Variable-air-volume systems utilize some of the latest technology available to control zone temperatures and save fan energy. In fact, the energy savings can be quite substantial. Then why do engineers and building managers have reservations about using this type of system? Probably the memory of past experiences. The chain of design, equipment selection, installation, and air balancing must be tailored to a building’s needs or conflicts will arise. There are many disciplines to consider when creating a VAV system, and if one link is weak, there can be trouble.

Over 90% of office workers would rather be served by natural ventilation systems, so why is it not normal practice?
Many architects and consultants argue that serious technical difficulties make it impossible to implement.               

In order to improve the indoor air quality a change in the ventilation system is often one of the actions. The mean ventilation effectiveness or contaminant removal effectiveness is then often presented as a measure. Great care should however be taken when evaluating a system using these parameters. Measurements have shown that in displacement ventilation the mean ventilation effectiveness can fluctuate very much for the same air flow, the same cooling load, the same inlet - outlet devices and the same height of the tracer gas supply.

The performance of a ventilation system, particularly that which is incorporated in centralised air-conditioning system, can be evaluated in several ways. The "ventilation efficiency and ventilation effectiveness" and "air exchange efficiency" are two of the most commonly employed methods in ventilation analysis.

Modelling techniques were used to verify the success of a "minimal duct" ventilation system proposed for an underground carpark in a prestigious project in Singapore. The procedure to determine the various model scaling parameters, to select the appropriate fans to model the supply and exhaust fans, as well as the "dilution fans"; and to simulate the movement of air through the vehicle access ramps are presented. Measurements from the model were found to be reasonable when compared with results from numerical simulation. However, certain modifications were needed to improve the system.