Patent Application
20070101984
The present invention pertains generally to HVAC systems and more particularly to furnaces such as forced-air furnaces relying upon a pneumatic signal to control a gas valve.
Many homes rely upon forced-air furnaces to provide heat during cool and/or cold weather. Typically, a forced-air furnace employs a burner that burns a fuel such as natural gas, propane or the like, and provides heated combustion gases to the interior of a heat exchanger. A circulating blower forces return air from the house over or through the heat exchanger, thereby heating the air. The combustion gases proceed through the heat exchanger to a collector box, and are then exhausted. In some cases, a combustion gas blower pulls the combustion gases through the heat exchanger and the collector box. The heated air is subsequently routed throughout the house via a duct system. A return duct system returns air to the furnace to be re-heated.
A gas valve controls how much fuel is provided to the burner. In some instances, a pressure drop across the heat exchanger, i.e., between the burner and the collector box, may be used as a signal to the gas valve to regulate gas flow to the burner, as this pressure drop is known to be at least roughly proportional to the combustion gas flow through the heat exchanger. However, this pressure signal is subject to transient spikes resulting from the combustion gas blower cycling on and off, system harmonics, and the like. Thus, a need remains for improved devices and methods of controlling furnaces such as forced-air furnaces.
The present invention pertains to improved devices and method of controlling furnaces such as forced-air furnaces. In some instances, a conditioned pneumatic signal may be used as an input signal to a gas valve in aiding operation of the furnace.
Accordingly, an example embodiment of the present invention may be found in a pneumatic signal conditioning device that has a first fluid path and a second fluid path. The first fluid path includes a first inlet and a first outlet, and is configured such that the first outlet provides a first conditioned signal representing a pressure at the first inlet. Similarly, the second fluid path is configured such that the second outlet provides a second conditioned signal representing a pressure at the second inlet.
In some instances, the first fluid path may include an internal flow restriction. At least one of the first inlet and the first outlet may include a conditioning orifice. In some cases, the first inlet may include a first inlet conditioning orifice and the first outlet may include a first outlet conditioning orifice. In some cases, the second fluid path may include an internal flow restriction. At least one of the second inlet and the second outlet may include a conditioning orifice. In some cases, the second inlet may include a second inlet conditioning orifice and the second outlet may include a second outlet conditioning orifice.
The pneumatic signal conditioning device may also include a third fluid path that is disposed between the first fluid path and the second fluid path, thereby providing fluid communication between the first fluid path and the second fluid path. A bleed orifice may be disposed within the third fluid path.
In some instances, a fourth fluid path may be disposed between the first fluid path and the second fluid path, thereby providing fluid communication between the first fluid path and the second fluid path. A fixed bleed orifice disposed may be disposed within the third fluid path and an adjustable bleed orifice may be disposed within the fourth fluid path.
In some instances, the pneumatic signal conditioning device may include a reference vent that is in fluid communication with at least one of the first fluid path and the second fluid path. The reference vent may, in some circumstances, also be in fluid communication with the atmosphere exterior to the pneumatic signal conditioning device.
Another example embodiment of the present invention may be found in a forced-air furnace that includes a heat exchanger having an upstream port and a downstream port, a burner that is configured to provide combustion products to the heat exchanger, and a gas valve that is configured to provide fuel to the burner. The gas valve may include a first pressure port and a second pressure port.
The forced-air furnace also includes the pneumatic signal conditioning device described above. The first inlet of the pneumatic signal conditioning device may be in fluid communication with the upstream port of the heat exchanger, the second inlet of the pneumatic signal conditioning device may be in fluid communication with the downstream port of the heat exchanger, the first outlet of the pneumatic signal conditioning device may be in fluid communication with the first pressure port of the gas valve and the second outlet of the pneumatic signal conditioning device may be in fluid communication with the second pressure port of the gas valve. In some instances, the upstream port may be located proximate the burner. The furnace may also include a collector box that is positioned proximate the downstream port of the heat exchanger.
Another example embodiment of the present invention may be found in a furnace that includes a burner manifold, a collector box and a heat exchanger. The heat exchanger may include an inlet that is in fluid communication with the burner manifold and an outlet that may be in fluid communication with the collector box. The furnace also includes a gas valve that is configured to provide fuel to the burner manifold in response to a signal that represents a pressure drop between the burner and the collector box.
The furnace may include structure or apparatus that is configured to condition the signal. For example, the structure or apparatus that is configured to condition the signal may be adapted to dampen transient pressure spikes. In some instances, the furnace further includes a blower that is adapted to blow air across the exterior of the heat exchanger.
