U.S. patent application number 11/863331 was filed with the patent office on 2008-04-10 for space heater with microprocessor control.
This patent application is currently assigned to SEACOMBE TECHNOLOGIES AUSTRALIA PTY LTD.. Invention is credited to Siegfried Karl Rappold.
Application Number | 20080083404 11/863331 |
Document ID | / |
Family ID | 39268024 |
Filed Date | 2008-04-10 |
United States Patent
Application |
20080083404 |
Kind Code |
A1 |
Rappold; Siegfried Karl |
April 10, 2008 |
Space Heater with Microprocessor Control
Abstract
A space heater has a microprocessor control that is configured
to receive signals from at least the (i) ignition sensor associated
with the burner, (ii) the flue pressure sensor, (iii) the secondary
header temperature sensor, (iv) the fire box thermistor, and (v)
the condensate sump level sensor, and in response thereto, control
at least the operation of (a) the inducer, (b) the convection fan,
(c) the condensate pump, (d) the burner ignitor, (e) the burner gas
valve, and (f) the main gas valve.
Inventors: |
Rappold; Siegfried Karl;
(Wheelers Hill, AU) |
Correspondence
Address: |
THOMPSON COBURN, LLP
ONE US BANK PLAZA
SUITE 3500
ST LOUIS
MO
63101
US
|
Assignee: |
SEACOMBE TECHNOLOGIES AUSTRALIA PTY
LTD.
71-73 Overseas Drive
Noble Park
AU
3174
|
Family ID: |
39268024 |
Appl. No.: |
11/863331 |
Filed: |
September 28, 2007 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
60828404 |
Oct 6, 2006 |
|
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|
Current U.S.
Class: |
126/524 |
Current CPC
Class: |
F24H 3/087 20130101;
F24B 1/1808 20130101 |
Class at
Publication: |
126/524 |
International
Class: |
F24B 1/188 20060101
F24B001/188 |
Claims
1. A space heater comprising: a burner assembly having a plate
supporting a burner and burner valve operatively connected to a gas
supply regulated by a main gas valve of the space heater, the plate
supporting an ignitor for igniting gas discharged from the burner,
the plate supporting at least one ignition sensor configured for
sensing the presence ignited gas exiting the burner; a fire box
having a generally box shape with left and right heat exchanger
surfaces, top and bottom heat exchanger surfaces, and a rear heat
exchanger surface defining an interior of the fire box, the burner
assembly disposed in the fire box interior, the fire box having a
fire box thermistor adapted to sense fire box temperature; panels
spaced from and surrounding portions of the fire box to form a
plenum; a secondary heat exchanger disposed in the plenum and
exterior to the fire box adjacent the rear heat exchanger surface
of the fire box, the secondary heat exchanger operatively connected
to the fire box and receiving a flow of combustion gases from the
fire box, the secondary heat exchanger comprising a corrugated
flexible steel tube with a turbulator disposed inside the tube to
induce spiral flow of the combustion gases passing through the
secondary heat exchanger; a primary header disposed in the plenum
and exterior to the fire box adjacent the rear heat exchanger
surface of the fire box in a generally vertical arrangement, the
primary header operatively connected to an outlet of the secondary
heat exchanger; a secondary header disposed in the plenum and
exterior to the fire box adjacent the rear heat exchanger surface
of the fire box in a generally vertical arrangement, the secondary
header having a temperature sensor adapted for sensing temperature
of combustion gases flowing through the secondary header; a
tertiary heat exchanger disposed in the plenum and exterior to the
fire box adjacent the rear heat exchanger surface of the fire box
below the secondary heat exchanger, the tertiary heat exchanger
comprising a plurality of finned tubes supported by and
communicating with the primary header and the secondary header
whereby combustion gases exiting the secondary heat exchanger pass
through the primary header into the tertiary heat exchanger and
flow into the secondary header, the tubes of the tertiary heat
exchanger having turbulators disposed therein for inducing a spiral
flow therein; a condensate collection assembly arranged in the
plenum below and operatively connected to the secondary header
through a depending flow portion of the secondary header, the
condensate collection assembly comprising a pump and a sump, the
pump being configured to pump condensate entrained in the
combustion gases from the sump to a condensate tray disposed atop
the top heat exchanger surface of the fire box, the condensate
collection assembly having at least one sensor adapted to sense a
level of condensate in the sump; an inducer mounted on the
depending flow portion of the secondary header, the inducer being
configured to draw combustion gases out of fire box and through the
secondary and tertiary heat exchangers and discharge to a flue
having a pressure sensor for monitoring pressure in the flue
downstream of the inducer; a convection fan located in the plenum
configured to draw air from a room in which the space heater is
situated into the plenum below the fire box and to pass the air
over the secondary and tertiary heat exchangers and over the
condensate tray before discharging the air to the room; and a
microprocessor control for the space heater being configured to
receive signals from at least the (i) ignition sensor associated
with the burner, (ii) the flue pressure sensor, (iii) the secondary
header temperature sensor, (iv) the fire box thermistor, and (v)
the condensate sump level sensor, and in response thereto, control
at least the operation of (a) the inducer, (b) the convection fan,
(c) the condensate pump, (d) the burner ignitor, (e) the burner gas
valve, and (f) the main gas valve.
2. The space heater of claim 1 wherein the secondary heat exchanger
tubulator is made from a material that is anodic relative to the
combustion gases and the material forming the tube of the second
heat exchanger.
3. The space heater of claim 1 wherein the tertiary heat exchanger
tubulators are made from a material that is anodic relative to the
combustion gases and the material forming the finned tubes of the
tertiary heat exchanger.
4. The space heater of claim 1 wherein an interior of the tubes of
the tertiary heat exchanger are accessible via at least on of the
primary and secondary header.
5. The space heater of claim 1 wherein an interior of the tube of
the secondary heat exchanger is accessible via the primary
header.
6. The space heater of claim 1 wherein the burner assembly includes
first and second burners.
7. The space heater of claim 6 wherein the microprocessor operates
the inducer at a variable rate depending upon a number of burners
in operation.
8. The space heater of claim 6 wherein the microprocessor is
further configured to sense a temperature in the room and operate
at least one of the first and second burners in response
thereto.
9. The space heater of claim 8 further comprising a thermostat
configured to generate a signal in response to a temperature in the
room.
