Patent Publication Number: US-2021172651-A1

Title: Electric space heater

Description:
TECHNICAL FIELD 
     The present invention relates to electric appliances for space heating, particularly forced circulation air heaters. 
     BACKGROUND OF THE INVENTION 
     Heat storage devices may be used in electric space heaters in order to cover a heat demand with stored heat, for instance, to avoid using electricity when its price is higher. A high thermal storage capacity is needed if heat must be delivered for many hours after the storage has been charged with heat, however more modest amounts of thermal storage may still allow a useful extension of heating operation without consuming electricity, or else may provide advantageous thermal buffering on starting of the heater in colder conditions. 
     A number of competing requirements influence the design of electric appliances for space heating. Particularly in the case of freestanding, portable heaters and also, but to a lesser extent, those intended for permanent installation, there is a need for a heat storage device which has a low mass, requires little space and yet offers a high storage capacity. Manufacturers have heretofore been unable to meet this need with an optimal solution at a price point that is commercially attractive. It is an object of the present invention to address this need or, more generally, to provide an improved electric space heater. 
     SUMMARY OF THE INVENTION 
     According to one aspect of the present invention there is provided an electric space heater comprising: 
     a housing; 
     a fan arranged for drawing ambient air into the housing and ejecting an air stream from an air outlet port in the housing; 
     at least one electrical heating element in the housing for heating the air stream, and 
     a solid thermal storage element disposed in or adjacent the air outlet port. 
     By virtue of the solid thermal storage element in or adjacent the air outlet, this solid thermal storage element can be heated by means of the same electrical heating element used for ordinary output, heat can be stored efficiently and provided later using electric energy, particularly in a relatively low mass portable, freestanding forced circulation air heater. 
     Preferably a duct is disposed in the housing for bounding the air stream. 
     Preferably the at least one electrical heating element is disposed in the duct between the fan and the air outlet. 
     Preferably the at least one electrical heating element is a resistance heating element. 
     Optionally the solid thermal storage element itself may form the at least one resistance heating element. For instance, electrodes may be arranged at opposite ends of the solid thermal storage element to allow an electric current through the solid thermal storage element. 
     Preferably solid thermal storage element comprises at least one opening therethrough for the passage of air. 
     Preferably the solid thermal storage element is substantially coextensive with a cross-sectional area of the air outlet. 
     Preferably the solid thermal storage element is foraminous. 
     The solid thermal storage element may be of any suitable solid material, particularly of a material selected from a metal, mineral or ceramic, that is suitable for storing heat at a temperature level of at least about 200° C., and especially about 400° C. In particular, mineral material may comprise cement, magnesium oxide, or a natural stone, such as granite or marble. 
     Preferably the solid thermal storage element is formed of a ceramic material. When the solid thermal storage element itself forms the resistance heating element the material may be at least partially electrically conductive. 
     The ceramic may be formed of silicon carbide or aluminium nitride, for thermal conductivity in excess of that of carbon steel. 
     Preferably both the at least one heating element and the solid thermal storage element extend transversely to the air stream. 
     The solid thermal storage element may be formed in one piece. The solid thermal storage element may be of, for example, cuboid or prismatic, in particular rectangular prismatic, form. The solid thermal storage element may be formed by extrusion, casting or printing. 
     Optionally, the solid thermal storage element may be recessed inside the housing and spaced apart from the air outlet. A grill may also extend over the air outlet. 
     Optionally, the solid thermal storage element may be thermally separated from surfaces exposed on the exterior of the heater by means of at least one insulating layer surrounding the solid thermal storage element. The insulating layer may comprise a ceramic material of low thermal conductivity, or a vacuum insulation layer, for example. 
     Preferably the electric space heater further comprises a temperature sensor for sensing the temperature of the solid thermal storage element and generating a temperature signal, an illuminated display provided externally on the heater, and a control circuit including a controller that receives the temperature signal and controls operation of the illuminated display to provide a visual indication of the temperature. 
     Preferably the control circuit is provided with power independently of a circuit providing power to the at least one electrical heating element, so that the visual display may be activated when the heating element is off. 
     The illuminated display may be disposed at a border of the solid thermal storage element or adjacent the perimeter of the grill. 
     The illuminated display may flash at a rate proportional to the sensed temperature. 
     Optionally, the illuminated display comprises a plurality of light emitters. The light emitters may be configured to provide two or more distinct colour outputs. The light emitters means may be activated and deactivated sequentially in response to the temperature signal indicating an increase or decrease in temperature. 
     Optionally, the control circuit may further comprise an ambient temperature sensor, and the illuminated display indicates a temperature that is a function of both ambient temperature and the temperature of the solid thermal storage element. 
     The control circuit may further comprise an input device, whereby the visual display is actuated after receiving a user input from the input device. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Preferred forms of the present invention will now be described by way of example with reference to the accompanying drawings, wherein: 
         FIG. 1  is a schematic sectional view through a first embodiment of a heater according to the invention; 
         FIG. 2  is an enlarged view of the air outlet port of the heater of  FIG. 1 ; 
         FIG. 3  is an enlarged view of an air outlet port of a second embodiment of a heater according to the invention; 
         FIG. 4  is an exploded view showing the principal components of a third embodiment of a heater according to the invention, and 
         FIG. 5  is an exploded view of the fan/heater sub-assembly of  FIG. 4 . 
     
