preheats in AHUs

[lfg2007]

I am having problems with preheats in AHUs. Inside each AHU is a heating coil (Brasch)and an ultrasonic humidifier. The distance between the heating coil and the humidifier is approx 8". The unit pulls air from the outside across the heating coils to the humidifier to the cooling coil. Some coils are glowing red, sagging, and breaking. Does anyone have experience with this configuration. I would like to rule out airflow as a problem.

 

[trashcanman]

Airflow might be exactly the problem. Sounds like the coils are overheating due to low airflow. Usually there is a sail switch in front to prevent the coils from coming on if there is no air flow. Is there a sail switch or something to indicate air flow? Better cut the power to the ones glowing red till you check it out.

 

[RossABQ]

If this is a variable flow unit, you need a thermostat and stepped or SCR control on the heater to prevent coil overheating at reduced flows.