BRIEF DESCRIPTION OF THE DRAWINGS
The invention will be better understood with reference to the drawings, in which:
FIG. 1 is a cross-section of an embodiment of the electric air heating device of the invention;
FIG. 2 is a schematic circuit diagram of an embodiment of an electric circuit for the heating device of FIG. 1;
FIG. 3 is an exploded isometric view of the heating device of FIG. 1, drawn at a smaller scale, showing a grille removed from a housing body;
FIG. 4 is a rear view of the device of FIG. 1 with part of the housing body removed;
FIG. 5 is a top view of the device of FIG. 1 with a portion of the housing body removed;
FIG. 6 is a front view of an embodiment of a heat generator of the invention, drawn at a larger scale; and
FIG. 7 is a graph of airflow versus power based on data resulting from testing of an embodiment of the device of FIG. 1.
DETAILED DESCRIPTION
Reference is first made to FIGS. 1-5 to describe an embodiment of an electric heating device in accordance with the invention indicated generally by the numeral 20. Preferably, the device 20 includes a fan 22 for moving a volume of air (indicated generally by the numeral 24) at a rate substantially corresponding to a speed of rotation of the fan 22, and a fan motor 26 for rotating the fan 22 over a predetermined range of speeds. The device 20 preferably also includes a heat generator 28 and a control subassembly 30. In one embodiment, the heat generator 28 preferably includes one or more PTC elements 32 (FIG. 4) for generating heat, and for transferring the heat to the moving volume of air. Preferably, the heat generator 28 also includes one or more heat transfer elements 34 (FIG. 4) providing relative large exposed surface areas, for effective heat transfer from the PTC elements 32 to the air flowing through the heat generator. The control subassembly 30 (FIG. 2) is adapted for proportionate control of the fan motor 26 based on a variable required heat output so that the rate of movement of the moving volume of air (i.e., moving through the heat generator 28) varies in proportion to changes in the required heat output, as will be described.
In one embodiment, the fan motor 26 is adapted to rotate the fan 22 over a range of speeds in proportion to a range of voltages of electricity supplied to the fan motor 26. The control subassembly 30 preferably includes a triac for altering voltages of electricity supplied to the motor 26 in proportion to variations in measured differences between ambient temperature and a preselected set temperature. The measured differences are determined by any suitable temperature sensor.
The control subassembly 30 preferably is adapted for proportionate control of the fan motor 26 based on measured differences between ambient temperature and a preselected set temperature. Preferably, the proportionate control is effected via a closed loop control system, i.e., a control system in which feedback is provided to the system which determines whether the fan motor is activated. The feedback preferably is provided any suitable ambient temperature-sensing means. For example, a suitable thermostat (e.g., including a thermistor for sensing ambient temperature) could be used to provide feedback. Because such feedback-providing devices and closed loop control systems generally are well-known in the art, further description thereof is not needed.
As shown in FIG. 2, the heating device 20 preferably includes a circuit 35 to which the control subassembly 30 is operatively connected, for controlling the fan motor 26 based on settings input by a user via a control device 36, and also based on input from a thermistor 38. The control device 36 permits control of the set temperature, which is compared to information about ambient temperature provided by the thermistor 38. The control circuit 30 controls the speed of the motor 26 based on differences between the set temperature and ambient temperature. As noted above, the control circuit 30 preferably controls the speed of the motor 26 by causing the triac included therein to vary the voltage of the electricity supplied to the motor 26 based on differences between the set temperature and the ambient temperature.
As shown in FIGS. 3-5, the volume of moving air preferably is directed to the heat generator 28 by a channelling device 40. The channelling device 40 preferably is positioned in a housing body 42 in a housing subassembly 43. The housing subassembly 43 is made of any suitable material and preferably includes a grille 44 with an inlet portion 46 and an outlet portion 48. The channelling device 40 preferably includes two substantially parallel side portions 41 (FIG. 4) generally extending from the fan 22 to the heat generator 28, and a floor portion 47. Preferably, the moving volume of air is generally defined by the space enclosed by the channelling device 40 and a curved portion 45 of the housing body 42 (FIG. 1). The channelling device 40 preferably is made of any suitable material, e.g., light sheet metal.
