Patent Application
20100024794
The invention relates to heaters typically used in temporary applications and more specifically to direct-fired ductable heaters.
Heaters are typically used in temporary applications, such as construction sites, as a temporary heat source before a primary and permanent heat source is functional and usable or for example for heating event tents. Traditionally, most heaters for this type of application comprise a burner inside a tubular housing, with a fan behind the burner blowing air around the burner and out of the end of the heater. This is known as a direct-fired heater in that the combustion gases flow directly into the heated space. There are also indirect-fired construction heaters that incorporate a heat exchanger to permit the venting of combustion gases out of the heated space. Indirect-fired heaters are inherently less efficient in that a portion of the heat is normally lost through the exhaust. Indirect-fired heaters are also inherently larger because they require a heat exchanger and therefore a larger cross-section to handle the airflow.
Most construction heaters that are used with ductwork are of the indirect-fired type. The main reason for this is that the variation in airflow when a heater is ducted can significantly impact the quality of combustion in a direct-fired heater, leading to increases in harmful emissions such as carbon monoxide. This is because of the increase in backpressure inherent with the attachment of ductwork to the heater. Heaters used in temporary applications must be able to function safely within the full range of installations in which they may be employed.
Due to the high operating temperatures inherent to heaters, the operational lifetime of various components, such as the burner, gas lines, the walls of the combustion chamber, etc., tend be short unless higher grade or heavier materials are used.
A need therefore exists to provide a direct-fired heater suitable for use with ductwork that overcomes one or more of the shortcomings outlined above or in the art.
A direct-fired heater suitable for use either with or without ductwork is provided. The heater uses one or more airflow zones surrounding a combustion chamber for guiding air between a fan blade and an outlet of the heater. Hot exhaust from the combustion chamber is mixed with the air exiting from the one or more airflow zones. The heater may contain a nose cone positioned to create a venturi effect with the heated air and the air passing through one or more of the airflow zones. Back pressure inherent from the attachment of ductwork to the heater has a minimal effect on airflow through the combustion chamber as a positive pressure zone is created between a burner plate of the combustion chamber and the fan blade by extending the wall of the combustion chamber, or a heat shield separating the combustion chamber and the outer shell of the heater, past the burner plate and toward the fan blade. As a result, the direct-fired heater may be used with ductwork without a significant drop in combustion quality.
In one embodiment, there is provided a direct-fired heater connectable to ductwork, the heater comprising:
In another embodiment there is provided a direct-fired heater connectable to ductwork, the heater comprising:
A fan motor 40 is used to drive a fan blade 50 and is powered by any conventional means.
A blower plate 60 is used to prevent or minimize recirculation of air past the fan blade 50. The clearance between the blower plate 60 and the fan blade 50 may be small enough to stop the recirculation, thereby increasing the efficiency of the heater 10.
A combustion chamber 55 of the heater 10 is defined by a combustion chamber wall 90, a burner plate 100 at one end and an exhaust plate 140 at an opposite end. Combustion takes place in what will be referred to for the purposes of this specification as a combustion zone C in the combustion chamber 55. The burner plate 100 has a series of openings 150 that allow for air to be pushed through the burner plate 100 by the fan blade 50. Although only two openings 150 are illustrated in
A nose cone 130, positioned exterior the exhaust plate 140, directs exhaust from the combustion chamber 55 and out of the outlet 120. An optional heat shield 80 is situated between the combustion chamber wall 90 and the outer shell 70. An air passage is defined by the gap between the heat shield 80 and the combustion chamber wall 90. For the purposes of this specification, this air gap will be referred to as zone B. An additional air passage is defined by the gap between the heat shield 80 and the outer shell 70. For the purposes of this specification, this air gap will be referred to as zone A. The heat shield 80 is shown as being connected to the combustion chamber wall 90 using a plurality of brackets 160. It should be understood that any suitable connection device may be used to secure the heat shield 80 in the heater 10. The heat shield 80 may additionally or alternatively be secured to the outer shell 70 using spacers or by any suitable connection device. As outlined above, any suitable device may be used to secure the heat shield 80 to the combustion chamber wall 90 and/or the outer shell 70, however, at least zone A or zone B must be maintained to allow for airflow between the outlet 120 and recirculation zone D. In one embodiment, no heat shield is used and a single airflow zone is defined by the space between the combustion chamber wall 90 and the outer shell 70.
