BACKGROUND OF THE INVENTION
1. Technical Field
[0001] The present invention relates to a complex heat source apparatus which is made up
of: first and second, i.e., a total of two, heat exchangers; a first burner for heating
the first heat exchanger; and a second burner for heating the second heat exchanger,
wherein the first burner has a larger rated burning capacity than the second burner.
2. Background Art
[0002] As this kind of complex heat source apparatus, there is known, e.g., in
JP-A-2006-38423, a complex heat source apparatus in which both the first and the second burners are
constituted by Bunsen burners such as rich and lean combustion burners and the like,
and in which combustion air (primary air and secondary air) is supplied by a fan which
is common to both the burners.
[0003] According to this arrangement, by making the fan to commonly serve both the burners,
the costs can be reduced, but the following disadvantages exist. That is, at the time
of a single operation in which only one of the first burner and the second burner
is combusted to heat one of the heat exchangers corresponding to the said one burner,
the air is supplied also to the other of the burners. This air passes, as it is, through
the other heat exchanger corresponding to the other of the burners and, as a result,
this heat exchanger is cooled. The thermal efficiency of this heat exchanger therefore
becomes lower when the heat exchanger is heated again.
[0004] By the way, although not a complex heat source apparatus, there is known, e.g., in
JP-A-2010-151395 the following heat source apparatus. That is, in a heat source apparatus having a
plurality of burners for heating a single heat exchanger, the plurality of burners
are constituted by totally aerated combustion burners (or "fully primary aerated burners").
In a common air supply passage connected to these burners there is interposed a single
fan which supplies primary air. The downstream end of the fuel gas supply passage
is connected to that portion of the air supply passage which is on an upstream side
or a downstream side of the fan. It is thus so arranged that the mixture of the primary
air and the fuel gas can be supplied to the plurality of burners through the air supply
passage. The gas supply passage has interposed therein a flow control means which
enables to vary the fuel gas feed amount in proportion to the amount of primary air
supply so as to make the air-fuel ratio of the air-fuel mixture constant. Also the
connection portions between each of the burners and the air supply passage are provided
with on-off valves.
[0005] By applying this art to a complex heat source apparatus, the following arrangement
is conceivable. That is, each of the first and the second burners to respectively
heat each of the first and the second heat exchangers is constituted by a totally
aerated combustion burner. The air-fuel mixture is supplied to both the first and
the second burners through an air supply passage in which a single fan is interposed.
Also, the first and the second on-off valves are respectively provided at a first
connection portion connecting the first burner and the air supply passage and at a
second connection portion connecting the second burner and the air supply passage.
At the time of simultaneous operation in which both the first and the second burners
are combusted, both the first and the second on-off valves are opened. At the time
of single operation, on the other hand, in which only one of the first and the second
burners is combusted, only one of the on-off valves corresponding to the valve in
question is opened. According to this arrangement, the other heat exchanger corresponding
to the burner that is not combusted at the time of single operation can be prevented
from being cooled by the air flow from the fan.
[0006] In this case, ordinarily setting is made at the time of simultaneous operation such
that, in a state in which the amount of the air-fuel mixture supply to the first burner
becomes maximum corresponding to the rated amount of combustion in the first burner,
the amount of the air-fuel mixture supply to the second burner also becomes maximum
corresponding to the rated combustion amount of the second burner. In this arrangement,
however, in order to enable the maximum amounts of air-fuel mixture supply respectively
to the first burner and to the second burner at the time of simultaneous operation,
the fan must be made larger in capacity. Furthermore, the fan noises at the time of
simultaneous operation become large.
SUMMARY
Problems that the Invention is to Solve
[0007] In view of the above-mentioned points, this invention has a problem of providing
a complex heat source apparatus which supplies air-fuel mixture through an air supply
passage common to the first and the second burners and in which downsizing of the
fan as well as reduction in the noises at the time of the simultaneous operation is
possible.
