FLEXIM Resource

Clamp-on Transit-time Difference Ultrasonic Flowmeters Ideal for HVAC
There are many reasons for large commercial buildings, medical centers, museums, airports, sports complexes, federal institutions and military complexes to invest in building energy optimization efforts. Better and more efficient operation of HVAC equipment can reduce the buildings energy and operational costs significantly.
Controlling flow, temperature and pumps can provide energy cost savings of over 20%. Many campus energy managers believe that the biggest user of energy in any complex is the HVAC system, and the key to saving energy in HVAC systems is an accurate and reliable flow metering capability.

Better efficiency of the heating and cooling infrastructure of a building also leads to more environmentally friendly buildings, something that has become a social prerogative of building owners and operators. Older buildings were not built with BTU meters as metering requirements were added to buildings through increased regulations.
Submetering the buildings heating and cooling systems have become increasingly more important, as building owners are both mandated to meter these utilities and have a financial interest in the accuracy of these BTU measurements. The problem historically is that nearly all flow meters are designed for gradual failure due to direct contact with the fluids they are monitoring and the particulate accumulation on the sensors.
How Transit-time Difference Ultrasonic Flowmeters Work
The flowmeter sends ultrasonic pulses through the process medium – one in the same direction as the flow and one in the opposite direction. The flowmeter’s transducers alternate as emitters and receivers. The transit time of the signal going with the flow is shorter than the one going against.
The flowmeter measures transit-time difference and determines the average flow velocity of the process medium. Since ultrasonic signals propagate in solids, the flowmeter can be conveniently mounted directly on the pipe and measure flow non-invasively.
Energy metering diagram
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