Note: Descriptions are shown in the official language in which they were submitted.
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VENT PROVING SYSTEM
FIELD OF THE INVENTION
[0004] This invention relates to gas fired appliances and more
particularly,
to a vent proving system for use with a gas fired appliance.
BACKGROUND OF THE INVENTION
[0005] A typical gas fired appliance, such as a boiler, includes a gas
burner for generating heat. For example, with a boiler the burner is used for
heating water. The appliance typically includes a draft hood or diverter. A
vent
from the draft hood exhausts products of combustion from the appliance. The
vent may include a vent damper.
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[0006] A typical gas fired appliance, in one known form, includes a
relay control for operatively controlling the vent damper and the gas
burner to open the damper if the gas burner is on. For example, when
heat is called for the relay control sends a control signal to the vent
damper to open the damper. Once the damper is open, then a signal is
returned to the gas fired appliance to ignite the gas burner. Once sensed
temperature exceeds the setpoint, then the control signal to the damper is
terminated, causing the damper to close and removing the signal via the
vent damper to the gas valve or burner control, causing it to shut off the
gas supply to the burner. Closing the damper retains latent heat.
[0007] With current construction techniques, it is common for
homes to be sealed tighter to provide fewer air flow paths between the
homes' interior and exterior. This can result in depressurization of the
home, or other building. Particularly, if other exhausting appliances such
as a clothes dryer or exhaust fans are being used, then air is being drawn
out of the house so that the home may become depressurized as there is
no makeup air. When a building is depressurized, it will try to equalize by
drawing in air from any openings to the outside including the gas fired
appliance's venting system. This can result in the appliance's products of
combustion spilling into the home. Some appliances, such as boilers, are
equipped with a thermal switch to shut the boiler off if it is not drafting
properly due to a blocked vent. However, this switch may not shut the
boiler off if it is not drafting properly due to back drafting caused by cold
air entering the home through the vent.
[0008] The present invention is directed to solving one or more of
the problems discussed above, in a novel and simple manner.
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SUMMARY OF THE INVENTION
[0009] In accordance with the invention, there is provided a vent
proving system to monitor vent gas temperature of a gas fired appliance
to ensure that the appliance is venting properly.
[0010] Broadly, there is disclosed in accordance with one aspect of
the invention a vent proving system for use with a gas fired appliance.
The gas fired appliance includes a gas burner and a relay control for
operatively controlling the gas burner. The vent proving system
comprises a sensor for sensing a variable in the vent representing air flow
direction in the vent. An electrical switch is connected to the relay control.
A controller is operatively connected to the sensor, the electrical switch
and to the relay control. The controller determines if a back draft
condition is present in the vent when the gas burner is on and selectively
operates the electrical switch to signal the relay control if a back draft
condition is present in the vent when the gas burner is on.
[0011] There is disclosed in accordance with another aspect of the
invention a vent proving system for use with a gas fired appliance. The
gas fired appliance includes a gas burner, a vent damper for selectively
opening or closing an exhaust vent from the gas fired appliance and a
relay control for operatively controlling the vent damper and the gas
burner to open the damper when the gas burner is on. The vent proving
system comprises a sensor for sensing a variable in the vent representing
air flow direction in the vent. An electrical switch is connected in series
between the relay control and the vent damper. A controller is operatively
connected to the sensor, the electrical switch and to the relay control.
The controller determines if a back draft condition is present in the vent
when the gas burner is on and selectively operates the electrical switch to
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open the connection between the relay control and the vent damper if a
back draft condition is present in the vent when the gas burner is on.
[0012] It is a feature of the invention that the sensor senses vent
temperature. The sensor may comprise a thermostat.
[0013] It is another feature of the invention that the electrical switch
comprises a relay operated by the controller and having a contact in
series between the relay control and the vent damper. The relay may
comprise a first relay and a second relay may be operated by the
controller and having a second relay contact in series with the first relay
contact between the relay control and the vent damper for redundancy.
