Field Controls Air Cleaner CC 2000 User Manual

Efficiency Of Bacterial Disinfection  
By A  
Duct Mounted UV-AireÔ Air Purifier  
By:  
Kane Environmental Assays  
Sanitary & Environmental Microbiology  
Bernard E. Kane, Ph.D.  
1706 Canterbury Rd  
Greenville, NC 27858  
Ph. 252.355.6789  
For:  
 
Background  
This product study evaluates the effectiveness of the UV-Aire air purifier in reducing the  
levels of bacteria with a single pass through a simulated air duct system. This device is  
designed to irradiate the air as it circulates through the home, so the single pass  
evaluation is the worst-case scenario use of this device. The air in the home will pass  
through the heating and air conditioning system many times a day, as the air is  
circulated throughout the home. Knowing the effectiveness of the UV-Aire in a single  
pass application, enables us to project how effectively the device will treat the air with  
multiple passes a day.  
UV light technology has been successfully used for the disinfection of drinking water for  
years. Applications for air disinfection with the use of UV light technology include:  
commercial air treatment in hospitals, clean rooms, meat packing plants, bakeries,  
dairies, breweries, bottling plants and large commercial HVAC systems.  
ORGANISM:  
Serratia marcescens (ATCC 14756) was chosen as the test bacterium. The distinctive  
red colonies made it easy to evaluate from any background organisms. A raw test  
suspension of the organism of approximately 95,000 CFU/ml was used. As dispersed  
into the test system, this suspension yielded bacterial counts of 269 CFU/ft3 @ 500 ft/min  
airflow and 107.5 CFU/ft3 @ 1000 ft/min airflow. (CFU = Colony Forming Units)  
TESTING STRUCTURE:  
An 18” x 18” galvanized air duct, 38 feet long was constructed as the test chamber (see  
Figure 1). A fan was mounted at the exit end of the chamber and the treated air  
exhausted to the outdoors. To reduce contamination of the intake air, all air intakes on  
the exhaust side of the building were sealed. The exhaust fan was equipped with a flow  
adjustment to allow for adjustable air speeds measured in feet per minute (FPM) through  
the duct.  
TESTING AIRFLOW RATE:  
The airflow rate through the ductwork was adjusted to two nominal velocities of 500 ft/min  
and 1000 ft/min. The airflow velocities were measured at the center of the duct at the  
intake end of the test duct.  
Page 3  
 
ORGANISM APPLICATOR:  
An atomizing humidifier spray nozzle mounted at the center of the test duct intake was  
used to distribute the organism into the air stream. The application flow rate was 0.45  
gallons per hour.  
UV DEVICE:  
A Field Controls UV-Aire air purifier model UV-18 was mounted onto the center of the  
side of the test duct 6 feet from the exit end of the chamber. The lamp is a UVC  
germicidal lamp (non ozone producing) 18 inches long with a UV output rating of 73  
mW/cm2 at 1 meter from the lamp.  
AIR SAMPLING METHOD:  
An Andersen N6 single stage “bioaerosal” sampler was used to take the air samples and  
distribute the sampled air onto agar medium. The test medium was Tryptic Soy Agar  
from PathCon, Inc. The air sampling pump airflow rate was 1 CFM.  
The Anderson sampler method requires corrections to the actual colony counts on the  
plates. This provides a more accurate measure of the bacteria per cubic foot of the  
sample air. In the following tables, the Serratia marcescens Positive Hole Count values  
are the actual plate counts and the Corrected Particle Count values are corrected value  
based on Anderson correction tables.  
Test Apparatus  
Figure 1  
Page 4  
 
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/FT3 of air) for the 500 FPM airflow and  
(107.5 CFU/FT3 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/FT3 of air for the UV-18 and 2.56 CFU/FT3 of air for the UV-18X) at 500 FPM airflow.  
They were 31.18 CFU/FT3 of air for the UV-18 and 10.40 CFU/FT3 of air for the UV-18X  
at 1000 FPM airflow.  
Page 5  
 