10. The space heater of claim 6 wherein the first and second
burners have different heat generation ratings.
11. The space heater of claim 10 wherein the burner plate has
openings adjacent each burner and the openings are dimension to
regulate air flow to the burner to maximize combustion in
accordance with the burner rating and inducer fan capacity.
12. The space heater of claim 1 wherein the flue comprises an inner
pipe surrounded by an outer pipe and air for combustion flows
through the outer pipe before being introduced to the burner.
13. The space heater of claim 12, wherein the inner and outer pipe
are made from a polyvinyl chloride material.
14. The space heater of claim 1, wherein the tertiary heat
exchanger tubulators are removably insertable into the finned tubes
of the tertiary heat exchanger.
15. The space heater of claim 1 wherein the secondary heat
exchanger turbulator is removably insertable into the corrugated
tube of the secondary heat exchanger.
16. The space heater of claim 1, wherein the secondary header is
made from a polyvinyl chloride material.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] This application claims the benefit of provisional
application Ser. No. 60/828,404, filed Oct. 6, 2006, the disclosure
of which is incorporated by reference herein.
FIELD OF THE INVENTION
[0002] This invention relates to a high efficiency, condensing gas
log space heater with an integrated microprocessor control where
combustion gases are exhausted through a three stage heat exchanger
system allowing exhaust temperatures to be no more than 125.degree.
F.
BRIEF DESCRIPTION OF THE DRAWINGS
[0003] FIG. 1 is a perspective view of a space heater;
[0004] FIG. 2 is a sectional cross-section taken along the line 2-2
of FIG. 1 in the direction of the arrows shown;
[0005] FIG. 3 is a sectional side view taken along the line 3-3 of
FIG. 2;
[0006] FIG. 4 is a part sectional plan view from above taken along
the line 4-4 of FIG. 3;
[0007] FIG. 5 is a part sectional plan view from above taken along
the line 5-5 of FIG. 3;
[0008] FIG. 6 is a part sectional plan view from above taken along
the line 6-6 of FIG. 3;
[0009] FIG. 7 is a top view of the burner assembly of FIG. 1;
[0010] FIG. 8 is a front view of the burner assembly of FIG. 1;
[0011] FIG. 9 is a front view of a secondary heater exchanger, a
tertiary heater exchanger, a primary header extending between the
secondary and tertiary heat exchanger, an inducer fan assembly, and
a secondary header extending between the tertiary heater exchanger
and the inducer fan assembly;
[0012] FIG. 10 is a front view of a turbulator inserted into the
secondary heat exchanger of FIG. 8;
[0013] FIG. 11 is a front view of a turbulator inserted into the
tertiary heat exchanger of FIG. 8;
[0014] FIG. 12 is a left side view of the secondary header of FIG.
8;
[0015] FIG. 13 is an exploded perspective view of an impeller of
the inducer fan assembly of FIG. 8;
[0016] FIG. 14 is a cross sectional view of an intake/exhaust pipe
used with the space heater;
[0017] FIG. 15 is a front view of a condensate pump assembly;
[0018] FIG. 16 is a state diagram for a microprocessor control of
the space heater;
[0019] FIG. 17 is a continuation of the state diagram for the
microprocessor control shown in FIG. 16;
[0020] FIG. 18 is a state diagram for the microprocessor
control;
[0021] FIG. 19 is a block diagram of inputs to and outputs from the
microprocessor control;
[0022] FIG. 20 is a use case diagram for the microprocessor
control; and
[0023] FIG. 21 is a chart showing diagnostic and fault logic for
the microprocessor.
DETAILED DESCRIPTION OF DISCLOSED EMBODIMENTS
[0024] The space heater disclosed herein comprises a concealed
three-stage heat exchanger that captures more than 90 percent of
the heat energy from the burner and directs warm air into the room
in which the space heater is located. Because so much of the heat
is extracted by the three-stage heat exchanger, the exhaust can be
vented outdoors in conventional PVC piping, thereby saving money,
labor, and space on installation when compared to traditional
direct vent systems. Additionally, because so much heat is removed
by the three-stage heat exchanger, the space heater stays cool to
the touch and may be installed in zero clearance applications
against combustible building materials.
[0025] Referring to FIG. 1 of the drawings, the space heater 5 is
illustrated as seen from inside the room in a building to be heated
and there is shown the outer casing 6 of the heater with its large
neo-ceramic door glass 7, which may include a screen (not shown)
fitted thereon. The heater may include external controls 40 for
activation of the space heater and lights 42 indicating its mode of
operation. The controls may include a transmitter 44 to allow the
space heater to be operated remotely. As explained below, the
indicating lights may also be used in a diagnostic/fault
application.
[0026] Referring to FIG. 2, the heater heats the ceramic logs 9 in
a fire box or primary heater exchanger 8 and the products of
combustion are drawn through a secondary exchanger 17 and a
tertiary exchanger 19 by combustion fan 26 through the depending
portion of the secondary header. The space heater is a high
efficiency heater and combustion air is drawn into the fire box
from outside of the room in which the space heater is located. As
will be explained below, the preferably combustion air is drawn
from the atmosphere and the combustion products and gases are
discharged to atmosphere.
[0027] Referring to FIG. 2, a convection fan 30 draws air through a
lower front opening 32 of the heater casing 6. The convection air
passes under the fire box 8 through an electrical enclosure
compartment 50 and into a plenum 52 behind the fire box where the
convection air flow over and around the tertiary and secondary heat
exchanger 19,17, up and over the top fire box 8, where it returns
into the room via a return vent 54 at the top front of the space
heater.
[0028] As shown in FIGS. 2-6 the fire box or primary heat exchanger
8 is cubically shaped enclosure dimensioned to accommodate the
ceramic logs. The fire box is adapted to be fitted within the
external casing 6 of the space heater. Heat shielding is provided
around the fire box between the casing to the protect the casing.