Means for Solving the Problems
[0008] In order to solve the above-mentioned problems, this invention has an advantage in
providing a complex heat source apparatus comprising: first and second, i.e., a total
of two, heat exchangers; a first burner for heating the first heat exchanger; a second
burner for heating the second heat exchanger in which the first burner is larger in
rated amount of combustion than the second burner, both the first and the second burners
being constituted by totally aerated combustion burners; a single fan for supplying
primary air, the fan being interposed in a common air supply passage connected to
both the first and the second burners, a downstream end of a gas supply passage for
supplying fuel gas being connected to that portion of the air supply passage which
is on an upstream side or a downstream side of the fan, whereby a mixture of the primary
air and the fuel gas is supplied through the gas supply passage to both the first
and the second burners. A flow control means is interposed in the gas supply passage,
the flow control means serving to vary the amount of fuel gas supply in proportion
to the amount of primary air supply so that the air-fuel ratio of the air-fuel mixture
becomes constant. The complex heat source apparatus is characterized in: that a first
on-off valve is disposed at a first connection portion for connecting the air supply
passage and the first burner and a second on-off valve is disposed at a second connection
portion for connecting the air supply passage and the second burner such that, at
a time of simultaneous operation in which both the first and the second burners are
combusted, both the first and the second on-off valves are opened and that, at a time
of single operation in which only one of the first and the second burners is combusted,
only one of the first and the second on-off valves corresponding to said one burner
is opened; and that an air-flow resistance at the second connection portion is set
such that, in a state in which the amount of air-fuel mixture supply to the first
burner, at the time of simultaneous operation, becomes a maximum amount corresponding
to the rated combustion amount of the first burner, the amount of air-fuel mixture
supply to the second burner becomes smaller than the maximum amount corresponding
to the rated combustion amount of the second burner.
[0009] According to this invention, in a state in which the amount of the air-fuel mixture
supply to the first burner, at the time of simultaneous operation, becomes the maximum
amount, the amount of the air-fuel mixture supply to the second burner becomes smaller
than the maximum amount. Therefore, the maximum value of the total amount of air-fuel
mixture supply will decrease. Accordingly, the fan can be downsized and the noises
at the time of simultaneous operation can be reduced.
[0010] Further, in this invention, at the time of simultaneous operation, when a required
combustion amount of the second burner has fallen below a minimum amount of combustion
capable of continuous combustion of the second burner, an on-off control is preferably
performed in which the second on-off valve is opened or closed to thereby intermittently
perform combustion of the second burner. According to this arrangement, even if the
upper limit amount of combustion of the second burner is limited below the rated amount
of combustion at the time of simultaneous operation, the lower limit amount of combustion
of the second burner can be made lower, by the on-off control, than the minimum amount
of combustion that is capable of continuous combustion. The reduction in the turndown
ratio can be prevented.
BRIEF DESCRIPTION OF THE DRAWINGS
[0011]
FIG. 1 is a schematic sectional view showing the complex heat source apparatus according
to an embodiment of this invention.
FIG. 2 is a graph showing variable ranges of amounts of combustion of the first burner
and the second burner at the time of respective operations.
PREFERRED EMBODIMENTS
FOR CARRYING OUT THE INVENTION
[0012] A complex heat source apparatus according to an embodiment of this invention as shown
in FIG. 1 is made up of: a first heat exchanger 1
1 for hot water supply; a second heat exchanger 1
2 for space heating; a first burner 2
1 for heating the first heat exchanger 1
1; and a second burner 2
2 for heating the second heat exchanger 1
2.
[0013] Each of the first and the second burners 2
1, 2
2 is constituted by a totally aerated combustion burner which ejects and combusts air-fuel
mixture of fuel gas and primary air through a multiplicity of flame holes (not illustrated)
formed in a combustion plate 22 that covers one surface of a box-shaped burner body
21, and is disposed in a posture facing downward with the combustion plate 22 lying
on the lower side. Each of first and second combustion boxes 3
1, 3
2 that enclose the combustion space at the lower side of each of the first and second
burners 2
1, 2
2 is disposed so as to house therein each of the first and second heat exchangers 1
1 ,1
2, respectively. Further, there is provided an exhaust duct 4 which is in communication
with the lower ends of both the first and second combustion boxes 3
1, 3
2. It is thus so arranged that the combustion exhaust gases from each of the first
and second burners 2
1, 2
2 can flow through each of the first and second heat exchangers 1
1, 1
2 to the exhaust duct 4.
[0014] By the way, since hot water supply requires a larger heating capacity than space
heating, the first burner 2
1 is arranged to be a large burner having a larger rated combustion amount (maximum
combustion amount) than the second burner 2
2. Further, the exhaust duct 4 is partitioned by a partition plate 41 disposed therein
into a duct portion through which the combustion exhaust gases from the first burner
2
1 flow and the other duct portion through which the combustion exhaust gases from the
second burner 2
2 flow.
