US3538307A - Electric baseboard heater - Google Patents

Description

Nov. 3, 1970 N. BIRDWELL 3,533,307

' ELECTRIC BASEBOARD HEATER Filed Sept. 5, 1968 mvmon NELSON lRowELL BY mds ArroRNEYs United States Patent O U.S. Cl. 219-341 3 Claims ABSTRACT OF THE DISCLOSURE A residential heating system employing a series of baseboard radiator units connected end-to-end by pressfitted connectors in a series array about the walls of a room. All units but the unit at one end of the array comprise a standard commercial cast iron baseboard unit having an interior heat-transfer liquid circulation chamber. Each unit has `a smooth front and a finned back over which fins room air circulates by convection. The one end unit is modified to have an enlarged fluid receiving chamber in which is mounted an electric heating element and is provided with temperature and pressure control switches in circuit with the heating element to prevent build-up of excessive temperature and pressure in the system. The chambers are at least two-thirds but less than nine-tenths iilled with a heat-transfer liquid, such as diethylene glycol, and are connected by upper and lower fluid conduits for convective circulation of the heat transfer liquid therebetween.

It is known to heat rooms or buildings with a baseboard heater comprising upper and lower channels for transmission and return of a heated fluid at least one of these channels being integral with heating fins for conducting heat from the tube to surrounding air. It is also known to provide electric heaters for certain types of baseboard heating elements. However, prior arrangements do not provide the desired flexibility of installation by use of standard parts in conjunction with heater element parts manufactured for routine connection to a furnace, nor has it been known to provide a closed system consisting of conventional circulating elements without the employment of an expansion chamber, such units generally being subject to hammering, creaking or hangin-g during intermittent heating and cooling. A less expensive and more readily adapted system avoiding these objects is desired.

It is accordingly an object of this invention to provide a simplified electric baseboard heater by modification of a standard element.

It is a further object of the invention to provide a single baseboard heater unit having external connections compatible with standard units for ready connection with such standard units in a group of elements one of which is electrically heated.

It is a further object of the invention to provide a baseboard heater unit of closed system type with provision for circulation which avoids noisy operation accompanying intermittent heating under thermostatic control, while not requiring the addition of an expansion chamber.

These and other objects are accomplished by a minor modification of preexisting cast iron baseboard units designed for single or double pipe circulation of water heated from a central boiler, the pipe connections being removed. One unit in each string `has a temperature sensor and a resistive heater element projecting into and along the interior of the baseboard unit somewhat enlarged to receive the element. The invention further includes a pressure sensor to open a safety switch, a temperature switch in series therewith for opening and closing the electrical heating circuit in accordance with inside temperature, and a relatively large expansion chamber achieved by filling the baseboard internal chamber less than full to provide for a wide range of temperature change without excesslve pressure `build up. The operation will be better understood as:

FIG. 1 is a perspective view of a unitized electrical baseboard heater including several connected units;

FIG. 2 is a rear elevational view partly in section showmgd connecting means yand controls for a composite unit; an

FIG. 3 is a cross section taken along line 3 3 of FIG. 2.

Baseboard heaters are generally constructed with finned water tubes or with one finned heating tube and a return tube in the same unit connected by piping to upper and lower portions of a central water heater. Such units are normally completely filled with liquid and a separate expansion chamber is provided to accommodate the increasing volume of heating liquid as the furnace is operated in accordance with la demand signal at a thermostatic control device normally employed therewith. Considerable hammering and creaking is encountered. Also such systems are normally adapted for use with a central furnace, which is sometimes not desired. Small heating units of electrical types are usually not arranged as baseboard heaters, and it is desirable to employ elements I which are made in large quantity for reduction of manufacturing costs. This invention provides such a system by the modification of one such commercial unit within standard dimensions therefor and with connections for a group of such units providing an electric heater element in an enlarged portion of the heating tube while still providing a return path for conduction of circulated heating fluid in the connected upper and lower channels of a baseboard unit, or assembly of units.

