Series counterflow chillers are shown in Figure 41. This arrangement differs from the series chillers system shown in Figure 39 in that the condenser flow passes through both chillers in series, counterflow to the chilled water. Series counterflow condenser water improves the chiller performance as explained in the Series counterflow chiller example.
Figure 39 shows two chillers in series. All the system flow goes through both chillers. As a result, the water pressure drops through the evaporators are additive. The chilled water loop can be either constant or variable flow. Variable flow systems increase the complexity but offer significant pump savings. Variable flow systems are covered in Primary/Secondary Systems and Variable Primary Flow Design. A condenser loop is required for water cooled chillers. This includes a condenser pump, piping and a cooling tower or closed circuit cooler. The condenser loop operates whenever the chillers operate.