Referring to FIG. 2, in the fire box or primary heat exchanger,
ceramic logs 9 are supported on ceramic grate 10 having apertures
11 therein to allow passage of gas flames from a burner plate
assembly 12 mounted above an air inlet manifold 13 that extends
below and through the rear 14 of the casing. The air inlet manifold
13 communicates with an intake portion 15 and intake/exhaust pipe
as discussed below in reference to FIG. 14. A gas control valve 33
is located at the back of the heater and connected to a gas supply
and to the burner plate assembly 12. The ceramic grate 10 acts as
an insulating medium for the gas and electronic components located
in the electronics enclosure 50. The ceramic grate 10 and logs 9 at
the same time act as an agent in improving the combustion process
in fire box 8 by keeping a high temperature after the gas flames
have issued from burners 12 and thereby producing a clean total
combustion. The ceramic logs 9 absorb heat from the gas flames
whereby thermal energy from logs 9 radiates as infra-red heat
through the transparent or semi-transparent door glass 7 at the
front of the heater 5.
[0029] Referring to FIGS. 7-8, the space heater burner late
assembly 12 comprises two burners 60,62 rated for delivering
different amounts of heating, for instance, the first burner
delivering 9,000 BTUs and the rear burner delivering 19,000 BTUs.
The front burner 60 may be operated alone as desired, and when
additional heating is required, the second burner 62 may be
switched on to maximize heat output. As will described in greater
detail below, the space heater is provided with a control system
that allows operation of the front burner 60 or the rear burner 62
independently, or both burners together. The space heater may also
be provided with a thermostat to control the operation of the
burners in accordance with ambient room temperature.
[0030] Referring to FIGS. 7-8, the front and rear burners 60,62 are
mounted on a burner plate 64 along with a respective hot surface
igniter 66,68 and flame detector 70,72 adjacent each burner so that
each burner may be operated independently, as discussed previously.
The burner plate 64 has openings 74,76 surrounding each burner.
Combustion air is directed to air manifold 13 and into the fire box
from under the burner plate 64 and through the openings 74,76
around the burner. The openings in the burner plate are dimensioned
to maximize the combustion process by allowing the proper amount of
combustion air to be introduced into the burner, taking into
account the burner capacity and the capacity of the inducer fan
26.
[0031] In one embodiment, the inducer motor capacity remains fixed
regardless of whether the front, rear, or both front and rear
burners are activated in order to simplify construction. Thus, the
amount of air introduced to the front burner and rear burner is the
same regardless of whether the front, rear, and/or front and rear
burners are activated. Thus, the amount of combustion air is
dictated by the burner plate openings for each of the respective
burners.
[0032] In another embodiment, the inducer fan speed is varied in
accordance with the burner operation, as will be explained below in
greater detail with respect to the inducer motor control. By way of
example, for the burner arrangement shown in FIGS. 7-8, the inducer
fan may operate at three speeds: a first speed when the smaller
rated front burner is operated; a second speed higher than the
first speed setting when the rear burner is operated; and a third
speed higher than the second speed setting, when both the front and
rear burners are operated. In this way, the efficiency of the
combustion process can be maximized.
[0033] Referring to FIGS. 3-4, a baffle chamber 16 is located at
the upper part of the fire box 8 which allows combustion products
from the fire box 8 to pass around the edges thereof (FIG. 4) into
a secondary heat exchanger 17. The baffle chamber 16 acts to ensure
even distribution and balanced extraction of final combustion
gases.
[0034] Referring to FIGS. 3-4, after exiting the primary heat
exchanger 8 through the baffle chamber 16, the combustion gases
enter the secondary heat exchanger 17 located in the plenum 52
behind the firebox that communicates with the main convection
blower fan 30. The secondary heat exchanger 17 comprises a
corrugated flexible stainless steel tube 18, such as a flex parco
hose, that relieves thermal expansion stresses between connections
of the primary heat exchanger 8 and the tertiary heat exchanger 19.
Preferably, the hose is stainless steel although other materials
may be used for the hose. Corrosion is generally not a concern in
the secondary heat exchanger due to the elevated temperatures at
which the secondary heat exchanger operates. A turbulator as shown
in FIG. 10, may be provided in the secondary heat exchanger to
improve the efficiency of heat transfer. A further discussion of
the turbulators follows below.
[0035] Referring to FIGS. 3 and 9, once the combustion products
exit the secondary heat exchanger 17, they are directed to the
primary header 22 that is in communication with the tertiary heat
exchanger 19. The primary header 22 is arranged vertically in the
compartment behind the firebox with the top of the header receiving
the combustion gases from the secondary heat exchanger and the
bottom of the header directing the combustion gases into the
tertiary heat exchanger. The primary header 22 comprises a header
cover 80 attached to a header plate 82 with quick disconnect
fasteners 84. The quick disconnect fastener facilitate access to
both the secondary heat exchanger and the tertiary heat exchanger
by removing the header cover 80 from the header plate 82. The tubes
comprising the secondary and tertiary heat exchanger may be secured
to their respective header plates.
[0036] Referring to FIG. 3 and FIG. 9, the tertiary heat exchanger
19 comprises a plurality of externally finned tubes 23 also located
in the plenum 52 behind the firebox and below the secondary heat
exchanger. The finned tubes 23 extend generally horizontally but
angled slightly downward from the primary header 22 and the
secondary header 24. The secondary header 24 is also arranged
vertically in the compartment behind the firebox. The finned tubes
23 may be secured to the primary and secondary headers 22,24, by
expanding the ends of the tubes 23 in their attachment to the
headers to expand both surface sides of the header plates thus
creating a very strong crimp fixture which is reliably gas tight
with no requirement for welding. The finned tubes are expanded into
header plates to avoid welding of finned tubes to primary and
secondary header plates to avoid corrosion taking place. When
welding is performed on stainless steel, it tends to remove surface
protection of the stainless steel, and eventually, due to the
presence of condensation, the finned heat exchanger tubes may
corrode in areas where they have been welded to the header plates.
The finned tubes 23 preferably comprise stainless steel tubes with
attached helical corrugated fins 28 (FIG. 9) on the external
surfaces thereof to increase the thermal energy transfer to the
outer surface of tubes 23. The finned tube 23 may be made from
29-4C stainless steel, as the tertiary heat exchanger may
experience some condensation as the combustion products are cooled.
The angled arrangement of the finned tubes facilitates draining of
condensate from the tubes into the secondary header 24.
