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States that current applications of direct digital controls (DDC) in variable water volume (VWV) systems are significantly inferior to DDC-based variable air volume (VAV) systems. Discusses conventional methods of controlling VWV systems and compares those methods with the proposed DDC-based VWV system. Simulated head flow curves show that substantial operating costs can be saved with the use of DDC for hydronic (wet) systems. Also discusses the system's capability in enhancing environmental controllability. States the proposed DDC system has a closed loop scheme for controlling the terminal unit's output. Flow information from each circuit is used in a 'feedforward' loop for pump control based on total system flow and computed system head.

KEYWORDS: Controls, computer controls, fluid flow, water, heating, cooling.

Citation: Symposium, ASHRAE Transactions, vol.97, Pt. 1, New York 1991