Introduction to Upper Room GUV

"Dogs are always going to come up short if you insist on defining them as a weird kind of cat."

Peter Watts- Echopraxia

What is Upper-Room UVGI?

Germicidal Ultraviolet (GUV) development dates back to 1878, when Arthur Downes and Thomas Blunt discovered that sunlight hindered microbial growth. Since then, researchers have been trying to harness the power of ultraviolet as a sanitizing agent against pathogens without harming people, plants, or animals.

Today, we have Far-UVC, an eye and skin-safe form of GUV. However, despite Nukit’s best efforts to lower prices, it is often prohibitively expensive for large spaces.

Fortunately, there is Upper-Room UVGI (UltraViolet Germicidal Irradiation is used interchangeably with Germicidal UltraViolet)- one of the oldest, most effective forms of GUV dating from 1937 when Wells et al. used Upper-Room UVGI to prevent the epidemic spread of measles in suburban Philadelphia classrooms.

The "Upper-Room" designation refers to the placement of special fixtures at ceiling height or just below, where they create a disinfection zone. This approach minimizes UV exposure to occupants in the lower-room space, ensuring safety while effectively reducing airborne pathogens.

The UVC light in the upper part of the room inactivates microorganisms such as bacteria, viruses, and fungi by damaging their DNA or RNA, rendering them incapable of reproduction and infection.

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 because the louvers on each fixture blocks direct the light upwards.

Air circulates between the upper and lower rooms, either naturally or through mechanical means, bringing pathogens into the upper zone, where they are inactivated by UVC light. This effectively reduces the concentration of airborne microorganisms in the room without exposing occupants to direct UVC light, ensuring safety.

To do this, specialized fixtures are used:

These fixtures contain a UVC light source (usually 254nm mercury vapor, although a few 260-280nm LED fixtures have entered the market) and a means of directing that light so it stays well above the room's occupants.

To ensure safety, upper-room UVGI is usually installed only with high ceilings. After installation, each part of the lower room is carefully measured to ensure that no dangerous UVC bounces down from reflective ductwork or light fixtures.

How much does Upper-Room UVGI cost?

Upper-Room UVGI is somewhat labor-intensive to install, but once completed, it is by far the cheapest and most effective way to eliminate airborne pathogens from very large rooms such as gymnasiums, auditoriums, and other public spaces.

Although Upper-Room UVGI is much less expensive than filtration or Far-UVC for the same level of effectiveness, at $1000-$2000 per unit, and at least that much for professional installation, it is still quite an upfront investment. However, once installed, electricity and replacement bulbs cost only a few dollars a year.

There are options for institutions and municipalities to lower that cost- small-scale fabrication of Open-Source Upper-Room UVGI fixtures. These fixtures can be made in almost any wood or sheetmetal shop equipped with a laser or plasma cutter:

There are even parametic designs that can be customized for different spaces and 3D printed:

The drawback to these is that they do not come with the relevant required certifications or data sheets- although getting those certifications could be cost-effective depending on how many units you are making.

Types of Upper-Room UVGI

Upper-Room UVGI fixtures can be loosely broken down into two types- Louvered and Open.

Below Left- Louvered UVGI for low (8-9 ft or 2.4-2.7 m) ceilings

Below Right- Open UVGI for high (>9 ft or >2.7 m) ceilings

Open fixtures generally have a higher level of UV output into the room per input watt and a far larger field of inactivation. Louvered fixtures are less effective, but much safer, easier to install, and can be used with lower ceilings.

A highly effective compromise exists between the two—Egg-Crate GUV—which will be covered in a later article. For most modern Upper-Room UVGI installations, louvered fixtures are the best choice.

LED Upper-Room UVGI

Nukit Upper-Room LED-UVGI test unit.

UVC LEDs are still quite expensive, run hot, and are short-lived, but they show a great deal of potential. One advantage is very little light is wasted outside the target portion of the UV spectrum- so almost no bleed into the visible spectrum. The other is that with a built-in lens, the LEDs can have a very narrow field of irradiation, so they don't need louvers or a reflector - and none of the light is lost inside an enclosure.

How is Upper-Room UVGI installed?

Upper-Room UVGI requires some specialized training and is not suitable for novice Do-It-Yourselfers. However, this training can be completed in a day or two, so should it become more popular, it will not be a substantial hurdle to Upper-Room UVGI deployment at scale. For now, it can be challenging to find trained installers, particularly outside large urban areas.

Typically, Upper-Room UVGI is specified for installation in one of two ways. The first way, usually employed for a few rooms in existing construction, is a simple formula that has proven to usually, be close to optimal. For effective inactivation of airborne pathogens, either 1.87 W per m2 of floor area or 6 W per m3 of irradiated-zone volume, where W refers to watts of UV emission rate of the lamps, not the fixtures. (The emission rate of UV lamps is roughly 30% of the lamp’s electrical input).

