We present two methods for sizing the network for the transport of the air, from the air handling unit to the terminal units, for a dual duct system, where air flows in the “cold” duct at a temperature less than the ambient temperature, while air flows in the “hot” duct at a temperature higher than the ambient temperature. The methods, compared to the traditional design criteria, lead to a reduction of channel size and, therefore, of overall network size and cost as well. The first method requires the “cold” channel to transport air at a temperature value slightly lower (1 ÷ 2°C) than the minimum inlet temperature (variable with time) required by the zones. The second requires the “hot” channel to transport air at a temperature value slightly higher (1 ÷ 2°C) than the maximum inlet temperature (variable with time) required by the zones. The methods have been applied to some reference networks. The saving of side surface of the networks varies between 14 and 27% with respect to the traditional approach; the constraint on the maximum speed of the air through the ducts is always respected, while this does not always occur with traditional criteria.
Part of the book: HVAC System