Direct measurement of air volumes with flow sensors

Regulated ventilator outputs allow the air volumes in ventilation and air-conditioning systems to be adjusted to the actual demand, thus substantially reducing energy consumption. This is based on accurate volumetric flow measurement. The new flow sensors SS 20.250 from SCHMIDT Technology have been precisely designed for this purpose.

Ventilation and air-conditioning systems in residential buildings, but in particular in office and production buildings and in public buildings, are among the largest energy consumers. The centerpieces of such systems are fans whose energy consumption is directly related to the air volumes to be transported. The use of frequency-controlled fans and adequate control technology allow these air volumes to be reduced to the minimum demand required for maintaining the air quality and the thermal environment. However, this requires an accurate measurement of the volumetric flows over a wide measuring range. It ranges from almost zero, as is the case when the fans are started, to the maximum, which in systems of this type can be 20 m/s.

Thermal flow sensors are ideally suited to the direct measurement of volumetric flows. This technology offers a wide measurement range, completely covering all relevant air flows in air-conditioning technology. This includes minimum air velocities, such as the ones observed during idle periods, and maximum flows at full load. The particular advantage of the so-called thermal anemometry is that it allows easy and accurate measurement and ultimately simple evaluation.

Perfect flow measurement

The new flow sensor SS 20.250 from SCHMIDT Technology is a device developed on the basis of thermal flow measurement selectively for applications such as ventilation and air-conditioning systems. A robust metal sensor tube of only nine millimeters in diameter houses the complete electronics. Thus, the smallest all-rounders of their type offer particular advantages. Since they require little space, they are easy to mount by means of a flange, welding sleeve or through-bolt joint from the accessories and present minimum resistance in the air flow. For installation in different pipe diameters, sensor lengths of 300 and 500 millimeters are available. The patented dumbbell head, featuring a high flow angle of radial 360° and axial ±45°, can be positioned safely and quickly in the gas flow. and does not require accurate alignment in the flow channel. In addition to that, the completely seamless design of the sensor head free of undercuts inhibits the adhesion of dirt particles, thus making it easy to clean. As a result, the new SCHMIDT® flow sensors SS 20.250 are also predestined for use in dust-containing gases.

The standardized flow rate is detected over a measuring range of 0.06 to 20 m/s. The measuring accuracy of the SS 20.250 is ±5% and ±3% when using high-precision calibration and an ISO calibration certificate. In addition to the flow rate, the temperature of the medium is also measured in quick response. A skillfully integrated two-colored LED display (red, green) at the back end of the sensor tube shows the operating status in clearly visible form.

At a list price of 340 €, the sensors are an adequate solution for use with frequency-controlled fans for saving energy in ventilation and air-conditioning systems.

Author: Rolf Bürssner, Director of Marketing and Distribution in the Sensor Division of SCHMIDT Technology GmbH in St. Georgen.