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46 TRG-TRC016-EN
notes
period two
Chilled-Water System Design
Obviously, in order to achieve variable flow at the distribution pump, the load
terminals must be configured to vary the system flow. This requires the use of a
modulating two-way control valve for each coil. Typically, no three-way valves
or wild coils need to be used in a primary-secondary system. Their use
decreases the energy savings potential from the variable-flow distribution
pump. In fact, ASHRAE/IESNA Standard 90.1–1999 (Section 6.3.4.1) requires
the use of modulating two-way control valves, and thus variable water flow,
in most systems. Primary-secondary systems comply with this requirement.
Some systems, however, will use one three-way valve at the load terminal
furthest from the distribution pump, to ensure that cold water is immediately
availability to all terminals in the system.
Primary-Secondary System Rules
▲ The bypass pipe should be free of restrictions
▲ Load terminals should use two-way
modulating control valves
Figure 52