However, for the two zone examples considered here, the mixing of air from the "hot" and "cold" ducts of the dual-duct system enables it to operate without the use of simultaneous cooling and heating and, therefore, with a lower system capacity than the single-duct system.
System Effectiveness Effectiveness Season Time of Day Single-Duct Dual-Duct System System 8:00 0.
For the two-zone system considered here, the dual-duct system is able to operate without the need for zonal re-heat and therefore has a higher effectiveness than the single-duct system.
Figures 1 and 2 illustrate "conventional" single-duct and dual-duct systems, the only unusual feature of these systems being the use of zone-based humidifiers (rather than a single centrally located humidifier).
Both the single-duct and dual-duct systems use the central recirculation of the extract air from all zones.
Although this applies to both the single-duct and dual-duct systems, it is not the case for the conceptually optimum system configuration (Figure 3) since there is no central recirculation of the extract air (in effect, each zone has an independent outdoor air supply).
The dual-duct system
turned into a single-duct VAV system even without retrofit of the terminal boxes (Liu and Claridge 1999).
This paper provides a method for verifying the accuracy of computer models that simulate the performance of the air-handling components of four types of heating, ventilating, and air-conditioning systems: the dual-fan VAV dual-duct system, the single-zone system, the four-pipe fan-coil system, and the four-pipe induction system.
The data presented here have been produced by analysis of the performance of four different types of air-handling systems (the dual-fan VAV dual-duct system, the single-zone system, the four-pipe fan-coil system, and the four-pipe induction system) for six different sets of outdoor and room conditions, using spreadsheets.
2005) provided similar test cases for a constant volume terminal reheat system, a variable air volume system, and a single-fan constant volume dual-duct system.
These are: the dual-fan VAV dual-duct system (VAVDD), the single-zone system (SZ), the four-pipe fan-coil system (FC), and the four-pipe induction system (IU).
1997b) studied the impact of low static pressure in dual-duct systems
on fan energy consumption.