[0014] It is still another feature of the invention that the controller
includes a timer for operating the electrical switch to close the connection
between the relay control and the vent damper for a select time after the
relay control ignites the gas burner and after the select time operating the
electrical switch to open the connection between the relay control and the
vent damper if a back draft condition is present in the vent when the gas
burner is on.
[0015] It is yet another feature of the invention to provide an
indicator to indicate if a back draft condition has been sensed.
[0016] It is still another feature of the invention that the controller
includes a timer for disabling operation of the electrical switch after a back
draft condition has been sensed.
[0017] It is still another feature of the invention that the controller
includes a timer for retrying operation of the electrical switch after a back
draft condition has been sensed to determine if the back draft condition
has been corrected.
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[0018] It is yet another feature of the invention that vent proving
system is integral with the vent damper and comprising a duct mounting
the vent damper and the sensor.
[0019] There is disclosed in accordance with another aspect of the
invention a vent proving system comprising a housing for mounting to the
vent. A control board in the housing includes a first connection means for
connection to the gas fired appliance and a second connection means for
connection to the vent damper. A thermostat is secured to the housing
and includes a sensing probe protruding into the vent for sensing
temperature in the vent. An electrical switch in the housing is connected
between the first connection means and a second connection means for
connection in series between the relay control and the vent damper. A
controller on the control board is operatively connected to the sensor, the
electrical switch and to the first connection means and the second
connection means. The controller determines if a back draft condition is
present in the vent when the gas burner is on and selectively operates the
electrical switch to open the connection between the relay control and the
vent damper if a back draft condition is present in the vent when the gas
burner is on.
[0020] Further features of the invention will be readily apparent
from the specification and from the drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0021] Fig. 1 is a perspective view of a vent proving system in
accordance with the invention mounted to a gas fired appliance;
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[0022] Fig. 2 is a side elevation view of the vent proving system in
accordance with the invention;
[0023] Fig. 3 is a front elevation view of the vent proving control of
Fig. 2 with a cover removed;
[0024] Fig. 4 is a block diagram of a control system for the gas fired
appliance of Fig. 1;
[0025] Fig. 5 is a detailed block diagram for the vent proving
system of Fig. 2;
[0026] Fig. 6 is a detailed block diagram for the vent proving
system of Fig. 2 without a damper;
[0027] Fig. 7 is a perspective view of the vent proving system
integral with a vent damper; and
[0028] Fig. 8 is a detailed block diagram for the integral vent
proving system and damper of Fig. 7.
DETAILED DESCRIPTION OF THE INVENTION
[0029] Referring to Fig. 1, a gas fired appliance 10 of conventional
construction is illustrated. The gas fired appliance 10 may comprise, for
example, a boiler. For simplicity herein, the gas fired appliance 10 will be
referred to as a boiler, it being understood that the invention is not limited
to use in connection with a boiler. The boiler 10 includes an exhaust pipe
12 connected to a draft hood 14. A vent damper 16 may be connected to
the draft hood 14 and is in turn connected to a vent pipe or stack 18 -
through a wall opening 20 to exhaust products of combustion from the
boiler 10 to the exterior of the building. Again, for simplicity herein, the
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ducts and/or pipes used in venting from the boiler 10 will be referred to as
a "vent". The present invention is not directed to any particular gas fired
appliance or configuration of the venting system. In accordance with the
invention, a vent proving system 22 is installed on the vent 18
downstream of the vent damper 16. As described below, the vent proving
system 22 may be used in installations that do not include the vent
damper 16.
[0030] Referring to
Figs. 2 and 3, the vent proving system 22 is
illustrated. The vent proving system 22 comprises a housing 24 including
a base 26 and a removable cover 28. The vent proving system 22 is
shown with the cover 28 removed in Fig. 3. A pair of screws 30 thread
into tabs 32 on opposite sides of the base 26 for securing the cover 28
thereto. A temperature sensor in the form of a thermostat 34 is secured
to the base 26 and extends rearwardly therefrom, as shown in Fig. 2. As
will be apparent, a thermocouple or thermistor could also be used as a
temperature sensor. The thermostat 34 includes a probe 36 protruding
into the vent 18 incident to the vent proving system 22 being mounted to
the vent 18 using a flange 38, as shown in Fig. 1. A stalk 40 extends
between the flange 38 and a mount 42 and houses the probe 36. The
mount 42 is secured to the base 26 in a conventional manner, not shown.
