Two fans in series for VAV air conditioning systems

Early variable air volume (VAV) air conditioning systems are designed with a single fan (supply air fan). With the development of VAV air conditioning systems, more and more VAV air conditioning systems are designed with two fans in series, namely supply air fan with return air fan or supply air fan with exhaust air fan. This paper theoretically explains why the design of two fans in series is more energy-efficient than the design of single fan, analyses the advantages and disadvantages of the two types of two fans in series designs, and discusses how to design and control the VAV air conditioning system with two fans in series.