[0015] Each of the first and second heat exchangers 1
1, 1
2 is made up of: a multiplicity of heat absorbing fins 11 which are laminated with
one another in the direction perpendicular to the paper surface of FIG. 1; and a snaking
heat absorbing tube 12 which penetrates through these heat absorbing fins 11. Although
not illustrated, the heat absorbing tube 12 of the first heat exchanger 1
1 has connected thereto a water supply pipe on an upstream side and a hot water delivery
pipe on the downstream side. It is thus so arranged that, when a hot water faucet
on the downstream side of the hot water delivery pipe is opened to let the water flow
to the first heat exchanger 1
1, the first burner 2
1 is combusted, so that hot water at a set temperature is delivered from the hot water
faucet. Although not illustrated, the heat absorbing tube 12 of the second heat exchanger
1
2 is connected to the heating circuit of floor heating, and the like through a forward
tube and a return tube. Space heating can thus be performed by circulating hot water
to the heating circuit through the second heat exchanger 1
2.
[0016] Further, the first and second burners 2
1, 2
2 have connected thereto a common air supply passage 5. This air supply passage 5 has
interposed therein a single fan 6 which supplies primary air. To that portion of the
air supply passage 5 which is on an upstream side of the fan 6 is connected a gas
outlet 71 which is on a downstream end of a gas supply passage 7 for supplying fuel
gas. That portion of the of the air supply passage 5 to which the gas outlet 71 is
connected is arranged to constitute a venturi portion 51 having a constricted sectional
area.
[0017] The gas supply passage 7 has interposed therein a main valve 72, and a zero governor
73, as a flow control means, which controls the secondary gas pressure to a pressure
equivalent to the atmospheric pressure. It means that the amount of fuel gas supply
varies with a differential pressure between the atmospheric pressure which is the
secondary gas pressure and that suction negative pressure of the fan 6 which operates
on the venturi portion 51. Since the suction negative pressure of the fan varies in
proportion to the rotational speed of the fan. Therefore, the amount of fuel gas supply
varies in proportion to the rotational speed of the fan, i.e., the amount of the primary
air supply. The air-fuel ratio of the air-fuel mixture becomes constant.
[0018] Further, the first connection portion 52
1 connecting the first burner 2
1 and the air supply passage 5 together is provided with a first on-off valve 8
1. The second connection portion 52
2 connecting the second burner 2
2 and the air supply passage 5 together is provided with a second on-off valve 8
2. The first on-off valve 8
1 and the second on-off valve 8
2 are respectively driven by an actuator 81 such as an electromagnetic solenoid, and
the like.
[0019] At the time of single operation of hot water supply in which only the first burner
2
1 is combusted to thereby heat the first heat exchanger 1
1, the first on-off valve 8
1 is opened to feed the air-fuel mixture to the first burner 2
1 and, at the same time, the second on-off valve 8
2 is closed to stop the air-fuel mixture supply to the second burner 2
2. Further, in order for the amount of the air-fuel mixture supply to the first burner
2
1 to become a value corresponding to the hot water demand combustion amount (amount
of combustion required for supplying the hot water of a set temperature), adjustment
is made by the rotational speed of the fan 6. In addition, at the time of single operation
of space heating in which only the second burner 2
2 is combusted to thereby heat the second heat exchanger 1
2, the second on-off valve 8
2 is opened to feed the air-fuel mixture to the second burner 2
2 and, at the same time, the first on-off valve 8
1 is closed to stop the air-fuel mixture supply to the first burner 2
1. Further, in order for the amount of the air-fuel mixture supply to the second burner
2
2 to become a value corresponding to the space heating demand combustion amount (amount
of combustion required for supplying the hot water of a set temperature to the heating
circuit), adjustment is made by the rotational speed of the fan 6.
[0020] With reference to FIG. 2, at the time of single operation of hot water supply, the
amount of combustion of the first burner 2
1 is made variable with the hot water demand combustion amount between the rated combustion
amount Qmax
1 of the first burner 2
1 and the minimum combustion amount capable of performing continuous combustion thereof
(lower limit of combustion amount free from back firing) Qmini
1. At the time of single operation of space heating, the amount of combustion of the
second burner 2
2 is made variable with the space heating demand combustion amount between the rated
combustion amount Qmax
2 of the second burner 2
2 and the minimum combustion amount Qmini
1 capable of continuous combustion.
[0021] At the time of simultaneous operation of hot water supply and space heating by combusting
the first burner 2
1 to heat the first heat exchanger 1
1 and also by combusting the second burner 2
2 to heat the second heat exchanger 1
2 respectively, priority is given to the hot water supply in a state in which both
the first and the second on-off valves 8
1, 8
2 are left open. In this manner, adjustment is made by the number of rotation of the
fan 6 so that the amount of the air-fuel mixture supply to the first burner 2
1 becomes the value corresponding to the hot water demand combustion amount. Here,
at the time of simultaneous operation, if setting is made such that the amount of
the air-fuel mixture supply to the second burner 2
2 becomes a maximum amount corresponding to the rated combustion amount Qmax
2 of the second burner 2
2 in a state in which the amount of air-fuel mixture supply to the first burner 2
1 becomes a maximum amount corresponding to the rated combustion amount Qmax
1 of the first burner 2
1, it becomes necessary to enlarge the size of the fan 6 so as to correspond to the
maximum value of a total amount of the air-fuel mixture supply. In addition, the noises
of the fan at the time of simultaneous operation become larger.