[0037] Referring to FIGS. 10 and 11, inside the secondary heat
exchanger tube 18 and the tertiary heat exchanger tubes 23 are
helical aluminium strip or tape 21,29, which acts as a turbulator
to the combustion gases travelling through tubes. The turbulators
are formed in an arrangement which is helical or twisted. As the
combustion gases are drawn through the tubes of the respective heat
exchangers and over the turbulators, the flow rate of the gases is
slowed and the gases are spiraled outward to the tube wall for more
efficient heat transfer.
[0038] The turbulators in the secondary and tertiary heat exchanger
not only act to increase efficiency, they also act as sacrificial
anodes to protect the complete heat exchanger against corrosion,
i.e., the secondary heat exchanger, primary header plates,
secondary header plates, and the tertiary heat stainless steel
finned tubes. With condensation in the system, the turbulators will
corrode first before the other materials are attacked. When the
turbulators sufficiently corrode, they are no longer efficient in
creating a spiral flow of exhaust gases in their respective heat
exchanger tubes. Accordingly, after significant corrosion, the
temperature through the heat exchangers may increase to a level
sufficient to activate the secondary header over temperature limit
switch, as discussed further below, which will then shut the gas
supply to the heater to protect the heat exchanger and PVC
components in the heat exchanger. Thus, the turbulators provide
benefits in increasing the efficiency of the heat exchangers and
protecting the materials used in the heat exchanger construction to
the point where the heat exchanger need not be replaced, but rather
the turbulators. The primary and secondary headers are constructed
in such a way that they are removable from the secondary and
tertiary heat exchangers so that the turbulators can always be
replaced and inserted into each tube when corroded.
[0039] This is especially critical in the tertiary heat exchanger
where condensation is formed. Preferably, the turbulators 29 in the
tertiary heat exchanger 19 are made from thin aluminum. By using
the turbulators which are removable and act as sacrificial anodes,
the finned tubes 23 comprising the tertiary heat exchanger may be
made from more inexpensive materials. Thus, the turbulators protect
the materials used in the secondary and tertiary heat exchangers to
extend the useful life of the heat exchangers and to increase the
efficiency of the heat exchangers.
[0040] Referring to FIGS. 3, 9 and 12, after exiting the tertiary
heat exchanger 19, the combustion gases are directed to the
secondary header 24 comprising a header cover 90 and a header plate
92. The header cover 90 may be made from a PVC plastic and attached
to the header plate with quick disconnect fasteners 94 to allow
access into the tertiary heat exchanger by removing the header
cover 90 from the header plate 92. The secondary header 24 has an
angled depending portion 100 which communicates with a condensate
pump assembly 25 via an outlet port drain 101. The angled arranged
ensures that condensate entrained in the combustion gases flows out
of the tubes 23 of the tertiary heat exchanger into the secondary
header 24 and into the condensate container 31. The secondary
header 24 and depending portion 101 may be made from PVC
rectangular pipe and include an elbow 102 that provides the
necessary angle for draining condensate.
[0041] To maximize efficiency of the heat exchanger, the
temperature of the combustion gases exiting the tertiary heat
exchanger is controlled to be no more than 150.degree. F. degrees.
A temperature sensor 104 may be provided on the secondary header to
monitor the temperature of the combustion products in the secondary
header and provide signaling to shut the space heater off in the
event the temperature exceeds a desired amount. Given that the
materials comprising the secondary header and the components
located downstream of the secondary header are made from PVC or
other low temperature materials, continuous monitoring of the
temperature of the gases in the secondary header is needed.
[0042] A pressure sensor 106 may be provided on the secondary
header 24 to assist in the purging cycle of the space heater at
start-up. As will be described below, the pressure sensor 106
senses the pressure in the secondary header 24 and compares the
signal to atmospheric pressure to determine whether the inducer fan
assembly 26 is operating properly and/or the flow path of
combustion air and products is unobstructed.
[0043] Referring to FIGS. 3, 9, and 13, after exiting the secondary
header 24, the combustion gases are drawn to the inducer fan
assembly 26. As shown in FIG. 9, the inducer fan assembly may be
mounted on the angled depending portion 101 of the secondary
header. The inducer fan assembly draws combustion gases from the
fire box 8 through the secondary heat exchanger 17 and the tertiary
heat exchanger 19 and discharges the gases through a flue pipe 27.
The secondary header depending portion 101 is formed with an inlet
108 on its top surface to allow the inducer fan to draw directly
from the secondary header without significantly drawing condensate
into the inducer fan. The inducer fan assembly 26 comprises a motor
110 and an impeller 112 with a capacity to draw combustion air and
gases through the heat exchanger and exhaust them through the
equivalent of 60 feet of two inch diameter piping. As will be
described below, the combustion products may be directly vented to
the outer atmospheric air through either a co-axial intake/exhaust
pipe 120 (FIG. 14) or through a convention chimney or flue. As
shown in FIGS. 2 and 3, the inducer fan assembly 26 may also be
mounted on a horizontal portion of the secondary header. As shown
in FIG. 14B, the inducer fan motor 110 has a corrosive resistant
shaft 114, and a corrosive resistant housing and impellor. Because
the three-stage heat exchanger of the space heater is very
efficient, the exit temperatures of the combustion products are no
greater than 125.degree. F. degrees. This allows the inducer motor
housing and impeller to be made from low cost materials such as PVC
or plastic. As discussed previously, the inducer fan speed may be
set for a constant rate or may be varied in accordance with the
burner operation.
[0044] Referring to FIG. 14, once the combustion products exit the
inducer fan assembly 26, they are directed to the intake/exhaust
pipe 120. The intake/exhaust pipe may have a coaxial arrangement
with an outer tube 112 surrounding an inner tube 114. Inlet air is
drawn through the outer tube 112 and into the air inlet portion 15,
and the combustion products exit through the inner tube 114 as
shown in FIG. 14.
