1. Field of the Invention
The present invention generally relates to a system for deicing roof edges equipped with gutter and downspout assemblies. More particularly, the present invention relates to an apparatus for placement in gutter systems mounted in adjacency to roof edging for preventing the formation of ice dams at the roof edging and for maintaining the roof edging, outfitted with a gutter assemblage, in an ice-free state.
2. Description of the Prior Art
Building structures located in regions having significant snowfall experience any of a number of problems associated with large amounts of snowfall. For example, over time, roof-bound snow tends to accumulate moisture, which can lead to damaging structural strain. Furthermore, the buildup of moisture in roof-bound snow can often lead to the formation of ice dams. Ice dams, in turn, can cause water to migrate into interior walls and ceilings thus causing significant damage to interior structures, including plaster, paint, wallpaper, wiring, etc. The repair of structural damage resulting from ice dam formation and the like can often result in substantial repair costs.
There is a complex interaction among the amount of heat loss from a building structure, snow cover, and outside temperatures that leads to ice dam formation. For ice dams to form there must be snow on the roof, and, at the same time, higher portions of the roof's outside surface must be above 32° F. on average while lower surfaces are below 32° Fahrenheit (F) on average. For a portion of the roof to be below 32° F., outside temperatures must also be below 32° F. The snow on a roof surface at temperatures above 32° F. will melt. As water from the melting snow flows down the roof it reaches the portion of the roof that is at a temperature below 32° F. and freezes. Thus, it will be understood that an ice dam is likely to form at roof edging.
The ice dam increases in size as it is fed by the melting snow above it, but it will limit itself to the portions of the roof that are at a temperature that is, on average, below 32° F. When water above the dam backs up behind the formed ice dam, it often remains liquid and thus enters into the building structure via cracks and openings in the exterior roof covering. Since most ice dams form at the edge of the roof, it is evident that a heat source warms the roof in areas other than at the roof edge. The noted heat source is primarily the building structure itself, although it should be noted that in rare instances solar heat gain may cause the noted temperature differences.
Heat from the building structure travels to the roof surface in three primary ways, namely, conduction, convection, and radiation. Conduction is the term given to the transfer of heat energy through a solid; convection is the term given to the transfer of heat energy via air currents formed as heated air rises and cooler air sinks; and radiation is the term given to the transfer of heat energy via electromagnetic wave energy. In a building structure, heat is transferred through the ceiling and insulation by conduction through the slanted portion of the ceiling. In many building structures there is little space in regions like this for insulation, so it is important to use an insulative material with a high R-value per inch to reduce heat loss by conduction. The top surface of the insulation is warmer than the other surroundings in the attic. Therefore, the air just above the insulation is heated and rises, carrying heat by convection to the roof. The higher temperatures in the insulation's top surface compared to the roof sheathing transfers heat outward by radiation. These two modes of heat transfer can be reduced by adding insulative materials. The addition of insulative materials will make the top surface temperature of the insulation closer to surrounding attic temperatures directly affecting convection and radiation from this surface.
There is another type of convection that transfers heat to the attic space and warms the roof, namely by air leakage. In many building structures this is the major mode of heat transfer that leads to the formation of ice dams. Exhaust systems like those commonly found in kitchens or bathrooms that terminate just above the roof may also contribute to snow melting. These exhaust systems may have to be moved or extended in building structures located in regions that receive significant amounts of snow fall. Other sources of heat in the attic space include chimneys. Frequent use of wood stoves and fireplaces allow heat to be transferred from the chimney into the attic space.
Inadequately insulated or leaky duct work in the attic space will also be a source of heat. Thus, improving insulation values and repairing these areas are well within any plan to limit or reduce the likelihood of ice dam formation. However, these methods of preventing and/or eliminating ice dam formation tend to be prohibitively expensive for many home and building owners. Thus, less costly means for preventing and/or eliminating ice dam formation become more attractive to owners of building structures desirous of keeping their building structures in a well-maintained state.
One means to prevent and/or eliminate ice formation is to apply a chemically-active compound (most often salt) to the frozen water thereby depressing the freezing point of the frozen water and melting the ice. Many types of chemical ice melters are used on streets, driveways, parking lots, and sidewalks, some of which are described hereinafter.
Halite (rock salt) is the most common ice melting salt. Halite is mined throughout the world. The primary chemical in rock salt is sodium chloride (NaCl). Halite is usually medium to dark gray in color if mined from shaft or pit mines. Purer forms of sodium chloride can be solution mined (forcing water into an underground salt dome and evaporating the brine that is forced out to recover the dissolved salt), but these methods are rather expensive for ice melting. Calcium chloride (CaCl2) and magnesium chloride (MgCl2) can be manufactured or evaporated from naturally occurring brines like the Great Salt Lake in Utah. Both chlorides release heat (are exothermic) as they dissolve, which helps it melt ice at very low temperatures. Further features and advantages of calcium chloride, in particular, are described in more detail hereinafter in the section entitled, Detailed Description of the Preferred Embodiment.
