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TRG-TRC016-EN 57
period two
Chilled-Water System Design
notes
The direction and quantity of flow in the bypass pipe may be determined either
directly by using a flow meter or indirectly by sensing temperatures.
Direct flow measurement can be accomplished using a variety of flow-meter
technologies. These include pressure-based flow meters (pitot tubes, venturi
meters, orifice plates, and differential pressure sensors), turbine and impeller
meters, vortex meters, magnetic flow meters, and ultrasonic transit-time
meters. The accuracy, ease of installation, required maintenance, and cost of
these meter technologies vary widely. The accuracy and reliability of the flow
meter will directly impact the efficiency and reliability of the chilled-water
system. High-quality flow meters are critical to proper system operation.
When using a flow meter, it is important to understand the range of flows and
velocities that the specific device can accurately measure. The accuracy of
some flow meters is dependent on the velocity of the flow and the development
of a smooth flow profile in the stream being measured. To obtain accurate
measurements, several diameters of straight pipe may be required, both
upstream and downstream of the meter. Finally, in order to give accurate
results, many types of flow meters require periodic calibration. This is often
overlooked in the maintenance of chilled-water systems.
Types of Fluid Flow Meters
▲ Pressure-based
◆ Pitot tube
◆ Venturi
◆ Orifice plate
◆ Differential pressure
▲ Turbine and impeller
▲ Vortex
▲ Magnetic
▲ Ultrasonic
Figure 63