Heating system

An improved heating system is disclosed for providing heated air to a heated space, preferably using a gaseous fuel as the energy source. The system preferably includes an air heating sub-system, a compact combustion chamber, a separate cold air supply sub-system for conveying cold air from the heated space to the air heating sub-system, a combustion chamber heat exchanger in fluid with the cold air supply sub-system for transferring heat thereto, and a separate air circulating sub-system for withdrawing cold circulating air from the heated space. A mixing chamber is provided for mixing heated air from the air heating sub-system with the cold circulating air to provide heated air to the space. The system also preferably includes separate sub-systems for supplying pressurized combustion air and pressurized gaseous fuel to the air heating sub-system and for forcibly conveying exhaust gases therefrom without the need for a draft-type chimney or stack. In another preferred embodiment, a vortex-type air separator separates higher temperature and lower temperature combustion air, with the higher temperature air being used for combustion and the lower temperature air being heated in an exhaust gas heat exchanger before being conveyed to the heated space. A novel control sub-system is also provided for controlling the system, preferably in response to both indoor and outdoor temperatures, and for minimizing the number of energy wasting on/off cycles in operating the system.

BACKGROUND AND SUMMARY OF THE INVENTION 
The invention relates generally to heating systems primarily adapted to 
providing heated air to a space to be heated, such as a building or on 
enclosed portion thereof. More specifically, the invention relates to such 
a heating system fueled by a gaseous fuel. 
Previous conventional forced-air heating systems for residential or 
commercial buildings, or for enclosed portions thereof, have included 
furnaces that burn a mixture of fuel and air in order to produce heat. 
Heat exchangers are included for transferring the heat from such 
combustion to an air flow system that is circulated through the heated 
space and then returned to the heat exchanger. Such conventional furnace 
systems have been found, however, to be wasteful in terms of their use of 
the thermal energy available from the combustion process, largely because 
exhaust gases are discharged into the atmosphere at considerably high 
temperatures, frequently in excess of 300 F. (149 C.), which is well in 
excess of the desired room temperature in the space to be heated. 
Even the best of the above-described conventional furnace systems are 
estimated to waste at least fifteen percent to twenty percent of the gross 
heating value of the fuel consumed when operating at steady state 
conditions. Such waste of thermal energy is further compounded by the fact 
that when the furnace and the circulating fan of such a conventional 
heating systems are shut off in response to a signal from a thermostat in 
the heated space, the typical draft-type chimney continues to draw warm 
air from the furnace and from inside the building and then discharges such 
warm air to the atmosphere. Then when the thermostat again calls for heat, 
the system must restart and warm up before being capable of supplying 
heated air. In the northern states of the United States, this on/off 
cycling operation is estimated to occur over twenty thousand times per 
year in a typical forced-air heating system, thus resulting in an overall 
loss or waste of thermal energy estimated to be approximately forty 
percent of the available heating value of the fuel consumed. 
In addition to the above disadvantages, such conventional heating systems 
have become economically unfeasible in large residential or commercial 
structures requiring very high draft-type chimneys. Because of the low 
cost effectiveness of the construction and maintenance of such large 
chimneys, such heating systems have frequently been constructed and 
installed on the roof of such buildings, therefore complicating their 
installation and increasing their cost. Alternately, especially in 
multi-tenant or multi-dwelling residential or commercial buildings, 
electric heating systems have been installed in order to reduce the 
initial construction cost, allow individual heating control for multiple 
units of the building, and eliminate the need for the building management 
to account for, and separately re-bill, the cost of each unit's share of 
the overall cost of operating a centralized heating system. Such alternate 
electric heating systems have included electric resistance-type heating 
units or heat pumps, for example, but suffer the disadvantage of being 
relatively expensive to operate in comparison with heating systems fueled 
by gaseous fuels, such as natural gas. 
Because of the above-discussed disadvantages and shortcomings of 
conventional forced-air heating system and of typical electric heating 
systems, one of the primary objects of the present invention is to provide 
a forced air heating system, preferably fueled by a gaseous fuel, that 
effectively uses a much higher percentage of the available heating value 
of the fuel being consumed and that more effectively recovers a high 
percentage of the thermal energy present in the exhaust gases discharged 
to the atmosphere. 
