Patent Application
20070175879
1. Field of the Invention
The present invention relates to a floor heating system, and, more particularly, to an electrical floor heating system.
2. Description of the Related Art
Under floor heating systems date back thousands of years including Roman and Korean heating system where stone slabs are installed on an upper part of flues in a hypocaust connected with a fuel feeding port and a chimney. A burning fuel, such as wood or coal is burnt thereby heating the floor from the underneath side. The problem with this system is that a lot of thermal energy is drawn off by way of the fuel feeding hole and the chimney when a fire is not kindled therein. Some modem floor heating systems include the circulation of a heated thermal medium fluid through long, thin seamless pipes disposed beneath a floor. A floor heating system that involves the circulation of a thermal medium fluid has a portion of a floor that is heated to a higher temperature than a portion of the floor associated with the end of the circulation path. For example, the temperature of the heated thermal medium as it circulates gradually decreases in temperature causing the portion that is first heated to be heated to a higher temperature than the area of the floor associated with the end of the circulation path.
The installation of electrical heating wires disposed in or beneath the floor have to be selected for their resistivity, which will result in a proper resistance load for the power system. In order to provide an adequate selection of resistivities a large stock of heating wires are required to provide an adequate power density and yet still meet the power constraints of the power source. A problem with this approach is that a significant number of resistive wires must be inventoried to meet a range of floor areas.
Typical systems for the heating of a floor using a single heating cable, which is a current practice requires fifteen different cables depending upon the square footage in a range of 15 to 180 square feet of floor area, when using 120 volt power to supply a heat flux of no more than 8 Watts per square foot. As shown in the following table:
Additionally if 240 volts is considered there is a requirement for seven additional resistance heating cables to cover the range from 30 to 168 square feet. The combination of which would require the manufacture to stock twenty-two different heater cable resistance values resulting in an uneconomic inventory and ordering situation. It is uneconomic to purchase or manufacture resistance wires in quantities of less than 50,0000 feet of each type. This would require stocking up to 1.1 million feet of cable to accommodate the voltage and floor area variations.
What is needed in the art is a method of providing an under floor heating wiring that will reduce the required inventory to not exceed the maximum power density for heating the floor.
The present invention provides a multi-segment heater for use in a floor heating system.
The invention comprises, in one form thereof, a floor heating system including a sub-floor, a plurality of fasteners, at least one resistive conductor and a capacitor. The at least one resistive conductor is fastened to the sub-floor by way of the plurality of fasteners. The capacitor is electrically in series with the at least one resistive conductor.
An advantage of the present invention is that the heating system reduces the number of different resistivity wires that must be stocked to meet the power density required for heating a range of floor areas.
Another advantage of the present invention is that the segments can be easily butt spliced together.
Yet another advantage of the present invention is that the selective inclusion of the capacitor allows for greater flexibility in the selection of resistive conductors.
The above-mentioned and other features and advantages of this invention, and the manner of attaining them, will become more apparent and the invention will be better understood by reference to the following description of an embodiment of the invention taken in conjunction with the accompanying drawings, wherein:
Corresponding reference characters indicate corresponding parts throughout the several views. The exemplification set out herein illustrates one preferred embodiment of the invention, in one form, and such exemplification is not to be construed as limiting the scope of the invention in any manner.
Referring now to the drawings, and more particularly to
Now, additionally referring to
In the current art many different resistances of heater wire have to be stocked, often over twenty, in order to have sufficient values of total resistance of a single wire to provide an adequate power density to the floor, while not being too low of a resistance for the length to avoid overdrawing the power source and tripping a circuit breaker. Wire manufacturers charge premium prices for wire purchased in lengths of less than 100,000 feet, so there is an advantage to purchasing fewer types of resistivity wire. The present invention teaches a method of spanning variable floor area of a factor of eight with only three wire resistances. This constitutes an area range of approximately 8:1 with only three required resistances.
