Various methods and computer programs can be used to simulate airflow through a duct system. However, simulation methods can only model ductwork systems. No simulation method by itself produces an optimized air distribution system and no "standard" optimization program currently exists. [Scott, 1986]
The ASHRAE Handbook recommends the T-Method, which allows a user to select duct sizes and fan pressure, for duct simulation and "generalized" optimization that minimizes life-cycle cost. This design technique was incorporated into the 2001 ASHRAE Fundamentals Handbook. The T-method integrates the life-cycle cost of the air distribution system—first-cost, energy cost, and hours of operation—into the analysis of ductwork and fan selection. The system total pressure is optimally derived while costs are minimized. According to Shepard et al. (1995), "…the size and the energy use of the fan can be about 45 to 75 percent smaller with [the] T-method…" than with the conventional "equal friction" sizing method. However, acceptance of the T-method has not been widespread because hand calculation of the results is time-consuming. [Shepard et al., 1995; Tsal, 1995]
Quality duct design can be achieved only by using a comprehensive computer simulation program. A comprehensive simulation program allows an engineer to model changing cross sections; closing and opening dampers; removing, adding, and modifying fittings and duct-mounted equipment; selecting different diffusers; and changing fans or motors. A good computer program adjusts the fan-system operating point and shows new airflow quantities, velocities, pressure profiles, and how they differ from a preceding design. In other words, a comprehensive computer simulation program allows design engineers to model "what-if" in order to design laboratory environments that are as energy-efficient and flexible as possible. Ideally, a simulation program is user-friendly, window-driven, and capable of calculating supply, exhaust, and return systems using ducts of any shape. A comprehensive simulation program requires an extensive library of fittings and duct roughness. Finally, a good simulation program performs air balancing based on mass flow rate rather than on volumetric flow. The program should provide an opportunity to model control dampers, and fire/smoke dampers, and it should help evaluate and improve ductwork layout. [Tsal, 1999] [T-DUCT, 1994]
Existing Duct Simulation Methods
T-Method Computerized Duct Simulation
T-Method Ductwork Simulation Program
