Because the ACC operate under saturated steam conditions, e.g. the condensate is always in contact with the steam from whence it came and therefore sub-cooling is of little concern for provided that the ACC is free from air ingress. For an ACC operating in automatic with a fixed backpressure setpoint sub-cooling will occur if air ingress is greater than the air extraction equipments’ capabilities. As the air collects and blinds the surface area, ACC backpressure will increase resulting in the control system in either speeding up the operating fans (VFD equipped) or starting additional fans. It is the increased air flow that will cause the condensate and the air take off NCG’s to become sub-cooled. Sub-cooling can also occur without major air ingress should the ACC be operated in manual mode supplying more air flow than is required. In this case the backpressure and saturation temperature will decrease.
