,
to thereby detect the combustion amount of the burner 2. Then, the
process proceeds to STEP 9, where a discrimination is made as to
whether a rate of decrease (=(Qmax/Qlow)-1) of the combustion
amount Qlow of the burner 2 as detected in the secondary inspection
operation relative to the actually measured maximum combustion
amount Qmax is above a predetermined threshold value (e.g., 4%) or
not.
[0027] Then, if the rate of decrease of the combustion amount Qlow
of the burner 2 as detected in the secondary inspection operation
relative to the actually measured maximum combustion amount Qmax is
above the predetermined threshold value, a judgment is made that
the primary pressure of the fuel gas is not abnormal although it is
rather insufficient. A processing is thus performed to lower the
upper limit value, for control purpose, of the rotational speed of
the combustion fan 5. In other words, the process proceeds to STEP
10, where computation is made of the saturated value Nsat based on
the above-mentioned rate of decrease, and the upper limit value,
for control purpose, of the rotational speed of the combustion fan
5 is changed to the saturated value Nsat whose upper limit value
has been computed. With reference to line "b" in FIG. 3, the
proportional constant of the combustion amount relative to the
rotational speed of the combustion fan is defined to be k. Then, we
obtain Qlow=kNlow, Qmax.apprxeq.kNsat. Because the above-mentioned
rate of decrease is approximately equal to (Nsat/Nlow)-1, the
saturated value Nsat can be computed based on the above-mentioned
rate of decrease. Thereafter, displaying is made in STEP 11 of the
changed upper limit value, i.e., of the upper limit value showing
the saturated value Nsat by using the remote control unit 9a. It is
to be noted here that displaying of this upper limit value may
alternatively be of the rate of the rotational speed of the
combustion fan 5 relative to the normal upper limit value Nmax,
that is, the rate of the combustion amount to be obtained at the
changed upper limit value relative to the set maximum combustion
amount YQmax. Or else, the displaying of the upper limit value may
be to show the combustion amount that can be obtained at the
changed upper limit value.
[0028] On the other hand, in case the primary pressure of the fuel
gas is largely insufficient due to clogging of the gas pipe or the
like, as illustrated by line "c" in FIG. 3, the saturated value
will be below, or substantially equivalent to, the rotational speed
Nlow of the combustion fan 5 at the time of the secondary
inspection operation. The rate of decrease will thus be as small as
below the threshold value. In this case, the process proceeds to
STEP 12, where displaying is made of "primary pressure abnormal" to
show that the primary pressure of the fuel gas is abnormal by using
the remote control unit 9a.
[0029] According to this embodiment, in case the supply/exhaust
resistances are large although the primary pressure of the fuel gas
is normal, and even if the actually measured maximum combustion
amount Qmax is reduced, a comparison is made between the maximum
set combustion amount YQmax that corresponds to the supply/exhaust
resistances as detected in the inspection operation and the
actually measured maximum combustion amount Qmax. Therefore, the
deviation between the two will be within the allowable range. The
upper limit value of rotational speed of the combustion fan 5 will
therefore not be changed in the secondary inspection operation.
Accordingly, the upper limit value of rotational speed of the
combustion fan 5 can be prevented from being unnecessarily lowered
under the influence of the supply/exhaust resistances.
[0030] Further, by performing the displaying in STEP 4 of "air
supply tube and exhaust pipe abnormal," the displaying in STEP 7 of
"primary pressure normal," and the displaying in STEP 12 of
"primary pressure abnormal," a discrimination can be easily made by
the installer of the combustion apparatus as to whether the air
supply tube 6, the exhaust pipe 7 and the fuel gas supply passage
81 have problems such as clogging, disconnection and the like.
Further, if there are problems, he can easily discriminate where
the problems lie. Still furthermore, by making in STEP 11 the upper
limit value displaying, the user can be informed of the lowering of
the heating capacity even if the heating capacity is lowered as a
result of changing of the upper limit value of the rotational speed
of the combustion fan. In this manner, the user can be prevented
from wrongly taking the phenomenon as a mechanical trouble.
[0031] A description has so far been made of the embodiment of this
invention with reference to the drawings, but this invention shall
not be limited to the above. For example, it is also possible in
the secondary inspection operation: to gradually lower the
rotational speed of the combustion fan 5 from the upper limit value
Nmax; to compare the combustion amount at the rotational speed of
each stage with the combustion amount at the rotational speed of
one stage lower; and to obtain the saturated value Nsat based on
the change in the difference between the two. However, this
procedure takes time in performing the secondary inspection
operation. Therefore, the above-mentioned embodiment is more
advantageous, i.e., the embodiment in which the combustion
apparatus is operated only once in a state in which the rotational
speed of the combustion fan 5 is lowered from the above-mentioned
upper limit value Nmax by a predetermined rate and subsequently the
secondary inspection operation is performed.
[0032] Further, in the above-mentioned embodiment, zero governor
system of gas amount regulating means 8 is employed, but
proportional valve system of gas amount regulating means may also
be used. In this case, the value of the electric current to be
charged to the proportional valve can be the operational quantity
of the gas amount regulating means. Further, the to-be-heated
object that is contained in the combustion box 4 may be other than
the heat exchanger 3. In the above-mentioned embodiment, both the
air supply tube 6 and the exhaust pipe 7 are provided as an
auxiliary tube. This invention is however similarly applicable as a
method of controlling the combustion apparatus that is provided
with only one of the air supply tube 6 and the exhaust pipe 7.
TABLE-US-00001 Explanation of Reference Marks 2 burner, 3 heat
exchanger (to-be-heated object) 4 combustion box 4a exhaust port 5
combustion fan 6 air supply tube 7 exhaust pipe 8 gas amount
regulating means
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