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West Tennessee State Penitentiary UV Light Addition
$310,000 | July 2010
The facility had several cases of Tuberculosis (TB) and asked us to design a system that would help prevent the spread of the infectious disease. Each air handling unit (AHU) was analyzed based on airflow, coil size, and accessibility to determine the type/quantity of UV lights required to prevent the TB from spreading. It was determined that multiple low-intensity UV lamps would be required within each AHU to not only prevent the spread of TB but to provide redundancy in the event of several lamps failing. A bracket system, which slides completely out of the AHU allowing easy lamp change-out, was designed to hold the lamps in the air stream for full irradiation. As the TB passes through the AHU, it is irradiated by the UV lights, its DNA mutates so that the virus can no longer reproduce, thereby preventing the spread of the virus.
The UV lights were positioned downstream of the chilled water coils for several reasons. First, this is the point within the AHU where the air is moving the slowest and therefore allows the longest UV exposure time to the virus. Second, by shining UV rays at the downstream side of a chilled water coil, the coil is ultimately kept clean of bacterial growth caused from standing moisture. Finally, the AHU’s coil efficiency will stay high with clean coils compared to dirty coils due to greater heat transfer.
To prevent maintenance staff from being exposed to UV rays while servicing the AHU, door safety switches were installed to disconnect the UV lights upon the door being opened. The picture above shows the UV lights illuminated while a staff member has the door safety switch depressed. Additionally, all AHU’s were designed to house lamps that were 1 of 2 lamp lengths. This was done to prevent the facility from having to stock multiple lengths of lamps and coordinate which lamp went with which AHU. All together there were 270 total lamps and 6 AHU’s were replaced.
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