Another example embodiment of the present invention may be found in a negative pressure conditioning device that is designed for use with a forced air furnace that includes a gas valve, a burner manifold and a collector box. The negative pressure conditioning device may include a first gas valve port and a second gas valve port that are adapted to be in fluid communication with the gas valve. A first conditioning orifice is disposed within the first gas valve port. A second conditioning orifice is disposed within the second gas valve port.
The negative conditioning device may include a burner manifold port that is adapted to be in fluid communication with the burner manifold as well as a collector box port that is adapted to be in fluid communication with the collector box. A burner manifold conditioning orifice may be disposed within the burner manifold port. A collector box conditioning orifice may be disposed within the collector box port.
Another example embodiment of the present invention may be found in a method of controlling a forced-air furnace that includes a burner, a collector box and a gas valve that controls gas flow to the burner. A first pressure at the burner may be monitored. A second pressure at the collector box may be monitored. A conditioned signal may be provided that represents a difference between the first pressure and the second pressure. The operation of the gas valve may be affected by the conditioned signal. In some instances, the conditioned signal may be a pneumatic signal in which transient spikes are damped.
The above summary of the present invention is not intended to describe each disclosed embodiment or every implementation of the present invention. The Figures, Detailed Description and Examples which follow more particularly exemplify these embodiments.
The invention may be more completely understood in consideration of the following detailed description of various embodiments of the invention in connection with the accompanying drawings, in which:
While the invention is amenable to various modifications and alternative forms, specifics thereof have been shown by way of example in the drawings and will be described in detail. It should be understood, however, that the intention is not to limit the invention to the particular embodiments described. On the contrary, the intention is to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the invention.
The following description should be read with reference to the drawings, in which like elements in different drawings are numbered in like fashion. The drawings, which are not necessarily to scale, depict selected embodiments and are not intended to limit the scope of the invention. Although examples of construction, dimensions, and materials are illustrated for the various elements, those skilled in the art will recognize that many of the examples provided have suitable alternatives that may be utilized.
A circulating blower 22 accepts return air from the building or home's return ductwork 24 and blows the return air through heat exchanger 14, thereby heating the air. The heated air then exits heat exchanger 14 and enters the building or home's conditioned air ductwork 26. For enhanced thermal transfer and efficiency, the heated combustion products may pass through heat exchanger 14 in a first direction while circulating blower 22 forces air through heat exchanger 14 in a second, opposite direction. In some cases, as illustrated, a combustion gas blower 23 may be positioned downstream of collector box 16 and may pull combustion gases through heat exchanger 14 and collector box 16.
In some instances, for example, the heated combustion products may pass downwardly through heat exchanger 14 while the air blown through by circulating blower 22 may pass upwardly through heat exchanger 14, but this is not required.
As noted, gas valve 18 provides fuel, via fuel line 20, to burner compartment 12. Gas valve 18 may, in some instances, rely at least partially on a measurement of the pressure drop through heat exchanger 14 in order to regulate gas flow to burner compartment 12. In order to provide an improved, conditioned, signal to gas valve 18, furnace 10 may include a signal conditioning device 28. The internal structure of an illustrative signal conditioning device 28 is more fully described in subsequent Figures.
The illustrative signal conditioning device 28 includes a first inlet 30 and a first outlet 32, and a second inlet 34 and a second outlet 36. First inlet 30 is in fluid communication with a burner compartment pressure port 38 while second inlet 34 is in fluid communication with a collector box pressure port 40. First outlet 32 is in fluid communication with a first pressure port 42 present on gas valve 18 while second outlet 36 is in fluid communication with a second pressure port 44 present on gas valve 18.
It can be seen that a pneumatic signal at first inlet 30 represents a pressure at burner compartment 12, i.e,. at the top or inlet of heat exchanger 14 while a pneumatic signal at second inlet 34 represents a pressure at collector box 16, i.e, at the bottom or outlet of heat exchanger 14. Thus, the difference therebetween provides an indication of the pressure drop across heat exchanger 14.
However, as noted previously, this pressure signal may be subject to various transient interruptions. Consequently, signal conditioning device 28 is configured to provide a conditioned (e.g. damped) pneumatic signal from first outlet 32 and/or second outlet 36. As a result, gas valve 18 may be provided with a stable pneumatic signal across first pressure port 42 and second pressure port 44. Signal conditioning device 28 may take several different forms, as outlined in subsequent Figures. Signal conditioning device 28 may be formed of any suitable polymeric, metallic or other material, as desired. In some instances, signal conditioning device 28 may be molded as an integral unit. In other cases, signal conditioning device 28 may be formed by joining tubular sections together using any suitable technique such as adhesives, thermal welding, sonic welding and the like.
