Patent Application
20050130576
Not applicable (There is no related application)
Not applicable (Invention is not a result of any sponsored research)
Not applicable (None)
The references used in the discussion of this SPECIFICATION are listed as follows:
1. Brief History of the Invention
During a cold evening in January 2003, the applicant discovered that the fireplace in his home was malfunctioning, emitting smoke into the room rather than expelling the smoke through the chimney. This has brought some concern to the applicant, and raised his curiosity as to the cause. Since that evening was unusually windy, wind was suspected as being the cause or the culprit. In the days and months following that incident, the applicant being a wind engineer who has taught wind engineering at University of Missouri-Columbia, and has written a book on the subject (see Reference 1), has been thinking about the incident, and trying to explain the phenomenon observed by using principles of fluid mechanics and wind engineering. Consequently, he has come to the realization that the reverse chimney flow that brought smoke into the room must have been induced by a low building internal pressure caused by wind. He also spent days in thinking to find a practical means to prevent such reverse chimney flow from occurring, and came up with the subject invention.
2. Operational Principles
This invention is based on the principles of building internal pressure, chimney effect, and stagnation tube, which are subjects of wind engineering, industrial aerodynamics, and fluid mechanics, respectively. Through a proper integration and utilization of these principles, which have not been done before in any prior art or practice, this invention was produced. In what follows, the three underlying principles are first reviewed briefly, and then their proper combination and utilization pertaining to the subject invention are described.
A. Building Internal Pressure
From wind engineering such as described in Reference 1, it is known that when wind blows over a building, it generates both an external pressure on the building exterior surface and an internal pressure inside the building. The external pressures on the windward wall and on the windward part of a steep roof are positive (i.e., above atmospheric or above ambient), whereas the external pressures on the side walls, leeward wall, and the roof (including flat roofs, roofs of mild slope, and the leeward part of any roof) are negative (i.e., below atmospheric or ambient). If the building has openings distributed approximately uniformly over various walls and the roof as it is usually the case, the internal pressure will be negative as explained in References 1 and 2. It is for this reason that the building internal pressure is usually negative during windy days, and the magnitude of this negative pressure (i.e., suction) increases as the square of the wind speed. This negative pressure inside buildings is detrimental to the proper operation of any type of indoor burners, which relies on the chimney to expel the combustion exhaust gases, including smoke, carbon dioxide and carbon monoxide, to the outdoor environment. The situation is especially dangerous when the combustion rate is reduced near the end of burning the last pile of wood in a fireplace at night when people were asleep. Due to the negative internal pressure or suction generated in the house or building by wind, the combustion exhaust including carbon monoxide and smoke can be sucked into the room rather than expelled outdoors through the chimney or flue. This can cause tragedy in winter time when one fails to extinguish the fire in a burner or fireplace before going to bed. Such tragedies can be prevented by controlling the internal pressure of the room in which the burner is used—making the internal pressure always positive.
This invention presents two effective and practical means to maintain a positive internal pressure needed for safe indoor combustion. The first means is to use an air pump, be it a fan, a blower or a compressor, to pump outdoor fresh air into the house, which will result in a rise of the building internal pressure. The second method is to use a specially designed stagnation tube, also called “simple pitot tube,” that is always facing the wind in order to generate a stagnation pressure at the tube inlet. The stagnation pressure in turn drives the outdoor fresh air into the pitot tube and through the connecting tubing into the room in which the burner is located.
B. Chimney Effect with and Without Wind
The “chimney effect” (also called the “stack effect”) refers to the rise of the hot buoyant gas exhaust through the chimney of a house or building—a phenomenon relied upon for proper operation of any chimney based on natural convection instead of forced (mechanical) convection. By using fluid mechanics as given in References 3, it can be proved that in the absence of wind, the flow of the exhaust gas through a chimney exists as long as the density (temperature) of the air entering the chimney is larger (smaller) than the density (temperature) of the exhaust gas leaving the chimney. However, in the presence of wind, the wind causes a negative pressure inside the building, counteracting the chimney effect in a manner analyzed and discussed in detail by Liu [4]. When the wind is sufficiently high, it generates a high negative building internal pressure, which in turn overpowers the normal chimney effect. In such a case, the exhaust gas from the burner, including carbon monoxide and smoke, cannot rise through the chimney. Rather, it flows back into the room in which the burner is located, causing a dangerous condition to the building occupants. Generally, the stronger the wind is, the greater this reverse chimney flow becomes and the greater the danger becomes. Therefore, proper control of the building int mal pressure during windy days is the key to the prevention of the dangerous reverse chimney flow, and is the salient feature of this invention.