The thermostat 34 includes switch contacts, shown schematically in Fig.
5, connected to terminals 44, 45 and 46 secured to the base 26, as shown
in Fig. 3, using a bracket 47. Wires 48, 49 and 50 connect the respective
terminals 44-46 to a control board 52. The control board 52 is mounted to
the base 26 using standoffs 54, screws 56 and nuts 58. A first cable 60
comprises four conductors for electrically connecting circuitry on the
control board 52 to a relay control, as described below. A second cable
62 comprises four conductors likewise connected between circuitry on the
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control board 52 and an electrical connector 64 secured to the base 26.
The connector 64 is provided for connection to a cable from the vent
damper 16, as discussed below.
[0031] Referring to Fig. 4, a block diagram of the boiler 10 and vent
proving system 22 is illustrated.
[0032] The boiler 10 includes a relay control 70 for controlling the
vent damper 16 and a gas burner 72. In an exemplary embodiment of the
invention, the vent proving system 22 is described for use in connection
with the relay control 70 in the form of an AquastatO L8148-E relay.
Aquastate is a registered trademark of Honeywell. The termination points
for the relay control 70 are as set forth in specifications for the Honeywell
AquastatO L8148-E relay. Likewise, in the exemplary embodiment to the
invention, the vent damper 16 may comprise a GVD-series vent damper
from Field Controls. The gas burner 72 comprises a pilot module 74,
such as a Honeywell S8160 Series, and a gas valve 76.
[0033] In accordance with a typical application for an Aquastate
L8148-E relay, a room thermostat 78 is connected to T and TV terminals
of the relay control 70. A circulating pump 80 is connected to Cl and 02
terminals. 120 volt AC power is connected to terminals 1 and 2 of the
relay control 70. In such a typical application, without the vent proving
system 22, the Z, B1 and B2 terminals of the relay control 70 would be
connected to a cable 82 from the vent damper 16 via brown, orange and
black conducting lines, respectively. The brown line carries 24V power
and the black line is a common. The orange line carries a 24V command
signal used when heat-is called for. The cable 82 also includes a yellow
line to be connected to a TH-W input of the pilot module 74. The yellow
line carries a 24V return signal from the damper 16 to ignite the gas
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burner 72. The Z and B2 terminals of the relay control 70 are also
connected to the pilot module 74 to provide power.
[0034] In accordance with the invention, the vent proving system 22
is connected between the relay control 70 and the vent damper 16.
Particularly, the vent damper cable 82 is connected to the vent proving
system connector 64 and the vent proving system cable 60 is in turn
connected to a suitable connector 84, see Fig. 5, to provide the indicated
connections to the relay control 70 and pilot module 74.
[0035] Referring to Fig. 5, a block diagram for circuitry of a
controller 86, on the control board 52 of the vent proving system 22, is ,
illustrated. The controller 86 includes conductors 88, 89 and 90 for
directly connecting the yellow, brown and black lines from the cable 60 to
the connector 64. The first conductor 88 is also referred to as the yellow
line or return line. The second conductor 89 is also referred to as the
brown line or power line. The third conductor 90 is also referred to as the
black line or common line. Finally, a conductor 91 for connecting the
orange line from the cable 60 to the connector 64 is also referred to as the
orange line or command line. The control board 52, see Fig. 3, includes
first and second control relays R1 and R2. As is conventional, each relay
R1 and R2 includes a coil and switch contact. The coil is indicated with a
suffix C while the switch contact is indicated with a suffix S, see Fig. 5.
First and second relay contacts R1S and R2S are connected in series in
the orange line 91. The orange line 91 carries a 24 volt command signal
from the relay control 70 when heat is called for, while the yellow line 88
carries a 24 volt return signal from the damper 16 when the damper has
opened.