As illustrated in
The heat shield 80, in addition to both shielding the outer shell 70 from heat and defining airflow zone B, also serves to cool the combustion chamber wall 90 by allowing for airflow propelled by the fan blade 50 to absorb heat as it passes through zone B. By cooling the combustion chamber wall 90, the operational lifetime of the combustion chamber wall 90 is increased as the higher temperature causes increased fatigue on the material.
Typical heaters used in the art tend to increase the distance between the burner plate 100 and the fan blade 50 in an attempt to minimize recirculation as objects placed in front and in proximity to the fan blade 50 deflect airflow back towards the fan, especially towards the center of the fan blade 50 where the pushing effect of the fan blade 50 is lower. As a side effect, this results in a physically larger heater and also in the burner plate 100, the injector 110, and the gas line feeding the injector 110 having a very high temperature during operation.
Heaters 10 of the present invention, however, have a layout with the burner plate 100 placed in close proximity to the fan blade 50, relative to conventional heaters. The burner plate 100 is placed at a distance from the fan blade 50 suitably close to cause sufficient recirculation of the air in zone D to cool the injector 110 during operation. This recirculation increases the operational lifetime of the injector 110, the burner plate 100, and the gas line feeding the injector.
As is understood in the art, an ideal air to gas mixture is desired to obtain an efficient combustion. Connection of ductwork to heaters, such as direct-fired heaters, causes a variation in airflow due to the inherent backpressure caused by the connection of the ductwork. Airflow zones A and B are provided to reduce fluctuations of airflow in the combustion chamber 55. As outlined above, a single airflow zone may be used if no heat shield is used.
Due to the shape of the fan blade 50 and its proximity to the outer shell 70 and the burner plate 100, an inherent negative pressure field is generated generally in front of a center region of the fan blade 50 and a positive pressure field is generated generally in an outer region of the recirculation zone D. By extending the combustion chamber wall 90 and the heat shield 80 past the burner plate 100 and into the recirculation zone D, the pressure field increases and stabilizes particularly near the outer edges of the burner plate 100. It should be understood that although
Although the injector 110 is shown having six gas streams 210, it should be understood that the injector may emit any number of gas streams 210, with a minimum of two gas streams required for a balanced flame.
A plurality of brackets 160 are shown connecting the heat shield 80 to the combustion chamber wall 90, the heat shield 80 and the combustion chamber wall 90 defining airflow zone B as outlined above. The brackets 160 are shown in an angled orientation thereby guiding the airflow from the fan blade 50 in a spinning path. Alternatively, the brackets 160 may be oriented to straighten out airflow in zone B as desired.
Airflow zone A is shown defined by the heat shield 90 and the outer shell 70 as outlined above. A spacer (not shown) may be used to connect the heat shield 80 and the outer shell 70.
As can be seen in
The burner plate 100 with microburners 200, such as those described above, forces the flame away from the injector 110 keeping the injector 110 at a lower temperature from the start. The microburners 200 may be oriented in such a way as to form a circle of multiple burners. The openings 150 of the microburners 200 may be oriented for example for balancing combustion air rotation with each opening's dimension and position creating a staged combustion which can result in low CO production and can further result in a primary recirculation for low CO and NOx generation.
The openings 150 may be extruded in the burner plate 100 in such a way that the perimeter of the opening 150 penetrates into the combustion chamber 55. This results in an enlarged recirculation zone at the base of the flame between openings 150, thereby reducing CO and NOx generation.
In one example, the increase in efficiency of the heater allowed for a ¾ horsepower (hp) motor to be used in place of a 1 hp motor and a larger diameter fan blade 50 was used in place of a smaller diameter fan blade. This requires less energy to drive the motor while maintaining heated air out of the outlet 120 and through any ductwork if attached. An increase in airflow through connected ductwork has been observed. For example, a heater such as that described in
It will be appreciated that heaters as described herein may operate with or without ductwork connected to the outlet of the heater. Furthermore, it will be appreciated that heaters of the present invention may comprise inlet gas piping and valving as desired or required for feeding gas to the injector from a gas source.
The present invention has been described with regard to a plurality of illustrative embodiments. However, it will be apparent to persons skilled in the art that a number of variations and modifications can be made without departing from the scope of the invention as defined in the claims.