Ammonium Sulphate ([NH4]2SO4) is a fertilizer ingredient that is infrequently used in ice melting salts. Potassium chloride (KCl, potash) commonly takes the form of red or white granules. The red grade comes from traditional shaft mines and gets it's color from iron contamination. The pure white grade is solution mined. Potassium chloride is not as effective at very low temperatures, making pure potassium chloride impractical unless used in conjunction with other ingredients. Urea is another compound utilized for melting ice. In its pure form, urea is not corrosive making it a good choice for use around corrosion-sensitive machinery, such as airplanes. In this regard, it is noted that urea must meet strict contamination regulations before being approved to use at airports.
Ethylene glycol is a liquid deicer. It is commonly mixed with liquid urea and applied using bulk sprayers and tanker trucks and is applied primarily at airports. Potassium acetate is a biodegradable liquid deicer. It is also primarily used for deicing purposes at airports. Because potassium acetate is corrosive it is often mixed with a corrosion inhibitor. Calcium magnesium acetate (CMA) was developed as an environmentally responsible alternative to road salt. While CMA is one of the safest of all ice melting chemicals, it also has a high cost and thus the practicality of using CMA is limited. Further, CMA is not effective at very low temperatures. Alpha methyl glucoside (MG-104) is a corn by-product that is most effective when combined with other ingredients. MG-104 provides a catalytic affect that speeds melting, helps other chemicals to work at lower temperatures, and assists in the extension of freeze-thaw cycles to reduce surface damage.
When ice and water are placed in contact with one another at an ice-water interface, molecules on the surface of the ice escape into the water (melting), and molecules of water are captured on the surface of the ice (freezing). When the rate of freezing is the same as the rate of melting, the amount of ice and the amount of water will not change on average (although there are short-term fluctuations at the surface of the ice). The ice and water are then said to be in dynamic equilibrium with each other. The balance between freezing and melting can be maintained at 0° Celsius (C) or 32° F. unless conditions change in a way that favors one of the processes over the other.
The balance between freezing and melting processes can easily be upset. If the ice/water mixture is cooled, the molecules move slower. The slower-moving molecules are more easily captured by the ice, and freezing occurs at a greater rate than melting. Conversely, heating the mixture makes the molecules move faster on average, and thus, melting is favored.
Adding salt (or other chemically active compounds such as those hereinabove described) to the system will also disrupt the equilibrium. Consider replacing some of the water molecules with molecules of some other substance. The foreign molecules dissolve in the water, but do not pack easily into the array of molecules in the solid. Notably, there are fewer water molecules on the liquid side because the some of the water has been replaced by salt. The total number of waters captured by the ice per second goes down, so the rate of freezing goes down. The rate of melting is unchanged by the presence of the foreign material, so melting occurs faster than freezing.
To re-establish equilibrium, one must cool the ice-saltwater solution (or chemical-water solution) to below the usual melting point of water. For example, the freezing point of a 1 M NaCl solution is roughly −3.4° C. Solutions will always have such a freezing point depression or depressed freezing point. Generally, the higher the concentration of salt or chemically-active compound, the greater the freezing point depression. For every mole of foreign particles dissolved in a kilogram of water, the freezing point goes down by roughly 1.7°–1.9° C. Sugars and alcohols, for example, will also lower the freezing point and melt the ice. Salt is most often used as an ice-melting agent (e.g. on roads and walkways) because it is inexpensive and readily available.
It is important to realize that freezing point depression or a depressed freezing point occurs because the concentration of water molecules in a solution is less than the concentration in pure water. The nature of the solute does not matter. One might expect that solutes with large molecules are better at blocking water molecules traveling towards the surface of the ice. The hypothesis that solutes with large molecules cause a larger freezing point depression than those with smaller molecules is not in accord with experimental data.
As ice begins to freeze out of the salt water, the fraction of water in the solution becomes lower and the freezing point drops further. This does not continue indefinitely, because eventually the solution will become saturated with salt. The lowest temperature possible for liquid salt solution is −21.1° C. At that temperature, the salt begins to crystallize out of solution (as NaCl.2 H2O, for example), along with the ice, until the solution completely freezes. The frozen solution is a mixture of separate NaCl.2H2O crystals and ice crystals, not a homogeneous mixture of salt and water. This heterogeneous mixture is called a eutectic mixture.
Thus, it will be understood that ice and snow melting chemistry is straightforward, progressing based on the colligative property known as freezing point depression. Colligative means that the property depends only on the number of particles present, and not on chemical properties of the particles. Typically, a chemical is chosen that dissolves in water easily and quickly, dissociates into ions, and is safe for application. All ice melting salts dissociate into ions as they dissolve into the melting ice and snow. This multiplies the molar quantity, and multiplies the effect of freezing point depression. Rock salt for instance, releases a ratio of one sodium ion (Na+) to one chloride ion (Cl−) for twice the effect. Calcium chloride releases one calcium ion (Ca+) for every two chloride ions for three times the effect.