In the illustrative embodiment, first fluid path 52, second fluid path 58 and third fluid path 60 of signal conditioning device 46 are diagrammatically shown as being approximately the same size. It should be recognized that while each of first fluid path 52, second fluid path 58 and third fluid path 60 may have similar or even identical dimensions, this is not required.
In a particular embodiment, for example, signal conditioning device 46 may have an overall length of about 1.375 inches, an overall width of about 1.63 inches and an overall thickness of about 0.46 inches. First inlet 48 and second inlet 54 may each have an internal diameter of about 0.26 inches. First outlet 50 and second outlet 56 may each have an internal diameter of about 0.325 inches. These inlet and outlet dimensions may be altered by inclusion of appropriately sized conditioning orifices, as will be more fully discussed with respect to subsequent Figures. It will be recognized that these dimensions may also be varied to accommodate various combinations of particular gas valves and particular furnaces.
It can be seen that first inlet 48 includes a first inlet conditioning orifice 80 while first outlet 50 includes a first outlet conditioning orifice 82. Similarly, second inlet 54 includes a second inlet conditioning orifice 84 and second outlet 56 includes a second outlet conditioning orifice 86. Third fluid path 60 includes a bleed orifice 88. In some instances, first inlet conditioning orifice 80 and second inlet conditioning orifice 84 may be referred to, respectively, as a burner manifold conditioning orifice and as a collector box conditioning orifice.
In some instances, pneumatic signal conditioning device 46 may be constructed in a way to facilitate placement of bleed orifice 88 within third fluid path 60. In some cases, the tubing or other structure forming first fluid path 52 may, for example, include a removable plug or other structure that provides access to third fluid path 60 yet can be inserted to retain the fluid properties of first fluid path 52.
In some cases, pneumatic signal conditioning device 46 may be constructed by combining a first tee, a second tee and a short length of tubing. For example, a first tee may form first fluid path 52 while a second tee may form second fluid path 58. Third fluid path 60 may be formed by extending a short length of tubing between the first and second tees. It will be recognized that such a structure would provide ready access to an interior of third fluid path 60 for placing and/or replacing bleed orifice 88.
It can be seen that first inlet 48 includes a first inlet conditioning orifice 80 while first outlet 50 includes a first outlet conditioning orifice 82. Similarly, second inlet 54 includes a second inlet conditioning orifice 84 and second outlet 56 includes a second outlet conditioning orifice 86. Unlike
Third fluid path 92 may include a fixed bleed orifice 96 and fourth fluid path 94 may include an adjustable orifice 98. Adjustable orifice 98 may be any structure that provides an opportunity for adjusting airflow permitted through adjustable orifice 98. In some cases, for example, adjustable orifice 98 may be adjustable via a set screw or other similar structure. In some cases, fixed bleed orifice 96 may provide a fixed minimum bleed while adjustable orifice 98 may be adjusted in order to modify or fine tune the relative amount of bleeding that occurs through pneumatic signal conditioning device 90.
In some instances, first inlet conditioning orifice 80 and second inlet conditioning orifice 84 may be referred to, respectively, as a burner manifold conditioning orifice and as a collector box conditioning orifice. As discussed with respect to
Cylindrical conditioning orifice 100 may be secured within the appropriate inlet or outlet using any suitable technique, such as a compression fit, adhesives, solder, or the like. Alternatively, cylindrical conditioning orifice 100 may be integrally molded within the appropriate inlet or outlet.
Tapered conditioning orifice 104 may be secured within the appropriate inlet or outlet using any suitable technique, such as a compression fit, adhesives, solder, or the like. Alternatively, tapered conditioning orifice 104 may be integrally molded within the appropriate inlet or outlet.
Cylindrical conditioning orifice 112 includes threads 116 on an exterior surface thereof, and thus may be screwed into the appropriate inlet or outlet, if desired.
In the embodiments discussed above, it has been considered that the apertures extending the length of the conditioning orifices have constant or perhaps tapering diameters. It is contemplated, however, that these apertures may well have a more complicated geometry. For example, an aperture through a conditioning orifice may have a diameter that changes one or more times, in a step-wise manner.
Control passes to block 122, wherein a conditioned signal is provided that represents a difference between the first and second pressures. The conditioned signal may, for example, be a pneumatic signal that is provided as a pressure difference between first outlet 32 and second outlet 36 of signal conditioner 28 (
The invention should not be considered limited to the particular examples described above, but rather should be understood to cover all aspects of the invention as set out in the attached claims. Various modifications, equivalent processes, as well as numerous structures to which the invention can be applicable will be readily apparent to those of skill in the art upon review of the instant specification.