Baseboard units have been manufactured for end-to-end assembly in a series array about the wallsof a room for piped connection to a hot water furnace. Such a unit is modified for individual room heating without a furnace, to provide a self-contained heating unit which is expandable as to radiating surface by the addition of unmodified units in series with a unit modified to receive the heating element and controls according to this invention. Generally, such baseboard units have a smooth front exterior and a finned back either made from tubing to which fins are attached or of cast iron for greater permanence. For the purpose of this invention a modification of a standard cast unit will be described to illustrate the principle and the improved controls. Thus a cast hollow body having a pair of holes at each end is illustrated, but it will be understood that upper and lower passages within the baseboard unit might comprise tubes interconnected vertically at the ends and centers of the units and in which the lower tube is sufficiently enlarged to receive a heating unit 33 in end portion 38, later to be described.

According to this invention a baseboard unit 40 is provided with an electrical heater element such as 33 comprising resistive conductors 31 and 32 formed as an immersion liquid heater which may be supported by inserting through end portion 38 of the unit and permanently connected by pipe threads as at 41. The heater element is mounted through a plug having external threads 26 and flange 27 for watertight connection to end portion 38. Unit 40 is filled with a liquid S0 to a level 60 approaching but not reaching the upper wall 36.

As shown in PIG. l a number of units 40, 46, etc. are connected together in series to provide a sufiicient length of radiating surface for the heat loss condition of that room. Standard connecting fitments used in furnaceheated assemblies are employed for extension along a single line or around a corner of the room. The present 3 invention relates to the modication of one of a group of said units to facilitate electrical heating controlled by temperature of the room and provides water temperature sensing and safety pressure switches for preventing accidental injury due to overheating or an'y other malfunction which would constitute a hazard.

Element 33 consists preferably of a loop of resistive heater element material encased in a vapor tight covering such as the commercially available Calrod or the like, suitable for immersing in a liquid, and may be mounted through a plug connection inserted in the lower tube supply hole of baseboard unit 40. A water temperature limit control o1' thermostat 16 attaches to the immersion heater element assembly and preferably has connected thereto a maximum pressure switch 19 mounted in a plug inserted in the upper hole of unit 40 to which the upper pipe of a circulating system would normally be connected. Thermostat 13 is of a conventional type generally mounted on the wall of a room. Thermostat 13 controls power to the heating element by a power switch which is preferably mounted in a box enclosing thermostat 16 and connected to the AC line by leads 11 and 12.

In FIG. 2 thermostat 13 is shown schematically as having contacts 14 and'15 in one of the leads to the power line while thermostat 16 includes normally closed contacts 17 and 18 also in series with one lead to the power line. Pressure switch 19 having normally closed contacts 21, 22 in serie-s with one lead to the power line, mounts within the upper portion of the base unit 40 and includes a pressure sensor 20, either diaphragm or bellows type, which operates to open contacts 21, 22 whenever the pressure exceeds a predetermined limit. Pressure switch 19 is preferably secured in the end wall 38 of unit 40 by a threaded portion 23 to which the bellows 24 is attached being suitable for inserting in internally threaded aperture 39 of the end wall 38 either by standard tapered piped threads or by use of a gasket between flange 25 and the end wall 38. Switch 19 may thus be removed for filling unit 40 and replaced as desired. Thermostat 16 is preferably attached to externally threaded plug member 26 through which tube 29 extends to temperature sensor 28.

Heating element 33 may consist merely of heater portions 31 and 32 extended throughout the major portion of the length of unit 40, in which the individual portions 31 and 32 are preferably insulated electrically so as to avoid the possibility of shorting to the enclosing walls of unit 40. Alternatively, unit 33 may be enclosed in a closed end vapor proof tube of diameter to pass through threads 41 to support and enclose the heating element with suitable internal electrical insulation from resistive elements 31, 32.

