US20050191956A1 - Radon mitigation heater pipe - Google Patents

Abstract

An apparatus and method for radon mitigation using natural convection to remove radon-contaminated air from beneath the slab foundation of a structure, building, or dwelling, comprising a section of vertically mounted convection duct including an internal heat source, an inlet duct extending from said convection duct through the slab into the gas permeable sub-slab layer, an outlet duct extending from said convection duct through the structure and out the roof thereof, the internal heat source comprising a thermally conductive tube disposed concentrically within said convection duct and heated by one or more electrical heater elements to assist the upward airflow of the radon-contaminated air from the structure.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS
• This application is a continuation-in-part of U.S. patent application Ser. No. 10/773,076 filed on Feb. 5, 2004, which claims priority from U.S. Provisional Patent Application Ser. No. 60/445,135, filed on Feb. 5, 2003.
BACKGROUND OF THE INVENTION
• The present invention relates generally to devices for radon mitigation in homes and other structures. More specifically, the present invention relates to an improved system for ventilating the foundation of a structure to remove radon gas so that it does not accumulate inside the structure.
• Radon is a radioactive gas generated by the natural (radioactive) decay of the uranium that is found in nearly all soils, and can be found all over the United States. The breakdown of uranium in soil, rock and water releases radon into the air we breathe. Radon can get into any type of building—homes, offices, and schools—and cause an elevated indoor radon level. It typically moves up through the ground to the air above and into a dwelling or other structure through cracks, fissures and other holes in the foundation. The structure traps radon inside, where it can accumulate if the structure is not well ventilated. A radon problem can exist in any home, regardless whether the home is new, old, well sealed, or drafty, and may even occur in a home without a basement.
• Like other environmental pollutants, there is some uncertainty about the magnitude of radon health risks. However, we know more about radon risks than risks from most other cancer-causing substances because of studies that have been done of cancer in underground miners.
• One method of radon mitigation in new home construction includes placing a gas permeable layer beneath the concrete slab of the foundation. This layer typically includes 4″ to 6″ of gravel. A polyethylene or equivalent flexible sheeting material is placed on top of the gas permeable layer. At one end of the slab, a hole is cut in the flexible sheeting material. A section of PVC pipe, typically of 3″ or4″ diameter, extends vertically upward from the gas permeable layer, through the hole in the flexible sheeting material and slab, and through the internal space of the structure and out through the roof. At its bottom end, the PVC pipe is supported by a pipe tee located within the gas permeable layer. An inline fan may be installed in the PVC piping, usually in the attic or sometimes outside the structure.
• If a fan is installed, it draws the air up through the bottom inlet (located within the gas permeable layer) and creates a vacuum in the gas permeable layer. The air is exhausted from the outlet of the PVC pipe above the roof. Because this system usually does not have a fresh air input into the gas permeable layer below the slab, airflow is restricted. The effectiveness of this system relies largely on reduced air pressure within the column, i.e., the vacuum created by the fan within the vertical pipe, to pull the radon gas out. The reliance of this method on a fan causes problems with noise and condensation building up on the inside of the pipe. The condensation then drips down on the fan, increasing the noise. Because of the mechanical nature of the fan, its life span is limited.
• Various examples of existing radon mitigation systems are known. U.S. Pat. No. 4,988,237 [Crawshaw] discloses a fan-driven sub-slab ventilation system having an attic mounted fan unit, a sub-slab inlet, and an above-roofline outlet. U.S. Pat. No. 6,524,182 [Kilburn, et al.] discloses a fan-driven system having a sump well inlet and a band-board outlet that is suboptimal, since it does not get the radon-contaminated air sufficiently away from the dwelling. U.S. Pat. No. 4,885,984 [Franceus] discloses a fan-driven system with a sub-slab inlet and an externally mounted fan with an external vertical vent pipe. U.S. Pat. No. 4,922,808 [Smith] discloses a fan-driven system with an inlet drawing air directly from the basement of a house and a band-board outlet. However, all of these fan-inclusive devices suffer from the drawback of having the fan, a mechanical component that is prone to failure. Also, these devices do not heat the cool air being drawn from the sub-slab region (or the basement) and are therefore prone to develop condensation in the outlet piping.
• The United States Environmental Protection Agency Publication EPA/402-K-01-002 (April 2001) entitled “Building Radon Out: A Step-by-Step Guide on How to Build Radon-Resistant Homes” discusses the preparation of building foundations for use with sub-slab ventilation systems and discloses both passive (no driving force for flow other than the free convection stack effect of having the exhaust pipe pass through the heated interior structure space) and active (fan-driven) sub-slab depressurization systems. However, neither these patents nor the EPA Publication suggests the use of an internally heated duct to drive a natural convective flow in a sub-slab depressurization system comparable to that utilized in the present invention.
• Various examples of devices for creating free convection in pipes, all distinguishable from the application of the present invention, are known. U.S. Pat. No. 1,389,252 [Lucas] discloses a heat driven forced draft ventilator which includes a high temperature radiative heating element mounted inside an enlarged section duct which heats the walls of the duct in order to drive the upward flow of heated air. In contrast, the present invention uses a low temperature heating element that will not significantly heat the walls of the duct in which it is mounted. In fact, it is critical that the device of the present invention not heat the duct walls significantly since they are typically made from PVC and not metal. Similarly, the electric heater disclosed in U.S. Pat. No. 1,401,500 [Scott] is intended to be heated to near the point of incandescence (to a point of dull red heat) and therefore will heat not only the air in the duct but also the walls of the duct. For that reason, this device also would not be compatible with PVC piping. U.S. Pat. No. 1,759,830 [Blanchard] discloses a resistance heater that is in contact with and intended to directly heat the metal walls of a chimney cap, again an application that is incompatible with creating an updraft of airflow in PVC piping.
