Note: Descriptions are shown in the official language in which they were submitted.
-BP Fi~e No. 3491-016
1- 2066870
Title: GAS-FIRED R~AT~R
FIELD OF THE lNV~NllON
This invention relates to a gas-fired heater,
and more particularly is concerned with a gas-fired
baseboard heater having a similar profile to conventional
electric baseboard heaters.
RACRGRouND
Electric baseboard heaters are well known.
Conventionally, electric baseboard heaters are elongate
and have a low profile. Usually, they have an elongate
finned heating element and a simple control switch,
optionally with a thermostat, at one end. Elongate top
and bottom openings are provided in an outer housing, to
enable natural convection to transfer the heat to the room
air.
With the introduction of flexible gas
distribution systems for buildings, opportunities for new
applications have developed. One such opportunity
involves using a gas-fired baseboard heater in
applications where electric baseboard heaters are
currently used. The attractiveness of using gas as an
original or a replacement source of energy has increased
due to the large increases in electricity rates compared
to the more steady gas prices.
There are known designs for gas-fired baseboard
heaters, but these are large and bulky, often resembling
room heaters more than baseboard heaters.
Known gas baseboard heaters currently use a
natural draft sealed combustion system with a standing
pilot and a conventional gas control valve. Based on
conventional gas technology, the flame is oriented
vertically and the heat exchanger is relatively bulky. As
a result, the whole device is bulky and unattractive and
occupies a lot of space. Such existing baseboard heaters
use multi-port burners, which again increases the bulk of
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the device.
Heat is readily transferred from the heat
exchanger to the surrounding air by natural convection.
Cooler air at the floor level enters via the lower grille
and is heated as it rises past the heat exchanger and
exits from a top mounted discharge grille. Most heaters
of this type are equipped with a local thermostat mounted
on the heater itself, to regulate the operation of the
heater.
SUMMARY OF ln~ PRESENT INVENTION
In accordance with the present invention, there
is provided a gas-fired heater, for mounting on a wall
within a building, the heater comprising: a gas inlet for
combustion gas; a combustion air inlet; a burner connected
to the combustion and gas inlets; and an elongate U-shaped
heat exchanger including a generally horizontal lower
section into which the burner discharges combustion gases,
and a generally horizontal upper section connected to the
lower section and having an outlet for exhaust combustion
gases. The gas-fired heating device of the present
invention has a low profile and is intended for
installation along a section of the wall in a room. For
this purpose, it preferably includes a casing having upper
and lower grilles for natural convection. One embodiment
of the invention uses a natural draft-sealed combustion
system with either a st~n~ing pilot or an intermittent
pilot and a gas control valve. Another embodiment of the
invention uses a power-vented sealed combustion system
with either hot surface ignition or spark ignition and a
gas control valve. The power-vented version preferably
includes additional control features such as a pressure
switch-based proof of flow, and a safety lockout timing
device. A gas control valve and an appropriately sized
gas orifice regulate the desired flow of gas. Preferably,
it includes a horizontally-directed mono-port burner.
During operation, air is drawn in from the
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outdoors and into the combustion air chamber where the gas
and air are mixed, and are then passed through the mono-
port burner and ignited. The resulting products of
combustion are passed through the U-shaped heat exchanger
and are preferably exhausted to the outside, by a tube
concentrically positioned inside the combustion air
passage. The tubular heat exchanger advantageously is
made up of two major sections; a lower section which is
connected to the combustion air chamber and an upper
section which is connected to the exhaust tube. The two
sections are joined together using elbows or other
transition components.
The diameter of the heat exchanger may be the
same for both the bottom and top sections, or the bottom
section may be of a larger diameter than the top section.
Finned tubing is preferably in the power-vented version,
for enhancement of heat transfer from the hot combustion
gases to the surrounding air. In known manner, the finned
tubing aids in heat transfer by effectively increasing the
heat transfer surface area.
In the power-vented version, a blower is used to
draw combustion air and push it through the U-shaped heat
exchanger and out the exhaust tube. A smaller diameter
tubing can be used for the heat exchanger than in the
natural draft version of this baseboard heater.
Additionally, in the power-vented version, heat transfer
is enhanced in the upper section by using an in-line
turbulator. The turbulator increases turbulence in the
heat exchanger by increasing the internal flow velocity,
which in turn increases the heat transfer rate to the wall
of the heat exchanger and then to the surrounding air.