Another object of the present invention is to provide such a heating system 
that does not require a conventional chimney or other draft-type exhaust 
gas discharge conduit. 
Another object of the present invention is to provide a heating system that 
maximizes the control over the function of the heating system and operates 
at a lower thermal energy input, but that operates for longer periods of 
time, thereby minimizing the number of on/off cycles required to maintain 
a desired temperature in the heated space, thereby maximizing the 
efficiency of the heating system. 
Still another object of the present invention is to provide a heating 
system that employs a separate system for air circulating at a relatively 
low velocity to and from the heated space and separate high-velocity air 
system for transferring the heat of combustion to the air supplied to the 
heated space, as well as providing separate pressurized combustion air and 
fuel supply systems that forcibly convey combustion exhaust gases out of 
the heating system. 
In accordance with one aspect of the present invention, a heating system 
for heating a space generally includes an air heating sub-system with a 
relatively compact combustion chamber adapted for burning a mixture of 
combustion air and fuel in order to produce heat, a separate cold air 
supply sub-system for conveying cold air from the heated space to the air 
heating sub-system, a combustion chamber heat exchanger in fluid 
communication with the cold air supply sub-system for transferring heat 
from the combustion chamber to the cold air withdrawn from the heated 
space by the cold air supply sub-system, and a separate air circulating 
sub-system for withdrawing cold circulating air from the heated space. The 
heating system also preferably includes an air mixing chamber in fluid 
communication with both the combustion chamber heat exchanger and the air 
circulating sub-system for mixing heated air with cold circulating air in 
order to provide heated circulating air to the heated space. 
In accordance with another aspect of the present invention, the heating 
system includes a combustion air supply sub-system having a combustion air 
compressor for supplying the combustion air to the combustion chamber at 
an elevated pressure, a gaseous fuel supply sub-system having a gaseous 
fuel compressor for conveying gaseous fuel from a gaseous fuel source to 
the combustion chamber at an elevated pressure substantially equal to the 
elevated pressure of the combustion air, with the pressure of the 
combustion air and the gaseous fuel being sufficient to forcibly convey 
the mixture of combustion air and gaseous fuel into the combustion chamber 
and to forcibly convey the products of combustion through a relatively 
small exhaust discharge conduit without the need for a draft-type chimney 
or conduit. 
In accordance with still another aspect of the present invention, the 
combustion air supply sub-system for a heating system includes a separator 
device, such as a vortex-type separator, that separates combustion air 
above a predetermined temperature from combustion air that is below such 
predetermined temperature. Such higher temperature combustion air is 
conveyed to the combustion chamber of the heating system, and the 
relatively lower temperature combustion air is conveyed to an exhaust gas 
heat exchanger for transferring heat from the exhaust gas to such 
relatively lower temperature combustion air. The combustion air that has 
been heated in the exhaust gas heat exchanger is then conveyed back to the 
heated space in order to effectively recover thermal energy that would 
otherwise have been wasted as the exhaust gas from the combustion chamber 
is discharged to the atmosphere. 
A further aspect of the present invention is the provision of combustion 
air and gaseous fuel bypass systems, including automatic bypass valves, 
for bypassing quantities of combustion air and gaseous fuel from the 
discharges to the intakes of the respective combustion air and gaseous 
fuel compressors. The bypass systems allow for selective control of the 
quantities of fuel and air being supplied to the combustion chamber in 
order to control the heat being supplied to the heated space without the 
need for the wasteful frequent on/off cycling operation mentioned above in 
connection with conventional heating systems. In addition, the heating 
system of the present invention preferably includes a mircoprocessor 
control system that operates and controls the above bypass systems and 
other components of the heating system in response to temperature input 
signals from both the heated space and the exterior surroundings. 
Additional objects, advantages and features of the present invention will 
become apparent from the following description and appended claims, taken 
in conjunction with the accompanying drawings.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
FIGS. 1 and 2 depict in diagrammatic form one preferred exemplary heating 
system for heating an enclosed space according to the present invention. 