• Somewhat less relevant is U.S. Pat. No. 6,141,495 [Roth], a fan-powered device with an electrical heating element designed to pre-heat a flue. Because the flow in this device is generated by a fan, it does not rely on natural convection. Also distinguishable is U.S. Pat. No. 1,699,739 [Kercher, et al.] that describes a natural convection heater located below the room to be heated. This device relies on the natural convective flow of higher density cool air from the room down ducting to the heater element as well as the natural convective flow of lower density warmed air back up to the room. Therefore, it does not anticipate that an internally heated duct may be used to create a negative pressure at its inlet to actually draw higher density cooler air up into the heated section as is done in the radon mitigation device of the present invention. The pipe heaters of U.S. Pat. No. 4,524,262 [Meyer] and U.S. Pat. No. 1,273,666 [Powers] are also inapposite to the present invention since each applies heat directly to the ducting and neither with the purpose of creating upward flow in the ducting.
• Accordingly, it is an object of the present invention to provide a radon removal device that eliminates the noise and limited lifespan that results from the use of a fan. It is another object of the present invention to provide a radon removal device that increases the temperature of the air being exhausted in order to reduce or eliminate condensation from forming on the inside of the exhaust pipe, but does not excessively increase the air temperature or the temperature of the ducting itself so as to require a temperature control device. It is a further object of the present invention to provide a radon removal device that is more effective at removing the gas from beneath the slab of a building foundation for the reason that it is not susceptible to mechanical failures of the fan-based, vacuum-creating devices currently in use.
• Other objects will appear hereinafter.
SUMMARY OF THE INVENTION
• The present invention provides a simple, low-maintenance device for actively drawing radon-contaminated air from beneath the foundation of a structure, thus mitigating the risk that radon will enter into and accumulate inside of the structure. By using an internally heated section of duct to create a convective flow of air upward from the gas permeable sub-slab layer, expelling the radon-contaminated air above the roof of the structure, the device of the present invention eliminates the need for a fan. Therefore, the device of the present invention is quieter and less prone to failure than a similarly installed fan-powered radon mitigation device. Additionally, because the device of the present invention heats the air that is being withdrawn from beneath the slab, condensation within the ducting is reduced. The heat source utilized in the present invention is of low wattage so that the temperature of the withdrawn air is maintained within the capabilities of the PVC outlet piping and no temperature control mechanism is required.
BRIEF DESCRIPTION OF THE DRAWINGS
• For the purpose of illustrating the invention, there is shown in the drawings forms which are presently preferred; it being understood, however, that the invention is not limited to the precise arrangements and instrumentalities shown.
• FIG. 1 is an isometric view of the radon mitigation heater pipe of the present invention.
• FIG. 2 is a bottom view of the radon mitigation heater pipe of the present invention, looking upward.
• FIG. 3 is a sectional view taken along Line3-3 ofFIG. 2 showing the interior components of the radon mitigation heater pipe of the present invention.
• FIG. 4 is a diagrammatic view of the use of the radon mitigation heated exhaust pipe and associated air inlet pipe of the present invention installed through and beneath the concrete slab foundation of a building.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
• The following detailed description is of the best presently contemplated mode of carrying out the invention. The description is not intended in a limiting sense, and is made solely for the purpose of illustrating the general principles of the invention. The various features and advantages of the present invention may be more readily understood with reference to the following detailed description taken in conjunction with the accompanying drawings.
• Referring now to the drawings in detail, where like numerals refer to like parts or elements, there is shown inFIG. 1 an exterior view of theradon mitigation device10. The device is comprised of anexternal shell portion12 and an internal heating portion31.
• Theexternal shell portion12 is fabricated by welding several components together; however a one-piece metal casting would be a preferable construction technique for a mass produced device. Thebase14 is made from a round flat plate or flange having a centrally disposed hole matching the outer diameter of thelower section16 of theexternal shell portion12. Thebase14 has a plurality of mountingholes18 for securing thedevice10 to the foundation or flooring of a building. In one embodiment, thebase14 is formed from ⅛″ thick steel and is 9″ in diameter with a centered6″ diameter hole. Thelower section16 of theexternal shell portion12 is a length of 6″ diameter metal pipe approximately two feet long that is received into the 6″ diameter hole in thebase14.
• Since the typical exhaust pipe of a radon mitigation system is either 3″ or4″ in diameter, a reducingsection20 and anexhaust pipe section22 provide a transition from thelower section16 of theexternal shell12 to that smaller diameter. The reducingsection20 may be made from ⅛″ thick steel having an outer diameter of 6″, with a centered hole nominally4″ in diameter for receiving the 4″diameter exhaust pipe22. Theexhaust pipe22 may be manufactured from a short (approximately 6″ long) piece ofschedule40 steel pipe. Typically, theexhaust pipe22 is coupled to a 4″ diameter PVC (polyvinylchloride)outlet pipe24 via aflexible rubber coupler26, as shown inFIG. 4. ThePVC outlet pipe24 extends vertically from theexhaust pipe22 and is preferably routed up through the heated interior space of the dwelling or structure and out through the roof. Thebase14, thelower section16 ofexternal shell12, the reducingsection20, and theexhaust pipe22 may be welded together or may be cast as a unitary piece.