Heat is readily transferred to the surrounding air by
natural convection. The cooler air enters the casing via
the lower grille and is heated as it rises past the heat
exchanger and exists from a top mounted discharge grille.
To distribute the heat more evenly in the lower
section, it is preferred for a layer of thin insulation
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material to be placed in the mouth of the lower section of
the heat exchanger. This permits more heat to be
transmitted to the other end of the lower section and
reduces the wall temperature at the burner end of the heat
exchanger.
For the power-vented version, advantageously a
differential pressure switch is used to ensure that an
adequate flow of combustion air is present before the
ignition controls are made operative. In the event of a
blower malfunction, the pressure switch would sense that
there is inadequate combustion air and would de-energize
the gas supply mechanism. Another safety feature that is
advantageously employed in the heater is a lockout timing
mechanism. This feature, once again, would de-energize
the gas valve, thus stopping the flow of gas to the
burner, in the event of the burner flame being
extinguished due to a temporary loss of gas supply. To
re-activate the ignition control system, a manual reset of
the thermostat would be required.
The thermostat for this heater may be located
within the casing of the heater or it may be located
remotely on a wall in the room. This latter feature
permits better climate control of the room being heated.
In the drawings as hereinafter described, an
embodiment of the power-vented version of the baseboard
heater is described. Also described is an embodiment of
a naturally vented version of the baseboard heater.
However, various other modifications and alternate
construction, including a variation in the length of the
heat exchanger can be made without departing from the true
scope and intent of the invention.
A typical power-vented baseboard heater can be
enclosed in a casing having the dimensions of about 19 cm
high, 13 cm deep and 122 cm long (7~ x 5 x 48 inches) with
a firing rate of about 1.5 kW (5,000 BTU/h).
The firing rate of the baseboard heater is about
.37 kW (1,250 BTU/h) per linear foot of appliance length.
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The typical embodiment uses 4 linear feet for a total
input of about 1.5 kW (5,000 BTU/h).
DESCRIPTION OF '1'~ DRAWING FIGURES
For a better understanding of the present
invention and to show more clearly how it may be carried
into effect, reference will now be made by way of example,
to the accompanying drawings, in which:-
Figure 1 is a perspective view of a power-vented
embodiment of a baseboard heater in accordance with the
present invention;
Figure 2 is a schematic diagram of the control
circuit used in the baseboard heater of Figure 1;
Figure 3 is a vertical section through the
internal components of the baseboard heater of Figure 1,
with a casing removed;
Figure 4 is a plan view of the baseboard heater
components of Figure 3;
Figure 5 is an end view of the baseboard heater
components shown in Figures 3 and 4; and
Figure 6 is a perspective view of a typical
naturally-vented embodiment of the baseboard heater in its
casing.
DESCRIPTION OF THE PREFERRED EMBODIMENT
The baseboard heater components are enclosed in
a casing 1, which is generally rectangular. While a
variety of dimensions can be chosen, the casing 1 has the
dimensions 19 x 13 x 122cm (7~ x 5 x 48 inches). The
casing 1 comprises a separate front panel 2 which can be
removed, a lower grille 3 which permits the cooler air at
the floor level to enter the casing, and a top mounted
discharge grille 4 which allows for the heated air to rise
into the heating space.
Referring to Figure 2, the control circuit for
the heater has input lines 40 and a ground connection 41,
which in known manner would be connected to a conventional
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domestic 120 volt AC supply. A probe type temperature
sensor 6 and coil 7 of a relay A are connected in series
between the two lines. A combustion air blower 9 is also
connected between the lines. In the top line, a
thermostat 5 and a differential pressure switch 10 are
connected in series. The switch 10 is in turn connected
to a gas valve 12. The valve 12 includes a holding coil
12a, a secondary coil 12b and a booster coil 12c. The
valve 12 in turn is connected to contact 8 of the relay A
and to contacts 14 of a second relay B having an
energizing coil 13. The contact 8 can be switched between
contacts 8a and 8b, while further contacts 8' are either
in an open or closed position; with relay A powered, the
contact 8 connects to 8a, and contacts 8' are closed.
Contact 14 is normally open, and is closed when relay B is
activated. An igniter 11 is connected in series with a
time-delay switch 23 which in turn is connected to the
contact 8a, as is a connection to the gas valve 12. The
switch or contacts 14 and the contact 8b are connected to
the further pair of contacts 8'. The contact 8b and
output of contacts 14 are also connected to the coil 13 of
relay B, and the output of contacts 8' is connected to a
time-delay heater 22. The heater 22 and time-delay switch
23 with related components form a lockout-timing mechanism
21.