Thus, the notion developed that use of a chemically-active compound (preferably salt) may be used to prevent and/or eliminate ice formation at roof edging. Some of the more pertinent prior art relating to the prevention of and/or elimination of ice formation at roof edging is described briefly hereinafter. Notably, some of the prior art briefly described hereinafter does not teach the application of chemical ice-melting agents to roof edging, but the prior art is cited as being generally relevant to the state of art relating to prevention and/or elimination of ice formation at roof edging.
U.S. Pat. No. 6,225,600 ('600 patent), which issued to Burris, discloses a Snow Melting Device for Gutters. The '600 patent teaches a snow melting device comprising an elongate strip member encasing a heating coil, which encased heating coil is positionable within a closed lower end of a gutter. Upon activation, the heating coil serves to melt snow accumulated in or about the gutter to allow proper drainage of water through the downspouts of the gutter assemblage.
U.S. Pat. No. 6,282,846 ('846 patent), which issued to Nocella, discloses a Roof Drain De-Icer Apparatus. The '846 patent teaches a sleeve-like container fabricated from a waterproof material, comprising an upper and lower surface with a hollow interior filled with rock salt. At least a portion of the lower surface is perforated with a plurality of openings and is positioned with the lower perforated surface in contact with the upper surface of a flat, sloped roof to provide wicking absorption of water flowing down the roof into the salt. Absorption of water by the salt leads to release of the resulting saline solution through the perforated openings to the surface of the roof, preventing formation of ice on the roof downstream of the plastic sleeve and in the roof drain. The waterproof container with the packed salt is secured to the surface of the roof by an adhesive tape, or a weight attached to or lying upon opposite ends of the container.
U.S. Pat. No. 6,484,456 ('453 patent), which issued to Nocella, discloses a Roof Drain De-Icer Apparatus and Method. The '453 patent teaches a de-icer formed of a solid block of a pressed, granulated salt comprising at least a top portion water-proofed to prevent rapid deterioration due to precipitation. An exposed bottom surface is in contact with the upper surface of a flat, sloped roof to provide wicking absorption of water flowing down the roof into the salt. Absorption of water by the salt leads to release of the resulting saline solution to the surface of the roof, preventing formation of ice on the roof downstream of the de-icer and in the roof drain. The de-icer may be maintained in place on the surface of the roof by an adhesive tape, or by its own weight.
U.S. Pat. No. 6,694,678 ('678 patent), which issued to Schneider, discloses an Apparatus and Methodology for Limiting Ice Build-Up. The '678 patent teaches an apparatus for limiting ice build-up in a gutter, the apparatus deployable in a gutter which has a bottom, the apparatus comprising sidewalls and a base comprising a top side, the sidewalls joined to the top side of the base with the side walls defining a salt block opening through which the salt block is loadable into the housing, with one of the side walls defining a flow opening for allowing frozen precipitation to pass therethrough and contact the salt block and melt.
U.S. Pat. No. 6,700,098 ('098 patent), which issued to Wyatt et at., discloses a System for Preventing and Clearing Ice Dams. The '098 patent teaches a system comprising a plurality of wire holding assemblies, each of which has a base for attachment to a gutter and length-adjustable arm for contact with a roof adjacent the gutter. The arm is rotatably and pivotally mounted to the base. The system includes a PTCR heating cable that is held in a desired position by the wire holding assembly arms. The system includes roof and gutter temperature sensors and a moisture sensor. The heating cable is connected to the control unit, the control having a mode selector switch for controlling operation of the cable.
From an inspection of these patent disclosures and other art generally known in the relevant art, it will be seen that certain obstacles become evident when one considers how to most effectively apply ice-melting salts or other chemically-active compounds to roof edging so as to prevent and/or eliminate ice dam formation, such as may be seen, for example, from the '453; '846; and '678 patents. It will be seen from an inspection of the noted disclosures, for example, that the devices utilized for salt-delivery are removably affixed to the roof edging or gutter system and comprise structures that do not readily remove themselves or self-destruct at the end of a winter season. In other words, the salt-delivery devices are not environmentally disposable but require active user participation for removal or clean up at the end of an ice dam or winter season.
Thus, it will be seen that the prior art does not teach a chemical-delivery assembly for removing ice at a roof edge, which chemical-delivery assembly comprises a flexible, biodegradable mesh casing and a solid, chemically-active fill material, which assembly may be positioned or placed in superior adjacency to a trough portion of a gutter assembly attached to a roof edge. In this regard, it will be further seen that the prior art does not teach a flexible, biodegradable mesh casing comprising an inner matter-retaining surface, an outer matter-engaging surface, a casing thickness, and a plurality of mesh apertures for effectively delivering the chemically-active fill material to the areas in and around the trough portion of a gutter assembly for maintaining the trough portion in an ice free state and/or for eliminating ice from the areas in and around the trough portion of a gutter assembly. Further, the prior art does not teach a flexible, biodegradable mesh casing comprising a biodegradable fabric having inherent seasonal durability, the inherent seasonal durability for self-destructing the mesh casing when the chemically-active fill material has decremented to substantially zero at the end of an ice dam season, the self-destructed mesh casing being removable by flowing water and thus being environmentally disposable.