Patent Application
20140158115
This application is directed, in general, to heating, ventilation and air conditioning (HVAC) systems and, more specifically, to a high-efficiency furnace having a velocity zoning heat exchanger air baffle.
A conventional high-efficiency furnace typically employs several heat exchangers to warm an air stream passing through the furnace. A high-efficiency furnace is one where approximately 90% of the energy put into the furnace is converted into heat for the purposes of heating the targeted space. These high-efficiency furnaces include “clamshell” or individual panel halves formed by stamping mirror images of the combustion chambers into corresponding metal sheets and coupling them together. Often high-efficiency furnaces comprise a primary heating chamber that includes the clamshell heat exchangers or heating chambers and they often include a secondary heat exchanger/condenser. The air passes through the secondary heat exchanger/condenser from a blower or fan and then passes through the primary heat exchanger. High-efficiency furnaces are also characterized by high operating temperatures, which consistently exceed 1000 degrees. As a result, hot spots can occur at certain points in the passageway of the clam shell heat exchanger. The high operating temperatures that create these hot spots can create cracking problems in the clamshell heat exchanger panels. When such cracks appear, their occurrence is considered a failure of the system.
One aspect of this disclosure provides a zoning baffle for a high-efficiency gas furnace. This embodiment comprises a housing, a primary heating zone located in the housing and comprising one or more heating chambers. A blower having an exhaust opening is located adjacent the primary heating zone and is positioned to force air through the primary heating zone. A zoning baffle is located between the blower and the primary heating zone. The zoning baffle comprises spaced apart baffles oriented substantially parallel with the one or more heating chambers.
A method of fabricating a high-efficiency furnace is also provided. One method embodiment comprises providing a housing, placing one or more heating chambers in the housing to form a primary heating zone, placing a blower having an exhaust opening within the housing and adjacent the primary heating zone and positioned to force air through the primary heating zone, and placing a zoning baffle between the blower and the primary heating zone. The zoning baffle comprises spaced apart baffles oriented substantially parallel with one or more of the heating chambers.
Reference is now made to the following descriptions taken in conjunction with the accompanying drawings, in which:
Described herein are various embodiments of a zoning baffle that may be employed in a gas furnace. In one embodiment, the zoning baffle is designed to be placed within a primary heating zone of a furnace that comprises one or more heating chambers and between the primary heating zone and the blower, where it increases the air velocity and guides the air to one or more known hot spots located on one or more of the heating chambers. The purpose of the zoning baffle, as provided herein, is to reduce the temperature at the hot spots associated with each heating chamber without detrimentally increasing cubic feet per minute (CFM) airflow of the furnace, or without increasing the wattage requirements of the blower motor.
The heating chambers of current high-efficiency gas furnaces have higher surface temperatures at maximum leaving air conditions, which is typically more than 1000° F. At this temperature, a low strength steel (extra deep drawing steel known as EDDS), which is the material of choice for many manufactures, will not survive the required reliability tests. To circumvent these problems, some manufactures turn to more expensive materials or tolerate a shorter operational life of the furnace.
To use EDDS material in current high-efficiency furnace designs, it is necessary to reduce the surface temperatures of the heating chambers. Embodiments of the zoning baffle, as presented herein, have been found to lower the temperatures of the heating chambers to about 926° F., which is enough of a drop to significantly increase the life of the heating chambers, even when using EDDS materials. Certain embodiments of the zoning baffle also split or create various velocity zones and reduce the turbulence within the furnace and delivers more air to the hot spots.
Additionally, the zoning baffle can be positioned such that the higher velocity air can be directed through the maximum number of condensing coils or tubes and the lower velocity air can be directed through the minimum number of condensing coils or tubes. Within these zones, air can be redirected to known hot spots on the heating chambers without affecting airflow in the other zones. Thus, embodiments of the zoning baffles, as presented herein, increase heat transfer in the secondary or heat exchanger/condenser, which increases the annual fuel utilization efficiency (AFUE) rating of the unit. The embodiments of the zoning baffle, as presented herein, may increase AFUE up to 0.60 percent, which improves secondary tube reduction in the heat exchanger/condenser. Further, the zoning baffle sits substantially parallel to the flow velocity coming from the main blower, so it does not increase any blower watt consumption.
Additionally, it has been recognized that the gap between the fin stock of the secondary or heat exchanger/condenser and the zoning baffle improves the furnaces AFUE performance. For example, an improvement was shown for gaps ranging from about 0.125 to about 1.00 inches, with better results being obtained for a gap of about 0.50 inches. Further, the components of the zoning baffle can also be oriented in an angular position with respect to the heating chambers. Improvements were observed in angular positions that range from 0 degrees to about 25 degrees.
