Trane TRG-TRC016-EN manual Temperature-Based Calculations

period two

Chilled-Water System Design

notes

Temperature-Based Calculations

					supply
					tee
				e
				ip
			p
			s
		s
	a
p
y
b

		system-level
return		controller
	tee

Figure 64

The advent of microprocessor-based controls has led to another method for determining flow in the bypass pipe. Temperature sensors are placed in the supply and return pipes of the production and distribution loops, and in the bypass pipe. With these temperatures, a chiller-plant control system, programmed with fluid mixing equations, can determine the quantity of excess or deficit flow that exists at any time. Because a small change in temperature may indicate a relatively large change in load or flow in the bypass pipe,

it is important to use accurate, calibrated sensors to ensure acceptable system operation.

The primary advantage of this method is that it does not depend on flow velocity in the pipe. Also, it is reliable and cost effective because the temperature sensors are relatively-low-cost devices.

Integrating the chiller controls with a chiller-plant control system, however, is imperative for efficient system operation. The control of chilled-water systems will be discussed further in Period Four.

58 TRG-TRC016-EN