HVAC Water Chillers Chiller Configurations Pump Parallel Configuration parti 1

HVAC Water Chillers
Chiller Configurations Pump Parallel Configuration
parti 1

Multiple-Pump chiller 

One-Pump Parallel Configuration:

The one-pump parallel chiller configuration is shown in Figure 2.3 and the overall system performance and temperature conditions are summarized in Table 2.2.
With this configuration, there is an inherent problem. If both machines were operated for the full-load range (15–100% of peak capacity), by the time the total system load drops to 30% of full load, each individual chiller would be operating very inefficiently. Thus, most designers utilize controls to shut off one chiller
when the total system load, as evidenced by the return chilled water temperature, falls below 40% of full load.

One-pump parallel chiller configuration.

One-pump parallel chiller configuration.

One-pump parallel chiller configuration with isolation valves.

However, with this piping arrangement, if one chiller is not in operation, chilled water from the operating chiller will mix (blend) with the return water passing through the nonoperating chiller, effectively raising the system’s chilled water supply temperature. In many cases, this may not be a problem. But, generally the interior spaces of large buildings still require more or less full cooling even when the perimeter spaces require no cooling at all and an elevated chilled water supply temperature may not satisfy these interior load conditions. In hot, humid climates, an elevated chilled water supply temperature may result in loss of humidity control. To attempt to eliminate the blended supply water problem with the one-pump
configuration, some designers have used chiller flow isolation valves, as shown in Figure 2.4. With this configuration, flow through the nonoperating chiller is  closed off when the chiller is not in operation. This arrangement results in increased flow through the operating chiller, but does reduce the blending problem, as illustrated in Table 2.3.

Multiple-Pump Parallel Configuration:

To ensure that the blended water condition does not occur, the multiple-pump parallel chiller configuration shown in Figure 2.5 is widely used.

One-Pump Parallel Configuration

Multiple-pump parallel chiller configuration.
With this configuration, each chiller has an individual chilled water pump. Thus, when one chiller is not operating, one pump is off, flow through the nonoperating chiller is zero, and no blending results.
Table 2.4 summarizes the performance and temperature conditions for this configuration at various load conditions.

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