Rapidly Deployable System to Suppress Airborne Epidemics

Abstract

This patent presents a method, and some devices based on the method, to achieve near zero air based transmission of disease within a business, while still allowing people to approach each other closer than arms length touching distance. This can be achieved with rapidly deployable portable units. It also presents a simple method to test whether the airflow structure requirements of the system have been met, and to adjust it if not.

Claims

1. A method whereby a business can significantly reduce airborne spread, where: a pool of clean air is created above its patrons, and air is drawn from this pool in a near laminar manner thru space occupied by patrons, and air is removed from the patron space via exhaust ports located below where heads are expected to be, and the flow around each patron is sufficient to prevent exhalations from one patron reaching another patron's mouth or nose.

2. The method of claim 1, where: people facing others are separated from them by a barrier dropping at least to neck level.

3. A simple method to test whether an installation meets airflow requirements of claim 1, where: A wall is covered with black sheets, and Smoke generators are hung where patron's heads are expected to be located, and The system is run for sufficient time, then the smoke generators are started, and The room is observed with black background and side illumination, and No smoke is visible, except directly below a smoke generator, plus leading from there to a nearby exhaust port.

4. A one pass system implementing the method of claim 1 where: the pool is created by fans and ductwork bringing in clean outside air, and has a diffuser that blocks turbulence within the pool from reaching into the patron space and starts the laminar flow in the patron space, and has one or more appropriately placed exhaust ports sufficiently below patron heads that collect air from the patron space and vent it to the outside.

5. A recirculating system implementing the method of claim 1 where: the pool is created from air that has been cleaned, and Has a diffuser that blocks turbulence within the pool from reaching into the patron space and starts the near laminar flow into the patron space, and Has one or more exhaust ports sufficiently below patron heads that collect air from the patron space and deliver it to one or more cleaning systems, and The cleaning systems are good enough to remove smoke and live pathogen, and The clean air output of the cleaning system is delivered to the clean pool.

6. A method to convert an existing air conditioning system with overhead recirculation intakes into the system of claim 5 where: The diffusers are replaced with ones designed not to cause turbulence near patrons, and The filters are replaced with ones effective enough to remove smoke and pathogen, and Ducts are fitted to the air intakes to bring floor level air to the intakes.

7. the system of claim 5 where: The exhaust port, filters, sterilizing system, fans, and a duct rising up to deliver clean air to the pool are combined into a floor standing unit.

8. the system of claim 5 where: The exhaust port, cleaning system, fans, and a duct bringing up air from exhaust port level to the clean pool are combined into a ceiling hung device.

9. the system of claim 5 where: The exhaust ports, filter, sterilizing system, and fans are combined into a unit, and One or more such units are placed along a line along a wall, and The duct returning air to the pool is created by a false wall attached to those devices and the real wall adjacent to the line.

10. the system of claim 5 where: The exhaust ports, cleaning systems, and fans are combined into a unit, and One or more such units are placed along a line within the space, and The duct returning air to the pool is constructed using two false walls on either side of the line.

11. An improvement to a commuter train carriage or plane, where: The device of claim 9 is installed against the side wall(s) of the carriage or plane.

12. (canceled)

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0033] FIG. 1 shows the components of a system implementing this invention. The business first creates a pool (1) of “clean” (free of live pathogens) and conditioned air above the heads of its patrons. This point (or before) is where mixing should take place. Air is then drawn down from this pool to the space (3) occupied by patrons (4) through a diffuser (2) that blocks turbulence in the pool from entering the patron space (3). The goal is to create a flow in the patron space (3) above patron (4) heads that is essentially laminar with very little or no mixing. Sufficiently below patron heads, air is removed from the patron space by one or more appropriately placed exhaust ports (5). If outside air is considered “clean” enough and it is economic to do so, the pool can be filled with outside air without any treatment other than normal air conditioning (6). This is what we would use for commuter vehicles, or for densely packed situations like nightclubs.

