UVGI Dosage Calculation for Clarifier Four and Two Lamp Systems

The calculation of the average efficacy of the ultra violet germicidal lamps is a function of the resident time of the bacteria within sight of the ultra violet light and the intensity of the light within this "Kill Zone". Calculations are quite a complex integration; however, the basic "easy to understand" value, approach within 2 to 3% of the rigorous integrations (noted below), and is therefore, conservatively:

Resident Time = CFM/area/airflow path/60 seconds per minute.
= *300*/1.51 sq.ft. = 200 fpm/60 = 3.333 feet per second average speed
= Circular or twisting airflow pattern is 3.9 feet@3.333 feet per second
= 1.17 second
Lamp Intensity

= 32.9 microwatts/cm squared at 1 meter (lamp mfg data)
Median distance from lamp to unit wall is 3.3"
Intensity multiplier at 3.3" = 39.37"/meter/3.3" = 11.93
(From N.A. Philips Lighting Handbook, light intensity varies with square of distance)

= 11.93 squared x 32.9 microwatts/cm squared
= 4682 microwatts per cm squared per lamp

Reflection of measured UV light is a 22% increase at cabinet surface = 1.22 increase
Total Efficacy = 1.17 second x 4682 x 1.22 x 4 lamps Alzak (1.22=1.86) 2 lamps w/o alzak
= 26,732 microwatt-seconds/cm sq'd. 40,756 13,366

Lamp life is rated at 8000 hours or 1 year.

NOTE: As unit airflow decreases on slower fan speeds this UV dosage increases in proportion to the airflow change, for example the dosage at low speed for four lamps at 100 cfm = 300/100 x 26,732

= 80,196 or
= 122,268 microwatt-seconds/cm squared with alzak reflector @ low speed