Field Controls CC 2000 - Manual (Page 5)

Page 5
Testing Procedure
The testing was performed in two stages. The first stage operated the test chamber with
the lamp off. (See table 1) This developed the control data or the base line bacterial
levels for the comparison. The second stage operated the test chamber with the lamp on.
(See table 2)
Two airflow rates were used to evaluate the lamp effectiveness based on exposure time.
Airflow velocities through the ducts of a typical residential heating and cooling system
range from 300 to 500 feet per min (fpm). For this study a base air velocity of 500 fpm
was used. To decrease the exposure time, a second test was conducted with the airflow
in the duct doubled to 1000 fpm. Since the effectiveness of UV lamps is based on the UV
light output and exposure time, doubling the airflow reduces the effectiveness of the lamp.
The bacterium was cultured and the cells harvested to provide a suspension of known
cell density. This was further diluted to provide gallon quantities of a test suspension
containing an estimated 95,000 CFU/ml. This suspension was pumped through the spray
nozzle mounted in the center of the duct inlet.
Five air samples were taken for each of the test velocities at short intervals (typically ½ to
2 minutes). This produced a large sample volume of air and reduced the levels of back
ground bacteria and molds counts. The plate counts (colony forming units or CFU) for
each of the five tests were totaled and divided by the total test volume of air. This
produced the comparison value of (269 CFU/FT
3
of air) for the 500 FPM airflow and
(107.5 CFU/FT
3
of air) for the 1000 FPM airflow. Due to apparent efficiency losses in the
sampling method at the 1000 FPM velocity, the bacterium count yielded a 60% drop
instead of the anticipated 50% reduction due to the velocity change.
Four air samples were taken at 1, 2.5, 3, 5, 6 & 10 minute intervals for each of the test
velocities with the lamp on. The longer sample times with the lamp on were needed to
obtain plate counts which would provide reliable estimates of the efficiency of disinfection,
but with this, more background organisms were found. The plate counts were (18.00
CFU/FT
3
of air for the UV-18 and 2.56 CFU/FT
3
of air for the UV-18X) at 500 FPM airflow.
They were 31.18 CFU/FT
3
of air for the UV-18 and 10.40 CFU/FT
3
of air for the UV-18X
at 1000 FPM airflow.