• As is illustrated inFIGS. 2 and 3, analuminum draft pipe30 is disposed inside thelower section16 ofexternal shell12. Thedraft pipe30 is suspended concentrically and co-axially within thelower section16 ofexternal shell12 by a mountingbracket32, asupport bar34, and one or more mountingarms36. Thebracket32 is welded to the inner wall of thelower section16 ofexternal shell12, near the lower end thereof. Thesupport bar34 is fastened to thebracket32 by two or more screw-like fasteners33 that pass through thesupport bar34 and thread into tapped holes in thebracket32. Thesupport bar34 extends vertically upward inside of and parallel to theexternal shell12. Thedraft pipe30 is suspended from thesupport bar34 by the mountingarms36 that extend through thepipe30 and are threadedly secured to thesupport bar34 by nuts37. Spacingnuts35 are used to appropriately position thedraft pipe30 at the approximate center of theexternal shell12. Other equivalent mechanical means may be used to secure thedraft pipe30 to thesupport bar34 and properly position thepipe30 within theexternal shell12.
• In one preferred embodiment, thebracket32 has the dimensions of about 1-½″ in width, 3″ in height and ¼″ in thickness, having two tapped holes. Thevertical support34 has the dimensions of about 1″ in width, 16″ in length (vertical dimension) and ¼″ in thickness. Thealuminum draft pipe30 is preferred to have a 2″ diameter and be about 16″ long, with a wall thickness of approximately 1/4″.
• Thedraft pipe30 is electrically heated by at least oneband heater40. Theband heater40 clamps around thedraft pipe30 and is powered via anelectrical cord42 plugged into a standard grounded wall outlet. Abracket44 is welded to the inside wall of theexternal shell12 to provide agrounding lug46 for the ground lead of theelectrical power cord42. The power and neutral leads of theelectrical cord42 are connected through aconnector48 mounted in theexternal shell12 to opposite ends of theband heaters40.
• In a preferred embodiment, thebracket44 has the dimensions of about 1-½″ in width, 3″ in height and ¼″ in thickness and includes a tapped hole for receiving thegrounding lug46. Theband heaters40 have dimensions of about 1-½″ in length and an inner diameter allowing it to be clamped securely around the 2″diameter draft pipe30. Theband heaters40 are powered by 120 VAC and produce approximately 75 watts of power that is converted to heat. Theelectrical cord42 is a high temperature three-conductor cable with a standard three-pronged grounded plug at one end to fit a standard grounded wall outlet. Theelectrical cord42 passes through the wall of thelower section16 ofexternal shell12 via a sealedconnector48 which provides a reinforced mount and strain relief for theelectrical cord42 extending outwardly from the wall of thelower section16.
• FIG. 4 is a simplified diagrammatic view of a typical installation of theradon mitigation device10 in a concrete basement slab foundation. Unless otherwise noted, all PVC pipe and connections are typically 4″ in diameter. On top of theground52, a gaspermeable layer54 is normally laid to a depth of 4″ to 6″, comprising crushed stone between about ½″ and about 2″ in size. A polyethylene or equivalentflexible sheeting material56 is placed on top of the gaspermeable layer54, extending to the walls at the perimeter of the foundation of the building. On top of theflexible sheeting material56, theconcrete slab58 is poured to complete the foundation of the building.
• At the lower end of theradon mitigation device10, aPVC tee60 sits in the gaspermeable layer54 with two of its openings oriented horizontally and one opening oriented vertically upward. The horizontal openings of thePVC tee60 may have perforated PVC piping extending within the gaspermeable layer54 up to five feet in either direction to improve gas flow into theradon mitigation device10. A short piece of PVC pipe extends from the upward-facing opening of thePVC tee60 to be flush with the top of theslab58, passing through a hole in theflexible sheeting material56. Optionally, a second PVC tee60A may be similarly placed in the gaspermeable layer54, the upward-facing opening thereof connecting to anair inlet pipe62 which extends through the hole in theflexible sheeting material54 and to the outside of the structure to provide fresh air to the sub-slab gaspermeable layer52 as air is drawn out from below theslab58 by theradon mitigation device10 in order to maintain a positive airflow pressure. Above theradon mitigation device10,outlet PVC pipe24 is attached toexhaust pipe22 by aflexible coupling26 and extends vertically to direct the radon-contaminated air out above the roof of the structure.
• In operation, theband heaters40 provide electrical power to heat thedraft pipe30. Since thedraft pipe30 is aluminum, or another material with a high heat conductivity, thedraft pipe30 reaches a relatively uniform and stable temperature along its length. Theband heaters40 are sized appropriately to keep the temperature of thedraft pipe30 low enough that the resultant exhaust gas is not too warm to be handled by thedownstream PVC pipe24. In a preferred embodiment, oneband heater40 provides 75 watts. The advantage of such a lowwattage band heater40 is that it can remain on 100% of the time and need not be cycled on and off, thus improving the lifespan of theband heater40 and saving cost that would be incurred by the requirement for a temperature measuring and switching unit. More than oneband heater40 may be used to provide the required heating of thedraft pipe30.
• Theheated draft pipe30 creates a natural convective flow of air in the upward direction, along both the inner and outer walls thereof, at an approximate flow rate of 37 cfm. To the extent that the inside structure temperature may be warmer than the temperature of thedraft pipe30, supplemental natural convection may be gained as the air passes through theexhaust pipe24 on its way out of the structure.
• The present invention may be embodied in other specific forms without departing from the spirit or essential attributes thereof and, accordingly, the described embodiments are to be considered in all respects as being illustrative and not restrictive, with the scope of the invention being indicated by the appended claims, rather than the foregoing detailed description, as indicating the scope of the invention as well as all modifications which may fall within a range of equivalency which are also intended to be embraced therein.