In general, the various embodiments of the zoning baffle provides airflow to one or more known hot spots by providing one or more high air velocity zones and a surface along which airflow travels, thereby effectively guiding the airflow to the desired area on the heating chamber and at higher velocities. Without being limited by any theory of operation, it is believed that the airflow guidance is based on the coanda effect, wherein the fluid airflow is attracted to the flat surfaces of the zoning baffle. The guidance of the airflow causes the air to be directed more toward hot spots of the heating chambers, thereby reducing the temperature of the heating chambers and keeping their operating temperature within design parameters, which prevents premature stress and cracking in the area of the hot spot, even with EDDS type materials are used. This advantage allows manufacturers to use the cheaper construction materials without sacrificing operation life, while at the same time reducing manufacturing costs.
Though the zoning baffle, as presented herein, could be used in any furnace chamber, it provides particular benefits when employed in high-efficiency furnaces where 90% of the total amount of fuel used is converted directly into heat. The benefits arise from the fact that these high-efficiency furnaces reach higher operational temperatures, which causes the heating chambers to prematurely stress and crack at the above-mentioned hot spots. As stated above, the zoning baffle guides more airflow at high air velocities to these hot spots, which reduces stress and premature cracking in the heating chambers.
A burner assembly 140 contains a thermostatically-controlled solenoid valve 142, a manifold 144 leading from the valve 142 and across the burner assembly 150, one or more gas orifices (not shown) coupled to the manifold 144 and one or more burners (not shown) corresponding to and located proximate the gas orifices. The illustrated embodiment of the burner assembly 140 has a row of six burners. Alternative embodiments of the burner assembly 140 have more or fewer burners arranged in one or more rows. A flue 146 allows undesired gases (e.g., unburned fuel) to be vented from the burner assembly 140. In an assembled configuration, the burner assembly 140 is located proximate the heat exchanger assembly 120 such that the burners thereof at least approximately align with the inlets 132.
A draft inducer assembly 150 contains a manifold 152, a draft inducing exhaust fan 154 having an inlet coupled to the manifold 152 and a flue 156 coupled to an outlet of the exhaust fan 154. In an assembled configuration, the draft inducer assembly 150 is located proximate the heat exchanger assembly 120, such that the manifold 152 thereof at least approximately aligns with the outlets 134 and the flue 156 at least approximately aligns with the flue 146 of the burner assembly 140.
A blower 160 is suspended from the shelf 110 such that an outlet 162 thereof approximately aligns with the opening 115. An electronic controller 170 is located proximate the blower 160 and, in the illustrated embodiment, controls the blower, the valve 142 and the exhaust fan 154 to cause the furnace to provide heat. A cover 180 may be placed over the front opening 105 of the housing 100.
In the illustrated embodiment, the controller 170 turns on the exhaust fan to initiate a draft in the heat exchangers (including the primary heating zone 130) and purge potentially harmful unburned gases or gaseous combustion products. Then the controller 170 opens the valve 142 to admit gas to the manifold 144 and the one or more gas orifices, whereupon the gas begins to mix with air to form primary combustion air. Then the controller 170 activates an igniter (not shown in
In one embodiment, the zoning baffle 400 is positioned between the blower 160 and the primary heating zone 130. (See
In another aspect, the zoning baffle 400 further includes a cross baffle 415 that extends between the baffles 405, 410. In one embodiment, the cross baffle 415 comprises an elongated plate that is bent to form opposing plates having an angle of separation between and extends perpendicularly between the baffles 405, 410. The cross baffle 415 may be rotated from a horizontal position by 0 degrees to about 45 degrees, with about degrees giving better results than other orientations. Additionally, as with the baffles 405, 410, the location of the cross baffle 415 within the primary heating zone 130 will depend on the location of the hot spots that are positioned more toward the back end 205 of the heating chambers 130a. In one embodiment, the cross baffle 415 creates a higher velocity zone than is created by the baffles 405, 410. The high velocity provides greater air flow through that portion of the primary heating zone 130, thereby reducing the occurrence of hot spots that cause premature cracking.
With reference to
In one embodiment, an angle of orientation of the baffles 405, 410 from the substantially parallel or vertical orientation with respect to the heating chambers 130a ranges from 0 degrees to about 25 degrees. In another embodiment, the step of placing a zoning baffle further comprises placing a cross baffle 415 between the baffles 405, 410 and that extends between the baffles 405, 410. In one aspect of this embodiment, the cross baffle 415 comprises an elongated plate that is bent to form opposing plates having an angle of separation between. In another aspect, zoning baffles 205, 210, 215 create a first air velocity zone and a second higher air velocity zone.
In another embodiment, the method further comprises placing a secondary heat exchanger/condenser zone 135 within the housing 102, located adjacent the primary heating zone 130, wherein the secondary heating zone is located between the zoning baffle 400 and the primary heating zone 130.
Those skilled in the art to which this application relates will appreciate that other and further additions, deletions, substitutions and modifications may be made to the described embodiments.
