Electric resistance heating devices – Heating devices – Convection space heater
Utility Patent
1999-07-29
2001-01-02
Walberg, Teresa (Department: 3742)
Electric resistance heating devices
Heating devices
Convection space heater
C392S355000, C392S373000, C392S375000
Utility Patent
active
06169851
ABSTRACT:
BACKGROUND TO THE INVENTION
Space heaters generally divide into two types. The first type is the so-called “radiator”, which usually consist of a fluid-filled body having a large surface area and which dissipates appreciable amounts of heat by radiation. The second type is the so-called “convector heater”. Convector heaters consist of a housing, a heat source within the housing and a plurality of openings which allow air to convect through the housing and over the heat source. In an electrical convector heater, for example, the heat source is a resistive heating element; in a storage heater, the primary heat source may again be a resistive heating element, but the primary source acts to heat a secondary heat source, usually in the form of a stack of bricks, in a charging mode. The secondary heat source releases heat to the convecting air when the heater is in a space heating mode. Convector heaters dissipate only very small quantities of heat by radiation.
Convector heaters are regarded as generally unsatisfactory as room heaters for a number of reasons. Firstly, because most of the heat is dissipated by convection, the tendency is for hot air from the heater to rise to and collect in the ceiling. As time goes on, more and more hot air collects in the ceiling and progressively lower regions of the room heat up. However, since the heat transfer from the heater to the room is effected by heating the air as it passes over the heat source in the heater, this has the effect of gasifying any water vapour in the air, which then condenses on cool surfaces in the room. Consequently, the air collecting in the ceiling is rather dry and unpleasant to breath. Hitherto, there has been no real alternative to conventional convector heaters, apart from fan heaters, which are both noisy and relatively inefficient.
Radiators, on the other hand, heat relatively little by convection and consequently do little to take the chill off the air. Rather, radiators tend to heat surfaces in the room which are faced by the radiating surface. For a person sitting next to a radiator, this can result in one of his sides being warm and the other cold. In addition, radiators are relatively large compared with convector heaters, since the temperature to which the radiating surface can be heated is limited by safety considerations. They do, however, preserve the pleasant humidity of the air.
SUMMARY OF THE INVENTION
The present invention involves a new kind of space heater from the convector heater mould, but which tends to preserve the humidity of the air. A space heater according to the invention comprises a housing, a heat source within the housing and a plurality of openings to allow the convection of air through the housing, in which the heat source comprises a pair of panels defining between them a closed compartment, a liquid within the compartment and an electrical heating element within the compartment and in thermal contact with the liquid and in which the openings in the housing allow radiant heat from the heat source to escape from the housing.
As will be readily understood, this space heater heats both by convection through the housing and by radiation from the panels of the heat source. Adjustment of the physical parameters of the heater allows a better balance between the convective and radiative mechanisms to provide a more pleasant heat. In addition, the panels of the heat source can be painted black to promote radiation, since the heat source will in large measure be hidden by the housing. Indeed, painting the heat source black makes it even less visible.
The best way of ensuring that radiated heat can escape from the housing is to perforate one or both sides of the housing to form a grille. For convected heat, on the other hand, it is the top of the housing which should be perforated to form a grille. Clearly, the radiative processes are encouraged if at least one of the panels of the heat source faces outward through at least one of the grilles.
For convenience, the space heater may be portable; for example, the housing may be provided with wheels or castors.
Because the heat source is contained within the housing, and therefore kept away from prying fingers or accidental contact, the temperature of the heat source may rise well above the permissible safety limit for exposed heaters. As a result, the liquid within the heat source will expand to a greater extent. The danger is that the liquid within the compartment may expand to the extent that the increase in pressure in the heat source causes deformation, such as so-called “pillow” distortion, of the panels themselves. This will stress the peripheral seam between the panels of the heat source and any spot welds which may exist in the body of the heat source. Indeed, the pressure applied to the panels may be enough to cause one or more of the spot welds or, over time, the peripheral seam to burst apart, allowing hot liquid to escape under pressure.
This problem is addressed in a preferred embodiment of the invention, in which the liquid partially fills the compartment and the compartment is sub-divided into a lower liquid chamber, which at room temperature contains liquid, and an enlarged upper expansion chamber, which at room temperature contains no liquid. The advantages of this arrangement will be discussed below.
Although the problem which the preferred embodiment of the invention addresses has been described above in relation to a space heater having a housing and a heat source, the solution to that problem is applicable to a wider field.
It is applicable in particular to any situation where a heat source is not constrained in temperature by safety considerations or where there is a greater risk than usual of deformation of the panels of the heat source. Thus, this wider application of the present invention is embodied by a space heater in which the heat source comprises a pair of panels defining between them a closed compartment, a liquid partially filling the compartment and an electrical heating element within the compartment and in thermal contact with the liquid, in which the compartment is sub-divided into a lower liquid chamber, which at room temperature contains liquid, and an enlarged upper expansion chamber, which at room temperature contains no liquid.
An advantage of this arrangement is that when the liquid expands, air is compressed in the enlarged expansion chamber to relieve the pressure which would otherwise build up. The degree of alleviation of the pressure depends upon a number of factors including the ratio of the volume of the expansion chamber to that of the compartment as a whole. Strictly speaking, it is the fraction of the volume of the compartment which is not filled with liquid at room temperature which determines the pressure within the chamber at any particular temperature, but the ratio of the volume of the expansion chamber to that of the compartment as a whole gives an upper limit on pressure. The ratio chosen will depend upon a number of factors including the working temperature of the heat source, the coefficient of volumetric expansion of the liquid and the highest pressure which the heat source can safely withstand, but the range for a preferred embodiment of the present invention is between 40% and 60%.
In a preferred embodiment, the upper expansion chamber is enlarged to the extent that the horizontal cross-sectional area of the lower liquid chamber where it meets the expansion chamber is less than that of the expansion chamber.
In a further preferred embodiment there is provided, a space heater comprising a housing, a heat source within the housing and a plurality of openings to allow the convection of air through the housing, in which:
the heat source comprises a pair of panels defining between them a closed compartment, a liquid within and partially filling the compartment and an electrical heating element extending within the compartment, substantially parallel to the panels and in thermal contact with the liquid;
the compartment is sub-divided into a lower liquid chamber and an upper expansion ch
Naughton Martin Lawrence
Purton Arthur Joseph Patrick
Warren Ronald Michael
Basic Patents
Bromberg & Sunstein LLP
Dahbour Fadi H.
Walberg Teresa
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