[0034] FIG. 2 shows a cleaning/recirculating unit when recirculation is needed. An intake port (7) near floor level, which is a form of the exhaust port (5) of FIG. 1, leads to a filter (8), followed by a sterilization section (9), if necessary. A fan (10) placed anywhere in the airstream pumps the air through the cleaning system to an output port (11) which is located in the clean pool (1) of FIG. 1. In this invention this unit is intended to normally be constructed as a “portable” device that can be deployed when conditions warrant.

DETAILED DESCRIPTION OF THE INVENTION

[0035] In the method contemplated by this invention each patron (4) breathes in “clean” air that comes down from the pool (1). The potentially contaminated air they exhale is entrained by the flow, taking it below their heads and thus preventing re-breathing of the possible contaminants by other patrons. The diffuser acts to evenly distribute the air from the clean pool over the patron space, and to prevent any eddies that would cause one patron to breathe unfiltered air exhaled by another patron. It can be as simple as a cloth screen between the pool and patron space. Even adequate distance between the ports that bring air into the clean pool and the patron space can act as the diffuser. Note that diffusers in standard ventilation practice are usually designed to enhance mixing—the opposite of what we want to do here! Even without any recirculation and using the ASHRAE “people outdoor air rate”, each patron in this airflow will be breathing air that will be cleaner than that provided by a “well mixed” room.

[0036] Downward flow is best for most situations. Gravity pulls down large particles, and the airflow pulls down small particles. However for a situation like people on a choir stand you want the flow to be perpendicular to the average plane of heads, and/or have a physical barrier to prevent the throw of droplets by people in back rows over the heads of the people in front of them. Note that with the recommended airflow, face gear that directs exhalations downward instead of over the front row is a sufficient physical barrier.

[0037] A downward speed of 3 inches per second should be sufficient to prevent exhaled air from a calm seated person reaching the mouth or nose of another person 2 feet (or more) away. This is close enough for people to reach out and touch each other. The ambient cross/downward flow is extremely important. Without an ambient flow there is mathematically no limit to the range of an exhalation. This is especially true given the possibility of ring vortices being generated by a cough. It has been demonstrated that in still air a cough or sneeze could spread contaminants up to 22 ft away. This range is reduced if there is a cross flow that overwhelms and sweeps away the eddies caused by a cough—essentially the range where the energy of the cough results in eddy velocities less than that of the cross flow. Where a person can be facing another, ballistic distribution of larger drops is a problem; so a physical barrier can be installed between them that at least drops below neck level, and an exhaust port can be located close to the bottom edge of the barrier. With the recommended downward flow, face gear on a person that directs exhalations downward would be quite effective as this physical barrier. Generally it does not need to cover the nose when there is an ambient downward flow, as emanations from the nose are also directed downward, and tend to fill the space emptied by the reduced chest and abdominal volume generating the exhalation. Another advantage of face gear covering the mouth is that it will reduce the frequency at which a person touches their own mouth, reducing transmission via contact. A fast moving sheet of down flowing air can also act as a physical barrier. This will allow people to see each other, and to even hold hands under the barrier. If the patrons in the establishment are expected to be more active, the down flow speed should be increased.

[0038] The filter needs to be able to eliminate particles large enough to show a laser beam, like smoke particles. Ideally, it would also clear the target pathogens from the air stream flowing through it, making the sterilization section unnecessary. The CDC says the SARS-Cov-2 virus mostly transmits via respiratory droplets, which are about 5 μl, but the virus itself is estimated to be 60-140 nm. A regular high grade filter available at retail should be good enough to suppress droplet based transmission. However, if the health authorities decide live airborne virus needs to be removed, we would need a ULPA grade filter, turning the patron space (3) almost into a laminar flow clean room. Or we can use a sterilization section to kill pathogen that gets past the filter.