[0045] Referring to FIG. 15, the condensate pump assembly 25
comprises a pump 130 located in the condensate container 31. The
condensate container 31 accumulates condensate entrained in the
combustion gases for humidification purposes and may be made from
PVC or other low temperature material. The condensate pump 130
pumps condensate from the condensate container 31 through an outlet
134 into a condensate pan 150 (FIG. 2). As will be described in
greater detail below, convection air circulating over the top of
the primary fire box runs over the top of the condensate pan 150
(FIG. 2) before it exits from the top of the heater through the
room return vent 54 thereby automatically restoring air humidity in
the room. The condensate pump assembly 25 comprises of a high level
alarm sensor 136 and two actuation sensors 138. The sensors 136,138
have probes which extend from a top plate of the container 31 into
an interior of the container. The probes are adjustable in the
vertical direction in the container interior to adjust their
respective set points. The probes measure electrical conductivity
of the condensate and have no moving parts. The probes operate via
low voltage control circuit provided in the heater, preferably, 12
VDC. Thus, the pump sensing probes 138 actuate the condensate pump
130 when the condensate level in the container reaches a
predetermined level. The high level alarm sensor 136 shuts down the
space heater when the condensate level in the sump reaches an
excess level, possibly indicating that the pump has failed or the
actuation sensors are inoperative. The pressure switch and high
condensate level alarm sensor are also incorporated into the system
to monitor the combustion process to ensure the combustion exhaust
products will not exceed the CO/CO.sup.2 guidelines, as well as
protecting the heat exchanger from building up carbon through the
secondary and tertiary heat exchanger.
[0046] Referring to FIGS. 2 and 3, a condensate pan is provided
adjacent the top of the fire box or primary heat exchanger 8. The
condensate pan is sized to accommodate the maximum amount of
condensate extracted from the combustion process when the heater is
operating between 85 and 92 percent and its rated thermal capacity.
The condensate tray 150 is arranged in the path of the convection
blower 30 so that air entering the room in which the space heater
is located is humidified. The pan 150 may be arranged in a
generally flat orientation to provide greater surface area for
evaporation and humidification. The condensate pan is filled by a
stainless steel or aluminum tube which communicates with the
condensate container 31 via the pump outlet 134.
[0047] Referring to FIG. 2, the combustion fan 30 is located inside
and at the bottom of the heater structure 5 in the electrical
compartment 50 to ensure that the cooler room air drawn through a
louvered opening 32 at the lower front of the heater is continually
moving past the combustion fan and the space heater electronic
components thereby extending the reliability and life of the
combustion fan motor and other components of the space heater. The
outlet of the combustion fan 30 is directed to the plenum behind
the fire box, first over the tertiary heat exchanger 19, then over
the secondary heat exchanger 17, then up and around the top of the
primary heat exchanger 8, over the condensate pan 150, and finally
out of the space heater through the return vent 54 and into the
room.
[0048] In one embodiment of the space heater rated for 28,000 BTUs,
the effluent may be vented at temperatures below 150.degree. F.
degrees. The space heater has the following general
characteristics: [0049] a 160 CFM convection blower fan. [0050] a
primary heater exchanger fire box made from thin 304 stainless
steel plate having dimensions of approximately 25 inches wide by 17
inches high by 91/2 inches deep. [0051] a secondary heat exchanger
tube comprises a 21/2 outer diameter 304 stainless steel tube
approximately 351/2'' long with 2 9/16'' outer diameter
corrugations spaced at 4 corrugations per inch along its length.
The secondary heat exchanger tube is arranged to exit the center of
the rear wall of the fire box primary heat exchanger and looped
half way back over itself to fit within the confines of the space
heater enclosure thereby creating in effect two passes in the
secondary heat exchanger. The secondary heat exchanger is arranged
to lower the temperature of the effluent combustion products from a
temperature in excess of 800.degree. F. degrees to a temperature of
between 400.degree. F. and 450.degree. F. degrees with the space
heater operating burners rated for 28,000 BTUs. [0052] a tertiary
heat exchanger comprising 5 finned tubes, each approximately
201/2'' long with a 3/4'' outer diameter with roughly 11/2''
diameter fins spaced at nominally 11 fins per inch along the length
of the tube. The tertiary heat exchanger has been found capable of
reducing combustion gases introduced at a temperature of between
400.degree. F. and 450.degree. F. to a temperature of no greater
than 150.degree. F.
[0053] The space heater of the present invention is very compact
and portable and usable in other applications, such as conventional
HV AC, gas logs, and hot water heaters. The heat exchangers in the
space heater may be appropriately scaled for applications rated for
32,000, 36,000, 64,000 or 120,000 BTUs, while maintaining their
compact and efficient arrangement. Gas and fan controls ensure that
the desired room or space temperature is maintained. Automatic
thermostat controls may be used with the space heater and computer
controlled solid state electronic controls may be built into the
heater to provide safety and efficiency of the heater in use.
[0054] In one embodiment, described in further detail below, the
computer controlled solid state electronic controls comprise a
microprocessor. State diagrams associated with the microprocessor
control are shown in FIGS. 16-18. A general arrangement of the
inputs to and outputs from the microprocessor control is shown in
FIGS. 19 and 20.
[0055] The hardware and firmware of the heater are arranged such
that, the microprocessor deals with all functional operations of
the space heater. Any fault conditions that are detect, are dealt
with by the microprocessor and its firmware on a first line basis.
This is achieved, by having the timings shorter for the firmware
control, than the hardware supervisory circuits. There are some
exceptions to this, in that the flue pressure, external watchdog
timer and the external disable signal, cause the gas valves to be
de-energized, without processor intervention.
[0056] The electronics hardware comprises a power supply, a control
microprocessor, input signal conditioning, output drivers and
isolation and safety monitoring and cutout functions. These are
arranged so that failure of the microprocessor will result in the
gas valves being disabled. There are a number of mechanisms to
ensure this: [0057] Failure of the microprocessor to service the
internal watchdog timer within the allotted timeout of
approximately one (1) second will result in the microprocessor
being reset. This reset will lock the program into a loop, locking
up all functions. Thus, the external watchdog will cause the gas
valves to be disabled. [0058] Failure of the micro processor to
service the external watchdog timer within the allotted timeout of
approximately 1 second. This will allow the external watchdog
circuit to disable the valves. [0059] Failure of the gas valves to
be turned off, if no flame detected within 15 seconds. With the
control micro processor working correctly, the no flame condition
would be detected within the allotted time out. If however this
does not occur the external cutout will take place. [0060] Failure
of the flue fan to effectively reduce the pressure within the flue.
This directly disables the valves relay drivers. [0061] An
externally wired disable input, which may be driven by such
devices, as a gas or smoke detector that once connected to the
ground/common contact, directly disables the valves relay
drivers.