As will become apparent from the following discussion, however, the 
principles of the present invention are not limited to the particular 
space heating application depicted diagrammatically in the drawings, and 
that the principles of the present invention are equally applicable to 
heating system arrangements other than that shown in the drawings. 
Referring primarily to FIG. 1, an examplary heating system 10 according to 
the present invention generally includes an air heating sub-system 12, a 
cold air supply sub-system 14, an air circulating sub-system 16, a 
combustion air supply sub-system 18, a gaseous fuel supply sub-system 20, 
and a control sub-system 22. 
The air heating sub-system 12 includes a combustion chamber 30 adapted for 
combustion of a mixture of combustion air and a gaseous fuel respectively 
supplied to the combustion chamber 30 from the combustion air supply 
sub-system 18 and the gaseous fuel supply sub-system 20 described below. 
The combustion air and the gaseous fuel are preferably mixed in adjustable 
and preselected proportions in an adjustable venturi device 32, which is 
in fluid communication with the combustion chamber 30 by way of an intake 
conduit 42. The mixture of gaseous fuel and combustion air is preferably 
ignited by an electronic ignition device 40, or other known ignition 
devices, disposed for fluid communication in the intake conduit 42, and 
injected into the combustion chamber 30. The combustion chamber 30 is 
preferably relatively small, preferably very close to the size of the 
flame of the burning fuel and air mixture itself, in order to minimize 
wasted energy in unnecessarily heating an empty space around the flame. 
The adjustable venturi device 32 preferably includes a generally annular 
gas chamber 34 with a pair of externally-threaded inspirator tubes 36 
threadably and adjustably engaged with peripheral portions of the gas 
chamber 34. The inspirator tubes are spaced apart within the gas chamber 
34 to form an opening 38, the size of which is preselectively adjustable 
by threadably moving the inspirator tubes 36 toward or away from one 
another. Thus, for a particular application, the proportions of gaseous 
fuel and combustion air mixed together in the ajustable venturi device 32 
can be preselectively adjusted in order to provide a range of fuel-to-air 
ratios that are consistent with the desired operating conditions in the 
particular application. 
The air heating sub-system 12 also includes a small exhaust conduit 44 in 
fluid communication with the interior of the combustion chamber 30 for 
conveying the products of combustion from the combustion chamber 30 to the 
exterior or ambient surroundings 46 of the heated space 48. A combustion 
chamber heat exchanger 50 is also associated with the combustion chamber 
30 and is adapted to transfer heat produced in the combustion chamber 30 
to cold air supplied from the cold air supply sub-system 14 (described 
below) in order to produce heated air that is in turn conveyed through a 
heated air discharge conduit 52 to an air mixing chamber 54, which is part 
of the air circulating sub-system 16 described below. 
The air circulating sub-system 16 generally includes a cold air return 
conduit 56 and a return air fan 58 for withdrawing cold air from the 
heated space 48 and conveying such cold air to the air mixing chamber 54 
by way of a cold air conduit 59. The cold air from the air circulating 
sub-system 16 is mixed in the air mixing chamber 54 with heated air from 
the combustion chamber heat exchanger 50 and from an exhaust gas heat 
exchanger 94 (described below). Such mixing in the air mixing chamber 54 
produces a heated air mixture that is conveyed, under the force of the 
return air fan 58, outwardly from the air mixing chamber 54 to the heated 
space 48 by way of one or more heated air supply conduits 60. 
Cold air is supplied to the combustion air heat exchanger 30 from the 
heated space 48 by the cold air supply sub-system 14. Such cold air is 
withdrawn from the heated space by a cold air supply fan 74 and conveyed 
to the combustion chamber heat exchanger 30 by way of a cold air conduit 
76. 
In order to effectively transfer a very high percentage of the thermal 
energy produced in the combustion chamber 30 to the air that is introduced 
into the air mixing chamber 54, the combustion chamber heat exchanger 50 
is preferably of a configuration that substantially fully envelopes the 
combustion chamber 30. The combustion chamber 30 is enclosed by a 
combustion chamber enclosure wall 64 composed of a heat-transmissive 
material having a high thermal conductivity. The enclosure wall 64 is 
generally surrounded or enveloped by an inner cold air chamber 66, which 
is in turn surrounded or enveloped by an outer cold air chamber 68, with 
one or more intermediate cold air chambers 70 disposed therebetween. The 
inner cold air chamber 66, the outer cold air chamber 68, and the 
intermediate cold air chambers 70 are separated by het transmissive 
chamber walls 72 having high thermal conductivity. 
