Patent Application
20190063742
The present disclosure is directed to heating, ventilation and air conditioning systems (HVAC), and more particularly to premixes for furnaces.
A low NOx premix combustion system typically requires the gas-air linkage to maintain a consistent gas-air ratio at different firing rates (2-stage or modulating). Traditionally, a negative regulator type gas valve is applied to provide this control linkage. Such a regulator will be pneumatically coupled to both the air supply and the fuel supply. The mixing chamber will receive the air supply downstream of the regulator coupling and direct the air through flow restrictors (or another component) that lowers the pressure in that portion of the mixing chamber. The fuel supply will enter through an inlet in the portion of the mixing chamber with a lowered pressure. Because the air supply and fuel supply were at equal pressures prior to the flow restrictors, the lowered pressure created by the flow restrictors helps to draw the fuel supply into the mixing chamber. Typically, high negative pressures provide better overall performance, but at a penalty of increased pressure drop.
One embodiment under the present disclosure comprises a premix combustion system for a furnace in an HVAC system, comprising: a chamber operable to receive gas and air and deliver a gas-air mix to a combustion chamber, the chamber comprising an air inlet operable to receive an air supply; a gas valve, the gas valve comprising a gas line extending from the gas valve to the chamber at a location downstream from the air inlet, the gas valve further comprising a gas supply inlet operable to receive gas from a gas source; a regulator comprising; an air interface pneumatically coupled to the air supply; a secondary interface proximate the air interface and pneumatically coupled to a secondary location in the HVAC system; and a regulator linkage coupled to the gas valve, the regulator linkage configured to detect a pressure differential between the air supply and the secondary location, and to cause the gas valve to apply an amplified pressure to gas in the gas line.
Another possible embodiment under the present disclosure comprises a furnace for use in an HVAC system, comprising: a premix combustion system, comprising; a chamber operable to receive gas and air and deliver a gas-air mix to a combustion chamber, the chamber comprising an air inlet operable to receive an air supply; a gas valve, the gas valve comprising a gas line extending from the gas valve to the chamber at a location downstream from the air inlet, the gas valve further comprising a gas supply inlet operable to receive gas from a gas source; a regulator comprising; an air interface pneumatically coupled to the air supply; a secondary interface proximate the air interface and pneumatically coupled to a secondary location in the HVAC system; and a regulator linkage coupled to the gas valve, the regulator linkage configured to detect a pressure differential between the air supply and the secondary location, and to cause the gas valve to apply an amplified pressure to gas in the gas line; one or more heat exchangers operable to receive combusted gas-air mix from the combustion chamber; one or more inducers operable to induce the flow of combusted gas-air mix through the one or more heat exchangers; one or more blowers operable to direct air flow across the one or more heat exchangers; and an exhaust operable to direct combusted gas-air mix from the one or more heat exchangers to an exhaust vent.
Another possible embodiment under the present disclosure comprises a method of operating a furnace in an HVAC system, comprising: providing a premix chamber configured to receive an air supply and a gas supply and to supply a gas-air mix to a combustion chamber; providing a gas valve comprising a gas supply inlet configured to receive the gas supply from a gas source and a gas line configured to deliver the gas supply to the premix chamber; receiving the air supply in the premix chamber at an air inlet; receiving the gas supply in the premix chamber from the gas line connected to the premix chamber downstream of the air inlet; providing a regulator operable to detect a pressure differential between a first interface and a second interface, and further operable to apply an amplification of the pressure differential to the gas supply in the gas line; coupling the first interface pneumatically to the air supply; coupling the second interface pneumatically to a secondary location in the HVAC system; receiving the gas-air mix in the combustion chamber; igniting the gas-air mix in the combustion chamber; and providing the ignited gas-air mix to another component of the furnace.