The present invention involves a binary scheme. Each of the three wire resistivities span a 2:1 floor area range, based on a tolerance of power density that can be reasonably imparted to floor 12, by way of a controller. Next, within any area range, resistive conductor assemblies 20, 22, 24 and 26 can be selected for the individual lengths, thereby spanning potentially significant variations in area. For example, assuming that resistive conductor assembly 20 has a length of 200 feet; then resistive conductor assembly 22 has a length of 100 feet; resistive conductor assembly 24 has a length of 50 feet; and resistive conductor assembly 26 has a length of 25 feet. For a floor area 12 that requires two conductor assemblies, such as that illustrated in
To further illustrate the potential range of areas that can be heated at a substantially similar heat density, the following tables illustrate a range from 13 square feet to 100 square feet that is covered with three resistivities of wire. Each installation kit has a single resistivity of wire with four resistive conductor assemblies of lengths as described herein.
In the tables that follows:
L0 = Base heater wire length (feet)
L1 = First selectable heater wire length (feet)
L2 = Second selectable heater wire length (feet)
L3 = Third selectable heater wire length (feet)
TOT = Total heater wire length (feet)
OHMS = Resistance of total heater wire length (ohms)
WATTS = Total power dissipated by the heater wire (watts)
AMPS = Heater current (amps)
AREA = Heated floor area (feet2)
The foregoing tables illustrate the connection of certain combinations of lengths of resistive conductors, which are utilized based upon the square footage of the area to be heated. For example, if the area of floor to be heated is 75 square feet then the installation kit, which corresponds to Table 1 would be selected and then within the selected kit a 200 foot and a 100 foot resistive conductor assembly would be chosen and installed, which would provide a potential total of 1,067 watts, of heating capacity. In a like manner if the area to be heated is 23 square feet then a kit, which corresponds to Table 3 would be selected and all four wires would be serially connected by way of butt slices 40 to arrive at a total wire length of 94 feet.
The line current referred to in each table is an average current needed to provide the watts of heater power. The controller alters the duration and/or the amount of current being applied to the resistive conductors. The heater power referred to in each table is the desired heat, which in each table is met by each of the wiring combinations presented therein.
The present invention includes spanning nearly a ten fold difference in floor area with three resistances of wire, with each of the three kits having conductor assemblies 20-28 of four different, binarilly weighted lengths.
The advantages of the invention are economic by reducing the amount of wire necessary to be inventoried and provide kits, with a substantial range of heated floor capacity. Another advantage of the present invention is that in the event one segment of the heater cable is damaged during installation, the damaged piece can be removed making it unnecessary to replace the entire cable in the event of damage.
Now, additionally referring to
Referring first to power reduction circuit 42, illustrated in
Power limiting is desirable so that the resistive conductors are limited to operation of between two and four watts per linear foot. The calculations that follow show the desirability for power limiting along with the two suggested embodiments that accomplish the power limiting result. The power flux, defined as the heater rating in Watts per foot of length, must be limited to a maximum value that can be established during safety testing. For the following example the limit is assumed to be four watts per foot of resistive conductor. This is also expressed as the equation Flux Max=4 watts per foot of resistive conductor.
Based upon experience, the minimum flux should be not less than Flux Min=2 watts per foot of resistive conductor. For purposes of calculation it is assumed that a range of 30 to approximately 60 square feet of floor area will be heated. The maximum floor area is approximately twice the minimum value and use of a binary number relative to the lengths of cables in a installation kit cause the actual maximum area to be:
Max Area=30×(1+0.5+0.25+0.125)=56.25 square feet.
Assume that the heating system operates from 120 volts, which will be represented in the equations by the label Vline. Without power limiting, the maximum power flux occurs at the minimum area and that a minimum power flux occurs at the maximum area. Assume that the minimum flux is two watts per foot and the cable spacing is three inches. This yields a minimum power density of eight watts per square foot.
Calculation of the resistant gradient for the resistive conductors follows:
Minimum power=Max Area×Minimum density=56.25×8=450 watts.
Maximum resistance=Vline2/minimum power=1202/450=32 ohms.
Maximum length of resistive conductor=Minimum power/minimum flux =450 watts/2 watts per foot=225 feet.
The resistive value of the cable then is calculated in ohms per foot, which is:
=Maximum resistance/Maximum length=32 ohms/225 feet=0.14222 Ohms/ft.