Turning to Figures 3, 4 and 5, and details of
the mechanical components, at the right hand end of the
unit, there is a housing 42 including an inlet chamber 43.
An inlet pipe 15 opens into this, as best shown in Figure
4. Figure 4 also shows schematically the lockout-timing
mechanism 21. The fan or blower 9 includes the actual fan
element at 9a and a fan motor 9b. As shown by the arrow
44, the fan or blower 9 draws combustion air through the
inlet 15 and forces it into a combustion chamber 45. A
differential pressure switch is mounted at 10, and the gas
valve 12 is mounted below it. Relays A and B are shown at
the bottom of the housing 42.
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The gas valve 12 includes an inlet 12d, for gas,
which in known manner, would be connected to a gas supply,
and has an outlet connected to a flow-controlling orifice
25. This in turn discharges into a burner tube 26, with
the orifice 25 and the burner 26 being configured in known
manner.
At the outlet of the burner tube 26, there is
mounted the igniter 11 and also the temperature sensor 6,
as shown. The arrow 46 indicates the flow of combustion
gases from the burner tube 26.
The combustion zone 45 is defined within the
first part of a lower tubular heat exchanger section 16.
The combustion chamber 45 is lined with flexible
insulation 17, to reduce the wall temperature, and hence,
ensure more uniform heat transfer from the tubular heat
exchanger section 16.
As shown in Figure 3, at the left hand end of
the heat exchanger 16, there is an elbow 18 connecting the
lower section to an upper finned tubular heat exchanger
section lg. A tubulator 24 is located within the finned
tubular heat exchanger 19, both to create turbulence and
to increase internal flow velocity, thereby to promote
heat transfer from the hot combustion gases to the body of
the upper section 19.
At its end, the heat exchanger section 19 turns
through 90 and is connected to an exhaust tube 20. The
tube 20 is coaxial within the combustion air in the inlet
pipe 15, the combustion gases flowing counterflow to the
incoming air. This effects further heat transfer and
promotes overall thermal efficiency. Residual heat in the
combustion gases is transferred to the incoming combustion
air.
In use, with the baseboard heater connected to
line voltage, connected to a domestic gas supply and in
standby mode (heat not called for), the thermostat 5 is in
the open position, the probe-type temperature sensor 6 is
in the closed position and the coil 7 of relay A is
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energized. With the above relay coil 7 energized, the two
contacts 8, 8', for the relay are in the swing left
position, i.e. as shown in Figure 3 with contact 8a closed
and contacts 8' closed.` At this point some current will
flow through the holding coil 12a, but this will be
insufficient to open the valve 12.
On a call for heat, the following sequence would
occur: the room thermostat switch 5 closes thereby
energizing the combustion air blower 9. When the blower
9 is at its operating speed, the differential pressure
switch 10 senses that the difference in pressure between
the intake and discharge sides of the blower 9 is at or
above a preset value, indicating an adequate supply of
combustion air, and it closes. When the pressure switch
10 closes, the igniter 11 is energized and begins to heat
up. The temperature sensor 6, due to its placement in
close proximity to the igniter 11, also heats up. When
the temperature sensor 6 heats up to its critical
temperature, it opens and de-energizes the coil 7 of relay
A which causes the contacts of relay A to swing to the
right, i.e. contact 8 closes at 8b and contacts 8' open,
and de-energize the igniter 11. The gas valve 12 is thus
energized, and current flows through the secondary and
booster coils 12b, c. This opens the valve 12 and gas
starts to flow, which gas is ignited by the igniter 11
while it is still hot. Simultaneously, since the contact
8b of relay A is closed, the coil 13 of relay B is
energized and the contacts 14 of relay B closes. The
temperature switch 6 is kept open by maint~ining it above
its critical temperature by sensing heat generated from
the flame.
The baseboard heater operates until the
thermostat 5 is satisfied that the required temperature
has been reached, at which point it opens and de-energizes
the blower 9 and the gas valve 12. The temperature switch
6 cools down and closes. The system is once again in the
standby mode, shown in Figure 2.
