Flow Measurement Devices for HVAC-R

Flow Measurement Overview

Flow is defined as a quantity of material passing a given area in a unit time period. Flow measurement is used to calculate how much liquid, gas, air, steam or energy is moved, and is vital to understanding, among other things, system capacities and energy efficiencies. There are numerous methods used to measure flow and Siemens SITRANS F is a comprehensive line of flow measurement devices for all flow related applications.

Magnetic Flow Meters

The SITRANS FM magnetic flow meters are designed to measure the flow of conductive liquids in a full pipe. It works on the principle of Faraday’s law of electromagnetic induction where a voltage induced as a conductor is passed through a magnetic field. The mag meter flow tube creates the required magnetic field and the fluid passing through it is the conductor.

At zero flow there is no induced current, however, as the flow rate increases so too does the current which is registered by strategically placed electrodes that come into contact with the fluid being measured.


  • High Accuracy

  • Very low permanent pressure loss

  • No moving parts

  • Process Variables have no effect on the measurement

  • Minimal straight run requirements


  • Requires conductive fluids (min 5µs/cm)

  • Material compatibility with the process fluid

Clamp-on Ultrasonic Flow Meters

The SITRANS FU clamp-on ultrasonic flow meters consist of a flow display computer, ultrasonic clamp-on transducers, and mounting hardware and cables; configurations can also include temperature sensors for calculating thermal energy consumption. Clamp-on ultrasonic flow meters utilize either transit-time or Doppler technology – or in some cases, both.


  • Non-Invasive

  • No permanent pressure loss

  • Fast and inexpensive installation


  • Cannot measure steam

  • High temperature limitations

Vortex Flow Meters

Vortex Flowmeters for HVAC-R

The SITRANS FX vortex flow meters are designed to measure flow of liquids, gases and steam in a pipe. The principle behind the operation of a vortex meter is the Von Kármán effect.


  • Can measure liquids, gases and steam

  • High process temperatures

  • No moving parts


  • Low flow cutoff

  • Meters are usually sized smaller than the pipe to increase velocity

  • Moderate permanent pressure loss

  • Upstream pipe requirements

Differential Pressure Flow Meters

Pressure Measurement for HVAC-R

Differential pressure flow meters have been employed to measure the flow of liquids, gases and steam for many years. It is one of the oldest methods of flow measurement and the most widely utilized and accepted methods in the world.

There is a wide variety of primary flow elements – orifice, venturi, averaging pitot tubes, etc.- available to meet the needs of virtually any application.


  • Low cost

  • Simple construction

  • No moving parts

  • Years of research and data available


  • Low turndown

  • Flow is non-linear function of DP

  • Potential leak points

Valve Positioners

Valve positioners for HVAC-R

Though not a flow measurement device, valve positioners are a critical component for regulating the flows of liquids, gases and steam. Valve positioners are devices that ensure the correct position of a control valve in relation to a controlling signal.  

Siemens SIPART PS2 is an industry leader in intelligent positioners and has been providing accurate and trouble-free operation of all valve types for over 17 years.


  • Improved speed of response & accuracy over pneumatic and electro-pneumatic positioners

  • Very low bleed design reducing carbon footprint and cost of ownership

  • Standard control valve diagnostic reduces maintenance and provides system operating characteristics continuously to the BMS


  • Requires a pneumatic air source