Overheating of the baseboard unit is controlled in part by temperature sensor 28, illustratively of the thermallyexpansive liquid-filled type connected by capillary tube 29 through plug 26 and liange 27 to pressure responsive bellows 30 which in turn connects by actuator 30 to close contacts 17, 18 whenever the temperature sensed at 28 is less than a predetermined maximum, and open contacts 17, 18 when the temperature exceeds that value. Instead of the illustrated temperature sensor other forms of temperature sensor may be employed for actuating 30 to open contacts 17, 18 at a predetermined maximum liquid temperature. Sensor 28 extend-s longitudinally beyond heater 33, or laterally therefrom, to avoid contact with the heater element so as to respond to average liquid temperature.

Base unit 40 shown in section in FIG. 3 illustrates a casting having upper wall 36, lower 4wall 37, end walls 38, and internally threaded apertures 39 and `41 at one end thereof. To improve heating by air convection the base unit has therethrough air ducts 42 and 43 cast in place by which air may be circulated past the rear surface and out through the front face of the unit below the upper surface line. A modified unit `40 is connected to an adjacent unit 46 preferably by tapered nipples 44 pressfitted in upper and lower apertures 45 at adjacent ends of units and 46 accommodated at enlarged portions of the casting. When units 40 and 46 have been forced together to make liquid-tight connections at 44 and 45 they are secured in place by bolt 59 through lugs 57, 58 at the respective ends of units 40, 46.

Unit 40 has front face 51 preferably including a rounded upper corner 52 and rear surface 53 extending rearwardly from conventionally formed rear wall 55, being joined by horizontal portion 54 to the upper portion of vertical wall 55 of an unmodified unit 46. Fins 47 extend along wall 55 and to lower wall 37 along wall 53 at 47'. Wall 37 is generally raised above the floor level by feet 56 to provide circulation of air along back wall 53, 54, 55. Threaded hole 39 corresponds in size to aperture 45 being threaded to receive plug threads 23 of switch 19 and serves also as a filling hole. Threaded aperture 41 is an enlarged aperture 45 to receive heater element 33 and temperature sensor 28 passing through threaded plug 26, 27.

When a single unit 40 is to be installed both upper and lower apertures 45 opposite holes 39 and 41 are closed, as by a press-fitted plug, or otherwise as may be desired. When a second or third unit as at 46 is attached by press-fitted nipples 44 or by elbow corner connections of conventional design termination plugs are used in apertures y45 of the end unit as described in connection with a single element 40.

`Closed liquid heating systems normally require an expansion chamber, which would be inconvenient and unsightly in a baseboard. According to this invention it is not necessary to provide an external expansion chamber since expansion is accommodated within the self-contained heating module. When heating element 33 has been inserted and a watertight joint made between plugs 26, 27 and aperture `41 pressure switch 19 may be removed and the unit lled with a suitable heat transfer liquid 50 to a level substantially below top wall 36. A liquid such as Zerex, a commercial diethylene glycol liquid used as an antifreeze, is preferable since it provides heating with very little accompanying noise in contrast to those filled with other anti-freeze liquids. A preferred liquid level as at 60 -below the level of aperture 23 has been found satisfactory for heat transfer and permits filling of the unit after it is put in place with as little as two-thirds of the volume of a unit filled. When circulation between units is required the level 60 is sufiiciently high to permit flow from one to the next unit as shown in FIG. 2, some 10% of the volume being air space for expansion without pressure buildups sufiicient to open switch 19 upon large excursions of temperature. Filling to this level is preferable when the heated unit 40 interconnected with one or more units y46 as required for the particular room. A heating module when heated by element 33 circulates the liquid upwardly to and around ports 42 and 43, and as heating continues, extends by convection progressively through connectors 44 along the full length of the series-joined units. As the liquid is heated expansion takes place so as to vary somewhat the level 60. However, the space above the liquid level 60v is air-filled and serves to receive the increase in volume of liquid 50 for normal changes of temperature necessary to provide the requisite degree of heat. Excessive changes of temperature and pressure due to malfunction in any respect are prevented both by thermostat 16 and pressure switch 19.

