Sunday, October 11, 2009

Smart buildings

Environmental sensors make smart buildings more comfortable

Carlo Gavazzi has introduced a range of sensors to measure environmental variables including CO2 levels, humidity, temperature and airflow. The new CGES sensors complement the company’s existing offerings to provide complete solutions for energy management, HVAC and smart building applications.

When carbon dioxide levels rise to an unacceptable level it creates poor air quality and stuffy rooms. CO2 and airflow sensors can control extra ventilation to increase the fresh air supply and improve the indoor air quality. Similarly these new devices can be used to control humidity level in wet climates: improving comfort and discouraging the growth of mildew.

Standards introduced by the American Society of Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE) define a maximum CO2 level of 1000ppm; and the ASHRAE 62-1989 norm has been widely adopted in countries including Sweden, France and Japan as well as the USA. CGESCO2 sensors use non-dispersive infrared (NDIR) technology to provide measurement ranges 0-2000 or 0-5000ppm. Using a patented auto-calibration procedure to compensate for drift caused by ageing, the sensors ensure traceable high accuracy and outstanding long-term stability. Operation in a closed-loop airstream avoids pollution of the CO2 sensor.

Humidity measurements are based on a thin-film polymer, which releases or absorbs water vapour according to the ambient humidity, varying its dielectric properties accordingly. The instruments’ electronics measure the resulting change in capacitance, with excellent reproducibility that delivers accuracy of ±3% from 10% to 90% RH. High quality HC101 sensors guarantee excellent long-term stability and resistance to chemical pollutants.

The air velocity sensors utilise the principles of thin-film anemometry, in which a heated resistive mesh is maintained at a constant temperature above that of the medium. Air flowing over the resistor cools it and the power required to maintain the offset is used to determine air speed. Carlo Gavazzi’s cutting-edge thin film technology guarantees excellent accuracy over working ranges up to 20m/s. Moreover, the sensor is insensitive to dust and dirt, and has low angular dependence. Measuring range and response time are selectable by jumpers.

Temperature measurement is available using Pt100, Pt1000, PTC or NTC resistance elements, ensuring typical accuracy of ±0.3degC at 20°C.

The sensors are available in duct or wall mounting formats, and a switching output offers an alternative to the standard 0-10V DC voltage or 2-40mA current analogue outputs. Environmental sensors can be combined in either wall or duct-mounted units. For example, the CGESHTPD duct-mounted model features HC101 humidity sensors combined with passive Pt100/Pt1000 temperature measurement; whilst the CGESCO2TW provides CO2, temperature and humidity functions in a simple-to-install room transmitter on the wall.

All the CGES family benefit from traceability through international standards such as NIST, PTB and BEV: the sensors carry CE marks and are RoHS-compliant.

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