UVGI Dosage Calculation for CARE 2000
Four Lamp Reflective Chamber 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 lamp 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. (ASHRAE Fundamentals)
= *150*/1.46 sq.ft. = 103 fpm/60 = 1.72 feet per second average speed
= Circular or twisting airflow pattern is 3.9 feet@1.72 feet per second
= 2.27 seconds
Lamp Intensity

= 47 microwatts/cm squared at 1 meter (lamp mfg data)
Median distance from lamp to unit wall is 3.5"
Intensity multiplier at 3.5" = 39.37"/meter/3.5" = 11.25
(From N.A. Philips Lighting Handbook, light intensity varies with square of distance)

= 11.25 squared x 47 microwatts/cm squared
= 5948 microwatts per cm squared per lamp

Reflection of measured UV light is a 86% increase at cabinet alzak = 1.86 increase
Total Efficacy = 2.27 second x 5948 x 1.86 x 4 lamps
= 100,455 microwatt-seconds/cm squared.

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 50 cfm = 150/50 x 100,455 = 301,365 microwatt-seconds/cm squared @ low speed

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