Electrical heating system for building structures

An electrical heating system for building structures in which side walls form a space for fill material supporting a slab floor and containing an electrical heating cable, the fill material functioning as a heat sump for absorbing heat while the heating cable is in operation and releasing it over a period of time whether the cable is operating or not. A moisture regulator is included in the system consisting of one or more distribution units connected to a source of water and a probe sensing the amount of moisture for registering on a gauge or for operating a valve in the line for maintaining the desired amount of moisture in the fill material. The fill material may be divided by a plurality of vertical walls into compartments, and a water distributing unit and a moisture sensor probe are disposed in each of the compartments for controlling the moisture in each compartment. A thermal and moisture insulating material is preferably disposed between the fill material and the earth to prevent escape downwardly of the heat generated in the fill material and to assist in controlling the moisture content of the fill material.

A particular type of heating system for homes and other building structures 
consists of an electrical heating cable buried in sand or other material 
beneath a concrete slab floor, the material beneath the floor storing the 
heat generated from time to time by the electrical heating cable, and 
gradually releasing the heat through the concrete floor throughout the day 
and night. This type of heating system, which usually provides a rather 
uniform heat supply to the living space of the building, is generally more 
economical than the conventional electrical heating system which primarily 
heats the air in the living space from a centrally located heating unit, 
or by separate space heating units in the various rooms of the house. The 
use of the electrical system to heat the material under the floor permits 
the electrical system to be operated during the hours of low electrical 
demand from the electric power companies, and to be inoperative or on low 
output during times of peak demand. Further, conduction of heat from the 
material below the floor upwardly through the floor dissipates the heat 
where it is most needed and where it can best be utilized for effective 
heating of the living space and for optimum comfort of those in the living 
space. 
While the heat storage type system just described has a number of 
advantages, there are some disadvantages which decrease its efficiency, 
and hence the acceptance of that type of system in homes where it could 
otherwise be effectively used. One of the major problems of the foregoing 
electric heating systems is to maintain sufficient moisture in the fill 
material to provide optimum conductivity of heat between the particles of 
sand or other granular material, and between the fill material and the 
layer forming the slab for the floor of the building structure above the 
fill material. In the conventional heat sump of the foregoing type, the 
heat generated by the heating cable will normally drive off the moisture, 
and the heat transfer efficiency of the fill material consequently 
decreases and remains indefinitely below optimum performance, thus 
requiring excessive temperatures in the heating cable to achieve a given 
level of heat input. It is therefore one of the principal objects of the 
present invention to provide a heat sump system for building structures, 
which effectively maintains the moisture in the fill material at a level 
for optimum efficiency of the heating system, and which can be regulated 
manually or automatically to supply moisture to the fill material of the 
system as required for maximum efficiency. 
Another object of the invention is to provide a heat sump system which 
includes a moisture sensing and indicating system for determining the 
moisture content of the fill material at various locations in the 
material, and which is capable of supplying moisture selectively to any of 
the sensed locations having a deficiency of moisture, and further, which 
substantially improves the performance and efficiency of the 
aforementioned type of heating system. 
Still another object is to provide a heat sump system of the aforesaid type 
which is simple to construct and operate and virtually service free, and 
which will give optimum performance over extended periods of time with no 
attention, and yet is responsive to the heat requirements of the living 
space above the sump system. 
The invention is primarily concerned with a heating system in which an 
electric heating cable is buried in fill material such as sand, beneath a 
concrete slab floor. The heating cable, which is preferably about one to 
three inches in depth, heats the material, which is confined on all 
lateral sides by retainer walls, normally of concrete, and usually the 
foundation of the building structure. The present heating system 
preferably includes a thermal barrier beneath the fill material to 
eliminate or minimize the loss of heat downwardly into the earth, so that 
substantially all of the heat generated by the electric heating cable is 
available for conduction upwardly through the fill material and floor into 
the living space of the building structure. While the concrete foundation 
forming the lateral sides of the heat sump serves as a barrier to reduce 
heat loss between the fill material and the surrounding earth or 
atmosphere, preferably an additional barrier to both moisture and heat 
loss is included along the lateral sides, normally along the inside 
surface of the foundation. 