C. Stagnation Tube
To counteract the negative internal pressure generated by wind, which is the prime culprit for causing smoke and carbon monoxide to be sucked into the room during windy days, a stagnation tube is utilized in this invention to increase the building internal pressure. The concept of stagnation tube is explained in most fluid mechanics books and hence need not be explained here. Suffice to mention that it is based on the Bernoulli equation and the fact that when a tube with an open end is pointed into a flow of fluid (gas or liquid), the velocity of the fluid at the nose of the tube (i.e., the stagnation point) is always zero, and the pressure of the fluid there rises above the ambient pressure by an amount equal to 0.5 times (multiplies) the density of the fluid and times (multiplies) the square of the free-stream velocity. By attaching a vane to a pivoted stagnation tube, in a manner similar to attaching vanes to anemometers or some windmills, the stagnation tube opening will always be facing the wind. By connecting the other end of the stagnation tube to a pipe or tubing which in turn is connected to a room in which the building occupant is staying, the internal pressure of this room and other rooms is raised. This counteracts the detrimental effect caused by low internal pressure, and prevents the release of smoke and carbon monoxide into the building.
D. Integration and Utilization of the Three Principles to Yield the Subject Invention
The subject invention represents an integration and utilization of the three principles stated above. For effective use of these principles, the opening of the stagnation tube must be always pointed into the wind (i.e., facing the wind). This requires the use of a properly designed and properly constructed stagnation tube that can rotate in a horizontal plane, having a vane attached to the stagnation tube. Furthermore, the size of the stagnation tube and the size of the conduit (tubing or pipe) used to connect the stagnation tube to the room should be sufficiently large—say, at least of 0.25-inch inner diameter. Otherwise, the system will be ineffective because it will not significantly increase the building internal pressure.
3. Alternative Invention
An alternate embodiment of this invention is to use a small air pump (i.e., a fan or a blower) to draw fresh outdoor air into the house to increase the internal pressure whenever there is a build-up of carbon monoxide or smoke indoor caused by reverse chimney flow. In the event of any reverse chimney flow, it is much better to pump fresh air into the house, such as into one or more than one bedroom in which the occupants are sleeping, in order to build-up the internal air pressure and to restore the normal upward chimney flow through the burner, than to pump the indoor air out, which would cause a further reduction in the internal pressure, drawing more burner exhaust into the house.
The air pump of the alternate embodiment is to be driven by an electric motor, which in turn is controlled by a carbon monoxide or smoke sensor or detector. Whenever the sensor or detector measures a dangerous level of carbon monoxide or smoke indoor, the detector not only sends off an alarm but also triggers the motor, which turns on the air pump. The air pump sends the outdoor fresh air into the building and raises the building internal pressure. The increased internal pressure stops the release of chimney exhaust into the building, and sends the exhaust off the building through the chimney as it should be. This counteracts the dangerous reverse chimney flow generated by wind. In the event that the high level of carbon monoxide or smoke is generated by a blocked or dogged chimney, the fan bringing fresh air into the building is still very helpful because it causes venting of the building, which drives out the carbon monoxide and replaces it with fresh air. This shows that whatever may be the cause of the indoor buildup of carbon monoxide, having the air pump bring fresh air into the building and raise the building internal pressure is always effective in solving the problem. It is more effective than having the pump operate in reverse direction (i.e., expelling indoor air) as it is normally done in venting buildings, which decreases building internal pressure and draws more exhaust into the building through the chimney. This shows the merit of this invention.
4. Salient Features of the Invention
Salient features of the subject invention include the following:
Although the invention is intended mainly for preventing indoor release of carbon monoxide and smoke resulting from indoor burners, it is also effective to a lesser degree for reducing the danger caused by building fires. In the even of any building fire, the invented device (both embodiments) causes the building internal pressure to rise, which in turn causes a portion of the smoke in the building to enter and exit through chimneys. This reduces the amount of smoke spreading inside the building. Also, since the increased internal pressure directs the internal airflow towards chimneys which act as fire and smoke sinks, spreading of the fire indoor will be retarded by using the invented device. In spite of this benefit, one should never rely on this invention as the principal means for protection against building fires. Other conventional means, such as having fire sprinklers and smoke alarms, are more effective. Therefore, this invention should be used only as a secondary means for reducing the danger against building fires. Its principal purpose is for reducing the danger of carbon monoxide and smoke generated by indoor burners.
