I recently had a request to come up with a way of controlling an Ultraviolet-C (UVC) light bulb inside a home heat pump. The ask was to be able to synchronize the UVC lamp with the on/off cycles of the blower fan. The reason is that UVC radiation is a very effective disinfection system to help improve the air quality and minimize mold growth inside the air handler box.
I researched commercial options and couldn’t find anything that would work… oh well! Guess I’ll need to create one. I learned that the fan control signal was 24VAC and this would need to be signal conditioned to operate the solid state relay (SSR). So my approach would be to condition the fan signal to drive the control input on the SSR.
The base circuit can be seen on the initial schematic picture. It uses a full wave bridge rectifier and filtering resistors and capacitor components. I then ran the circuit through a Spice Simulator and determined we were good to go. The output was R3 which was the SSR for controlling the lamp.
Next I built up the circuit and installed it into the air handler. It worked like a champ! On to the next opportunity. The value of this project is that the UVC lamp is only on during the fan on cycle, thereby increasing the lifespan of the bulb. The readily available commercial units kept the bulbs on 100% and they’re rated for 8000hrs, or about one year. Perhaps some commercial value in the future, time will tell.
Bob 01/29/2020
Engineering Consultants 