Air-conditioning systems with dual ducts: An innovative approach to the design of the transport network of air

This article describes a method to dimension the transport networks of air, from the air handling unit to terminal units, for dual duct systems, which provide air distribution through the use of two parallel networks. The method, compared to the methodologies usually adopted or proposed, leads to a reduction of the channel size and therefore of the overall network size and cost as well. Dimensioning criteria usually adopted require the air to flow in the “cold” duct at a temperature lower than the room temperature, while air flows in the “hot” duct at a temperature higher than the room temperature. As an alternative to the traditional design criteria, we present a dimensioning method that requires the “cold” channel to transport air at a temperature value slightly lower (1◦C–2◦C) than the minimum supply temperature (variable with time) required in each zone. The method is applied here to some reference networks, and the results are compared with those obtained with traditional design criteria. The obtained reductions of the surfaces of the networks (therefore, to a first approximation, of their total weight) range between 15% and 34%; that depends as well on the temperature of the hot channel keeping it constant and ranging between 35◦C and 45◦C. The air speed through the ducts is always lower or equal to the fixed values; this constraint is not always respected using traditional dimensioning methods.