Dynamic Germicidal UV System Treats Airflow

With the pandemic continuing to disrupt our daily lives, organizations are looking to create a safer environment for workers, students and customers. KCI is retrofitting the rooftop air handler units at our national headquarters to incorporate dynamic treatment of airflow using germicidal UV (ultraviolet) light. The goal is to limit community spread of COVID-19 as well as other viruses.

“We’re making a commitment to creating a safer workspace for our employees,” said KCI CEO and President Nathan J. Beil, PE, D.WRE. “The engineering industry has always been relied upon to generate solutions during crises, and we felt it was critical to lead by example.”

By designing and installing a custom retrofit, KCI hopes to inspire other commercial and institutional organizations to consider this and other approaches that can help Americans get back to work and school.

Germicidal UV

Ultraviolet is an electromagnetic radiant energy within a specified range of wavelengths. Shortwave UV (also referred to as UV-C) has been proven to disarm many bacteria and viruses by deactivating their ability to replicate.

As a supplemental air-cleaning measure, UVGI (Ultraviolet Germicidal Irradiation) is effective in reducing the transmission of airborne bacterial and viral infections in hospitals, military housing and classrooms.

CDC, July 2019

Static UV applications for commercial spaces focus on in-room or surface-treatment systems, many of which are not feasible or cost-effective in office, institutional or commercial environments. Static treatment of surfaces can range from hand-held applications to installations downstream of coils in air handlers. For instance, a national airline recently announced deployment of germicidal UV treatment carts that will clean seats and other surfaces on their planes nightly. In-room systems can be placed at ceiling height to treat the air. Many of these systems pose cost and implementation challenges in larger open environments or even multi-room facilities.

Dynamic Application

Unlike static installations, dynamic systems treat air as it moves and may provide compounding treatment. As air is recirculated, molecules that may not have received a full dose during the first pass will continue to be irradiated until they are exhausted from the building.

At KCI, 30 bulbs installed in the three air handlers on the roof [also called rooftop units (RTUs)] will irradiate airflow before it is dispersed throughout the workspaces in the 120,000-square-foot office building. Together, each group of lights will deliver a dosage of 6.6 millijoules of germicidal UV-C as air moves from the unit’s fans and into the supply air ductwork.

UV RTU Diagram
Rows of UV lights mounted in the plenum of KCI’s RTUs can treat almost 100,000 cubic feet per minute (CFM) of airflow.

A key component of the project was determining the appropriate dosage. Research is ongoing specific to SARS-CoV-2, the virus that causes COVID-19. The KCI team used the best science available and consulted with academic experts to calculate intensity and duration for the new system. Earlier testing completed by the manufacturer, American Ultraviolet, resulted in specific dosages for a host of different viral and bacterial treatments. Our engineers built in a 25 percent factor of safety by exceeding recommendations for a log-3 or 99.9 percent deactivation of coronaviruses.

Design considerations also included the size of the building, RTUs and ducts as well as airflow through the system. “Many assume that adding UV-C to an existing system will be complicated and costly. We wanted to prove that it didn’t have to be,” said KCI Vice President and Mechanical/Electrical Regional Practice Leader Adam Rickey, PE, CPD. “These systems aren’t one-size-fits-all, but that doesn’t mean they aren’t efficient, cost-effective solutions that can be deployed quickly.” In the case of the headquarters building, the three RTUs were not all the same size and required different light configurations to ensure the system would meet the targeted dosage.

The goal was to find a simple solution, complete the calculation, and incorporate it into our system without costly major changes like new air handlers, fans, or ductwork. During design, engineers created a sizing and cost model that can help owners of commercial, educational and government buildings to quickly consider the feasibility of a UV retrofit.

Three RTUs sit atop KCI’s national headquarters in Sparks.
Three RTUs sit atop KCI’s national headquarters in Sparks.

Safety was another serious concern. UV-C is harmful to humans through direct exposure. With the units secured inside the building’s RTUs, potential exposure is limited to maintenance personnel. Our team added a safety cutoff to the system to cut power to the lights if the access door to a unit is opened.

With design complete and installation scheduled for the Sparks building, KCI is planning to discuss opportunities to add UV treatment to other existing and future office locations.

Implementation

When evaluating an installation, building owners and tenants should consider the following:

  • Always have a professional engineer review the as-built plans and any updates to your system or conduct a thorough site visit in order to identify cost and operationally effective alternatives.
  • Systems do not need to treat an entire building. Smaller installations can support individual tenants, even in multi-story skyscrapers.
  • Calculations can be completed quickly to identify the number and strength of bulbs needed.
  • Manufacturers are currently estimating delivery turnaround times of 8-10 weeks. During that time, engineers can finalize details for needed power, safety cutoffs and any necessary phasing.
  • The CARES act provides private companies with tax benefits through higher allowed depreciation for retrofits related to COVID-19.

Until the scientific testing is complete, and even with those results, it is impossible to guarantee that the system will eliminate all viruses from the air. Employees will still have to follow local health regulations, including social distancing, hand washing, and masks to avoid potential near-field exposures. Regardless of specific reduction in virus, the system is creating a healthier environment for all workers and visitors and is an added tool as we all continue with our lives during the pandemic and beyond.

Cover Photo Credit: American Ultraviolet