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Attic insulation with desiccant

Attic insulation with desiccant description/claims

The present invention relates to insulation products, such as batt and loose-fill insulation, and board products such as duct liner and duct boards, having better thermal properties for cooling dominated climates.

Most residential construction includes an attic space between the ceiling and the roof deck. The structure that supports the roof and provides the ceiling plane is often constructed with pre-assembled wood trusses. The structure can also be built on-site using traditional ceiling joists and roof rafters. Properly insulating the attic is essential to reducing home energy consumption (“building load”). Thermally isolating the attic from the rest of the house also increases the comfort of the living space below in both winter and summer.

Attic ventilation serves two purposes: prevention of moisture condensation in the winter and attic cooling in the summer. Ventilation during the heating season removes moisture-laden air from the attic before it condenses. Summer-time venting allows cooler air to flush heat out of the attic space. Typically, a good ventilation system has 50 percent of the required ventilation area high on the roof and 50 percent in the eave area. With properly spaced vents, the attic will have good circulation. Batt insulation is often a good bet for long-term thermal performance. Loose-fill insulation may also be used, including cellulosic and glass fiber loose-fill insulation. Loose-fill insulation should be installed at the same thickness throughout the attic. Voids and low spots behind framing should be eliminated.

Despite the many attempts to properly insulate attics, the attic space of most buildings is perceived as a source of a nuisance. In winter, moisture condensation on the attic ceiling encourages mildew growth. In summer, the heat build-up in the attic space increases the cooling load. Generally during the night, the high attic air relative humidity is caused by an air exchange with the outdoor environment. The wood framing materials, generally having a lower air relative humidity at the surface, adsorb moisture. During the daytime the attic air relative humidity is reduced due to the heat gain caused by solar heat. There is a higher air or relative humidity at the surface of the wood framing materials which results in moisture being desorbed by wood attic framing materials. The attic space during the daytime will typically be elevated above the outdoor environment.

In modern residences, the challenge of achieving a continuous air infiltration barrier and thermal insulation barrier at the interior ceiling level is especially difficult. The air barrier, used to isolate the living space from the attic, is usually the taped drywall ceiling, while the thermal barrier is the insulation placed on top of the drywall. Typically, the ceiling is not a single horizontal plane, but a series of horizontal planes, vertical planes (knee walls), and sloped planes, all intersecting to create the ceiling.

Current building codes across the United States require attic ventilation. Lstiburek, “Vented and Sealed Attics in Hot Climates” ASHRAE SYMPOSIUM ON ATTICS AND CATHEDRAL CEILINGS, TORONTO, (JUNE, 1997). In cold climates, the primary purpose of the attic ventilation is to maintain a cold roof temperature to avoid ice damage created by melting snow, and to vent moisture that moves from the conditioned space to the attic. Id., p. 3 Melted snow, in this case, is caused by heat loss from the conditioned space. When water from melted snow runs out over the unheated eave portion of the house, it freezes and expands, often driving its way back up the roof and between shingles. Id.

In hot climates, the primary purpose of attic ventilation is to expel solar heated hot air from the attic to lessen the building cooling load. Id., p. 4 Roof shingle temperatures will be higher during no-wind conditions leading to a higher heat load on the attic. Id. Therefore, the greatest need for attic ventilation is when there is a little wind pressure to force air in and out of the attic.

Building heating and cooling loads from roofs for all single-family detached buildings were measured to be 446 trillion BTUs for heating and 128 trillion BTUs for cooling in the U.S. in 1999. Y. J. Huang et al. “Residential Heating and Cooling Loads Components Analysis,” LBNL-44636, Lawrence Berkeley National Laboratory, Berkley, Calif., (1999). Compared to the net heating and cooling loads at 2,958,814 trillion BTUs, the percent of roof loads are 15.1 percent and 15.8 percent, respectively. Therefore, roof load reduction can greatly reduce the total building loads. Although there are many ways to reduce roof loads, the most common way is to add more roof insulation. Due to limited attic space, adding more roof insulation may not always be a feasible way to reduce the total building loads in many instances.

Accordingly, there remains a need to reduce roof loads, thereby building loads by alternative means.

