HVAC Water Chillers Chiller Configurations Pump Parallel Configuration parti 2

HVAC Water Chillers
Chiller Configurations Pump Parallel Configuration
parti 2

Multiple-Pump Parallel 

Primary–Secondary Parallel Configuration:

Each of the configurations discussed above is essentially a constant flow system that utilizes three-way control valves at the cooling coils. Constant flow systems circulate the same amount of chilled water, no matter what the imposed cooling load, and, consequently, impose high pumping energy requirements.
To reduce these costs, the primary–secondary variable flow piping arrangement illustrated in Figure 2.6 is very commonly applied. Here, the production loop through the two chillers is hydraulically isolated from the distribution loop by a piping bridge. The bridge is a short section of piping shared by both loops
and designed to have little or no pressure drop. Thus, the flow in one loop is not affected by flow in the other.On the primary or production loop side, the system acts as multiple-pump parallel chiller installation, as described in the section “Multiple-Pump Parallel

Multiple-Pump Parallel Configuration
Primary–secondary parallel chiller configuration.

Configuration.” Flow in this loop varies in “steps” as the chillers are staged on or off and their respective pumps are started and stopped. However, in the secondary or distribution loop, the cooling coils utilize two-way control valves and the distribution pump(s) utilize a variable frequency drive(s) so that the
chilled water flow rate is modulated from 0% to 100% of peak design flow as a function of the imposed cooling load. Thus, this loop has fully variable flow, but maintains a constant temperature range. At any load condition, the supply water temperature is the same as the water temperature leaving the chiller(s),as long as the production loop flow rate equals or exceeds the distribution loop flow rate.  Table 2.5 summarizes the performance and temperature conditions for this configuration at various load conditions. 

Primary–Secondary Configuration Flows and Temperatures

Variable flow primary parallel chiller configuration

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