Claims (7)

1. An apparatus for withdrawal of radon-contaminated air from below the slab of a structure, comprising a vertical convection duct mounted on top of the slab, an inlet duct extending downwardly through the slab from said convection duct into the gas permeable sub-slab layer of the foundation of a structure, an outlet duct extending upwardly from said convection duct passing through the interior of the structure and exiting through the roof, the improvement comprising:

a heat source disposed internally to said convection duct to heat the radon-contaminated air and create an upward convective flow of said air from the gas permeable sub-slab layer into said inlet duct, through said convection duct, and exhausting said air from said outlet duct above the roof of the structure.

2. The apparatus ofclaim 1 wherein said heat source comprises a concentrically mounted heat conductive metallic conduit disposed vertically within said convection duct and at least one heater element in thermal contact with said concentrically mounted pipe.

3. The apparatus ofclaim 2 wherein said at least one heater element is electrically powered.

4. The apparatus ofclaim 1 wherein said heat source comprises a concentrically mounted heat conductive metallic conduit disposed vertically within said convection duct to provide a uniform heat source for said radon-containing residual air causing a more uniform upward air flow within the convection duct.

5. A method for removing radon-containing residual air from beneath the slab of a structure by providing at least one opening through the slab, an inlet duct extending down through said opening beneath said convection duct into the permeable layer below the slab, an outlet duct extending from the upper outlet end of said heated convection duct, through the structure, and out the roof of the structure, the improvement comprising the steps of:

providing a vertical internally heated convection duct mounted on the slab and disposed above one of said openings through the slab, establishing a convection flow of air from the sub-slab gas permeable layer to above the roof of the structure through said inlet pipe, said internally heated convection duct, and said outlet pipe by means of a heat source mounted internally to said heated convection duct.

6. The method ofclaim 5 further comprising the additional steps of providing at least one electrically powered heater element mounted concentrically around a heat conductive metallic conduit disposed vertically within said convection duct to form said heat source and providing thermal contact between said at least one electrically powered heater element and said heat conductive metallic conduit.

7. The method ofclaim 6 further comprising the additional step of concentrically aligning said heat conductive metallic conduit, disposed in a vertical orientation within said convection duct, to provide a uniform heat source for said radon-containing residual air causing a more uniform upward air flow within the convection duct.

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