Filter
Top Products
38 TRG-TRC016-EN
notes
period two
Chilled-Water System Design
Series Configuration
Another way to connect multiple chillers is to configure the chiller evaporators
in series. Series chilled-water systems typically use three-way valves at the coils
to ensure constant system flow. With two chillers in series, both the
temperature mixing and the flow problems associated with the parallel
configurations shown previously disappear. All of the chilled water passes
through both chillers, and there is full system-water flow at all loads.
However, the flow rate through each individual chiller is equal to the entire
system flow rate. When compared to chillers piped in parallel at the same
system ∆T, this is twice as much water flowing through each chiller. This means
that the chiller-tube pass arrangement must accommodate double the water
quantity within acceptable velocity and pressure drop limits. This typically
requires a reduced number of passes in the evaporator and may impact chiller
efficiency. This efficiency impact, however, is often offset by the gain in system
efficiency due to thermodynamic staging.
System pressure drop also increases because the pressure drops through the
chillers are additive. This can result in increased pump size and energy costs.
This increase in pumping energy can be substantially reduced by designing the
system for a higher system ∆T and, therefore, a reduced water flow rate.
Because of the pressure drop limitations, it is difficult to apply more than two
chillers in series. Systems involving three or more chillers typically use either
the primary-secondary configuration or parallel sets of two chillers in series.
Chillers Piped in Series
three
three
-
-
way valve
way valve
absorption
absorption
chiller
chiller
electric
electric
chiller
chiller
Figure 44