A fixture installed according to this rule of thumb will require careful testing to ensure safety and may have to be moved to a more optimal location in the room, but it’s proven to be quite effective.

The second way is to do a full site assessment, take room dimensions, air circulation patterns, and occupancy levels, and then use precise measurements of the fixture’s output and specialized CAD software to optimize lamp placement and safety in software.

This method is far more precise and ideal when you have a floor plan and intend to install many units- like in a hospital or other semi-public space. Or when they will be in a space where rooms are duplicated, the installation can be appropriately designed for one room, which can then be transferred to others.

In order to do this, we need a spectral analysis of the lamp with complete gonioradiometeric data to enter into the CAD software. This is accomplished using a gonioradiometer, which is a device to accurately determine a light fixture's spectral output on multiple axes. This information tells us not just the power but also the shape of the UV beam and how it will irradiate a room.

With both of the above methods, once the Upper-Room UVGI fixture has been installed, it must be tested for safety. This means dividing the room into a grid:

...and measuring each intersection of that grid at eye level to ensure that the UVC coming from the fixture does not exceed the permissible limit (usually 0.2 mW/cm2) in any part of the room.

This step is absolutely required, and Upper-Room UVGI cannot be installed without it. However, once completed, there is almost no chance of problems. You have cheap, safe, quiet protection against a broad range of bioaerosols.

If you have mechanical filtration, why bother with GUV?

If you’ve bought a well-reviewed air purifier for your office (which means reviewed by HouseFresh, the only trustworthy source on the subject) why would you mess about with GUV, which sounds a little dodgy and potentially dangerous?

The reason for the quote at the beginning of this article is people tend to try and compare GUV to mechanical filtration- two very different things, because they accomplish something that seems similar. But, GUV is very bad at being mechanical filtration and very good at being GUV- and vice versa.

Think of it like mopping and vacuuming. Imagine someone were to ask, “Which should you own mop or vacuum?.” Well, spill some dirt from a flowerpot on the floor- you want to deal with particulates and get the vacuum; your dog pees on the floor, you want to deal with biologicals, so you get the mop. But both clean the floor so if you aren't clear on their roles, you might try to compare them when it’s really best to own both so you can deal with all the potential messes.

Likewise for air- filters for particles, GUV for robust mitigation of bioaerosols. The two technologies achieve similar things but go about it in complementary and completely different ways.

Nevertheless, sometimes, we need to discuss the two in comparative terms to explain why you want both. Clean air is usually discussed in terms of mechanical filtration, like CADR and ACH. Sometimes, e-CADR and e-ACH (equivalent) are used for GUV, but they do not map very well because it really depends on which pathogens you are measuring. Engineers and scientists are still working on the best way to combine the two to greatest effect.

When it comes to bioaerosols- nothing even comes close to GUV. You would have to walk on a floor of filter cubes turned up to a deafening volume to equal the effect of a modest GUV installation.

Upper-Room UVGI can offer up to 22 e-ACH, Far-UVC installs have reached 184 e-ACH. This doesn’t mean as much as vendors would like you to think because that's only against bioaerosols. Both Upper-Room UVGI and Far-UVC only do this one thing really, really well- and that’s inactivate bioaerosols. Far-UVC can also do fomites on surfaces while people are in the room, which is quite useful. So with well installed GUV you won’t get sick from viruses and bacteria- but for PM2.5 size particles, dust, pollution, and smoke from wildfires- Upper-Room UVGI will do absolutely nothing and those can make you ill as well. It's min-maxed just for bioaerosols- and that is far from being the only part of indoor air quality that must be addressed.

The smaller the organic particles are, the more effective Upper-Room UVGI is at inactivating them. Large or enveloped infectious particles take a longer time to inactivate. Mechanical filtration does larger particles better, but any smaller particles may require several passes through the filtration medium. During either delay, those particles have the opportunity to infect the room occupants.
Upper-Room UVGI is up to 50% more effective with good air circulation and mixing- something that most mechanical air filters can provide.
Upper-room UVGI is silent, meaning you don’t have to run your mechanical filtration at high levels where the noise can be intolerable to get the maximum effect against bioaerosols.
Upper-room UVGI has been proven safe through over 80 years of use and countless peer-reviewed studies. The worst-case scenario is temporary sunburn and eye irritation, which is easily avoided with proper installation.

If you take nothing else away from this article, it should be that GUV and mechanical filtration are complementary. Every effort should be made to use them in tandem. Together, they are far more powerful and cost-effective than either intervention used alone.

What if we already have GUV in our HVAC system?

In-duct GUV is an excellent, cost-effective intervention that can practically eliminate the spread of infectious pathogens between separate rooms in a building. In-duct GUV also compliments Upper-Room UVGI- but it can’t replace it.

Upper-room UVGI directly treats air within occupied spaces, reducing pathogens immediately. This approach is particularly beneficial in high-occupancy areas, as it continuously reduces airborne contaminants.

