Piping system design using a primary/secondary three-tier arrangement is reviewed. The tiers are defined (1) the terminal (coil), (2) the transport loop, and (3) the generator (chiller).

Solving flow and heat transfer problems in each tier is the most beneficial way to maintain minimum horsepower consumption, highest water temperature rise, and lowest GPM in hydronic variable-flow systems. The formula – Btu = (500) x DELTA T x GPM – shows us the importance of holding high temperature rise in the water while varying the flow with load. Gpm costs money. Delta-t is free.

The terminal requires the most attention and is investigated for teh most efficient flow arrangement to obtain high delta-t at all load conditions.

With high delta-t and stable gpm/Btu, chillers can be loaded and matched to the variable-volume system at minimum power consumption per Btu generated. This allows maximum chiller energy management.

Units: I-P