[0062] The circuit module will be described below in greater
detail. Firmware within the micro processor monitors the inputs and
controls the gas valves 33, fan motors 26,30, igniters 66,68, pump
130 and indicators 42,44. To provide the necessary features for
both function and safety, the microprocessor is equipped with an
internal watchdog timer and an external watchdog timer, the output
of which feeds a safety cutout circuit.
[0063] The various input signals into the microprocessor are
conditioned. For instance, for the flame detectors 70,72, a low
power 120 V AC 10 kHz signal is fed to the flame detector rods and
earth. A flame from the earthed gas jets, rectifies this signal and
so the DC value will be altered slightly. Only the DC value of the
signal is considered. The small DC offset is detected and amplified
to logic levels. The signal is generated by firmware in the
microprocessor. Failure of this signal results in the failure to
detect a flame, which will disable the gas valves.
[0064] The signal from the sump level detectors 136,138 is also
conditioned prior to its processing in the microprocessor. As
described above, the passage of air though the heat exchangers
causes condensate to form within it which runs down to the sump
container. The sump level detectors 138 determine when the pump
should be started to reduce the level in the sump. The high level
sensor 136 is placed near the top of the sump to determine if the
level has risen an excessive amount possibly indicating that the
pump 130 may have failed. The signal from the high level sensor
effects turning off of the heater, thereby preventing the formation
of additional condensate.
[0065] The signal indicating the fire box temperature is also
conditioned prior to its processing in the microprocessor. The
signal is generated via a thermistor 160 (FIGS. 3,4) mounted on the
side of the fire box. The fire box temperature signal is used to
control the multi-speed convention fan 30 blowing air from the room
over the heat exchanger. As the fire box increases in temperature,
the speed of the convection fan increases. Increasing convection
fan speed will eventually cool the firebox. In one embodiment, the
convection fan is operated at a speed setting which generally
corresponds to the number of burners operating. Thus, if the front
(smaller) burner is operating alone, the fire box temperature
control will generally sense a lower temperature and generate a
corresponding signal to operate the convection blower at a low
setting; if the rear (larger) burner is operating alone, the fire
box temperature control will generally sense a medium level of
temperature and generate a corresponding signal to operate the
convection blower at a medium setting; and if both burners are
operating, the fire box temperature control will generally sense a
higher level of temperature and generate a corresponding signal to
operate the convection blower at its higher speed.
[0066] The signal indicating the secondary header temperature is
also conditioned prior to its processing in the microprocessor.
When the temperature in the secondary header is acceptable, the
temperature sensor 104 generates a signal that enables power to the
gas valves to keep them open and operating. If the temperature in
the secondary header exceeds a set point, the sensor 104 generates
a signal that effects disconnecting power to the gas valves,
thereby shutting down the space heater.
[0067] The sensor 160 sensing fire box temperature also generates a
signal that enables power to the gas valves to keep them open and
operating. If the temperature in the fire box header exceeds a set
point, the sensor 160 generates a signal that effects disconnecting
power to the gas valves, thereby shutting down the space
heater.
[0068] The signal from flue pressure detector 106 is also
conditioned prior to its processing in the microprocessor. The
sensor 106 comprises both normally on and normally off contacts
with the normally on signal being fed to the safety circuits. The
flue fan is used to evacuate any unburnt gas and fumes from the
heater and environs prior to emission and ignition of the gas from
the burner jets. Confirmation of the proper operation of the flue
fan is determined by a mechanical diaphragm switch set to toggle at
35 Pa below atmospheric pressure caused by the reduction of the
pressure in the flue in comparison with the atmospheric pressure.
In one embodiment, the pressure detector is a model RSS 495/498
provided by Cleveland Controls, a division of UniControl, Inc. of
Cleveland, Ohio 44109. If the flue fan is working properly, the
pressure in the flue should be less than atmospheric pressure and
the switch will activate.
[0069] As an extra safety feature, the controller is also design
with an external disable circuit. This feeds directly to the safety
cutout circuit and disables the valves from being turned on. This
could be used in conjunction with an external smoke or gas
detector. The circuit element involved with this is a diode.
[0070] The microprocessor drives certain output devices while being
isolated therefrom. Apart from the indicator LEDs on the front
panel 42,44, all output devices are driven by 240 V AC, and are
switched by semiconductor Triacs or in the case of the gas valves,
by relays. The switching signal for the Triacs is derived from an
opto-isolated triac driver, which only switches at, or near, the
zero crossing portion of the AC power waveform. Some of the AC
outputs have detectors to determine if the load, for example the
igniters 66,68 are still operational or disconnected. This is also
the case for the main valve 33, as it is possible for the over
temperature switch to disconnect the power from the valves. This
can be detected by the microprocessor, and a fault condition alerts
the user to a problem to be rectified.
[0071] In one embodiment, isolation is provided by the
opto-couplers (M0C3063) which are rated at 7500V for 1 second, 600
volts continuous. Design of the PCB layout ensures the continued
validity of this isolation by keeping all high voltage traces and
components in an isolated area.
[0072] In one embodiment of the space heater, the space is provided
with three gas valves: a main gas valve 33, and front and rear gas
valves 170,172 (FIGS. 7,8). Each gas valve is switched via a relay.
For instance, the relay may comprise a 1 pole 3A Slim Type Relay
FTR-F3 Series provided by Fujitsu Components America of Sunnyvale,
Calif. One relay is used for each of the burner valves, and another
relay having contacts are in series, for the main valve. These
relays provide isolation from the 240 V AC power source. The
positive input drive of the relay coils are each driven from
control outputs of the microprocessor. These turn on the various
burner valves in accordance with the desired operation of the
heater. The common negative power lead for these relay coils is
controlled by the disabling circuits.