The presence of moisture in the fill material improves the heat 
conductivity by providing a coupling effect between the grains of sand or 
other particulated material of the fill material, so that the heat will 
transfer readily from grain to grain through the moisture which has better 
conductivity than the air otherwise separating the particles. The heat is 
also transferred by the flow of the moisture itself in the interstices of 
the particulate material. While the present system contemplates the use of 
a barrier both below and around the sides of the fill material, there is 
likely to be sufficient moisture leakage or non-uniform distribution 
thereof in the fill material, that the heat transfer may be inefficient or 
at least substantially less than optimum in performance. The present 
invention contemplates the maintenance and good distribution of the 
moisture in the fill material so that maximum efficiency of the system can 
be maintained.

Referring more specifically to the drawings, the building structure shown 
in FIGS. 1 and 2 includes a foundation 10 having vertical side walls 12 
and 14, a floor 16 consisting of a concrete slab laid on fill material 18 
which forms a part of the heat sump indicated generally by numeral 20. 
Outside walls 22 and 24 and wall partition 26 of the building are shown 
supported by the foundation and on the concrete slab. Foundation sides 12 
and 14 are supported by footings 28 and 30, respectively, poured in 
trenches made at the time the excavation for the building is made. For the 
purpose of the present invention, this construction is considered 
conventional and will not be described in further detail. The present 
heating system is adaptable to a variety of different types of buildings, 
including single and multiple family homes, and commercial and industrial 
buildings; however, the description herein will be directed primarily to 
the application of the invention to home structures. 
After the excavation for the foundation and heating system 20 has been made 
down to surface 32 of the earth 34, a layer of thermal insulating material 
40 is laid on surface 32. The insulating material may be of a variety of 
different substances, preferably cellular polyurethane, of sufficient 
strength to support fill material 18 and concrete slab 16. In any event, 
the thermal insulating structure must have substantial thickness, 
preferably at least two to four inches, and be capable of withstanding 
moisture and not be subject to rot or disintegration under adverse 
conditions over long periods of time. While the foregoing thermal 
insulating structures illustrate suitable ways of providing a thermal 
barrier, other types of thermal insulating structures may be used if they 
satisfy both the thermal and strength requirements, the thermal 
characteristic of the material used determining the amount and thickness 
of the material used. Different types of reinforcement may be required for 
different insulating materials, to obtain the required strength to support 
the fill material and slab thereon. 
In order to seal the heat sump 20 to assist in retaining the desired level 
of moisture in the fill material, a plastic sheet 50 is placed beneath the 
thermal insulating material where it will minimize the flow of moisture 
between the ground and the fill material. In addition to the thermal 
insulating material 40, insulating materials 51 and 54 are preferably 
installed along the inner surface of foundation sides 12 and 14 to 
minimize the loss of heat through the concrete foundation. Moisture 
barrier sheets 55 and 56, normally of plastic material, are also 
preferably disposed between the concrete foundation and the respective 
thermal barriers, and a sheet is preferably disposed beneath slab 16, to 
reduce the flow of moisture from the heat sump material, thereby assisting 
in maintaining the proper moisture level in the material. Plastic sheets 
57, 58 and 59 may also be placed above and on the inside of the insulating 
layers to maintain maximum insulating efficiency as well as to improve the 
seal around the sump fill material, and a similar sheet 60 may be placed 
on top of the fill material. 
In the embodiment of FIGS. 1 and 2, an electric heating system, indicated 
generally by numeral 61, consists of a plurality of spaced electric 
heating cable sections 62, preferably buried between one and six inches 
beneath the concrete slab. The cable is electrically insulated and 
waterproof and has cold leads 64 and 66. In the embodiment illustrated in 
the drawings, the thickness of the fill material 18 is approximately 28 
inches, with the electric heating cable being disposed approximately five 
inches from the bottom of the slab. In order to assist in laying the 
cable, it may be mounted on a carrier, the carrier and cable assembly 
normally being fabricated in a plant and rolled for shipping and then 
unrolled onto the surface of the partially filled fill material in the 
excavation. An additional heating cable or cable 68 in place of cable 61 
may be buried in the floor slab as illustrated in FIG. 2. 