[0022] As a solution, in this embodiment, the following arrangement has been made. That
is, the second connection portion 52
2 is provided with a resistance portion 53. In a state in which, at the time of simultaneous
operation, the amount of the air-fuel mixture supply to the first burner 2
1 becomes a maximum amount, setting is made so that the amount of air-fuel mixture
supply to the second burner 2
2 becomes smaller than the maximum amount corresponding to the rated combustion amount
Qmax
2. According to this arrangement, since the maximum value of the amount of the total
air-fuel mixture supply is reduced, the size reduction of the fan 6 as well as the
reduction in the noises at the time of simultaneous operation can be attained.
[0023] The second on-off valve 8
2 may be arranged to be of a needle-valve construction so that, even in an opened state
of the second on-off valve 8
2, the second connection portion 52
2 can be adequately throttled, whereby the flow resistance through the second connection
portion 52
2 can be set as described above.
[0024] In case the flow resistance through the second connection portion 52
2 is set in the above-mentioned manner, as shown in FIG. 2, the upper limit combustion
amount Qmax
2' of the second burner 2
2 at the time of simultaneous operation becomes lower than the rated combustion amount
Qmax
2. As a result, the turn down ratio of the second burner 2
2 at the time of simultaneous operation will become smaller if no measure is taken.
[0025] As a solution, in this embodiment, in case the required amount of combustion of the
second burner 2
2 at the time of simultaneous operation falls below the minimum amount of combustion
Qmin
2 that is capable of continuous combustion of the second burner 2
2, an on-off control is performed in which the second on-off valve 8
2 is opened or closed so that the second burner 2
2 is intermittently combusted in an amount of combustion above the minimum amount of
combustion Qmin
2. According to this arrangement, even if the upper-limit amount of combustion Qmax
2' of the second burner 2
2 is limited below the rated combustion amount Qmax
2 at the time of simultaneous combustion, the lower limit combustion amount of combustion
Qmin
2' of the second burner 2
2 can be made lower, by means of the on-off control, than the minimum amount of combustion
Qmin
2 that is capable of continuous combustion. As a result, the turn down ratio of the
second burner 2
2 can be prevented from becoming small.
[0026] Description has so far been made of the embodiment of this invention with reference
to the drawings. This invention, however, shall not be limited to the above, but the
following arrangement may be employed. For example, a venturi portion is provided
in that portion of the air supply passage 5 which is on the downstream side of the
fan 6. The downstream end of the gas supply passage 7 is connected to the venturi
portion. Then a zero governor, which adjusts the secondary gas pressure to an equal
pressure as the outlet pressure of the fan 6, may be interposed in the gas supply
passage 7 as the flow amount adjusting means. In this case, the differential pressure
between the outlet pressure of the fan 6 and the venturi portion is proportional to
the amount of the primary air supply by the fan 6. The amount of the fuel gas supply
will also be proportional to the amount of the primary air supply.
[0027] Further, it is also possible to interpose a proportional valve, as the flow control
means, in the gas supply passage 7 in order to make adjustments with the proportional
valve so that the amount of the fuel gas supply is proportional to the amount of the
primary air supply. In this case, the downstream end of the gas supply passage may
be connected to either of an upstream portion and a downstream portion of the fan
in the air supply passage 5. Further, the above embodiment is a complex heat source
apparatus of serving the dual purpose of hot water supply and space heating in which
the first heat exchanger 1
1 is for supplying hot water, and the second heat exchanger 1
2 is for space heating. However, this invention can similarly be applicable to the
one in which the second heat exchanger 1
2 is used other than for space heating such as for reheating a bath tab.
EXPLANATION OF MARKS
[0028]
- 11
- first heat exchanger
- 12
- second heat exchanger
- 21
- first burner
- 22
- second burner
- 5
- air supply passage
- 521
- first connection portion
- 522
- second connection portion
- 6
- fan
- 7
- gas supply passage
- 71
- gas outlet (downstream end of the gas supply passage)
- 73
- zero governor (flow control means)
- 81
- first on-off valve
- 82
- second on-off valve