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[0036] The controller 86 includes a control block 92 connected to
the brown line 89 and black line 90 for receiving power and to the yellow
line 91 to receive the 24 volt command signal from the relay control 70.
Relay coils R1C and R2C, associated with the relay contacts R1S and
R2S, respectively, are connected between the control block 92 and the
black common line 90 for selectively operating the relays R1 and R2.
Likewise, an indicator light L1 is connected between the control block 92
and the common line 90. The thermostat 34 comprises a single pole
double throw (SPDT) thermostat and includes the common terminal 44
connected to the orange line 91 via the conductor 48, the normally closed
contact terminal 46 connected via the line 50 to the control block 92, and
the normally open contact terminal 45 connected via the line 49 to the
control block 92. A reset switch Si is connected between the brown line
89 and the control block 92.
[0037] In accordance with the invention, the control block 92
comprises a microcontroller, such as a programmed processor and
associated memory for operating in accordance with a control program to
control operation of the vent proving system 22. Operation of the control
program is as described below. Alternatively, the control block 92 could
be implemented using firmware or hard wired logic circuitry for performing
the same functionality as the programmed processor.
[0038] The sequence of operation of the program begins in a
standby state with the command signal on the orange line 9110w. The
relay coils RIC and R2C are deenergized. When the orange line 91 goes
high the program starts a 5 minute delay timer and energizes the relay
coils R1C and R2C. This closes the contacts R1S and R2S. The delay
time could be a different length of time. After 5 minutes, the program
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determines if the thermostat NO contact is now closed, indicating a
sufficiently high vent temperature. If so, then the relay coils R1C and R2C
remain energized. If not, or if the sensed vent temperature later drops,
representing a back draft condition, then the program deenergizes the
relay coils R1 C and R2C to open the contacts R1S and R2S and close
the damper and shut off the burner. A fault condition flag is then set and
the indicator L1 is illuminated until reset by the reset switch Si. A three
hour timer is started by the program to provide a lockout state. The
lockout state ends if the command signal on the line 91 is removed or
after a three hour delay. After the three
hour delay the program will
repeat the operating cycle discussed above. Anytime the command
signal on the command line 91 is removed the program returns to the
standby state.
[0039] Conventional
operation of boiler 10 is first described
ignoring operation of the vent proving system 22 (assuming that it is not
present). This operation is controlled by the relay control 70 in a
conventional manner. If the room thermostat 78 calls for heat, then the
relay control 70 energizes the circulating pump 80. This moves water
from the boiler 10 to the appropriate zone. The relay control 70 includes a
thermostat (not shown) for sensing water temperature. If water
temperature is below a given set point, then the relay control applies
power to the B1 terminal to provide a 24 volt command signal on the
orange line to the vent damper 16. This causes the vent damper 16 to
open. Once the vent damper 16 is open, then the 24 volt signal is
returned on the yellow line to the pilot module 74. The pilot module 74
operates as an ignition control to provide a spark in connection with
opening the gas valve 76. This ignites the burner 72. Once the water
temperature exceeds the set point, then the 24 volt command signal is
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removed from the terminal B1 of the relay control 70 which in turn causes
the vent damper 16 to close which in turn removes the ignition power on
the yellow line to the pilot module 74 to turn off the gas burner 72. The
closing of the vent damper 16 retains latent heat in the boiler 10, as is
known.
[0040] The operation of
the boiler 10 with the vent proving system
22 is now described. Particularly,
the vent proving system 22 is
connected in series between the boiler 10 and the damper 16, as
discussed above. As noted, direct connections are provided, except for
the orange line 91 which includes the two normally open relay contacts
R1S and R2S associated with the corresponding relay coils R1C and
R2C. The vent proving system 22 is a device intended to monitor the vent
gas temperature from the boiler 10 to ensure the boiler 10 is venting
properly. The control board 52 provides an interface between the SPDT
thermostat 34, the relay control 70 of the gas fired boiler 10 and the
automatic vent damper 16. The control board 52 incorporates time delay
functionality which monitors the status of the thermostat 34 relative to the
presence of a 24 volt command signal from the boiler 10 and operates
redundant relays R1 and R2 to signal the vent damper 16 accordingly.
