Some systems are constant volume by design. Others, such as dual duct systems, are comprised of individual constant-volume systems—i.e., are designed to deliver a specific volume of air at a constant temperature. Some energy-conserving opportunities for such systems, either as a whole or as a part, are:
1. Determine the minimum amount of airflow that is needed for each zone, either by computer, calculation, or field experimentation. Reset the constant-volume device to this flow rate.
2. Investigate the potential to convert the system to a step-controlled volume system, with the necessary controls. Almost any system modification that reduces airflow has savings in fan horsepower as well as in the quantity of energy that must be delivered by the hydronic fluid.
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Excerpt from Energy Conservation Projects.