Trane SYS-APM001-EN manual Condenser-Water System, Cooling tower, Primary-secondary system

Primary System Components

Figure 13. Primary-secondary system

CV

Pump

Chillers

CV

Pump

Bypass (Decoupler)

Two-Way	VV
Control	Pump
Valve
Load

Figure 14. Variable-primary system

VV

Pump

~

Chillers

VV

Pump

~

the series, or another pumping arrangement can be considered. Reducing the flow rate affects this system type’s energy use all the time, so careful attention to flow rates and temperature is critical (refer to “System Design Options” on page 27).

Primary-secondary system

In this configuration (Figure 13), the distribution piping is decoupled from the chiller piping and is known as the primary-secondary or decoupled system. There is constant primary flow through the operating chiller(s) and variable secondary flow through the loads. A bypass pipe between the two balances the primary flow with the secondary flow. Because there are more pumps and a bypass, this system costs more than a constant flow system to install. Details on this system type are in “Primary–Secondary (Decoupled) Systems” on page 45.

Variable-primary system

This pumping arrangement (Figure 14) was made possible in recent years by advanced chiller controls that permit varying the flow through the chillers. Like a constant flow system, the distribution piping is directly connected to the chiller piping. Flow is varied through at least most of the loads and the chillers. A smaller bypass (compared to the primary-secondary system) ensures chiller minimum flow rates are avoided. Fewer pumps and smaller bypass lead to lower first costs compared to the primary-secondary system. Operation costs can also be lower, but the plant is controlled differently than in other pumping arrangements and operator training is essential. This system type is covered in detail in “Variable-Primary-Flow Systems” on page 55.

Minimum Flow Bypass Valve

Two-Way

Control

Valve

Load

SYS-APM001-EN

Condenser-Water System

As in chilled-water distribution systems, condenser-water system piping— most commonly steel, copper, or plastic—is sized to meet a project’s operating pressure, pressure loss, water velocity, and construction cost parameters. Pressure drop through piping and the chiller’s condenser, plus the cooling tower static lift, is overcome by use of a condenser-water pump.

To ensure optimum heat transfer performance, the condenser-heat transfer surfaces must be kept free of scale and sludge. Even a thin deposit of scale can substantially reduce heat transfer capacity and chiller efficiency. Specifics of cooling-tower-water treatment are not discussed in this manual. Engage the services of a qualified water treatment specialist to determine the level of water treatment required to remove contaminants from the cooling tower water.

Cooling tower

To reject heat, water is passed through a cooling tower where a portion of it evaporates, thus cooling the remaining water. A particular cooling tower’s effectiveness at transferring heat depends on water flow rate, water temperature, and ambient wet bulb. The temperature difference between the

Chiller System Design and Control 13