The foregoing has outlined rather broadly the features and technical advantages of the present invention in order that the detailed description of the invention that follows may be better understood. Additional features and advantages of the invention will be described hereinafter which form the subject of the claims of the invention. It should be appreciated by those skilled in the art that the conception and specific embodiment disclosed may be readily utilized as a basis for modifying or designing other structures for carrying out the same purposes of the present invention. It should also be realized by those skilled in the art that such equivalent constructions do not depart from the spirit and scope of the invention as set forth in the appended claims. The novel features which are believed to be characteristic of the invention, both as to its organization and method of operation, together with further objects and advantages will be better understood from the following description when considered in connection with the accompanying figures. It is to be expressly understood, however, that each of the figures is provided for the purpose of illustration and description only and is not intended as a definition of the limits of the present invention.
For a more complete understanding of the present invention, reference is now made to the following descriptions taken in conjunction with the accompanying drawings, in which:
As stated, a negative regulator is typically used in a low NOx premix combustion system, as this is necessary to induce gas flow through the metering orifice. Embodiments under the present disclosure can improve upon the prior art by using a positive pressure amplified gas-air valve. This gas valve provides a positive gas manifold pressure through the gas metering orifice and as a result a negative pressure in the chamber to induce gas flow is optional and not required. Positive pressures in the mixing chamber can also be used because the pressure applied to the gas supply will be stepped up or amplified by a regulator to increase the gas pressure as compared to the air supply pressure or mixing chamber pressure. In embodiments under the present disclosure, the effective pressure across the gas metering orifice can be higher (preferably 4 times higher), which provides improvements in firing rate control, gas-air mixing, and ignition. Embodiments can also have the safety benefit of limiting maximum gas manifold pressure to prevent over-firing through the use of a conventional positive pressure type regulator. In contrast, a conventional negative-regulator system has no such limit on firing rate, and can drastically over-fire if negative pressures become excessive. In addition, since a negative pressure in the mixing chamber is not required, the improved system offers the ability to reduce system pressure drop by utilizing pressure sources upstream or downstream of the mixing chamber that may already be present in the system (such as inducer, hot box, cold end header box, venturi tube or flow meter) to control firing rate rather than an inlet orifice or other flow restriction which is required for the negative regulator system. Another unique feature of this system is the ability to use a positive signal pressure to the gas valve rather than the traditional negative to drive regulation providing and additional degree of system design freedom.
Referring now to
A furnace with a premix system is shown in
An embodiment of a prior-art premix combustion system 300 is shown in
Other embodiments under the present disclosure could move the gas inlet 450 upstream of the air inlet 410. This can provide an additional advantage by providing users with more design flexibility.
One benefit of embodiments under the present disclosure is that, depending on the location 438 providing pressure to secondary face 436, the system may automatically shut down during dangerous operations or situations. For example, location 438 could be placed on an outlet or exhaust with 1 inch of pressure. If somehow the outlet or exhaust were unintentionally and otherwise unknowingly disconnected, then the location 438 would be exposed to atmospheric pressure (0 inch pressure). In such a situation gas valve 420 would be shut off by the regulator 439, thereby shutting down the system. Another benefit of the embodiments is the capability of applying an optional outlet pressure regulator to limit the maximum outlet pressure possible in the event of excessive amplifier pressure which would typically result in an unsafe over-firing condition.
Although the present invention and its advantages have been described in detail, it should be understood that various changes, substitutions and alterations can be made herein without departing from the spirit and scope of the invention as defined by the appended claims. Moreover, the scope of the present application is not intended to be limited to the particular embodiments of the process, machine, manufacture, composition of matter, means, methods and steps described in the specification. As one of ordinary skill in the art will readily appreciate from the disclosure of the present invention, processes, machines, manufacture, compositions of matter, means, methods, or steps, presently existing or later to be developed that perform substantially the same function or achieve substantially the same result as the corresponding embodiments described herein may be utilized according to the present invention. Accordingly, the appended claims are intended to include within their scope such processes, machines, manufacture, compositions of matter, means, methods, or steps.