A method of reducing the amount of cooling energy required to cool a building is provided. The building generally includes an enclosed room partially defined by an outer wall, a horizontal upper wall plate, and an attic space exposed above the upper wall plate. The attic space is defined by a ceiling of the room and a roof of the building. The method includes the steps of (1) disposing a porous insulating material substantially covering the ceiling in said attic space to a substantial depth, the porous insulating material including a desiccant, (2) permitting the desiccant-bearing fibrous insulating material to adsorb water moisture from the attic space, and (3) permitting the adsorbed water moisture to desorb from the desiccant-bearing fibrous insulating material into the enclosed room, whereby the temperature of the desiccant-bearing fibrous insulating material is reduced resulting in a reduction in the amount of cooling energy required to cool the building.

In the more preferred embodiments of the present invention, the desiccant is a silica gel which is added to loose-fill or batt insulation used in attics in climates dominated by a cooling. As a result of the heat energy in the attic expended in evaporating the moisture in the silica gel in the insulation in the summer cooling season, the heat flow from the attic into the living space is reduced. The simulated, calculated net energy savings in a 1500 square-foot house in Miami with a 20 percent silica gel content (by volume) in R30 insulation can potentially reduce net annual energy costs by about $50.00.

The silica gel, or other desiccant, such as montmorillonite clay, synthetic zeolite (molecular sieve), calcium oxide (CaO), calcium sulfate (CaSO4), carbon molecular sieve, activated alumina, or activated carbon, or sodium polyacrylate, for example, may be added to the preferred mineral fiber or cellulose insulation during the manufacturing process. For blanket mineral fiber insulation, the silica gel, for example, may be added to the forming section as a dry powder blown into the upper area of the forming section of a rotary glass plant (similar to the manner that admix materials are typically added today) and/or mixed with the mineral fibers and binder in the forming section as an applied coating or ingredient, for example. The silica gel in a water slurry form may also be added to mineral fiber insulation in the forming section by spraying the slurry onto the hot mineral fibers. For mineral fiber loose-fill insulation, the silica gel may be added as a dry powder to the mineral fibers in the forming section or to the mineral fibers in the blowing machine hopper before the insulation is blown into the attic or wall. For cellulose insulation, the silica gel may be added to the cellulose insulation in the manufacturing process at the time the fire retardant, for example, is added to the shredded cellulose or to the mineral fibers in the blowing machine hopper before the insulation is blown into the attic.

In computer simulation models, it was determined that negative heat flux flowing from the living space into the attic increases due to higher thermal conductivity of the present invention's desiccant insulation mixture containing fiberglass and silica gel in the winter climate. Additionally, negative moisture fluxes flowing from the living space into the attic were reduced to a very small amount due to the high level of moisture in the desiccant insulation mixture in the winter. These results were compared to a fiberglass only insulation control in the attic space during the same climate conditions. In the summer months, the fiberglass insulation with silica gel resulted in a reduced positive heat flux flowing from the attic into the living area, in the model, since heat energy in the attic was being used to evaporate moisture from the desiccant. It also resulted in an increase in the positive moisture flux flowing from the attic into the living area due to extra moisture from evaporation from the desiccant into the living area. In the cooling dominated climate of Miami, the addition of desiccant to the attic insulation reduced the total roof energy load in the computer models of this invention. In heated dominated climates like Baltimore, Minneapolis, and San Francisco, the addition of desiccant to the insulation increased, rather than decreased, the total roof energy load in computer simulations.

Accordingly, the present invention is designed to assist “cooling dominated climates,” such as Miami, where the average monthly temperature is above 45° F. year round, as opposed to “heat dominated climates,” which typically experience between 4500 and 8000 heating degree days. In heated dominated climates, the dry air is outside and the moist air is inside. In the Southern United States where most cooling dominated climate constructions are located, the conditions are exactly the opposite. The air conditioners create dry air inside the dwelling, while the outside air is very humid most of the year.

In further embodiments of the present invention, a building insulation material is provided which includes randomly oriented fibers made of a cellulosic or inorganic composition disposed in a substantial thickness to provide insulation for a building, and a desiccant in an amount sufficient to enable said insulating material to absorb enough water moisture to reduce the temperature of said insulating material by at least 1° F.

In a further embodiment of the present invention, a method of manufacturing an insulating material is provided which includes the steps of forming glass fibers from molten streams of glass, combining glass fibers with a desiccant, and consolidating the fibers and desiccant on a conveyor.

In still a further embodiment of the present invention, a method of manufacturing cellulosic insulation material is provided which includes the step of forming cellulosic fibers from a paper source and admixing a fire retardant and desiccant onto the cellulosic fibers.

The above and other features of the present invention will be better understood from the following detailed description of the preferred embodiments of the invention that is provided in connection with the accompanying drawings.

• Provisional Patent
• Utility Patent

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