Next a calculation of a maximum flux and power is undertaken.
Minimum area=30 square feet of floor area
Minimum length=Minimum area×length of cable per ft2=30×4=120 feet
Minimum resistance=Minimum length×ohms per foot =120 ft×0.14222 Ohms/ft=17.067 Ohms
Maximum power=Vline2/Minimum resistance=1202/17.067 Ohms =843.75 Watts
Now the calculation of the maximum flux and power density is undertaken:
Maximum Flux=Maximum power/Minimum Length=7.0313 watts/ft
Maximum Power Density=Maximum power/Minimum Area=843.75/30 =28.125 Watts/ft2
In this case both the flux and power density considerably exceed the maximum limits, therefore power limiiiting is required.
Utilizing the power limiting of power reduction circuit 42, illustrated in
V2=(V1×ω×C×R)/square root (1+ω2×C2×R2)
Where R is the total resistance of the resistive conductors. The power applied to the resistive conductors follows:
Power=Flux×Minimum length, but the resistive conductor power is equal to V22/R, thereby V22 is equal to P×R and
P×R=V22=(V12×ω2×C2×R2)/(1+ω2×C2×R2)
But: P=Flux×Minimum length; and
Flux×Minimum length×R=(V12×ω2×C2×R2)/(1+ω2×C2×R2)
C=1/(377×Minimum resistance×square root (V2/(Minimum resistance×Minimum length×Flux Min)−1)
C=1/(377×17.067×square root of (1202/(17.067×120×3)−1)
C=134.08 microfarads
Utilizing the above equations results in the following table:
As can be seen in the foregoing table the first three installations, which utilized wire lengths of up to 150 feet, equivalent to 1.25 times the minimum wire length of 120 feet, utilize the first embodiment of power reduction circuit 42 to reduce the wattage per foot, which is needed due to the wire lengths. Had the first embodiment of power reduction circuit 42 not been utilized, with shunt 50 removed, the power in watts per foot of the first three installations would be respectively, 7.0, 5.6 and 4.5, which is above the desirable maximum of 4.0 watts per foot.
The installation system of the present invention requires the installer to incorporate power reduction circuit 42 and then, based upon the selected number of resistive conductors, which are connected in series, shunt 50 is either installed or removed. Shunt 50 may be in the form of a wire that is cut or removed when called for pursuant to the installation method.
An alternate method of controlling the flux of the resistive conductors is to keep the system current constant independent of the length, using an electronic regulator as shown in
TRIAC 54 can be triggered in at least two different ways. Since both produce the same current flowing through conductors 44 and 46 the choice depends upon cost and power line quality. A first triggering method is a whole cycle switching method. TRIAC 54 is alternately triggered on and off so that the RMS value of the current remains essentially constant when averaged over an extended period of time such as ten seconds. One problem that may be encountered with this method is a tendency to cause light flicker in other circuits attached to the power source. This is particularly evident if fluorescent lamps are in use. A second method is to employ phase triggering. TRIAC 54 starts conducting at some point between the beginning of a half cycle to near its end, thereby providing a smooth control of the current. One potential problem in utilizing this method is the production of a large harmonic content that can result in radio frequency radiation and poor power factor.
Additionally, either power reduction circuit 42 is also controlled by a thermostat, that is not shown, which may utilize temperature sensor 16 for the regulation of the temperature of the heated floor.
While this invention has been described as having a preferred design, the present invention can be further modified within the spirit and scope of this disclosure. This application is therefore intended to cover any variations, uses, or adaptations of the invention using its general principles. Further, this application is intended to cover such departures from the present disclosure as come within known or customary practice in the art to which this invention pertains and which fall within the limits of the appended claims.
This is a continuation-in-part of U.S. patent application Ser. No. 11/343,782, entitled “FLOOR HEATING SYSTEM”, filed Jan. 31, 2006.
| Number | Date | Country | |
|---|---|---|---|
| Parent | 11343782 | Jan 2006 | US |
| Child | 11372289 | Mar 2006 | US |