The cold air chambers 66, 68, and 70 of the combustion chamber heat 
exchanger 50 are serially disposed outwardly with respect to one another, 
with each of the chambers being in fluid communication with its inwardly 
adjacent chamber such tht cold air from the cold air supply sub-system 14 
(described above) flows serially therethrough from the outer cold air 
chamber 68, through the intermediate cold air chambers 70, and into the 
inner cold air chamber 66. The heat produced by the combustion process in 
the combustion chamber 30 is thus transferred through the heat 
transmissive combustion chamber enclosure wall 64 and serially through the 
inner cold air chamber 66, through the intermediate cold air chambers 70, 
and to the outer cold air chamber 68, thus serially heating the air as it 
serially flows through the combustion chamber heat exchanger 50. The 
number of cold air chambers surrounding or enveloping the combustion 
chamber 30 is readily determined by one skilled in the art from the 
desired cold air inlet and heated air outlet temperatures for a given air 
flow in a particular application. Optionally, the outer cold air chamber 
68 can be covered or surrounded by any of a number of well-known suitable 
heat insulating materials in order to further minimize thermal energy 
loss. 
The combustion air supply sub-system 18 shown in FIG. 1 preferably includes 
a combustion air cleaner or filter device 80, which can comprise any of a 
number of well-known suitable air cleaner or air filter intake devices 
known to those skilled in the art. Combustion air is withdrawn from the 
heated space 48 through the combustion air cleaner device 80, and conveyed 
through an air conduit 82 to the intake or suction side 83 of a combustion 
air compressor 84. The combustion air compressor 84 raises the pressure of 
the combustion air to a predetermined pressure level and discharges the 
compressed combustion air through its discharge side 85 to the air heating 
sub-system 12 by way of an air conduit 86. 
Prior to being introduced into the adjustable venturi device 32, the 
compressed combustion air preferably passes through a separator device 88. 
The separator device 88 is preferably a vortex-type separator device, such 
as those well-known to persons skilled in the art, preferably equipped 
with a noise-reducing muffler 89. The separator device 88 functions to 
separate combustion air that is above a predetermined temperature from 
combustion air that is below such predetermined temperature by separating 
the relatively heavy, cooler air molecules from the relatively light, 
higher temperature air molecules. The separated combustion air that is 
above such predetermined temperature is conveyed through a hot separated 
air conduit 90 to the adjustable venturi device 32, described above, to be 
intermixed with gaseous fuel from the gaseous fuel supply sub-system 20 
described below. 
The separated combustion air that is below the above-discussed 
predetermined temperature is separated in the separator device 88 and 
conveyed by way of a cold separated air conduit 92 to an exhaust gas heat 
exchanger 94 shown generally in FIG. 1, and diagrammatically depicted in 
more detail in FIG. 2. 
As shown in FIG. 2, the exhaust gas heat exchanger 94 preferably includes a 
plurality of exhaust gas baffles 95 disposed within an inner housing 93. 
The inner housing 93 is generally surrounded or enveloped by an outer 
housing 91, which is spaced outwardly apart from the inner housing 93 to 
allow air from the cold separated air conduit 92 to flow therebetween and 
to be discharged through an air conduit 96 to the air mixing chamber 54 
described above. Preferably, a number of air baffles 97 are disposed in 
the space between the inner and outer housings 93 and 91, respectively, in 
order to cause the air flowing therethrough to flow evenly over 
substantially all of the inner housing 93, thereby effectively 
transferring heat from the exhaust gas, which may be in the range of 
approximately 300 F. (149 C.) to approximately 360 F. (182 C.) in many 
operating conditions, to the air flowing through the exhaust gas heat 
exchanger 94. By such an arrangement, and by choosing an 
appropriately-sized exhaust gas heat exchanger 94, as is well within the 
capabilities of one skilled in the art, a substantial portion of the 
thermal energy contained in the exhaust gas can be recovered such that the 
exhaust gas discharged to the exterior ambient surroundings 46 is at a 
very low temperature, preferably below the temperature desired in the 
heated space 48, such as at or below 60 F. (16 C.), for example, in many 
applications. Furthermore, because of the relatively low temperature of 
the exhaust gas, the exhaust gas conduit 44 can advantageously be 
constructed of relatively common conduit materials, including common 
copper tubing, for example, in many applications. 
