Patent Application
20090053664
1. Field of the Invention
The present invention relates to an apparatus for heating a relatively open outdoor space such as a patio. More particularly the invention relates to a catalytic heater which provides for a high proportion of radiant heat per unit of fuel consumed. More particularly the invention relates to a vertically oriented heater which radiates heat to users from the face down to about the knees.
2. Related Information
In outdoor environments where wind can divert convected heat a heater which produces radiant energy is essential. Conventional patio heaters are based upon open flame combustion heating a porous metal structure which radiates heat. Typically the burner is positioned at the top of a pole which is mounted on a base which may or may not house a fuel tank. The burner and radiating metal structure are covered by a dome which protects the burner from the weather and reflects energy from the burner downward to the patio.
The conventional patio heaters have several disadvantages. First, the radiant heat from the glowing metal has a wave length of from 1-3 microns, which is not especially useful for warming cloth or flesh. Second, the heat is generated at a height and must be directed downward which results in a warm head but a cold body—the heat patterns are not uniform. Thirdly, much of the heat is in the form of convected heat (hot air) rather than radiant heat and is lost due to heat rising from the burner and is thus rendered useless for heating.
The conventional catalytic heater comprises a container with four walls and a back with an open front. The open box thus formed is filled with a spacer to create an open volume next to the back. This spacer is made from a porous metal to allow gas permeability. Next a layer of dense ceramic fiber mat is inserted which acts as a thermal insulator and flow distributor. Finally, a low-density ceramic fiber mat which has been coated with platinum is inserted. The contents are held in the box using a wire mesh with large holes. Fuel gas is delivered from an orifice and a fitting on the back of the heater. The fuel fills the cavity and diffuses through the ceramic fiber pad and the platinum coated pad. Air contacts the gas in the pad or at its outer surface. If the outer surface is heated to the temperature required for catalytic ignition the fuel and air mixture will combust flamelessly.
In the conventional catalytic heater the air and fuel are not pre-mixed. However systems wherein some air is pre-mixed (10-20% of the theoretical air) are disclosed in U.S. Pat. Nos. 5,037,293 and 6,470,874
The catalyst in catalytic heaters must be heated to about 250° C. to get catalytic ignition. An electrical heater is typically embedded in the catalytic layer in order to provide the heat for ignition. The ignition starts near the electrical heater and eventually spreads after the catalyst has ignited. The time required for steady state can be long, on the order of ten to twenty minutes. In the case where the fuel and air are pre-mixed and electrical discharge may be used for ignition.
Catalytic heaters in general produce much more radiant energy per unit of fuel consumed and furthermore, the radiant energy is in the wave length of between 1-10 microns, which is the most useful for heating clothing and flesh. The prior catalytic heaters have several disadvantages when used as patio heaters. First, the flat surface directs the heat in only one direction. Second, the time to get to temperature is too long. Third, extensive use of stainless steel or other metal to contain the heater results in high cost and weight. Forth, there is significant heat loss from the rear of the heater.
The object of the present invention is to offer a new and enhanced patio heater which will more efficiently heat a three dimensional volume with lower fuel cost and lower emissions of smog producing chemicals.
Broadly the present invention is a patio heater comprising a cylindrical catalytic heating chamber vertically mounted on a base. Preferably the catalytic heating chamber is comprised of a low density ceramic pad coated with a highly dispersed oxidation catalyst; a high density ceramic insulating pad; wherein the low density ceramic pad and the high density ceramic pad are rolled together to form a cylinder around the outer surface of a perforated metal cylinder to form a fuel chamber with the high density ceramic pad being located between said low density ceramic pad and the perforated metal cylinder; a cylindrical sleeve around the catalytic heating chamber, said sleeve being formed from expanded metal and having openings of from one-quarter square inch to five square inches with a total open area of from 50% to 90%; and caps covering either end of said catalytic heating chamber, overlapping said sleeve and sealing said fuel chamber. In a preferred embodiment an expanded metal cylinder spaced away from and around said catalytic heating chamber forms a vapor cavity annular to said catalytic heating chamber with the vapor cavity being from one-half inch to two inches in diameter outside the catalytic heating chamber.
Among the features of the patio heater of the present invention there is a base to physically support a cylindrical catalytic heating chamber which is mounted inside a fuel vapor cavity. The catalytic heating chamber provides a cylindrical heating zone capable of heating a nearby human form the knee to the face. A fuel vapor compartment surrounds the catalytic heating chamber and acts to accumulate sufficient fuel and air mixture to ignite to provide uniform and sufficient heat to the catalyst surface to attain catalytic ignition. The base offers physical stability for the assembly and storage space for a fuel tank. In addition the base also houses the fuel delivery system and ignitor controls.
For a detailed description of one embodiment of the invention the reader is directed to the accompanying figures in which like components are given like numerals for ease of reference.
Referring first to
Referring now to
In the embodiment shown, a fuel chamber 100 for air and fuel is produced by forming a vapor cavity 100 for the catalytic heating chamber 110. The catalytic heating chamber is centered on the base 19 and surrounded by the protective screen 1 and the cap 22 to form an annular space 103 around the surface of the catalytic heating chamber 110 and is held to catalytic heating chamber by nuts 28 and 29 on bolt 25. When the fuel diffuses through the catalyst, it blends with air in this cavity. When the mixture of the fuel and air are ignited, the heat generated in this cavity is sufficient to raise the temperature of the catalyst pads 6 and 7 high enough (250° C.) to light off catalytic (flameless) combustion. The annulus dimensions between spacer cylinder 102 and the perforated cylinder 10 should be between one-half and two inches in diameter since it is essential to have sufficient fuel of the heat required.
The fuel distribution system comprises one or more tubes 101 connected to the manifold assembly 16 which is connected to the propane bottle. As shown, the tube 101 extends through the spaced cylinder 102 into the fuel chamber 100 of the catalytic heating chamber. The end of the tube contains a precision orifice sized to deliver between 5,000 BTU/hr to 80,000 BTU/hr when using natural gas (methane), propane, butane or mixtures thereof. An fuel igniter 104 located in the pilot light assembly 18 is provided to heat the catalytic pad 6 to auto ignition temperature of the fuel in the fuel chamber. More detail of the fuel manifold 16 is shown in
In an alternate embodiment a thin electrical heating wire (not shown) is wrapped around the insulating pad 7. The electrical heating wire is connected to a battery-operated circuit which has a control system and sensing element for the temperature of the catalyst pad. The heating pad is operated with the initial flow of gas but is shut off automatically when the temperature on the pad reaches catalytic heating ignition requirements.
Overall the surface temperature of the catalytic heating element can reach from between 500° F. and 1100° F., but the outside surface of the protective screen 1 is less than 120° F. The radiant energy produced has a wave length of between 1 and 15 microns.
