Since the entire facility template of the dual-duct system
is available, we do not need to make any complicated connection between the templates, using ducts, pipes, and control signals.
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.
Initially, the university sought to install a dual-duct system
. Although exemplary in terms of the comfort they provide, these systems are quite costly.
The dual-duct system
turned into a single-duct VAV system even without retrofit of the terminal boxes (Liu and Claridge 1999).
Regarding the modification of the dual-duct system
, my mentor, the great Walter Spiegel, Presidential Member/Fellow ASHRAE, once improved a dual-duct system
by using the return air as the heat source for the hot deck.
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 existing system contained a single-fan, dual-duct system
with air-handling units that were located in the penthouses on the roof.
Generally, on the dual-duct system
the primary air duct is carried at a constant volume, varying the temperature according to the outside and supplying minimum ventilation air.
Air conditioning is provided on the office floors by all-air dual-duct systems
. The main plant is in the basement and with the cooling towers on the roof of the services tower.
MZS DCV control logic should apply to both single-path and multiple-path systems, including the following VAV systems: single-path reheat with dual maximum logic,  dual-path parallel fan-powered, dual-path series fan-powered and dual-fan dual-duct systems
. Since some of these systems allow some of the C[O.sub.2] generated in a given zone to be recirculated to the zone locally, and mixed with primary air that contains C[O.sub.2] from all other zones, the interpretation of readings from the zone breathing level C[O.sub.2] sensors must carefully account for the effect of recirculation paths.
(1997b) studied the impact of low static pressure in dual-duct systems
on fan energy consumption.
Among the variations are single-duct and dual-duct systems
, a range of capacities and numbers of zones, chilled water or direct expansion cooling coils, and a range of heat sources for space heating, when needed.