Steimle F, Glimpel T
Bibliographic info:
10th AIVC Conference "Progress and trends in air infiltration and ventilation research" Espoo, Finland, 25-28 September 1989

In central units of air heating systems the supply air flow must meet the actual heating demand. Most of central units for air heating systems have only one fan , which is designed for the maximum air flow at the maximum heating capacity . Fan motors are designed for variable - voltage-drive to enable a reduction of air flow to the necessary value at different heating demands. However, the electrical efficiency is decreasing strongly. The supply air fan is working mostly under part - load conditions . Therefore the control strategy used now is very ineffective . It is suggested to install 2 fans in an air handling unit. One of them is working at full capacity all over the year , but the second one starts only to deliver the additional air flow required in case of higher heat demand. Charts basing on calculations will demonstrate the relation between outdoor air temperature and the demand of energy for both systems.