[0073] In one embodiment of the space heater, a number of
conditions will disable the operation of the gas valves, without
regard to the microprocessor. Inputs to this circuit are: (i) flue
pressure sensor normally closed contact; (ii) the external watch
dog timer reset output; (iii) external disable signal; and (iv)
flame detector combined with valve drive signal delayed to a
greater timeout than the microprocessor programmed "wait for flame"
timeout. If the flue pressure drops below the set limit, the gas
valves are disabled. This occurs whenever the heater is turned off,
so in the static state, the heater is in the shutdown mode. If the
external watchdog timer is not strobed within the time limit, the
gas valves are disabled. If the external disable signal is shorted
to ground, the gas valves are disabled. If the valves are being
turned on and no flame is detected, then 15 seconds later the gas
valves are disabled. If this is greater than the 10 seconds total,
then the microprocessor will wait for the flame to stabilize. If
the microprocessor does not turn off the gas valves, the external
circuit will do so 5 seconds later. It should be noted, that errors
in the micro processor, would most likely fail to strobe the
external watchdog, and in so doing, disable the gas valves within
1.2 seconds, well before the flame detectors have registered
errors.
[0074] The flame detector signal is combined with valve drive and
delay circuits. The circuit element used to combine the flame
detector output and the valve drive is an exclusive "or" gate.
Below illustrates the logic of these signals and the gate.
TABLE-US-00001 Flame Detector Valve Drive off Output 0 0 0 0 1 1
fault 1 0 1 fault 1 1 0
These input signals are fed to a switching element which
disconnects the negative power feed to the relay coils. This action
also latches the element in the "off" condition so the valves
remain off, even if the disabling signal is removed. The latch is
reset by the micro processor, prior to safe operation. This latch
is set whenever a disabling signal is active (active=low), thus
every time the flue pressure is low, as in the off condition, the
gas valves are disabled. Consequently, the microprocessor must
re-enable this latch, before further operation can take place.
[0075] The space heater may be provided with a front panel circuit
that contains the interface to the switches 40,44 and thermostats,
as well as the low voltage LEDs that form the indicators 42
illuminating through the front panel. The front panel circuit is
connected via ribbon cable to the main PCB.
[0076] The microprocessor may be arranged to operate the inducer
motor at a variable rate depending upon burner operation. As the
microprocessor processes signals to activate one or more burners,
the microprocessor is programmed to signal the inducer motor
controller to increase the inducer fan speed. For instance, in the
burner arrangement shown in FIGS. 7 and 8, the inducer fan may
operate at three speeds: a first speed when the smaller rated front
burner is operated; a second speed higher than the first speed
setting when the rear burner is operated; and a third speed higher
than the second speed setting, when both the front and rear burners
are operated. The microprocessor may process the signals when the
front controls 40,44 are activated or when a thermostat associated
with space heater passes through pre-determined set points. As
discussed below, when the microprocessor enters the PURGE state
discussed below, the inducer fan may be brought up to speed in
accordance with the burner to be operated.
[0077] In one embodiment, the firmware for the gas fire controller
has the following structure: (i) the source code is written in C;
(ii) the target processor is MC9S12C32; and (iii) the compiler used
is Imagecraft ICC 12 Ver. 6.16A. The source code directory may be
structured as follows. TABLE-US-00002 Root. -> Project files bin
->compiler output include -> header files of main source main
-> main source code files OS drv -> processor specific source
and header files
[0078] The operational structure of the code may be as follows.
TABLE-US-00003 initialization of hardware and software. endless
super loop Polling COP Polling Main PCB Inputs and Outputs Polling
front panel PCB inputs and outputs Polling pump functions Polling
convection fan functions Polling finite state machine.
Within the endless loop, the independent functions of the
controller are maintained: (i) the computer operation properly
timer is reset; (ii) the inputs and outputs of the main PCB are
read from and written to; (iii) maintaining the various variables
for the other functions; (iv) the pump is serviced by checking the
level sensor values and determining the need for the pump to
operate; (v) the convection fan is operated at various speeds
determined by the value of the temperature sensor on the fire box;
(vi) the code which determines the state and action of the fire
controller is executed. This is the main function of the code,
where the flue purge, ignition sequence and shutdown occurs.
[0079] One interrupt is used to provide a stable time base for the
timers used to sequence various features. All other interrupts lead
to the safe shutdown and lockout (halting) of the code.
[0080] The microprocessor has several finite states as shown in
FIGS. 16, 17 and 18. The microprocessor creates a number of
discreet states, and one "super" state for the ON condition, which
itself contains a number of discreet states. Initial entry into the
state diagram is the reset condition, which then defaults to the
OFF condition. A transition out of this OFF condition is via: (i) a
user input in the form of the front panel switches turning on
either or both burners; (ii) a fault in the flue pressure being
detected low: or (iii) a flame being detected.
[0081] Each of the states will be discussed below in greater
detail. Normal operation will be a transition from the OFF state
the FLUE WINDUP state. The FLUE WINDUP state allows a delay before
testing the flue pressure to allow the flue fan to get up to speed
and evacuate some of the air in the flue. Once the flue pressure
has dropped, this triggers a transition to the PURGE state.
[0082] The PURGE state occurs during the initial running of the
flue fan, when fumes and unburnt gas is evacuated through the flue.
This purge lasts 40 seconds, during which time the hot surface
igniters are tested for failure. After the 40 second purge the
PURGE state moves to the ON super state.
[0083] In the ON super state, the first discreet state is the OFF
sub-state where the microprocessor switches the valves of the
transits to the WARMUP state. The WARMUP state is a 5 second
preheat stage for the hot surface igniter. During this time the
valves are off. After the 5 seconds, the valves are turned on and
the state transits to the IGNITE state. The IGNITE state is the 4
second period within which the gas should be ignited. After this 4
seconds the hot surface igniter are turned off, and the state
transits to the HOLDOFF state. The HOLDOFF state is time during
which the flame is expected to be detected. If after 5 seconds the
flame is not detected the state transits to the UNLOCK state with
the gas valves off. If the flame is detected the state transits to
the ON state. The ON state is the stable state of the controller
when the space heater is operating normally. Within this state, the
controller monitors the flame detectors and flue pressure, and
turning off the heater, as appropriate. For a two burner system,
two sets of states are kept in the ON super state, one for each
burner.