5. Description of and Comparison with Prior Art
Existing devices and methods for reducing the danger of having carbon monoxide in buildings are generally based on the detection (measurement) of the existence of carbon dioxide in a building, and then either to trigger an alarm (e.g., Reference 5), or to activate a venting mechanism, such as opening a window or starting a exhaust fan (e.g., Reference 6). Some more complex systems do both, i.e., triggering an alarm and activating a venting mechanism (e.g., Reference 7); they offer greater protection. However, all these systems depend on the use of electricity—either batteries or the alternating electrical current (60 hertz in the United States) supplied to buildings. Those that rely on batteries would not operate when the batteries are drained, and those that rely on the ac power would not work when the electricity is cut off, such as during a blackout. In contrast, the system invented here based on stagnation tube is wind powered; it needs no electricity to function. Through a literature search and patent search, the inventor has not found any existing device or method based on this mechanism.
The alternative embodiment of this invention, which is to pump outdoor air into the bedrooms of the house whenever there is a build-up of carbon monoxide in the house, is also unique. No prior art or invention based on the same concept has been found through a literature search and a patent search. The alternative embodiment is different from ordinary carbon monoxide venting systems which use fans to pump air out of the building, rather than into the building, which is less effective because they cause a reduction in the building internal pressure and a worsening of the revers chimney flow.
The object of the invention is a new means to prevent indoor release of carbon monoxide and smoke from any indoor burner (stove, fireplace, furnace, etc.), in order to protect the building occupants from being poisoned by these dangerous exhaust gases. The invention is based on the concept of increasing the building internal pressure in order to enhance the upward movement of combustion exhaust through chimneys, and to prevent any reverse chimney flow which releases smoke and carbon monoxide into buildings. The invention contains two embodiments. The first is to use an air pump (i.e., a fan or a blower) to pump outdoor fresh air into a building whenever a dangerous level of carbon monoxide or smoke is detected indoor. The air pump must be triggered by a carbon monoxide or smoke detector or sensor. This is different from existing means to venting buildings when a high level of carbon monoxide or smoke is detected. The existing means either pumps the indoor air out of the building (rather than the outdoor air into the building), or opens a window or vent when carbon monoxide or smoke is detected. The former (i.e., the existing means) often causes a drop of the building internal pressure, which may cause a reverse chimney flow, and draws more carbon monoxide and smoke into the building from the burner. The first embodiment of this invention, on the other hand, causes the building internal pressure to rise, Thus, the first embodiment is more effective than conventional means to vent buildings by pumping indoor air out or by opening a window or vent when carbon monoxide or smoke is detected. The second embodiment uses a stagnation tube automatically oriented into the wind (i.e., facing the wind) in order to generate the stagnation pressure, which in turn forces the outdoor air into the building. As in the case of the first embodiment, use of the second embodiment results in the increase in the building internal pressure, which prevents the release of any smoke and/or carbon monoxide into the building from an indoor burner. Thus, the second embodiment has more or less the same advantage of the first embodiment over existing means. The second embodiment has the further advantage over existing means in that it is powered by wind and hence does not rely on electrical power supply or batteries. It protects the building occupants even when the power supply is failed and/or batteries are drained. These two alternative embodiments can be used either separately or jointly. When used jointly, they provide greater protection than a single system can, regardless of the cause of the carbon monoxide buildup in a building. Either of the embodiments can and should also be supplemented with a conventional carbon monoxide alarm system and/or a smoke alarm system to offer further protection to the building occupants. The greatest protection can be achieved by using both embodiments plus a carbon monoxide alarm and a smoke alarm operated by battery. In doing so, whether or not there is a blackout (power outage), or whether or not it is windy, there will always be plenty of protection for the building occupants against carbon monoxide and smoke.
The two embodiments of the current invention (both the air pump system and th stagnation tube system) are a method and device (system) to increase the building internal pressure during windy time and/or when the indoor concentration of carbon monoxide is high for whatever reasons. Both systems work by increasing the internal pressure of the building in which a burner is used, so that the exhaust of the indoor burner containing carbon monoxide and smoke will be vented out through the chimney rather than being released into the building, thereby preventing the accumulation of carbon monoxide indoor. The only difference between the two embodiments is the way that internal pressure increase is achieved. While the air pump system relies on the actuation of an air pump to draw fresh air into the building and to enhance the building internal pressure, the other embodiment uses a stagnation tube that orients itself into the wind (facing the wind) in order to accomplish the same. The operation of the two alternate systems (embodiments) will now be described one by one in detail with reference to the nine figures provided.
