This invention is related to electric heating devices.
Various types of electric air heating devices using PTC (“positive temperature coefficient”) elements are known. A PTC element has a given resistivity at any given temperature, and the resistivity of the PTC element rises or falls with its temperature. In particular, the PTC element's resistivity rises exponentially once its temperature is increased over a certain temperature. Accordingly, once the PTC element's temperature is high enough, the resistivity of the PTC element becomes sufficiently high that the flow of current therethrough is nearly stopped. Because of this property, PTC elements have the beneficial characteristic of being self-limiting, thereby reducing the risk that an electric heater which includes a PTC element may cause a fire. However, in the prior art, PTC elements have been used primarily as sensors, to severely limit current when necessary for safety.
In addition, a heater with a heating element including one or more PTC elements which produces a specified output for a specified airflow is known. However, this prior art device does not provide for proportionate (i.e., variable) control of the heating element. Instead, this device produces a preselected power output for a preselected airflow when activated, i.e., the control is fixed because the heater can only be activated or de-activated, and if activated, only a certain output is provided thereby. Repeatedly turning this prior art heater on and off in response to signals from a thermostat tends to create significant changes in the ambient temperature, i.e., the typical thermostat does not signal for more heat until room temperature is relatively far below the setpoint temperature. Also, the typical thermostat does not stop a heater from operating until the setpoint temperature is exceeded, generally to an extent which is noticeable by those in the room.
There is therefore a need for an electric heating device which overcomes or mitigates one or more of the defects of the prior art.
In its broad aspect, the invention provides an electric heating device including a fan for moving a volume of air at a rate substantially corresponding to a speed of rotation of the fan and a fan motor for rotating the fan over a range of speeds. The device also includes a heat generator with one or more PTC elements for generating heat, and for transferring the heat to the moving volume of air. Also, the device has a control subassembly adapted for proportionate control of the fan motor based on a variable required heat output so that the rate of movement of the moving volume of air varies in proportion to changes in the required heat output.
In another of its aspects, the invention provides a method of heating air having an ambient temperature. The method includes, first, providing a fan for moving a volume of air at a rate substantially corresponding to a speed of rotation of the fan, and subsequently, providing an electric fan motor for rotating the fan over a range of speeds. Next, a heat generator is provided which includes one or more PTC elements for generating heat, and for transferring the heat to the moving volume of air. Finally, a control subassembly is provided which is adapted for proportionate control of the motor based on a variable required heat output so that the rate of movement of the volume of air varies in proportion to changes in the required heat output.
In yet another aspect, the invention provides an electric heating device including a fan for moving a volume of air at a rate substantially corresponding to a speed of rotation of the fan, and an electric fan motor for rotating the fan over a range of speeds. The device also includes a heat generator having one or more PTC elements for generating heat and one or more heat transfer elements for transferring the heat from the PTC element to the moving volume of air. Also, the device includes a control subassembly adapted for proportionate control of the fan motor based on a variable required heat output so that the rate of movement of the moving volume of air varies in proportion to changes in the required heat output.
In yet another of its aspects, the invention provides an electric heating device including a fan for moving a volume of air at a rate substantially corresponding to a speed of rotation of the fan, and a fan motor for rotating the fan over a range of speeds. The device also includes a circuit having one or more heating resistors for generating heat and one or more PTC elements electrically connected in series with the heating resistor for generating heat and for controlling current flowing through the circuit. Also, the device includes one or more heat transfer elements for transferring the heat from the heating resistor and the PTC element to the moving volume of air. In addition, the device has a control subassembly adapted for proportionate control of the fan motor based on a variable required heat output so that the rate of movement of the moving volume of air varies in proportion to changes in the required heat output.
The invention will be better understood with reference to the drawings, in which:
Reference is first made to
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
As shown in
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
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
Another embodiment of the invention is disclosed in
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 (
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
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.
This application claims the benefit of U.S. Provisional Application No. 60/801,044, filed May 18, 2006.
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Number | Date | Country | |
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20070280650 A1 | Dec 2007 | US |
Number | Date | Country | |
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60801044 | May 2006 | US |