[0084] The microprocessor may have the following program files and
functions: TABLE-US-00004 Main.c void main(void) /* Application
entry point, initialization calls, main loop. */ This is the start
point of the program. The hardware and software variables are
initialized, then the main program loop is executed. This is an
endless loop, within which the features, both operational and
safety are carried out. The static void init(void) function also
resides in the main.c file, and is used to call the various
initialization functions. Pump.c / * Pump controller. */ This file
contains the function to initialize and manage the sump pump and
level detectors. The void pump_poll(void) function is called from
the main endless loop code in main.c. / * Pump is run when water is
detected, and for TIME_PUMP after is * no longer detected; this is
to prevent oscillation. * Call this function periodically. */ Fan.c
/* Convection Fan Controller. / This file contains the function to
run the convection fan. This is determined by the temperature of
the fire box, and runs at 3 different speeds, void fan_poll(void)
This function is called from the main endless loop code in main.c.
/ * Fan is run at the appropriate speed when a particular
temperature * is reached, and at the lower speed when the
temperature is dropped * below. There is a delay when dropping down
speeds to prevent * oscillation. There are four speeds (off, low,
med, high) based around *three temperature points */ fsm.c */State
machine for sequencing functionality. */ This file contains the
functions to implement the Finite State Machine used to sequence
through the various operational and safety features of the
heater.
[0085] The main states of the microprocessor are shown below in the
following chart: TABLE-US-00005 ENTER Start the FSM system. RESET
Reset all the states. OFF The stable heater off state. LOCKOUT TEST
A transient state that tests the operation of the lockout circuit
on the main valve. ON The stable heater on state with either one or
both burners. FLUE WINDUP The delay as the fan starts up, before a
lack of flue pressure will cause a fault. FLUE_WINDDOWN The delay
as the fan slows down, before a false flue pressure will cause a
fault. PURGE The start of the ignition sequence, evacuation of the
fire box and flue. FAULT_NO_FLUE_PRESSURE A transient state which
shuts down and sets the front panel LEDs, then moves onto the Fault
Recovery state. FAULT_FALSE_FLUE_PRESSURE A transient state which
shuts down and sets the front panel LEDs, then moves onto the Fault
Recovery state. FAULT_HIGH_WATER A transient state which shuts down
and sets the front panel LEDs, then moves onto the Fault Recovery
state. FAULT_FLAME_OUT A transient state which shuts down and sets
the front panel LEDs, then moves onto the Fault Recovery state.
FAULT_RECOVERY A state that determines the shutdown path, either
restarting after a turnout, or going into a lockout, which requires
the front panel switches to be both turned off. LOCKOUT A static
state which shuts done the gas flow and requires the front panel
switches to be both turned off.
[0086] The discreet states of the microprocessor within the ON
"super" state are shown in the below chart. TABLE-US-00006 ENTER A
transient state which moves onto the ON superstate OFF state. OFF A
transient state which makes sure the burner valve is off, and if
the specific burner is required, moves onto the hot surface igniter
warm-up state. WARMUP A static state which times the warm-up phase
of the hot surface igniter's operation IGNITE A static state which
times the ignition phase of the hot surface igniter's operation
HOLDOFF The state which times the flame stabilization phase of the
ignition sequence. UNLOCK A transient state that is the default
failure mode of the ON superstate, this moves to retry the ignition
via the off state. ON The stable state of the normal operation of
the burners. Thermostat or front panel controls will move the state
to the OFF state within normal operation. Any failure will change
the state to the appropriate shutdown or lockout state.
There is a function for each of the states that is called with a
passed variable of the type, transition_t, which can be: (i)
transition_enter, which sets the function variables to support the
new state; (ii) transition_do, which performs the operations
required of that state; or (iii) transition_exit, which sets the
variable and performs the operations to exit this state and move to
the next state. The "call to" the appropriate state function is
done by a call to "fsm_do( )" within the endless loop in the main.c
code. The call to fsm_do( ) uses a function pointer lookup table to
call the state function.
[0087] The function "m_function_lookup a[m_state] (Transition_do)"
is called with the "Transition_do" variable. With this passed
variable, the functions of that state are performed, including
determining if a transition is required. If the transition to
another state is required, that state's function is called with the
"Transition enter" variable, which sets the state the new state. So
the next call will be to this function with the "Transition_do"
variable and the transition to the next state is invoked by the
macro TO_STATE. For example: TABLE-US-00007
TO_STATE(State_FAULT_FALSE_FLUE_PRESSURE,
fp_flue(FpFlue_switch_fault); #define TO_STATE (new_state,
transition_code) \ m_function_lookup_a[m_state] (Transition_exit);
\ {transitioncode} \ m_state = new state; \
m_function-lookup_a[m_state](Transition enter);
[0088] At the point that this call is invoked, the "m_state" is
still the present state, and so the call m_function_lookup
a[m_state] (Transition_exit); calls the same routine to perform the
exit state operations. This then depends whether the functions used
in this way are re-entrant. Any required function calls are then
made by the line:
[0089] {transitioncode} \
[0090] The m_state is then changed to the new state, and the
function for that code is called by the line:
[0091] m_function_lookup_a[m_state] (Transition_enter);
[0092] For transition within the "ON" super state, the above
program flow is slightly modified as follows: TABLE-US-00008
#define TO_STATE_ON(burner, new_state, transition_code) \
m_ON_function_lookup_a[m_ON_state_a[bumer]](burner,
Transition_exit); \ {transitioncode} \ m_ON_state_a[burner] =
new_state; \ m_ON_function_lookup_a[m_ON_state_a[bumer]](burner,
Transition_enter);
As there are 2 burners that have an ON state, the burner in
question is added to the Macro.
[0093] The microprocessor may be provided with fault sensing
capabilities and diagnostics. Depending upon the nature of the
fault, the system will may: a) become inoperative with all valve
terminals de-energized; b) proceed to safety-shut-down, or lockout;
c) continue to operate, the fault being identified at the next
startup sequence; and/or (d) remain operational. FIG. 21 shows a
chart of the fault responses processed.
[0094] The embodiments were chosen and described in order to best
explain the principles of the invention and its practical
application to thereby enable others skilled in the art to best
utilize the invention in various embodiments and with various
modifications as are suited to the particular use contemplated.
[0095] As various modifications could be made in the constructions
and methods herein described and illustrated without departing from
the scope of the invention, it is intended that all matter
contained in the foregoing description or shown in the accompanying
drawings shall be interpreted as illustrative rather than limiting.
Thus, the breadth and scope of the present invention should not be
limited by any of the above-described exemplary embodiments, but
should be defined only in accordance with the following claims
appended hereto and their equivalents.
* * * * *