In order to maintain the moisture in the fill material at the optimum 
level, a water distribution system indicated generally by numeral 70 is 
embedded in the fill material, preferably near the top of the material, as 
can best be seen in FIG. 2. In the embodiment illustrated in FIG. 1, three 
water lines 72, 74 and 76 are connected to a source of water, such as a 
municipal water supply system, by a pipe 78, and each of the lines 
contains valves 80, 82 and 84 for controlling the flow of water through 
the respective lines. In this embodiment, line 72 is connected to water 
distribution units 86 and 88 which distribute the water through a 
plurality of perforated tubes 90, extending radially from head 91 and 
having a sufficient number of holes that the water is effectively 
distributed by the tubes. The two units with the water distributing arms 
are so located that a substantial portion of the fill material will be 
penetrated by the water delivered to the two units. Line 74 is connected 
to a unit 92 having a plurality of perforated radially extending tubes 90 
for supplying water to the center of the fill material. Line 76 is 
connected to units 94 and 96 of similar construction to units 86, 88 and 
92 for supplying moisture to the respective end of the fill material. The 
number of units on a line or the number of units with separate lines will 
be determined by the length of the radial tubes of the units used. A 
single unit could be used under some conditions with a configuration of 
radial arms or tubes branching from a single line to provide even 
distribution of water to the fill material. In the embodiment illustrated, 
moisture sensing probes 98 and 100 are connected by leads 102 and 104 to 
gauges 106 and 108, respectively, for indicating the amount of moisture in 
the fill material so that an operator can operate any one or all of the 
valves to provide the proper amount of moisture to the fill material as 
indicated by the gauges. In place of gauges, the probes may be connected 
to a control which automatically turns on and turns off the various valves 
to maintain the proper moisture content in the bed without the supervision 
of an operator. 
In the operation of the installation illustrated in FIGS. 1 and 2, the 
electrical heating system, containing the foregoing moisture regulating 
system, is operated as required to provide the desired temperature in the 
living space above; however, the heat sump may be most economically 
operated by heating the fill material at off peak periods of electrical 
demand at the power company, to store the heat for gradual release from 
the fill material through the concrete slab into the living space. Since 
the cable is disposed at least several inches below the concrete floor, a 
relatively slow response from the electrical system is obtained, in that a 
period of time is required for the heat to flow from the electric heating 
cable through the fill material and concrete slab into the living space 
thereabove. However, an effective, prolonged heat release is obtained from 
this type of system, so that a relatively even heat is obtained from the 
heat sump through the concrete slab floor. From time to time the moisture 
injection system 70 may be used either manually or automatically to 
control the amount of moisture in the fill dirt. Whenever additional 
moisture is required in any location in the fill material, one or more of 
the three valves 80, 82 and 84 are turned on to supply water to the area 
or areas low in moisture content. 
With reference to the embodiment disclosed in FIGS. 3 and 4, a plurality of 
partitions 120 and 122 extending in one direction across the fill material 
and partitions 124 and 126 extending at right angles to the other 
partitions divide the fill material into a plurality of compartments, 
indicated by numerals 130 through 138. The compartments are connected by 
water lines, indicated generally by numeral 140, to a source of supply 
such as a city water system and to units 150 in each compartment. The 
units 150 are similar in construction and operation to units 86 and 88 
previously described herein. A probe 152 is disposed in each compartment 
and is connected to one of the gauges 154, 156 and 158. When moisture is 
indicated for one of the compartments, the corresponding valve, indicated 
generally by numerals 160, 162 and 164, is opened, either manually or 
automatically, to supply the water to that compartment and raise the 
moisture content in the fill material in the respective compartment to the 
desired amount. The partitions 120, 122, 124 and 126 may be of various 
materials, preferably of plastic, and preferably extend from the bottom to 
the top of the fill material and are substantially water impervious so 
that the moisture will not flow readily from one compartment to another. 
Thus, with the compartmented structure of the fill material, the moisture 
can effectively be controlled throughout the entire area so that the heat 
is transmitted to and through the slab substantially uniformly over its 
entire area. In some instances where there tends to be a cold area in the 
building, such as in a corner, the moisture content in the compartment 
beneath the area can be controlled to provide a variation in temperature 
in that area. The combination of the compartment heating and moisture 
control results in effective regulation of the heat in any area throughout 
the living space above the concrete slab floor. 
While only two embodiments of the present electrical heating system for 
building structures have been described in detail herein, various changes 
and modifications may be made without departing from the scope of the 
invention.