[0039] There is no need to rebuild the air handling system of an establishment to achieve these goals. The cleaning system can be packaged with ductwork leading from ground level to ceiling level as a portable recirculation unit. For example, one can package a HEPA filter, a fan, and a duct leading up to ceiling level into a single floor standing portable device that cleans and recycles air. A weight near the bottom of the unit can be used to stabilize the device. Or one can hang such a combination from the ceiling, and that reaches down to a table, around which people meet. Or one can place units that contain the filter and a fan on the floor along a wall, and then install a false wall making the space between the false wall and the real wall the recirculation duct. This is particularly useful in a commuter train or bus. UV lights in the recirculation duct could make it a sterilization section too. Or one can place the units containing the filter and fan in a line in the middle of the establishment space, with two false walls on either side of the line, and the space between the false walls becomes the recirculation duct. These portable systems can be designed to carry advertising or decorative features on the recirculation duct, making them fit into the decor of the establishment. The only thing that will usually be necessary to retrofit in an existing air handling system is to install/replace a diffuser to defeat the mixing within the patron space that is designed into most air conditioning systems. If the existing air conditioning recirculation intake is near the ceiling, a simple floor standing (or hanging) duct can bring air up from floor level to the intake. One needs to ensure that there are enough recirculation units to generate an adequate downward flow everywhere in the patron space. For example, if the patron space measured 900 square feet (30′×30′), and the required downward flow velocity was 3″/second, then the total upward flow in the portable units must be at least 225 cubic ft/second. If the upward flow in the units was 9 ft/second, the total floor area of the units would be 25 sq ft. The ability to reposition the recirculation units, and/or to adjust the airflow in them, gives the business a measure of control over the laminar airflow within the patron space.

[0040] This system also suggests an improvement to home air purifiers that boosts the speed at which they can clean air in a room. Home air purifiers are generally floor or table top units that suck in room air, clean it, and eject the clean air back into the room at approximately the same position, thus mixing it with the remaining dirty air. They have to move multiple times the room volume through the device to achieve a certain level of purification through progressive dilution, and that is never complete. However, if we attach a duct so that the clean air is delivered at the diagonally opposite corner of the room from the intake (and achieve zero mixing and even flow), then only one room volume needs to be moved through the purifier to perfectly clean the air in the room.

[0041] One consideration when using UV light to kill pathogens is the total hold time of air illuminated with UV light. That can be traded against UV intensity. Hold time is correlated with hold volume. If one has high ceilings, this is easy to achieve, as in the “upper room UV” concept used in the 1940s. One can also use half of the business space as pathogen kill space, or use a neighboring closed business as the kill space. In the case of underground commuter rail, the tunnel between stations can be the kill space. Another thing to consider using UV is the mutagenicity of the pathogen; if the sterilization is imperfect, the UV radiation is likely to speed up the mutation rate. UV radiation can be carcinogenic, so one must avoid exposing patrons.

[0042] A big reason for not using laminar air flow designs is the uncertainty of whether a specific implementation is sufficiently good, or actually achieves the desired laminarity. This is typically determined using a computer simulation of the airflow in the space—something that is beyond the typical capability of the average small business. Also, the simulation may not include small details in high KE parts of the airflow, and so may be fatally incorrect. [This is less of an issue if the high KE parts are near the exhaust ports.] So this patent also presents a simple method to test whether an implementation is good enough. The method is as follows:—Cover a wall with black, non-reflective sheets. Install smoke generators (like a burning incense stick) at approximately the positions where patron's heads would be. Run the system for a few minutes, and then turn on the smoke generators. Observe with the smoke trails between you and the black sheeting. There should not be smoke visible anywhere except below the smoke generators, and trails leading down from them to a nearby exhaust port. After running this setup for a while, test the clean pool for contamination, and the space between smoke generators for diffuse smoke. Note that since many incense sticks are usually designed to be “smokeless” once their output has diffused, they are not appropriate smoke generators for diffuse smoke tests.

[0043] Note that this test does NOT confirm that the air is pathogen free, as those particles may be too small to be visible. It only confirms the airflow structure is proper. This simple method can be used by health inspectors and the business to determine whether they have properly implemented the airflow. They will still need to inspect the output from the filters and sterilization system. This method can also be used by the establishment to tune the airflow in and placement of the various recirculation units so the proper airflow is achieved in the patron space.

[0044] Restaurants using this system should be aware that plating will be very important, since flavors will be undetectable until food is actually placed in the patron's mouth. Similarly, bars should realize an individual's pheromones will undetectable until there is actual contact.