The gaseous fuel supply sub-system 20 as illustrated in FIG. 1, wherein a 
gaseous fuel is withdrawn from a gas source 102, which can consist of a 
conventional natural gas supply system or other gaseous fuel sources 
well-known in the art. The gaseous fuel is conveyed through a safety valve 
104, which is preferably adapted to be automatically closed or to 
automatically fail in a closed condition in the event of a malfunction in 
the heating system 10. The gaseous fuel is then conveyed through the gas 
conduit 103 into the intake or suction side 106 of a gaseous fuel 
compressor 108, which raises the pressure of the incoming gaseous fuel to 
a predetermined pressure level substantially equal to that of the 
compressed combustion air described above. The compressed gaseous fuel is 
then expelled through the discharge side 110 of the gaseous fuel 
compressor 108 and conveyed by way of a gas conduit 112 to the 
above-described adjustable venturi device 32, wherein it is intermixed at 
predetermined proportions with the compressed combustion air before being 
ignited by the ignition device 40 and injected into the combustion chamber 
30. 
Because of the elevated pressure of the combustion air and the gaseous 
fuel, the exhaust gases are also pressurized and thus forcibly conveyed 
through the exhaust gas conduit 44. Therefore, the exhaust gas conduit 44 
does not have to be connected to a draft-type chimney or other conduit and 
can be relatively small, perhaps as small as a 1/2 inch (1.3 cm.) or (0.95 
cm.) copper tubing, or even smaller, in certain applications. 
In order to control the flow rates of the combustion air and gaseous fuel 
being supplied to the air heating sub-system 12 by the combustion air 
supply sub-system 18 and the gaseous fuel supply sub-system 20, bypass 
systems are included in association with the combustion air compressor 84 
and the gaseous fuel air compressor 108, respectively. In the combustion 
air supply sub-system 18, a bypass conduit 116 is connected in fluid 
communication with the air conduits 86 and 82 in order to allow bypass air 
flow from the discharge side 85 to the suction or intake side 83 of the 
combustion air compressor 84. The flow rate of the combustion air flowing 
through the bypass conduit 116, and thus the discharge flow rate through 
the air conduit 86, are controlled by modulating an air control valve 118 
provided in the bypass conduit 116. Similarly, a bypass conduit 120 is 
provided in fluid communication with the gaseous conduits 112 and 103 in 
order to allow gaseous fuel bypass flow from the discharge side 110 to the 
intake or suction side 106 of the gaseous fuel compressor 108, with the 
gaseous fuel bypass flow rate being controlled by modulation of a gas 
control valve 122. Thus, the respective pressures and flow rates of both 
the combustion air flow and the gaseous fuel flow can be preselectively 
regulated by modulating the combustion air control valve 118 and the 
gaseous fuel control valve 122, respectively. Further regulation of these 
flow rates can optionally be accomplished by regulating the speeds of 
variable-speed gas and air compressors in addition to, or in lieu of, the 
bypass systems described above. Regulation of the combustion air supply 
and the gaseous fuel supply is accomplished by the control sub-system 22 
described below. 