The control board 52 also incorporates an indicator light L1 with a manual
reset switch Si to indicate if the vent proving system 22 has detected that
a backdraft condition has been detected during the call for heat (excluding
the first five minutes), meaning that improper venting has occurred.
[0041] If the boiler 10
is in a standby mode, then the vent proving
system 22 is likewise in standby mode and the vent damper 16 is in. the
closed position. When the control block 92 receives a call for heat on the
orange line 91, then the control block 92 starts the 5 minute timer. The
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relay contacts R1S and R2S close sending the 24 volt command signal on
the orange line 91 to the vent damper 16. The vent damper 16 should
prove open in about 15 seconds and send the 24 volt return signal back to
the vent proving system 22 on the yellow line 88 and to the boiler 10 to
operate the burner 72, as described above. The boiler 10 fires its main
burner 72 and its products of combustion heat up the thermostat 34
causing it to actuate as sensed by the thermostat 34 switching to provide
connection between the terminals 44 and 45 to the control block 92. The
control block 92 in response to sensing the high signal on the terminal 45
holds in the relay coils R1C and R2C when the time delay expires. Once
the boiler 10 satisfies the call for heat and removes the 24 volt signal on
the orange line 91 then the damper 16 is closed, as discussed above, the
gas burner 72 is turned off, the internal timers of the control 92 reset and
the relay coils R1C and R2C are de-energized to open the contacts R1S
and R2S.
[0042] If, on the other
hand, the products of combustion do not heat
up the thermostat 34 during the five minute delay implemented by the
control 92, then the thermostat 34 remains in its normal state with
connection between the terminals 44 and 46. The fact that the
temperature in the vent 18 has not reached the necessary temperature
represents a condition in which the air flow direction in the vent 18
comprises a back draft condition. Thus, when the five minute time delay
expires and the temperature has not been satisfied, then the cOntrol block
92 deenergizes the relays R1 and R2 to open the relay contacts R1S and
R2S removing the command signal to the damper 16 on the orange line
91. This in turn removes the return signal on the yellow line 88 back to
the boiler 10 to turn off the gas burner 72. The vent damper 16 closes
and the boiler 10 will shut off its burner 72 even though the relay control
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70 is still sending a command signal to the vent proving system 22.
Thereafter, the control block 92 includes the three hour time delay
comprising the lockout state, discussed above. During this three hour
time delay, further operation is prevented unless the thermostat 34 is
cycled. The indicator L1 flashes until the reset switch Si is manually
reset.
[0043] Once the three hour time delay expires, then the sequence
of operation is repeated as discussed above, until venting is proven or the
control relay 70 removes the signal on the orange line 91 to the vent
proving system 22.
[0044] As will be apparent, the vent proving system 22 monitors
vent gas temperature continuously and if it falls below the set point after
the five minute delay to break has expired, then the control block 92 will
shut off the appliance main gas burner 72 even though the boiler 10 may
have been venting properly initially. In the illustrated embodiment of the
invention, the thermostat terminals 45 and 46 are directly connected to
the control block 92. As will be apparent, the terminal 45 could be
connected to the high side of the relay coils R1C and R2C to directly
operate the relays R1 and R2 responsive to the vent proving having been
satisfied.
[0045] Thus, in accordance with the invention, the controller 86
determines if a back draft condition is present in the vent 18 when the gas
burner 72 is ignited and selectively operates the relays R1 and R2 to open
the electrical switch contacts of the relays R1 and R2 to open the
connection between the relay control 70 and the vent damper 16 if a back
draft condition is present, represented by vent air temperature, when the
gas burner is ignited.