1. The Air Pump System (Embodiment 1)
The air pump system, hereafter also referred to simply as “the system,” or “embodiment 1,” is illustrated by
The conduit, 4, can be mad of a number of materials, such as steel, copper, or plastic. It can be either rigid or flexible. When using rigid conduits, bends or elbows will be needed at locations of the change of direction. When using flexible conduits or tubing, one should make sure that the tubing will not kink or collapse to restrict the air flow. The conduit must be sized according to the length required and the needed air flow rate, using standard calculation methods in fluid mechanics, or in piping handbooks. It can also be standardized for buildings of various sizes. When multiple conduits are used to connect a single air inlet to various rooms, the conduits can be connected through a manifold. The air pump, 3, can either be a fan or blower, depending on the air flow rate and the pressure required. Usually, a fan is for low pressure but high flow rate, whereas a blower generates higher pressure but lower flow rate than a fan. Use of a compressor will be inappropriate because the compressor is for high pressure and low flow rate, a situation unlike that encountered by air flow through buildings. An engineer or technician with knowledge in sizing venting systems and selecting the size and the type of air pumps is required to determine the appropriate components of any given system. They will depend on the building size, the permeability of the building, and the length and size of the conduit or connecting tubing.
A typical operation of the foregoing system (embodiment 1) is described as follows. As soon as a conventional carbon monoxide alarm mounted in a building has been set off by the presence of a high concentration of carbon monoxide over a significant period, such as 100 parts per million over a period of ten minutes, depending on the type of alarm used, the device sends out an electric, electromagnetic, or acoustic signal to a detector (receiver) of such signal connected to the air pump. In lieu of a carbon monoxide alarm, a smoke alarm may also be used in the same manner. The detector turns on a switch which starts the air pump. Because the control valve, item 2D in
This invention follows an accidental discovery and a great deal of subsequent scientific analysis conducted by the applicant, as described in Brief History of the Invention. The invention had not been obvious even to the applicant, who is an expert in fluid mechanics and wind engineering, until recently through the discovery and the scientific analysis presented in Reference 4 and in this invention. As with other engineering devices, successful use of this invented means and system requires proper maintenance of the system. Not only should the system shown in
2. The Stagnation Tube System (Embodiment 2)
Referring first to
Not shown in
The stagnation tube system also may work without any restrainer, especially if the rotating probe is made of steel or another heavy material. In such a case, the weight of the rotating probe may be sufficient to resist the uplift generated by high winds. Thus, whether to include a restrainer or not is a matter of consideration for each individual system design, depending on the probe materials used and the size of the probe. Generally, larger and heavier systems may not need the restraining mechanism, and vise versa.
The connecting tubing, part 6 shown in
In
To operate the stagnation tube system (i.e., embodiment 2), all what one needs to do is to make sure that the valve(s) is (are) open whenever the burner is on. On a highly windy day, one may want to adjust the control valve somewhat so the air flow (draft) entering the room is not excessive. This can be done manually. To control the valves automatically will require sophisticated electronics, such as transducers and a PLC (programmable logic controller), and will require the use of a motor-driven control valve, and a solenoid driven on-off valve. Doing so will not only increase the cost significantly, it will also make the system to rely on electric power, which would render the system inoperative when there is an interruption of the electric power such as caused by a power failure. For these reasons, manual operation of valve(s) is recommended here, which is rather easy to do for this system that requires only infrequent closure and opening of valves. For the maintenance of a stagnation tube system, one should conduct periodic visual checks of the parts above the roof to make sure that they are not damaged by wind, rain, hail or birds. One must also make sure that the tubing is not dogged. This can be done by connecting an inflated balloon to the outlet, and to see if the balloon deflates quickly. If so, the line is not clogged. Clogged lines can be cleared by hooking the outlet to a small compressor such as that used in household for pumping bicycle tires and car tires. The compressor will clear the lines rapidly.
The above detailed description illustrates the invented method—how it can be designed, constructed, installed, used and maintained, and how it achieves the stated purpose of increasing the building internal pressure when wind is blowing outside, so that smoke and dangerous exhaust gases including carbon monoxide can be expelled through the chimney. There can be many alternative designs of the various parts as described herein without departing from the scope of this invention. Therefore, the above detailed description and the nine drawings shall be interpreted as being illustrative and not limiting.