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If, during normal operation, there is a loss of
flame, for example, due to a loss of gas pressure, the
lockout timing mechanism 21 would operate to stop the flow
of gas to the heater within a preset time, here 60
seconds. Upon a loss of flame, the thermostat S remains
closed since it is not yet satisfied. The pressure switch
10 also remains closed since the blower 9 continues to
operate, which in turn ensures that contacts 14 of relay
B remains closed and the coil 13 of relay B is still
energized. When the temperature sensor 6 cools down, due
to the loss of heat from the flame, to its preset
temperature, it closes. This energizes the coil 7 of
relay A; its contacts 8 swing to the left and close 8a and
contacts 8' close. Since the contacts 14 of relay B are
closed, the coil 13 for relay B remains energized. The
igniter 11 and the time delay heater 22 are then
energized. The igniter 11 heats up, thereby heating the
temperature switch 6 and at its preset temperature, the
switch 6 opens. Again, simultaneous coils 12b and c are
energised and the gas valve 12 opens to permit the flow of
gas. Coil 7 of relay A is de-energized and thus its
contacts swing to the right.
If the gas pressure has been restored and there
is a flow of gas to the heater, then ignition will take
place as described earlier and the heater will continue to
operate in its normal manner until the thermostat 5 has
been satisfied. If ignition does not take place, the
temperature switch 6 will again cool down and close and a
second trial for ignition will take place.
Consider further the initial trial for ignition
on the loss of flame. While the relay A is energized, the
time delay heater 22 is also energized. During this time,
the time delay heater 22 begins to heat up the thermally
operated time delay switch 23. The time delay switch 23
is selected to reach its critical temperature after a pre-
selected time, here 60 seconds. When this time is reached
it opens to close gas valve 12b and hence it allows no
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more than 60 seconds of gas flow after loss of flame.
When further trials for ignition occur, as the
temperature switch 6 opens and the coil 7 of relay A is
de-energized, the contacts 8' of relay A are opened, to
de-energize the time delay heater 22. The time delay
switch 23 then slowly cools down. However, the time delay
switch 23 does not cool down to its original temperature
before the ignition sequence repeats itself and the time
delay switch 23 begins to heat up again. In this manner,
after a few trials for ignition, the time delay switch 23
reaches its preset temperature and opens, thereby
preventing the igniter 11 from being energized any
further. The time delay switch 23 must then be manually
(from the thermostat 5) reset before another trial for
ignition can take place.
The heater is designed to operate at a firing
rate of approximately 1.5kW (5,000 BTU/h). The firing
rate is controlled by the combination regulator and
control gas valve 12 and the flow controlling orifice 25.
While an embodiment of the power-vented version
of this heater having a firing rate of 1.5kW (5,000 BTU/h)
has been described, the heater may be operated at
alternate firing rates. The heat exchanger components
(comprising of 16, 18 and 19) may be of selected sizes to
permit higher inputs by using a firing rate of about .37
kW (1,250 BTU/h) per linear foot.
The natural draft version of this invention
operates in much the same way as the power-vented version,
and is shown in Figure 6. Here, a standing pilot 26 is
lit using a piezo-electric igniter 27, in known manner.
When there is a call for heat, the gas valve Z8 opens to
permit gas to flow from its inlet 28a to the single port
burner 29. Combustion air and gas mix and are ignited at
the mouth of the heat exchanger 30 by the standing pilot
26. The single port burner 2g provides the necessary
momentum to move the combustion products through the U-
shaped heat exchanger 30 and vent them to the outdoors.
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When the local thermostat 31 is satisfied, it deactivates
the gas valve 28 and the flow of gas is stopped. If
during normal operation, there is a flame outage, such as
due to a loss of gas pressure, the outage would be sensed
by a thermocouple 32 and the gas valve 28 would be de-
energized. Upon restoration of gas pressure, the pilot 26
would have to be manually relit using the piezo-electric
spark igniter 27. The configuration of the heat exchanger
could be generally similar to that in the first embodiment
with a similar exhaust outlet or tube. However, as it
relies on natural draft, the interior of the duct would
have generally larger dimensions, and the turbulator 24
would be omitted. As shown at 50, a rectangular intake
duct provides ample space for incoming air while reducing
flow resistance. This surrounds the exhaust or outlet
duct 20.
It will be appreciated that while two preferred
embodiments have been described, numerous variations are
possible. For example, the heat exchanger could have a
clamshell-type of construction. Such construction
includes two sheets configured to be joined together along
their edges. The sheets are then shaped to give a desired
internal configuration. Here, the sheets would be
configured to give the upper and lower heat exchanger
sections, and would be generally symmetrical about a
central plane.