Table 1: Control Data (testing with lamp off)  
Airflow  
Velocity  
fpm  
Sample Air Sampling  
Number Duration (min)  
Serratia marcescens Corrected Particle  
CFU/FT3of air  
(count/min)  
Positive hole count  
Counts  
1
2
3
4
5
1
1
500  
500  
500  
500  
500  
181  
193  
208  
117  
118  
241  
263  
294  
138  
140  
1
0.5  
0.5  
Total Corrected  
Particle counts  
Total min. = 4  
= 1076  
269.00  
1
2
2
2
1
1
1000  
1000  
1000  
1000  
1000  
168  
167  
169  
91  
218  
216  
220  
103  
103  
2
3
4
5
92  
Total Corrected  
Particle counts  
Total min. = 8  
= 860  
107.50  
Table 2: UV-18 Test data and results (testing with lamp on)  
Air  
Serratia  
marcescens  
Positive hole  
count  
Airflow  
Velocity  
(fpm)  
Corrected  
Particle  
Counts  
CFU/FT3  
of air  
(count/min)  
Sample  
Number  
Sampling  
Duration  
(min)  
%Survival  
CFU/Control Reduction Effective  
Log  
%
1
2
3
4
1
1
3
6
1000  
1000  
1000  
1000  
30  
32  
31  
33  
88  
99  
145  
180  
Total Corrected  
Particle Counts  
Total min = 11  
= 343  
31.18  
29.01  
0.54  
1.17  
70.99  
93.31  
Control:  
13  
107.50  
1
2
3
4
1
1
3
6
500  
500  
500  
500  
13  
19  
57  
92  
19  
61  
105  
Total Corrected  
Particle Counts  
Total min = 11  
= 198  
Control:  
18.00  
6.69  
269.00  
Page 6  
 
Table 3: UV-18X Test data and results (testing with lamp on)  
Air  
Serratia  
marcescens  
Positive hole  
count  
Airflow  
Velocity  
(fpm)  
Corrected  
Particle  
Counts  
CFU/FT3  
of air  
(count/min)  
Sample  
Number  
Sampling  
Duration  
(min)  
%Survival  
CFU/Control Reduction Effective  
Log  
%
1
2
3
4
2.5  
2.5  
2.5  
5
1000  
1000  
1000  
1000  
21  
27  
28  
48  
22  
28  
29  
51  
Total Corrected  
Particle Counts  
Total min = 12.5  
= 130  
10.40  
9.67  
0.95  
1.01  
2.02  
90.33  
99.05  
Control:  
107.50  
1
2
3
4
5
5
500  
500  
500  
500  
8
8
10  
17  
28  
10  
17  
29  
5
10  
Total Corrected  
Particle Counts  
Total min = 25  
= 64  
Control:  
2.56  
269.00  
Page 7  
 
Conclusion  
UV-Aire  
Model  
Airflow  
velocity  
(fpm)  
Percent Reduction Percent Survival of Log Reductions  
of Bacteria  
Bacteria  
of Bacteria  
UV-18  
UV-18  
UV-18X  
UV-18X  
500  
1000  
500  
93.31  
71.99  
99.00  
90.33  
6.69  
29.01  
0.95  
1.17  
0.54  
2.02  
1.01  
1000  
9.67  
The testing showed the UV-Aire lamp yields at least a 90% reduction of the test bacteria  
with a single airflow pass through a duct system at typical airflow rates. This efficiency  
will not be the same for all bacteria and molds since each organism requires different  
exposure times at the same UV output energy level.  
At the higher velocity, the lamp still reduced the bacterial levels by at least 71 % at a 50%  
decrease in the exposure time. Since the reduction efficiency is based on lamp UV  
output and exposure time, the assumption can be made that decreasing the exposure  
time to the UV light is similar to testing an organism that requires a higher UV energy  
requirement to kill the bacteria. The log reductions in bacterial levels were very close to  
theoretical values. Within the limits of testing accuracy, twice as many log reductions  
(0.54 vs. 1.17 and 1.01 vs. 2.02) occurred with twice the exposure time.  
This testing and the results clearly show that the exposure of the air to the UV light of the  
UV-Aire will reduce levels of airborne bacteria.  
Form #4291 08/01  
 

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