Egg-Crate Germicidal Ultraviolet - named after the "egg crate" ceiling tiles used - is a powerful, inexpensive and safe way to combat infectious bioaerosols that can be DIY'd with parts available at your local hardware store.
222nm Far-UVC is a new, safe, and effective way to eliminate harmful airborne pathogens, but as hard as we're working here at Nukit to bring the cost down, it's still very expensive.
Fortunately, Far-UVC is not necessary for all applications. One of the best alternatives is Egg-Crate GUV. It's very safe, very powerful, and usually cheaper than almost anything else. If you already have a drop ceiling, it can often be installed in a day with parts you can get at the hardware store. The result is a high level of protection from almost any infectious bioaerosol for a monthly operating cost of less than a cup of coffee.
Click the above image, wait for the 3D model to load then click and drag to move it, pinch to zoom. Notice that you cannot see the UV lights on the wall from the lower portion of the room as the egg-crate grid acts as louvers and blocks them. Note: UV fixture size and number are exaggerated for clarity.
Egg-Crate GUV is a form of Upper-Room GUV (Germicidal Ultraviolet), a powerful tool against airborne pathogens that we have written about before on this blog. Upper-Room GUV typically uses 254nm UVC (the type of UV that is not safe for the eyes or skin), but only in the upper part of the room, over people's heads. It is ideal for large rooms with high ceilings.
Although Upper-Room GUV is typically much less expensive than mechanical filtration of equivalent performance against pathogens, at about $1000 per fixture and starting at least that much for installation, it is still quite an up-front investment-although once installed, the cost is only a few dollars for electricity and replacement bulbs once a year.
There is another option - more powerful than traditional Upper-Room GUV, safer, cheaper to install and operate, and requires no special parts or fixtures - just a UVC meter. This option is called Egg-Crate GUV, after the egg-crate grid ceiling tiles it uses.
What Egg-Crate GUV does is take advantage of common, inexpensive suspended ceiling hardware - either pre-existing or newly installed. This can be done inexpensively by virtually any general contractor with standard hardware store parts and no special skills required.
Once the grid is hung, instead of using traditional solid tiles, egg-crate tiles are used in the center of the room, with a perimeter of solid tiles around the outside.
Fluorescent fixtures are then mounted on the wall above the ceiling:
This means that UV lights placed just above the solid tiles will only illuminate the upper part of the room - but since the UV light cannot make a right-angle turn, the egg-crate grating acts as a louver to contain the light and prevents it from entering the lower part of the room. All this while still allowing air to pass freely through the grille between the upper and lower parts of the room and be continuously disinfected.
Typically, ceiling fans are placed above or through the egg-crate panels to provide good air circulation between the top and bottom of the room and rapid disinfection of the entire room. This also provides some mitigation of near-field transmission through destratification (preventing exhaled aerosols from moving on a lateral plane to be inhaled by other room occupants by pulling them up into the UV field).
Parts list for Egg-Crate GUV:
Grid and hangers- Home Depot
Matte black paint- Home Depot
Black solid ceiling tiles- Home Depot, Amazon, ISCSupply
Black egg-crate ceiling tiles- Amazon (plastic), ISCSupply (plastic), 1800Ceiling (aluminum)
Ceiling fan- Home Depot, Amazon, 1800Ceiling (the more fans, the better)
Ceiling fan mount- Home Depot, Amazon
Or, if the drop ceiling is very low with little clearance above it, a flush drop-in ceiling fan- Home Depot, Amazon
Mercury vapor bulbs are being phased out, but UVC LEDs are not really cost-effective for their output yet, so you may have some trouble finding matching UVC fluorescent bulbs and fixtures in stores - although they are usually easy to find online. It doesn't really matter what size you use as long as the total wattage is correct, they are "ozone-free 254nm" and the UV leakage into the lower part of the room is below the daily limit.
8w germicidal lamp + fixture- Amazon
-OR-
15w 18in T8 germicidal lamp- Home Depot, Bulbs.com
15w 18in T8 fluorescent fixture- BuyLightFixtures.com, Spectrum Hulett, Lighting Design, Amazon (remove cover)
-OR-
25w 3ft T8 germicidal lamp- Home Depot, Bulbs.com
25w 3ft T8 fluorescent fixture- Bulb Wizards
The UV meter required for safe installation isn't cheap, but it costs less than an upper-room GUV fixture, and it's a one-time expense that quickly pays for itself with multiple installations. If you have a Mask Bloc, you can certainly train a few members to use the meter properly to verify safe GUV deployment with Egg-Crate GUV.
Hopoocolor HPL220UV-254 (230-280nm) UVC meter- Aliexpress
(There are cheaper ones, but they either don't measure UVC or don't have sufficient resolution for our purposes. The HPL220UV-254 is about as inexpensive as it gets and still does what we need it to).