The only thing better than Upper-Room UVGI for eliminating bioaerosols in occupied spaces is Far-UVC- which can address near field transmission and inactivate bioaerosols as they travel short distances person-to-person.

What maintenance does Upper-Room UVGI require?

Mercury vapor bulbs need to be changed every 8,000- 10,000 hours, and they need to be wiped clean of dust about every six months.

Occasionally it is worth re-measuring the room with a UV spectrometer if there have been significant changes in the layout—new wallpaper or paint, a new reflective surface but it's usually not needed otherwise.

Is Upper-Room UVGI safe?

Yes, although “safe” is a relative term. Risk is mathematical and can be quantified so from a purely mathematical perspective, Upper-Room UVGI poses almost no risk of significant injury to humans or animals.

In 80+ years, Upper-Room UVGI has killed or permanently injured precisely zero people. Rare adverse events have been the equivalent of a bad sunburn and have cleared up within a week or two. Nothing on record more severe than that has been documented.

The most extensive Upper-Room UVGI safety study was the Tuberculosis Ultraviolet Shelter Study (TUSS). It examined the effect of Upper-Room GUV over seven years on 3,611 unhoused participants in 14 facilities in six US cities.

There was only one adverse event during that time: a bunk bed was moved, placing a single resident in the path of the UV beam. They suffered from keratoconjunctivitis (eye irritation), which was resolved within a few days with eye drops.

In recent years, there has been speculation about respiratory issues possibly associated with GUV. The compounds in question have never been measured at dangerous levels in pre-existing, real world GUV installations- even though there are many thousands that could be tested, so the problem remains purly hypothetical from lab simulations that newer studies have failed to replicate.

That said, logically, if there were respiratory issues, we would have seen clusters of related occupational illnesses among workers exposed to GUV in settings like the TUSS study above.

In this Russian GUV study that used a novel dual-purpose Upper-Room Whole-Room UVGI fixture:

There were a few cases of mild eye irritation (due to the inadvisable use of Whole-Room UVGI) but no lung irritation or harm.

Since the 1990s, ultraviolet dish sterilizers have been standard in millions of Chinese homes, most in small, poorly ventilated spaces.

In that time, there have been no clusters of eye, skin, or lung ailments, even among domestic workers in close proximity where it would have been spotted quickly.

Laboratory workers, who spend decades working with laminary flow hoods with built-in GUV - no reported issues.

There are no issues with "sick buildings" or clusters of symptoms in HVAC workers who work with UV daily or workers on buildings with in-duct UV installed in the HVAC systems.

If there were an issue with GUV, we would see it with long-term occupational exposure in one or more of the above professions- as we do with chefs. .

But is GUV as safe as mechanical filtration? Probably not (it’s hard to quantify the effects of the millions of tons of microplastics that end up in the environment due to mechanical filtration). But just like seatbelts are safer than airbags, they work in different ways and together save far, far more lives than even injuries caused- neither should be set aside because it’s thought one measure is adequate.

Statistically, GUV is safer than most household appliances—like washing machines (3000 injuries a year in the US), dryers (10 deaths, 310 injuries), microwaves (10 deaths, 120 injuries), and any number of things that save no lives for the risk they present. The risk-reward ratio of GUV far exceeds that of one of our most trusted protection measures: the seatbelt.

Unfortunately, the idea of GUV, and course, the word “radiation,” causes fear in consumers far out of proportion to the actual threat posed. That fear is Upper-Room UVGI's greatest weakness. People are irrationally afraid of it, so it is seldom used- when widely deployed, it would save lives and prevent illness.

Where should Upper-Room UVGI be considered?

Upper-Room UVGI is generally not suitable for residential settings. It does best in larger open spaces with high ceilings- the smallest viable space being a hospital room. It is ideal for:

Healthcare Facilities: Emergency rooms, waiting areas, and operating theaters benefit from continuous air disinfection.
Educational Institutions: Classrooms and lecture halls reduce the risk of respiratory illness transmission.
Public Spaces: Airports, restaurants, houses of worship, and gyms where large groups gather.
Workplaces: Offices and factories to maintain productivity and reduce sick days.
High-Risk Settings: Homeless shelters, correctional facilities, and long-term care homes where ventilation is limited.

How to get Upper-Room UVGI installed?

That is the conundrum: while the fixtures can easily be bought online from retailers, the limited popularity of Upper-Room UVGI can make it difficult to find trained installers. Add to this it is far, far less profitable for HVAC companies to install than filters or in-duct UVC and you’ll find few have interest in training their technicians and do everything they can do steer potential customers towards indoor air quality measures that come with lucrative maintenance contracts- and maintenance on Upper-Room UVGI is anything but lucrative. Call around your local HVAC companies; if nothing else you may convince one there’s enough of a market for them to start selling and installing Upper-Room UVGI.