An innovative approach for the design of the transport network of the air for dual-duct systems

A method for sizing the network for the transport of the air, from the Air Handling Unit to terminal units, for a dual duct system, is described. The method of the calculation for the channels presented here leads to a reduction of their size thus reducing cost and size of the network, with respect to the methodologies usually adopted or proposed. As an alternative to the design criteria traditionally used, we present a method for sizing that requires that the "cold" channel transports air at a temperature value slightly lower (1 - 2 °C) than the minimum inlet temperature (variable with time) required by the zones. The method was applied to some reference networks and the results were compared with those obtained using the design criteria traditionally used. The obtained reductions of the total area of the channels, and therefore as a first approximation of their total weight, range between 15 % and 34%, also depending, over that on the system, on the temperature of the hot channel, kept 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 in the sizing of the ductworks with the traditional method.