May 01, 2020 Upper Air UV-C – Improving IEQ
The air in buildings often contains health menacing bacteria and viruses. To reduce disease transmission, the air can be disinfected in three ways: dilution, filtration, and purification by ultraviolet germicidal irradiation (UVGI) or UV-C. These approaches are applicable for controlling colds, flu, measles, and bioterror agents.
Dilution reduces the concentration of infectious agents by increasing the amount of outside air brought into the occupied space. Dilution does not destroy microbes, but rather it reduces their concentration by spreading them over a larger volume of air.
Filtration reduces the concentration of infectious agents by passing the air through high-efficiency air filters that trap bacteria and viruses, removing them from circulation.
Purifying the air destroys infectious agents by exposing them to UV-C energy which damages their DNA. This damage stops them from replicating. Lamps are placed in ventilation ducts or in the upper air of a room. UV-C is favored in all spaces where people are present.
What is the effectiveness of UV-C purification?
It is measured in two ways. One is based on equivalent air changes per hour; i.e., the number of air changes required to reduce the concentration of microorganisms by the same amount as filtering. Using this method, UV-C can provide air cleansing of up to 35 air changes per hour, based on the UV intensity and time of exposure. The second way is by its cost effectiveness or dollars per case of infection prevented per year. One study estimates the cost to avoid an infection was $133 for UV-C, $420 for HEPA filtration and $1708 for additional ventilation in 2000 dollars. UV-C was the most cost effective.
How is upper room UV-C achieved?
Upper room UV-C is simple and decades old. A UV lamp in a specially designed fixture directs UV energy to the upper room area. The lamps 254 nanometer wavelength causes DNA damage to bacteria and viruses. The lamp also emits some visible light that appears blue.
How does it work?
Infectious particles typically move from the lower part of a room to the germicidal zone in the upper room. Complete microbial inactivation occurs through the cumulative effect of exposure over time as infectious particles are carried repeatedly to the upper room. Each pass inactivates the infectious particles until their concentration in the lower part of the room are effectively diluted.
How do I choose an upper air fixture?
The dose delivered by a particular product is based on the UV-C irradiance and the duration of exposure. These two components are interchangeable, either a high irradiance for a short time or a low irradiance for a long time is equally effective. In practice, the effectiveness of a UV-C installation is determined by the following factors:
- The UV lamp used, because that determines the output of UV-C radiation
- The fixture and reflector design in which the lamp is housed, because that determines how much of the actual radiation is discharged from the fixture and how it is distributed
- The distance of airborne infectious agents from the fixture, because that determines the number of units required
- The construction, cost and ease of installation are also important factors
What advice exists for upper air UV-C?
The designer needs to know how many fixtures to use, and where they should be located. Guidelines are published by the CDC and in several peered reviewed papers. Most manufacturers offer guidelines that are based on the latest recommendations of UV-C energy at different distances, this is the most accurate method. Upper room fixtures are used in rooms with ceiling heights of 7 feet and higher. Original guidelines recommended 30 watts of UV lamp power for each 200 sq. ft. of floor area. That has been replaced by the much more accurate method of microwatts of UV-C energy at various distances from the fixture. This best determines the number and placement of fixtures to cover the upper room.
What does an upper room UVGI installation cost?
More efficient products can cost much less because costs are considered in three parts: the cost to purchase, the sot to install the fixtures, and the cost to operate them. Efficient products reduce both the first cost and operating costs. Generally, efficient products cost about $2.80 per square foot in 2015 dollars. Operation costs include electricity and lamp replacement and again, efficient products cost less. The annual cost of electricity per efficient fixture is $22 per year, assuming 25 watts per fixture, 24 hours per day, and $0.10 per kWh. Lamps are replaced annually at a list price of $43 per lamp.
What is the future of upper room UVGI?
Per ASHRAE’s “Position Document on Airborne Infectious Diseases”, upper room UV must become a common feature of buildings. Upper room UV is effective against all types of viruses and bacteria, including those used for bioterrorism. The technology is well-researched and developed. It’s been shown to be quite effective in all studies of representative environments and it’s easily retrofitted in many building types, including hospitals, health clinics, urgent care locations, childcare facilities, colleges, prisons, jails, virtually all building types. Its cost effectiveness supports its use over the alternatives of dilution and filtration. The foregoing facts support the value of using upper room UV-C for infectious diseases such as colds and flu and all other infectious agents.