Thermostat 13 is schematically shown as a bimetal actuator for contacts between terminals 14 and 15 of a wall switch. While shown as in series with line 111 in FIG. 2 it is common practice to employ a relay for conducting the heavier currents of a heating circuit so that the conductors from thermostat 13 to the thermostat assembly at 16 may be of usual control wire dimensions and flexibility. This arrangement is shown schematically at FIG. l. Thermostat 16 includes normally closed contacts 17 and 18 which may conveniently receive the power leads 11', 12' since a pressure type thermostat as at 30 has adequate actuating force to control contacts 117 and 18. Similarly, pressure switch 19 may be directly in series with the power lead 12 or lead :11 since contacts 21 and 22 are opened in response to a considerable actuating force from bellows 24, or from a diaphragm operating to open contacts 21 and 22 whenever pressure in unit 40 exceeds a normal operating range in the vicinity of 20 to 30 p.s.i.

In operation a single baseboard heating unit 40' is connected to a power line by leads 11, 11', 12, 12 through normally open contacts 14, 115 closed by thermostat 13 and normally closed contacts 17, 18 of thermostat 30 actuated by temperature sensor 28 immersed in the liquid 50, and in series with a pressure limiting switch 119 having normally closed contacts 21, 22 actuatable to open at a rise in pressure above a desired limit such as 30 p.s.i. Thus two controls are effective to prevent runaway heating, one by control of the temperature of liquid 50 and the other by control of the pressure within the unit 40. In this way danger of overheating is avoided and de structive pressure rise is prevented.

It is to be understood that the above described heater is illustrative of a preferred embodiment and that numerous other and varied arrangements can readily be devised in accordance with the principles of the invention by those skilled in the art without departing from the spirit and scope of the invention expressed in the following claims.

What is claimed is:

1. A baseboard heating assembly comprising a plurality of cast iron baseboard units connected end-to-end and each having a chamber substantially filled with a heat transfer liquid, said chambers being interconnected by upper and lower fluid conduits for convection circulation of a heat transfer liquid therebetween and each unit being finned at one side thereof for increased heat exchange with the surrounding air, said assembly being closed at both ends to form a closed system,

nippled press-fitted connector means for tightly coupling said upper and lower conduits of adjacent unit of said plurality,

one said unit having an enlarged liquid-filled chamber portion throughout at least a portion of the length thereof for receiving therein an electrical heating element,

other said units being uniformly finned along a rear face where said one unit has said enlarged portion,

a heating element arranged along the length of said enlarged portion said element being electrically insulated and supported through said lower conduit at one end of the unit to form thereat a liquid seal,

said unit including a filling port and a pressure sensor means therein operative to open a normally closed first power switch at pressure within said unit above a preset value within a pressure range of 20 to 30 p.s.i. above atmospheric pressure,

said unit further including a temperature sensor means responsive to temperature therein and a second power switch in series circuit with said first switch being normally closed at room temperature and responsive to a rise in temperature above a set value in the range of to 200 F., to break the circuit, and

room thermostat means controlling electrical power to said element being in series with said first and second switches.

2. A baseboard heating assembly according to claim 1, said chambers being filled to substantially less than ninetenths of the volume therein and substantially more than two-thirds of the volume therein, thereby to provide an enclosed liquid volume beneath an airspace.

3. A baseboard heating assembly according to claim 1, said one unit being equipped with said heating element said temperature sensor and said pressure sensor means, other said units of said plurality not including a heating element and a sensor means, being heated by convection flow of liquid from said one unit through said other units.

References Cited UNITED STATES PATENTS 1,775,152 9/1930 Barker 237-17 1,778,464 10/1930 Ogilvie 219-341 2,051,485 8/1936 Katten 219-341 2,432,917 12/1947 Maurer 219-341 2,797,295 6/ 1957 Aitken-Smith et al. 219-341 2,894,108 7/1959 Brand et al. 219-365 X 3,166,666 1/1965 Williams 219-341 3,179,788 4/1965 Uhlig 219-341 FOREIGN PATENTS 230,458 4/ 1944 Switzerland.

ANTHONY BARTIS, Primary Examiner U.S. Cl. X.R.

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