The control sub-system 22 includes an air temperature sensor 126 located in 
the heated space 48 and can consist of a conventional thermostat device 
such as that well-known in the art. The air temperature sensor 126 is 
operatively connected by way of a suitable conductor 128 with a preferably 
programmable central microprocessor 130 and is adapted to transmit signals 
to the central microprocessor 130 in response to varying air temperatures 
in the heated space 48. The central microprocessor 130 is in turn 
operatively connected by way of suitable conductors 133 and 135 to the 
combustion air control valve 118 and the gaseous fuel control valve 122, 
respectively, in order to transmit appropriate signals for actuating, 
deactuating, or modulating the respective air and gas bypass systems. The 
central microprocessor 130 is also in turn operatively connected with the 
combustion air compressor 84 and the gaseous ful compressor 108 by 
suitable conductors 132 and 134, respectively, in order to transmit 
appropriate signals thereto for purposes of actuating, deactuating, or 
regulating the speed of, the combustion air compressor 84 and the gaseous 
fuel compressor 108. The central microprocessor 130 is also operatively 
connected with the electronic ignition device 40 by way of a suitable 
conductor 136 in order to transmit actuating or deactuating signals 
thereto for purposes of igniting the mixture of combustion air and gaseous 
fuel during start-up of the heating system 10, and with the safety valve 
104, by way of conductor 105 in order to shut down the system in the event 
of an emergency or a malfunction. 
The control sub-system 22 also includes suitable conductors 150 and 152 for 
electrically interconnecting the central microprocessor 130 with the cold 
air supply fan 74 of the cold air supply sub-system 14 and the return air 
fan 58 of the air circulating sub-system 16. The control sub-system 22 is 
thus adapted to transmit actuating and deactuating signals, or modulating 
signals, to both the cold air supply sub-system 14 and the air circulating 
sub-system 16. By way of this control arrangement, as well as the control 
arrangement discussed above in connection with the combustion air supply 
and the gaseous fuel supply, the central microprocessor 130 is adapted to 
control the heating system 10 in response to sensed air temperatures in 
the heated space 48 and thereby maintain the air temperature in the heated 
space 48 at any of a number of preselected temperatures. 
Because the ambient temperatures and conditions in the surroundings or 
exterior 46 of the heated space 48 can have a dramatic effect upon the air 
temperature in the heated space 48 by way of heat loss or heat gain, it is 
desirable to also control the operation of the heating system 10 in 
response to outside temperatures. Therefore, the control sub-system 22 
optionally, but preferably, includes an outside air temperature sensor 140 
operatively and electrically connected by way of a suitable conductor 142 
with the central microprocessor 130. In response to sensed outside 
temperatures, the outside air temperature sensor 140 can therefore 
transmit appropriate signals to the central microprocessor 130, which in 
turn can preferably be programmable to control the heating system 10 in 
response to signal inputs relating to both the internal air temperature of 
the heated space 48 and the outside temperature of the exterior 
surroundings 46. For example, the central microprocessor 130 can 
preferably be programmed to respond appropriately in a situation where the 
heated space air temperature sensor 126 calls for heated air but the 
outside temperature is concurrently increasing, thereby avoiding the 
duplicative effect of adding heat to the heated space 48 by the heating 
system 10 while the heated space 48 is also experiencing a heat gain as a 
result of increasing outside temperatures. Likewise, for example, the 
central microprocessor 130 can be programmed to respond to decreasing 
outside temperature in order to cause the heating system 10 to supply 
additional heated air to the heated space 48 somewhat before the internal 
air temperature sensor 126 actually calls for more heat. Furthermore, by 
maintaining close control of the operation of the heating system 10, by 
way of the above-described control sub-system 22, the heating system 10 
can be operated for longer periods of time, but at variable heat output 
levels, thereby decreasing the number of on/off operating cycles and thus 
decreasing the opportunity for wasteful heat loss as compared with 
conventional furnaces and other conventional heating systems. 
It should be noted that the central microprocessor 130 can consist of any 
of a number of conventional, and preferably programmable, microprocessor 
units well-known to those skilled in the art and adaptable for performing 
the functions described above. In this regard, it should also be noted 
that although the control sub-system 22 is schematically depicted in the 
drawings as an electric control system, one skilled in the art will 
readily recognize that pneumatic, hydraulic or other control systems for 
actuating and deactuating the various components described above can 
readily be substituted for the electric control sub-system 22 depicted for 
purposes of illustration in the drawings. 
The foregoing discussion discloses and describes exemplary embodiments of 
the present invention. One skilled in the art will readily recognize from 
such discussion that various changes, modifications and variations may be 
made therein without departing from the spirit and scope of the invention 
as defined in the following claims.