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[0046] The vent proving system 22 is described above in an
installation in which a vent damper 16 is present. The vent damper 16
typically used for efficiency. The damper is not generally used with
furnaces. Fig. 6 is a block diagram similar to Fig. 5 for the controller 86
on the control board 52 when a damper is not present. The principal
difference is that the relay contacts R1S and R2S are connected in series
between the orange line 91 and the yellow line 88 of the cable 60. This
could alternatively be accomplished by jumpering the orange and yellow
terminals of the connector 64, see Fig 5, and ignoring the vent damper
connections. This circuitry effectively provides a signal to the relay control
70 corresponding to the condition that the damper vent is open. The vent
proving system 22 operates as described above, ignoring operation of the
vent damper.
[0047] Particularly, if the boiler 10 is in a standby mode, then the
vent proving system 22 is likewise in standby mode. When the control
block 92 receives a call for heat on the orange line 91, then the control
block 92 starts the 5 minute timer. The relay contacts R1S and R2S close
sending the 24 volt command signal on the orange line 91 back to the
yellow line 88 and to the boiler 10 to operate the burner 72, as described
above. The boiler 10 fires its main burner 72 and its products of
combustion heat up the thermostat 34 causing it to actuate as sensed by
the thermostat 34 switching to provide connection between the terminals
44 and 45 -to the control block 92. The control block 92 in response to
sensing the high signal on the terminal 45 holds in the relay coils RIC and
R2C when the time delay expires. Once the boiler 10 satisfies the call for
heat and removes the 24 volt signal on the orange line 91, the gas burner
72 is turned off, the internal timers of the control 92 reset and the relays
R1 and R2 are de-energized to open the contacts R1S and R2S.
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[0048] If, on the other hand, the products of combustion do not heat
up the thermostat 34 during the five minute delay implemented by the
control 92, or thereafter, then the thermostat 34 will be in its normal state
with connection between the terminals 44 and 46. The fact that the
temperature in the vent 18 has not satisfied the necessary temperature
represents a condition in which the air flow direction in the vent 18
comprises a back draft condition. Thus, after the five minute time delay
expires and the temperature is not satisfied, then the control block 92
deenergizes the relay coils R1 C and R2C to open the relay contacts R1S
and R2S removing the command signal on the yellow line 88 back to the
boiler 10 to turn off the gas burner 72. The boiler 10 will shut off its
burner
72 even though the relay control 70 is still sending a command signal to
the vent proving system 22.
[0049] Referring to Fig. 7, a vent proving system 100 is illustrated
integral with a vent damper. Particularly, a cylindrical duct 102 pivotally
supports a damper 104, as is conventional. The damper 104 is driven by
a motor M, see Fig. 8. A temperature sensor 106 extends into the duct
102 and is connected by a wire 108 to the controller 82, see Fig. 8, in a
housing 110 secured to the duct 102 by a bracket 112.
[0050] The controller 82 directly operates the motor M. The motor
circuit includes limit switches S2, S3 and S4 operatively associated with
the damper 104, as is conventional with vent dampers. The switch S2 is
normally closed and opens when the damper 104 opens or closes. The
switches S3 and 54 are closed if the damper is open and otherwise are
closed. The switch S2 is connected in series in the orange line 91. The
motor M is connected across the lines 90 and 91. The switches S3 and
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S4 are connected in series between the orange line 91 and the yellow line
88.
[0051] The temperature sensor 106 comprises a thermocouple. As
is apparent, a thernnistor or thermostat could also be used.
[0052] Operation of the controller 82 is as described above relative
to Fig. 5.
[0053] The present invention has been described with respect to a
program sequence of operation and block diagrams. It will be understood
that each step of the sequence and block of the block diagrams can be
implemented by computer program instructions. These program
instructions may be provided to a processor to produce a machine, such
that the instructions which execute on the processor create means for
implementing the functions specified in the steps and/or blocks. The
computer program instructions may be executed by a processor to cause
a series of operational steps to be performed by the processor to produce
a computer implemented process such that the instructions which execute
on the processor provide steps for implementing the functions specified.
Accordingly, the description and illustrations support combinations of
means for performing a specified function and combinations of steps for
performing the specified functions. It will also be understood that each
block and combination of blocks can be implemented by special purpose
hardware-based systems which perform the specified functions or steps,
or combinations of special purpose hardware and computer instructions.