    
    
     DESCRIPTION OF THE EMBODIMENTS 
     With reference to  FIGS. 1 and 2  of the drawings, an electric fan heater  10  of the present invention may include a fan  11  to the rear of a housing  12 , and an outlet port  13  on a front of the housing  12 . 
     High-temperature radiant heating elements  14  may be disposed in an air duct  15  leading to the outlet  13  and connected to the outlet of the fan  11 . 
     An intake port  16  in the housing  12  is provided on the intake side of the fan  11 . 
     In a first mode of operation, the fan  11  draws in air through the intake port  16 , and at the same time as air begins to be blown into the air duct  15 , energization of the radiant heating elements  14  is started. 
     The radiant heating elements  11  may be of the quartz tube type that heated red hot, to about 700° C. or higher, and when subject to the air stream driven by the fan  11 , energy is released to heat the air forced toward the air outlet  13 . 
     A solid thermal storage element  17  may be disposed in the air outlet port  13  and have a foraminous form so as to be quickly charged with heat when the heating elements  11  and fan  11  are operating. The solid thermal storage element  17  provides a second mode in which regenerative heating is performed, allowing continued heat output from the heater after electrical current to the heating elements  11  has stopped. Moreover, the storage element  17  can provide thermal buffering on starting of the heater, while also modulating heat output when the heating elements  11  are cycled on and off. 
     The heater  10  is thus operated in one of two modes: a first mode in which the fan  11  and heating elements  11  are simultaneously operated while the solid thermal storage element  17  is charged with heat, or its temperature is maintained; and a second mode in which only the fan  11  is operated for heating in which heat is transferred to the air from the solid thermal storage element  17 . However, as in the case where the demand slightly exceeds what can be supplied from the solid thermal storage element  17  alone, in a third mode the heating elements  11  may be operated at a low temperature to supplement the heat from the storage element  17 . 
     In the first mode the heating elements  11  may be visible through the air outlet port  13  in the housing, providing an indication to users of the operation of the heater that is not available in the second and third modes. For providing a visual indication of the operation of the heater, particularly in the second and third modes, and preferably in all three modes, the heater may further comprise a temperature sensor  20 , such as an NTC thermistor, disposed on the solid thermal storage element  17  for sensing its temperature and generating a temperature signal, an illuminated display  21  provided externally on the heater, and a control circuit  22  including a controller that receives the temperature signal and controls operation of the illuminated display  21 . 
     The illuminated display  21  may comprise a linear array of light emitters, such as LEDs, disposed on or adjacent the outlet port  13   
     In use, a user may select the operating temperature of the heater  12  by actuating a user control. Initially, all the light emitters of the display are switched off. As the air temperature gradually increases the first light emitter at one end of the display is illuminated in response to the signal received from the sensor  20 . As the temperature of the air increases further, an adjacent light emitter is illuminated, so two light emitters are operating. This process continues, each light emitter extending the length of the illuminated array, as the air temperature increases, until all the light emitters are operating. Thus, the light emitters are sequentially activated in response to the temperature signal indicating an increase in temperature. Correspondingly, as the sensor  20  indicates a temperature decrease, illuminated light emitters from one end of the illuminated section of the display are deactivated. In this way, the number of illuminated light emitters is proportional to temperature and Illumination of all of the light emitters in the array indicates a maximum temperature of the solid thermal storage element  17 . In particularly preferred embodiments, where the outlet port  13  is generally rectangular, the illuminated display  21  extends adjacent a long edge of the outlet port  13 , so as to be readily visible to a user toward whom the air stream from the outlet port  13  is directed. 
     In addition, for safety, an insulating layer (not shown), as of flock material, may cover the (high temperature) surfaces of the solid thermal storage element  17  that may otherwise be touched by a user. 
     In a second embodiment of the heater  110  shown in  FIG. 3 , the solid thermal storage element  117  is disposed in the duct  15  adjacent the air outlet port  113 , and may be recessed behind a grill  25  that covers the air outlet port  113 . The solid thermal storage element  117  is thus inaccessible to users so, still without risking exposing users to a high surface temperature, a higher storage temperature may be maintained without the need for applying an external insulating layer, such as flock material.  FIG. 3  also shows an alternative configuration of the solid thermal storage element  117 , where the heating elements  14  are disposed in passages extending between opposing transverse sides of the solid thermal storage element  117 . 
     A third embodiment of the invention is shown in  FIGS. 4 and 5 , and essentially differs from the second embodiment of  FIG. 3  in that the solid thermal storage element  17  is downstream, with respect to the air stream induced by the fan  11 , from the heating elements  14 . The fan  11  may be a part of a subassembly  30  in which the duct  15  generally also provides a structural element by which the fan  11 , heating elements  14  and solid thermal storage element  17  are connected. 
     A front panel  31  may cooperate with an outlet assembly  37  to generally close a front opening in the housing  12 , whereas the intake port  16  may be formed in a rear panel  32  in which a power supply  33  is received. The fan  11  may be of the centrifugal type comprising elongate blades  35  disposed parallel to one another in a circular array. The duct  15  may be generally rectangular in cross-section with its long axis parallel to the axes of the blades  35  and inclined to rise toward the outlet assembly  37 . Corresponding to the duct  15 , the air outlet port  113  may be rectangular. In this embodiment, the air outlet port  113  is covered by the grill  25 , so that the solid thermal storage element  17  is recessed behind the grill  25 . The illuminated display  21  extends adjacent a long edge of the outlet port  113 . 
     Aspects of the present invention have been described by way of example only and it should be appreciated that modifications and additions may be made thereto without departing from the scope thereof.