This is frequently an electrical heater. When the outside air receives to all-around 6*c (forty two.8F) the heater will come on and warmth the air up to protect the parts inside from frost. If not this could freeze the heating and cooling coils inside of and burst them. Platelet rely https://airhandlingunitsahus42840.dailyblogzz.com/32341876/facts-about-air-handling-unit-ahu-hire-revealed