Conflict of interest

The author declares that she has no conflict of interest.

#### Nomenclature

Acronyms ACH air changes per hour

AHU air handling unit


#### Symbols

(variable with time) required by the zones, while the cold duct delivers air at a constant

The method has been applied to some networks of channels, and results were compared with

The comparison was carried out in terms of diameters, network factors, and total side surfaces of the network. It shows that the overall dimensions of the networks decrease compared to the traditional sizing methods; the factor Fnet varies between 1.21 and 1.37, while in traditional sizing, it assumes values around 1.7. As it has been seen in previous works [19], the decrease of network factor (and of side surfaces) is more significant for higher temperature of the hot duct (method 1) and lower temperature of cold duct (method 2). The constraint on the maximum speed of the air in the various trunks of the network is always respected, while it does not always occur with traditional criteria. The saving in terms of side surface varies between 27 and 21% with reference to the traditional approach for method 1 and between 14 and 17% for method 2. Both methods imply lower network factors, with respect to the traditional method, but it is preferable to use one method rather than another according to the summer and winter design temperatures. In our study, a lower winter design temperature implies an increase in savings by using method 2.

These new methods of sizing a dual duct network allow for a lighter network, with obvious economic advantages, and are easier to place. The network is able to guarantee the thermohygrometric comfort conditions for all conditions of thermal load, even in the medium periods; in addition, it allows a control of the air speed, always remaining below the maximum allowed

It must be remembered that, unlike the traditional method that plans fixed temperature values for the hot and cold ducts, the proposed methods require a more complex control system that, starting from the value of the minimum or maximum supply temperatures of the different

For method 1, which guarantees better results compared to method 2, a further postheating

temperature, lower than the absolute minimum value of the zone supply temperature. The new approach implies reduced overall dimensions and cost of the channel network.

those obtained, on the same networks, using the traditional sizing criteria.

values (this does not always happen with the traditional method).

battery dedicated to the cold duct must be provided.

The author declares that she has no conflict of interest.

Conflict of interest

Nomenclature

ACH air changes per hour

AHU air handling unit

Acronyms

44 HVAC System

zones (which vary over time), can vary the temperature of the cold or hot duct.


#### Subscripts