How much UVC:
How much UVC wattage you can put into the upper room depends mainly on the quality of your suspended ceiling installation. If there are gaps in the ceiling grid, or if there are reflective spots - you'll get a lot of UV leakage from the upper room to the lower room. With a little experience, the better your drop ceiling, the more UV wattage you can use and the greater the effect.
A good rule of thumb to start with for egg-crate GUV is 0.5 watts of UVC mercury vapor lamp per square meter of room size. So if your room is 5m x 15m, or 75 square meters, that's 37 watts. Two 15-watt UVC fixtures or four 8-watt UVC fixtures on opposite walls would be a very good place to start. Add or remove fixtures at evenly spaced intervals depending on how much UV leakage you are getting into the lower room.
Measuring the room:
Traditional Upper-Room GUV installations are more challenging and should be left to those with specialized training (although it can be learned quickly). Egg-crate GUV installation is on par with working with mains (AC) wiring. If you are careful, educate yourself first, and use the proper tools, it can be done safely by a meticulous do-it-yourselfer or general contractor.
Of course, there are those who disagree, just as there are those who believe that non-professionals should never do electrical work, plumbing, or cut down trees. GUV and UVC have killed or permanently injured exactly zero people in the last 100 years, so it is a far safer DIY activity than most things people do with power tools on the weekend.
That said- the UVC fluorescent (mercury vapor) tubes should be kept off-premises or locked up until the installation is finished. Workers may decide to test the lights and grab what's handy- not knowing they are dealing with UVC, particularly considering labeling and language barriers. All initial and electrical testing should be done with standard white fluorescent tubes. It's too easy to leave UVC lamps on for "just a minute" while you fix something and cause painful eye or skin irritation. No one can hurt themselves with UVC if UVC is not even in the building.
Once the ceiling is painted matte black, the fluorescent fixtures are mounted and wired to the walls, the drop ceiling grid is installed, the white lights should be placed in the wall fixtures. Then put all the ceiling tiles in place, solid on the outside, egg-crate on the inside, turn on the white lights above the ceiling, and turn off all the other lights in the room. We use the white light to simulate UV so we can look for leaks and reflections.
If from anywhere in the room, high or low, you can see the white tubes themselves (not their reflection, but the actual fluorescent bulb) through the egg-crate grid, then additional solid panels are needed around the perimeter. If you can see white light through gaps in the grid, seal them with tape or silicone caulk before replacing the white fluorescent bulbs with UVC bulbs. Anywhere that white light seems to be strongly reflected down into the room, mark it, it is likely that the UV will also be reflected down.
Generally, no modifications or extra sealing is needed- a regular dropped ceiling does a very good job of keeping the UV light in. But, you always have to check.
Once you are sure, turn the white lights off, replace them with the UV lights. Only after you have closed the dropped ceiling back up should you turn the UV lights on. At this point, simple UV protective glasses are sufficient while you take measurements. The white light would have shown any significant leakage into the lower room.
Divide the room into a 1m x 1m grid; spots of masking tape on the floor work well, as you can also write your measurements for that spot on them. With your UV meter on a pole or tripod (a zip tie or rubber band works well), measure the UV output at 6 feet (1.83 m) from the floor.
UVC leakage from the ceiling to the lower part of the room should not exceed 0.2 µW/cm2 and ideally be well below 0.1 µW/cm2.
A little matte black paint on shiny ductwork and a few extra solid tiles in place of the egg crate where levels are high will ensure that the lower part of the room has UV levels almost indistinguishable from those in an untreated room. As a last resort, you can use thicker egg-crate tiles or reduce the amount of UV in the upper part of the room and, thus, the lower part by disconnecting one or more of the UV fixtures - but this is rarely necessary once you get the hang of it.
Remember, a public space with Egg-Crate GUV will be the safest in the neighborhood and ideal for a field hospital or quarantine in the event of an emergency. Make sure your space is safe no matter what it is used for.
Take the time, do it right, double check your grid, get the lower room µW/cm2 numbers down while keeping the upper room high, and you'll be saving lives and preventing disease for many years at very low cost and with little maintenance.
Examples:
5 Point Cafe, Seatle, Washington
Marlaina's Mediterranean Kitchen, Burien, Washington- Media
References:
Eggcrate UV: a whole ceiling upper-room ultraviolet germicida irradiation system for air disinfection in occupied spaces
Bare-bulb Upper-Room Germicidal Ultraviolet-C (GUV) Indoor Air Disinfection for COVID-19
Influence of Bioaerosol Source Location and Ceiling Fan Direction on Eggcrate Upper-room Ultraviolet Germicidal Irradiation