Accordingly, the moving volume of air preferably is directed through the heat generator 28 by the channelling device 40. The air thus directed passes through apertures 29 in the heat generator 28. As noted above, the heat generator 28 preferably includes PTC elements 32 which generate heat when current is passed therethrough, and heat transfer elements 34 configured for transfer of heat from the PTC elements to the air moving through the apertures 29. In one embodiment, the heat transfer elements 34 are integrally formed parts of the PTC elements 32, shaped as appropriate for optimal heat transfer characteristics. However, the heat transfer elements 34 may alternatively be formed of a suitable heat-conducting material and suitably connected to the PTC elements 32, as will be described.
In use, the fan 22 is mounted in a bottom area 50 of the housing 42. The fan 22 is configured to draw air into the housing 42 through the inlet portion 46, as indicated in FIG. 1 by arrow “A”. Moving air is then directed by the fan 22 into the channelling device 40, as indicated by arrow “B”. The channelling device 40 directs the moving air over (or through) the heat generator 28 and subsequently through the outlet portion 48 of the grille 44, as indicated by arrow “C”. The positioning of the fan 22 below the heat generator 28, and also the positioning of the outlet portion 48 above the inlet portion 46, are important because they take advantage of the fact that a volume of warm air (i.e., relative to air thereby surrounding) rises.
The control subassembly 30 controls the fan motor 26 based on a required heat output. As noted above, the control subassembly 30 preferably includes a triac which is adapted to alter the voltage supplied to the fan motor in proportion to the measured differences between ambient temperature and the preselected set temperature. For instance, if the preselected set temperature is 20° C. and the ambient temperature is 18° C., the triac, which preferably is operatively connected to a thermistor, adjusts the voltage of the electricity supplied to the fan motor 26 accordingly. However, if the ambient temperature were, for example, 17° C., then proportionately more voltage would be applied to the fan motor 26. Increasing the voltage of the electricity supplied to the fan motor 26 results in a proportionate increase in the speed of rotation of the fan 22.
It will be understood that an increase in the speed of the fan 22, which results in a proportionate increase in the rate of movement of the moving air which moves over the heat generator, lowers the temperature of the PTC element. Lowering the temperature of the PTC element results in more current being allowed to pass through the PTC element (i.e., the heat generator).
As shown in FIG. 7, in one embodiment, the relationship between airflow and power is nearly linear, although it is not exactly linear. Instead, the curve on the graph of airflow versus power shows that although the power output is at approximately 800 watts with an airflow of approximately 1.7 m/sec., at approximately 1200 watts, the airflow is approximately 5.3 m/sec. The relatively flat profile of the curve shown in FIG. 7 indicates that the heater of the invention has a relatively high degree of operational stability, i.e., the relationship is almost linear.
Another embodiment of the invention is disclosed in FIG. 6, in which elements are numbered so as to correspond to like elements shown in FIGS. 1-5. In an embodiment 120 of the heating device, a heat generator 128 includes one or more PTC elements 132 for generating heat and one or more heat transfer elements 134 for transferring heat from the PTC elements 132 to the moving volume of air (FIG. 6).
Preferably, the heat transfer elements 134 are fins configured for optimal heat transfer characteristics (i.e., for transfer of heat from the elements 134 to the air moving past such elements), and suitably connected to the PTC elements (FIG. 6) for maximum heat transfer from the PTC elements 132 to the heat transfer elements 134. The heat transfer elements preferably are any suitable heat-conducting material, such as aluminium.
In one embodiment, the heat generator 128 is approximately 9.5 inches long, approximately 0.5 inch wide, and approximately 3.3 inches high. As can be seen in FIG. 6, the heat generator 128 preferably includes a plurality of apertures 129, to provide a relatively large surface area, for effective heat transfer. The solid volume is approximately 8.9 in.3, and the surface area therein is approximately 187 in.2.
Any element in a claim that does not explicitly state “means for” performing a specified function, or “step for” performing a specific function, is not to be interpreted as a “means” or “step” clause as specified in 35 U.S.C. §112, paragraph 6.
It will be appreciated by those skilled in the art that the invention can take many forms, and that such forms are within the scope of the invention as claimed. Therefore, the spirit and scope of the appended claims should not be limited to the descriptions of the preferred versions contained herein.
Patent Application
20070280650
