Trane TRG-TRC016-EN manual Chillers Piped in Series, notes, Chilled-WaterSystem Design, period two

period two

Chilled-Water System Design

notes

Chillers Piped in Series

electric chiller

absorption chiller

three-wayvalve

Figure 44

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.

38 TRG-TRC016-EN